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Spinning Mills


COSTING FOR A SPINNING MILL INTRODUCTION:

It is better to review the basics concepts, costing methods and techniques and elements of costing before we work out a costing for a spinning mill. Cost accounting is a system of determining the costs of products or services. It has primarily developed to meet the needs of management. It provides detailed cost information to various levels of management for efficient performance of their functions. Financial accounting provides information about profit , loss, cost etc., of the collective activities of the business as a whole. It does not give the data regarding costs by departments, products, processes and sales territories etc. Financial accounting does not fully analyze the losses due to idle time, idle plant capacity, inefficient labour, sub-standard materials, etc. Cost accounting is not restricted to past. It is concerned with the ascertainment of past, present and expected future costs of products manufactured or services supplied. Cost accounting provides detailed cost information to various levels of management for efficient performance of their functions. “A cost is the value of economic resources used as a result of producing or doing the things costed” Cost is ascertained by cost centres or cost units or by both. For the purpose of ascertaining cost, the whole organisation is divided into small parts of sections. Each small section is treated as a cost centre of which cost is ascertained. A cost centre is defined as ” a location, person, or item of equipment(or group of these) for which costs may be ascertained and used for the purpose of control. A cost accountant sets up cost centres to enable him to ascertain the costs he needs to know. A cost centre is charged with all the costs that relate to it. The purpose of ascertaining the cost of cost centre is cost control. The person in charge of a cost centre is held responsible for the control of cost of that centre. Cost unit breaks up the cost into smaller sub-divisions and helps in ascertaining the cost of saleable products or services. A cost unit is defined as a ” unit of product , service or time in relation to which cost may be ascertained or expressed.” For example in a spinning mill the cost per kg of yarn may be ascertained. Kg of yarn is cost unit. In short Cost unit is unit of measurement of cost.

METHODS OF COSTING:

Method of costing refers to the techniques and processes employed in the ascertainment of costs. The method of costing to be applied in a particular concern depends upon the type and nature of manufacturing activity. Basically there are two methods of costing 1.Job costing: Cost unit in job order costing is taken to be a job or work order for which costs are separetely collected and computed. 2.Process costing: This is used in mass production industries manufacturing standardised products in continuous processes of manufacutring. Cost are accumulated for each process or department. For spinning mills , process costing is employed.

TECHNIQUES OF COSTING:

These techniques may be used for special pupose of control and policy in any business irrespective of the method of costing being used there. Standard costing: This is the valuable technique to control the cost. In this technique, standard cost is predetermined as target of performance and actual performance is measured against the standard. The difference between standard and actual costs are analysed to know teh reasons for the difference so that corrective actions may be taken. Marginal costing: In this technique, cost is divided into fixed and variable and the variable is of special interest and importance. This is because, marginal costing regards only variable costs as the costs of products. Fixed cost is treated as period cost and no attempt is made to allocate or apportion this cost to individual cost centres or cost units. Cost Ascertainment is concerned with computation of actual costs. Ascertainment of actual costs reveals unprofitable activities losses and inefficiencies . Cost Estimation is the process of predetermining costs of goods or services. The costs are determined in advance of production and precede the operations. Estimated costs are definitely the future costs and are based on teh average of the past actual costs adjusted for future anticipated changes in future. Cost estimates are used in the preparation of the budgets. It helps in evaulating performance. It is used in preparing projected financial statements. Cost estimates may serve as targets in controlling the costs. CLASSIFICATION OF COSTS:

Costs are classified into direct costs and indirect costs on the basis of their identifiability with cost units or processesses or cost centres. DIRECT COST: These are the costs which are incurred for and conveniently indentified with a particular cost unit, process or equipment. For a spinning mill, costs of rawmaterial used, packing material, freight etc are direct costs

INDIRECT COST:

These are general costs and are incurred for the benefit of a number of cost units, processes or departments. These costs cannot be conveniently identified with a particular cost unit or cost centre. In a spining mill, power cost, administrative wages, managerial salaries, materials used in repairs etc are indirect costs. The terms direct and indirect should be used in relation to the object of costing. An item of cost may be direct cost in one case and the same may be indirect in the other case.It is the nature of business and the cost unit chosen that will determine whether a particular cost is direct or indirect.

FIXED AND VARIABLE COSTS:

 Costs behave differently when level of production rises or falls. Certain costs change in sympathy with production level while other costs remain unchanged. As such on the basis of behaviour or variability, costs are classifed into fixed, variable and sem-variable. FIXEDCOSTS;

These costs remain constant in “total” amount over a wide range of activity for a specified period of time. They do not increase or decrease when the volume of production changes. VARIABLE COSTS:

 These costs tend to vary in direct proportion to the volume of output. In other words, when volume of output increases, total variable cost also increases and vice-versa. ELEMENTS OF COST: A cost is composed of three elements i.e. material , labour and expense. Each of these elements may be direct or indirect. DIRECT COST INDIRECT COST Direct material Indirect material Direct labour Indirect labour Direct expenses Indirect expenses

COSTING FOR A SPINNING MILL – Cost Accounting – Page 2 MATERIAL COST: DIRECT MATERIAL is that which can be conveniently identified with and allocated to cost units. Direct materials generally become a part of the finished product. For example, cotton used in a spinning mill is a direct material. INDIRECT MATERIAL is that which can not be conveniently identified with individual cost units. In a spinning mill, engineering department spares, maintenance spares, lubricating oils, greases, ring travellers etc LABOUR COST: DIRECT LABOUR cost consists of wages paid to workers directly engaged in converting raw materials into finished products. These wages can be conveniently identified with a particular product, job or process. INDIRECT LABOUR is of general character and cannot be conveniently identified with a particular cost unit. In other words, indirect labour is not directly engaged in the production operations but only to assist or help in proudciton operations. For example in a spinning mill, the number of maintenance workers, no of workers in utility department etc EXPENSES; All costs other than material and labour are termed as expenses. DIRECT EXPENSES are those expenses which are specifically incurred in connection with a particular job or cost unit. Direct expenses are also known as chargeable expenses. INDIRECT EXPENSES can not be directly identified with a particular job, process and are common to cost units and cost centres. PRIME COST = Direct material +Direct labour + Direct expenses OVERHEAD = Indirect material + Indirect labour + Indirect expenses TOTAL COST = PRIME COST + OVERHEAD ADVANTAGES OF COST ACCOUNTING: · It reveals profitabale and unprofitable activities. · It helps in controlling costs with special techniques like standard costing and budgetary control · It supplies suitable cost data and other related information for managerial decision making such as introduction of a new product, replacement of machinery with an automatic plant etc · It helps in deciding the selling prices, particularly during depression period when prices may have to be fixed below cost · It helps in inventory control · It helps in the introduction of a cost reduction programme and finding out new and improved ways to reduce costs · Cost audit system which is a part of cost accountancy helps in preventing manipulation and frauds and thus reliable cost can be furnished to management ESSENTIALS OF A GOOD COST ACCOUNTING SYSTEM: · The method of costing adopted. It should be suitable to the industry · It should be tailor made according to the requirements of a business. A ready made system can not be suitable · It must be fully supported by executives of various departments and every one should participate in it · In order to derive maximum benefits from a costing system, well defined cost centres and responsibility centres should be built within the organisation · controllable and uncontrollable costs of each responsiblity centre should be separately shown · cost and financial accounts may be integrated in order to avoid duplication of accounts · well trained and educated staff should be employed to operte the system · It should prepare an accurate reports and promptly submit teh same to appropriate level of management so that action may be taken without delay · resources should not be wasted on collecting and compiling cost data not required. Only useful cost information should be compiled and used whenever required. CASE 1. Project costing for a POLY/COTTON PLANT with autodoffing and link to autoconer:(IN INDONESIA) Following information is required to work out a costing for a new plant: · The average count of the plant · Capacity of the plant – No of spindles to be installed and the number of back process and winding machines required · Investment on machineries · Investment on land · Investment on building · working capital required · product lay out, the count pattern · Selling price of individual counts · rawmaterial cost(including freight, duty etc) · packing cost per kg of yarn · freight per kg of yarn · direct labour cost · indirect labour cost · fixed power cost · variable power cost · spares consumption · administration costs · selling overheads Let us work out a project cost: For this , i have used the details of the modern mill which is running in Indonesia from year 2000 STEP NO.1: Contribution to be calculated. In general for a spinning mill ,contribution per kg ofa particular count is calculated to work out the economics for a new project as well as for a running mill. Cotribution = selling price – direct cost Direct cost for a spinning mill includes rawmaterial price, packing cost, freight. All other costs are either fixed costs or semi variable costs. The other costs can not be conveniently allocated to per kg of a particular count. The basic idea of a new project or a running plant is to maximise this contribution. Because once the plant is designed, spares cost, power cost, administration cost,labour cost etc almost remain constant. There will not be significant changes in these costs for different count patterns if the plant is utilisation is same. COSTING FOR A SPINNING MILL – Cost Accounting – Page 3 The following table gives the details of count pattern, selling price, rawmaterial price, packing cost and contribution per kg of different counts for a particular period ( year 2000). This is just an example , one should understand that the selling price, rawmaterial price and all other costs keep changing. THis is the reason why costing is important for a running mill. All the costs are changing. Some costs change every month, some once in a year. Therefore costing plays a major role to run the plant efficiently. count no. of spls no of mcs prdn/mc prdn kgs/day raw material cost/kg packing cost /kg freight per kg commn 2% on selling price selling price / kg contribn per kg 20s CVC 4480 4 1109 4436 1.456 0.046 0.051 0.04 2.2 2674 24s CVC 4480 4 881 3525 1.456 0.046 0.051 0.05 2.3 2470 30s CVC 5600 5 679 3394 1.456 0.046 0.051 0.05 2.4 2712 30s TC 4480 4 679 2716 1.240 0.046 0.051 0.04 2.15 2091 36s TC 6720 6 552 3315 1.240 0.046 0.051 0.05 2.4 3365 23 17385 contrbn/ day 13312 In the above table, all the costs are in US$. The ringframes are with 1120 spindles per machine with automatic doffing and link to autoconer. Packing cost is based on indonesian packing material prices for carton packing. The ultimate aim of the project is to maximise the contribution. Looking into the cotribution per kg of yarn, the project should produce only 36s TC. But in this project they have considered 5 different counts. Because · yarn market is not stable. It needs a lot felxibility · customers are not same, the price depends on the customers · the end uses are not same, the price depends on the enduse · this unit exports 80% of the yarn, it can not depend on one country, eg. 36sTc is only for Philippines market, it can not be sold in Malaysia, eventhough the quality is good · the count pattern depends upon the market requirement and the major counts in the market, not only on the contribution · A linear programming technique can be used to maximise the contribution, considering all market constraints, and production constraints. · flexibility needs more investment and more day to day expenses, if a project has to be more flexible, it has to invest more money on infrastructure · the major factor which will make the project feasible with less felexibility is YARN QUALITY in a spinning mill · Since this is a critical step for a new project, management should be clear about their Yarn quality , Flexibility required for marketing and should make use of Linear Programming Techniques to find out the best product mix to maximise the contribution. STEP NO. 2: To work out the Total Investment cost ( machineries, accessories, land and builidng, humdification and electrical instruments) The following table gives the requirement of produciton machines. To calculate the number of back proess and winding drums required, a detailed spin plan should be worked out with speeds and efficiencies to be achieved in each machine. While calculating the no of machines required, m/c utilisation, m/c efficiency , waste percentage, twist multipliers, delivery speeds etc should be considered properly. These factors should be decided based on yarn quality required, end breakge rates and the capacity of machine. INVESTMENT ON MACHINERY MACHINERY NO. OF MCS RATE / MC TOTAL COST Trutzschler Blowrrom line for cotton 1 line 416,640 416,640 Trutschler Blowrrom line for Polyester 1 Line 321,365 321,365 Trutshcler DK-903 cards 22 92,500 2,035,000 Rieter RSB-D30 draw frames (with autoleveller) 6 1,648,000 Rieter double delivery drawframe 10 Rieter unilap 2 Rieter E62 combers 10 Howa speed frames with overhead blower 7 144530 1,011,710 Ring frames with autodoffer 23 148,960 3,426,080 winding machines ( 26 drums per mc) 23 93,200 2,143,600 Roving transport ( manual) 1 150,000 150,000 Argus fire system 1 50,000 50,000 TOTAL 11,202,395 Some of the following points can be considered while deciding the machines. From the above table it is clear that, 23 ringframes with 1120 spindles are working with auto doffing and with link to autoconer. The major advantage of this automation is to reduce labour and to reduce the problems related to material handling. One has to really work out the benefits achieved because of this and the pay back for the extra investment. Drawframe contributes a lot to the yarn quality and the ringframe and winding machine working. It is always better to go in for the best drawframes like RSB-D30 drawframes with autoleveller. It is not wise to buy a cheaper drawframe and save money. It is always better to keep excess carding and autoleveller drawframes, so that flexibility of the project is also maintained. If the coarser counts contributes more and the market is good, overall production can be increased. If the market is for finer count, both the machines (carding and drawframes)can be run at slower speeds, which will surely contribute to yarn quality. Speeds of speedframe , combers and ringframes do not affect the yarn quality as it is affected by card and drawframe speeds. Blow room capacity should be utilised to the maximum, as it consumes a lot of power ,space and money. Ringframe specification should be perfect, because the working performance and power consumption of the ringframe depends on the specifications like, lift, ring dia, no of spindles etc. Ring frame specification should be decided to get the maximum production per spindle and to reduce the power consumed per kg of yarn produced by that spindle. Because the investment cost and the power consumption for the ringframe is the highest in a spinning mill. INVESTMENT ON ACCESSORIES: The following table gives the details of the accessories like cans for carding, rawframe, bobbins, trollies etc ACCESSORIES NO. OF MCS RATE / MC TOTAL COST Carding cans 36″ x 48″ 120 160 19,200 comber cans 24″ x 48″ 350 85 29750 Drawframe cans 20″ x 48″ 1100 53 58,300 Identification bands 20″ 400 1.2 480 Identification bands 24″ 50 1.8 90 Roving and spinning bobbins 36,000 Plastic crates 400 6 2,400 trolleys 10,000 Cone trolly 80 200 16,000 Fork lift 1 27,000 27,000 hand truck 3 1000 3,000 TOTAL 202,220 SERVICE AND MAINTENANCE EQUIPMENTS: The following table gives the details about the investments required on service and maintenance equipments SERVICE AND MAINTENANCE EQUIPEMENTS NO OF MCS RATE/MC TOTAL PRICE Cots buffing machine and accessories 1 20000 20000 Card room accessories 1 set 60,000 60,000 Spindle oil lubricator 1 4000 4000 Clearer roller cleaning machine 1 3000 3000 Vacuum cleaner 5 3000 15000 pneumatic cleaners 6 500 3000 Weighing balance 3 2000 6000 Strapping machine 2 2000 4000 Premier autosorter 1 2500 2500 Premier uster tester 1 45000 45000 Premier strength tester 1 45000 45000 premier fiber testing 1 45000 45000 Premier Classidata 1 25000 25000 Erection charges 150000 TOTAL 427500 Card service machines like Flat tops clipping machine and flats grinding machine are very important for yarn quality. One should not look for cheaper machine. It is always better to go for reputed manufacturers like GRAF, HOLLINGSWORTH etc. Rubber cots contributes a lot to yarn quality. Bad buffing in ring frame can increase the imperfections by 15%. Poor quality of buffing in drawframe and speedframes can affect both production and quality. It is better to go for the best cots mounting machine and cots buffing machine. HUMIDIFICATION AND ELECTRICAL EQUIPMENTS: The following table gives the details about the investments required on umdification and electrical istruments Electrical installation including transformer, incoming and outgoing panels, bus duct, capacitor, etc for 3800 KVA 350,000 Cables 125,000 Compressor, Dryer and pipe lines 180,000 humidifaction system 767,000 chillers 176,000 Ducting and installation for humidification system 125,000 workshops, hydrant and other equipments 100,000 TOTAL 1,823,000 In indonesia, most of the units use PLN power and some of the spinning mills use Gensets. A detailed costing has to be done to compare the cost per unit to decide, Whether to use the PLN power or to go in for Gensets. while working out the costing finance cost on investment , overhauling cost, running cost, efficiency of the machine should be considered for cost caluculation in the case of Genset. In case of PLN power, the losses due to power interruption( based on the area data), finance cost on initial investment, md charges, unit charges to be considered. It is better to use 50% PLN and 50 % own generation. The following table gives the details about land and builiding investments Land cost 200,000 Land development 40,000 Factory building Including Service ally 192 x 62 meters 11,712 Square meter @ 120 usd/sq meter 1,405,440 Road and others 40,000 TOTAL 1,445,440 STEP NO.3: To calculate the expenses ( labour, power, stores,working capital, insurance etc) WorWorking capital = 3,000,000 LABOUR:The following table gives the details about labour requirement DEPARTMENT No of people required Production 140 packing 15 maintenance 30 utility 17 administration and personal dept 20 Total no of people required per day 222 wages at 50 usd/month including bonus and insurance 111,00 other facilities at 35 % 3,885 salaries for managerial staff 10000 Other facilities at 35 % 3500 Total labour cost / month 28485 POWER: The following table gives the details about the power Total units(KWH) produced (consumed)per day 69559 Unit cost (cost / KWH) 0.03 Total production in Kgs 17,390 KWH/ Kg of yarn 4.0 TOTAL POWER COST /DAY 2087 SPARES:The following table shows the spares cost, repair , and insurance spares cost at usd 8/1000 spindle shift 222,566d repairs and other overheads 200,000 Insurance at 0.175% on investment and working capital 31320 TOTAL cost per year 453886 STEP NO.4: PAY BACK CALCULATION DETAILS IN USD INVESTMENT: Land and building 1,444,440 Machinery, accessories & service equipments 11,832,115 Electrical and Humidification ducts 1,823,000 TOTAL INVESTMENT 15,099,555 WORKING CAPITAL 3,000,000 GRAND TOTAL 18,099,555 RECURRING EXPENDITURES PER DAY Salaries and Wages 949.5 Power cost 2087 Stores , repairs and insurance 1260.8 TOTAL 4297.3 INTEREST CALCULATION (per day) On capital 8% 3355.5 on working capital 9% 750 TOTAL EXPENSES INCLUDING INTEREST 8402.8 TOTAL CONTRIBUTION PER DAY 13312 NET PROFIT( before depreciation & taxation) 4909.2 PAY BACK PERIOD 8.54 years MIXING MIXING (COTTON) Cotton is a hygroscopic material , hence it easily adopts to the atmospheric airconditions. Air temperature inside the mxing and blowroom area should be more than 25 degree centigrade and the relative humidity(RH%) should be around 45 to 60 %, because high moisture in the fibre leads to poor cleaning and dryness in the fibre leads to fibre damages which ultimately reduces the spinnability of cotton. Cotton is a natural fibre. The following properties vary very much between bales (between fibres) fibre micronaire fibre length fibre strength fibre color fibre maturity Out of these , fibre micronaire, color, maturity and the origin of growth results in dye absorption variation. There fore it is a good practice to check the maturity , color and micronaire of all the bales and to maintain the following to avoid dye pick up variation and barre in the finished fabric. BALE MANAGEMENT : In a particular lot · Micronaire range of the cotton bales used should be same for all the mixings of a lot · Micronaire average of the cotton bales used should be same for all the mixings of a lot · Range of color of cotton bales used should be same for all the mixings of a lot · Average of color of cotton bales used should be same for all the mixings of a lot · Range of matutrity coefficient of cotton bales used should be same for all mixings of a lot · Average of maturity coefficient of cotton bales used should be same for all mixings of a lot Please note, In practice people do not consider maturity coefficient since Micronaire variation and maturity variation are related to each other for a particular cotton. It the cotton received is from different ginners, it is better to maintain the percentage of cotton from different ginners throught the lot, even though the type of cotton is same. It is not advisable to mix the yarn made of out of two different shipments of same cotton. For example , the first shipment of west african cotton is in january and the second shipment is in march, it is not advisable to mix the yarn made out of these two different shipments. If there is no shadevariation after dyeing, then it can be mixed. According to me, stack mixing is the best way of doing the mixing compared to using automatic bale openers which picks up the material from 40 to 70 bales depending on the length of the machine and bale size, provided stack mixing is done perfectly. Improper stack mixing will lead to BARRE or SHADE VARIATION problem. Stack mixing with Bale opener takes care of short term blending and two mixers in series takes care of long term blending. why? · Tuft sizes can be as low as 10 grams and it is the best way of opening the material(nep creation will be less, care has to be taken to reduce recyling in the inclined lattice) · contaminations can be removed before mixing is made · The raw material gets acclamatised to the required temp and R.H.%, since it is allowed to stay in the room for more than 24 hours and the fibre is opened , the fibre gets conditioned well. Disadvantages: · more labour is required · more space is required · mixing may not be 100% homogeneous( can be overcome by installing double mixers) If automatic bale opening machine is used the bales should be arranged as follows let us assume that there are five different micronaires and five different colors in the mixing, 50 bales are used in the mxing. 5 to 10 groups should be made by grouping the bales in a mixing so that each group will have average micronaire and average color as that of the overall mixing. The position of a bale for micronaire and color should be fixed for the group and it should repeat in the same order for all the groups It is always advisable to use a mixing with very low Micronaire range.Preferably .6 to 1.0 . Because · It is easy to optimise the process parameters in blow room and cards · drafting faults will be less · dyed cloth appearance will be better because of uniform dye pickup etc It is advisable to use single cotton in a mixing , provided the length, strength micronaire , maturity coefficient and trash content of the cotton will be suitable for producing the required counts. Automatic bale opener is a must if more than two cottons are used in the mixing, to avoid BARRE or SHADE VARIATION problem. It is better to avoid using the following cottons · cottons with inseparable trash (very small size), even though the trash % is less · sticky cotton (with honey dew or sugar) · cotton with low maturity co-efficient Stickiness of cotton consists of two major causes. Honeydew from Whiteflies and aphids and high level of natural plant sugars. The problems with the randomly distributed honey dew contamination often results in costly proudction interruptions and requires immediate action often as severe as discontinuing the use of contaminated cottons.An effective way to control cotton stickiness in processing is to blend sticky and non-sticky cotton. Sticky cotton percentage should be less than 25%. COTTON STICKINESS Cotton Stickiness occurs when excessive sugars present on fibers are transferred to equipment and interfere with processing. Sugars may be insect- or plant-derived. Though sugars are ubiquitous in lint, they usually occur at levels that pose no processing difficulties. This details the sources and components of problem sugars on harvested lint, the processing impacts of stickiness, and strategies for avoiding or mitigating stickiness. Cottons contaminated with stickiness cause multiple problems in the spinning mills. The honeydew present on the cotton lint is able to contaminate all the mechanical instruments used in the transformation process from fiber to yarn, i.e. opening, carding, drawing, roving and spinning operations. These contaminants are mainly sugar deposits produced either by the cotton plant itself (physiological sugars) or by the feeding insects (entomological sugars), the latter being the most common source of contamination. Honeydew, when present in sufficient quantity, is the main source of sugars that can result in sticky lint. Honeydew is excreted by certain phloem-feeding insects including such common pests of cotton as aphids and whiteflies. These insects are capable of transforming ingested sucrose into over twenty different sugars in their excreted honeydew. The major sugars in cotton insect honeydew are trehalulose, melezitose, sucrose, fructose and glucose. Another source of stickiness is free plant sugars sometimes found in immature fibers. Cotton fiber is largely cellulose that is formed from sugars synthesized by the plant. Dry, mature cotton fibers contain little free sugar, while immature cotton fibers contain glucose, fructose, sucrose, and other sugars. If immature cotton fiber is subjected to a freeze, complex sugars may be broken down to release additional simple sugars. Less commonly, oils released by crushed seed coat fragments can also result in stickiness. In this case, raffinose is the characteristic sugar. Sugars differ in their stickiness. For example, sucrose, melezitose, and trehalulose are all significantly stickier when deposited on fiber than are glucose or fructose. Further, trehalulose-contaminated fiber is stickier than fiber with an equivalent amount of melezitose. Mixtures of sugars, such as occur in honeydew, tend to be stickier than single sugars. Localized concentration of sugars like honeydew is at higher risk of causing stickiness than more evenly distributed sources like plant sugars. Sticky cotton can reduce cotton gin output (in bales/hr) by up to 25%. At the textile mill, excessive wear and increased maintenance of machinery may occur even with slightly sticky cotton. In severe instances mill shutdown with a thorough cleanup is required. COTTON APHIDS: Aphids are slow-moving, soft-bodied insects. Adult cotton aphids are approximately 1/10 of an inch long and roughly pear shaped. They may possess wings or may be wingless. Cotton aphids have two color phases: yellowish or dark green. The cotton aphid has two projections which arise from the upper side of the abdomen. These small tubes are called cornicles and are used to excrete defensive secretions. Both the adult and immature stages (called nymphs) of the cotton aphid have stylet like mouthparts, which they use to suck juices from the host plant. Consequently, cotton aphids are sometimes referred to as plant lice The cotton aphid, Aphis gossypii, excretes honeydew rich in melezitose (ca. 30–40%). Their droplets (inset, 50X) tend to be larger than those produced by whiteflies. Whiteflies, Bemisia spp., also excrete honeydew, but as trehalulose-rich (ca. 40–50%) droplets (inset, 50X). STICKINESS MEASUREMENT: ‘Stickiness’ is the physical process of contaminated lint adhering to equipment . The degree of stickiness depends on chemical identity, quantity, and distribution of the sugars, the ambient conditions during processing—especially humidity —and the machinery itself. Stickiness is therefore difficult to measure. Nonetheless, methods for measuring sugars on fiber have been and are being developed. These measurements may be correlated with sticking of contaminated lint to moving machine parts. The physical and chemical attributes of the lint and sugars that are correlated with stickiness have been measured in many ways, each with differing efficiency and precision. REDUCING SUGAR METHOD: Some textile mills use reducing-sugar tests based on reduction of the cupric ion to screen for sugar contamination. These tests are relatively quick and inexpensive. However, some insect sugars are not reducing sugars, and some others are measured at different levels of efficiency by various reducing-sugar methods. Thus conventional reducing-sugar tests are best reserved for screening lint that potentially has high levels of plant sugars. In these cases and with the potassium ferricyanide (KFeCN) test, lint with reducing sugar levels below 0.3% may be processed without difficulty. HIGH PERFORMANCE LIQUID CHROMATOGRAPHY: High Performance Liquid Chromatography (HPLC) identifies and measures both reducing and nonreducing sugars. The main sugars of insect honeydew, trehalulose (from whiteflies) and melezitose (from aphids), and of plant sugars (glucose, fructose & sucrose) are all readily identified in this test. The benefit of HPLC analysis is the identification of the source of contamination (whitefly, aphid, or plant) which may help identify specific mitigiation measures MINICARD METHOD: The physical interaction of all sugars on lint with equipment can be measured by several types of machines. The primary difficulty with these physical tests is in standardizing the stickiness measurement. As with chemical testing, these tests must be correlated with measures of fiber processing efficiency in order to interpret the results. One of these tests, the minicard, is a physical test that measures actual cotton stickiness of the card web passing between stainless steel delivery rollers of a miniature carding machine. Modeled after a production carding machine, the minicard must be run under strict tolerances. A ‘0’ minicard rating indicates that no sticking was observed, while progressively higher numbers (on a 0–3 scale) indicate progressively greater amounts of sticking during the process. Cottons with high plant sugar contents evenly distributed along the fibers may fail to be measured as sticky in this test. The minicard test is slow and has been replaced as the international standard by the manual thermodetector. COTTON STICKINESS – 2 STICKY COTTON THERMODETECTOR: The Sticky Cotton Thermodetector (SCT) measures the physical sticking points transferred to aluminum sheets by a conditioned lint sample that is squeezed and heated (to 82.5°C for 12 sec.). Levels of stickiness are categorized according to the number of specks left on the two sheets of foil. Lower numbers of specks are preferable to higher numbers; however, a specific threshold over which all cotton will result in processing problems has not been defined. The SCT takes about 5 minutes to process each sample, requires smaller initial investment costs than the minicard, is more mobile, and its results correlate well with predicted stickiness from the minicard. HIGH SPEED STICKINESS DETECTOR: The High Speed Stickiness Detector (H2SD) is a quicker, automatic version of the thermodetector. The cotton sample is pressed between a heated (54°C for 30 sec.) and an unheated pressure plate. Sticky points are counted and point size distribution determined by image-processing computer software. Plates are automatically cleaned between samples. The H2SD is able to analyze a sample in 30 seconds. FIBER CONTAMINATION TESTER: Like the thermodetector and H2SD, the Fiber Contamination Tester (FCT) measures physical sticking points (at 65% RH). The instrument feeds a thin web between two rollers. Contamination of the rollers interrupts a laser beam, resulting in a recording. Because the cleaning and recording is automated, samples may be processed as quickly as one per 45 seconds. While there is no reliable infield method for detection of stickiness predisposition, the insects responsible for honeydew deposits can be sampled and populations measured. Not all population levels of insects lead to sticky lint; however, chronic numbers of insects, especially during boll opening or an extended season, can lead to excessive insect sugars that result in stickiness. In addition, field factors associated with risk of excessive plant sugars are lateness of the crop, fiber immaturity, and freezing temperatures before harvest. STICKINESS CONTROL: The most efficient way now to prevent stickiness is by managing sugar sources in the field. Detailed integrated pest management plans (see references) for both aphid and whitefly. These honeydew-producing insects may be managed by avoiding conditions leading to outbreaks, carefully sampling pest populations, and using effective insecticides when populations reach predetermined thresholds. The risk of having excessive plant sugars can be minimized by harvesting mature seed cotton. This may be accomplished through plant management tactics that include: early and uniform planting, nitrogen management according to plant growth and yield goals, high first-position boll retention, and timely chemical termination and harvest. If a freeze is imminent and immature bolls are present, the use of boll-opening chemicals can greatly diminish the problem of plant sugar contamination. All these measures work towards early harvest, before freezing conditions that contribute to excess plant sugars. MITIGATING THE PROBLEM: When field management of sugar sources is inadequate to prevent excess accumulation of sugars, mitigation tactics may be necessary to remove excess sugars from the lint. This mitigation may be achieved through both natural and managed processes; however, the specific impact of these processes on stickiness is variable and may depend on the initial level of contamination. Natural processes include weathering, rainfall, and degradation by microorganisms. Since sugars are water soluble, rainfall will wash some honeydew from lint. If sufficient moisture is available, bacteria and molds living on the plants will decompose many honeydew sugars. Complex sugars are broken down to simpler sugars, and the simpler sugars, given sufficient time and moisture, are further broken down to carbon dioxide and water. Unfortunately, microbial action also leads to discoloration and to a weakening of the fibers as well as heating of cotton in modules that may result in reduced seed viability and problems in ginning. Potential in-field mitigation techniques include supplemental oversprays of enzymes or water. Certain carbohydrate degrading enzymes when sprayed on sticky cotton can reduce honeydew to simpler sugars. Microbial activity on the fibers then further degrades these simpler sugars, resulting in a significant decrease in fiber stickiness. However, these enzymes require water for activity, and metering the proper amount of water for activity is a problem yet to be solved. In some areas of the world, overhead and in-canopy irrigation has been used to remove honeydew from open bolls. The frequency of this type of irrigation may be more important than the volume applied. Use of sprinklers has been limited in the Western United States, where furrow irrigation is prevalent. If stickiness is a problem while ginning, the ginning rate of honeydew contaminated cotton can be increased by increasing the heat of the drying towers to reduce humidity. The potential for stickiness can be further reduced by lint cleaning. Both of these practices, however, can result in shorter fibers. Conventional textile lubricants may also be used. Stickiness due to high levels of plant sugars can be reduced by storing the cotton for approximately six months. However, storage of baled cotton will not appreciably reduce stickiness from insect sugars. At the textile mill, stickiness may be managed by blending bales and by reducing humidity during carding. A lubricant in fog form may be introduced at the end of the hopper conveyor, and card crush rolls may be sprayed sparingly with a lubricant to minimize sticking. REFERENCE: THE ABOVE INFORMATION IS FROM THE UNIVERSITY OF ARIZONA PUBLICATION ON COTTON STICKINESS, BLOWROOM · Basic operations in the blowroom: opening cleaning mixing or blending microdust removal uniform feed to the carding machine Recycling the waste · Blow room installations consists of a sequence of different machines to carry out the above said operations.Moreover Since the tuft size of cotton becomes smaller and smaller, the required intensities of processing necessitates different machine configuration. · TECHNOLOGICAL POINTS IN BLOWROOM Opening in blowroom means opening into small flocks.Technological operation of opening means the volume of the flock is increased while the number of fibres remains constant. i.e. the specific density of the material is reduced · The larger the dirt particle , the better they can be removed Since almost every blowroom machine can shatter particles, as far as possible a lot of impurities should be eliminated at the start of the process.Opening should be followed immediately by cleaning, if possible in the same machine. · The higher the degree of opening, the higher the degree of cleaning. A very high cleaning effect is almost always purchased at the cost of a high fibre loss. Higher roller speeds give a better cleaning effect but also more stress on the fibre. · Cleaning is made more difficult if the impurities of dirty cotton are distributed through a larger quantity of material by mxing with clean cotton. The cleaning efficiency is strongly dependent on the TRASH %. It is also affected by the size of the particle and stickyness of cotton. Therefore cleaning efficiency can be different for different cottons with the same trash %. There is a new concept called CLEANING RESISTANCE. Different cottons have different cleaning resistance. If cotton is opened well in the opening process, cleaning becomes easier because opened cotton has more surface area, therefore cleaning is more efficient If automatic bale opener is used, the tuft size should be as small as possible and the machine stop time should be reduced to the minimum level possible · If Manual Bale openers are used, the tuft size fed to the feed lattice should be as small as possible Due to machine harvesting , cotton contains more and more impurities, which furthermore are shattered by hard ginning. Therefore cleaning is always an important basic operation. In cleaning, it is necessary to release the adhesion of the impurities to the fibres and to give hte particles an opportunity to separate from the stock. The former is achieved mostly by picking of flocks, the latter is achieved by leading the flocks over a grid. · Using Inclined spiked lattice for opening cotton in the intial stages is always a better way of opening the cotton with minimum damages. Ofcourse the production is less with such type of machines. · But one should bear in mind that if material is recyled more in the lattice, neps may increase. Traditional methods use more number of machines to open and clean natural fibres. Mechanical action on fibres causes some deterioration on yarn quality, particularly in terms of neps . Moreover it is true that the staple length of cotton can be significantly shortened . Intensive opening in the initial machines like Bale breaker and blending machines means that shorter overall cleaning lines are adequate. · In a beating operation, the flocks are subjected to a sudden strong blow. The inertia of the impurities accelerated to a high speed, is substantially greater than that of the opened flocks due to the low air resistance of the impurities. The latter are hurled against the grid and because of their small size, pass between the grid bars into the waste box, while the flocks continue around the periphery of the rotating beater. By using a much shorter machine sequence, fibres with better elastic properties and improved spinnability can be produced. · Air streams are often used in the latest machine sequence, to separate fibres from trash particles by buoyancy differences rather than beating the material against a series of grid bars. · There are three types of feeding apparatus in the blowroom opening machines two feed rollers( clamped) feed roller and a feed table a feed roller and pedals · Two feed roller arrangements gives the best forwarding motion, but unfortunately results in greatest clamping distance between the cylinders and the beating element feed roller and pedal arrangement gives secure clamping throughout the width and a small clamping distance, which is very critical for an opening machine In a feed roller and table arrangement, the clamping distance can be made very small. This gives intensive opening, but clamping over the whole width is poor, because the roller presses only on the highest points of the web. · Thin places in the web can be dragged out of hte web as a clump by the beaters Honeydew(sugar) or stickiness in cotton affect the process very badly. Beacause of that production and quality is affected. Particles stick to metal surfaces, and it gets aggreavated with heat and pressure. Blowroom – Page 2 · These deposits change the surface characteristics which directly affects the quality and running behavior. · There are chemicals which can be sprayed to split up the sugar drops to achieve better distribution. But this system should use water solutions which is not recommended due to various reasons. It is better to control the climate inside the department when sticky cotton is used. Low temperature ( around 22 degree Celsius) and low humidity (45% RH). This requires an expensive air conditioning set up. · The easiest way to process sticky cotton is to mix with good cotton and to process through two blending machines with 6 and 8 doublings and to install machines which will seggregate a heavier particles by buoyancy differences. General factors which affect the degree of opening , cleaning and fibre loss are, · thickness of the feed web density of the feed web fibre coherence fibre alignment size of the flocks in the feed (flock size may be same but density is different) the type of opening device speed of the opening device degree of penetration type of feed (loose or clamped) distance between feed and opening device type of opening device type of clothing point density of clothing arrangement of pins, needles, teeth speeds of the opening devices throughput speed of material type of grid bars area of the grid surface grid settings airflow through the grid condition of pre-opening quantity of material processed, position of the machine in the machine sequence feeding quantity variation to the beater ambient R.H.% ambient teperature · Cotton contains very little dust before ginning. Dust is therefore caused by working of the material on the machine. New dust is being created through shattering of impurities and smashing and rubbing of fibres. · However removal of dust is not simple. Dust particles are very light and therefore float with the cotton in the transport stream.Furthermore the particles adhere quite strongly to the fibres. If they are to be eliminated they are to be rubbed off.The main elimination points for adhering dust therefore, are those points in the process at which high fibre/metal friction or high fibre/fibre friction is produced. · Removal of finest particles of contaminants and fibre fragments can be accomplished by releasing the dust into the air, like by turning the material over, and then removing the dust-contaminated air. Release of dust into the air occurs whereever the raw material is rolled, beaten or thrown about. Accordingly the air at such positions is sucked away. Perforated drums, stationary perforated drums, stationary combs etc…. are some instruments used to remove dust. CARDING INTRODUCTION “Card is the heart of the spinning mill” and “Well carded is half spun” are two proverbs of the experts. These proverbs inform the immense significance of carding in the spinning process.High production in carding to economise the process leads to reduction in yarn quality.Higher the production, the more sensitive becomes the carding operation and the greater danger of a negative influence on quality.The technological changes that has taken place in the process of carding is remarkable. Latest machines achieve the production rate of 60 – 100 kgs / hr, which used to be 5 – 10 kgs / hr, upto 1970. THE PURPOSE OF CARDING: to open the flocks into individual fibres cleaning or elimination of impurities reduction of neps elimination of dust elimination of short fibres fibre blending fibre orientation or alignment sliver formation TECHNOLOGICAL POINTS IN CARDING There are two types of feeding to the cards 1. feeding material in the form of scutcher lap 2. flock feed system (flocks are transported pneumatically) lap feeding linear density of the lap is very good and it is easier to maintain(uniformity) the whole installation is very flexible deviations in card output will be nil, as laps can be rejected autolevellers are not required, hence investment cost and maintenace cost is less transportation of lap needs more manual efforts( more labour) lap run out is an additional source of fault, as it should be replaced by a new lap more good fibre loss during lap change more load on the taker-in, as laps are heavily compressed flock feeding high performance in carding due to high degree of openness of feed web labour requirement is less due to no lap transportaion and lap change in cards flock feeding is the only solution for high prouduction cards linear density of the web fed to the card is not as good as lap installation is not felxible autoleveller is a must, hence investment cost and maintenance cost is more Rieter has devloped a “unidirectional feed system” where the two feed devices(feed roller and feed plate are oppositely arranged when compared with the conventional system. i.e. the cylinder is located below and the plate is pressed against the cylinder by spring force. Owing to the direction of feed roller, the fibre batt runs downwards without diversion directly into the teeth of the taker-in(licker-in) which results in gentle fibre treatment. This helps to reduce faults in the yarn. The purpose of the taker-in is to pluck finely opened flocks out of the feed batt, to lead them over the dirt eliminating parts like mote knives, combing segment and waste plates, and then to deliver the fibres to the main cylinder. In high production cards the rotational speed ranges from 700-1400 CARDING – Page 2 The treatment for opening and cleaning imparted by Taker-in is very intensive, but unfortunately not very gentle.Remember that around 60% of the fibres fed to the main cylinder is in the form of individual fibres. The circumferential speed of Taker-in is around 13 to 15 m/sec and the draft is more than 1000.It clearly shows that fibre gets deteriorated at this opening point. Only the degree of deterioration can be controlled by adjusting the following the thickness of the batt the degree of openness of the rawmaterial the degree of orientation of the fibres the aggressiveness of the clothing the distance between the devices the rotational velocity of the taker-in the material throughput Latest TRUTZSCHLER cards work with three licker-ins compared to one liker-in.The first one is constructed as needle roll. This results in very gentle opening and an extremely long clothing life for this roll. The other two rollers are with finer clothing and higher speeds, which results in feeding more %of individual fibres and smallest tufts compared to single lickerin, to the main cylinder. This allows the maing cylinder to go high in speeds and reduce the load on cylinder and flat tops. There by higher productivity is achieved with good quality. But the performance may vary for different materials and different waste levels. between the taker-in and main cylinder , the clothings are in the doffing disposition. It exerts an influence on the sliver quality and also on the improvement in fibres longitudinal orientation that occurs here. The effect depends on the draft between main cylinder and taker-in.The draft between main cylinder and taker-in should be slightly more than 2.0. The opening effect is directly proportional to the number of wire points per fibre. At the Taker-in perhaps 0.3 points/ fibre and at the main cylinder 10-15 points /fibre.If a given quality of yarn is required, a corresponding degree of opening at the card is needed. To increase production in carding, the number of points per unit time must also be increased. this can be achieved by more points per unit area(finer clothing) higher roller and cylinder speeds more carding surface or carding position speeds and wire population has reached the maximum, further increase will result in design and technological problems. Hence the best way is to add carding surface (stationary flats). Carding plates can be applied at under the liker-in between the licker-in and flats between flats and doffer Taker-in does not deliver 100% individual fibres to main cylinder. It delivers around 70% as small flocks to main cylinder. If carding segments are not used, the load on cylinder and flats will be very high and carding action also suffers. If carding segemets are used, they ensure further opening, thinning out and primarily, spreading out and improved distribution of the flocks over the total surface area.carding segments bring the following advantages improved dirt and dust elimination improved disentanglement of neps possibility of speed increase (production increase) preservation of the clothing possibility of using finer clothings on the flats and cylinder better yarn quality less damage to the clothing cleaner clothing In an indepth analysis, all operating elements of the card were therefore checked in regard to their influence on carding intensity. It showed that the “CYLINDER-FLATS” area is by far the most effective region of the card for. opening of flocks to individual fibres elimination of remaining impurities(trash particles) elimination of short fibres( neps also removed with short fibres) untangling the neps dust removal high degree of longitudinal orientation of the fibres The main work of the card, separation to individual fibres is done between the main cylinder and the flats Only by means of this fibre separation, it is possible to eliminate the fine dirt particles and dust. When a flat enters the working zone, it gets filled up very quickly. Once it gets filled, after few seconds, thereafter , hardly any further take-up of fibres occurs, only carding.Accordingly, if a fibre bundle does not find place at the first few flats, then it can be opened only with difficulty.It will be rolled between the working surfaces and usually leads to nep formation In principle, the flats can be moved forwards or backwards, i.e. in the same direction as or in opposition to the cylinder. In reverse movement, the flats come into operative relationship with the cylinder clothing on the doffer side. At this stage, the flats are in a clean condition. They then move towards the taker-in and fill up during this movement. Part of their receiving capacity is thus lost, but sufficient remains for elimination of dirt, since this step takes place where the material first enters the flats. At this position, above the taker-in, the cylinder carries the material to be cleaned into the flats. The latter take up the dirt but do not transport it through the whole machine as in the forward movement system. Instead , the dirt is immediately removed from the machine. Rieter studies show clearly that the greater part of the dirt is hurled into the first flats directly above the taker-in. Kaufmann indicates that 75% of all neps can be disentagled, and of these about 60% are in fact disentagled. Of the remaining 40% disentaglable nep 30-33% pas on with the sliver 5-6% are removed with the flat strips 2-4%are eliminated with the waste The intensity of nep separation depends on the sharpness of the clothing the space setting between the main cylinder and the flats tooth density of the clothing speed of the main cylinder speed of the flat tops direction of flats with reference to cylinder the profile of the cylinder wire The arrangement of the clothing between the cylinder and the doffer is not meant for stripping action, It is for CARDING ACTION. This is the only way to obtain a condensing action and finally to form a web. It has both advantages and disadvantages. The advantage is that additional carding action is obtained here and it differs somewhat from processing at the flats. A disadvantage is that leading hooks and trailing hooks are formed in the fibres , because the fibres remain caught at one end of the main cylinder(leading hook) and some times on the doffer clothing(trailing hook). There are two rules of carding The fibre must enter the carding machine, be efficiently carded and taken from it in as little time as possible. The fibre must be under control from entry to exit Carding effect is taking place between cylinder and doffer because, either the main cylinder clothing rakes through the fibres caught in the doffer clothing, or the doffer clothing rakes thro the fibres on the main cylinder. Neps can still be disentangled here, or non-separated fibre bundles can be opened a bit in this area and can be separated during the next passage through the flats A disadvantage of web-formation at the card is the formation of hooks. According to an investigation by morton and Yen in Manchester, it can be assumed that 50% of the fibres have trailing hooks 15% have leading hooks 15% have both ends hooked 20% without hooks Leading hooks must be presented to the comber and trailing hooks to the ring spinning frame. There must be even number of passages between card and comber and odd number between the card and ringframe. Fibre Dynamics in the Revolving-Flats Card A Critical Review C.A. Lawrence, A. Dehghani, M. Mahmoudi, B. Greenwood and C.Iype School of Textile Industries University of Leeds Over the last 30 years numerous developments have taken place with the cotton card. The production rate has risen by a factor of 5 with the main rotating components running at significantly higher speeds. Triple taker-in rollers and modified feed systems are in use, additional carding segments are fitted for more effective fibre opening, and improved wire clothing profiles have been developed for a better carding action. Advances in electronics have provided much improved monitoring and process control. Most of these developments have resulted in enhanced cleaning of cotton fibres, reduced neppiness of the card web and better sliver uniformity. Despite the various improvements made to the card a commonly held view is that more is known about the cleaning processes on the card than about the carding process itself . For instance, modern cards can achieve an overall cleaning efficiency of 95%. It is well established that the cleaning efficiency of modern taker-in systems is a round 30%, that the cylinder/flats action with the latest wire clothing profiles gives 90% cleaning efficiency and that effective cleaning is associated with lower neps in the card web . However, even though the nep content and the sliver Uster CV% are used as quality measures of carding performance they are not satisfactory indicators for anticipating yarn quality. This is because some fibre arrangements in the sliver may lead to nep formation and imperfections during up-stream drafting processes . In addition to the removal of trash and neps, important aspects of the carding process in relation to yarn quality and spinning performance are the degree of fibre individualisation, the fibre extent and the fibre hook configurations in the sliver. With regard to these factors, increased production rate can reduce carding quality . It is therefore of importance that a better understanding is established of the effect that carding actions have on such quality parameters, particularly at high production rates. The most widely accepted view of how fibres are distributed within the card under steady-state conditions is illustrated in Figure 1 . Reported studies into the fundamentals of the carding process have largely been concerned with how the principal working components of the card affect this distribution of fibre mass and interact with the mass to achieve:trash and nep removal from cottons; the disentangling of the fibre mass into individual fibres, with minimal fibre breakage; and the alignment of the fibres to give a sliver suitable for drafting in down stream processes. These actions occur at the interface of the card components within the three zones indicated in Figure 1. This paper therefore gives a critical review of published research on the: · mechanisms by which the fibre mass is broken down into individual fibres, · mechanisms of fibre transfer between the component parts of the card · effect of the saw-tooth wire geometry on these actions Figure 1: Distribution of Fibre Mass during Short-Staple Carding Q1: fibre mass transferred from cylinder to doffer K : transfer coefficient Q2: recycling layer QL: fibre mass transferred from taker-in to cylinder Qf : flat strips Qo : operational layer (where Q is mass per unit time) Zone 1: Fibre-Opening Separation and Cleaning of the Input Fibre Mass: The taker-in has effectively a combing action , which results in the breakdown of the tufts, consituting the fed fibre mass, into single fibres and smaller size tufts (tuflets), and in the liberation of trash particles ejected from the mass flow by the mote knives positioned below the taker-in. To effectively breakdown the fibre mass feed into tuftlets with minimal fibre breakage, the taker-in wire has to be coarse, with a low number of points per unit area (4.2 to 6.2 pcm-2) and not too acute an angle of rake. The objective is to obtain gentle opening of the fibre mass feed and easy transfer of the tuftlets to the cylinder. Angles of 80o – 85o are used for short and medium length cottons to give effective opening and cleaning. For longer cottons and synthetics, a 90o or negative rake may be needed to facilitate gentler opening and satisfactory fibre transfer to prevent lapping of the taker-in . Fibres, usually very short fibres, which are not adequately held by the teeth or present in the interspaces of the clothing are ejected causing fibre loss. However, it is the mote knives that govern the amount of fibre to trash (i.e. lint) in the extracted waste. Experimenting with the settings of two mote knives below the taker-in, Hodgson found that the absence of the knives greatly increased the lint content with little increase in trash. With the knives present, the best setting was that which gave the least waste since increasing the amount of waste did not improve cleaning. Artzt found that irrespective of teeth density and tooth angle the waste increased with taker-in speed but the increase was attributed to higher lint content. It is reasonable to assume that the smaller the tuftlet size and the greater the mass ratio of individual fibres to tuftlets the better the cleaning effect of the taker-in. Supanekar and Nerurkar suggest that the takerin breaks down the fibre feed into tuftlets of various sizes and mass, conforming to a normal frequency distribution. In the case of cotton, some tuftlets may consist of only fibres whilst others will contain seed or trash particles embedded among the fibres, these tuftlets constituting the heavier end of the distribution curve. Thus, the mean of the distribution would depend on the trash content of the material, as well as on the production rate, the taker-in speed and the wire clothing specification. However, the authors did not report any data to support their ideas. Little detailed information has yet been published on the mass variation of tuftlets or on the relative proportion of discrete fibres to tuftlets resulting from the combing action of the taker-in. Nittsu using photographic techniques studied the effect of process variables on tuftlet size. It was found that the total number of tuftlets decreases the closer the feed plate setting, the lower the feed rate, the smaller the steeper rake of the saw-tooth clothing and the higher the licker-in speed. Since th licker-in opens the batt into both tuftlets and individual fibres , a decrease in the total number of tuftlets suggests an increase in the mass of individual fibres. Liefeld calculated estimates of the opened fibre mass at various stages through the blowroom and gives a value of 50mg for tuftlets on the taker-in. Mills claims that the calculated optimum number of fibre per tooth is one, and that this should be maintained at increased production rates by increasing the taker-in speed. There is, however, the question of fibre damage at high taker-in speeds. Figure 2: Frequency distribution of tuftlet mass N: Taker-in speed (rpm), P: Production rate (kg/hr) Honold and Brown found no fibre damage occurred at speeds of up to 600 r/min. Krylov reports the absence of fibre breakage at speeds up to 1,380 r/min, and Artzt’s work shows taker-in speeds to have a negligible effect on fibre shortening and subsequently on yarn strength. In all cases cotton fibres of 26.5- 30.2 mm (2.5% span length) and 3.8 – 4.9 micronaire were processed. The level of fibre breakage, however, would seem to depend on production rate and the batt fringe setting to the licker-in. High production rates achieved by increased sliver counts and a close setting of the batt fringe result in significant fibre breakage.No fundamental studies have been reported on the forces involved in the fibre-wire interaction of revolvingflat card components. However, Li and etal report a simulated study of fibre-withdrawal forces for wool in high-speed roller- clearer cards. Although impact forces could cause damage , it was found that card component speeds had no significant effect on the withdrawal-force, and that fibre configuration and entanglement were the important factors. The importance of producing small size tuftlets is evident form the various components fitted in the fibreopening zone on modern short-staple cards. Saw-tooth wire covered plates, termed combing segments, fitted below the taker-in or built into the taker-in screen are claimed to give improved trash removal. Reportedly , the stationary flats fitted between the taker-in and the revolving flats provide extra opening of the tuftlets transferred to the cylinder from the taker-in. They also act as a barrier to large, hard, trash particles such as seed coats, protecting the wire of the revolving flats from damage, particularly at high cylinder speeds. This enables finer wire to be used for the revolving flats and thereby improves the cleaning effect of the interaction between cylinder and revolving flats. The chances are also reduced of longer length fibres becoming deeply embedded in the revolving flats to become part of the flat strips. These attachments are widely accepted by the industry as beneficial, particularly at high production speed. However, there is no published systematic study of their effectiveness in reducing tuft size, and the effect of stationary flats on the recycling layer, Q2, is unknown. The little information that is available attempts to illustrate the effectiveness of these components on yarn quality, but there is no evidence of analytical rigour in the way the data were obtained. Fibre Dynamics in the Revolving-Flats Card – 2 Fig 3. shows the effect of the combing segment and the stationary flats on dust deposits in rotor spinning and on the imperfections in several types of ring spun yarn. The figure includes values for the effect of stationary flats above the doffer, but this will be considered in a later section. It would appear that the added components in the taker-in region might well reduce the dust deposit in the rotor, but the results showing improvements in yarn quality are not convincing, and in all cases the stationary flats above the doffer appear the most effective. Leifeld reports that the cylinder – revolving flats carding action occurs when the fibre mass delivered to the cylinder is in a highly opened state. Tandem cards are said to give a high standard of carding with low nep and trash levels in the card web. This is because a uniform web of almost discrete fibres is fed to the second cylinder of the tandem card and closer revolving flat settings with higher cylinder speeds can be used . Single taker-in systems, even with combing segments and stationary flats, cannot give as high a degree of opening. However, Leifeld reports that a triple taker-in system facilitates high taker-in speeds and, fitted to a single-cylinder card, feeds a uniform web of discrete fibres to the cylinder, thereby offering a more cost-effective process than the tandem card, but no comparative data for the two types of card are given. Although it may be reasoned that a triple taker-in action should improve nep removal, it is of importance to compare the web qualities with regard to dust and trash content, the level and type of fibre hooks, and the degree of fibre parallelism since these greatly influence yarn quality. Figure 3: Effect of Combing Segment and Stationary Flats Contradicting the triple taker-in approach, Mills states that the fibrous material fed to the card should not be broken down into individual fibres by the taker-in system. This is because the fibres would remain largely disoriented with a high proportion of them lying transversely to the direction of mass flow when transferred to the cylinder and subsequently to the revolving flats. This can result in fibre loss during transfer to the cylinder and an unevenness of the fibre mass across the cylinder width, causing neps to be formed and degrading the carding action between the cylinder and the revolving flats. It is claimed that good carding requires a thin, uniformly distributed sheet of well-opened tuftlets fed to the cylinder from the taker-in. Fujino reports results that would appear to confirm the view that as the level of opening increases through faster taker-in speed, the degree of fibre parallelism on transfer to the cylinder decreases. The nep level in the card web was, however, observed to decrease noticeably with increased taker-in speed. This was attributed to the reduced speed ratio of the cylinder and taker-in. Artzt found that reducing the takerin/ cylinder draft ratio from 2.4 to 1.4 caused yarn imperfections to increase. In contrast to these findings Harrison states that increasing taker-in speed did not affect the nep level in the card web, the exception being for low micronaire cottons. The apparent contradictions in these results suggest that a better understanding of the transfer mechanism may be needed which takes into account fibre properties. Fibre Mass Transfer to Cylinder Two contrasting views have been reported on the mechanism of fibre transfer. Oxley suggests that the fibre mass on the taker-in is ejected between the cylinder wire and the back plate. Whereas Varga believes that the fibre mass is stripped from the taker-in in the following way. In the feed to the card, tufts and fibres lie randomly and by the action of the taker-in are brought into length-wise orientation in the direction of the roller rotation. The trailing ends of newly formed tuftlets protrude above the taker-in wire and are easily stripped by the cylinder wire clothing. This implies that the transfer involves a reversal of the leading and trailing ends of the fibres. Further orientation and parallelism of the fibre mass is thought to occur during the transfer onto the cylinder. No experimental work has been published which specifically involves a study of the transfer of fibres from the taker-in to the cylinder. Therefore it has yet to be established whether at the interface, the cylinder, which has the faster surface speed, strips the fibre mass with its clothing or the taker-in, through the action of centrifugal forces, ejects the tuftlets and single fibres onto the cylinder, or a combination of both occurs. It is also of interest to determine if the airflow in the region assists the fibre mass transfer. Whatever the case, the fibre mass is likely to be subjected to an uncontrolled drafting effect, which could introduce irregularities in the mass flow. Zone 2: The Fibre Carding Zone In the carding zone, it is the interaction of the fibre mass and the wire-teeth clothing of cylinder and flats that fully individualises the fibres and gives parallelism to the fibre mass flow. In considering how fibres enter and are individualised in the carding zone, Oxley suggests that tuftlets are not strongly held on the cylinder clothing because the tooth angle faces the direction of cylinder rotation. They are, thus, easily removed and more firmly held by the opposing teeth of the flats. It is therefore assumed that as a flat enters the carding zone it becomes almost fully loaded with fibres, the airflow within the region assisting the fibre mass transfer. Having been stripped of fibre mass, subsequent following areas of the cylinder wire clothing move past the fully loaded flat and proceed to comb fibres from the flat, carrying them towards the doffer. The action of combing causes the fibres to be hooked around the cylinder wire points and prevents them from being easily removed by other flats. Debar and Watson’s experiments of the movement of radioactive tracer fibres through a miniature card showed that some fibres caught by the flats were often only removed by the cylinder-wire clothing after many revolutions of the cylinder. Varga reports an alternative view to Oxley’s, stating that two types of action occur at the cylinder-flats interface. First, a carding action where the upper layer of a tuftlet or a loosely opened fibre group is caught and held by the flats whilst simultaneously the bottom layer is sheared away by the fast moving cylinder surface. This action causes the top to hang from the flats and to contact subsequent parts of the cylinder wire surface resulting in the second action which is combing, where the wire clothing of the cylinder hooks single or a small group of fibres and combs them from the top layer. A second flat catches the bottom layer on the cylinder and the actions are repeated. In this way tuftlets or groups of fibres are separated into individual fibres. By making abrupt changes in the colour of the fibre mass fed to the card, Oxley demonstrated that tuftlets from the load on a given flat are carried forward by the cylinder clothing and separated into individual fibres over a small number of preceding flats, typically 4. It was concluded that the interchange of fibres between cylinder and flats does not occur over the full carding zone. Sengupta ] made measurements of the carding/combing forces and showed that essentially these actions were on average confined to the first ten working flats. Figure 4: Relation of Flat Load and Working Time A study by Hodgson showed that moving in the direction of the cylinder rotation, a given flat acquires two-thirds of its final load directly it comes into position over the cylinder. The load then increases exponentially with time, reaching nine-tenths of the final value within 6-8 minutes. Completion of the load takes place slowly during the remainder of the working time. See Fig 4. As shown in the figure, with flats moving in the reverse direction the load first increases rapidly with time and then slows until the flat is about to leave the working area. Here it encounters the fibre layer being transported on the cylinder surface from the taker-in. The flat receives a sudden addition of fibre mass to become fully loaded, and, in agreement with other results , the load weighs more than for the forward direction of motion. Contrary to Oxley’s conclusions, it was found that 30% of the final load on a given flat resulted from fibre interchange between flats and cylinder over the full carding zone. It may be reasoned that the number of flats involved in separating a tuftlet depends on the tuftlet size, the mass flow rate and the flat setting. Large tuftlets will be pressed into the cylinder wire during the carding action, whereas small tuftlets will be more easily carded and will remain at the top of the cylinder wire teeth. The larger the tuftet, the higher the production rate and the closer the flat settings, the greater the number flats involved in the separation of a given tuftlet. Bogdan reports that flats tend to load quickly at the beginning of their cycle of contact with the cylinder. This, however, is only a partial loading, since the fibre mass tends to resist more fibres entering the space but, in the case of cotton, not the leaf and trash particles present. Analysis of the trash in cotton flat strips showed that initially the percentage of trash in a given flat strip is low and increases slowly during the first 10 minutes of carding, then remains at almost a constant value . The final percentage depends on the trash content of the cotton. For a fixed production rate, the amount of flat strips was found to be directly proportional to the flat speed, but provided the speed was such that the working time was not less than 10 minutes, both the weight and composition of the flat strips remained approximately constant. Feil claims that a high degree of air turbulence exists in the flat/cylinder zone. A combination of centrifugal forces, mechanical contact with the flat wire and air turbulence causes the trailing ends of fibres attached individually to the cylinder clothing to vibrate and shake loose trash and dust particles. Short fibres which cannot adequately cling to the cylinder clothing will also be shaken free, and along with impurities become part of the flat strips. Fibre Dynamics in the Revolving-Flats Card – 3 Fibres that are deeply embedded in the flats, and cannot be reached by the cylinder wires become flat strips. For this reason the closeness of the flats setting to the cylinder is important. It may be assumed that closer flats/cylinder setting and faster cylinder speeds will give more effective carding and combing actions as described by Varga and thereby improve web quality through reduced neps and trash . Cylinder diameters vary and Karasev showed mathematically that for a given cylinder rotational speed the carding power will be greater for a larger cylinder diameter with a higher number of working flats. However, because of lower mechanical stresses, smaller cylinders can be rotated at higher speeds than larger cylinders. The above advantage is therefore reduced the higher the speed of the smaller cylinder. Artzt studying the influence of card clothing parameters and cylinder speeds on yarn imperfections, report that the teeth density of the flats and cylinder, and the speed of the cylinder must prevent tuftlets lying within the spiral pitch of the cylinder clothing. If this occurs the tuftlets generally become the thick places in the yarn. It was found that high teeth densities and low cylinder speeds were as effective as lower teeth densities and high cylinder speed. High teeth densities with high cylinder speeds did not give effective carding, but no reason was reported for this. Since the action of the cylinder in this region is to individualise fibres, the wire clothing on the cylinder has a steeper rake and a higher point density than the wire clothing of the flats. Thus, with closer settings and higher cylinder speeds greater forces may be involved and may result in fibre breakage. However, the work of Li indicates that the withdrawal forces needed to separate an entangled fibre mass was largely dependent on the density of the fibre mass and the contact angle fibres made with the wire clothing, than on the machine speeds. Van Alphen reports that increasing cylinder speed causes more fibre breakage than increasing taker-in speed and that this is reflected in the yarn properties. Rotor yarn tenacity was reduced by up to 5% with increasing cylinder speeds between 480 –600 r/min. Whereas ring yarns showed a 5% reduction for speeds between 260 – 380 r/min and 10% at 600 r/min. The higher sensitivity of ring yarns to fibre breakage was attributed to the negative effect of short fibres during roller drafting. Krylov reports that no fibre shortening was observed for cylinder speeds up to 380 r/min. It may be reasoned that the smaller the tuftlets and the more parallel fibres in tuftlets are to the direction of mass flow the lower the probability of fibre breakage. Honold attributes fibre damage to the cylinder/flat interaction and suggested that the degree of damage depends on the size of the tuftlets entering the working area; the smaller the tuftlets, the closer the setting that can be used and the lower the fibre breakage . Hodgson’s work showed fibre length is also an important factor. For cottons, fibre breakage was only found to have occurred when the staple length was greater than 25mm. Increasing the flat speed appears to have no effect on fibre breakage. However, the amount of flat strips increased proportionally with the flat speed and the mean fibre length of the strips increased significantly. This means that faster flat speeds result in larger amounts of useable fibre in the waste. Interestingly, when carding cottons, immature fibres were not readily found in the flat strips. The coarser rigid fibres seem more easily retained by the flats. The effectiveness of the carding and combing actions within the cylinder/flats area is, inter alia, dependent on the quantity of fibre mass on the cylinder, and this includes the recycling layer, Q2. It is of interest therefore to consider how the Q2 is formed during fibre transfer from cylinder to doffer, and its importance to the card web quality. Zone 3: Cylinder / Doffer Interaction Varga reports that the action of fibre mass transfer to the doffer is similar to the transfer at the input to the cylinder-flats zone. The regions above and below the line of closest approach of the cylinder to the doffer (i.e. the setting line) are important to the mechanism of fibre mass transfer and the transfer coefficient, K. The two regions may be termed the top and bottom co-operation arcs or top and bottom zones. Simpson claims that transfer can occur in both zones and that the particular region in which transfer actually occurs influences the fibre configuration and the nep level of the card web, although cylinder-flats action is more important in reducing neps. Which zone transfer occurs in is dependent on the cylinder-doffer surface speed ratio, C/D. For high C/Ds, transfer occurs in the top zone and results in a larger number of trailing than leading hook fibres and a low nep level. The reverse occurs when transfer takes place in the bottom zone owing to lower C/Ds. Simpson does not however say at what C/D value transfer changes from one zone to the other. Although reference is made to other authors who have proposed a mechanism for fibre transfer in the top zone, no mechanism or experimental evidence is given to support the idea of fibre transfer in the bottom zone. Lauber and Wulfhorst used laser-doppler anemometry and high-speed cine photography to study fibre behaviour in the bottom zone, i.e. up to110 mm below the setting line. Their findings showed no evidence of fibre transfer within the bottom zone. Since Morton and Summers’ work in 1949 other researchers have confirmed that the values given in Table 1 for the five classes of fibre configuration observed in slivers. It is of interest to note that the hooked lengths are greater for leading than trailing hooks. Although, the calendar draft can be used to change the relative proportions, Gosh and Bhaduri showed that the method of removing the web from the doffer does not influence the propensity of any class of configuration. It is the mechanism of transfer that is seen as principally responsible for the shape fibres have in the sliver. Table 1: Classification of Fibre Configuration in Card Sliver Several studies have been reported on the fibre-mass-transfer mechanism. A number used tracer fibres with one end of a fibre dyed a different colour from the other. The reported findings suggest that fibre mass transfer occurs by fibres acting independently and not as a web of fibres. Observations showed that prior to transfer, nearly 70% of fibres on the cylinder had leading hooks, only 9% had trailing hooks. On transfer the relative proportions changed as indicated in Table 2. Half the number observed underwent reversals, with greater than 70% changing their configurations [e.g. leading hooks becoming trailing hooks]. Of those that transferred without reversals ca 90% did so with a change of configuration. Table 2: Mode of Fibre Transfer from Cylinder to Doffer Ghosh and Bhaduri report that tracer fibres were noted generally to go around with the cylinder for several revolutions before being transferred by the doffer. On occasions transfer only happened when the cylinder speed was increased. Debar and Watson’s work with radioactive viscose tracer fibres showed that a fibre on the cylinder wire passes the doffer up to a maximum 20 times before being removed by the doffer, sometimes interchanging several times between the cylinder and flats, during the 20 revolutions on the cylinder. Hodgson found that cotton fibres make between 10 and 25 cylinder revolutions before being removed by the doffer. With the continuity of fibre mass flow through the card, this means that the doffer web is built up over many cylinder revolutions and that the recycling layer, Q2, is comprised of multiple fractional layers of the fibre mass transferred from taker-in to cylinder during these cylinder revolutions . Figure 5: Mechanism of fibre transfer for trailing hook formation A proposed hypothesis for the mechanism of fibre transfer is illustrated in Figure 5. Here the trailing ends of fibres are lifted from the cylinder surface by centrifugal forces and become hooked around the teeth of the doffer clothing. The frictional drag of the doffer clothing eventually removes these fibre from the cylinder clothing. This mechanism only explains the formation, without reversal, of trailing hooks in the doffer web. However, the importance to fibre transfer of the relative angles and tooth lengths of the cylinder and doffer is self evident from the figure. Baturin developed equations that showed the importance of tooth angle and teeth density of the cylinder and doffer wires to the value of K and thereby Q2. Other investigators have reported experimental data that verify Baturin’s equations. It was found that the more acute the working angle of the doffer wire compared to the cylinder wire, the higher the value of K, and the lower Q2, and that higher teeth densities on the doffer increased K. These findings would tend to suggest that the proposed mechanism is a principal action by which fibres are removed from the cylinder. However, this mechanism of fibre transfer does not explain the change of fibre configuration with reversals and the formation of leading hooks in the doffer web. It also does not explain how fibres forming the recycling layer, Q2, are subsequently removed, even though an input layer of fibre mass is added to Q2 each time it passes the taker-in. The above studies did not take account of the degree of fibre parallelism on the cylinder prior to transfer, nor the number of fibres per tooth on the cylinder and consequently the likelihood of fibre interaction during transfer. Fujino and Itani used a microscopic technique to observe the orientation of fibres on the cylinder surface above the taker-in and just before the doffer, and in the doffer web. They found that fibres showed the highest degree of parallelism when on the cylinder surface just above the doffer. The degree of parallelism decreases on transfer to the doffer, and further deteriorates when the web is removed from the doffer to form the sliver, even though the calendar draft helps to maintain some degree of parallelism. Grimshaw and others report the use of fixed flats just before the cylinder/doffer top transfer zone, to improve fibre parallelism in the card web.; up to 20% reduction in fibre hooks and 25% improvement in fibre parallelism were obtained in the card web, resulting in improved yarn properties. Figure 3 shows that the fixed flats in this region are more effective in improving yarn properties compared with the fixed flats above the taker-in. The action of the flats fitted above the doffer is not fully understood. It is assumed that they tend to lift the fibres to the tip of the cylinder wire for more effective transfer to the doffer, particularly at high cylinder speed. Lauber and Wolfhorst , Kamogawa, report that in this region aerodynamic forces affect the parallelism of the fibres and the way they are transferred to the doffer. However, no details are given. Owing to the higher speed and larger diameter of the cylinder, it is assumed that during transfer in the top zone the fibres are more substantially affected by the flow of air transported with the cylinder’s than by the doffer’s wire clothing. High-speed photographs showed that in the bottom zone the main flow of fibre mass was with the doffer at close to the doffer speed, even when the fibres were just below the cylinderdoffer setting line. However, some fibres were seen to be free of both the doffer and cylinder and tended to move with the air currents and eventually with the motion of the cylinder surface. From the above discussion, it can be seen that work is still needed to establish a more detailed understanding of fibre mass transfer between the cylinder and doffer. The results of such work may also help in better explaining how fibres remain on the cylinder to form the recycling layer Q2. Varga suggests that with fibre transfer in the top zone, the thicker layer of web on the doffer surface protrudes above the doffer wire and into the gap setting between doffer and cylinder. The faster moving cylinder wire clothing combs through the doffer web and thereby pulls fibres back onto the cylinder surface. De Swann showed that fibres can be readily transferred from the doffer to the cylinder as well as from cylinder to doffer. In Hodgson’s study , changing cylinder/doffer setting affected the neppiness of the web but did not affect K, which seems to contradict Varga’s view. Baturin and Simpson however showed that K will increase if the region of interaction between the cylinder and doffer is reduced by decreasing the doffer or the cylinder diameter and this tend to supports Varga’s suggestion for a combing and robbing action of the cylinder. It is reasonable to assume that the combing action could lead to fibres in Class II and IV (Table 1), but there is still no verified explanation of how fibres in Classes I, III, and V are formed, with and without reversals. Much of the research on the cylinder / doffer interaction concerns the effect of machine variables on the size of Q2 (or the operational layer, Qo), on the web quality and changes to the relative proportions of the classified configurations, and on ultimately the yarn quality. Sing and Swani developed a Markovian model for the carding process in order to determine the probabilities of fibre transfer between cylinder and flats and cylinder and doffer, taking into account the recycling of fibres. It was shown that the times spent by a fibre on the cylinder, Tr, and in the flats/cylinder region, Td, are given by: Tr = 1 / K and Td = Tr . Pf …………. (1) Where K = Q1 / Qo and Pf = Qf / Qo Reported values for K would seem to vary between 0.2% to 20% , depending on doffer and cylinder speeds, on the relative profiles of the saw-tooth wire clothing, and on the sliver count. Simpson suggests that fibre properties are also of importance, in that there is a tendency for low micronaire cottons to give higher cylinder loading and for fibres with low shear friction and good compression recovery to result in higher K values. No physical explanation is given for these findings and no other studies are reported on the effect of fibre properties. Further work is therefore needed in this area. Figure 6: Effect of Cylinder and Doffer Speed on K and Pf A popular view is that a low fibre mass entering the cylinder/flats interface, i.e. a low fibre load on the cylinder, results in better quality carding . This would seem to imply that the higher the value of K the better the carding since less fibre mass is recycling to be added to the mass transferred from the taker-in. However, there are several ways of increasing K and not all of them result in improved carding quality. Figure 6, shows that for a given cylinder speed and sliver count, increased doffer speed increases K and reduces Pf , whereas keeping the doffer speed and sliver count constant and increasing the cylinder speed increase both K and Pf . For constant cylinder and doffer speeds, increased sliver count was found to reduce K and Pf. If the same up stream machinery is used, then the best measure of effective carding is the quality of the carded ring-spun yarns produced . Gosh and Bhaduri’s work showed that for a fixed carding rate, with increasing doffer or cylinder speed, K increases but Qo and the yarn imperfections decrease; no trend was found with yarn tenacity or irregularity. Singh and Swani studied the properties of yarns made from slivers corresponding to differing K and Pf values and found that Pf was the more important of the two parameters, in that the higher the value of Pf the better the yarn quality. Kaufman reports that the lighter the fibre load is on the flats, the better the carding quality. Thus, the use of Pf does not give an adequate understanding of the importance of the recycling layer nor of the size of the fibre mass load at the cylinder/flats interface. Figure 7: Effect of Doffer Speed on Carding Parameters Baturin reports an alternative approach to the above in which the following expression was derived for the number of cycles, Np, under steady state conditions that fibres on the cylinder clothing make pass the flats before being removed by the doffer: Np = 1 + Vc/KVd ………….. (2) Where K is the transfer coefficient Vc and Vd are cylinder and doffer surface speeds (m/min). Since this gives the number of times the recycling fibre mass is subjected to the carding action, it may be a better indication than Pf of the importance of Q2. From the expression, Np decreases when K increases by increasing doffer speed. Figure 7 shows that for a constant production rate, web quality decreases when Np decreases with doffer speed, even though the cylinder load decreases and a high number of cylinder teeth per fibre is obtained. The last two parameters are usually taken as indicative of good carding. Figure 8 shows the effect of increased doffer speed and sliver count on web quality and there is a consistent trend which suggests that increasing the production rate by increasing the sliver count, instead of doffer speed, gives better web quality. With regard to sliver irregularity, several investigators report theoretical and experimental studies showing that increasing the recycling layer, Q2, reduces the short-term irregularity. Figure 8: Effect of Doffer Speed and Sliver Count on Web Quality Karasev attempted to show experimentally the importance of Q2 by removing it during carding using a suction extractor. It was found that without Q2 a large proportion of the fibre mass transferred from the takerin became embedded into the empty teeth of the cylinder clothing. Only the larger tuftlets and groups of individual fibres would then be subjected to the carding and combing actions. Hence, there is a greater chance of small groups of entangled fibres being removed by the doffer. Q2 therefore acts as a support to new layers of fibre mass being transferred form the taker-in, keeping the new fibre mass at the tips of the cylinder wire teeth and thereby promoting the interaction of tuftlets with the flats and cylinder clothing. This idea, however, does not facilitate an explanation of the mechanism by which fibres leave the recycling layer to form part of the doffer web, Q1 . Gupta suggest that the rotating cylinder could be considered as a large centrifuge that would cause fibres, impurities and seed fragments to migrate to the cylinder periphery and thereby make contact with the flats clothing and, presumably, the doffer teeth. However, no experimental verification of this hypothesis is reported. Many of the authors have reported the effect of machine variables on fibre configurations within the card sliver and several have related yarn properties to the observed configurations. Generally it was found that for a fixed sliver count increasing the carding rate by increasing the doffer speed, increased the number of minority hooks and reduced the number of majority hooks, irrespective of cylinder speed. However, for a given doffer speed, increased cylinder speed gave the reverse trend for minority hooks, but no clear trend for majority hooks. Baturin and Brown showed that increased cylinder speed decreases cylinder load owing to the effect of centrifugal forces and Simpson showed that increased cylinder speed also increased minority hooks and decreased majority hooks. Bhaudri reports that when the fibres are forced nearer the surface of the cylinder teeth, either by increasing the fibre load or increasing the centrifugal force on the cylinder, the proportion of minority hooks increases. Simpson found that there was a direct relation between yarn imperfections and increased occurrence of minority hooks and that spinning end breakage rates and yarn imperfection increased with increased card production speed owing to minority hooks. Gosh and Simpson found that heavier slivers had fewer minority hooks. However, the increased draft needed to process the heavier slivers into yarn led to increased yarn imperfections. Conclusions 1. The taker-in action separates the fed fibre mass into tuftlets and individual fibres. Although it is reported that the taker-in action gives a normal mass distribution of tuftlet sizes, this is speculation. Little research has been reported on the effect of taker-in parameters, fibre properties and the blowroom process on tuftlet size distribution and on the relative proportions of tuftlets to individual fibres. 2. The perceived benefits of combing segments built into the taker-in under-screen and of stationary flats fitted before and after the revolving flats are well known, but only limited experimental findings have been reported to support the use of these attachments. There are conflicting views on the benefits of triple taker-in systems, concerning whether the fibre opening by such systems would give a high misalignment of fibres to the direction of mass flow during transfer to the cylinder and degrade the subsequent carding action. A better understanding is therefore required of the fibre mass transfer from taker-in to cylinder, since the surface speed ratio of these components is seen as a key factor in the proper functioning of high production cards. 3. The cylinder-flats and cylinder-doffer interactions have been well researched. Published findings show that each flat acquires two-thirds of its load at the beginning of its cycle of contact with the cylinder, and that separation of a given tuftlet occurs over a few flats. With regard to clothing parameters and cylinder speed, high teeth densities and lower cylinder speeds gave similar results to the converse arrangement. However, a high teeth density and cylinder speed did not give effective carding. Results showed that high cylinder speeds caused more fibre breakage than high taker-in speed. 4. A high cylinder to doffer speed reduces cylinder load, gives a higher K value and a better web quality. Increasing doffer speed was also found to increase K, but the web quality deteriorated. The reported mechanism of fibre transfer from cylinder to doffer does not adequately explain the effect of the cylinder– doffer speed ratio, or the various reported changes in fibre configuration during transfer. Further work is therefore still needed in this area. METALLIC CARD CLOTHING INTRODUCTION: As Carding machine design improved in 1950’s and 60’s, it became apparent that card clothing was a limiting factor Much time and effort was spent in the development of metallic card clothing. There are two rules of carding The fibre must enter the carding machine, be efficiently carded and taken from it in as little time as possible The fibre must be under control from entry to exit Control of fibres in a carding machine is the responsibilitgy of the card clothing Following are the five types of clothings used in a Carding machine Cylinder wire Doffer wire Flat tops Licker-in wire Stationary flats CYLINDER WIRE: The main parameters of CYLINDER Card clothing Tooth depth Carding angle Rib width Wire height Tooth pitch Tooth point dimensions TOOTH DEPTH: Shallowness of tooth depth reduces fibre loading and holds the fibre on the cylinder in the ideal position under the carding action of the tops. The space a fibre needs within the cylinder wire depends upon its Micronaire/denier value and staple length. ould have to be reduced. The recent cylinder wires have a profile called “NO SPACE FOR LOADING PROFILE”(NSL). With this new profile, the tooth depth is shallower than the standard one and the overall wire height is reudced to 2mm , which eliminates the free blade in the wire. This free blade is responsible for fibre loading. Once the fibre lodges betweent the free blade of two adjacent teeth it is difficult to remove it.Inorder to eliminate the free blade, the wire is made with a larger rib width FRONT ANGLE: Front angle not only affects the carding action but controls the lift of the fibre under the action of centrifugal force. The higher the cylinder speed , the lower the angle for a given fibre. Different fibresM have different co-efficients of friction values which also determine the front angle of the wire. If the front angle is more, then it is insufficient to overcome the centrifugal lift of the fibre created by cylinder speed. Therefore the fibre control is lost, this will result in increasing flat waste and more neps in the sliver. If the front angle is less, then it will hold the fibres and create excessive recyling within the carding machine with resulting overcarding and therefore increased fibre damage and nep generation. Lack of parallelisation, fibre damage, nep generation, more flat waste etc. etc., are all consequences of the wrong choice of front angle. TOOTH PITCH: Each fibre has a linear density determined by its diameter to length ratio. Fine fibres and long fibres necessitates more control during the carding process. This control is obtained by selecting the tooth pitch which gives the correct contact ratio of the number of teeth to fibre length. Exceptionally short fibres too require more control, in this case , it is not because of the stiffness but because it is more difficult to parallelise the fibres with an open tooth pitch giving a low contact ratio. RIB THICKNESS: The rib thickness of the cylinder wire controls the carding “front” and thus the carding power. Generally the finer the fibre, the finer the rib width. The number of points across the carding machine is determined by the carding machine’s design, production rate and the fibre dimensions. General trend is towards finer rib thicknesses, especially for high and very low production machines. Rib thickness should be selected properly, if there are too many wire points across the machine for a given cylinder speed, production rate and fibre fineness, “BLOCKAGE” takes place with disastrous results from the point of view of carding quality. In such cases, either the cylinder speed has to be increased or most likely the production rate has to be reduced to improve the sliver quality POINT POPULATION: The population of a wire is the product of the rib thickness and tooth pitch per unit area. The general rule higher populations for higher production rates, but it is not true always. It depends upon other factors like production rate, fineness, frictional properties etc. TOOTH POINT: The tooth point is important from a fibre penetration point of view. It also affects the maintenance and consistency of performance. Most of the recent cylinder wires have the smallest land or cut-to-point. Sharp points penetrate the fibre more easily and thus reduce friction, which in turn reduces wear on the wire and extends wire life. BLADE THICKNESS: Blade thickness affects the fibre penetration. The blade thickness is limited by practical considerations,but the finer the blade the better the penetration of fibres. Wires with thin blade thickness penetrate the more easily and thus reduce friction, which in turn reduces wear on the wire and extends wire life. BACK ANGLE: A lower back angle reduces fibre loading, but a higher value of back angle assists fibre penetration. Between the two extremes is an angle which facilitates both the reduction in loading and assists fibre penetration and at the same time gives the tooth sufficient strength to do the job for which it was designed. Metallic card Clothing – Page 2 HARDNESS OF WIRE: The cylinder wire needs to be hard at the tip of the tooth where the carding action takes place.The hardness is graded from the hard tip to the soft rib. High carbon alloy steel is used to manufacture a cylinder wire and it is flame hardened. Rib should not be hardened, otherwise, it will lead to mounting problems. The design or type of clothing, selected for the fibre to be carded is important,but it is fair to state that within reason, an incorrect design of clothing in perfect condition can give acceptable carding quality whereas a correct clothing design in poor condition will never give acceptable carding quality. There is no doubt that the condition of the clothings is the most important single factor affecting quality at high rates of production. Wire condition and selection of wire are considered to be the two most important factors which influence the performance of modern high production carding machines. The condition of the clothing may be defined as the collective ability of the individual teeth of the clothing to hold on to the fibre against the opposing carding force exerted by other teeth acting in the carding direction. For a given design of clothing the condition of the teeth determines the maximum acceptable production rate that can be achieved at the card. The speed of the main cylinder of card provides the dynamic force required to work on separating the fibres fed to the card but it is the ability of the carding teeth on the cylinder to carry the fibre forward against the opposing force offered by the teeth of the tops which determines the performance of the card. Increasing cylinder speed increases the dynamic forces acting upon the carding teeth and thus the condition of teeth becomes more important with increased speed.If the condition and design of the cylinder wire is poor, the teeth will not be able to hold onto the fibre through the carding zone, thus allowing some of the freed fibre to roll itself into nep. DOFFER WIRE: The doffer is a collector and it needs to have a sharp tooth to pickup the condensed mass of fibres circulating on the cylinder. It also requires sufficient space between the teeth to be efficient in fibre transfer from the cylinder, consistent in the transfer rate and capable of holding the fibre under control until the doffer’s stripping motion takes control. A standard doffer wire has an overall height of approx. 4.0 mm to facilitate the deeper tooth which must have sufficient capacity to collect all the fibre being transferred from the cylinder to meet production requirements. Heavier webs require a deeper doffer tooth with additional collecting capacity to hanndle the increased fibre mass. The doffer wire’s front angle plays a very important part in releasing the fibre from the cylinder wire’s influence. A smaller angle has a better chance of enabling the doffer wire’s teeth to find their way under the fibres and to secure the fibre’s release from the cylinder with greater efficiency. A 60 degree front angle for Doffer has been found to give the optimum performance under normal carding conditions. Too small an angle results in cloudy web and uneven sliver whilst too large an angle results in fibre recirculation and nep generation. Having collected the fibre, it is important for the doffer to retain it until it is stripped in a controlled manner by the doffer stripping motion. The tooth depth, tooth pitch and rib width combine to create the space available for fibre retention within the doffer wire. Thus they directly influence the collecting capacity. If the space is insufficient, fibre will fill the space and any surplus fibre will be rejected. When the surplus fibre is left to recirculate on the cylinder, cylinder loading can take place. Unacceptable nep levels and fibre damage will also result. In severe cases pilling of the fibre will take place. The point of the doffer wire normally has a small land which helps to strengthn the tooth. The extremely small land of around 0.05 mm ensures that the doffer wire height is consistent, has no adverse effect on fibre penetration and is considred essential for efficient fibre transfer from the cylinder. The land has micropscopic striations which are created during manufacturing or grinding. The striations help to collect the fibres from the cylinder and keep them under control during the doffing process. It has been found that a cut-to-point doffer wire penetrates the fibre better than does the landed point wire but is less likely to keep the fibre under control during the doffing process. Sometimes a cut-to-point doffer wire is accompanied by striations along one side of the tooth for this reason. Until recently 0.9mm rib thickness is standardised for doffer wire, regardless of production and fibre characteristics.This rib thickness has been found to give optimum results. However doffer wires with a 0.8mm rib thickness have been introduced for applications involving finer fibres. In general 300 to 400 PPSI(points per square inch) has been found to perform extremely well under most conditions. Doffer wire point population is limited by the wire angle and tooth geometry. Higher population for doffer does not help in improving the fibre transfer. As the production rate rises, the doffer speed also increases. The doffer is also influenced by the centrifugal force, as is the cylinder.But cylinder wire front angle can become closer to counter the effect of centrifugal force, to close the front angle on a doffer wire would reduce its collecting capacity and result in a lowering of the production rate. The solution is to use the wire with striations, which will hold the fibre until the doffer is stripped. The hardness of the doffer wire is a degree lower than that of the cylinder but sufficiently hard to withstand the forces generated in doffing and the resultant wear of the wire. The reason for this slightly lower hardness requirement is the longer and slimmer tooth form of the differ wire. The fibres which are not able to enter the wire will lay on top, i.e.completely out of control. There fore instead of being carded by the tops the fibres will be rolled. Similarly a fibre buried too deep within the cylinder wire will load the cylinder with fibre, weaken the carding action and limit the quantity of new fibres the cylinder can accept. Therefore, the production rate would have to be reduced. LICKER-IN WIRE: Licker-in with its comparatively small surface area and small number of carding teeth, suffers the hardest wear of all in opening the tangled mass of material fed to it. Successful action of the Licker-in depends upon a penetrating sharp point rather than a sharp leading edge as with the cylinder wire. Therefore the licker-in wire cannot be successfully restored to optimum performance by grinding. The most satisfactory system to adopt to ensure consistent performance is to replace the licker-in wire at regular intervals before sufficient wear has taken place to affect carding quality. The angles most widely used are 5 degrees negative or 10 degrees. There is no evidence to suggest recommendation of a tooth pitch outside the range of 3 to 6 points per inch. It is better to use Licker-in roller without groove. Interlocking wires are used for such type of licker-ins. This avoids producing the eight precise grooves and to maintain them throughout its life. Interlocking wire is almost unbreakable and thus no threat to the cylinder, tops and doffer in the event of foreigh bodies entering the machine. FLAT TOPS: The flat tops are an equal and opposite carding force to the cylinder wire and it should be sharp, well maintained and of the correct design. The selection of flexible tops is very much related to the choice of cylinder wire, which in turn is related to the cylinder speed, production rate and fibre charactersitics, as previously stated. The modern top is of the semi-rigid type, having flexible foundation and sectoral wire. The points are well backed-off and side-ground to give the necessary degree of fineness. The strength of the top from a carding point of view is in the foundation and is affected by the number of plies and the type of material used. The position of the bend in the wire is determined by stress factors, at around 2:1 ratio along the length of the wire protrusion. The modern top is made from hardened and tempered wire to increase wear resistance , thus improving the life of the flat top. Life of the cylinder wire depends upon Material being processed production rate cylinder speed settings Wear is the natural and unavoidable side effect of the work done by the vital leading edge of the metallic wire tooth in coping with the opposing forces needed to obtain the carding action which separates fibre from fibre. When the leading edge becomes rounded due to wear, there is a loss of carding power because the point condition has deteriorated to an extent where the leading edge can no longer hold on to the fibre against the carding resistance of the flats. This ultimately leads to fibres becoming rolled into nep with consequent degradation of carding quality. Therefore it is important to recognise that, due to the inevitable wear which takes place during carding, metallic wire must be reground at regular intervals with the object of correctly resharpening the leading edge of each tooth. Metallic card Clothing – Page 3 GRINDING: GRINDING A CUT-TO-POINT CYLINDER WIRE: Wire points of cylinder have become finer and the tip is cut-to-point.Because of this new profile, it has beccome necessary to recommend a little or no grinding of the cylinder wire following mounting. TSG grinding machine of GRAF(wire manufacturer) can be used to sharpen these modern wires. TSG grinding is a safe method of grinding. Picture1. BARE CYLINDER GRINDER Before grinding , the wire should be inspected with a protable microscope to ascertain the wear. Based on this and the wire point land width, no of traverse for TSG grinding should be decided. If the width of the wire point tip is bigger and the wear out is more, the number of traverse during grinding should be more. For a new wire, 3 or 4 traverses may be enough. But it may require 10 to 30 traverses for the last grinding before changing the wire, depending upon the maintenance of the wire. GRINDING A NORMAL CYLINDER AND DOFFER WIRE: The first grinding of the metallic wire on the cylinder and doffer is the final and most important step leading up to providing the card with a cylinder in the best possible condition for carding well at maximum produciton rate.Grinding the lands of the teeth provides the leading edge of each tooth with the final sharpness reqauired for maximum carding power. The first grinding should be allowed to continue until at least eighty percent(for cylinder) and 100% (for doffer) of the lands of the teeth have been ground sufficient to sharpen the leading edge of the tooth. To ascertain this stage of grinding, it is necessary to stop the cylinder regularly and use a simple microscope to examine the teeth at random across and round the cylinder. If the wire on the cylinder is of good quality and has been correctly mounted, the initial grinding period should be completed with in 20 min. It is essential to avoid over-working the wire before taking corrective action. The regrinding cycle must be determined accurately for the conditions applying in the individual mill, by using the microscope. If regrinding is done properly, there are several advantages carding quality will remain consistent There is no risk of overworking the wire Time required for regrinding is very short The exact condition of the clothing is known The working life of the wire is likely to be longer because the points are never allowed to become worn beyond recovery To obtain acceptable grinding conditions at the low grinding speed, the grindstone must always be SHARP, CLEAN and CONCENTRIC. If the grinding stone is gradually allowed to become dull and glazed through constant use, the limited cutting action available will eventually disappear, resulting in burning and hooking of the carding teeth. Due to the low peripheral speed of the grindstone which has to be used, it is most important that the speed of the wire to be ground is as high as is practicable to provide a high relative speed between the grindstone surface and the cardig teeth.If wire speed is low, the individual carding tooth spends too long a time in passing under the grindstone, thereby increasing the risk of hooking and burning the tooth, which is usually irreparable. With cylinder grinding, speed is no problem because the normal operating speed of the cylinder is more than sufficient. The speed of the doffer for grinding is more commonly a problem and this should be driven at a minimum speed of 250 m/min, to avoid damage when grinding the wire, the design which is particularly susceptible to hooking due to the long fine, low angled teeth needed on the doffer. The directions of rotation for metallic wire grinding are normally arranged so that the back edge of the tooth is first to pass u nder the grindstone. This is termed grinding “back of point” Flat end Milling Machine Multi roller Mounting machine GRINDING FLAT TOPS: Flat tops provide the opposing carding force against the cylinder wire and hence can equally effect carding quality.It is essential to ensure that the tops are kept in good condition to maintain maximum carding power with the cylinder.Again, the only reliable approach is to examine the tops with the microscope and decide whether grinding is required or not. For cards fitted with regrindable tops, it is good practice to regrind the flats at regular intervals thus ensuring that the conditions of the two principal carding surfaces are always complementary one to other. Introduction to Open End Spinning · 1.In conventional spinning ,the fibre supply is reduced to the required mass per unit length by drafting & then consolidated into a yarn by the application of twist. · 2.There is no opportunity for the internal stresses created in the fibres during drafting to relax. · 3.In open end spinning, the fibre supply is reduced, as far as possible , to individual fibres, which are then carried forward on an air-stream as free fibres. · 4. This permits internal stresses to be relaxed & gives rise to the term “free fibre spinning”. · 5.These fibres are then progressively attached to the tail or “open end” of already formed rotating yarn. · 6.This enables twist to be imparted by rotation of the yarn end. · 7.Thus the continuously formed yarn has only to be withdrawn & taken up on a cross-wound package. RING FRAME The ring spinning will continue to be the most widely used form of spinning machine in the near future, because it exhibits significant advantages in comparison with the new spinning processes. · Following are the advantages of ring spinning frame · It is universaly applicable, i.e.any material can be spun to any required count · It delivers a material with optimum charactersticss, especially with regard to structure and strength. · it is simple and easy to master · the know-how is well established and accessible for everyone o Functions of ringframe § to draft the roving until the reqired fineness is achieved § to impart strength to the fibre, by inserting twist § to wind up the twisted strand (yarn) in a form suitable for storage, transportaion and further processing. DRAFTING o Drafting arrangement is the most important part of the machine. It influences mainly evenness and strength The following points are therefore very important § drafting type § design of drafting system § drafting settings § selection of drafting elements like cots, aprong, traveller etc § choice of appropriate draft § service and maintenance § o Drafting arrangement influence the economics of the machine – directly by affecting the end break rate and indirectly by the maximum draft possible. o If higher drafts can be used with a drafting arrangement, then coarser roving can be used as a feeding material. This results in higher production rate at the roving frame and thus reducing the number roving machines required, space, personnel and so on. o In fact increase in draft affects the yarn quality beyond certain limit. Within the limit some studies show that increase in draft improves yarn quality. The following draft limits have been established for practical operation: § carded cotton- upto 35 § carded blends – upto 40 § combed cotton and blends(medium counts) – upto 40 § combed cotton and blends(fine counts) – upto 45 § synthetic fibres – upto 50 o The break draft must be adapted to the total draft in each case since the main draft should not exceed 25 to 30. It should be noted that higher the break draft, more critical is the break draft setting o The front top roller is set slightly forward by a distance of 2 to 4mm relative to the front bottom roller, while the middle top roller is arranged a short distance of 2mm behind the middle bottom roller. o Overhang of the front top roller gives smooth running of the top rollers and shortens the spinning triangle. This has a correspondigly favourable influence on the end break rate. o Rubber cots with hardness less than 60 degrees shore are normally unsuitable because they can not recover from the deformation caused by the pressure on the top roller while running. o Soft rubbercots for toprollers have a greater area of contact, enclose the fibre strand more completely and therefore provide better guidance for the fibres.However softer cots wear out significantly faster and tend to form more laps. o o Normally harder rubbercots are used for back top rollers, because the roving which enters the back roller is compact , little twisted and it does not require any additional guidance for better fibre control. o In the front top roller, only few fibres remain in the strand and these exhibit a tendency to slide apart. Additional fibre guidance is therefore necessary.Therefore rubbercots with hardness levels of the order 80 degrees to 85 degrees shore are mostly used at the back roller and 63 degrees and 65 degrees at the front roller. o If coarse yarns and synthetic yarns are being spun, harder rubbercots are used at the front roller because of increased wear and in the case of synthetic yarns to reduce lapups. o Three kinds of top roller weighting(loading) are presently in use § spring loading § pneumatic loading § magnetic weighting o With pneumatic loading system, the total pressure applied to all top rolers is obtained by simple adjustment of the pressure in the hose using pressure reducing valve. Moreover the rubbercots will not get deformed if the machine is stopped for a longer duration, because the pressure on top rollers can be released to the minimum level. o o The fibre strand in the main drafting field consists of only a few remaining fibres. There is hardly any friction field and fibre guidance provided by the rollers alone is inadequate. Special fibre guiding devices are therefore needed to carry out a satisfactory drafting operation. Double apron drafting arrangements with longer bottom aprons is the most widely used guding system in all the modern ringframes. o o In doube apron drafting system two revolving aprons driven by the middle rollers form a fibre guiding assembly. In order to be able to guide the fibres, the upper apron must be pressed with controlled force against the lower apron. For this purpose, a controlled spacing (exit opening), precisely adapted to the fibre volume is needed between the two aprons at the delivery. This spacing is set by “spacer” or “distance clips”. Long bottom aprons have the advantage in comparison wiht short ones, that they can be easily replaced in the event of damage and there is less danger of choking with fluff. o o Spindles and their drive have a great influence on power consumption and noise level in the machine The running characteristics of a spindle, especially imbalance and eccentricity relative to the ring flange, also affect yarn quality and of course the number of end breakage. Almost all yarn parameters are affected by poorly running spindles. Hence it should be ensured that the centering of the spindles relative to the rings is as accurate as possible. Since the ring and spindle form independent units and are able to shift relative to each other in operation, these two parts must be re-centered from time to time. Previously, this was done by shifting the spindle relative to the ring, but now it is usually carried out by adjusting the ring. o o In comparison with Tangential belt drive, the 4-spindle drive has the advantages of lower noise level and energy consumption, and tapes are easier to replace. o Lappet guide performs the same sequence of movements as the ringrail, but with a shorter stroke, this movement of the guide ensures that differences in the balloon height caused by changes in the ring rail positions do not become too large. This helps to control the yarn tension variation with in control, so that ends down rate and yarn charactersitics are under control. o o Spindles used today are relatively long. The spacing between the ring and the thread guide is correspondigly long, thus giving a high balloon. This has two negative influence § A high balloon results in large bobbin diameter leading to space problems § Larger the balloon diameter , higher the air drag on the yarn.This inturn causes increased deformation of the balloon curve out of hte plane intersecting the spindle axis.This deformation can lead to balloon stability, there is increase danger of collapse. Both these disadvantages result in higher yarn tension, thereby higher endbreaks.In order to avoid this, balloon control rings are used. It divides the balloon into two smaller sub-balloons. Inspite of its large overall height, the double-balloon created in this way is thoroughly stable even at relatively low yarn tension. o o Balloon control rings therefore help to run the mahcine with long spindles(longer lift) and at high spindle speed, but with lower yarn tension. Since the yarn rubs against the control ring, it may cause roughening of the yarn. o o Most ends down arise from breaks in the spinning triangle, because very high forces are exerted on a strand consisting of fibres which have not yet been fully bound together in the spinning triangle. RING FRAME – 2 Page 1 2 3 · RING and TRAVELLER COMBINATION: · The following factors should be considered o materials of the ring traveller o surface charecteristics o the forms of both elements o wear resistance o smoothness of running o running-in conditions o fibre lubrication · For the rings two dimensions are of primariy importance. 1.internal diameter 2. flange width. · Antiwedge rings exhibit an enlarged flange inner side and is markedly flattened on it upper surface. This type of profile permitted to use travellers with a lower centre of gravity and precisely adapted bow(elliptical travellers), which in turn helped to run the machine with higher spindle speeds. Antiwedge rings and elliptical travellers belong together and can be used in combination. · Low crown profle has the following advantage. Low crown ring has a flattened surface top and this gives space for the passage of the yarn so that the curvature of the traveller can also be reduced and the centre of gravity is lowered.In comparison with antiwedge ring, the low crown ring has the advantage that the space provided for passage of the yarn is somewhat larger and that all current traveller shapes can be applied, with the exception of the elliptical traveller. The low crown ring is the most widely used ring form now. · · The ring should be tough and hard on its exterior. The running surface must have high and even hardeness in the range 800-850 vikcers. The traveller hardness should be lower (650-700 vickers), so that wear occurs mainly on the traveller, which is cheaper and easier to replace. Surface smoothness should be high, but not too high, because lubricating film can not build up if it too smooth. · · A good ring in operation should have the following features: o best quality raw material o good, but not too high, surface smoothness o an even surface o exact roundness o good, even surface hardness, higher than that of the traveller o should have been run in as per ring manufacturers requirement o long operating life o correct relationship between ring and bobbin tube diameters o perfectly horizontal position o it should be exactly centered relative to the spindle · In reality, the traveller moves on a lubricating film which builds up itself and which consists primarily of cellulose and wax. This material arises from material abraded from the fibres.If fibre particles are caught between the ring and traveller, then at high traveller speeds and with correspondingly high centrifugal forces, the particles are partially ground to a paste of small, colourless, transparent and extremely thin platelets. The platelets are continually being replaced during working. The traveller smoothes these out to form a continuous running surface.The position, form and structure of lubricating film depends on o yarn fineness o yarn structure o fibre raw material o traveller mass o traveller speed o heigh of traveller bow Modern ring and traveller combination with good fibre lubrication enable traveller speeds upto 40m/sec. · Traveller imparts twist to the yarn. Traveller and spindle together help to wind the yarn on the bobbin. Length wound up on the bobbin corresponds to the difference in peripheral speeds of the spindle and traveller. The difference in speed should correspond to length delivered at the front rollers. Since traveller does not have a drive on its own but is dragged along behind by the spindle. · · High contact pressure (upto 35 N/square mm)is generated between the ring and the traveller during winding, mainly due to centrifugal force. This pressure leads to generation of heat. Low mass of the traveller does not permit dissipation of the generated heat in the short time available. As a result the operating speed of the traveller is limited. · · When the spindle speed is increased, the friction work between ring and traveller (hence the build up) increases as the 3rd power of the spindle rpm. Consequently if the spindle speed is too high, the traveller sustains thermal damage and fails. This speed restriction is felt particularly when spinning cotton yarns of relatively high strength. · · If the traveller speed is raised beyond normal levels , the thermal stress limit of the traveller is exceeded, a drastic change in the wear behaviour of the ring and traveller ensues. Owing to the strongly increased adhesion forces between ring and traveller, welding takes place between the two. These seizures inflict massive damage not only to the traveller but to the ring as well.Due to this unstable behaviour of the ring and traveller system the wear is atleast an order of magnitude higher than during the stable phase. The traveller temperature reaches 400 to 500 degrees celcius and the danger of the traveller annealing and failing is very great. · · The spinning tension is proportional o to the friction coefficient between ring and traveller o to the traveller mass o to the square of hte traveler speed and inversely proportional o to the ring diameter o and the angle between the connecting line from the traveller-spindle axis to the piece of yarn between the traveller and cop. · The yarn strength is affected only little by the spinning tension. On the other hand the elongation diminishes with increasing tension, for every tensile load of hte fibres lessens the residual elongation in the fibres and hence in the yarn. Increasing tension leads also to poorer Uster regularity and IPI values. · · If the spinning tension is more, the spinning triangle becomes smaller . As the spinning triangle gets smaller, there is less hairiness. · SHAPE OF THE TRAVELLER: · The traveller must be shaped to match exactly with the ring in the contact zone, so that a single contact surface, with the maximum surface area is created between ring and traveller. The bow of the traveller should be as flat as possible, in order to keep the centre of gravity low and thereby improve smoothness of running. · However the flat bow must still leave adequate space for passage of the yarn. If the yarn clearance opening is too small, rubbing of the yarn on the ring leads to roughening of the yarn, a high level of fibre loss as fly, deterioration of yarn quality and formation of melt spots in spinning of synthetic fibre yarns. RING FRAME – 3 Page 1 2 3 · WIRE PROFILE OF THE TRAVELLER: · Wire profile influences both the behaviour of the traveller and certain yarn characteristics, they are o contact surface of the ring o smooth running o thermal transfer o yarn clearance opening o roughening effect o hairiness MATERIAL OF THE TRAVELLER · The traveller should o generate as little heat as possible o quickly distribute the generated heat from the area where it develops over the whole volume of the traveller o transfer this heat rapidly to the ring and the air o be elastic, so that the traveller will not break as it is pushed on to the ring o exhibit high wear resistance o be less hard than the ring, because the traveller must wear out in use in preference to the ring · In view of the above said requirements, traveller manufacturers have made efforts to improve the running properties by surface treatment. “Braecker” has developed a new process in which certain finishing components diffuse into the traveller surface and are fixed in place there. The resulting layer reduces temperature rise and increases wear resistance. · · Traveller mass determines the magnitude of frictional forces between the traveller and the ring, and these in turn determine the winding and balloon tension. Mass of the traveller depends upon o yarn count o yarn strength o spindle speed o material being spun If traveller weight is too low, the bobbin becomes too soft and the cop content will be low. If it is unduly high, yarn tension will go up and will result in end breaks. If a choice is available between two traveller weights, then the heavier is normally selected, since it will give greater cop weight, smoother running of the traveller and better transfer of heat out of traveller. · When the yarn runs through the traveller, some fibres are liberated. Most of these fibres float away as dust in to the atmosphere, but some remain caught on the traveller and they can accumulate and form a tuft. This will increase the mass of traveller and will result in end break because of higher yarn tension. To avoid this accumulation , traveller clearers are fixed close to the ring, so that the accumulation is prevented. They should be set as close as possible to the traveller, but without affecting its movement. Exact setting is very important. · · Specific shape of the cop is achieved by placing the layers of yarn in a conical arrangement. In the winding of a layer, the ring rail is moved slowly but with increasing speed in the upward direction and quickly but with decreasing speed downwards. This gives a ratio between the length of yarn in the main (up) and cross(down) windings about 2:1. · · The total length of a complete layer (main and cross windings together) should not be greater than 5m (preferably 4 m) to facilitate unwinding. The traverse stroke of the ring rail is ideal when it is about 15 to 18% greater than the ring diameter. · · End break suction system has a variety of functions. o It removes fibres delivered by the drafting arrangement after an end break and thus prevents mulitple end breaks on neighbouring spindles. o It enables better environmental control, since a large part of the return air-flow of the aircondition system is led past the drafting system, especially the region of the spinning triangle. o In modern installations, approx. 40 to 50 % of the return air-flow passes back into the duct system of the airconditioning plant via the suction tubes of pneumafil suction system. o A relatively high vacuum must be generated to ensure suction of waste fibres § for cotton – around 800 pascals § for synthetic – around 1200 pascals o A significant pressure difference arises between the fan and the last spindle. This pressure difference will be greater , the longer the machine and greater the volume of air to be transported. The air flow rate is normally between 5 and 10 cubic meter/ hour. o o Remember that the power needed to generate an air-flow of 10 cubic meter/ hour , is about 4.5 times the power needed for an air-flow of 6 cubic meter/ hour, because of the significantly higher vacuum level developed at the fan. SPINNING GEOMETRY: · From Roving bobbin to cop, the fibre strand passes through drafting arrangement, thread guide, balloon control rings and traveller. These parts are arranged at various angles and distances relative to each other. The distances and angles together are referred to as the spinning geometry,has a significant influence on the spinning opeartion and the resulting yarn. They are o yarn tension o number of end breaks o yarn irregularity o binding-in of the fibres o yarn hairiness o generation of fly etc. · Spinning Triangle: Twist in a yarn is generated at the traveller and travel against the direction of yarn movement to the front roller. Twist must run back as close as possible to the nip of the rollers, but it never penetrates completely to the nip because, after leaving the rollers, the fibres first have to be diverted inwards and wrapped around each other. There is always a triangular bundle of fibres without twist at the exit of the rollers, this is called as SPINNING TRIANGLE. Most of the end breaks originate at this point. The length of the spinning triangle depends upon the spinning geometry and upon the twist level in the yarn. · The top roller is always shifted 3 to 6 mm forward compared to bottom roller. This is called top roller · overhang.This gives smoother running and smaller spinning triangle. The overhang must not be made too large, as the distance from the opening of the aprons to the roller nip line becomes too long resulting in poorer fibre control and increased yarn irregularity. · · Continuous variation of the operating conditions arises during winding of a cop.The result is that the tensile force exerted on yarn must be much higher during winding on the bare tube than during winding on the full cop, because of the difference in the angle of attack of the yarn on the traveller. When the ring rail is at the upper end of its stroke, in spinning onto the tube, the yarn tension is substantially higher than when the ring rail is at its lowermost position. This can be observed easily in the balloon on any ring spinning machine. · · The tube and ring diameters must have a minimum ratio, between approx. 1:2 and 1:2.2, in order to ensure that the yarn tension oscillations do not become too great. · · Yarn tension in the balloon is the tension which finally penetrates almost to the spinning triangle and which is responsible for the greater part of the thread breaks. It is reduced to a very small degree by the deviation of the yarn at the thread guide. An equilibrium of forces must be obtained between the yarn tension and balloon tension. RINGS And TRAVELLERS In most cases, the limit to productivity of the ring spinning machine is defined by the traveller in interdependence with the ring, and yarn. It is very important for the technologist to understand this and act on them to optimize the yarn production. · The following factors should be considered o materials of the ring traveller o surface charecteristics o the forms of both elements( ring and traveller) o wear resistance o smoothness of running o running-in conditions o fibre lubrication o TRAVELLER: Traveller imparts twist to the yarn. Traveller and spindle together help to wind the yarn on the bobbin. Length wound up on the bobbin corresponds to the difference in peripheral speeds of the spindle and traveller. The difference in speed should correspond to length delivered at the front rollers. Since traveller does not have a drive on its own but is dragged along behind by the spindle. High contact pressure (upto 35 N/square mm)is generated between the ring and the traveller during winding, mainly due to centrifugal force. This pressure leads to generation of heat. Low mass of the traveller does not permit dissipation of the generated heat in the short time available. As a result the operating speed of the traveller is limited. Heat produced when by the ringtraveller is around 300 degree celcius. This has to be dissipated in milliseconds by traveller into the air. Parts of a traveller: Height of bow: It should be as low as possible for stable running of traveller. It should also have sufficient yarn pasage. Yarn passage: According to count spun the traveller profile to be selected with required yarn passage. Toe gap : This will vary according to traveller number and flange width of the ring Wire section: It plays an important role for yarn quality, life of traveller. Ring contact area: This area should be more, uniform, smooth and continuous for best performance. Inner width: This varies according to traveller profile and ring flange. SALIENT FEATURES OF A TRAVELLER: · Generate less heat · dissipate heat fastly · have sufficient elasticity for easy insertion and to retain its original shape after insertion · friction between ring and traveller should be minimal · it should have excellent wear resistance for longer life · hardness of the traveller should be less than the ring When the spindle speed is increased, the friction work between ring and traveller (hence the build up) increases as the 3rd power of the spindle rpm. Consequently if the spindle speed is too high, the traveller sustains thermal damage and fails. This speed restriction is felt particularly when spinning cotton yarns of relatively high strength. If the traveller speed is raised beyond normal levels , the thermal stress limit of the traveller is exceeded, a drastic change in the wear behaviour of the ring and traveller ensues. Owing to the strongly increased adhesion forces between ring and traveller, welding takes place between the two. These seizures inflict massive damage not only to the traveller but to the ring as well.Due to this unstable behaviour of the ring and traveller system the wear is atleast an order of magnitude higher than during the stable phase. The traveller temperature reaches 400 to 500 degrees celcius and the danger of the traveller annealing and failing is very great. The spinning tension is proportional · to the friction coefficient between ring and aveller · to the traveller mass · toto the square of hte traveler speed and inversely proportional · to the ring diameter · and the angle between the connecting line from the traveller-spindle axis to the piece of yarn between the traveller and cop. · · In order to maintain the same friction or spinning tension with different coefficients of friction, different traveller weights must be used. The coefficient of friction is determined by the fiber lubrication and is subject to fluctuation. Dry cotton means higher coefficient of friction. For manmade fibres depending upon the manufacturer, lower to medium coefficient of friction. The coefficient of friction with fiber lubrication can vary from 0.03 and 0.15. R = Co ficeint of friction x N where R – traveller friction in mN N = Normal force >= (Fc x ML x V xV)/(R) Fc – centrifugal force ML – mass of the traveller in mg V – traveller speed in m/s R – radius of the ring (inside) · · The yarn strength is affected only little by the spinning tension. On the other hand the elongation diminishes with increasing tension, for every tensile load of the fibres lessens the residual elongation in the fibres and hence in the yarn. Increasing tension leads also to poorer Uster regularity and IPI values. · If the spinning tension is more, the spinning triangle becomes smaller . As the spinning triangle gets smaller, there is less hairiness. RINGS And TRAVELLERS – 2 Page 1 2 3 4 · SHAPE OF THE TRAVELLER: · The traveller must be shaped to match exactly with the ring in the contact zone, so that a single contact surface, with the maximum surface area is created between ring and traveller. The bow of the traveller should be as flat as possible, in order to keep the centre of gravity low and thereby improve smoothness of running. However the flat bow must still leave adequate space for passage of the yarn. If the yarn clearance opening is too small, rubbing of the yarn on the ring leads to roughening of the yarn, a high level of fibre loss as fly, deterioration of yarn quality and formation of melt spots in spinning of synthetic fibre yarns. WIRE PROFILE OF THE TRAVELLER: · Wire profile influences both the behaviour of the traveller and certain yarn characteristics, they are o contact surface of the ring o smooth running o thermal transfer o yarn clearance opening o roughening effect o hairiness o MATERIAL OF THE TRAVELLER · The traveller should o generate as little heat as possible o quickly distribute the generated heat from the area where it develops over the whole volume of the traveller o transfer this heat rapidly to the ring and the air o be elastic, so that the traveller will not break as it is pushed on to the ring o exhibit high wear resistance o be less hard than the ring, because the traveller must wear out in use in preference to the ring · In view of the above said requirements, traveller manufacturers have made efforts to improve the running properties by surface treatment. “Braecker” has developed a new process in which certain finishing components diffuse into the traveller surface and are fixed in place there. The resulting layer reduces temperature rise and increases wear resistance. · Traveller mass determines the magnitude of frictional forces between the traveller and the ring, and these in turn determine the winding and balloon tension. Mass of the traveller depends upon o yarn count o yarn strength o spindle speed o material being spun If traveller weight is too low, the bobbin becomes too soft and the cop content will be low. If it is unduly high, yarn tension will go up and will result in end breaks. If a choice is available between two traveller weights, then the heavier is normally selected, since it will give greater cop weight, smoother running of the traveller and better transfer of heat out of traveller. · When the yarn runs through the traveller, some fibres are liberated. Most of these fibres float away as dust in to the atmosphere, but some remain caught on the traveller and they can accumulate and form a tuft. This will increase the mass of traveller and will result in end break because of higher yarn tension. To avoid this accumulation , traveller clearers are fixed close to the ring, so that the accumulation is prevented. They should be set as close as possible to the traveller, but without affecting its movement. Exact setting is very important. · For the rings two dimensions are of primariy importance. 1.internal diameter 2. flange width. – · Antiwedge rings exhibit an enlarged flange inner side and is markedly flattened on it upper surface. This type of profile permitted to use travellers with a lower centre of gravity and precisely adapted bow(elliptical travellers), which in turn helped to run the machine with higher spindle speeds. Antiwedge rings and elliptical travellers belong together and can be used in combination. · Low crown profle has the following advantage. Low crown ring has a flattened surface top and this gives space for the passage of the yarn so that the curvature of the traveller can also be reduced and the centre of gravity is lowered.In comparison with antiwedge ring, the low crown ring has the advantage that the space provided for passage of the yarn is somewhat larger and that all current traveller shapes can be applied, with the exception of the elliptical traveller. The low crown ring is the most widely used ring form now. · The ring should be tough and hard on its exterior. The running surface must have high and even hardeness in the range 800-850 vikcers. The traveller hardness should be lower (650-700 vickers), so that wear occurs mainly on the traveller, which is cheaper and easier to replace. Surface smoothness should be high, but not too high, because lubricating film can not build up if it too smooth. · A good ring in operation should have the following features: o best quality raw material o good, but not too high, surface smoothness o an even surface o exact roundness o good, even surface hardness, higher than that of the traveller o should have been run in as per ring manufacturers requirement o long operating life o correct relationship between ring and bobbin tube diameters o perfectly horizontal position o it should be exactly centered relative to the spindle · · In reality, the traveller moves on a lubricating film which builds up itself and which consists primarily of cellulose and wax. This material arises from material abraded from the fibres.If fibre particles are caught between the ring and traveller, then at high traveller speeds and with correspondingly high centrifugal forces, the particles are partially ground to a paste of small, colourless, transparent and extremely thin platelets. The platelets are continually being replaced during working. The traveller smoothes these out to form a continuous running surface.The position, form and structure of lubricating film depends on o yarn fineness o yarn structure o fibre raw material o traveller mass o traveller speed o heigh of traveller bow Modern ring and traveller combination with good fibre lubrication enable traveller speeds upto 40m/sec. RINGS And TRAVELLERS – 3 Page 1 2 3 4 TECHNOLOGICAL GUIDELINES: · When the ring diameter is less, balloon diameter will be small. This leads to more yarn tension. Hence use lighter travellers. · When the ring diamter is bigger, balloon diamter will be more. This leads to less yarn tension and the balloon touches the separator. Hence use heavier travellers · When the tube length is short, the yarn tension will be more. Hence use lighter travellers · When the tube length is long, the yarn tension will be less, hence use heavier travellers · When the yarn contact area and ring contact area in traveller is closer, fibre lubrication is better especially in cotton. For this use heavier travellers · · When spindle speed is increased use lighter traveller with low bow height. At higher speeds, lighter travellers give lesser yarn tension. When low bow height travellers are used centre of gravity will be closest to the ring which aids in running of traveller. · Use lighter travellers on new rings. This is done to reduce end breakages by reducing the yarn tension. · Use heavier travellers on old rings. This is done to avoid bigger balloons · Heavier travellers reduce hairiness · When using lighter travellers, yarn stretch will be less. It helps for better yarn elongation · During running-in the endbreakage rate should be kept minimum, hence use lighter travellers. · The shorter the balloon, the lighter the traveller to be used, the higher traveller speeds can be achieved. · The ring traveller, together with the yarn as a pull element, is set into motion on the ring by the rotation of the spindle. If the direction of pull deviates too much from the running direction of the traveller (spinning angle less than 30 degrees) the tension load will be too high. Preconditions for good operating results The maximum ability of the ring/traveller system to withstand occuring stress situation during operation determines the performance limit of the ring spinning and twisting machine. Traveller wear does not only depend on traveller material; problems of heat dissipation are of crucial importance, too. The heat generated between ring and traveller must be reduced as quickly as possible to avoid local temperature in the traveller wear zones. The ability of the traveller to resist to stress is determined by several factors. Investigations regarding improvements of rings and travellers aimed at a further increase of performance should above all make sure that all other conditions with a certain influence on the spinning process are optimal. Therefore make sure that: ¥ the rings are correctly centered with regard to the spindles ¥ the yarn guide eyelet is well centered with regard to the spindle ¥ the spindle bearing is in good condition, thus preventing spindle vibrations ¥ the ratio between bobbin diameter and ring diameter is correct ¥ the concentricity of the ballon control ring with regard to the spindle is correct ¥ the fibre tufts which accumulate on flange travellers are removed by means of suitable traveller cleaners ¥ the climatic conditions (temperature and relative air humidity) are favourable for the spinning process ¥ the air in the mill is free from disturbing particles that influence efficient performance of the traveller It has to be stressed that a smooth and well run-in track is of most importance. Concentricity of spindle, ring, yarn guide and balloon control ring Especially at high spindle speeds concentric positioning of ring, spindle, yarn eyelet and balloon control ring is required for keeping the ends down rate at low level. Spindles and rings must be aligned and centered absolutely parallel. Ring rails or ring holders should, therefore, be installed absolutely horizontally compared to the vertically fitted spindles. Ring and traveller form the main elements in ring spinning and twisting. They determine to a large extent performance and operating conditions of the machine. The traveller accomplishes two main tasks while running on the ring at high speeds: a) It gives the roving supplied by the feed rollers the necessary twist. b) It assists in winding the yarn onto the bobbin in the form of a cop with ã correct tension. During this operation the ring guides the traveller, which is essential for the perfect positioning of the yarn and the formation of the cop. The traveller is pressed against the ring track by centrifugal forces. The resulting frictional forces reduce traveller speed, which is dragged along by the passing-through yarn, and provide the yarn with the tensile forces necessary for assembling the individual fibres into the spun yarn as well as for limiting the yarn balloon. Steel travellers are hardened to a certain degree and polished to a mirror finish. They can be adapted in shape, weight and surface finish to the ring, yarn type and yarn count. Nylon travellers of standard quality (for HZ and J rings) are made of highly wear-resistant polyamide. Extremely aggressive yarns are processed with glass-fibre-reinforced a Super Nylon travellers. Twisting and winding carried out by the traveller must be performed with appropriate yarn tension. The ratio between spindle speed and the speed at which the yarn is supplied determines yarn twist. Any change of this ratio is easily compensated by the traveller without having an influence on twisting, winding and tensioning. On flange rings, the gliding speed of travellers having a suitable shape can be as rapid as 130 ft/s (88 MPH) or 40 m/s (140 km/h); on DIA-DUR coated rings the speed can to some extent reach 147 ft/s (100 MPH) or 45 m/s (160 km/h) . Having an average life span of 200-300 operating hours the traveller covers a distance of more than 18.000 miles (30.000 km) – a tremendous task for a small part of wire weighing only a few milligrams. These standards can even be surpassed by nylon travellers used on HZ rings, if operating conditions are favourable. These high traveller speeds involve pressures of up to 35 N/mm 2 . But even if high-quality materials with an optimum of hardness and resistance to wear are used, these standards can only be reached if ¥ in the case of flange rings, a film of lubricating fibres is produced continuously, ¥ in the case of HZ and J rings, a sufficient amount of lubricant is consistently provided. d 1 = spinning ring diameter d 2 = fitting diameter h 1 = ring height h 2 = ring height above ring rail b = flange width flange 1 = 3.2 mm flange 2 = 4.1 mm Spindles operating without vibrations contribute a great deal to a smooth operation of the traveller. Non-concentric spindles and spindles not running smoothly cause constant changes in yarn tension , because the traveller cannot run around the ring without being shaken. Vibration-free movements of ring rail and ring holder The ring rail should move smoothly without jerking. Vibrations and hard jolts at the reversing points of the ring rail disturb the operation of the traveller. Repeated changes in yarn tension cause the traveller to flutter. This results in increasing yarn breaks and in accelerated wear of ring and traveller. Correct ratio between bobbin diameter, bobbin length, ring diameter and spindle gauge RINGS And TRAVELLERS – 4 Page 1 2 3 4 Ratio bobbin length (H) : Inside ring diameter (D) Thread tension increases with growing bobbin length. In view of the limited thread tension, the total bobbin length should not exceed 5 times the ring diameter. Only when using balloon control rings or similar devices this value can be exceeded. H : D = 5 : 1 Ratio bobbin diameter (d) : Inside ring diameter (D) The bobbin diameter d is equivalent to the mean outer bobbin diameter d 1 + d 2 The following values are recommended: for spinning: d : D = 0.48 – 0.5 (a = 29°-30°), (minimum value a = 26°) for twisting d : D = 0.44 – 0.5 (a = 27°-30°), (minimum value a = 22°) For light and heavy bobbins, the values for light bobbin types are decisive for calculating d : D. If the ratio d : D is reduced thread tension increases. Correct surface smoothness, i.e. optimum peak-to-valley height and evenness of the ring track The traveller contact surfaces must be smooth and even. Only then a smooth operation of the traveller will be possible. The contacted surfaces should be clean and preferably without traces of wear. In addition, they should be designed in such a way that they offer sufficient adherence for potential lubricants (e.g. fibres, oil, grease). Once the sliding surfaces have lost their original quality, even the best ring traveller will not be able to run smoothly. For maintaining the surface of the running track in a good condition, it is very important – besides a certain degree of maintenance – to run the ring well in. Balloon control rings and separators The influence of balloon control rings is quite considerable, especially at long cops. A reduction of the yarn balloon is advantageous or may even be the prerequisite for optimum performance. If balloon control rings are mounted at correct distance (the yarn balloon should be restricted as long as possibleduring one lift of the ring rail) then a marked performance increase is possible. The balloon control rings are removed when sensitive materials are processed and sufficiently long separators are installed to avoid many yarn breaks and to prevent fibre fly from accumulating on the adjacent spindles. Traveller cleaners Traveller cleaners are an excellent method for removing all fibre fly that accumulates on the outer part of C and El travellers. The traveller cleaner should have the right distance to the outside ring flange. A distance of about 0.5 mm between cleaner and traveller (in operating position) is recommended. When adjusting the distance between outside ring flange and cleaner, the size of the traveller should be taken into consideration. Room climate Constant temperature and air humidity have positive effects on the operation of the traveller. Changes of the room climate, such as raised air humidity will increase wear by friction. Besides the regular exchange of air, the purity of the air is of great importance for the traveller. Any dust (also dust from unsuitable floors) or other impurities may impair traveller operation and lead to more ring/traveller wear. Flange width and ring height Optimal operating results are reached when the ideal flange width is chosen for flange rings and the ideal ring height is obtained for self-lubricating HZ and J rings, dependent on yarn count range, yarn quality and traveller type. Ring profile and traveller shape Determining the most favourable ring and traveller shapes is a precondition for obtaining the optimal individual performance. If ring profile and traveller shape match well, the traveller will adopt a stable position in the ring. It should have sufficient tolerance of movement, so that any obstacles which may occur especially when the machine is started are avoided. A satisfactory large yarn clearance counteracts yarn breaks and yarn damage. Running-in of rings Normally the running-in procedure is decisive for the future positive/nega tive behaviour of the ring and the length of its service life. Every ring requires a certain degree of running-in time if it is to maintain high traveller speeds with as little ring and traveller wear as possible. During running-in the use of steel travellers without surface treatment is recommended. After the termination of the running-in process, steel travellers with surface treatment or nylon as well as bronze travellers can be used. The running-in process, beginning with the starting phase, consists of improving the initial running properties of the metallic running surface up to the optimal values by smoothing and passivation(oxidation) as soon as possible. In this way, together with fibre lubrication, constant minimum mixed friction conditions and minimum thermal stressing can be attained for the ring traveller. A careful running-in process will improve the lifetime of the rings. In order to keep the stress on the traveller as low as possible during the starting phase, it is advisable to always change the traveller in the upper third part of the cops. Further advantages are brought with the use of a traveller running-in program(reduction of the speed by about 10% for 10 to 20 minutes, only available on modern spinning machines). Spindle speed should be reduced atleast for the first 10 traveller changes. If final speed is higher than 32m/sec, reduce by atleast 20%. If final speed is lower than 32m/sec, reduce by at least 10%. New rings should not be degreased, but only rubbed over with a dry cloth. In general, the running in should be done with the same traveller type which is used for normal operation with the 10 to 20% less than normal speed. It is not advisable to do running with the same speed but with 1to 2 numbers lighter travellers than usual. The first traveller change should be carried out after 15 min The second traveller chage should take place after 30 min The third traveller change should be made after 1 to 1.5 hours. The fourth traveller change should be made after the first doff. Further traveller changes are to be made according to the manufacturers recommendations HAIRINESS: Following are the reasons for higher yarn hairiness due to ring and travellers Poorly centered spindles, anti balloon rings and yarn guides lead to inconsistent yarn tension. Rough surfaces roughen the yarn(due to damaged parts) Open anti balloon ring The clearance between ring and cop should not be too small. Traveller will cut the fibres protruding from the cop. the fibres get electrostatically charged poor twist propagation to the spinning triangle due to lighter travellers Heavy friction of the balloon on the anti-balloon ring respectively impact on the balloon separator( due to lighter traveller) Poor ring centering crooked tubes yarn getting roughened in narrow yarn passage in the traveller scratched up yarn passages catch the yarn and roughen it (due to very high traveller running time) friction of the yarn due to very high traveller weight rough gliding surface of the ring ( due to worn out rings) COM-4 (Comfor spin) AND ELITE YARNS COM-4 CONCEPT: With the Comfor Spin technology a new yarn with perfect yarn structure – the COM4 yarn – has been established in the market. With the help of a microscope the structure of the yarns can easily be compared: The conventional ring yarn shows to be far less perfect than commonly assumed. The long, protruding fibres cause a number of problems in downstream processing. COM4 yarn shows a very compact structure with highly parallel fibres and much less disturbing hairiness. The air current created by the vacuum generated in the perforated drum condenses the fibres after the main draft. The fibres are fully controlled all the way from the nipping line after the drafting zone to the spinning triangle. An additional nip roller prevents the twist from being propagated into the condensing zone. The compacting efficiency in the condensing zone is enhanced by a specially designed and patented air guide element. Optimal interaction of the compacting ele-ments ensures complete condensation of all fibres. This results in the typical COM4 ® yarn characteristics. The ComforSpin ® technology allows aero-dynamic parallelization and condensation of the fibres after the main draft. The spinning triangle is thus reduced to a minimum. The heart of ComforSpin machine is the compacting zone, consisting of the following elements: • perforated drum • suction insert • air guide element The directly driven perforated drum is hard to wear and resistant to fibre clinging. Inside each drum there is an exchangeable stationary suction insert with a specially shaped slot. It is connected to the machine’s suction system. THE ELITE YARN: The operating method of the SUESSEN EliTe Spinning System is well-known. After the fibres leave the drafting system they are condensed by an air-permeable lattice apron,which slides over an inclined suction slot.The fibres follow the outer edge of this suction slot and at the same time they perform a lateral rolling motion. Above the front bottom roller of the drafting system, the fibre band influenced by high draft is spreading.In the area of the suction slot,which is covered by the lattice apron,the fibre band is condensed.Commencing from the semi-dotted clamping line of the EliTe Q Top Roller,twist is being inserted.There is no spinning triangle. The improvement achieved is shown in Fig .The left side displays the fibre triangle at the exit of a conventional ring frame drafting system.The twist imparted by the spindle cannot flow up to the clamping line.The outer fibres spread out and are thus more highly tensioned than those on the inside. The right side of the picture does not show a spinning triangle.The yarn twist flows right up to the clamping line.The yarn is round and smooth. Since the spinning triangle is very very small, the end breaks will be very less and therefore the fly liberation will also be less. Condensing of the fibr bundle,which follows the drafting process,can already be seen as a significant development of the ring spinning technology.Condensed ring yarn is more than a speciality.In view of its manifold advantages. It is of technological importance that the suction leve l relevant for the condensing operation is exactly the same for all spinning positions. To fulfil this criteria,individual motors combined with suction units for 6 spinning positions,have been arranged accordingly.This provides short air-flow distances with identical negativ pressures at all spinning points . During yarn formation all fibres are perfectly condensed and gathered parallel to each other in the compacting zone. Consequently all fibres are twisted in and contributing to the superior fibre utilisation rate compared to conventional ring yarn. The result is exceptionally low hairiness combined with higher yarn tenacity and elongation. These are the unique characteristics of these yarns. COM-4 (Comfor spin) AND ELITE YARNS – 2 Page 1 2 ADVANTAGES OF COMPACT YARN: • higher fibre utilisation • higher tenacity with same twist factor, or • same tenacity with reduced twist factor for higher production • lowest hairiness (highest reduction in hairs longer than 3 mm) • fewer weak points • better imperfections (IPI) values • higher abrasion resistance • greater brilliance of colour • intensive dye penetration • no singeing before printing · Due to better utilization of fibre substance it is possible to reduce yarn twist of these Yarns,particularly of knitting yarns,by up to 20%,maintaining the yarn strength of conventional ring yarns.This increases yarn production. The ends-down rate in spinning these Yarns is reduced by 30 to 60%,which improves machine efficiency. · · Applying the same winding speed as with conventional ring yarns,there are less raised points in these Yarns and the increase in yarn imperfections is reduced because they have a better resistance to shifting. Higher winding speeds are therefore possible with compact yarns Yar ns . · In accordance with up to 20%twist reduction in spinning compact yarns ,the twisting turns can be reduced for certain types of yarn.As a result,production of twisting frame is increased and twisting costs are reduced. · Owing to the lower hairiness and higher tenacity of compact Yarns,the ends-down rate in beaming is reduced by up to 30%.Higher beamer efficiency,higher produc tion and fewer personnel for repair of ends-down in beaming are the consequence. · Compact Warp yarns help to save up to 50%of sizing agent,while the running behaviour of weaving machi-nes is the same or even better. Cost can be saved in sizing and desizing processes. · Owing to the better work capacity of compact Yarns ,ends down can decreased by up to 50% in the warp and by up to 30%in the weft. Efficiency is consequently increased by 2 to 3%, production is increased and weaving costs are reduced. In practice,the average ends-down rate is reduced by 33% per 100,000 weft insertions of compact Yarns on rapier weaving machines and by 45% on air-jet weaving machines. Instead of a weft insertion of 500 –600 m/min with conventional ring yarn,700-800 m/min is possible with compact Yarns on air-jet weaving machines. · Due to reduced Yarn hairiness,singeing can sometimes be dispensed with,or it can be carried out at a higher cloth advance speed.As a result,production costs are considerably reduced. · fibres upto 7% can be saved because singing can be avoided · Dyeing and Printing Improved structure of compact Yarns and their reduced twist favours the absorption of colour pigments and chemical finishing agents.Saving of dyestuff is possible. · Owing to the improved yarn strength, compact Yarns are well suited for non-iron treatment of woven fabrics. In the course of such treatment,the strength of fabrics made from conventional ring yarns can decrease by up to 25%,with frequent problems in the manufacture of clothes. compcat Yarns make up for this loss in strength. · Knitting :Compact Yarns with their increased yarn strength and reduced formation of fluff permit to achieve higher machine efficiency and therefore production on knitting machines at a reduced ends-down rate,less interruptions and less fabric faults. Production costs therefore decrease. The enormously low hairiness of compact Yarns often permits to dispense with usual waxing. Considerable cost saving is achieved because of this. · In knitting fibre abrasion reduced by 40% due to low hairiness. Fewer defects/ yarn breaks and better quality. Less contamination on all machines by foreign fibres . Less wear of needles, guide elements and sinkers due to less dust in the compact Yarn . Low hairiness has positive impact on loop structure . L Low pilling values get more and more important . In many cases single compact Yarns substitute conventional ply yarns. Waxing can be reduced or completely dispensed with . · Compact Yarns are much more suitable for warp knitting than conventional ring yarns,because of their higher work capacity and lower hairiness. They are predestined to bear the high load due to numerous deflecting points with high friction in the warp knitting machine. · Due to better embedding of fibres (including short ones)in compact Yarn,approx.6%fewer combing noils are possible. · Cheaper carded qualities instead of combed qualities can be spun with the Compact Spinning ystem. · in many cases single EliTe ® Yarns can substitute conventional ply yarns · new qualities can be developed, opening up a new creative scope for products Hairiness Testing of Yarns Hairiness of yarns has been discussed for many years,but it always remained a fuzzy subject. With the advent of compact yarns and their low hairiness compared to conventional yarns,the issue of measuring hairiness and the proper interpretation of the values has become important again.Generally speaking,long hairs are undesirable, while short hairs are desirable (see picture ). The picture shown below just give a visual impression of undesirable and desirable hairiness at the edge of a cops. Figure: RING YARN COMPACT YARN There are two major manufacturers of hairiness testing equipment on the market,and both have their advantages and disadvantages. Some detail is given below. USTER USTER is the leading manufacturer of textile testing equipment. The USTER hairiness H is defined as follows . H =total length (measured in centimeters) of all the hairs within one centimeter of yarn . (The hairiness value given by the tester at the end of the test is the average of all these values measured, that is,if 400 m have been measured,it is the average of 40,000 individual values) . The hairiness H is an average value,giving no indication of the distribution of the length of the hairs. Let us see an example 0.1cm 0.2cm 0.3cm 0.4cm 0.5cm 0.6cm 0.7cm 0.8cm 0.9cm 1.0cm total yarn 1 100 50 30 10 5 6 0 2 1 0 398 yarn 2 50 10 11 5 10 0 5 10 0 11 398 Both yarns would have the same hairiness index H, even though yarn is more desirable,as it has more short hairs and less long hairs,compared to yarn 2. This example shows that the hairiness H suppresses information,as all averages do. Two yarns with a similar value H might have vastly different distributions of the length of the individual hairs. The equipment allows to evaluate the variation of the value H along the length of the yarn. The “sh value “is given, but the correlation to the CV of hairiness is somehow not obvious.A spectrogram may be obtained. 2. ZWEIGLE Zweigle is a somewhat less well known manufacturer of yarn testing equipment. Unlike USTER,the Zweigle does not give averages. The number of hairs of different lengths are counted separately, and these values are displayed on the equipment. In addition, the S3 value is given,which is defined as follows: S3 =Sum (number of hairs 3 mm and longer) In the above example,the yarns would have different S3 values: S3yarn 1 =2 . S3yarn 2 =4 . A clear indication that yarn 2 is “more hairy “than yarn 1. The CV value of hairiness is given a histogram (graphical representation of the distribution of the hairiness) is given. The USTER H value only gives an average,which is of limited use when analyzing the hairiness of the yarn.The Zweigle testing equipment gives the complete distributionof the different lengths of the hairs. The S3 value distinguishes between long and short hairiness, which is more informative than the H value. Ten Fundamental Rules for Successful Operation of EliTe Ring Spinning Machines: 1.EliTe Q Spinning Machines produce yarn of supreme quality and come up to the expectations. Installation of the machine in the spinning mill EliTe Q Spinning Machines have a considerable air flow rate –a machine with .1008 spindles sucks in about 60 cubic meter of air per minute,i.e. it has the effect of a vacuum cleaner. The ambient air is sucked into machine and most of the fly and dirt contained in it is deposited on the EliTe Q Machine. Although EliTe Spinning Machines generate considerably less fly than standard ring spinning machines, they are soon covered with dust and fly if they are installed in the same room as conventional spinning machines. The fly has a negative effect on the yarn in the condensing zone and the smooth running of the lattice apron. As a result,the yarn is of substandard quality. Rule .:EliTe Q Spinning Machines must be separated from conventional spinning machines. 2.Spinning room conditions: The fibres in the condensing zone are exposed to the room conditions without any protection. Our recommendations on the room conditions suitable for processing cotton and man-made fibres should be followed, therefore. If the air humidity is too high, there will be a higher tendency towards roller laps. If the air is too dry,t here will be more fly. If the room temperature is too high, there will be higher friction values and premature wear. Rule 2:maximum room temperature:33 .C humidity should be · max…,5 g water/kg air for cotton · min.9,0 g water/kg air for cotton · max..0,0 g water/kg air for synthetics · min.9,0 g water/kg air for synthetics 3.Position of the Eli Top in relation to the front bottom roller of the drafting system: If the setting is correct, the top edge of the suction slot in the Eli Tube is precisely set at the nip line of the delivery top roller. If the nip line cuts the slot, condensation is impaired. The hairiness of the yarn increases and the tearing strength is reduced. If the nip line is behind the slot, part of the spinning torsion may get into the condensation zone, resulting in an increased ends-down rate and damaged lattice aprons. Rule 3:The front top roller is precisely 3.5 mm offset towards the operator in relation to the front bottom roller of the drafting system. 4.Traverse mechanism: The roving must run over the slot in such a way, that, from the operator ’s view, the fibres move from the top right to the bottom left. If the fibres run over the slot top from the L.H. side,they make an S-shaped movement causing a certain unsteadiness in the condensing zone. This has a negative effect on the yarn values. Rule 4:The traverse mechanism for the sliver should be adjusted in such a way that the traverse motion at the front of the drafting system does not exceed 4 mm,and that the l.h.limit position of the sliver is level with the L.H..edge of the top of the slot. 5.Cleaning the Eli Tubes and lattice aprons :Eli Tubes and lattice aprons are the most important components of the EliTe Q Condensing System. Careful maintenance is an important prerequisite for optimum yarn values. In the centre area, where the suction is active, a permanent air flow keeps the lattice aprons clean. To the left and right of this area, the lattice apron can be clogged by fine dust. With the time, this results in a considerable increase of the friction between the lattice aprons and the EliTube. If this friction is too high, erratic running of the lattice apron and substandard yarn quality is the result. Therefore,lattice aprons and Eli Tubes should be removed from the machine from time to time and cleaned. This can be done when the machine is running. The time needed per box length is 5 min. The expenditure of time necessary for changing the EliTubes with lattice aprons is about 90 minutes for a machine with .1008 spindles, which corresponds to a loss of production of 90 minutes. For yarn count Ne 40, the production loss involved is less than 370 g. The cleaning frequency varies depending on the portion of fine dust of the cotton. As an average value, 500 operating hours may be taken into account. The aprons are cleaned in a washing machine or in an ultrasonic cleaning device.The EliTubes are cleaned using a damp piece of cloth. Damaged lattice aprons must be replaced. On EliTubes with considerable traces of wear, the inserts must be replaced. Rule 5:Lattice aprons and Eli Tubes must be cleaned from time to time. 6.Measures to be taken in the case of laps at the front top roller Laps may occur in the case of unsuitable room conditions or damaged or inappropriately buffed cuts, or if the fibre material used is prone to the formation of laps. Large laps may block the delivery and front rollers and damage the cot of the blocked roller. If spinning is continued with damaged cots,periodic yarn faults will be the result. Consequently, a blocked Eli Top must be replaced by a new Eli Top and repaired in the service room. For this purpose,all operators should carry a spare Eli Top with them. Rule 6:EliTops with blocked top rollers must be replaced by new top rollers. 7.Buffing the EliTe Q Top Rollers : The cots of the EliTe Q Top Rollers are subject to wear and should be buffed from time to time.The tension draft in the condensing zone –6 %as a general rule depends on the difference in diameter between the front top roller and the delivery top roller. Changed tension drafts may result in changed yarn parameters. Rule 7:Make sure that the difference in diameter of the front top roller and the delivery roller corresponds precisely to the desired tension draft. 8. Checking the partial vacuum As a general rule,continuous control of the vacuum pressure is not necessary. When the whole machine is cleaned, we recommend, however,to remove also the connecting hoses between the suction tubes and the fans and to clean them. Rule 8:Clean the connecting hoses with regular frequency. 9. Maintenance of the fans: Fans may be clogged after a time,which has a negative effect on the suction. Rule 9:The fans should be removed from the machine and cleaned once a year. 10. Spinning speed: In the case of EliTe Q Spinning Machines, return on investment is not based on higher production, but on the production of yarn of supreme quality. The Suessen recommendations concerning traveller speeds and running-in speeds for rings and travellers should be followed, therefore. Not the ultimate increase in speed, but the yarn quality leads to success. Rule 10:Yarn quality is more important than quantity. WINDING Ring spinning produces yarn in a package form called cops. Since cops from ringframes are not suitable for further processing, the winding process serves to achieve additional objectives made necessary by the requirements of the subsequent processing stages. Following are the tasks of winding process · Extraction of all disturbing yarn faults such as the short, long thick ,long thin, spinners doubles, etc · Manufacture of cones having good drawing – off properties and with as long a length of yarn as possible · paraffin waxing of the yarn during the winding process · introduction into the yarn of a minimum number of knots · achievement of a high machine efficiency i.e high produciton level The winding process therefore has the basic function of obtaining a larger package from several small ring bobbins. This conversion process provides one with the possibility of cutting out unwanted and problematic objectionable faults. The process of removing such objectionable faults is called as yarn ‘ clearing’ . Practical experience has proven that winding alters the yarn structure.This phenomenon does not affect yarn evenness, but affect the following yarn properties · thick places · thin places · neps · hairiness · standard deviation of hairiness If winding tension is selected properly, the following tensile properties are not affected · tenacity · elongation · work- to- break But excessive tension in winding will deteriarate the above said tensile properties. Changes in the yarn surface structure due to winding cannot be avoided. Since the yarn is accelerated from zero speed to 1200 or 1350 meters per min in a few milli seconds while being pulled off the bobbin, dragged across several deflection bars and eyelets, forced into a traverse motion at speed that make it invisible, and finally rolled up into a firm construction called package or cone. The factors that affect the yarn structure during winding include the frictional properties of the yarn itself, the bobbin geometry and the bobbin unwinding behaviour, winding speed, winding geometry as well as the number and design of the yarn / machine contact points. However, the bobbin unwinding behaviour is the major limiting factor for winding speed which also is the main reason for the above said changes in yarn structure. Most of the damage occurs at the moment when the end is detached and removed from the tight assembly of yarn layers on the bobbin and dragged along the tube at very high speeds. High speed automatic winders have frequently been blamed for causing higher nep counts but this is not a correct statement. typical nep-type imperfections, i.e shor mass defects, can be identified as tight fibre entanglements, clumps of immature or dead cotton fibres, or seed coat fragments. Naturally, such defects are not produced by the winding machine. The increase in nep counts after winding is related to the formation of loose fiber accumulations. These fibre accumulations represent a true mass defect, yet their apperance in the yarn and in the final fabric is clearly different from that of typical fibre entanglements or seed coat fragments. Some very fine and delicate yarns will result in marginal structural changes after winding. But this is not the result of mechancial stress like in winding but a natural reaction caused by the reversal of the yarn running direction. irectional influences are omnipresent, they become apparent in all subsequent processing stages. In earlier days, knotters were used in winding machine to join two ends after cutting the fault and after chaning the ringframe bobbin . But now , splicing of the yarn ends has become quite popular and has gradually replaced knotting by way of its better appearance while at the same time retaining sufficient strength. WAXING PROCESS: Waxing is the process which is almost exclusively used in all automatic and manual winding machines for yarns which are meant for knitting. This helps to reduce the coefficient of friction of yarns created during knitting process. Extensive tests have shown that the coefficient of friction of waxed yarn is not constant, but depends on the amount of wax on the yarn. It is proved that both too little and too much wax cause increase in coefficient of friction and thus detrioration in running efficiency on the knitting machine. The recommended wax pick up for different material are given below: I. cotton and its blends – wax take-up of 1.0 to 2.0 grams per kg of yarn II. synthetics – wax take-up of 0.5 to 1.5 gram per kg of yarn III. wool and its blends – wax takep-up of 2.0 to 3.0 grams per kg From the technical point of view, it is interesting to note that very small amounts of wax are already sufficient to give an optimal reduction in friction coefficient. If for example, we take 1 kg of 50s metric yarn, there are 50000 meters of yarn. It is quite sufficient to apply 1 gm of wax on this length of yarn, to obtain optimum reduction in friction. As the original coefficients of friction of non-waxed yarns are so varied, due to different raw materials and blends, dye-stuffs, additives, twist etc, so also are the values obtained with waxed yarns. The table shows several typical examples of coefficient of friction for unwaxed and waxed yarns. Absolute comments about coefficients of friction are not possible. It depends on several factors, such as type of material, count, twist, dyeing process, yarn moisture content, atmospheric conditions etc. KIND OF YARN COUNT (METRIC) friction coefficient of unwaxed yarn friction coefficient of waxed yarn percentage of friction coefficient decrease % cotton , 50s combed 0.285 0.145 49 cotton, 40 bleachd cbd 0.30 0.14 53 wool, 36s natural 0.33 0.155 53 wool,36s dyed 0.32 0.155 52 polyester 40s white 0.42 0.21 50 Even with efficient waxing , the results in knitting can still be adversely affected, if the package of waxed yarn is subsequently handled. A typical example is conditioning of waxed packages. The conditioning causes an increase in friction coefficient, and thus a deterioration in running properties. Therefore one should not condition waxed packages. An increase in moisture content causes an increase in friction coefficient. If too-damp bobbins are creeled at the winding machine, poor waxing results, because yarns with high moisture content take up hardly any wax. If bobbins have to be conditioned or steamed, the yarn should be allowed to stand for atleast 24 hours, so that it can return to its normal condition before winding. A further problem can arise during steaming, or any other treatment involving the application of heat to a waxed package. Low yarn tension will affect the wax pickup Dimensions and form of wax rollers will affect the wax uniformity As it is clear and is important that, if the waxed particles are to carry out their function, they must remain on the surface of the yarn. When the yarn is subjected to heat however, the wax melts and penetrates to the inside of the yarn body: it can then no longer work effectively. When choosing the wax, it is essential to consider the type of yarn and fibre, the temperature in the production area, etc., and the characteristics indicated by the wax manufacturer WINDING – 2 Page 1 2 3 4 YARN FAULTS AND CLEARING: It is still not possible to produce a yarn without faults for various reasons. Stickiness of cotton can contribute to the formation of thick and thin places. Fly liberation in Ringframe department is one of the major reasons for short faults in the yarn because of the fly gets spun into the yarn. Hence it is not possible to have fault free yarn from ringspinning, it is necessary to have yarn monitoring system in the last production process of the spinning mill. As physical principle for electronic yarn clearing the capacitive and the optical principle have established. Both principles have their advantages in specific applications. Depending upon the rawmaterial, the machiery set up, production and process parameters, there are about 20 to 100 faults over a length of 100 km yarn which do not correspond to the deisred appearance of the yarn. This means that the yarn exhibits a yarn fault every 1 to 5 km. These faults are thick and thin faults, foregin fibres and diry places in the yarn. The yarn faults which go into the woven or knitted fabric can be removed at very high costs or can not be removed at all. Therefore the yarn processing industry demands a fault free yarn. The difference between frequent yarn faults and seldom occuring yarn faults are mainly given by the mass or diameter deviation and size. These faults are monitored by classimat or clearer installation on winding. Each yarn contains, here and there, places which deviate to quite a considerable extent from the normal yarn corss-section. These can be short thick places, long thin places , long thick places or even spinners doubles. Eventhough such events seldom occur, they represent a potential disturbance in the appearance of the fabric or can negatively influnece subsequent processing of the yarn. Short thick places are those faults which are not longer than approximately 8 cms, but have a cross-sectional size approx. twice that of the yarn. These faults are relatively frequent in all spun yarns. To an extent they are the result of the rawmaterial ( vegetable matter, non-seprated fibres, etc). To a much larger extent, these faults are produced in the spinning section of the mill and are the result of spun in fly. Short thick places are easily determinable in the yarn. In many cases, they cause disturbances in subsequent processing. Once they reach a certain size( cross-section and length) , and in each case accoridng to the type of yarn and its application, short thick place fults can considerably affect the appearance of the finished product. Long thick places are much more seldom-occuring than the short thick places and usually have a length longer than 40cms. In some cases, their length can even reach many meters. Their cross sectional size approx. + 40% to +100% and more with respect of the mean cross-section of the yarn. Long thick places will affect the fabric apperance. Faults like spinners doubles are difficult to determine in the yarn, with the naked eye. On the other hand, they can produce quite fatal results in the finished product. A spinners double in the warp or in yarn for circular knitting can downgrade hundreds of meters of woven , or knitted fabric. Thin places occur in two length groups. Short thin places are known as imperfections, and have a length approx. three times the mean staple length of the fibre. Their frequency is dependent on the rawmaterial and the setting of the drafting element. They are too frequent in the yarn to be extracted by means of the electronic yarn clearing. Long thin places have lengths of approx. 40cms and longer and a cross-sectional decrease with respect to the mean yarn cross-section of approx.30 to 70%. They are relatively seldom-occuring in short staple yarns, but much more frequently-occuring in long staple yarns. Long thin faults are difficult to determine in the yarn by means of the naked eye. Their effect in the finished product however, can be extremely serious. The quite extensive application of electronic yarn clearing has set new quality standards with respect to the number of faults in spun yarns. It is therefore necessary to evolve a method of yarn fault classification before clearing the faults in winding. The most important aspect is certainly the determination of the fault dimensions of cross-sectional size and length. With such a cross-section and length classification and by means of the correct choice of the class limits, the characteristic dimensions of the various fault types can be taken into consideration, then a classification system will result which is suitable primarily for satisfying the requirements of yarn clearing and yet allows, to quite a large extent, for a selection of the various types of faults. The yarn faults are classified according to their length and cross-sectional size, and this in 23 classes. FIG: CLASSIMAT FAULTS: · The cross-sectional deviations are given +% or -% values. i.e theupper limit, respectively , lower limit with respect to the mean yarn fault cross-section is measure in %. The fault length is measured in cms. FIG: YARN CLEARING CONCEPT OF USTER QUANTUM CLEARER N – NEPS S- SHORT FAULTS L-LONG FAULTS CCP – COARSE COUNTS CCM-FINE COUNTS The classes and their limits are set out according to the following: · Short thick place faults: 16 classes with the limits, 0.1 cm, 2cm, 4cm, and 8cm for the lengths and +100%, +150%,+250%, and +400% for the cross-sectional sizes are provided. The classes are indicated A1…D4. The classes A4, B4,C4,D4 contain all those faults, according to their length, whose cross-sectional size oversteps +400%. · spinners doubles: This refers to a class (with the indication E) for faults whose length oversteps 8cms and whose cross-sectional size oversteps +100 ( open to the right and upwards) · Long thick place faults and thick ends: The long thin place faults are contained in 4 classes with the limits 8 cms and 32 cms for the lengths, and -30% , -45% and -75% for the cross-sectional sizes. The classes are designated H1…..I2. The classes I1 and I2 are open to the right. i.e they contain all those thin places having a size between -30 and -45%, respetively, -45% and -75% and whose lengths are longer than 32 cms. The classification of the shorter thin places is of no advantage in the analysis of the seldom-occuring faults. FIG: A DIAGRAM FROM LOEPFE YARN CLEARER MANUAL Types of Electronic Yarn Clearers Electronic Yarn Clearers available in the market are principally of two types –capacitive and optical. Clearers working on the capacitive principle have ‘ mass’as the reference for performing its functions while optical clearers function with ‘ diameter’ as the reference. Both have their merits and demerits and are equally popular in the textile industry. Besides the above basic difference in measuring principle, the basis of functioning of both the types of clearers are similar if not exactly same. Since most of the other textile measurements like, U% / CV%, thick and thin places etc., in various departments take into account mass as the reference parameter, the functioning of the capacitive clearer is explained in some detail in the following sections. Functioning Principle The yarn is measured in a measuring field constituted by a set of parallely placed capacitor plates. When the yarn passes through this measuring field (between the capacitor plates), an electrical signal is produced which is proportional to the change in mass per unit length of the yarn. This signal is amplified and fed to the evaluation channels of the yarn clearing installation. The number and type of evaluation channels available are dependent on the sophistication and features of the model of the clearer in use. Each of the channels reacts to the signals for the corresponding type of yarn fault. When the mass per unit length of the yarn exceeds the threshold limit set for the channel, the cutting device of the yarn clearer cuts the yarn. WINDING – 3 Page 1 2 3 4 Yarn Clearer Settings The yarn clearer has to be provided with certain basic information in order to obtain the expected results in terms of clearing objectionable faults. The following are some of them – a. Clearing Limit: The clearing limit defines the threshold level for the yarn faults, beyond which the cutter is activated to remove the yarn fault. The clearing limit consists of two setting parameters – Sensitivity and Reference Length. i. Sensitivity – This determines the activating limit for the fault cross sectional size. ii. Reference Length – This defines the length of the yarn over which the fault cross – section is to be measured. Both the above parameters can be set within a wide range of limits depending on specific yarn clearing requirements. Here, it is worth mentioning that the ‘ reference length’ may be lower or higher than the actual ‘ fault length’. For a yarn fault to be cut, the mean value of the yarn fault cross-section has to overstep the set sensitivity for the set reference length. b. Yarn Count : The setting of the yarn count provides a clearer with the basic information on the mean value of the material being processed to which the clearer compares the instantaneous yarn signals for identifying the seriousness of a fault. c. Material Number: Besides the yarn count there are certain other factors which influence the capacitance signal from the measuring field like type of fibre (Polyester / Cotton / Viscose etc.) and environmental conditions like relative humidity. These factors are taken into consideration in the ‘ Material Number’ . The material number values for different materials are provided in Table. Table :material number 7.5 cotton, wool, viscost 8.5 very damp material (80%Rh) 6.5 very dry material(50% RH) 6 natural silk 7 very damp material 5 very dry material 5.5 acetate, acrylonitrile polyamide 50 to 80% RH 50 to 80% RH 4.5 polypropylene, poly ethylene 50 to 80% RH 3.5 polyester 50 to 80%RH 2.5 polyvinyl chloride 50 to 80% RH From the values given in the table it could be seen that, for water absorbent fibres like cotton, the Material Number is changed by 1 for a 15% change in Relative Humidity. A reduction in material number results in a more sensitive setting causing higher fault removal. For blended yarns, the material number is formed from the sum of the percentage components of the blend. For instance, when a 67/33 Polyester / Cotton blend is run at an RH of 65%, the Material umber should be set at (0.67 * 3.5) + (0.33 * 7.5) = 4.8. d. Winding Speed: The setting of the winding speed is also very critical for accurate removal of faults. It is recommended that, instead of the machine speed, the delivery speed be set by actual calculation after running the yarn for 2-3 minutes and checking the length of yarn delivered. Setting a higher speed than the actual is likely to result in higher number of cuts. Similarly a lower speed setting relative to the actual causes less cuts with some faults escaping without being cut. In most of the modern day clearers, the count, material number and speeds are monitored and automatically corrected during actual running of the yarn. Fault Channels: The various fault channels available in a latest generation yarn clearer are as follows: 1. Short Thick places 2. Long Thick Places 3. Long Thin Places 4. Neps 5. Count 6. Splice The availability of one or more of the above channels is dependent on the type of the yarn clearer. Most of the modern clearers have the above channels. Besides detection of the various types of faults, with latest clearers, it is also possible to detect concentration of faults in a specific length of yarn by means of alarms(cluster faults). Contamination Clearing: Detection of contamination in normal yarn has become a requirement in recent times due to the demands by yarn buyers abroad. Therefore, some of the optical yarn clearers have an additional channel to detect the contamination in yarn. This is mostly used while clearing cotton yarn. The various facilities available in the yarn clearers nowadays enable precise setting and removal of all objectionable faults while at the same time ensure a reasonably high level of productivity. SPLICING: A high degree of yarn quality is impossible through knot, as the knot itself is objectionable due to its physical dimension, appearance and problems during downstream processes. The knots are responsible for 30 to 60% of stoppages in weaving. Splicing is the ultimate method to eliminate yarn faults and problems of knots and piecing. It is universally acceptable and functionally reliable. This is in spite of the fact that the tensile strength of the yarn with knot is superior to that of yarn with splice. Splicing is a technique of joining two yarn ends by intermingling the constituent fibres so that the joint is not significantly different in appearance and mechanical properties with respect to the parent yarn. The effectiveness of splicing is primarily dependent on the tensile strength and physical appearance. Splicing satisfies the demand for knot free yarn joining: no thickening of the thread or only slight increase in its normal diameter, no great mass variation, visibly unobjectionable, no mechanical obstruction, high breaking strength close to that of the basic yarn under both static and dynamic loading, almost equal elasticity in the joint and basic yarn. No extraneous material is used and hence the dye affinity is unchanged at the joint. In addition, splicing enables a higher degree of yarn clearing to be obtained on the electronic yarn clearer. Splicing technology has grown so rapidly in the recent past that automatic knotters on modern high speed winding machine are a thing of the past. Many techniques for splicing have been developed such as Electrostatic splicing, Mechanical splicing and Pneumatic splicing. Among them, pneumatic splicing is the most popular. Other methods have inherent drawbacks like limited fields of application, high cost of manufacturing, maintenance and operations, improper structure and properties of yarn produced. Pneumatic Splicing The first generation of splicing systems operated with just one stage without proceeding to trimming. The yarn ends were fed into the splicing chamber and pieced together in one operation. Short fibres, highly twisted and fine yarns could not be joined satisfactorily with such method. Latest methods of splicing process consist of two operations. During the first stage, the ends are untwisted, to achieve a near parallel arrangement of fibres. In a second operation the prepared ends are laid and twisted together. Principle of Pneumatic Splicing The splicing consists of untwisting and later re-twisting two yarn ends using air blast, i.e., first the yarn is opened, the fibres intermingled and later twisted in the same direction as that of the parent yarn. Splicing proceeds in two stages with two different air blasts of different intensity. The first air blast untwists and causes opening of the free ends. The untwisted fibres are then intermingled and twisted in the same direction as that of parent yarn by another air blast Structure of Splice Analysis of the longitudinal and transverse studies revealed that the structure of the splice comprises of three distinct regions/elements brought by wrapping, twisting and tucking / intermingling. Wrapping : The tail end of each yarn strand is tapered and terminates with few fibres. The tail end makes a good wrapping of several turns and thus prevents fraying of the splice. The fibres of the twisting yarn embrace the body of the yarn and thus acts as a belt. This in turn gives appearance to the splice. WINDING – 4 Page 1 2 3 4 Twisting The two yarn ends comprising the splice are twisted around the body of the yarn, each yarn strand twists on the body of the yarn on either side of the middle of the splice. The cross-section of this region distinctly shows the fibres of the two yarn strands separately without any intermingling of the fibres. Tucking / Intermingling The middle portion of the splice is a region (2-5 mm) with no distinct order. The fibres from each yarn end intermingle in this splice zone just by tucking. The studies on quantitative contribution of splice elements showed that intermingling/tucking contributes the most to the strength of splice (52%), followed by twisting (33%) and wrapping (about 15%). The lower strength of the splice is attributed to the lower packing coefficient of the splice zone. Spliced yarn has a lower breaking elongation than normal yarn. Breaking elongation is mainly affected by intermingling. Wrapping and twisting provides mainly transverse forces. The absence of fibre migration gives lower breaking elongation to splice. Effect of Variables on the Properties of the Spliced yarn Several studies have been conducted on the effect of various variables on the properties of the spliced yarn. Effect of Fibre Properties and Blend Fibre properties such as torsional rigidity, breaking twist angle and coefficient of friction affect splice strength and appearance. The lower torsional rigidity and higher breaking twist angle permit better fibre intermingling. Higher coefficient of friction of fibres generates more inter-fibre friction to give a more cohesive yarn. Thus, these properties of fibre contribute to better retention of splice strength. In blended yarn, usually the addition of polyester to other fibre blend like P/W, P/C both for ring and rotor spun yarn increases splice strength. Effect of Yarn Fineness Several studies on cotton, polyester and wool report that coarser yarns have higher breaking strength but a moderate extension. The coarse yarn cross section contains more fibres and provides better fibre intermingling during pre-opening, hence the splice is stronger than that of finer yarns. Effect of Yarn Twist An increase in the twist significantly increases the breaking load and elongation, even at higher pneumatic pressure. This could be due to better opening of the strands at higher pneumatic pressure. Splicing of twisted ply yarn is more complicated than single yarn due to the yarn structure having opposing twists in the single and doubled yarns. Twisted yarns also require a relatively longer time for complete opening of the yarn ends. Effect of Different Spinning Methods Yarn produced with different spinning methods exhibit different structure and properties. Therefore, these yarns show significant differences in splice quality. The ring spun yarn lent best splicing but the potential of splicing is affected by the spinning conditions. The breaking strength percentage of ring spliced yarns to a parent yarn is 70% to 85% for cotton yarn. However, the breaking strength and extension of splice vary with fibre and yarn properties. Rotor spun yarns, due to the presence of wrapper fibres, make it difficult to untwist and the disordered structure is less ideal for splicing. The breaking strength retention varies from 54% to 71% and is much lower compared to the splice of ring spun yarns. In case of friction spun yarns, the highest relative tensile strength obtained at the spliced joints can be above 80%, but a number of splicing failures occurs due to unfavourable yarn structure. The air-jet-spun (MJS) yarn and the cover spun yarn are virtually impossible to splice. Only very low tensile strengths and elongation values can be attained due to the inadequate opening of the yarn ends during preparation of the splicing. The coefficient of variation of these properties is also generally high. Effect of Opening Pressure A study on 50/50 polyester cotton, 25 tex ring spun yarn shows a rise in tensile strength up to a certain opening pressure. However, long opening time deteriorates the strength. An increase in pressure up to 5 bar caused release of fibre tufts and fibre loss from the yarn ends in P/C blend which is due to intensive opening, but beyond this pressure, drafting and twisting in the opposite direction may also occur. Effect of Splicing Duration With a given splicing length, when the splicing is extended for a long period of time, the breaking strength of the spliced yarn and also their strength retention over the normal value of the basic yarn increases because of increased cohesive force resulting from an increased number of wrapping coils in a given length. The effects are more pronounced at higher splicing lengths. It is desirable however, that splicing duration be as short as possible. The splicing duration alone has no conclusive effect on elongation properties of splice yarn. It has also been observed that, for maximum splice strength, different materials require different durations of blast. These are between 0.5 to 1.8 seconds. Effect of Splicing Length Studies on splicing of flyer and wrap spun yarns spun with different materials, showed that regardless of the splicing material, the breaking strength and strength retention of both yarn types increase with the splicing length because of the increased binding length of the two yarn ends. Elongation at break and retention of elongation of both flyer and wrap spun spliced yarns increase with the splice length. Compared to the splicing duration, the splicing length has more pronounced effect on the load-elongation properties of the spliced yarn. It can be therefore be stated that the splices made on longer lengths and for longer period of time have more uniform strength. Comparison of Dry and Wet Splicing The comparative studies on dry and wet splicing with water showed that the breaking load retention for wet spliced yarns are significantly greater than dry spliced yarns. In fact, wet splicing is more effective for yarn made from long staple fibres and for coarse yarn. This may be due to higher packing coefficient resulting from wet splicing. Effect of Splicing Chamber The factors like method and mode of air supply and pressure along with type of prism affect the splicing quality. It was observed that irregular air pressure has advantages over constant pressure for better intermingling in the splicing chamber, which varies with different staple fibres, filament yarns, and yarns with S and Z twists. It is not possible to make a general comment regarding potential of the splicing chamber due to the multiplicity of factors influencing splicing. Assessment of Yarn Splice Quality The two important characteristics of a splice are appearance and strength. Although quality of splice can be assessed by methods like load-elongation, work of rupture, % increase in diameter and evaluation of its performance in down stream process etc., the appearance can be assessed either by simple visual assessment or by comparing with photograph of standard splice. CHARACTERISTICS OF BOBBIN FORMATION: · Strectch length: It is the length of the yarn deposited on the bobbin tube during each chase (one up and down movement of ringrail ) of ring rail. The length should be around 3.5 to 5 meters. It should be shorter for coarser yarns and longer for fine yarns. · Winding ratio:It is the ratio of the length of yarn wound during the upward movement of the ring rail and the length wound during the downward movement of the ringrail. · Bobbin taper: The ratio of the length of the upper taper of the cop (bobbin with yarn) to the diameter of the bobbin must be 1:2 or greater. WINDING SPEED: It depends upon the following factors · count · type of yarn, (type of fibre, average strength and minimum strength) · type and charactersitics of bobbin · package taper · final use of package The best winding speed is the speed which allows the highest level of production possible for a given type of yarn and type of package, and with no damage whatsoever to the yarn.(abrasion and breaks due to excessive tension) WINDING PRODUCTION: It depends upon the following factors · winding speed · time required by the machine to carry out one splicing operation · bobbin length per bobbin( both bobbin weight and tpi to be considered, because TPI will affect the bobbin length). This decides the number of bobbin changes · the number of faults in the yarn and the clearer settings, this decides the clearer cuts · count · the number of doffs. It depends upon the doff weight. Higher the doff weight, lower the number of doffs · the time taken for each doff either by the doffer or by an operator · Down time due to red light. It depends upon, number of red lights, number of repeaters setting for red lights, clearer settings like off count channel, cluster setting which will result in red lights and others · bobbin rejections, it depends on weak yarn, wrong gaiting, double gaiting, bobbin characteritics etc. · WINDING PACKAGE DEFECTS: Following are some of the package defects which will result in complaints · Yarn waste in the cones. This is due to loose yarn ends that are wound on to the cone · Stitch, drop over, web: Yarn is visible on the small or on the big side of the cone either across the side , around the tube, or going back in the cone · Damaged edges or broken ends on the cone: The yarn is broken on the edges or in the middle of the cone. · Ring formation: The yarn runs in belt formation on to the package, because it is misguided · Without transfer tail: The desired transfer tail is missing or too short · Ribbon formation: Pattern or ring formation are made by the drum when rpm are stying the same · Displaced yarn layers: yarn layers are disturbed and are sliding towards the small diameter of the cone · Misguided yarn : The yarn is not equally guided over the hole package · Cauliflower: On the smaller side of the package, the yarn shows a wrinkle effect · Soft and Hard yarn layer: Some layer of yarn are pushed out on the small side of the cone · Soft and Hard cones: Great difference in package density from one winder head to another YARN CONDITIONING Why conditioning is required? Moisture in atmosphere has a great impact on the physical properties of textile fibres and yarns. Relative humidity and temperature will decide the amount of moisure in the atmosphere. High relative humidity in different departments of spinning is not desirable. It will result in major problems. But on the otherhand, a high degree of moisture improves the physical properties of yarn. Moreover it helps the yarn to attain the standard moisture regain value of the fibre. Yarns sold with lower moisture content than the standard value will result in monetary loss. Therefore the aim of CONDITIONING is to provide an economical device for supplying the necessary moisture in a short time, in order to achieve a lasting improvement in quality. In these days there is a dramatic change in the production level of weaving and knitting machines, because of the sophisticated manufacturing techniques. Yarn quality required to run on these machines is extremely high. In order to satisfy these demands without altering the rawmaterial, it was decided to make use of the physical properties inherent in the cotton fibres. Cotton fibre is hygroscopic material and has the ability to absorb water in the form of steam. It is quite evident that the hygroscopic property of cotton fibres depends on the relative humidity. The higher the humidity, more the moisture abosrption. The increase in the relative atmospheric humidity causes a rise in the moisture content of the cotton fibre, following an S-shaped curve. The relative humidity in turn affects the properties of the fibre via the moisture content of the cotton fibre. The fibre strength and elasticity increase proportionately with the increase in humidity. If the water content of the cotton fibre is increased the fibre is able to swell, resulting in increased fibre to fibre friction in the twisted yarn structure. This positive alteration in the properties of the fibre will again have a positive effect on the strength and elasticity of the yarn. CONTEXXOR CONDITIONING PROCESS BY XORELLA: The standard conventional steaming treatment for yarn is chiefly used for twist setting to avoid snarling in further processing. It does not result in lasting improvement in yarn quality. The steaming process may fail to ensure even distribution of the moisture, especially on cross-wound bobbins(cheeses) with medium to high compactness. The thermal conditioning process of the yarn according to the CONTEXXOR process developed by XORELLA is a new type of system for supplying the yarn package. The absence of Vacuum in conventional conditioning chambers, prevents homogeneous penetration. The outer layers of the package are also too moist and the transition from moist to dry yarn gives rise to substantial variations in downstream processing of the package, both with regard to friction data and strength. Since the moisture is applied superficially in the wet steam zone or by misting with water jets, it has a tendency to become re-adjusted immediately to the ambient humidity level owing to the large surface area. Equipment of this king also prevents the optimum flow of goods and takes up too much space. PRINCIPLE OF WORKING: Thermal conditioning uses low-temperature saturated steam in vacuum. With the vacuum principle and indirect steam, the yarn is treated very gently in an absolutely saturated steam atmosphere. The vacuum first removes the air pockets from the yarn package to ensure accelerated steam penetration and also removes the atmospheric oxygen in order to prevent oxidation. The conditioning process makes use of the physical properties of saturated steam or wet steam (100% moisture in gas-state). The yarn is uniformly moistened by the gas. The great advantage of this process is that the moisture in the form of gas is very finely distributed throughout the yarn package and does not cling to the yarn in the form of drops. This is achieved in any cross-wound bobbins, whether the yarn packages are packed on open pallets or in cardboard boxes. pic: XORELLA CONDITIONING SYSTEM · ADVANTAGES OF CONTEXXOR PROCESS: · saturated steam throughout the process · even penetration of steam and distribution of moister · lowest energy consumption with XORELLA ECO-SYSTEM · short process time · absolute saturated steam atmosphere of 50 degree C to 150 degreees C. · no additional boiler required, the steam is generated in the system · minimum energy consumption(approx. 25 KWh for 1000 kgs of yarn)No tube buckling in case of mad-made yarns · treatment of all natural yarns, blends, synthetics and microfibre yarns. · low installation and maintenance cost · preheating for trollys and plastic tubes to avoid drops (Wool) · standardize sizes · length up to 20 meters (66 feet) and max. temperature deviation of 1°C · various loading and unloading facilities · no contamination of the treated packages · energy recovery option offered by indirect heating system using steam or hot water · no special location required, the systems can be operated next to the production machines. · BENEFITS ACHIEVED OUT OF CONDITIONING: FOR KNITTING: The treatment temperature for knitting yarn is held below the melting point of the wax. Temperatures for unwaxed yarn are coordinated to the compatibility fo each individual type of yarn · Upto 20% greater efficiency due to a reduction in the unwinding tension · fewer needle breaks · uniform moisture content and friction values · regular stitch formation · no change in size of finished articles · no extra dampening required · free from electrostatic · less fly hence less problems. It helps if the yarn is running on a closer gauge machines NOTE: Please note that the wax applied should be able to withstand min 60 degree centigrade. If low quality wax is used, it will result in major problem. Conditioning should be done at 55 to 60 degree centigrade. FOR WEAVING: · upto 15% fewer yarn breaks due to greater elongation · less fly, resulting in a better weaving quality · increased strength · increased take-up of size, enhanced level of efficiency in the weaving plant · softer fabrics · Pic: improved strength Pic: improved elongation FOR TWISTING: Conditioning and fixing of the twist at the same time in a single process. FOR DYEING: · no streaks · better dye affinity Pic: dye pick up of conditioned and unconditoned yarn PROCESS PARAMETER IN BLOW ROOM With all harvesting methods, however, the cotton seed, together with the fibers, always gets into the ginning plant where it is broken up into trash and seed-coat fragments. This means that ginned cotton is always contaminated with trash and dust particles and that an intensive cleaning is only possible in the spinning mill. Nep content increases drastically with mechanical harvesting, ginning and subsequent cleaning process. The reduction of the trash content which is necessary for improving cotton grade and apperance unfortunately results in a higher nep content level. The basic purpose of Blow room is to supply small fibre tufts clean fibre tufts homogeneously blended tufts if more than one variety of fibre is used to carding machine without increasing fibre rupture, fibre neps , broken seed particles and without removing more good fibres. The above is achieved by the following processes in the blowroom · Pre opening · pre cleaning · mixing or blending · fine opening · dedusting CLEANING EFFICIENCY: Cleaning efficiency of the machine is the ratio of the trash removed by the machine to that of total trash fed to the machine, expressed as percentage Cleaning efficieny % =(( trash in feed % – trash in del %) x 100) / (trash in feed%) Following are the basic parameters to be considered in Blowroom process. · no of opening machines · type of beater · type of beating · Beater speed · setting between feed roller and beater · production rate of individual machine · production rate of the entire line · thickness of the feed web · density of the feed web · fibre micronaire · size of the flocks in the feed · type of clothing of the beater · point density of clothing · type of grid and grid settings · air flow through the grid · position of the machine in the sequence · amount of trash in the material · type of trash in the material · temp and relative humidity in the blow room department · PREOPENING: Effective preopening results in smaller tuft sizes, thus creating a large surface area for easy and efficient removal of trash particles by the fine openers. If MBO (Rieter) or BOW ( Trutzschler) type of machine is used as a first machine · the tuft size in the mixing should be as small as possible. Normally it should be less than 10 grams · since this machine does not take care of long term blending, mixing should be done properly to maintain the homogenous blending · the inclined lattice speed and the setting between inclined lattice and clearer roller decides the production of the machine · the setting between inclined lattice and clearer roller decides the quality of the tuft · if the setting is too close, the tuft size will be small, but the neps in the cotton will be increased due to repeated action of the inclined lattice pins on cotton. · the clearance should be decided first to confirm the quality, then inclined lattice speed can be decided according to the production required · the setting of inclined lattice depends upon the fibre density, fibre micronaire and the tuft size fed. If smaller tuft is fed to the feeding conveyor, the fibre tufts will not be recycled many times, hence the neps will be less. · if the machine is with beater, it is advisable to use only disc type beater. Saw tooth and Pinned beaters should not be used in this machine, becasue the fibre damage at this stage will be very high and heavier trash particles will be broken in to small pieces. · the beater speed should be around 500 to 800 rpm depending upon the rawmaterial. Coarser the fibre, higher the speed · the setting between feed roller to beater should be around 4 to 7 mm · this machine is not meant to remove trash , hence the fibre loss should also be less · trash removal in this machine will result in breaking the seeds, which is very difficult to remove · It is easier to remove the bigger trash than the smaller trash, therefore enough care should be taken to avoid breaking the trash particles · this machine is just to open the tufts into small sizes so that cleaning becomes easier in the next machines. · the fibre tuft size from this machine should be preferably around 100 to 200 milligrams. · If tuft size is small, removing trash particles becomes easier , because of large surface area PROCESS PARAMETER IN BLOW ROOM – 2 Page 1 2 3 4 If Uniflco11(Rieter) or Blendomat BDT 019(Trutzschler) is used as a first machine · It helps to maintain the homogeneity of the long term blending · cotton is opened gently without recyling as it is done in manual bale openers · with the latest automatic bale opening machines, the tuft size can be as small as 50 to 100 grams without rupturing the fibres · the opening roller speed should be around 1500 to 1800 rpm. · the depth of penetration of the opening should be as minimum as possible for better quality · It is better to use this machine with one mixing or maximum two mixing at the same. · If the production per feeding machine is less than 150 kgs, then four mixings can be recommended · production rate of this machine depends upon the no of mixings working at the same time · production rate depends upon opening roller depth, traverse speed and the fibre tuft density · in general , the machine parameters should be set in such a way that maximum number of take-off points are available per unit time. · with the latest machines (Rieter -Unifloc A11), around 60% of take-off points are more compared to earlier machines PRECLEANING: Precleaning should be gentle. Since removing finer trash particles is difficult , seeds and bigger trash particles should not be broken. Finer trash particles require severe treatment in Fine openers. This will lead to fibre damage and more nep generation. Therefore, precleaning should be as gentle as possible and no compromise on this. If preopening and precleaning are done properly, consistency in trash removal by fine openers is assured. Dust removal should be started in this machine. Enough care should be taken remove dust in this process. Rieter’s Uniclean B11 and Trutzschler’s Axiflow or Maxiflow are the machines which does this work · the fibre treatment in this machine is very gentle because the fibres are not gripped by the feed roller during beating. Fibre tufts treated by the pin beater when it is carried by air medium · all heavy trash particles fall down before it is broken · cleaning efficiency of this machine is very high in the blow room line · Mostly all heavy seeds( full seeds) fall in this machine without any problem · around 50 pascal suction pressure should be maintained in the waste chamber for better cleaning efficiency · beater speed, air velocity through the machine, grid bar setting and gap between grid bars will affect the cleaning efficiency · higher the cleaning efficiency, higher the good fibre loss, higher the nep generaion and higher the fibre rupture · the optimum cleaning means maximum cleaning performance, minimum loss of good fibres, a high degree of fibre preservation and minimum nep generation · Rieter has a unique concept called “VARIOSET”. With this machine, selective trash removal is possible. Waste amount can be changed in a range of 1:10. fig: from Rieter which shows , degree of cleaning, fibre loss, neps, fibre damage. · with normal machines like Monocylinder or axiflow, a lot of trials to be conducted to arrive at optimum beater speed, air velocity(fan speed), grid bar setting and grid bar gap. · in general the beater speed is around 750 and minimum 50 pascal suction pressure to be maintained in the suction chamber BLENDING: · Barre or streakiness is due to uneven mixing of different cottons. Hence mixing technology is a decisive factor in spinning mill technology · bigger the differences of cotton parameters like fineness, color and staple length, the greater the importance of mixing · if the cotton has honeydew, the intenisive mixing of the rawmaterial is a precondition for an acceptable running behavior of the complete spinning mill following fig is given by trutzschler for different mixing requirements standard standar- plus high high-end · Trutzschler’s tandem mixing concept is an ultimate solution, if the mixing requirement is very high. This principle guarantees a maximum homogeneous of the mix FIG.Tandem mixing concept from TRUTZSCHLER: PROCESS PARAMETER IN BLOW ROOM – 3 Page 1 2 3 4 FINE CLEANING: Fine cleaning is done with different types of machines. Some fine cleaners are with single opening rollers and some are with multiple opening rollers. · If single roller cleaning machines are used, depending upon the amount and type of trash in the cotton, the number of fine cleaning points can be either one or two. · If the production rate is lower than 250 kgs and the micronaire is less than 4.0, it is advisable to use single roller cleaning machines instead of multiple roller cleaning machine. · Saw tooth beaters can be used, if trash particles are more and the machine is not using suction and deflector blades. i.e beater and regualar grid bar arrangements · Normal beater speeds with sawtooth beater depends upon the production rate, fibre micronaire and trash content TYPE OF COTTON COTTON MICRONAIRE PROUDCTION RATE kgs/hr BEATER SPEED rpm more trash 3.5 to 4.0 200 to 300 kgs /hr 600 to 750 less trash 3.5 to 4.0 200 to 300 kgs/hr 600 to 750 more trash 4.0 to 4.5 200 to 300 kgs 700 to 850 less trash 4.0 to 4.5 350 to 500 kgs 1000 and above · the number of wire points depends on the proudction rate and trash. · setting between feed roller and beater depends on the production rate and micronaire. The setting should be around 2 to 3 mm. Wider setting always result in higher rawmaterial faults, if carding does not take care. · closer the setting between beater and moteknives, higher the waste collected. It is advisable to keep around 3 mm. · If it is a Trutzschler blowroom line, it is better to use CVT1 ( single opening roller machine) if roller ginned cotton is used. · CVT3 or CVT4 machines with 3 or 4 opening rollers can be used for saw ginned cotton. · The cleaning points in CVT1, CVT3, CVT4 etc consists of opening roller, deflector blades, moteknives and suction hood. Trash particles released due to centrifugal forces are separated at the moteknives and continuously taken away by the suction. This gives better cleaning FIG: trash removal concept in CVT cleaners: · suction plays a major role in these machines. If suction is not consistent , the performance will be affected badly. Very high suction will result in more white fibre loss and less suction will result in low cleaning efficiency. · The minimum recommended pressure in the waste chamber (P2) is 700 pascals. It can be upto 1000 pascals. · material suction (P1) should be around 500 pascals · Whenever the suction pressure is changed, the deflector blade settings should be checked · Deflector blade setting can not be same for all the three rollers or four rollers. The setting for deflector blades in the panel looks like this 3, 12, 30 for 1st, 2nd and 3rd deflector blades. · The deflector blade setting should be done in such a way that the setting should be opened till the fibres start slipping on the deflector blade. · wider the deflector blade setting, higher the waste. If the setting is too wide, white fibre loss will be very high. · for saw ginned cottons, the above concepts helps a lot because of constant suction concentrated directly at the moteknives, ensures much removal of dust from the cotton. PROCESS PARAMETER IN BLOW ROOM – 4 Page 1 2 3 4 DEDUSTING: Apart from opening cleaning of rawmaterial, dedusting is the very important process in blowroom process. · normally dedusting starts with precleaning · it is always better to have a separate machine like DUSTEX of TRUTZSCHLER for effecive dedusting · dedusting keeps the atmospheric air clean · dedusting in machines like unimix , ERM of Rieter is good · stationary dedusting condensers can be used for this purpose · in exhausts of unimix , condensers , ERM etc, positive pressure of 100 pascal should be maintained. Exhaust fan speed and volume should be accordingly selected · DUSTEX should be installed before feeding to the cards, because better the fibre opening better the dedusting · fine opners like ERM, CVT cleaners also help in dedusting · It is always better to feed the material through condenser for a feeding machine of cards. Because condenser continuously removes the dust from a small quantity of fibres and the material fed to the feeding machine is opened to some extent. · Since material is not opened well in Unimix, the dedusting may not be very effective, eventhough dedusting concept in Unimix is very good · for rotor spinning dedusting is very important. It is better to use a machine like DUSTEX after the fine opener. OTHERS: · setting between feed rollers is different for different types. It should be according to the standard specified by the manufacturer. For Unimix it should be around 1 mm. · it is advisable to run the fans at optimum speeds. Higher fan speeds will increase the material velocity and will create turbulance in the bends.This will result in curly fibres which will lead to entanglements. · If the feeding to cards is not with CONTI -FEED, the efficiency of the feeding machine should be minimum 90 % and can not be more than 95%. · if the cards are fed by CONTI-FEED system, the feed roller speed variation should not be more than 10%. If the variation is more, then the variation in tuft size also will be more. Hence the quality will not be uniform · If two feeding machines feed to 10 cards and the no of cards can be changed according the requirement, then frequent changes will affect the tuft size which will affect the quality, if the line is fixed with CONTI-FEED. · if contifeed system is tuned properly and there are no machine stoppages, continuous material flow will result in better opening and even feeding to the cards · If the production rate per line is high, the reserve chamber for the feeding machine should be big enough to avoid long term feed variations. · it is advisable to reduce the number of fans in the line. · fan speeds, layout of machines should be selected in such a way that material choking in the pipe line, beater jamming etc will not happen. This will lead to quality problems · all blowroom machines should work with maximum efficiency. The feed roller speeds should be selected in such a way that it works atleast 90% of the running time of the next machine. · blow room stoppages will always affect the sliver quality both in terms of linear density and tuft size. Blow room stoppages should be nil in a mill · heavy particles like metal particles, stones should be removed using heavy particle removers , double magnets etc, before they damage the opening rollers and other machine parts. · Number of cleaning points are decided based on type of ginning (whether roller ginned or sawginned), the amount of trash, and the number of trash particles and the type of trash particles. · machinery selection should be based on the type of cotton and proudction requirement. If the production requirement of a blowroom line is less than 200 kgs, CVT-4 cleaner can not be recommended, instead CVT-1 can be used. · Since blow room requires more space and power, it is better to make use of the maximum production capacity of the machines · material level in the storage chambers should be full and it should never be less than 1/4 th level. · grid bars should be inspected periodically, damaged grid bars should be replaced. · grid bars in the front rows can be replaced earlier · if the cotton is too sticky, the deposits on the machine parts should be cleaned atleast once in a week, before it obstruct the movement of the fibre · fibre rupture should be checked for each opening point. 2.5 % span length should not drop by more than 3% . If the uniformity ratio drops by more than 3%, then it is considered that there is fibre rupture. · high fan speed, which will result in high velocity of air will increase neps in cotton · nep is increased in the blowroom process. The increase should not be more than 100%. · the nep increase in each opening machine should be checked with different beater speeds and settings, and the optimum parameters should be selected. But please remember that everything should be based on yarn quality checking. e.g. if nep increase in blow room is more and the beater speed or feed roller setting is changed, the tuft size will become more. This may result in bad carding quality. Sometimes if the neps are slightly more and the fibre is well opened, the neps can be removed by cards and combers and the yarn quality may be better. Therefore all trials should be done upto yarn stage. No of neps and trash particles after different processes is given below.(an approximate value) · Blow room machinery lay out should be desined in such a way that there should be minimum number of bends, and there should not be sharp bends to avoid fibre entanglements. · fibre travelling surface should be smooth and clean · temperature should be around 30 degrees and the humidity is around 55 to 60%. A best blowroom can be achieved by selecting the following machines: 1.RIETER UNIFLOC- A11 ( pre opening) 2.RIETER UNICLEAN B11 ( pre cleaning) 3.TRUTZSCHLER MPM 6 + MPM6 ( two mixers for blending) 4.TRUTZSCHLER CVT-1 ( for roller ginned cotton) CVT-3 ( for saw ginned) 5.CONTAMINATION DETECTOR from either BARCO OR JOSSI 6.TRUTZSCHLER DUSTEX-DX ( for dedusting) 7.TRUTZSCHLER CONTI-FEED and others But enough care should be taken to synchronise the machines for better performace , and to run the line without any electrical system breakdowns. PROCESS PARAMETERS IN CARDING INTRODUCTION: Carding is the most important process in spinning. It contributes a lot to the yarn quality. The following process parameters and specfications are to be selected properly to prodce a good quality yarn with a lower manufacturing cost. cylinder wire(wire angle, height, thickness and population) flat tops specification licker-in wire specification doffer wire specification feed weight draft between feed roller and doffer cylinder grinding doffer grinding flat tops grinding cylinder, falt tops, doffer wire life Licker-in wire life Cylinder speed flat speed Licker-in speed setting between cylinder and flat tops setting between licker-in and feed plate setting between licker-in and undercasing elements like , mote knife,combing segement etc. setting between cylinder and doffer setting between cylinder and back stationary flats setting between cylinder and front stationary flats setting between cylinder and cylinder undercasing CYLINDER WIRE AND CYLINDER SPEED Cylinder wire selection is very very important , it depends upon cylinder speed ,the raw material to be processed and the production rate. The following characteristics of cylinder wire should be considered. · wire angle · tooth depth · wire population · rib thickness · tooth profile · tooth pitch · tooth point · overall wire height · Wire front angle depends on mainly cylinder speed and coefficient of friction of raw material. Higher the cylinder speed, lower the angle for a given fibre. The cylinder speed in turn depends upon the production rate. · Higher production means more working space for the fibre is required. It is the wire that keeps the fibre under its influence during carding operation.Therefore the space within the wire should also be more for higher production. Higher cylinder speed also increase the space for the fibre. Therefore higher cylinder speed is required for higher production. · · In the case of high production carding machines, the cylinder surface is very much higher, therefore even with higher number of fibres fed to the cylinder, the cylinder is renewing the carding surface at a faster rate. · Higher the cylinder speed, higher the centrifugal force created by the cylinder, this tries to eject the fibre from the cylinder, along with the trash.It is the cylinder wire’s front angle which overcomes the effect of this force. Low front angle With too low cylinder speed and with high frictional force, will result in bad quality, because the fibre transfer from cylinder to doffer will be less. Hence recyling of fibres will take place, whihc result in more neps and entanglements. · The new profile with less free blade avoids loading of the cylinder with fibre and/or trash. This helps in keeping the fibres at the tip of the tooth. The movement of the fibres towards the tip of the tooth, coupled with centrifugal action demands an acute front angle to hold the fibre in place during carding. · Lack of stiffness associated with fine and/or long fibres necessitates more control during the carding process.This control is obtained by selecting the tooth pitch, which gives the correct ratio of the number of teeth to the fibre length. Tooth pitch reduction is therefore required for exceptionally short fibres and those lack stiffness. · Number of points across the carding machine is decided by the rib width. It is selected based on the production rate and fibre dimensions. Finer the fibre, finer the rib width. The trend is to finer rib width for higher production. · The population of a wire is the product of the rib thickness and tooth pitch. The general rule is higher populations for higher production rates, but it depends upon the application. · Sharp tooth points penetrate the fibre more easily and help to intensify the carding action. Cut-to-point wires are sharp and they have no land at all.- · The effective working depth of a cylinder wire tooth for cotton is approximately 0.2mm and for synthetic materials approx.0.4mm. Manmade fibres require more space in their cylinder wire than does cotton.More tooth depth allows the fibre to recyle, resulting in damaged fibres and neps. If tooth depth is insufficient, there will be loss of fibre contro. This will result in even greater nep generaion. Looking into the above details, the following specifications can be used as a guideline · MATERIAL · PRODN. RATE · RIB WIDTH · ANGLE(degrees) · POPULATION Cotton low grade low 0.6 65 700 Cotton low grade high 0.5 55 840 Cotton Medium low 0.6 60 800 Cotton Medium high 0.4 to 0.5 55 840 to 950 Cotton fine low 0.5 60 840 Cotton long high 0.4 to 0.5 55 900 to 1100 Synth.coarse low 0.7 to 0.5 70 550 to 650 synth.coarse high 0.6 65 760 Synth.medium low 0.7 65 700 synth.medium high 0.5 65 760 Synth.fine low 0.6 65 700 synth.fine high 0.5 60 840 MATERIAL PRODCUTION RATE CYLINDER SPEED cotton low 360 to 400 cotton medium 430 to 470 cotton high 500 to 550 synthetic low 300 synthetic medium 380 synthetic high 460 PROCESS PARAMETERS IN CARDING – 2 Page 1 2 3 DOFFER, LICKER-IN AND FLAT TOPS: · The basic funtion of doffer is to strip the fibres from Cylinder. Please remember that the action between cylinder and doffer is carding action(or combing action or point to point action). · The doffer wire’s front angle plays a very important role in releasing the fibre from the cylinder. For most carding applications the optimum angle is 60 degrees. · Increased population over 400 ppsi does not give any advantage in the production of quality yarn. For smaller doffers, 5 mm doffer wire height helps in tranferring the fibres from cylinder to doffer. · If the fibre holding capacity of the doffer wire is less due to fibre friction or due to very high doffer speed, it is better to use a doffer wire with striations. For high production carding it is always better to use doffer wire with striations. · Licker-in plays a major role in opening the fibre tufts. In general 85 degrees is used both for synthetic and medium and long cottons. For coarse and dirty cottons 80 degrees can be used. · Strength, hardness and sharpness are very important for Lickerin wire. Licker-in wires should neverbe ground. Thinner blades penetrate the fibres more efficiently and increase the wire life. · Higher number of rows per inch gives better results. Now upto 12 rows per inch is being used. This is always better compared to 8 rows per inch. · If the wire pitch is not sufficient, it can be compensated by increasing the licker-in speed. Higher licker-in speeds for fine and long cottons will rupture the fibres. Licker-in speed depends upon the fibre type and the production rate. · It is better to use a flat top with more than one population. The general combination is 280/450. This is suitable for both cotton and synthetics. Please remember that the rigidity of the fillets is different for cotton and synthetic. If cotton flat tops are used for synthetic processing, the load on the cylinder will be more, more heat will be produced and hence the probability of cylinder loading due to electrostatic charge will be high. · Instead of using Rigid type flat tops, it is better to use semi-rigid type flat tops while processing synthetic fibres. SETTINGS: · The setting between cylinder and doffer is the closest setting in the card. This setting mainly depends upon the cylinder speed ,hank of the delivered sliver and the type of wire. Cylinder speed upto 360, the setting should be 0.1mm. For cylinder speeds more than 450 , the setting ranges from 0.125 to 0.15. · If the setting between cylinder and doffer is very close, the wires will get polished and this will affect the fibre transfer. If the setting is too wide, the fibres will not be transferred to doffer from the cylinder, hence cylinder will get loaded. While processing synthetic fibres cylinder loading will badly affect the yarn quality. Moreover, it is difficult to improve the wire condition if the loading is severe. The only solution would be to change the wire. Therefore enough care should be taken while processing synthetic fibres. · The most critical setting in a carding machine is between cylinder and flat tops. While processing cotton, it can be as close as 0.175 mm provided the mechanical accuracy of flat tops is good. Since most of the cards are with stationary flats at the licker-in side, the setting from the back to front for flats can be 0.25,0.2.0.2,0.2,0.2mm. · Closer the setting between cylinder and flats, better the yarn quality. Neps are directly affected by this setting. Of course, very close setting increase the flat waste. For processing cotton the setting can be 0.25,0.2,0.2,0.2,0.2mm. For synthetic fibres it can be 0.3,0.25,0.25,0.25,0.25mm · Most of the cards are with 6 to 11 stationary flats at the licker-in side. This setting can start with 0.4 mm and end with 0.25mm. · The wire points can start with 140 ppsi and end with 320 ppsi. The work done by the first few stationary flats is very high, therefore the wear of these flats is also high. It would be better if the first 50% of the flats are changed after 100000 kgs of production and the rest after 150000 kgs of production. · These stationary flats open the material so that, the setting between cylinder and flats can be as close as possible. · The setting between feed plate and Licker-in depends upon the type of feed plate. Conventional feed plate setting is decided mainly by the feed weight and to some extent by the fibre length and type. With the latest feed plate and feed roller arrangements, the setting is decided mainly by the fibre length and to some extent by the feed weight. · Normally the setting between the feed plate and Lickr-in is around 0.45 to 0.7mm, depending upon the feed weight and fibre type. · The setting between Licker-in and the first mote knife is around 0.35 to 0.5 mm. This helps to remove the heavier trash particles and dust. Closer the setting , higher the waste%ge. The setting between Licker-in and combing segments is around 0.45 to 0.6. This helps to open the material. · Some cards have two mote knifes in the Licker-in undercasing. The setting is around 0.4 to 0.5mm. This helps to remove the smaller trash and dust particles. · The setting between the cylinder and stationary flats at Doffer side, helps to transfer the fibres to doffer by stripping the fibres to the top of the cylinder wire. This setting can be as close as 0.15mm. The number of wire points on stationary flats also play a major role . It is normally around 300 to 400. For a high production application it can be as high as 600. · For cotton processing, the stationary flats are fixed with a knife attachement. The setting should be as close as possible,i.e.around 0.15mm. This helps to remove the trash particles of very small size. · The setting between cylinder and cylinder undercasing should be as per the manufacturer’s recommendation. The design of undercasing is different for different manufacturers. This setting is very important , as wrong settings will affect the fibre transfer and can also create air turbulance. PROCESS PARAMETERS IN CARDING – 3 Page 1 2 3 · SPEEDS: · Higher cylinder speed helps fibre transfer. Higher the production, higher should be the cylinder speed. · Higher cylinder speed improves carding action, thereby imperfections are reduced. · Higher Licker-in speed for coarse fibres and diry cotton helps to remove the trash and improves ,br> the yarn quality.For fine and long cottons , higher speed results in fibre ruputre, therefore, flat waste and comber noil will be more. · Higher flat speed, improves yanr quality and at the same time increases the flat waste · With the same flat speed, higher the carding production , lower the flat waste and vice-versa. · Very high tension drafts will affect carding U%. It is better to keep the draft between feed roller to doffer around 75 to 95. The results are found better with these drafts. · WIRE MAINTENANCE: · For a modern cylinder wire of 2mm height, grinding with the normal grinding stone is not recommended. It is better to use TSG grinder from GRAF. It is better to grind the wire every 2nd or 3rd month, so that the sharpness of the wire is always maintained. · TSG grinde does not grind the wire, therefore if the wire is worn out very badly the quality improvement using this grinding machine will be nil. Frequent grindings are recommended. If TSG grinder is not availbale, it is better not to grind 2mm wires. · The number of traverse should increase depending upon the life of the wire. The number of traverse for successive grindings should be like this 3,5,10,17 etc. Anyway the best method is to confirm with the microscope. If the grinding is not sufficient, the number of traverse should be increased. · Doffer is still working with a concept of Land formation. A normal grinding machine will be good for doffer grinding. All the wire points should be touched by the grinding stone. A slow and gradual grinding with the grind-out concept will give the best results. Harsh grindings will result in burr formation on the land. This will increase the number of hooks in the fibre, thereby the effective length of the fibre from this card will be reduced. · Flat tops grinding is very important. Everytime a flat top is ground, yarn quality is improved. It is better to use a grinding machine with the emery fillet. Frequent flat tops grinding will result in less neps and the yarn quality will be consistent. · Some mills increase the life of the flat tops compared to cylinder wire. But it is better to change flat tops and cylinder wire together for better and consistent yarn quality. · It is a good practice to check the individual card quality before changing the wire. · Licker-in wire should be changed for every 150000 kgs. Earlier changes will further improve the yarn quality. · Stationary flats should be changed for every 150000 kgs. But it is a good practice to change the first 3 or 6 stationary flats at Licker-in side for every 100000 kgs. This helps to maximise the carding effect between cylinder and doffer which is critical for better yarn quality. OTHERS: · Lower the feed variation, better the carding quality. Even if the card is with an autoleveller, feed variations should be kept as low as possible (plus or minus 10%). With the latest chute feed systems, it is easy to control the feed variation with in 5%. Lower the feed variation, lower the draft deviation, therefore yarn quality will be consistent. · If the card is with autoleveller, the nominal draft should be selected properly. Improper selection will affect sliver C.V% and yarn quality. · Improper feed roller loading and the setting between feed roller and feed plate will affect the quality, especially C.V% and neps. · Before mounting , the eccentricity of cylinder and doffer should be checked. Eccentric cylinder and doffer will affect the U% and will affect C.V.% also. · Defective bearings , gears and timing belts will affect U%. · Uneven distribution of tension drafts will affect U%. · Selvedge of feeding bat should be good. It should not be folded and double. This will increase the neps and sometimes it may result in cylinder loading. Lap fed to the carding machine should be narrower than the nominal width of the machine. · For processing cotton, minimum 800 pascal suction pressure should be maintained at trash master (at knife)for effective removal of trash and dust particles. · Worn or damaged scraper blades will lead to web sticking to crush rollers. Insufficient pressure between scraper blade and crush roller will also result in web sticking. If the calender roller pressure is too high web sticking will also be high. · If Cylinder undercasing nose at doffer side is too long for the type of fibre being carded web disappearing problem will arise. If the nose is set too close to the cylinder, web disappearing problem will arise. Damaged and dull doffer wire also will result in web disappearing problem. PROCESS PARAMETERS IN COMBING INTRODUCTION Combing is a process which is meant for upgrading the cotton raw material so that the following yarn properties will improve compared to the normal carded yarn. U% of yarn tenacity gms/tex trash in the yarn(or kitties in the yarn) Lustre and visual appearance POINTS TO BE CONSIDERED Following parameters are very critical as far as the yarn quality of combed yarn is concerned · Noil percentage(waste percentage) · Type of feed · feed length · feed wight in grams per meter · Piecing length · Top comb penetration depth · The distance between unicomb to nipper · unicomb specification · Number of needles in top comb · The cleaning of unicomb · Variation in nipper grip · Variation in noil percentage · type of lap preparation · total draft between carding and comber i.e total draft employed in lap preparation · Drafting roller settings in comber · Drafting roller settings in lap prepartion machines · No of doublings in lap preparation · Short fibre content · Fibre micronaire · the type and the amount of trash in the card sliver WASTE PERCENTAGE The noil percentage from a comber depends upon the following · short fibre content · detaching distance · feed length · top comb penetration · The distance between unicomb to top comb · The basic idea of removing the waste is to remove the short fibres i.e to improve 50% span length or mean length. · The two impartant basic parameters to be considered in deciding the waste percentage are, · 1.Yarn quality requirement and · 2.Short fibre content in the raw material · Let us assume that the following cotton is used/> 2.5 span lenth = 28 to 30 mm uniformity ratio = 50 to 53% FFI % = 6 to 14 Micronaire = 3.8 to 4.2 fibre strength = 24 to 28 gms/tex and the quality requirement for counts 30s to 40s, is to meet 5% uster standards in U%, imperfection, strength and classimate faults. · To meet this quality requirement with the above rawmaterial ,the amount of noil to be extracted may be around 16 to 18% if E7/4(RIETER MAKE)comber is used or 15 to 16 % if E-62(RIETER MAKE) comber is used. The above example is given to highlight the effect of noil removed and the quality achieved. This is just an approximate figure, the parameters may vary depending upon the application. · Combing efficiency is calculated based on the improvement in 50% span length, expressed as a percentage over 50% span length of the lap fed to the comber multplied with waste percentage. i.e. ((S-L)/(L*W))*100 where S- 50% span length of comber sliver L- 50% span length of comber lap W- waste percentage · Higher the noil %ge , lower will be the combing efficiency. · Given a chance, it is better to remove waste more from top comb penetration than increasing the waste percentage by increasing the detaching distance. When the detaching distance is more the control during detaching will be less. · Given a chance, it is better to work with backward feed than forward feed for the same waste percentage.Nep removal will be better, loss of long fibres in the waste during detaching will be less. · With backward feed, top comb penetrates into the fibre fringe which is already combed by the unicomb, therefore combing action done by top comb will be better and there will not be longer fibres in the waste · Waste percentage depends upon the feed length and type of feed. In backward feed, higher the feed length, higher the waste percentage. In forward feed, higher the feed length, lower the waste percentage. · With backward feed, the detaching distance will be less for the same waste percentage compared to forward feed. Therefore fibre control during detaching and during top comb action will be better. · Higher the noil, higher the yarn strength. But this is true upto certain level of waste. Further increase may not increase the yarn strength. Very high %ge of noil will reduce the yarn strength and will increase the breakage rate in ring frames. PROCESS PARAMETERS IN COMBING – 2 Page 1 2 TOP COMB AND UNICOMB · The number of needles in Top comb depends on the Fibre micronaire , the lap weight and fibre parallelisation in the lap. If the fibre Micronaire is less than 3.6, number of needles per cenitmeter in top comb can be 30.In general for fibres above 3.8 Micronaire, 26 needles per centimeter is used. · Top comb plays a major role in removing the waste. Around 40 to 60% of noil is removed by top comb. But top comb will get damaged very fast. Top comb damage will result in slubs in the sliver. Even 4 ro 5 needle damages will result in bad webs. Top comb maintenance is very very important to produce good qyality yarn. · Different types of unicombs are used in different combers. The circumference of unicombs , the number of wire points and its variation in the unicomb are different. It is not true that 110 degree unicomb will produce good quality yarn compared to 90 degree unicomb. · In most of the cases, 75 degree unicomb has given better results compared to 90 degree unicomb in E7/4 combers, for different types of cottons. · Rieter has standardised 90 degree unicomb for its E-62 combers. 110 degree unicomb can not be used in this comber. · Unicomb action will be effective as long as nipper and unicomb moves in opposite direction.If unicomb and nipper move in the same direction, unicomb can not do its work properly. Moreover the finer needles will not be utilised properly. That may be the reason why 90 degrees unicomb do not produce a good qyality yarn compared to 75 degrees unicomb. · The setting between unicomb and nipper should be same. When nipper is loaded with the the feed roller, the setting may be around .4 to .5 for E7/4 combers and .5 to .7 for E-62 combers. This setting can be corrected by fixing spacers between unicomb and unicomb body. Some unicomb manufacturers supply the spacers along with the unicombs. LAP PREPARATION: · There are different types of lap preparation. The best combination is drawframe and unilap combination. Lap piecing will be less in this combination compared to sliver lap and ribbon lap combination. Every lap piecing is a major fault compared to sliver piecing. If number of lap piecings are less, top comb damages will also be less. · The total draft for sliver lap and ribbon lap combination should be around 9 . · If Micronaire is less than 3.8, the lap licking tendency will be more. For such fibres, the total draft between card and comber should be kept as low as possible, i.e around 8.5. · For drawframe and unicomb preparation the total draft can be from 9.5 to 11, depending upon the fibre and lap weight. · Fibre parallelisaion in a lap should be reasonably good, to avoid long fibres in the noil. With the modern cards, the fibre parallelisation is improved because of the stationary flats. · The self cleaning effect of the lap sheet arises from the retaining power of the fibres relative to the impurities. This depends on the lap weight. If lap weight is more, the unicomb efficiceny may not be good. But the nipper grip will be good for heavier lap weight. Therefore an optimum lap weight should be decided, It depends on · Fibre micronaire(the number of fibres present to the nipper) · Nipper type · For E7/4 comber, lap weight of 52 to 60 gms per meter can be selected to produce a fairly good quality yarn. In case of E-62 comber(latest from RIETER), it can range from 65 to 75 grams per meter to produce a fairly good yarn. · Lesser the number of piecings in comber , better the quality. Every piecing in comber is a defect. Therefore, it is better to increase the lap weight as high as possible. For modern lap preparation it is around 20 to 23 kgs/lap and for older lap preparation, it is around 12 to 13 kgs per lap. OTHERS · Piecing is a distinct source of fault in comber operation. It is a periodic variation. The amplitude of this fault should be as low as possible. The following affect this fault – detaching roller timing – arranging this fault before entering tthe draft zone, so that this faults cancel each other (by adjusting the delivery guide.) · Detaching roller timing depends upon the index setting and feed length. This setting should be selected in such a that with the minimum length of overlapping comber works without any problem. · Drafting setting should be done according to the recommendation. Trials can be taken with different setting to optimise the same.(both in lap preparation and in comber) · Lower the feed length, lower the production. But better the yarn quality. · But in some application ,lower feed length with forward feed(concurrent feed) has resulted in inferior quality.But in general lower feed will improve the yarn quality. It is always better to take a trial and confirm this. Feed length to some extent depends on the fibre staple length also. · With backward feed, the unicomb penetrates thro the fibre fringe more often than in the case of forward feed. Therefore the quality of the combing operation is increased in the case of backward feed. · In combing operation, the hank of the sliver will not affect the comber production. Therefore, if old type of combers are used, where the drafting is not good, lower drafts can be preferred in comber and the draft can be increased in a good drawframe like RSB-951 OR RSB-D-30 if it is used as a finisher. PROCESS PARAMETERS IN DRAW FRAME INTRODUCTION: Drawframe is a very critical machine in the spinning process. It’s influence on quality, especially on evenness is very big.If drawframe is not set properly, it will also result in drop in yarn strength and yarn elongation at break.The faults in the sliver that come out of drawframe can not be corrected . It will pass into the yarn. The factors that affect the yarn quality are · the total draft · no of drawframe passages · break draft · no of doublings · grams/meter of sliver fed to the drawframe · fibre length · fibre fineness · delivery speed · type of drafting · type of autoleveller · autoleveller settings · The total draft depends upon 1. material processed 2. short fibre content 3. fibre length · Following are some facts derived from trials 1. wider back roller setting will result in lower yarn strength 2. wider back roller setting will affect yarn evenness 3. wider back roller setting will increase imperfections 4. higher back top roller loading will reduce yarn strength 5. higher back top roller loading will reduce end breakage rate 6. wider front roller setting will improve yarn strength · Higher draft in drawframe will reduce sliver uniformity, but will imrprove fibre parallelisation. Somtimes the improvement in fibre parallelisation will overcome the detrimental effects of sliver irregularity. · Most of the improvement in fibre parallelization and reduction in hooks takes place at first drawframe passage than at second passage. · Better fibre parallelisation generally results in more uniform yarns and a lower end breakage rate in spinning. · Higher the weight of sliver fed to drawframe, lower the yarn strength, yarn evenness, and it leads to higher imperfections in the yarn and more end breakages in ring spinning · Irregularities arise owing to the instability of the acceleration point over time. The aprons and rollers are used in the drafting zone to keep the fibre at the back roller velocity until the leading end is firmly gripped by the front roller, but individual fibre control is not achieved. · Drafting wave is caused primarily not by mechanical defects as such but by the uncontrolled fibre movement of a periodic type resulting from the defects. As the fibre-accelerating point moves towards the front rollers, the draft increases( and vice versa), so that a periodic variation in linear density inevitably results. · With variable fibre-length distribution(with more short fibre content), the drafting irregularity will be high. · More the number of doublings , lower the irregularity caused due to random variations. Doublings does not normally eliminate periodic faults.But it reduces the effects of random pulses. Doubling does not have any effect on Index of Irregularity also, since both the irregularities are reduced by square root of the number of doublings. · Fibre hooks influences the effective fibre length or fibre extent. This will affect the drafting performance. For carded material normally a draft 7.5 in both breaker and finisher drawframe is recommended. Seven of a draft can be tried in breaker, since it is a carded material. · For combed material, if single passage is used, it is better to employ draft of 7.5 to 8. · If combers with four doublings are used, it is better to use two drawframe passages after combing. This will reudce long thick places in the yarn. · In case of two drawframe passage, first drawframe passage will reduce the periodic variation due to piecing. Therefore the life of servomotor and servo amplifier will be more , if two drawframe passage is used. Quality of sliver will also be good, because of less and stable feed variation. · For synthetic fibres (44 mm to 51 mm), 8 of a total draft can be employed both in breaker and finisher passage. · The number of doublings depends upon the feeding hank and the total draft employed. Most of the modern drawframes are capable of drafting the material without any problem, even if the sliver fed is around 36 to 40 grams per meter. · Especially for synthetic fibres with very high drafting resistance, it is better to feed less than 38 grams per meter to the drawframe. · Break draft setting for 3/3, or 4/3, drafting system is as follows 1. For cotton, longest fibre +(8 to 12 mm) 2. For synthetic fibre, fibre length + (20 to 30% of fibre length) PROCESS PARAMETERS IN DRAW FRAME -2 Page 1 2 · Break draft for cotton processing is normally 1.16 to 1.26. For synthetics it is around 1.42 to 1.6 · To meet the present quality requirements , finisher drawframe should be an autoleveller drawframe. · Since the drawframe delivery speed is very high the top roller shore hardness should be around 80 degrees. It should not be less than that. · It is advisable to buff the rubber cots once in 30 days(minimum) to maintain consistent yarn quality. · Coiler size should be selected depending upon the material processed. For synthetic fibres, bigger coiler tubes are used. This will help to avoid coiler choking and kinks in the slivers due to coiling in the can. · Speed of the coiler will also affect the coiling. Speed of the coiler should be selected properly. In drawframes like RSB D-30(RIETER) , any coiler speed can be selected through the variator type pully. Since, the option is open, there is also more probability for making mistakes. One should take enough care to set the coiler speed properly. · Whenever coiler speed is adjusted, the diameter of the coil is also changed. Hence it is necessary to check the gap between the sliver and can. If it is more than 5 mm, then turn table position (can driving unit) should be altered so that the gap between coil outer and can inner is around 5 mm. · Pressure bar depth plays a major role in case of carded mixing and OE mixings. If it is open, U% will be affected very badly.It should always be combined with front roller setting. If the pressure bar depth is high,Creel height should be fixed as low as possible (esepcially for combed material). · Top roller condition should be checked properly. While processing 100% polyester fibres, fibre scum should be removed by a wet cloth from the top roller atleast once in a shift. · Sliver funnel size should be selected properly. Very wide funnel will affect the U%. But very small funnel will end up in more sliver breaks at the front. · If the department humidity variation is very big, then corresponding correction to be made for checking the wrapping of sliver ( sliver weight). Otherwise, there will be unwanted changes in the drawframe which will affect the count C.V.% of yarn. · Most of the Autoleveller drawframes are working on the principle of OPEN LOOP control system. Sliver monitor should be set properly. Whenever there is a problem in sliver weight, this will stop the machine. Sometimes sliver monitor may malfunction. If it is found malfunctioning , it should be calibrated immediately. AUTOLEVELLING: · Most of the modern autolevllers are open loop autolevellers. This system is effective on short, medium and to some extent long tem variations. · Mechanical draft should be selected properly in autoleveller drawframes. To decide about the mechanical draft, drawframe should be run with autoleveller switched off.If the sliver weight is correct, then the mechanical draft selected is correct. Otherwise, the gears should be changed so that the sliver is weight is as per the requirement without autolevller. · Intensity of levelling and timing of correction are two important parameters in autolevellers. · Intensity of levelling indicates the amount of correction. i.e If 12% variation is fed to the drawframe the draft should vary 12% , so that the sliver weight is constant. · Timing of correction indicates that if a thick place is sensed at scanning roller, the correction should take place exactly when this thick place reaches the correction point(levelling point) · Higher the feed variation, higher the correction length. e.g. if feed variation is 1 %, and if the correction length is 8 mm, if feed variation is 5% the correction length will be between 10 to 40 mm depending upon the speed and type of the autoleveller. · Higher the speed, higher the correction length · Whenever the back roller setting, guide rails setting, delivery speed,break draft etc are changed, the timing of correction should also be changed. · U% of sliver will be high, if timing of correction is set wrongly · If intensity of levelling selected is wrong , then 1 meter C.V % of sliver will be high. · Most of the modern autolevellers can correct 25% feed variation. It is a general practice to feed 12% varition both in plus and minus side to check A%. This is called as Sliver test. The A% should not be more than 0.75%. A% is calculated as follows If no of sliver fed to drawframe is N, Check the output sliver weight with “N”, “N+1″, “N-1″ slivers. then A% = ((gms/mt(N-1) – gms/mt(N))/ gms/mt(N) ) x 100 A% = ((gms/mt(N+1) – gms/mt(N))/ gms/mt(N)) x 100 · Life of servo motor and servo amplifier will be good, if 1. it is used for carded material 2. feed variation is less 3. motor is checked for carbon brush damages, bearing damages etc periodically 4. if the delivery speed is less PROCESS PARAMETERS IN SPEED FRAME INTRODUCTIONRoving machine is complicated, liable to faults, causes defects, adds to production costs and deliversa product that is sensitive in both winding and unwinding.The following parameters are very important in SPEED FRAME. They are· Feed hank · Delivery hank · Roving tension · break draft · Drafting system · Bottom roller setting · Top roller setting · condensers and spacers · Twist in the roving · Bobbin content · flyer speed · Creel and creel draft · Drawframe sliverand can · Bobbin height · Breakage rate · Piecings DRAFTING SYSTEM· Since modern Ringframes are capable of handling higher drafts in ringframe without quality detriorationIt is better to have coarser hanks in the speed frame. This helps to increase the prodction in speed frame.Investment cost will also be less,because the number of speedframes required will be less and the cost per mchineis also high. The following table can be a guidle line for speed frame delivery hank · MATERIAL YARN COUNT HANK TOTAL DRAFT COTTON combed 36s to 40s 1.2 10 Cotton combed 24s to 30s 1.0 10 Cotton combed 14s to 24s 0.7 to 0.8 9 Cotton karded 36s to 40s 1.3 9 Cotton karded 24s to 36s 1.1 8 Poly/cotton 36s to 45s 1.2 11 Poly/cotton 24s to 36s 1.0 10 Poly/viscose 36s to 40s 1.0 11 Poly/viscose 24s to 36s 0.85 10 Poly/viscose 16s to 20s 0.7 8 The above said details are for producing a good quality yarn. This is suitable for 4 over 4 drafting system with front zone as a condensing zone without a draft. · With 4 over 4 drafting system, the toal draft can be upto 13, whereas in the case of 3 over 3 drafting system , the draft can not be more than 11. · The Roving thickness and Roving hairiness(yarn hairiness) will be less with 4 over 4 drafting system compared to 3 over 3 drafting system. · In 4 over 4 drafting system, since the fully drafted material is just condensed in the front zone, if the stikiness in case of cotton or static in case of synthetic is high, then the lapping tendency will be very high on second top roller or second bottom roller. But in case of front roller, since the twist is penetrating upto the nip, lapping on the front bottom or top roller will be less. · As long as stickiness, honey dew in cotton and static in synthetic fibres is less, 4 over 4 drafting system with front zone as condensing zone, will give better results upto even 51 mm fibre.Of course the humidity conditions should be good. · 4 over 4 drafting system can be described as follows 1. bottom roller diameter is 28.5 mm 2. Top roller diameter is 28 mm 3. Break draft is between 4th roller and 3rd roller 4. Main draft is between 3rd roller and 2nd roller 5. Bottom apron is run by a 3 rd roller 6. between front roller and 2nd roller is a condesning zone 7. front zone setting 35 mm( even for 51 mm fibre) 8. Main draft zone setting is 48 mm 9. Back zone setting depends on break draft, but it is normally 5o mm for cotton and T/c and 55 mm for synthetic fibres(44 to 51mm) · 3 over 3 drafting system is good for fibres longer than 51 mm. 30 or 32 mm bottom roller diameters will be used with this system. · Feed hank depends upon the total draft in speed frame. The drafts mentioned in the above table can be consdiered as a guide line. · While processing 51 mm synthetic fibres, if the delivery hank is coarser,and the delivery speed is verh high, the break draft and the back zone setting to be widened. Break draft and break draft setting does not depend only on T.M and fibre properties, it depends on the total production also. If the total production is very high, with low break draft and closer setting, roving breaks due to undrafted strand will increase. · Therefore, for very high production rate , higher break draft and wider break draft setting is required. This will result in very high “H” and “I” classimat faults(long thin faults). Therefore the breakage rate in spinning will increase. · Break draft setting and break draft should be nominal. Abnormal break drafts and wider break draft settings indicate that there is a major problem in the process. · Some times draw frame coiling is a very big problem with synthetic fibres . If kinks are formed in the sliver, the kink has to be removed before entering the draft zone. · Kinks in the drawframe sliver depends upon 1. drawframe delivery speed 2. delivery can diameter 3. coiler type · Higher the delivery speed, more the chances for kinks to be formed in the sliver. Lower the can diameter more the kinks. If a coiler which is meant for cotton is used, the kinks in the sliver will increase in case of synthetic fibres. · While processing synthetic fibres if kinks are more, it would be better if the creel is stopped. Sometimes it would be recommeded to use a rod between top arm and the first creel roll, so that the sliver takes a 90 degree bend before entering the top arm. This will help to remove the the kinks in the sliver. Otherwise, slubs in the roving will be more and the breakage rate in speed frame due to undrafted strand in the drafting zone will be more. PROCESS PARAMETERS IN SPEED FRAME – 2 Page 1 2 · ROVING TENSION · The roving tension depends on the delivery rate and the difference between peripheral speeds of flyer and the bobbin. · If the delivery length and the peripheral speed difference are same, then the tension is ideal.If delivered length is more than the difference in peripheral speed , then the roving tension will be loose. If the delivered length by the front bottom roller is less than the difference in pheripheral speeds of flyer and the bobbin, the roving tension will be tight. · Roving tension can be of three types 1. Roving tension at the starting. It depends upon the Bare bobbin diamter and the Cone drum belt position 2. Roving tension during build-up. It depends upon the Ratchet wheel and lifter wheel. The difference between peripheral speeds of flyer and bobbin should be same and it should be slightly more than the length delivered by the front roller. 3. Roving tension during up and down movement of the bobbin rail should be same. It depends upon the half tooth movement of the ratchet. If it is not exactly half tooth, then the tension will be different during up and down movement of the bobbin rail 4. With modern machines, cone drum is removed. Bobbin speed, bobbin rail speed and flyer speed is determined by the computer depending upon the tension settings.In some machines, it can be programmed and the tension sensor helps to control a bit.In some makes, the tension setting totally depends upon the sensing by sensors. The sensing accuracy depends upon the twist cap type, twist cape fixing, oil on top of twist cap etc. If only one roving tension is different due to various other reasons, then the entire machine tension will be altered. This is very dangerous. Enough care should be taken to avoid this problem. 5. If lifter wheel is changed, then tension during build up will also change, the ratchet has to be selected accordingly. For a particular roving hank, ratchet wheel depends on Lifter wheel also. 6. If the tension is low but unfiorm through out the bobbin, then the bobbin will be soft. Bobbin content will also be less. Chances of roving damages will be high. 7. If the roving tension is more, then the stretch on the roving will be more, thin places will be more. But it is better to increase the TPI little bit and increase the roving tension so that the bobbin content is more, roving damages are less, and creel stretch in the ring frame will also be less, because of higher TPI in the roving. OTHERS · It is better to adopt group creeling in speed frame. Because every piecing of sliver will result in a thin and thick place. Therefore it is preferable to change 30 upto 60 cans together and remove the sliver piecing from the roving. · Care should be taken so that no sliver piecing and roving piecing enters the ringframe and results in yarn. This yarn always results in thin and thick places from .6 to 2 meters length. This will not be cut by the yarn clearers if the difference in size is less. · Roving Breaks in speed frame should not be more 1 to 2 per 100 spindle hours.If it is more than that, the reasons should be analysed and corrective action should be taken immediately. · Spacers should be as small as possible, to improve yarn quality. If slubs and roving breaks due to undrafted is more, it would be better to use a bigger spacer(distance clip) instead of increasing the break draft and break draft zone setting to an abnormal level. · It is better to use good quality apron and rubber cots , since the quantity produced by one apron and top roller is very high compared to ringframe. If the apron breaks and top roller damages are under control, It is always better to use the best apron and rubber cots available in the market. One should not think about cost saving in this machine. Cost saving for apron and cots can be considered for ringframes. · Buffing should be done once in 3 months and the top roller shore hardness is around 80 to 85 degrees. After buffing, it is better to treat with acid or some special liquids which are being supplied to reduce lapping · Bottom and top clearers should rotate and should touch the top and bottom roller properly. · While processing cotton combed material, flyer speed is very critical. When the bobbin diamter is big, because of the centrifugal tension, surfact cuts will increase. i.e. roving breaks may occur at presser or in strand that have just been wound on the top surface of the package. To avoid this problem, it is better to use inverter drive system, to reduce the flyer speed, when the bobbin diameter is big. Otherwise the overall speed should be less for the entire doff, this will reduce the production of speedframe. Sometimes, higher Twist will also reduce the surface cuts. ROCESS PARAMETER IN SPINNING INTRODUCTION: Ringframe Technology is a simple and old technology, but the production and quality requirements at the present scenario puts in a lot of pressure on the Technologist to select the optimum process parameters and machine parameters, so that a good quality yarn can be produced at a lower manufacturing cost. Following are the points to be considered in a ringframe. · Draft distribution and settings · Ring and travellers · spindle speed · Twist · lift of the machine · creel type · feed material · length of the machine · type of drive, above all · Raw material chracteristic plays a major role in selecting the above said process parameters Technical information and guidelines are given below based on the learnings from personal experience and discussions with Technologists. This could be used as a guideline and can be implemented based on the trials taken at site. Some of this information can be disproved in some other applications, because many of the parameters are affected by so many variables. A same machine or rawmaterial cannot perform in the same way in two different factories. This is because of the fact that no two factories can be identical. DRAFTING: The break draft should depend upon the following, · fibre type · fibre length · roving T.M · main draft Some examples are given below, Normally 1.13 to 1.18 break draft is used for · 100%cotton , Poly/cotton blend, 100% synthetic · roving T.M. upto 1.3 for cotton and .80 for Poly/cotton blend, 0.5 to0.7 for synthetic · ring frame back zone setting of 60mm for fibres upto 44mm and 70mm for fibres upto 51mm · total draft in ringframe upto 35 1.24 to 1.4 break draft is used for · 100%cottton, poly/cotton blend, 100%synthetic fibre · strongly twisted roving i.e higher than the above mentioned T.M.s · total draft from 33 to 45 · back zone setting(R.F) around 52mm for fibres upto 44mm and 60mm for fibres upto 51mm- If the total draft is more than 45 or the fibre length is more than 51 and the fibre is a fine fibre(i.e more number of fibres in the cross section)with a very high interfibre friction, break draft more than 1.4 is used. Please note that for most of the application, lower break draft with wider setting is used. With higher break drafts, roller setting becomes very critical. Higher the break draft, higher the chances for thin places i.e. H1 classimat faults. Higher draft with improper back zone setting will lead to thin places and hence more end breaks even though more twist flows into the thin yarn. MAIN DRAFT ZONE: Mostly for cotton fibres, short cradles are used in the top arm. Front zone setting is around 42.5 mm to 44 mm depending upon the type of drafting system. The distance between the front top roller and top apron should be around 0.5to 0.7mm when correct size top roller is used. This is normally taken care of by the machinery manufcturer. If a technician changes this setting, this will surely result in more imperfections, especially with karded count the impact will be more. Therefore when processing cotton fibres, care should be taken that the front zone setting should be according to the machinery manufacturers recommendation. For synthetic fibres upto 44 mm , it is better to use short cradles. Even with 42.5 mm bottom roller setting, 44 mm fibre works well without any problem. Because, the clamping distance will be around 52 mm or 50 mm. The imperfections and U% achieved with short cradle is better than with medium cradle(52mm setting). Instead of using medium cradle for processing 44mm synthetic fibre, it is always better to use short cradle with 1 or 2mm wider setting than the recommended to avoid bottom apron damages. If a mill has got a problem of bottom roller lapping, the apron damages are extremely high, it is better to use short cradle for 44 mm fibre and widen the setting by 1 or 2mm. This will minimise the complaints and improve the basic yarn quality also. Please note that if the bottom apron breakages are high, then the mill is working with a lot of bottom apron which is defective and with a lot of top roller which is defective. Both the defective parts produces a defective yarn, which can not rejected by older version of yarn clearers, and improperly set new type of clearers. This yarn will very badly affect the fabric appearance. Therefore it is always advisable to use a wider front zone setting upto 2mm , if the mill faces a problem of excessive bottom roller lappings. Please note that the defective bottom apron and top roll will not only affect the quality, but also the production, because the defective bottom apron and top roll make the spindle a sick spindle which will be prone to end breaks. A wider front zone setting will increase the imperfection and uster, but there will not be major deviations of yarn quality. Nose bar height setting is very important. Depending upon the design, it is 0.7mm or .9 mm. Variation in heigh setting will affect the yarn quality and the apron movement. The distance between nose bar and middle bottom roller should be less than apron thick ness or more than 3 mm to avoid apron buckling if there is any diturbance in apron movement. PROCESS PARAMETER IN SPINNING – 2 Page 1 2 · RING AND TRAVELLER: · Ring diameter, flange width and ring profile depends upon the fibre, twist per inch, lift of the machine,maximum spindle speed, winding capacity etc. · Operating speed of the traveller has a maximum limit, because the heat generated between ring and traveller should be dissipated by the low mass of the traveller with in a short time available. · If the cotton combed yarn is for knitting, traveller speed will not be a limiting factor. Since yarn TPI is less, the yarn strand is not strong enough. Therefore the limiting factor will be yarn tension. · Following points to be considered 1. for 12s to 24s , 42mm ring with 180 mm lift can be used 2. for 24s to 36s, 40 mm ring with 180 lift can be used 3. for 36s to 60s , 38 mm ring with 170 mm lift can be used 4. for 70s to 120s, 36 mmring with 160 mm lift can be used. 5. If winding is a problem, it is better to go for reduced production with bigger ring dia. 6. Anti-wedge ring profile is better, because of better heat dissipation 7. Elliptical traveller should be used, to avoid start-up breaks in hosiery counts 8. special type of travller clearer can be used to avoid accumulation of fibre on the traveller as traveller with waste does not perform well during start-up. · For polyester/cotton blends and cotton weaving counts yarn strength is not a problem. The limiting factor will be a traveller speed. For a ring diameter of 40 mm, spindle speed upto 19500 should not be a problem. Rings like Titan(from Braecker), NCN(bergosesia) etc, will be able to meet the requirements. · For spindle speeds more than 20000 rpm, ORBIT rings or SU-RINGS should be used. As the area of contact is more with this rings, with higher speeds and pressure, the heat produced can be dissipated without any problem. Normal ring and traveller profile will not be able to run at speeds higher than 20000 to produce a good quality yarn. · ORBIT rings will be of great help, to work 100% polyester at higher spindle speeds. Because, of the tension, the heat produced between ring and traveller is extremely high. But one should understand, that ,the yarn strength of polyester is very high. Here the limiting factor is only the heat dissipation. Therefore ORBIT RINGS with high area of contact will be able to run well at higher spindle speeds when processing 100% polyester. · While running 100% cotton, the fibre dust in cotton, acts like a lubricant. All the cottons do not form same amount of lubricating film. If there is no fibre lubrication, traveller wears out very fast. Because of this worn out or burn out travellers, microwelding occurs on the ring surface,< which results in damaged ring surface, hence imperfections and hairiness increases in the yarn. · Lubrication is good with west african cottons. It may not be true with all the cottons from West africa. In general there is a feeling, cottons from Russia, or from very dry places, lubrication is very bad. If the fibre lubrication is very bad, it is better to use lighter travellers and change the travellers as early as possible. · Traveller life depends upon the type of raw material, humidity conditions, ringframe speeds, the yarn count, etc. If the climate is dry , fibre lubrication will be less while processing cotton. · Traveller life is very less when Viscose rayon is processed especially semi dull fibre, because of low lubrication. Traveller life is better for optical bright fibres. · Traveller life is better for Poly/cotton blends, because of better lubricatiion between ring and traveller. · Because of the centrifugal force excerted by the traveller on the yarn, the particles from the fibre fall on the ring where the traveller is in contact. These particles act like a lubricating film between ring and traveller. RUBBER COTS AND APRON: · For processing combed cotton, soft cots (60 to 65 degree shorehardness) will result in lower U%, thin and thick places. · There are different types of cores (inner fixing part of a rubber cot)available from different manaufacturers. Aluminimum core,PVC core,etc. It is always better to use softer cots with aluminium core. · When softer cots are used, buffing frequency should be reduced to 45 to 90 days depending upon the quality of the rubber cots, if the mill is aiming at very high consistent quality in cotton counts. · If the lapping tendency is very high when processing synthetic fibres for non critical end uses, It is better to use 90 degree shore harness cots, to avoid cots damages. This will improve the working and the yarn quality compared to working with 83 degree shore hardness. · If rubber cots damages are more due to lapping, frequent buffings as high as once in 30 days will be of great help to improve the working and quality. Of course,one should try to work the ringframe without lapping. The basic reasons for lapping in the case of processing synthetic fibre is · End breaks · Pneumafil suction · rubber cots type · fibre fineness · Oil content(electrostatic charges) · department temprature and humidity · Almost all the lappings orginate after an end break. If a mill has an abnormally high lapping problem the first thing to do is to control the end breaks, 1. after doffing 2. during speed change 3. during the maximum speed by optimising the process paramters. · It is obvious that fine fibres will have a stronger tendency to follow the profile of the roller. Therefore lapping tendency will be more. · If the fibre is fine, the number of fibres in the cross section will be more, therefore lapping frequency will be more. · If the pressure applied on the roller is more, then lapping tendancy will be more. Hence fine and longer fibres will have more tendency for lapping because of high top roller pressure required to overcome the drafting resistance. · If the pneumafil suction is less, the lapping tendency will be more both on top and bottom roller. But the pneumafil suction depends on the fan diamater, fan type, fan speed, duct design, length of the machine, profile of the suction tube etc. If any one of the above can be modified and the suction can be improved, it is better to do that to reduce the lapping. · The closer the setting between the suction nozzle and the bottom roller, the higher the suction efficiency and lower the lapping propensity. · Higher roving twist will reduce the lapping tendency to some extent. Therefore it is better to have a slightly higher roving twist, provided there is no problem in ringframe drafting, when the lapping tendency is more · With Softer rubber cots lapping tendency will be more due to more surface contact. · The most minute pores, pinholes in the rubber cots or impurities in the cots can cause lapping. Therefore the quality of buffing and the cots treatment after buffing is very important. Acid treatment is good for synthetic fibres and Berkolising is good for cotton. · Electrostatic charges are troublesome especially where relatively large amount of fibre are being processed in a loose state e.g drawframe, card etc.Lapping tendency on the top roll increases with increasing relative humidity. The frequently held opinion is that processing performace remains stable at a steady absolute relative humidity, i.e. at a constant moisture content per Kg of dry air. TWIST: The strength of a thread twisted from staple fibres increases with increasing twist, upto certain level. Once it reaches the maximum strength, further increase in twist results in reduction in yarn strength · Coarser and shorter fibres require more Twist per unit length than finer and longer fibres. · Twist multiplier is a unit which helps to decide the twist per unit length for different counts from the same raw material.This is nothing but the angle of inclination of the helical disposition of the fibre in the yarn. This is normally expressed as TWIST PER INCH = TWIST MULTIPLIER * SQRT(Ne) · If the two yarns are to have the same strength, then the inclination angles must be the same. · For 40s combed knitting application, if the average micronaire of cotton is 3.8 and the 2.5% span length is around 29 mm, Twist multiplier of 3.4 to 3.5 is enough . If the average micronaire is around 4.3, it should be around 3.6 to have better working in Ring frame. · cotton combed knitting T.M. = 3.4 to 3.6 · cotton combed weaving T.M. = 3.7 to 3.8 · cotton carded knitting T.M. = 3.8 to 4.0 · cotton carded weaving T.M. = 3.9 to 4.2 The above details are for cottons of 2.5% span length of 27 to 30 mm and the average Micronaire of 3.7 to 4.4. For finer and longer staple, the T.M. will be lower than tha above. In general for processing poly/viscose , the T.M. is as follows · 51 mm, 1.4 denier fibre : T.M. = 2.7 to 2.9 for knitting application · 51 mm, 1.4 denier fibre : T.M. = 2.9 to 3.1 for weaving application · 44 mm, 1.2 denier fibre : T.M. = 2.9 to 3.0 for knitting application · 44 mm, 1.4 denier fibre : T.M. = 3.0 to 3.1 for knitting application · 38 mm, 1.2 denier fibre : T.M. = 3.1 to 3.3 for knitting application The above detail is self explanatory OTHERS: The following ROVING parameters will affect the ring frame process parameters · Roving T.M. · Bobbin weight · Bobbin height · Higher the roving T.M., wider the back bottom roller setting or higher the break draft in ring frame. · For combed material the creel height should be as low as possible in ringframe. · Very long creel heights in ringframe, lower roving T.M. and heavier roving package will result in many long thin places in the yarn.(especially in combed hosiery counts) · In general 16 x 6 ” bobbins are used. This helps to increase the spare rovings per machine with higher creel running time. Therefore one should aim at increasing the bobbin weight as well as increasing the number of spare rovings in the ring frame. · Normally 6 row creels are used in modern ring frames. Six row creels will accomodate more spare rovings compared to 5 row creels.(around 150 rovings for 1000 spindle machine.) Creel height should be as low as possible for cotton combed counts.Spare rovings will improve the operators efficiency. · Shorter machines are always better compared to longer machines. But the cost per spindle will go up. For cotton , polyester/cotton blends, poly/viscose(upto 44mm length), number of spindles upto 1200, should not be a problem. But maintenance is more critical compared to shorter machines. · For synthetic fibres with very high drafting resistance, it is better to use shorter machines, because the load on break draft gears and on second bottom rollers will be extremely high. If long machines are used and the maintenance is not good for such application, the bearing damages, gear damages, bottom roller damages etc. will increase. This will result in coarse counts, higher count C.V., long thinand thick places. · Four spindle drive is always better compared to Tangential belt drive. Because small variation in machining accuracy of bolster , spindle beam etc will affect the spindle speeds, thereby the twist per inch. Waste accumulation between contact rollers, bent contact rollers, damaged contact rollers, oil spilling from any one spindle etc. will affect the spindle speeds and thereby TPI. The spindle speed variation between spindles in a 5 year old ringframe will be verh high incase of tangential belt drive compared to 4 spindle drive. · Noise level and energy consumption will be low in 4 spindle drive compared to Tangential belt drive. · Compared to Contact rollers, Jockey pully damages are nil. I have worked with 20 year old ring frames with Jocky pulleys,but the variations in spindle speed between spindles is very less compared to a 5 year old ringframe with Tangential belt drive. I have made this comment based on my personal experience. · When processing coarse counts at higher speeds, the air current below the machine is a big problem with 4 spindle drive . This is due to the more running parts like tinrollers and jockey pullys. This will lead to more fluff in the yarn, if humidification system is not good enough to suck the floating fluff. · If spindle speeds is high for cotton counts, every end breaks will result in more fluff in the department due to the free end of the yarn getting cut by the traveller when the distance between traveller and the bobbin with the yarn is less. Higher the delay in attending the end break , higher the fly liberation.If the number of openings of return air system for a ringframe is less and the exhaust air volume is not sufficient enough, then fly liberation from an end break will increase the endbreaks and thereby will lead to multiple breaks. End break due to a fly entering the traveller will get struck with the traveller and will result in heavier traveller weight and that particular spindle will continue to work bad. · Multiple breaks are very dangerous, as it will result in big variation in yarn hairiness and the ringframe working will be very badly affected due to heavier travellers because of the fluff in the traveller. · Dry atmosphere in ringframe department will result in more yarn hairiness, more fly liberation and more end breaks. · It is a good practice to change spindle tapes once in 24 months.Worn out spindle tapes will result in tpi variations which is determinetal to yarn quality. CONSTANTS AND CALCULATIONS FIBRE FINENESS, YARN COUNTS AND CONVERSIONS: Micronaire value(cotton) : The unit is micrograms per inch. The average weight of one inch length of fibre, expressed in micrograms(0.000001 gram). Denier(man-made fibres): Weight in grams per 9000 meters of fibre. Micron:(wool): Fineness is expressed as fibre diameter in microns(0.001mm) Conversions: · Denier = 0.354 x Micronaire value · Micronaire value = 2.824 x Denier YARN COUNTS: It is broadly classified into 1. DIRECT and 2.INDIRECT system. DIRECT SYSTEM: · English count (Ne) · French count(Nf) · Metric count(Nm) · Worsted count · Metric system: Metric count(Nm) indicates the number of 1 kilometer(1000 meter) lengths per Kg. Nm = length in Km / weight in kg (or) Nm = length meter / weight in grams INDIRECT SYSTEM: · Tex count · Denier CONVERSION TABLE FOR YARN COUNTS: tex Ne den Nm grains/yd tex den/9 1000/Nm gr.yd x 70.86 Ne 590.54/tex 5314.9/den Nm x .5905 8.33 / gr/yd den tex x 9 9000/Nm gr/yd x 637.7 Nm 1000/tex 9000/den 14.1 / gr/yd grains/yd tex / 70.86 den / 637.7 14.1/Nm Where, Nm – metric count, Nec – cottoncount CONVERSION TABLE FOR WEIGHTS: ounce grains grams kilograms pounds ounce 437.5 grains 28.350 grams grains 0.03527 ounces 0.0648 grams grams 0.03527 grains 15.432 grains 0.001 kgs kilograms 35.274 ounces 15432 grains 1000 grams 2.2046 pounds pounds 16.0 ounces 7000 grains 453.59 grams 0.4536 kgs CONVERSION TABLE FOR LINEAR MEASURES: yard feet inches centimeter meter yard 3 feet 36 inches 91.44 cms 0.9144 meter feet 0.3333 yards 12 inches 30.48 cms 0.3048 meter inches 0.0278 yards 0.0833 feet 2.54 cms 0.254 meter centimeter 0.0109 yards 0.0328 feet 0.3937 inches 0.01meter meter 1.0936 yards 3.281 feet 39.37 inches 100 cms CALCULATIONS: · grams per meter = 0.5905 / Ne · grams per yard = 0.54 / Ne · tex = den x .11 = 1000/Nm = Mic/25.4 · Ne = Nm/1.693 · DRAFT = (feed weight in g/m) / (delivery weight in g/m) · DRAFT = Tex (feed) / Tex(delivery) · DRAFT = delivery roll surface speed / feed roll surface speed · No of hanks delivered by m/c = (Length delivered in m/min) / 1.605 · CARDING: (1). P =( L x 1.0936 x 60 x effy ) / (hank (Ne) x 36 x 840 x 2.2045) P – production in kgs / hr L – delivery speed in m/min effy- efficiency Ne – English count ( number of 840 yards in one pound) 840 – constant 2.2045- to convert from lbs to kilograms (2).production in kgs / hr = (L x Ktex x 60 x effy) / ( 1000) L – delivery speed in m/min Ktex- sliver count in Ktex (kilotex) effy – efficiency 1000- to convert to kilograms from grams (3). production in kgs / 8 hrs = (0.2836 x L x effy) / (Ne) L – delivery speed in m/min effy – efficiency Ne – English count (4).prodn / 8 hrs = (Hank x Nd) /( Ne x 2.2045) Hank = no of hank (840 yards)delivered by the machine Nd = no of deliveries Ne = hank of the material (4).Total draft in card = (feed weight in g/m) / (sliver weight in g/m) DRAWFRAME: (1.)Break draft = surface speed of 2nd roller / surface speed of back roller (2).Main draft = surface speed of 1st roller / surface speed of 2nd( middle) roller (3).Total draft = surface speed of delivery roller / surface of feed roller (4).production in kgs / 8 hrs = (0.2836 x L x effy x Nd) / (Ne) L – delivery speed in m/min effy – efficiency Ne – english count Nd – No of delvieries (5.).prodn in kgs / hr = (FRD x FRrpm x 3.14 x 60 x effy x Nd) / (Ne x 840 x 36 x 2.2045) FRD – front roller dia in inches FRrpm – front roller rpm effy – efficiency Ne – Sliver hank Nd – number of deliveries SPEEDFRAME + RINGFRAME (1).Twist / Inch (TPI) = Spindle speed / FRS FRS – front roller surface speed in inches/min (2).FRS = FRrpm x 3.14 x FRD FRS – Front roller surface speed FRD – front roller diameter (3).T.P.I = T.M. x sqrt(count or hank) T.M. – Twist multiplier sqrt – square root (4).prodn in kgs / 8 hrs = (7.2 x SS x effy) / (TPI x Ne x 1000) SS – spindle speed (5).Spindle speed = m/min x TPI x 39.37 (6).hank delivered = spindle speed / ( tpi x 62.89) (7).Ring traveller speed in m/sec =( spindle speed x ring dia in mm x 3.14) / (60 x 1000) WINDING: (1). production in kgs / 8 hrs = (0.2836 x L x effy x Nd) / (Ne) L – delivery speed in m/min effy – efficiency Ne – english count Nd – No of delvieries (2). P =( L x 1.0936 x 60 x effy ) / (hank (Ne) x 36 x 840 x 2.2045) P – production in kgs / hr L – delivery speed in m/min effy- efficiency Ne – English count ( number of 840 yards in one pound) 840 – constant 2.2045- to convert from lbs to kilograms DETERMINATION OF THE TECHNOLOGICAL VALUE OF COTTON FIBRE: A COMPARATIVE STUDY OF THE TRADITIONAL AND MULTIPLE-CRITERIA DECISION-MAKING APPROACHES Abhijit Majumdar1, Prabal Kumar Majumdar2 & Bijan Sarkar3 1College of Textile Technology, Berhampore 742 101, India Email: abhitextile@rediffmail.com 2College of Textile Technology, Serampore 712 201, India Email: pkm5@rediffmail.com 3Department of Production Engineering, Jadavpur University Kolkata 700 032, India Email: bijonsarkar@email.com Abstract This paper presents a comparative study of the methods used to determine the technological value or overall quality of cotton fibre. Three existing methods, namely the fibre quality index (FQI), the spinning consistency index (SCI) and the premium-discount index (PDI) have been considered, and a new method has been proposed based on a multiple-criteria decision-making (MCDM) technique. The efficacy of these methods was determined by conducting a rank correlation analysis between the technological values of cotton and yarn strength. It was found that the rank correlation differs widely for the three existing methods. The proposed method of MCDM (multiplicative AHP) could enhance the correlation between the technological value of cotton and yarn strength. Key words: analytic hierarchy process, cotton fibre, fibre quality index, premium-discount index, spinning consistency index, technological value Introduction Determining the technological value of cotton fibre is an interesting field of textile research. The quality of final yarn is largely influenced (up to 80%) by the characteristics of raw cotton [1]. However, the level to which various fibre properties influence yarn quality is diverse, and also changes depending on the yarn manufacturing technology. Besides, a cotton may have conflicting standards in terms of different quality criteria. Therefore, the ranking or grading of cotton fibres in terms of different quality criteria will certainly not be the same. This will make the situation more complex, and applying multiple-criteria decision-making (MCDM) methods can probably deliver a plausible solution. The solution must produce an index of technological value or overall quality of cotton fibre, and the index should incorporate all the important fibre parameters. The weights of the fibre parameters should be commensurate with their importance on the final yarn quality. Traditionally, three fibre parameters have been used to determine the quality value of cotton fibre. These are grade, fibre length and fibre fineness. The development of fibre testing instruments such as the High Volume Instrument (HVI) and the Advanced Fibre Information System (AFIS) has revolutionised the concept of fibre testing. With the HVI it is pragmatically possible to determine most of the quality characteristics of a cotton bale within two minutes. Based on the HVI results, composite indexes such as the fibre quality index (FQI) and spinning consistency index (SCI) can be used to determine the technological value of cotton; this can play a pivotal role in an engineered fibre selection programme [2-3]. In this paper, a new method of determining the technological value of cotton using a multiplicative analytic hierarchy process (multiplicative AHP) of the MCDM method is postulated. The technological value of cotton was also determined by the three traditional methods, namely the fibre quality index (FQI), the spinning consistency index (SCI) and the premium-discount index (PDI). The ranking of cotton fibres produced by these four methods was compared with the ranking of final yarn tenacity, and a rank correlation analysis was carried out. Overview of MCDM and AHP Multiple Criteria Decision Making is a well-known branch of Operations Research (OR), which deals with decision problems involving a number of decision criteria and a finite number of alternatives. Various MCDM techniques, such as the weighted sum model (WSM), the weighted product model (WPM), the analytic hierarchy process (AHP), the revised AHP, the technique for order preference by similarity to an ideal solution (TOPSIS), and elimination and choice translating reality (ELECTRE), can be used in engineering decision-making problems, depending upon the complexity of the situation [4- 8] The Analytic Hierarchy Process (AHP), introduced by Saaty [9-12], is one of the most frequently discussed methods of MCDM. Although some researchers [13-16] have raised concerns over the theoretical basis of AHP, it has proven to be an extremely useful decision-making method. The reason for AHP’s popularity lies in the fact that it can handle the objective as well as subjective factors, and the criteria weights and alternative scores are elicited through the formation of a pair-wise comparison matrix, which is the heart of the AHP. Details of AHP methodology Step 1: Develop the hierarchical structure of the problem. The overall objective or goal of the problem is positioned at the top of the hierarchy, and the decision alternatives are placed at the bottom. Between the top and bottom levels are found the relevant attributes of the decision problem such as criteria and sub-criteria. The number of levels in the hierarchy depends on the complexity of the problem. Step 2: Generate relational data for comparing the alternatives. This requires the decision maker to formulate pair-wise comparison matrices of elements at each level in the hierarchy relative to each activity at the next, higher level. In AHP, if a problem involves M alternatives and N criteria, then the decision maker has to construct N judgment matrices of alternatives of M x M order and one judgment matrix of criteria of N x N order. Finally, the decision matrix of M x N order is formed by using the relative scores of the alternatives with respect to each criterion. In AHP, the relational scale of real numbers from 1 to 9 and their reciprocals are used to assign preferences in a systematic manner. When comparing two criteria (or alternatives) with respect to an attribute in a higher level, the relational scale proposed by Saaty [9-12] is used. The scale is shown in Table 1. Table 1. The fundamental relational scale for pair-wise comparisons DETERMINATION OF THE TECHNOLOGICAL VALUE OF COTTON FIBRE: 2 Page 1 2 3 Material and Methods Data collection and analysis Each year the International Textile Centre (USA) conducts a crop study for different varieties of cotton. The results of the crop study of 1997 and 1998, which includes 33 sets of fibre and yarn data for two different yarn counts (22 Ne and 30 Ne), were used in our investigation. We ranked the 33 cotton fibres according to their FQI, SCI, PDI and multiplicative AHP (MIAHP) values. We also ranked the 33 cottons according to the final yarn tenacity. Separate rankings were obtained for 22 Ne and 30 Ne. The difference between the two rankings (fibre quality ranking and yarn tenacity ranking) was calculated to measure the rank correlation coefficient between them by using the following equation. where Rs is the rank correlation, d is the absolute difference between the two rankings, and M is the total number of alternatives (33). The summary statistics of fibre properties are given in Table 3. Table 3. Summary statistics of cotton fibre properties Hierarchy formulation for multiplicative AHP The goal or objective of the present investigation is to determine the technological value of cotton, which should reflect the achievable level of yarn quality (yarn strength). In general, the cotton fibre criteria of this problem can be classified under three headings, namely tensile properties, length properties and fineness properties. Tensile properties can be divided into two sub-criteria, fibre bundle tenacity (FS) and elongation (FE). Similarly, UHML, UI and SFC are the relevant sub-criteria of length properties to be considered here. Fineness is solely represented by the micronaire (FF) value of cotton. At the lowest level of the hierarchy, there are 33 cotton fibre alternatives, which should be ranked according to their technological value. The schematic representation of the problem is depicted in Figure 1. Therefore, according to the multiplicative AHP model, the equation to calculate the technological value of cotton (MIAHP) is as follows: Determination of criteria weights With respect to the overall objective problem, the pair-wise comparison matrix of three criteria is given in Table 4. Here the comparisons are made according to Saaty’s scale given in Table 1. Table 4. Pair-wise comparison matrix of criteria with respect to objective It can be inferred from Table 4 that tensile properties moderately predominate over the fineness properties. However, the length properties demonstrate a strong preponderance over the fineness properties. The dominance of length properties over the tensile properties is between equal to moderate. The normalised GM column of Table 4 indicates that the length properties of cotton fibres have the most dominant influence with a relative weight of 0.581. The relative weights of tensile and fineness properties are 0.309 and 0.110 respectively. For the measurement of consistency of judgment, the original matrix is multiplied by the weight vector to obtain the product as shown below: The next step is concerned with finding the relative weights of various sub-criteria (Level 3) with respect to the corresponding criteria (Level 2). The pair-wise comparison between the sub-criteria of tensile and length properties and the derived weight vectors are shown in Tables 5 and 6 respectively. Then the global weights of sub-criteria are calculated by multiplying the relative weight of a sub-criterion with respect to the corresponding criterion and the relative weight of that criterion with respect to the objective. For example, the global weight of tenacity is 0.875 x 0.309 = 0.270. For tenacity, elongation, UHML, UI, SFC and FF, the values of global weights are 0.270, 0.039, 0.291, 0.145, 0.145 and 0.110 respectively. Table 5. Pair-wise comparison of sub-criteria with respect to tensile properties Therefore, according to the multiplicative AHP model, the equation to calculate the technological value of cotton (MIAHP) is as follows: Determination of premium-discount index formula The % contribution of various cotton properties on the ring yarn tenacity was determined separately for 22 Ne and 30 Ne, using the method described earlier. The results are shown in Table 7. The negative sign associated with UHML is unexpected, and may be ascribed to the prevailing autocorrelation among the fibre properties. The R2 values of the multiple regression equation were 0.745 and 0.676 for 22 Ne and 30 Ne respectively. The resultant formula to calculate the premium-discount index of cotton fibre is as follows: DETERMINATION OF THE TECHNOLOGICAL VALUE OF COTTON FIBRE: 3 Page 1 2 3 Results and Discussion The technological value of cotton fibre derived by various methods, as well as the rank correlation coefficient (Rs) between the technological value of cotton and yarn tenacity, are shown in Tables 8 and 9. It is observed that the RS ranges from a very low value of 0.098 to a very high value of 0.817. In general, the RS values were the lowest for the FQI model and highest for the PDI model. The proposed multiplicative AHP model, which can be considered as a variant of the traditional FQI model, demonstrates a reasonably good RS value of 0.738 and 0.716 for 22 Ne and 30 Ne respectively. The SCI model shows a moderate RS value of 0.401 and 0.459 for 22 Ne and 30 Ne respectively. The traditional FQI model is basically a multiplicative model where all the criteria weights (Wj) are considered to be unity. However, in practice this assumption is totally void, as the influence of various fibre properties on yarn properties will not be identical. Therefore, in a multiplicative type model, proper emphasis must be given to the weights of different decision criteria. This modification is introduced here in the multiplicative AHP model resulting in enhanced RS values. From Table 9, one may be tempted to conclude that in the given problem, the premium-discount index is the best method to determine the technological value of cotton. However, in the premium-discount index model, the decision maker receives a clear idea of the influence of fibre properties on yarn tenacity from the standardised ‘β’ coefficient values. The real accuracy of the premium-discount index model can be judged by subjecting it to some new test samples, which were not used for developing the regression equation relating the fibre properties and yarn tenacity. In case of the multiplicative AHP model, the relative weights of the cotton fibre properties are obtained from the pair-wise comparison matrix, where entries were made based on the past experience of the decision maker, without having any specific knowledge of the present case. Therefore, the multiplicative AHP is a very flexible tool, and can be used in any situation where the decision-maker has some prior knowledge of the problem. Table 8. Cotton fibre properties and the technological values Sample No FS FE UHML UI SFC FF FQI SCI PDI MIAHP 1 28.7 6.5 1.09 81 13.8 4.4 575.9 119.9 minus47.5 2.998 2 28.5 6.6 1.15 80.2 11.9 3.5 751.0 125.7 -37.7 3.182 3 28.7 5.7 1.1 79.2 18.4 3.7 675.8 118.9 -80.1 2.915 4 30.8 6.4 1.13 82.6 9.8 4.3 668.6 133.6 28.8 3.261 5 26.5 5.8 1.09 81.5 8.4 3.8 619.5 120.6 -20.2 3.193 6 27.5 6.3 1.07 82.8 8.4 4.5 541.4 120.6 -5.6 3.167 7 29.2 5.3 0.98 80 16.6 4.5 508.7 109.2 -49.7 2.809 8 29 6.7 1.05 81.9 10.9 4.2 593.8 124.3 -7.7 3.102 9 30.3 6.7 1.1 83.2 8.7 4.4 630.2 134.3 33.7 3.278 10 28.1 6.3 1.01 80.7 15.5 3.8 602.7 117.5 -51.6 2.909 11 30.6 6.6 1.07 83.1 9 4.7 578.9 130.1 33.6 3.219 12 28.7 6.7 1.05 81 11.8 3.9 625.9 120.2 -23.5 3.078 13 28.3 6.5 0.97 81.5 13.1 3.8 588.8 118.3 -21.4 2.959 14 29 6.6 1.06 80.7 11.3 3.1 800.2 129.1 -5.1 3.191 15 27.7 5.5 1.05 81.5 11.7 4.7 504.3 110.5 -33.5 2.970 16 29.1 6.1 1.05 81.7 11.2 4 624.1 123.9 -0.8 3.097 17 28.6 5.7 1.04 82.4 10.8 4.2 583.5 125.0 4.1 3.069 18 28.8 5.5 1.05 82.6 9.2 4.1 609.2 126.2 23.2 3.161 19 28.1 6.7 1.03 81.7 7.2 4.5 525.5 116.8 -1.5 3.223 20 29 6 1.04 81.4 6.8 5 491.0 114.0 8.9 3.233 21 31.7 6.3 1.03 80.6 8.9 3.7 711.3 131.0 46.2 3.284 22 29.3 6 1.03 81.2 8.1 4.4 556.9 119.9 13.5 3.195 23 29.1 6.9 1.05 83.2 5.6 4.6 552.6 128.0 36.0 3.398 24 30.8 6.4 1.01 81.7 6.8 3.7 686.9 132.0 60.5 3.378 25 26.7 6.9 1.04 82.6 7.5 4.8 477.8 111.7 -22.4 3.155 26 30.2 6.7 1.06 82.3 5.6 4.3 612.7 128.9 48.5 3.457 27 28.7 6.2 1.02 80.7 8.7 3.8 621.7 120.1 3.9 3.188 28 29.5 6.4 1.02 81.9 7.2 4.8 513.4 116.3 20.6 3.228 29 27.5 6.9 1.01 81.7 9.7 4.5 504.3 110.9 -27.8 3.054 30 28.9 6 1.07 81.1 7.7 4.6 545.2 116.3 1.9 3.226 31 30.3 6.1 1.1 80.6 8.4 4.6 584.0 121.7 8.6 3.252 32 34 6.6 1.2 82.8 6.8 3.8 889.0 155.6 99.7 3.649 33 26.8 5.3 1 80.8 6.8 4.9 441.9 101.7 -18.3 3.117 Table 9. Rank correlation value between the technological value of cotton and yarn tenacity Technological value model Yarn count 22 Ne 30 Ne FQIHVI 0.098 0.129 SCI 0.401 0.459 PDI 0.817 0.809 M IAHP 0.738 0.716 Conclusions A new multiplicative AHP model has been proposed to determine the technological value of cotton. The proposed method uses a variant of the traditional FQI formula, and enhances the rank correlation between the technological value of cotton and yarn tenacity. The incorporation of proper weights of cotton properties in the multiplicative formula is more logical than having the same weight for all the cotton properties. The past experience of the decision-maker plays a key role in determining the criteria weights in the proposed multiplicative AHP method. Of the four methods considered here, the premium-discount index method shows maximum rank correlation between the technological value of cotton and yarn tenacity. The multiplicative AHP, SCI and FQI models are the remaining three methods, in the order of descending rank correlation. Similar studies could also be initiated using other MCDM methods. POWER FACTOR RESISITVE LOADS: Resistive loads include devices such as heating elements and incandescent lighting. In a purely resistive circuit, current and voltage rise and fall at the same time. They are said to be “in phase.” TRUE POWER: All the power drawn by a resistive circuit is converted to usefulwork. This is also known as true power in a resistive circuit. Truepower is measured in watts (W), kilowatts (kW), or megawatts(MW). In a DC circuit or in a purely resistive AC circuit, truepower can easily be determined by measuring voltage and current. True power in a resistive circuit is equal to system voltage (E) times current (I). INDUCTIVE LOADS: Inductive loads include motors, transformers, and solenoids. In a purely inductive circuit, current lags behind voltage by 90°.Current and voltage are said to be “out of phase.” Inductive circuits, however, have some amount of resistance. Depending on the amount of resistance and inductance, AC current will lag somewhere between a purely resistive circuit (0°) and a purely inductive circuit (90°). In a circuit where resistance and inductance are equal values, for example, current lags voltageby 45°. CAPACITIVE LOADS: Capacitive loads include power factor correction capacitors and filtering capacitors. In a purely capacitive circuit, current leads voltage by 90°. Capacitive circuits, however, have some amount of resistance. Depending on the amount of resistance and capacitance, AC current will lead voltage somewhere between a purely resistive circuit (0°) and a purely capacitive circuit (90°).In a circuit where resistance and capacitance are equal values,for example, current leads voltage by 45°. REACTIVE LOADS: Circuits with inductive or capacitive components are said to be reactive. Most distribution systems have various resistive and reactive circuits. The amount of resistance and reactance varies,depending on the connected loads. REACTANCE: Just as resistance is opposition to current flow in a resistive circuit, reactance is opposition to current flow in a reactive circuit. It should be noted, however, that where frequency has no effect on resistance, it does effect reactance. An increase in applied frequency will cause a corresponding increase in inductive reactance and a decrease in capacitive reactance. For resistance R = E/I, Where R = resistance in Ohms, E = voltage and I = current For inductive Reactance XL = 2 x 3.14 x f x L , where XL is inductive reactance in ohms, f = applied freq and L = inductance in henrys For Capacitive reactance XC = 1 / (2 x 3.14 x f x C) where XC =capacitive reactance, f = applied freq and C = capacitance in farads ENERGY IN REACTIVE CIRUCUITS: Energy in a reactive circuit does not produce work. This energy is used to charge a capacitor or produce a magnetic field around the coil of an inductor. Current in an AC circuit rises to peak values (positive and negative) and diminishes to zero many times a second. During the time, current is rising to a peakvalue, energy is stored in an inductor in the form of a magnetic field or as an electrical charge in the plates of a capacitor. This energy is returned to the system when the magnetic field collapses or when the capacitor is discharged. REACTIVE POWER Power in an AC circuit is made up of three parts; true power,reactive power, and apparent power. We have already discussed true power. Reactive power is measured in volt-amps reactive(VAR). Reactive power represents the energy alternately stored and returned to the system by capacitors and/or inductors.Although reactive power does not produce useful work, it still needs to be generated and distributed to provide sufficient true power to enable electrical processes to run. APPARENT POWER: Not all power in an AC circuit is reactive. We know that reactive power does not produce work; however, when a motor rotates work is produced. Inductive loads, such as motors, have some amount of resistance. Apparent power represents a load which includes reactive power (inductance) and true power(resistance). Apparent power is the vector sum of true power,which represents a purely resistive load, and reactive power,which represents a purely reactive load. A vector diagram can be used to show this relationship. The unit of measurement for apparent power is volt amps (VA). Larger values can be stated inkilovolt amps (kVA) or megavolt amps (MVA). POWER FACTOR – 2 POWER AND POWER FACTOR IN AN AC CIRCUIT: Power consumed by a resistor is dissipated in heat and not returned to the source. This is true power. True power is the rate at which energy is used. Current in an AC circuit rises to peak values and diminishes to zero many times a second. The energy stored in the magnetic field of an inductor, or plates of a capacitor, is returned to the source when current changes direction. Power in an AC circuit is the vector sum of true power and reactive power. This is called apparent power.True power is equal to apparent power in a purely resistive circuit because voltage and current are in phase. Voltage and current are also in phase in a circuit containing equal values of inductive reactance and capacitive reactance. If voltage and current are 90 degrees out of phase, as would be in a purely capacitive or purely inductive circuit, the average value of true power is equal to zero. There are high positive and negative peak values of power, but when added together the result is zero. The formula for apparent power is: P = EI Apparent power is measured in volt-amps (VA).True power is calculated from another trigonometric function,the cosine of the phase angle (cos q). The formula for truepower is: P = EI cos q True power is measured in watts. In a purely resistive circuit, current and voltage are in phase.There is a zero degree angle displacement between current and voltage. The cosine of zero is one. Multiplying a value by one does not change the value. In a purely resistive circuit the cosine of the angle is ignored.In a purely reactive circuit, either inductive or capacitive,current and voltage are 90 degrees out of phase. The cosine of 90 is zero. Multiplying a value times zero results in a zero product. No power is consumed in a purely reactive circuit. CALCULATING APPARENT POWER IN A SIMPLE R-L-C CIRCUIT: In the following 120 volt circuit, It is equal to 84.9 milliamps.Inductive reactance is 100 W and capacitive reactance is1100 W. The phase angle is -45 degrees. By referring to atrigonometric table, the cosine of -45 degrees is foundto be .7071. The apparent power consumed by the cirucuit is P = EI P = 10.2 VA The true power consumed by the ciruit is P= EI COS (phi) = 120 x 0.0849 x 0.7071 = 7.2 watts another formula for true power is P = 0.0849 X 0.0849 X 1000 = 7.2 watts POWER FACTOR: Power factor is the ratio of true power to apparent power in an AC circuit. Power factor is expressed in the following formula: PF = PT/PA Power factor can also be expressed using the formulas for true power and apparent power. The value of EI cancels out because it is the same in the numerator and denominator.Power factor is the cosine of the angle. In a purely resistive circuit, where current and voltage are inphase, there is no angle of displacement between current and voltage. The cosine of a zero degree angle is one. The powerfactor is one. This means that all energy delivered by the source is consumed by the circuit and dissipated in the form of heat.In a purely reactive circuit, voltage and current are 90 degrees apart. The cosine of a 90 degree angle is zero. The powerfactor is zero. This means the circuit returns all energy it receives from the source to the source.In a circuit where reactance and resistance are equal, voltage and current are displaced by 45 degrees. The cosine of a 45degree angle is .7071. The power factor is .7071. This means the circuit has used approximately 70% of the energy supplied by the source and returned approximately 30%. LEADING AND LAGGING POWER FACTOR: Since current leads voltage in a capacitive circuit, power factor is considered leading if there is more capacitive reactance than inductive reactance. Power factor is considered lagging if there is more inductive reactance than capacitive reactance since current lags voltage in an inductive circuit. Power factor is unity when there is no reactive power or when inductive reactance and capacitive reactance are equal, effectively cancelling eachother. It is usually more economical to correct poor power factor than to pay large utility bills. In most industrial applications motors account for approximately 60% or more of electric power consumption, resulting in a lagging power factor (more inductive than capacitive). Power factor correction capacitors can be added to improve the power factor. POWER FACTOR PROBLEMS: It can be seen that an increase in reactive power causes a corresponding decrease in power factor. This means the power distribution system is operating less efficiently because not all current is performing work. For example, a 50 kW load with a power factor of 1 (reactive power = 0) could be supplied by a transformer rated for 50 kVA. However, if power factor is 0.7(70%) the transformer must also supply additional power for the reactive load. In this example a larger transformer capable ofsupplying 71.43 kVA (50 ÷ 70%) would be required. In addition,the size of the conductors would have to be increased, adding significant equipment cost. Power Factor. Power factor is the ratio between the KW and the KVA drawn by an electrical load where the KW is the actual load power and the KVA is the apparent load power. It is a measure of how effectively the current is being converted into useful work output and more particularly is a good indicator of the effect of the load current on the efficiency of the supply system. All current will causes losses in the supply and distribution system. A load with a power factor of 1.0 results in the most efficient loading of the supply and a load with a power factor of 0.5 will result in much higher losses in the supply system. A poor power factor can be the result of either a significant phase difference between the voltage and current at the load terminals, or it can be due to a high harmonic content or distorted/discontinuous current waveform. Poor load current phase angle is generally the result of an inductive load such as an induction motor, power transformer, lighting balasts, welder or induction furnace. A distorted current waveform can be the result of a rectifier, variable speed drive, switched mode power supply, discharge lighting or other electronic load. A poor power factor due to an inductive load can be improved by the addition of power factor correction, but, a poor power factor due to a distorted current waveform requires an change in equipment design or expensive harmonic filters to gain an appreciable improvement. Many inverters are quoted as having a power factor of better than 0.95 when in reality, the true power factor is between 0.5 and 0.75. The figure of 0.95 is based on the Cosine of the angle between the voltage and current but does not take into account that the current waveform is discontinuous and therefore contributes to increased losses on the supply. POWER FACTOR – 3 Power Factor Correction. Capacitive Power Factor correction is applied to circuits which include induction motors as a means of reducing the inductive component of the current and thereby reduce the losses in the supply. There should be no effect on the operation of the motor itself. An induction motor draws current from the supply, that is made up of resistive components and inductive components. The resistive components are: 1) Load current. 2) Loss current. and the inductive components are: 3) Leakage reactance. 4) Magnetising current. The current due to the leakage reactance is dependant on the total current drawn by the motor, but the magnetising current is independent of the load on the motor. The magnetising current will typically be between 20% and 60% of the rated full load current of the motor. The magnetising current is the current that establishes the flux in the iron and is very necessary if the motor is going to operate. The magnetising current does not actually contribute to the actual work output of the motor. It is the catalyst that allows the motor to work properly. The magnetising current and the leakage reactance can be considered passenger components of current that will not affect the power drawn by the motor, but will contribute to the power dissipated in the supply and distribution system. Take for example a motor with a current draw of 100 Amps and a power factor of 0.75 The resistive component of the current is 75 Amps and this is what the KWh meter measures. The higher current will result in an increase in the distribution losses of (100 x 100) /(75 x 75) = 1.777 or a 78% increase in the supply losses. In the interest of reducing the losses in the distribution system, power factor correction is added to neutralise a portion of the magnetising current of the motor. Typically, the corrected power factor will be 0.92 – 0.95 Some power retailers offer incentives for operating with a power factor of better than 0.9, while others penalise consumers with a poor power factor. There are many ways that this is metered, but the net result is that in order to reduce wasted energy in the distribution system, the consumer will be encouraged to apply power factor correction. Power factor correction is achieved by the addition of capacitors in parallel with the connected motor circuits and can be applied at the starter, or applied at the switchboard or distribution panel. The resulting capacitive current is leading current and is used to cancel the laging inductive current flowing from the supply. Capacitors connected at each starter and controlled by each starter is known as “Static Power Factor Correction” while capacitors connected at a distribution board and controlled independently from the individual starters is known as “Bulk Correction”. BULK CORRECTION: The Power factor of the total current supplied to the distribution board is monitored by a controller which then switches capacitor banks In a fashion to maintain a power factor better than a preset limit. (Typically 0.95) Ideally, the power factor should be as close to unity as possible. There is no problem with bulk correction operating at unity. STATIC CORRECTION: As a large proportion of the inductive or lagging current on the supply is due to the magnetising current of induction motors, it is easy to correct each individual motor by connecting the correction capacitors to the motor starters. With static correction, it is important that the capacitive current is less than the inductive magnetising current of the induction motor. In many installations employing static power factor correction, the correction capacitors are connected directly in parallel with the motor windings. When the motor is Off Line, the capacitors are also Off Line. When the motor is connected to the supply, the capacitors are also connected providing correction at all times that the motor is connected to the supply. This removes the requirement for any expensive power factor monitoring and control equipment. In this situation, the capacitors remain connected to the motor terminals as the motor slows down. An induction motor, while connected to the supply, is driven by a rotating magnetic field in the stator which induces current into the rotor. When the motor is disconnected from the supply, there is for a period of time, a magnetic field associated with the rotor. As the motor decelerates, it generates voltage out its terminals at a frequency which is related to it’s speed. The capacitors connected across the motor terminals, form a resonant circuit with the motor inductance. If the motor is critically corrected, (corrected to a power factor of 1.0) the inductive reactance equals the capacitive reactance at the line frequency and therefore the resonant frequency is equal to the line frequency. If the motor is over corrected, the resonant frequency will be below the line frequency. If the frequency of the voltage generated by the decelerating motor passes through the resonant frequency of the corrected motor, there will be high currents and voltages around the motor/capacitor circuit. This can result in sever damage to the capacitors and motor. It is imperative that motors are never over corrected or critically corrected when static correction is employed. Static power factor correction should provide capacitive current equal to 80% of the magnetising current, which is essentially the open shaft current of the motor. The magnetising current for induction motors can vary considerably. Typically, magnetising currents for large two pole machines can be as low as 20% of the rated current of the motor while smaller low speed motors can have a magnetising current as high as 60% of the rated full load current of the motor. It is not practical to use a “Standard table” for the correction of induction motors giving optimum correction on all motors. Tables result in undercorrection on most motors but can result in over correction in some cases. Where the open shaft current can not be measured, and the magnetising current is not quoted, an approximate level for the maximum correction that can be applied can be calculated from the half load characteristics of the motor. It is dangerous to base correction on the full load characteristics of the motor as in some cases, motors can exhibit a high leakage reactance and correction to 0.95 at full load will result in overcorrection under no load, or disconnected conditions. Static correction is commonly applied by using on e contactor to control both the motor and the capacitors. It is better practice to use two contactors, one for the motor and one for the capacitors. Where one contactor is employed, it should be upsized for the capacitive load. The use of a second contactor eliminates the problems of resonance between the motor and the capacitors. CAPACITOR SELECTION: Static Power factor correction must neutralise no more than 80% of the magnetising current of the motor. If the correction is too high, there is a high probability of over correction which can result in equipment failure with sever damage to the motor and capacitors. Unfortunately, the magnetising current of induction motors varies considerably between different motor designs. The magnetising current is almost always higher than 20% of the rated full load current of the motor, but can be as high as 60% of the rated current of the motor. Most power factor correction is too light due to the selection based on tables which have been published by a number of sources. These tables assume the lowest magnetising current and quote capacitors for this current. In practice, this can mean that the correction is often less than half the value that it should be, and the consumer is unnecessarily penalised. Power factor correction must be correctly selected based on the actual motor being corrected. The Busbar software provides two methods of calculating the correct value of KVAR correction to apply to a motor. The first method requires the magnetising current of the motor. Where this figure is available, then this is the preferred method. Where the magnetising current is not available, the second method is employed and is based on the half load power factor and efficiency of that motor. These figures are available from the motor data sheets. Static Power factor correction can be calculated from known motor characteristics for any given motor, either the magnetising current and supply voltage (method 1) or half load efficiency and half load power factor(method 2), or, as a last resort, table values can be used. These will almost always result in under correction Bulk power factor correction can be calculated from known existing power factor, required new powerfactor, line voltage and line current. Supply Resonance. Capacitive Power factor correction connected to a supply causes resonance between the supply and the capacitors. If the fault current of the supply is very high, the effect of the resonance will be minimal, however in a rural installation where the supply is very inductive and can be a high impedance, the resonances can be very severe resulting in major damage to plant and equipment. Voltage surges and transients of several times the supply voltage are not uncommon in rural areas with weak supplies, especially when the load on the supply is low. As with any resonant system, a transient or sudden change in current will result in the resonant circuit ringing, generating a high voltage. The magnitude of the voltage is dependant on the ‘Q’ of the circuit which in turn is a function of the circuit loading. One of the problems with supply resonance is that the ‘reaction’ is often well remove from the ‘stimulous’ unlike a pure voltage drop problem due to an overloaded supply. This makes fault finding very difficult and often damaging surges and transients on the supply are treated as ‘just one of those things’. To minimise supply resonance problems, there are a few steps that can be taken, but they do need to be taken by all on the particular supply. 1) Minimise the amount of power factor correction, particularly when the load is light. The power factor correction minimises losses in the supply. When the supply is lightly loaded, this is not such a problem. 2) Minimise switching transients. Eliminate open transition switching – usually associated with generator plants and alternative supply switching, and with some electromechanical starters such as the star/delta starter. 3) Switch capacitors on to the supply in lots of small steps rather than a few large steps. 4) Switch capaciotors on to the supply after the load has been applied and switch off the supply before or with the load removal. POWER FACTOR – 4 Solid State Soft Starter: Static Power Factor correction capacitors must not be connected to the output of a solid state soft starter. When a solid state soft starter is used, the capacitors must be controlled by a separate contactor, and switched in when the softstarter output voltage has reached line voltage. Many soft starters provide a “top of ramp” or “bypass contactor control” which can be used to control the power factor correction capacitors. The connection of capacitors close to the input of the soft starter can also result in damage to the soft starter if an isolation contactor is not used. The capacitors tend to cause transients to be amplified, resulting in higher voltage impulses applied to the SCRs of the Soft Starter, and the energy behind the impulses is much greater due to the energy storage of the capacitors. It is recommended that capcitors should be at least 50 Meters away from Soft starters to elevate the impedance between the inverter and capacitors and reduce the potential damage caused. Switching capacitors, Automatic bank correction etc, will cause voltage transients and these transients can damage the SCRs of Soft Starters if they are in the Off state without an input contactor. The energy is proportional to the amount of capacitance being switched. It is better to switch lots of small amounts of capacitance than few large amounts. Inverter. Static Power factor correction must not be used when the motor is controlled by a variable speed drive or invertor. The connection of capacitors to the output of an inverter can cause serious damage to the inverter and the capacitors due to the high frequency switched voltage on the output of the inverters. The current drawn from the inverter has a poor power factor, particulary at low load, but the motor current is isolated from the supply by the inverter. The phase angle of the current drawn by the inverter from the supply is close to zero resulting in very low inductive current irrespective of what the motor is doing. The inverter does not however, operate with a good power factor. Many inverter manufacturers quote a cos Ø of better than 0.95 and this is generally true, however the current is non sinusoidal and the resultant harmonics cause a power factor (KW/KVA) of closer to 0.7 depending on the input design of the inverter. Inverters with input reactors and DC bus reactors will exhibit a higher true power factor than those without. The connection of capacitors close to the input of the inverter can also result in damage to the inverter. The capacitors tend to cause transients to be amplified, resulting in higher voltage impulses applied to the input circuits of the inverter, and the energy behind the impulses is much greater due to the energy storage of the capacitors. It is recommended that capcitors should be at least 75 Meters away from inverter inputs to elevate the impedance between the inverter and capacitors and reduce the potential damage caused. Switching capacitors, Automatic bank correction etc, will cause voltage transients and these transients can damage the input circuits of inverters. The energy is proportional to the amount of capacitance being switched. It is better to switch lots of small amounts of capacitance than few large amounts Harmonic Power Factor correction is applied to circuits that draw either discontinuous or distorted current waveforms. Most electonic equipment includes a means of creating a DC supply. This involves rectifying the AC voltage, causing harmonic currents. In some cases, these harmonic currents are insignificant relative to the total load current drawn, but in many installations, a large proportion of the current drawn is rich in harmonics. If the total harmonic current is large enough, there will be a resultant distortion of the supply waveform which can interfere with the correct operation of other equipment. The addition of harmonic currents results in increased losses in the supply. Power factor correction for distorted supplies can not be achieved by the addition of capacitors. The harmonics can be reduced by designing the equipment using active rectifiers, by the addition of passive filters (LCR) or by the addition of electronic power factor correction inverters which restore the waveform back to its undistorted state. This is a specialist area requiring either major design changes, or specialised equipment to be used. INDUCTION MOTOR 1. Introduction: The Induction motor is a three phase AC motor and is the most widely used machine. Its characteristic features are- o Simple and rugged construction o Low cost and minimum maintenance o High reliability and sufficiently high efficiency o Needs no extra starting motor and need not be synchronized An Induction motor has basically two parts – Stator and Rotor The Stator is made up of a number of stampings with slots to carry three phase windings. It is wound for a definite number of poles. The windings are geometrically spaced 120 degrees apart. Two types of rotors are used in Induction motors – Squirrel-cage rotor and Wound rotor. INDUCTION MOTOR: All loads moved by electric motors are really moved by magnetism. The purpose of every component in a motor is to help harness, control, and use magnetic force. When applying an AC drive system it helps to remember you are actually applying magnets to move a load. To move a load fast does not require more magnets, you just move the magnets fast. To move a heavier load or to decrease acceleration time (accelerate faster) more magnets (more torque) are needed. This is the basis for all motor applications. STATOR CONSTRUCTION: The stator and the rotor are electrical circuits that perform as electromagnets. The stator is the stationary electrical part of the motor. The stator core of a NEMA motor is made up of several hundred thin laminations. STATOR WINDINGS; Stator laminations are stacked together forming a hollow cylinder. Coils of insulated wire are inserted into slots of the stator core. Each grouping of coils, together with the steel core it surrounds, form an electromagnet. Electromagnetism is the principle behind motor operation. The stator windings are connected directly to the power source. ROTOR CONSTRUCTION: The rotor is the rotating part of the electromagnetic circuit. The most common type of rotor is the “squirrel cage” rotor. Other types of rotor construction will be mentioned later in the course. The construction of the squirrel cage rotor is reminiscent of rotating exercise wheels found in cages of pet rodents. The rotor consists of a stack of steel laminations with evenly spaced conductor bars around the circumference. The laminations are stacked together to form a rotor core. Aluminum is die cast in the slots of the rotor core to form a series of conductors around the perimeter of the rotor. Current flow through the conductors form the electromagnet. The conductor bars are mechanically and electrically connected with end rings. The rotor core mounts on a steel shaft to form a rotor assembly. INDUCTION MOTOR – 2 ENCLOSURE: The enclosure consists of a frame (or yoke) and two end brackets (or bearing housings). The stator is mounted inside the frame. The rotor fits inside the stator with a slight air gap separating it from the stator. There is no direct physical connection between the rotor and the stator. The enclosure also protects the electrical and operating parts of the motor from harmful effects of the environment in which the motor operates. Bearings, mounted on the shaft, support the rotor and allow it to turn. A fan, also mounted on the shaft, is used on the motor shown below for cooling. ELECTROMAGNETISM: When current flows through a conductor a magnetic field is produced around the conductor. The magnetic field is made up of lines of flux, just like a natural magnet. The size and strength of the magnetic field will increase and decrease as the current flow strength increases and decreases. LEFT HAND RULE FOR CONDUCTORS: A definite relationship exists between the direction of current flow and the direction of the magnetic field. The left-hand rule for conductors demonstrates this relationship. If a currentcarrying conductor is grasped with the left hand with the thumb pointing in the direction of electron flow, the fingers will point in the direction of the magnetic lines of flux. ELECTROMAGNET: An electromagnet can be made by winding the conductor into a coil and applying a DC voltage. The lines of flux, formed by current flow through the conductor, combine to produce a larger and stronger magnetic field. The center of the coil is known as the core. In this simple electromagnet the core is air. Iron is a better conductor of flux than air. The air core of an electromagnet can be replaced by a piece of soft iron. When a piece of iron is placed in the center of the coil more lines of flux can flow and the magnetic field is strengthened. NO OF TURNS: The strength of the magnetic field in the DC electromagnet can be increased by increasing the number of turns in the coil. The greater the number of turns the stronger the magnetic field will be. CHANGING POLARITY: The magnetic field of an electromagnet has the same characteristics as a natural magnet, including a north and south pole. However, when the direction of current flow through the electromagnet changes, the polarity of the electromagnet changes. The polarity of an electromagnet connected to an AC source will change at the same frequency as the frequency of the AC source. This can be demonstrated in the following illustration. At Time 1 current flow is at zero. There is no magnetic field produced around the electromagnet. At Time 2 current is flowing in a positive direction. A magnetic field builds up around the electromagnet. The electromagnet assumes a polarity with the south pole on the top and the north pole on the bottom. At Time 3 current flow is at its peak positive value. The strength of the electromagnetic field is at its greatest value. At Time 4 current flow decreases and the magnetic field begins to collapse, until Time 5 when current flow and magnetic field are at zero. Current immediately begins to increase in the opposite direction. At Time 6 current is increasing in a negative direction. The polarity of the electromagnetic field has changed. The north pole is now on top and the south pole is on the bottom. The negative half of the cycle continues through Times 7 and 8, returning to zero at Time 9. This process will repeat 60 times a second with a 60 Hz AC power supply. INDUCED VOLTAGE: A conductor moving through a magnetic field will have a voltage induced into it. This electrical principle is used in the operation of AC induction motors. In the following illustration an electromagnet is connected to an AC power source. Another electromagnet is placed above it. The second electromagnet is in a separate circuit. There is no physical connection between the two circuits. Voltage and current are zero in both circuits at Time 1. At Time 2 voltage and current are increasing in the bottom circuit. A magnetic field builds up in the bottom electromagnet. Lines of flux from the magnetic field building up in the bottom electromagnet cut across the top electromagnet. A voltage is induced in the top electromagnet and current flows through it. At Time 3 current flow has reached its peak. Maximum current is flowing in both circuits. The magnetic field around the coil continues to build up and collapse as the alternating current continues to increase and decrease. As the magnetic field moves through space, moving out from the coil as it builds up and back towards the coil as it collapses, lines of flux cut across the top coil. As current flows in the top electromagnet it creates its own magnetic field. ELECTROMAGNETIC ATTRACTION: The polarity of the magnetic field induced in the top electromagnet is opposite the polarity of the magnetic field in the bottom electromagnet. Since opposite poles attract, the top electromagnet will follow the bottom electromagnet when it is moved. DEVELOPING A ROTATING MAGENETIC FIELD: The principles of electromagnetism explain the shaft rotation of an AC motor. Recall that the stator of an AC motor is a hollow cylinder in which coils of insulated wire are inserted. INDUCTION MOTOR – 3 STATOR COIL ARRANGEMENT: The following schematic illustrates the relationship of the coils. In this example six coils are used, two coils for each of the three phases. The coils operate in pairs. The coils are wrapped around the soft iron core material of the stator. These coils are referred to as motor windings. Each motor winding becomes a separate electromagnet. The coils are wound in such a way that when current flows in them one coil is a north pole and its pair is a south pole. For example, if A1 were a north pole then A2 would be a south pole. When current reverses direction the polarity of the poles would also reverse. POWER SUPPLY: The stator is connected to a 3-phase AC power supply. In the following illustration phase A is connected to phase A of the power supply. Phase B and C would also be connected to phases B and C of the power supply respectively. Phase windings (A, B, and C) are placed 120° apart. In this example, a second set of three-phase windings is installed. The number of poles is determined by how many times a phase winding appears. In this example, each phase winding appears two times. This is a two-pole stator. If each phase winding appeared four times it would be a four-pole stator. When AC voltage is applied to the stator, current flows through the windings. The magnetic field developed in a phase winding depends on the direction of current flow through that winding. The following chart is used here for explanation only. It will be used in the next few illustrations to demonstrate how a rotating magnetic field is developed. It assumes that a positive current flow in the A1, B1 and C1 windings result in a north pole. Winding Current Flow Direction Positive Negative A1 North South A2 South North B1 North South B2 South North C1 North South C2 South North START: It is easier to visualize a magnetic field if a start time is picked when no current is flowing through one phase. In the following illustration, for example, a start time has been selected during which phase A has no current flow, phase B has current flow in a negative direction and phase C has current flow in a positive direction. Based on the above chart, B1 and C2 are south poles and B2 and C1 are north poles. Magnetic lines of flux leave the B2 north pole and enter the nearest south pole, C2. Magnetic lines of flux also leave the C1 north pole and enter the nearest south pole, B1. A magnetic field results, as indicated by the arrow. TIME 1: If the field is evaluated at 60° intervals from the starting point, at Time 1, it can be seen that the field will rotate 60°. At Time 1 phase C has no current flow, phase A has current flow in a positive direction and phase B has current flow in a negative direction. Following the same logic as used for the starting point, windings A1 and B2 are north poles and windings A2 and B1 are south poles. TIME 2: At Time 2 the magnetic field has rotated 60°. Phase B has no current flow. Although current is decreasing in phase A it is still flowing in a positive direction. Phase C is now flowing in a negative direction. At start it was flowing in a positive direction. Current flow has changed directions in the phase C windings and the magnetic poles have reversed polarity. 360 degree ROTATION: At the end of six such time intervals the magnetic field will have rotated one full revolution or 360°. This process will repeat 60 times a second on a 60 Hz power supply. INDUCTION MOTOR – 4 SYNCHRONOUS SPEED: The speed of the rotating magnetic field is referred to as synchronous speed (NS). Synchronous speed is equal to 120 times the frequency (F), divided by the number of poles (P). Ns = 120 F / P If the frequency of the applied power supply for the two-pole stator used in the previous example is 60 Hz, synchronous speed is 3600 RPM. N s =( 120 x 60 )/ 2 N = 3600 RPM The synchronous speed decreases as the number of poles increase. The following table shows the synchronous speed at 60 Hz for the corresponding number of poles. no of poles synchronous speed 2 3600 4 1800 6 1200 8 900 The magnetic field rotates at synchronous speed, VS—the motor’s theoretical top speed that would result in no torque output. In actual operation, rotor speed always lags the magnetic field’s speed, allowing the rotor bars to cut magnetic lines of force and produce useful torque. This speed difference is called slip speed. Typical slip values range 2-5% of VS at running speed, but can be large at motor startup. Slip also increases with load, so for accurate control of speed, closed-loop control or feedback is needed. ROTOR ROTATION: PERMANENT MAGNET: To see how a rotor works, a magnet mounted on a shaft can be substituted for the squirrel cage rotor. When the stator windings are energized a rotating magnetic field is established. The magnet has its own magnetic field that interacts with the rotating magnetic field of the stator. The north pole of the rotating magnetic field attracts the south pole of the magnet, and the south pole of the rotating magnetic field attracts the north pole of the magnet. As the rotating magnetic field rotates, it pulls the magnet along causing it to rotate. This design, used on some motors, isreferred to as a permanent magnet synchronous motor. INDUCED VOLTAGE ELECTROMAGNET: The squirrel cage rotor acts essentially the same as the magnet. When power is applied to the stator, current flows through the winding, causing an expanding electromagnetic field which cuts across the rotor bars. When a conductor, such as a rotor bar, passes through a magnetic field a voltage (emf) is induced in the conductor. The induced voltage causes a current flow in the conductor. Current flows through the rotor bars and around the end ring. The current flow in the conductor bars produces magnetic fields around each rotor bar. Recall that in an AC circuit current continuously changes direction and amplitude. The resultant magnetic field of the stator and rotor continuously change. The squirrel cage rotor becomes an electromagnet with alternating north and south poles. The following drawing illustrates one instant in time during which current flow through winding A1 produces a north pole. The expanding field cuts across an adjacent rotor bar, inducing a voltage. The resultant magnetic field in the rotor tooth produces a south pole. As the stator magnetic field rotates the rotor follows. SLIP: There must be a relative difference in speed between the rotor and the rotating magnetic field. If the rotor and the rotating magnetic field were turning at the same speed no relative motion would exist between the two, therefore no lines of flux would be cut, and no voltage would be induced in the rotor. The difference in speed is called slip. Slip is necessary to produce torque. Slip is dependent on load. An increase in load will cause the rotor to slow down or increase slip. A decrease in load will cause the rotor to speed up or decrease slip. Slip is expressed as a percentage and can be determined with the following formula. % Slip = (Ns – Nr) x 100/Ns For example, a four-pole motor operated at 60 Hz has a synchronous speed (NS) of 1800 RPM. If the rotor speed at full load is 1765 RPM (NR), then slip is 1.9%. % Slip = (1800 – 1765) x 100 / 1800 % Slip = 1.9% WOUND ROTOR MOTOR: The discussion to this point has been centered on the more common squirrel cage rotor. Another type is the wound rotor. A major difference between the wound rotor motor and the squirrel cage rotor is the conductors of the wound rotor consist of wound coils instead of bars. These coils are connected through slip rings and brushes to external variable resistors. The rotating magnetic field induces a voltage in the rotor windings. Increasing the resistance of the rotor windings causes less current flow in the rotor windings, decreasing speed. Decreasing the resistance allows more current flow, speeding the motor up. SYNCHRONOUS MOTOR: Another type of AC motor is the synchronous motor. The synchronous motor is not an induction motor. One type of synchronous motor is constructed somewhat like a squirrel cage rotor. In addition to rotor bars coil windings are added. The coil windings are connected to an external DC power supply by slip rings and brushes. On start AC is applied to the stator and the synchronous motor starts like a squirrel cage rotor. DC is applied to the rotor coils after the motor reaches maximum speed. This produces a strong constant magnetic field in the rotor which locks in step with the rotating magnetic field. The rotor turns at the same speed as synchronous speed (speed of the rotating magnetic field). There is no slip. Variations of synchronous motors include a permanent magnet rotor. The rotor is a permanent magnet and an external DC source is not required. These are found on small horsepower synchronous motors. Induction motors have five major components of loss; Iron loss, Copper loss, Frictional loss, Windage loss and Sound loss. All these losses add up to the total loss of the induction motor. Frictional loss, windage loss and sound loss are constant, independent of shaft load, and are typically very small. The major losses are Iron loss and Copper Loss. The iron loss is essentially constant, independent of shaft load, while the copper loss is an I2R loss which is shaft load dependent. The iron loss is voltage dependent and so will reduce with reducing voltage. REFERENCE: SIEMENS GUIDELINES TO CUSTOMER BASICS OF ELECTRICITY ALTERNATING CURRENT (AC): The supply of current for electrical devices may come from a direct current source (DC), or an alternating current source(AC). In direct current electricity, electrons flow continuously in one direction from the source of power through a conductor to a load and back to the source of power. The voltage indirect current remains constant. DC power sources include batteries and DC generators. In alternating current an AC generator is used to make electrons flow first in one directionthen in another. Another name for an AC generator is analternator. The AC generator reverses terminal polarity manytimes a second. Electrons will flow through a conductor from the negative terminal to the positive terminal, first in onedirection then another. AC SINE WAVE: Alternating voltage and current vary continuously.The graphic representation for AC is a sine wave. A sine wave can represent current or voltage. There are two axes. The vertical axis represents the direction and magnitude of currentor voltage. The horizontal axis represents time. When the waveform is above the time axis, current is flowing in one direction. This is referred to as the positive direction.When the waveform is below the time axis, current is flowing in the opposite direction. This is referred to as the negative direction. A sine wave moves through a complete rotation of 360 degrees, which is referred to as one cycle. Alternating current goes through many of these cycles each second.The unit of measurement of cycles per second is hertz. In general it is 50Hz or 60 Hz depending upon the country. SINGLE PHASE AND THREE PHASE AC POWER: Alternating current is divided into single-phase and threephase types. Single-phase power is used for small electical demands such as found in the home. Three-phase power is used where large blocks of power are required, such as found in commercial applications and industrial plants. Single-phasepower is shown in the above illustration. Three-phase power,as shown in the following illustration, is a continuous series of three overlapping AC cycles. Each wave represents a phase, and is offset by 120 electrical degrees. AC GENERATORS: BASIC GENERATOR: A basic generator consists of a magnetic field, an armature,slip rings, brushes and a resistive load. The magnetic field is usually an electromagnet. An armature is any number of conductive wires wound in loops which rotates through the magnetic field. For simplicity, one loop is shown. When aconductor is moved through a magnetic field, a voltage is induced in the conductor. As the armature rotates through the magnetic field, a voltage is generated in the armature which causes current to flow. Slip rings are attached to thearmature and rotate with it. Carbon brushes ride against the slip rings to conduct current from the armature to a resistive load. BASIC GENERATION OPERATION: An armature rotates through the magnetic field. At an initial position of zero degrees, the armature conductors are moving parallel to the magnetic field and not cutting through any magnetic lines of flux. No voltage is induced. GENERATION OPERATION FROM 0 TO 90 DEGREES: The armature rotates from zero to 90 degrees. The conductors cut through more and more lines of flux, building up to a maximum induced voltage in the positive direction. BASICS OF ELECTRICITY – 2 GENERATION OPERATION FROM 90 TO 180 DEGREES: The armature continues to rotate from 90 to 180 degrees,cutting less lines of flux. The induced voltage decreases froma maximum positive value to zero. GENERATION OPERATION FROM 180 TO 270 DEGREES: The armature continues to rotate from 180 degrees to 270degrees. The conductors cut more and more lines of flux, butin the opposite direction. Voltage is induced in the negativedirection building up to a maximum at 270 degrees. GENERATION OPERATION FROM 270 TO 360 DEGREES: The armature continues to rotate from 270 to 360 degrees.Induced voltage decreases from a maximum negative valueto zero. This completes one cycle. The armature will continueto rotate at a constant speed. The cycle will continuouslyrepeat as long as the armature rotates. FREQUENCY: The number of cycles per second made by voltage induced in the armature is the frequency of the generator. If the armature rotates at a speed of 60 revolutions per second, the generated voltage will be 60 cycles per second. The accepted term for cycles per second is hertz. The standard frequency in theUnited States is 60 hertz. The following illustration shows 15 cycles in 1/4 second which is equivalent to 60 cycles in onesecond. FOUR POLE AC GENERATOR: The frequency is the same as the number of rotations per second if the magnetic field is produced by only two poles.An increase in the number of poles, would cause an increase in the number of cycles completed in a revolution. A two-pole generator would complete one cycle per revolution and a four-pole generator would complete two cycles per revolution.An ACgenerator produces one cycle per revolution for each pair of poles. VOLTAGE AND CURRENT: PEAK VALUE: The sine wave illustrates how voltage and current in an AC circuit rises and falls with time. The peak value of a sine wave occurs twice each cycle, once at the positive maximum value and once at the negative maximum value. PEAK TO PEAK VALUE: The value of the voltage or current between the peak positiveand peak negative values is called the peak-to-peak value. INSTANTANEOUS VALUE: The instantaneous value is the value at any one particulartime. It can be in the range of anywhere from zero to thepeak value. BASICS OF ELECTRICITY – 3 CALCULATING INSTANTANEOUS VOLTAGE: The voltage waveform produced as the armature rotatesthrough 360 degrees rotation is called a sine wavebecauseinstantaneous voltage is related to the trigonometric functioncalled sine (sin q = sine of the angle). The sine curve representsa graph of the following equation: e Epeak = ´sin q Instantaneous voltage is equal to the peak voltage times thesine of the angle of the generator armature. The sine value isobtained from trigonometric tables. The following table reflectsa few angles and their sine value. The following example illustrates instantaneous values at 90,150, and 240 degrees. The peak voltage is equal to 100 volts.By substituting the sine at the instantaneous angle value, theinstantaneous voltage can be calculated. EFFECTIVE VALUE OF AN AC SINE WAVE: Alternating voltage and current are constantly changingvalues. A method of translating the varying values into anequivalent constant value is needed. The effective value ofvoltage and current is the common method of expressing thevalue of AC. This is also known as the RMS (root-meansquare)value. If the voltage in the average home is said to be120 volts, this is the RMS value. The effective value figuresout to be 0.707 times the peak value. The effective value of AC is defined in terms of an equivalentheating effect when compared to DC. One RMS ampere ofcurrent flowing through a resistance will produce heat at thesame rate as a DC ampere.For purpose of circuit design, the peak value may also beneeded. For example, insulation must be designed to withstandthe peak value, not just the effective value. It may bethat only the effective value is known. To calculate the peakvalue, multiply the effective value by 1.41. For example, if theeffective value is 100 volts, the peak value is 141 volts. INDUCTANCE: The circuits studied to this point have been resistive. Resistance and voltage are not the only circuit properties that effect current flow, however. Inductance is the property of an electric circuit that opposes any change in electric current.Resistance opposes current flow, inductance opposes change in current flow. Inductance is designated by the letter “L”. The unit of measurement for inductance is the henry (h). CURRENT FLOW AND FIELD STRENGTH: Current flow produces a magnetic field in a conductor. The amount of current determines the strength of the magnetic field. As current flow increases, field strength increases, and as current flow decrease, field strength decreases. Any change in current causes a corresponding change in the magnetic field surrounding the conductor. Current is constant in DC, except when the circuit is turned on and off, or when there is a load change. Current is constantly changing in AC,so inductance is a continual factor. A change in the magnetic field surrounding the conductor induces a voltage in the conductor. This self-induced voltage opposes the change in current. This is known as counter emf. This opposition causes a delay in the time it takes current to attain its new steady value. If current increases, inductance tries to hold it down. If current decreases, inductance tries to hold it up. Inductance is somewhat like mechanical inertia, which must be overcome to get a mechanical object moving, or to stop a mechanical object from moving. A vehicle, for example, takes a few moments to accelerate to a desired speed, or decelerate to a stop. INDUCTORS: Inductance is usually indicated symbolically on an electricaldrawing by one of two ways. A curled line or a filled rectanglecan be used. Inductors are coils of wire. They may be wrapped around a core. The inductance of a coil is determined by the number of turns in the coil, the spacing between the turns, the coil diameter, the core material, the number of layers of windings,the type of winding, and the shape of the coil. Examples of inductors are transformers, chokes, and motors. SIMPLE INDUCTIVE CIRCUIT: In a resistive circuit, current change is considered instantaneous.If an inductor is used, the current does not change asquickly. In the following circuit, initially the switch is openand there is no current flow. When the switch is closed,current will rise rapidly at first, then more slowly as the maximumvalue is approached. For the purpose of explanation, aDC circuit is used. The time required for the current to rise to its maximum value is determined by the ratio of inductance, in henrys, to resistance, in ohms. This ratio is called the time constant of the inductive circuit. A time constant is the time, in seconds,required for the circuit current to rise to 63.2% of its maximum value. When the switch is closed in the previous circuit,current will begin to flow. During the first time constant current rises to 63.2% of its maximum value. During thesecond time constant, current rises to 63.2% of the remaining 36.8%, or a total of 86.4%. It takes about five time constants for current to reach its maximum value. Similarly, when the switch is opened, it will take five timeconstants for current to reach zero. It can be seen that inductanceis an important factor in AC circuits. If the frequency is60 hertz, current will rise and fall from its peak value to zero120 times a second. BASICS OF ELECTRICITY – 4 CALCULATING THE TIME CONSTANT OF AN INDUCTIVE CIRCUIT: The time constant is designated by the symbol ìtî. To determinethe time constant of an inductive circuit use one of thefollowing formulas: T( in seconds) = L(henrys) / R (ohms) T(in milliseconds) = L(millihenrys)/ R(ohms) In the following illustration, L1 is equal to 15 millihenrys andR1 is equal to 5 W. When the switch is closed, it will take 3milliseconds for current to rise from zero to 63.2% of itsmaximum value. FORMULA FOR SERIES INDUCTORS: Lt = L1+L2+L3+L4 Lt = 2mh+2mh+1mh+1mh = 6mh FORMULA FOR PARALLEL INDUCTORS: In the following circuit, an AC generator is used to supplyelectrical power to three inductors. Total inductance is calculatedusing the following formula: 1/Lt = 1/5 + 1.10 + 1/20 = 7/20 Lt = 2.86 mh CAPACITANCE: CAPACITANCE AND CAPACITORS: Capacitance is a measure of a circuitís ability to store an electrical charge. A device manufactured to have a specific amount of capacitance is called a capacitor. A capacitor is made up of a pair of conductive plates separated by a thin layer of insulating material. Another name for the insulating material is dielectric material. When a voltage is applied to the plates, electrons are forced onto one plate. That plate has an excess of electronswhile the other plate has a deficiency of electrons. The plate with an excess of electrons is negatively charged. The plate with a deficiency of electrons is positively charged. Direct current cannot flow through the dielectric material because it is an insulator. Capacitors have a capacity to hold aspecific quantity of electrons. The capacitance of a capacitor depends on the area of the plates, the distance between theplates, and the material of the dielectric. The unit of measurement for capacitance is farads, abbreviated “F”. Capacitors usually are rated in mF (microfarads), or pF (picofarads). CAPACITOR CIRCUIT SYMBOLS Capacitance is usually indicated symbolically on an electricaldrawing by a combination of a straight line with a curved line,or two straight lines. SIMPLE CAPACITIVE CIRCUIT: In a resistive circuit, voltage change is considered instantaneous.If a capacitor is used, the voltage across the capacitor does not change as quickly. In the following circuit, initially the switch is open and no voltage is applied to the capacitor.When the switch is closed, voltage across the capacitor will rise rapidly at first, then more slowly as the maximum value is approached. For the purpose of explanation, a DC circuit isused. CAPACITIVE TIME CONSTANT The time required for voltage to rise to its maximum value in a circuit containing capacitance is determined by the product of capacitance, in farads, times resistance, in ohms. This is the time it takes a capacitor to become fully charged. This product is the time constant of a capacitive circuit. The time constant gives the time in seconds required for voltage across the capacitor to reach 63.2% of its maximum value. When the switch is closed in the previous circuit, voltage will be applied.During the first time constant, voltage will rise to 63.2% of its maximum value. During the second time constant,voltage will rise to63.2% of the remaining 36.8%, or a total of 86.4%. It takes about five time constants for voltage across the capacitor to reach its maximum value. Similarly, during this same time, it will take five time constants for current through the resistor to reach zero. BASICS OF ELECTRICITY – 5 CALCULATING THE TIME CONSTANT OF A CAPACITIVE CIRCUIT: Time constant is decided by the symbol “T”.To determine the time constant of a capacitive circuit, use oneof the following formulas: T(in seconds) = R(megohms) X C(microfarads) T(in microseconds) = R(megohms) X C(pico farads) T(in microseconds) = R(ohms) X C (microfarads) In the following illustration, C1 is equal to 2 mF, and R1 is equalto 10 W. When the switch is closed, it will take20microseconds for voltage across the capacitor to risefrom zero to 63.2% of its maximum value. There are fivetime constants, so it will take 100 microseconds for this voltageto rise to its maximum value. FORMULA FOR SERIES CAPACITORS: Connecting capacitors in series decreases total capacitance.The effect is like increasing the space between the plates. Therules for parallel resistance apply to series capacitance. In thefollowing circuit, an AC generator supplies electrical power tothree capacitors. Total capacitance is calculated using thefollowing formula: 1/Ct = 1/C1+1/C2+1/C3 1/Ct = 1/5+1/10+1/20 = 7/20 = 2.86 FORMULA FOR PARALLES CAPACITORS: In the following circuit, an AC generator is used to supplyelectrical power to three capacitors. Total capacitance is calculatedusing the following formula: Ct = C1+C2+C3 INDUCTIVE AND CAPACITANCE REACTANCE: In a purely resistive AC circuit, opposition to current flow is called resistance. In an AC circuit containing only inductance,capacitance, or both, opposition to current flow is called reactance. Total opposition to current flow in an AC circuit that contains both reactance and resistance is called impedance designated by the symbol Z. Reactance and impedance are expressed in ohms. INDUCTIVE REACTANCE: Inductance only affects current flow when the current is changing. Inductance produces a self-induced voltage(counter emf) that opposes changes in current. In an ACcircuit, current is changing constantly. Inductance in an AC circuit, therefore, causes a continual opposition. This opposition to current flow is called inductive reactance, and is designated by the symbol XL. Inductive reactance is dependent on the amount of inductance and frequency. If frequency is low current has more time to reach a higher value before the polarity of the sine wave reverses. If frequency is high current has less time to reach a higher value. In the following illustration, voltage remains constant. Current rises to a higher value at a lower frequency than a higher frequency. In a 60 hertz, 10 volt circuit containing a 10 mh inductor, the inductive reactance would be: Xl = 2 x 3.14 x 60 x .010 = 3.768 ohms Once inductive reactance is known, Ohmís Law can be usedto calculate reactive current. I = E/Z = 10/3.768 = 2.65 amps PHASE RELATIONSHIP BETWEEN CURRENT AND VOLTAGE IN AN INDUCTIVE CIRCUIT: Current does not rise at the same time as the source voltage in an inductive circuit. Current is delayed depending on the mount of inductance. In a purely resistive circuit, current and voltage rise and fall at the same time. They are said to be ìinphase.î In this circuit there is no inductance, resistance andimpedance are the same. In a purely inductive circuit, current lags behind voltage by 90 degrees. Current and voltage are said to be “out of phase”. In this circuit, impedance and inductive reactance are the same. All inductive circuits have some amount of resistance. AC current will lag somewhere between a purely resistive circuit,and a purely inductive circuit. The exact amount of lag depends on the ratio of resistance and inductive reactance. The more resistive a circuit is, the closer it is to being in phase.The more inductive a circuit is, the more out of phase it is. In the following illustration, resistance and inductive reactance are equal. Current lags voltage by 45 degrees. When working with a circuit containing elements of inductance,capacitance, and resistance, impedance must becalculated. Because electrical concepts deal with trigonometric functions, this is not a simple matter of subtraction and addition. The following formula is used to calculate impedance in an inductive circuit: In the circuit illustrated above, resistance and inductive reactance are each 10 ohms. Impedance is 14.1421 ohms. A simple application of Ohmís Law can be used to find total circuit current. VECTORS: Another way to represent this is with a vector. A vector is a graphic representation of a quantity that has direction and 50 miles southwest from another. The magnitude is 50 miles,and the direction is southwest. Vectors are also used to show electrical relationships. As mentioned earlier, impedance (Z) is the total oppositon to current flow in an AC circuit containing resistance, inductance, and capacitance. The following vector illustrates the relationship between resistance and inductive reactance of a circuit containing equal values of each. The angle between the vectors is the phase angle represented by the symbol q. When inductive reactance is equal to resistance the resultant angle is 45 degrees. It is this angle that determines how much current will lag voltage. CAPACITANCE REACTANCE: Capacitance also opposes AC current flow. Capacitive reactance is designated by the symbol XC. The larger the capacitor,the smaller the capacitive reactance. Current flow in a capacitive AC circuit is also dependent on frequency. Thefollowing formula is used to calculate capacitive reactance: Xc = 1/2 x 3.14 x f x C Capacitive reactance is equal to 1 divided by 2 times pi, times the frequency, times the capacitance. In a 60 hertz, 10 volt circuit containing a 10 microfarad capacitor the capacitivereactance would be: Xc = 1/2 x 3.14 x f x C = 1/(2 x 3.14 x 60 x 0.000010) = 265.39 ohms Once capacitive reactance is known, Ohmís Law can be used to calculate reactive current. I = E/Z = 10/ 265.39 = 0.0376 amps PHASE RELATIONSHIP BETWEEN CURRENT AND VOLTAGE IN AN CAPACITIVE CIRCUIT: The phase relationship between current and voltage are opposite to the phase relationship of an inductive circuit. In a purely capacitive circuit, current leads voltage by 90 degrees.All capacitive circuits have some amount of resistance. AC current will lead somewhere between a purely resistive circuit and a purely capacitive circuit. The exact amount of lead depends on the ratio of resistance and capacitive reactance.The more resistive a circuit is, the closer it is to being in phase. The more capacitive a circuit is, the more out of phase it is. In the following illustration, resistance and capacitive reactance are equal. Current leads voltage by45 degrees. CALCULATING IMPEDENCE IN A CAPACITIVE CIRCUIT: The following formula is used to calculate impedence in a capacitive circuit In the cirucuit illustrated above, resistance and capacitivef reactance are each 10 ohms. Impedence is 14.1421 ohms. The following vector illustrates the relationship betweenresistance and capacitive reactance of a circuit containingequal values of each. The angle between the vectors is thephase angle represented by the symbol q. When capacitivereactance is equal to resistance the resultant angle is -45degrees. It is this angle that determines how much currentwill lead voltage. HUMIDIFICATION IMPORTANCE OF RH AND TEMPERATURE: The atmospheric conditions with respect to temperature and humidity play very important part in the manufacutring process of textile yarns and fabrics. The properties like dimensions, weight, tensile strength, elastic recovery, electrical resistance, rigidity etc. of all textile fibre whether natural or synthetic are influenced by Moisture Regain. Moisture regain is the ratio of the moisture to the bone-dry weight of the material expressed as a percentage. Many properties of textile materials vary considerably with moisture regain, which in turn is affected by the ambient Relative Humidity (RH) and Temparature. If a dry textile material is placed in a room with a particualr set of ambient conditions, it absorbs moisture and in course of time, attains an equilibrium. Some physical properties of textile materials which is affected by RH is given below: · Strength of COTTON goes up when R.H.% goes up · Strength of VISCOSE goes down when R.H.% goes up · Elongation %ge goes up with increased R.H.% for most textile fibres · the tendency for generation of static electricity due to friction decreases as RH goes up · At higher levels of RH , there is also a tendency of the fibres to stick together Temparature alone does not have a great effect on the fibres. However the temperature dictates the amount of moisture the air will hold in suspension and , therefore, temperature and humidity must be considered together. PSYCHROMETRY: psychrometrics is the study of the thermodynamic properties of air and water vapour mixture or simply the study of solubility of moisture in air at different temperatures , the associated heat contents and the method of controlling the thermal properties of air. There are various properties of moist air, they are · Dry bulb temperature · wet bulb temperature · dew point temperature · relative humidity · specific voulme · enthalpy etc.- DRY BULB TEMPERATURE: This is the temperature of air-moisture mixture as registered by an ordinary thermometer. WET BULB TEMPERATURE: It is the temperature of air-moisture mixture as registered by a thermometer where the Bulb is covered with the wetted wick. DEW POINT TEMPERATURE: This is the temperature of air at which moisture starts condensing when air is cooled. SPECIFIC HUMIDITY: This is the weight of water vapour present in unit weight of dry air. RELATIVE HUMIDITY: This is the ratio of the mass of water vapour to the mass of dry air with which the water vapour is associated to form the moist air. Relative humidity is a measure of how thirsty the air is at a given temparature. At 100%, the air is completely saturated. At 50%, the air holds one-half of what it could hold if saturated at the same temperature. The thirstier the air, the lower the percentage and the more it can rob fibres of moisture. SPECIFIC VOLUME: It is the volume per unit weight of air. ENTHALPY: It is the total heat contained in unit weight of air, taking the heat content of dry air at 0 degree centigrade. Enthalpy includes both the sensible heat and latent heat contained in the air. SENSIBLE HEAT AND LATENT HEAT: Sensible Heat is any heat that raises the temperature but not the moisture content of the substance. This is our regular and familiar every day heat. Because it raises the temperature it can be detected by the senses, and this in fact, is why it is called Sensible Heat. Latent Heat is the tricky one. When we talk of Latent Heat we mean ‘Latent Heat of Vaporisation’. It is that heat required to transform a liquid to vapour. Take water for example. Water can be heated to its boiling point of 100oC. If more heat is added at this point the temperature of the water does not increase. The water continues to boil and becomes steam. So where does all the heat go? Well, the heat goes into changing the water into steam. The latent heat of vaporisation in this instance is the heat required to change water from liquid at 100oC to vapour at the same temperature. TYPICAL AIR-CONDITIONING PROCESSES: SENSIBLE COOLING / HEATING: Involving a sensible change in the temperature of air with the specific temperature of air with the specific humidity or moisture content of air remaining the same. This process is shown as a horzontal line in Psychrometric chart as no moisutre has been added or removed from the air and the humidity ratio remains the same. The heat required to bring this change is shown below H = G(h2-h1) H = (Q/V)(h2-h1) Where, H is the rate of heat flow, kcal/h G is the mass rate of flow of air, kg/h Q is the volume rate of flow of air, meter cube / h h1,h2 are the enthalpy before and after heating, kcal/kg V is specific volume of air, meter cube/ kg COOLING AND DEHUMIDIFICATION: This is a process invoving reduction in both the dry bulb temperature and the specific humidity. If air is cooled to temperature below its dewpoint, condensation of moisture occurs. This condensation continues as long as the air is being further cooled. By noting the enthalpy of air before and after cooling, we can determine the heat to be extracted or the tonnage of refrigeration required for cooling air continuously. COOLING AND HUMDIFICATION: This is a process involving reduction in DRY BULB Temperature and increase in specific humidity. HEATING AND DEHUMIDIFICATION: This is a process where there is an increase in DRY BULB temperature and reduction in speccific humidity. LATENT HEATING: This is a process where there is only an increase in specific humidity. This is a process of steam injection. HEATING AND HUMIDIFICATION: This is the process where there is an increase in both DRY BULB temperature and specific humidity. EVAPORATIVE COOLING: This is a process of cooling and humdification but with no change in the enthalpy of air during the process. This is the process through an air-washer using recirculated water for spraying. This is the most commonly used humidification system in a textile mill. · HUMIDIFICATION – 2 · ADIABATIC SATURATION OR EVAPORATIVE COOLING: In this process air comes in direct contact with water in the air washer.There is heat and mass transfer between air and water. The humidity ratio of air increases. If the time of contact is sufficient, the air gets saturated. Latent heat of evaporation required for conversion of water into water vapor is taken from the remaining water.When equilibrium conditions are reached, water cools down to the wet bulb temperature of the air.In general it is assumed that, the wet bulb temperature and before and after the process is the same. If the air washer is ideal, the dry bulb temperature and wet bulb temperature of the air would be eqaual. If a process is adiabatic, heat is neither added or removed from the system · Dry bulb temperature of the air goes down in the process and the effect of cooling is due to the evaporation of some part of the water. That is why it is called EVAPORATIVE COOLING. · The sensible heat is decreased as the temperature goes down but the latent heat goes up as water vapour is added to the air.The latent heat required by the water which is evaporated in the air is drawn from the sensible heat of the same air.Thus it is transformation of sensible heat to latent heat. During this process the enthalpy of air remains the same. · If humidity ratios of saturated air and of the air before saturation is known, then the difference between the two would be the amount of water vapour absorbed by unit weight of dry air. · The amount of water sprayed in the air-washer to maintain misty condition can be as much as 200 times the quantity of water absorbed by the air during summer time. · AIR CONDITIONING PROCESS FOR THE TEXTILE INDUSTRY: Air is drawn in and is passed through the air washer, it gets saturated adiabatically. Since it is not saturated 100%, the dry bulb temperature of the saturated air will be 1 degree greater than WBT. · When this air is admitted into the conditioned space, it gets heated due to the heat load of the room. During this heating process the air does not lose or gain any moisture as latent heat load is absent. The air displaces an equal amount of air in the room which is pushed outside the room. · If we know the heat load of the room, we can easily calculate the rate of flow of air, G, which is the air circulation rate necessary to give the required relative humidity, from the following formula. · G = H(h2-h2) where, G-mass flow rate of dry air, KG/h H-total heat of air,Kcal/h h1-enthalpy of supply air, Kcal/kg h2-enthalpy of outgoing air,Kcal/kg · The air circulation rate is generally expressed in cubic meters per hour and not in terms of mass flow rate. (h2-h1) can be calculated from the initial and final temperatures. Therefore · H = (Q/V)* Cp * (DB2-DB1) · Where, Q-rate of air flow,metercube/h Cp- specific heat of air V-specific volume of air,metercube/kg DB1- supply air DBT,degree centigrade DB2- leaving air DBT,degree centigrade · However in practice, the air washer does not continuously supply air of 100% RH. The efficiency of air washer falls. It is considered satisfactory, if the difference between DBT and WBT of air after the air washer is 1 degree centigrade. · The following equation can be used for practical purposes. · (DB2-DB1) = ((3.39 H)/Q)+0.52 · Once the relative humidity to be maintained is decided, the quantity (DB2-DB1) is fixed. In other words, once the inside relative humidity is fixed, the minimum dry bulb temperature in the condition space is determined by the wet bulb temp. of the outside air. It is not possible to go below this DBT unless refrigeration is used. · Why refrigeration is required? · Let us assume that WBT of outside temp is 35 degrees. If the RH% to be maintained in the department is 60%, then DBT of the conditioned space should be 43.5 degrees. Whatever we do , we cannot reduce this temperature as long as we are maintaining a RH OF 60%. Underthis circumstance, refrigeration plant is required to bring down the WBT of the air inside, so that 60% RH can be maintained at lower DBT depending on the refrigeration capacity. · HUMIDIFICATION SYSTEM: Humidification system without chilling helps to maintain only the RH% without much difficulty. They can be classified generally as either unitary or central station. Central system is the most widely used sytem in the textile industry. The systems principal components are 1. Air moving devices- fans 2. mixing devices for air and washer- i.e Air washers Air moving devices are always broken into two halves, 1. Return Air fans and 2.Supply Air fans. The return air fans return the air to the plant room from where it may circulated or exhausted in the mill The supply air fans- supply air to the mill from the plant room. Air washer is a device for intimately mxing water and air. The intimate contact between these two elements is best brought about- for this application- by drawing air through a spray chamber in which atomized water is kept in transit. The following components are a must in a Humidification system · Return Air and Supply Air fans · Air washer · Return Air floor grills · Return Air trenches · Exhaust damper · Fresh air damper · Supply air ducts and grills · face and bypass dampers on the air washer · Automation control for damper operation to maintain conditions · HUMIDIFICATION – 3 · FANS: In any air handling system the fan is a key conponent. It is a device which moves the air. This is achieved by pressurising the air, the resultant pressure difference makes the air to move. Fans can be classifed as follows 1. Classification by air movement-1. centrifugal fan 2. Axial flow fan 2. Classification by housing design -1. Scroll fans 2. Tubular fans 3. Classification by pressure range- 1. high pressure 2. medium pressure and 3. low pressure 4. Classification by Blade configuration – 1.forward curved blades 2.backward curved blades From the fan laws the following relationship can be arrived · CFM is directly proportional to fan RPM · Pressure is directly proportional to sqaure of RPM · Shaft power is directly proportional to cube of RPM AIR WASHER: Basic factors that determine the size of air washer are · Velocity of air through the washer · Type of nozzle used · Water quantity in circulation · No.of spray banks The main components in an Air washer are · Distribution plates · Distribution Louvers · Water pipes · discharge headers · stand pipes · nozzles · Eliminators REFRIGERATION: Air conditioning is a process to remove the heat from the place to be conditioned and reject the heat to a place where it is not objectionable. In other words, a heat pump is required to accomplish the same. The heat pump is called the refrigeration machine. There are three types of refrigeration machines classified according to their type of operation. They are 1. vapour compression system 2. absorption system 3. vacuum Majority of the airconditioning systems used for commercial purposes work on vapour compression cycle. The main components used in the mechanical compression machines are 4. compressor 5. condenser 6. metering device 7. evaporator 8. operating controls 9. safety controls 10. accessories 11. THE COMPRESSOR: Under atmospheric temperature and pressure the refrigerant is in gaseous form. It is true that the cooling takes place when liquids evaporate to become gas. Therefore the gas refrigerant must be transformed into the liquid form. Most gasses can be made into the liquid form by raising its pressure (and cooling it, which is handled by the condenser). The equipment that increases the pressure of the gas by compressing it, is called the Compressor. Different types of compressors are 1.Reciprocating 2.Centrifugal 3.Rotary and 4.screw THE CONDENSER: During compression however the refrigerant becomes hot. This is because of two reasons: 12. Because of the work done on it (remember how warm the hand pump became when pumping air into your bicycle tires?) and 13. Because the refrigerant is converted from gas to liquid releasing its latent heat This heat has to be removed to enable the gas to condense into a liquid easily. The equipment that removes the heat is called the Condenser. Different types are 1.Air cooled 2.water cooled and 3.evaporative condenser EVAPORATOR: The Evaporator (‘Cooling Coil’ to most of us): From the condenser we now have the liquid refrigerant ready to go to work. This refrigerant can remove heat when it starts evaporating. The liquid refrigerant from the condenser is injected through a metering device called the capillary or expansion valve into the cooling coil which is a bundle of tubes. Inside the cooling coil the pressure is low, because of the metering/throttling device on one side and the compressor suction on the other side. In the low pressure, the liquid refrigerant Starts evaporating rapidly. While evaporating it needs sensible heat to transform itself from the liquid to the gas state. So it soaks up heat from the surrounding tubes, and from the air, with which the tubes are in contact. This is what causes the cooling. COMPRESSED AIR – Textile industry INTRODUCTION: English word Pneumatic is derived from the greek word ‘pneuma’ meaning “breath”.Pneumatic control system operate on a supply of compressed air, which must be made available in sufficient quantity and at a pressure to suit the capacity of the system. A compressor is a machine which takes in air, gas or vapors at a certain pressure and delivers the fluid at a higher pressure. Everything on earth is subjected to the absolute atmospheric pressure(pa), this pressure cannot be felt.The prevailing atmospheric pressure is therefore regarded as the base and any deviation is termed “gauge pressure”. Absolute pressure = Atmospheric pressure + gauge pressure Absolute pressure is approximately one bar greater than the gauge pressure. Charecteristics of interest on a compressor are, Delivery volume or capacity of the compressor Compression ratio Compressor capacity is usually expressed as air volume at ambient conditions at the compressor intake, namely in units of metercube per minute or litres per minute. Compression ratio is expressed by the discharge pressure measured in the generally accepted unit of bars. Compressors should be installed in a separate room. Special care is required to ensure that the compressors will be able to take in air that is preferably cool but above all dry and substantially dustfree. At locations where clean suction air is not available, the installation of a separate intake filter can answer this requirement. Piping leading from the filter to the compressor intake should be amply dimensioned. In this way it is also possible for clean suction air to be supplied to a multiple number of compressors via a common intake duct. Unnecessary costs in the production of compressed air can be avoided by functional and expert planning Clean condition of the suction air is one of the factors decisive to life of a compressor. Warm and moist suction air will result in increased precipitation of condensate from the compressed air. The amount of moisture condensing out of compressed air is a function of the relative humidity of the intake air and the temperature. Relative humidity is the amount of water vapor present in a given volume of air, whereas the humidity at saturation is the total amount of water vapor which that same volume of air can absorb at the given temperature. One metercube of compressed air is only capable of holding the same amount of water vapor as one metercube of atmospheric air. Discharge pressure of the compressor should not be appreciably higher than the working pressure required for operation of the pneumatic control devices. Delivering air at higher pressure will cost more for compression and will cause higher losses at leakage points. Air receivers are instlaled directly downstream of the compressors to receive the compressed air delivered, thereby balancing out pulsations in the air flow. Mostly they are also intended to serve as storage reservoirs for the overall air mains, thus additionally helping to cool the compressed air and separate condensate before it is distributed further. In large compressor systems an aftercoller incorporating a moisture separator will be installed between compressor and receiver so that a large part of the condensate will be removed before the air enters the receiver. Size of the receiver is governed by the rate at which compressed air is consumed and the capacity of the compressor. Volumetric capacity of the receiver in metercube equals the delivery capacity of the compressor in metercube per minute.But it is cheaper to use an air receiver or accumulator whose capacity is too large than one too small. Pressure-volume product is calculated by multiplying the volumetric capacity of the receiver in liters by multiplying the volumetric capacity of the receiver in liters by the working pressure in bars. pressure-volume product = p * v Air receivers should be installed outdoors(preferably on the shady side of the building). This contributes to better cooling of the compressed air and thus better separation of condensate, while avoiding overheating of an enclosed space that might be too small. Good ventilation must be provided if the receiver is setup indoors. Air accumulators are secondary receivers installed at intermediate locations to equalise pressure variations within the system so as to ensure that operating pressure is as constant as possible for all consumers. Such intermediate accumulators should be provided for each of several consumers. Pressure drops in long lines are thus compensated and flow velocity in the piping can be maintained at the optimum. Without intermediate accumulator, sudden large consumption of air may cause temporary breakdown of line pressure, resulting in abnormally high flow velocities in the air main, excessive cooling of air, and thus increased condensation at these points. AIR MAIN is the piping system into which the compressed air is led from the receiver. It is permanently installed system of interconnected pipes carrying the air to the connections for the various consumers. Main criteria to be considered are, flow velocities pressure drop in piping tight joints throughout the main PIPE SIZE: Pipe sizing is governed by permissible flow velocity permissible pressure drop; working pressure number of flow restrictors in piping length of piping “Rate of flow”, that is the air consumption rate, is a quantity that must be determined in advance by the planning engineer. Flow velocity and pressure drop are closely related to one another. Roughness of the inside walls of piping and the number of fittings installed will also affect pressure drop. “Flow velocity” of compressed air in the mains should be between 6 and 10 m/sec. Every effort should be made to keep the velocity below 10 m/sec. Pipe elbows, valves, reducers and hose couplings cause the flow velocity to rise above the permissible figures at many points. Temporary increase in flow velocity also on actuating devices using air at a high rate. “Pressure drop” should preferably not exceed 0.1 bar. Another measure used in practice is 5% of wokring pressure. “Flow restrictions” are formed in air mains by the valves, bends and tees installed. For calculation of the inside pipe diameter such restrictions must therefore be converted to the equivalent pipe length, which is then added to the remaining pipe length of the main. Permanently installed air mains piping should be accessible from all sides. Horizontal runs of air pipe should be slope downwards 1-2 % in the direction of flow. Vertical main lines should not terminate at a consumer take-off, but should run further down so that condensate precipitated in the main will collect at the lowest point of the branch line where it can be drained off and will not pass to the consumer. Air mains are preferably constructed of steel pipe with welded joints. In the long run welds are more durable than any screwed joint. A drawback associated with welding is the formation of scale during welding, with the tendency of the weld to rust in time. The advantage of welding pipe lies in the tight sealing of joints and lower cost. Isolating valves(gate valves) must be installed to divide the air main into sections so that it will not be necessary to shutdown and depressurize the entire main when maintenance or repairs become necessary. COMPRESSED AIR – Textile industry-Page 2 WHAT IS THE COST PER CFM? Let us assume that motor service factor = 110% power factor = 0.9 A typical compressor produces 4 CFM per 1 HP 1 HP = 110% x 0.746 KW/0.9 = 0.912KW Therefore, 1 CFM =0.228KW At 0.06 $KW/HR, 1CFM = $0.0137/hr Therefore, 10 CFM over 8000 hr will cost : 10 x 8000 x 0.137 = $1096 In a typical plant, air leaks account for 20% of the total air usage !! One 1/4″ air leak will result in 100 CFM loss IMPORTANCE OF DRY COMPRESSED AIR : The atmospheric air taken in by the compressor always contains a proportion of moisture in the form of water vapour. The higher the air temperature, the greater the quantity of water vapour which it can take up, expressed in percentage of relative humidity. If the saturation point of RH 100% is reached, the water is precipitated in the form of droplets. The effects of this process can be explained by means of an example. A compressor with a delivery of 10 m /min. takes in approximately 36 litres of water with air at 7 bar pressure (at 20° C and 50% RH). Because of the compression heat, the water is first taken up completely (the absorption capacity of air increases as the temperature rises). When the air is cooled to 40° C, 5.1 litres of condensate are precipitated out immediately after the compressor. In the course of further cooling, a further 21.6 litres are precipitated out at 20° C. If this moisture is allowed to enter the pneumatic system, the consequences would be as follows: Corrosion in pipes,cylinders and other components. This increases wear and maintenance costs. The basic lubrication in the cylinders is washed out. The switching function of valves is impaired, ie., more malfunctions during the operating sequence. Contamination and damage at points where the compressed air comes directly in contact with sensitive materials (e.g. in paint-shops, food industry). Rust and scale formation within pipelines Sluggish and inconsistent operation of air valves and cylinders Freezing in exposed lines during cold weather Further condensation and possible freezing of moisture at the exhaust whenever air devices are rapidly exhausted. It therefore follows that the water must in all cases be removed from the compressed air before it can cause damage; i.e. the air must be dried. Before discussing about various types of driers, let us familiarise ourselves with a few terminologies. Dew point = Temperature at which air is saturated with water vapour (Relative Humidity 100%). Pressure dew point = Dew point at operating pressure. Atmospheric dew point = Absolute humidity of compressed air referred to dew point (relative humidity of air). The measure employed in drying of air or gases is the dew point, which is the temperature at which air is fully saturated with moisture. Cooling below the dewpoint will cause condensation of the water vapor. The lower the dew point, the less moisture the air is able to absorb or hold. Absorptive capacity of air for moisture in the form of water vapor is a function of volume and temperature only, not of pressure, but it is still necessary to consider the working pressure of the system when comparing different facilities for the dehydration of air. This brings in thet term “pressure dew point”, which means the temperature representing the dew point at the respective operating pressure. In drying air by refrigeration, pressure dew point defines the lowest air temperature attainable in the dryer at the operating pressure of the system. Another term encountered in drying of air is atmospheric dew point. This assumes that, for example, compressed air of a given volume and a given pressure dew point contains an amount of water vapor corresponding to the dew point of the air. Since the volume changes with a reduction in pressure, the dew point also changes, decreasing in accordance with the initial pressure and the corresponding proportional change of volume. Drying of compressed air can be performed by three processes Absorption Adsorption Refrigeration DRYING BY REFRIGERAION: Reduction of the dew point means that the capacity of the air to absorb moisture is reduced also.This is the principle applied in drying of air by refrigeration, the compressed air thereby being cooled to temperatures between about 1.7 and 5 degrees celcius. The equipment required for this method is a refrigerating unit and a heat exchanger. Drying by refrigeration is only suitable for pressure dew points over 0 degree celcius Adsorption drying is the most expensive method when regeneration of the adsorbent is performed with cold air, but the second cheapest with hot-air regeneration. Absorption drying costs almost as much as adsorption drying with cold air regeneration, but is comparable with the hot-air- regeneration version when the pressure dew point is allowed to increase to 17 degrees celciius. Refrigeration drying is the least expensive of these processes, running to about 13% of the cost of the most expensive method. As a general guide, the cost of drying compressed air can be placed at approximately 10 – 20 % of the cost of compressing the air. Drying by refrigeration will remove oil approx. 80%. An oil separating filter should always be installed upstream of the air consumption points. More recent designs of ultrafilters are capable of separating oil and water aerosols down to a size of 0.01 micron. Production of compressed air free from oil to the greatest extent for pneumatic applications requires the combination of either drying the air by refrigeration or production of oil-free air by non-lubricated compressor and the use of non-lubricated compressor and the use of ultrafilters in the air line. ABSORPTION DRYING: Absorption drying is purely a chemical process. Absorb is to take up a gaseous substance in a solid or liquid substance. A prefilter separates larger drops of water and oil from the compressed air. On entering the device, the compressed air is made to swirl. The drying chamber is filled with a flux(drying agent) which extracts the water drops contained in the air. The flux combines with the water and passes into the collection chamber at the bottom. In the drying chamber, the flux is slowly used up. It must therefore be replaced at regular intervals.The consumption of flux is kept smallest if the inlet temperature of the air is kept at 20 degree centigrade. The special features of the absorption process are: simple installation of the equipment low mechanical wear(no moving parts) no external energy requirement ADSORPTION DRYING: Adsorption drying is based on a physical process.Adsorption means substances are deposited on the surface of solid bodies. This process is also known as regenerative drying. The drying agent is a granual material. The porous surface of the granules are filled with liquid when the compressed air flows through. The saturated gel bed is regenerated by a simple method. Warm air is blown through the dryer and takes up the moisture. As a rule, two dryers are connected in parallel. While one of this drying the air, the other is regenerated. The capacity of gel bed is limited. Under normal conditions, it will be necessary to replace the drying agent every 2 to 3 years. PNEUMATIC CYLINDERS: The component in a pneumatic control system which performs the work or functions as the actuator is the air cylinder.An air cylinder is an operative device in which the static input energy of compressed air, i.e pneumatic power, is converted into mechanical output power by reducing the pressure of the air to that of the atmosphere. Following are the different types of pneumatic cylinders Single acting cylinders double acting cylinders special type cylinders Single acting cylinder is only capabale of performing an operating motion in one direction. Double acting cylinders are capable of performing an operation motion in both directions of piston travel. Single acting cylinders require only about half the air volume consumed by a double acting cylinder for one operating cycle. Opposed thrust or multi-position cylinders, rotary cylinders, impact cylinders etc. are some special type cylinders. CYLINDER THRUST: The thrust developed in the cylinder, that is the piston power, is a function of the piston diameter, the operating air pressure and the frictional resistance. Thrust = (piston area) * (air pressure) AIR CONSUMPTION: The eompressed air supplied to a pneumatic cylinder is consumed with its energy being converted into a power output. On reversal of the piston stroke in the cylinder, the consumed air is exhausted to the atmosphere. Air consumption = compression ratio * piston area * Stoke length compression ratio = (1.033 + operating pressure in bar)/ 1.033 PISTON VELOCITY: Factors governing the velocity of the piston are operating pressure opposing forces inside diameter length of air line between control valve and cylinder size of control valve The piston velocity may additionally be affected by any throttle or quick-exhaust valve installed. With single-acting cylinder, the advance movement can be throttled only by throttling the supply air. The return speed of a single-acting cylinder can be increased by using a QUICK EXHAUST VALVE. Fan Laws allow us to predict compressor and expansion turbine performance as their speed changes. Changing the speed of an impeller effects the pressure ratio (Head) and the flow, which in turn effects the horsepower. Speed change is the most efficient way to operate at off-design points. By observing the Fan Laws we can pick the correct speed to match an off-design point. This is particularly important when you have a variable speed driver, such as a steam turbine. Fan Laws state that the flow is directly proportional to the speed. Therefore if the speed decreases to 90% of design speed, the compressor will operate at 90% of design flow. Speed change ———Flow change The head of the compressor is proportional to the speed² or the square root of the speed. This will yield the head change. Therefore if the speed decreases to 90% of design speed, the compressor will operate at 81% head. SQRT(SPEED CHANGE ) ————Head change The power of the compressor is proportional to the speed³ or the cube root of the speed. This again will yield the power change. Therefore if the speed decreases to 90% of design speed, the compressor will operate at 73% power. cube rute(speed change )————-Power change The above reflects the relationship of flow, head and power to speed. Once again, by understanding this equation, you are able to set your compressor at the right speed to provide the most efficient operating condition. ENERGY SAVING IN COMPRESSOR: The three major areas are Compressed Air generation Compressed Air distribution Compressed Air Utilisation GENERATION: The following points to be considered The compressor type,(single stage or multi stage), capacity required and capacity utilisation Screw and centrifugal compressors are suitable for base load or full load applications but not for part load operations. Reciprocating compressors are suitable for variable loads where no-load power is 10 to 12% of the full load power. minimum and maximum pressure required type of cooling required space requirement type of capcacity control On/Off control Load and Unload Throttling control Speed control initial cost Where there are more than one compressor then modulation should be based on If all are of similar size then one compressor should handle load variation If all are of different size then smallest compressor is allowed to modulate IF all are of different type then allow screw/centrifugal compressors to run on full load In general allow the compressor whose no-load power consumption is less to modulate DISTRIBUTION: Efficient air distrubution Air Receiver installation Optimum pipe sizes Avoiding leaks and wastage Avoiding unnecessary pressurization of piping system system Proper location of moisture separators and drain valves UTILISATION: Use of blower air instead of compressed air Use of PRV for low pressure air requirement Use of electrical tools instead of pneumatic tools Replacing pneumatic conveying by mechanical conveying Avoiding misuse of compressed air Misuses such as body cleaning, liquid agitaion, floor cleaning,drying, equipement cooling, and other similar uses have to be discouraged to save compressed air and energy. DRAWFRAME TASKS OF DRAWFRAME 1. Through doubling the slivers are made even 2. doubling results in homogenization(blending) 3. through draft fibres get parallelised 4. hooks created in the card are straightened 5. through the suction ,intensive dust removal is achieved 6. autoleveller maintains absolute sliver fineness · Quality of the drawframe sliver determines the yarn quality. o Drawing is the final process of quality improvement in the spinning mill o Drafting is the process of elongating a strand of fibres, with the intention of orienting the fibres in the direction of the strand and reducing its linear density.In a roller drafting system, the strand is passed throgh a series of sets of rollers, each successive set rotating at a surface velocity greater than that of the previous set. o During drafting, the fibres must be moved relative to each other as uniformly as possible by overcoming the the cohesive friction. Uniformity implies in this context that all fibres are controllably rearranged with a shift relative to each other equal to the degree of draft. o In drawframe, the rollers are so rotated that their peripheral speed in the throughflow direction increases from roller pair to roller pair, then the drawing part of the fibres, i.e.the draft, takes place. Draft is defined as the ratio of the delivered length to the feed length or the ratio of the corresponding peripheral speeds. o Drawing apart of the fibres is effected by fibres being carried along with the roller surfaces. For this to occur, the fibres must move with the peripheral speed of hte rollers. This transfer of the roller speed to the fibres represents one of the problems of drafting operation. The transfer can be effected only by friction, but the fibre strand is fairly thick and only its outer layers have contact with the rollers, and furthermore various, non-constant forces act on the fibres. o o Roller drafting adds irregularities in the strand.Lamb states that,though an irregularity causing mechanism does exist in drafting, drafting also actually reduced the strand irregularities by breaking down the fibre groups. Drafting is accompanied by doubling on the drawframe, this offsets the added irregularity. Variance(sliver out) = Variance(sliver in) + Variance(added by m/c) In Statistics , Variance is the square of standard deviation o Two passages of drawing with eight ends creeled each time would produce a single sliver consisting of 64 ribbons of fibre in close contact with each other.In the ultimate product, each ribbon may be only a few fibres thick, and thus the materials of the input slivers are dispersed by the drawing process. The term doubling is also used to describe this aspect of drawing o o Drafting arrangement is the heart of the drawframe. The drafting arrangement should be 1. simple 2. stable design with smooth running of rollers 3. able to run at higher speeds and produce high quality product 4. flexible i.e suitable to process different materials , fibre lenths and sliver hanks 5. able to have good fibre control 6. easy to adjust o Roller drafting causes irregularities in the drafted strand since there is incomplete control of the motion of each individual fibre or fibre group.The uniformity of the drafted strand is determined by 1. draft ratio 2. roller settings 3. material characteristics 4. pressure exerted by the top roller 5. hardness of top roller 6. fluting of the bottom rollers 7. distribution of draft between the various drafting stages o drafting is affected by the following rawmaterial factors 1. no of fibres in the cross section 2. fibre fineness 3. degree of parellelisation of the fibres 4. compactness of the fibre strand 5. fibre cohesion which depends on 1. surface structure 2. crimp 3. lubrication 4. compression of the strand 5. fibre length 6. twist in the fibre 7. distribution of fibre length o 3-over-3 roller drafting arrangements with pressure bar is widely used in the modern drawframes Bigger front rollers are stable and operated at lower speeds of revolution, this necessitated pressure bar arrangement for better control of fibres. Some drawframes are with 4-over-3 drafting arrangement, but strictly speaking it behaves like a 3-over-3 drafting system except for the fact that fourth roller helps to guide the sliver directly into the delivery trumpet. o DRAFTING WAVE: Floating fibres are subject to two sets of forces acting in opposite directions. The more number of fibres which are moving slowly because of the contact with the back rollers restrain the floating fibres from accelerating. The long fibres in contact with the front rollers tend to accelerate the floating fibres to the higher speed. As the floating fibres move away from the back roller, the restraining force by back roller held fibres reduces, and the front roller influence increases. At some balance point, a fibre accelerates suddenly from low to high speed. This balance point is compounded by the laws of friction, static friction being higher than dynamic friction.When one floating fibre accelerates, the neighbouring shor fibres suddenly feel one more element tending to accelrate them and one fewer trying to restrain them. Thus there may be an avalanche effect which results in drafting wave. DRAW FRAME AUTOLEVELLER Autoleveller is an additional device which is meant for correcting the linear density variations in the delivered sliver by changing either the main draft or break draft of the drafting system, according to the feed variation. There are two types of Autolevelling systems. They are Open loop system closed loop system Most of the drawframe autolevellers are open loop auto levellers. In open loop autolevellers , sensing is done at the feeding end and the correction is done by changing either a break draft or main draft of the drafting system. In closed loop system, sensing is at the delivery side and correction is done by changing either a break draft or main draft of the drafting system. Most of the earlier card autolevellers are closed loop autolevellers. But the latest cards have sensing at the feed rollers and as well as at the delivery calender rollers. We can say , both closed loop and open loop systems are being used in such autolevellers. Open loop system is very effective, because the correction length in open loop system is many fold lower than closed loop system. But in case of closed loop system, it is confirmed that the delivered sliver is of required linear density. In case of openloop system, since the delivered material is not checked to know whether the correction has been done or not, Sliver monitor is fixed to confirm that the delivered sliver has the required linear density Let us discuss about an autoleveller system which is being used in most successful drawframes like RSB-951, RSB-D-30 etc. This system is an electronic levelling system. The major componenets in the system are Scanning roller signal converter levelling CPU servo drive(servo motor and servo leveller) Differential gear box(Planetary gear box) Function of the scanning roller is to measure the variation in the feed material. All slivers fed to the machine pass thro a pair of scanning rollers. One of the scanning roller is moveable. These scanning rollers are loaded either by a spring loading system or a pneumatic loading system. Pneumatic loading is alwyas better, because the pressure in kgs will be always same(consistent), irrespective of the sliver feed variation. But in the case of spring loaded, the pressure on scanning rollers may vary depending upon the feed variation. The variations in sliver mass of the incoming slviers displace the scanning roller. The distance moved by the scanning is proportional to the slvier mass fed. This displacement of scanning rollers are transformed into volatage by a signal converter and is fed to an Electronic Levelling processor. With analogue system, electronic levelling processor is a servo amplifier, but in the case of digital system, it a CPU. It is the Electronic Levelling processor which furnishes the correct target value to the servodrive.(servo motor and servo leveller). Delivery speed of the machine and electric signal values arrived at by the slivers fed are the two important signals for the correction. Servo drive takes the information and is converted in such a way that servomotor RPM and direction is decided for appropriate correction. Planetary gearing (Differential gearing) with its controlled output speed drives the middle and back roller. i.e. Sliver entry of the drafting system Because the servo motor RPM and direction varies according to the feed variation, and the servo motor and servo leveller generates a control speed of the planetary gearing, the required change in main draft is accomplished, compensating for the weight variation of the sliver fed. If the slivers fed are too heavy, the entry speed is reduced i.e draft increased If the slivers fed are too light, the entry speed is increaed i.e. draft reduced Delivery speed ( the front roller speed) remains constant and hence the production remains constant. POINTS TO BE CONSIDERED: Mechanical draft or nominal draft should be selected properly. Before switching on the autoleveller, gears should be selected such that, the wrapping average (linear density of sliver) should be less than plus or minus 3%. If the feed variation indicated in the A% display of sliver fed is continuously showing more than -5% or +5%, then the mechanical draft selected is not correct. If the mechanical draft selected is correct, then the indication in A% display of sliver fed should be between -5% red lamp and 0% green lamp or +5% red lamp and 0% green lamp. In other words, green lamp(0% variation indication) should be on atleast for 80% of the running time. Atuo leveller is meant for correcting continuous long term varition in the fed slvier medium term variation seldom occuring abnormal variations in the sliver fed due to deviations in carding and comber short term variations in the sliver fed variations like comber piecings Scanning rollers should be selected properly. In some drawframes like DX7-LT OR DXA7-LT, the scanning roller is same for all sliver weights and all types of material. But in case of RSB drawframes, there are different sizes of scanning rollers. It depends on sliver weight fed and the type of material processed. Scanning roller pressure is not a constant. It depends on the material being used. It is selected so that minimum A% is achieved in the sliver. For the same material if the scanning roller pressure is changed, the linear density of the delivered material will also change. Hence enough care should be taken so that whenever the pressure is changed, the wrapping should be checked and adjusted. Following are the two important parameters for Quality Levelling Levelling action point ( time of correction) Levelling intensity Both feed variation sensing and correction are being done when the machine is running (continuous process) at two different places(i.e sensing is at one place and correction is at an other place). Hence the calculated correction should be done on the corresponding defective material. This is decided by Levelling action Point. The time required for the defective material to reach teh correction point should be known and correction should be done at the right time. Levellling action point depends upon break draft main draft roller setting delivery speed DRAW FRAME AUTOLEVELLER – Page 2 Levelling Intensity is to decide the amount of draft change required to correct feed variation. The correlation between mass and volume for different fibres is not same. Therefore the levelling intensity may be different for different fibres. Levelling intensity is selected based on the following trial. Wrapping of the delivered sliver should be checked with “n”, “n+1″, “n-1″ sliver at the feeding side. The sliver weight of the delivered sliver should be same for all the three combinations or should be the minimum. This can be cheked if the sliver is checked at UT 3(uster)or premier tester 7000 for mass variatons ( U%). If Levelling correction point and levelling intensity is selected properly, then the cul length C.V% of 1 meter will be less than 0.5, if the sliver is tested in UT-3 instrument. ADVANTAGES OF AUTOLEVELLER: All variations are corrected Count C.V.% will be consistent and good, hence the yarn will be suitable for knitting Off counts will be very very less in the yarn, hence off count cuts will come down drastically in autoconers Thin places in the sliver, hence in the yarn will be low Ring frame breaks will come down, hence pneumfil waste will be less fluff in the department will be less, therefore uster cuts will be less fabric quality will be good because of lower number of fluff in the yarn labour productivity will be more machine productivity will be more idle spindles will be less RKM C.V.% will be low, because of low number of thin places. Workability in warping and weaving will be good, because of less number of thin places and lower end breaks in spinning and winding. Sliver U%, hence yarn U% will be good Production calculated will be more accurate in autoleveller drawframe compared to non autolevller drawframe Variation in Blend percentage will be very less, if both the components are autolevelled before blending, hence fabric appearance after dyeing will be excellent. IMPORTANT: As long as the autolevelling system is set properly and all the components are working properly, the above said benefits can be achieved. Otherwise, the negative impact will be very big compared to working without autoleveller. If the autoleveller malfuctions, it is better to run the machine without autoleveller. COMBER Combing is the process which is used to upgrade the raw material. It influences the following yarn quality yarn evenness strength cleanness smoothness visual appearance In addition to the above, combed cotton needs less twist than a carded yarn. TASK OF THE COMBER: To proudce an improvement in yarn quality, the comber must perform the following operation. elimination of short fibres elimination of remaining impurities elimination of neps The basic operation of the comber is to improve the mean length or staple length by removing the short fibres. Since fineness of short fibres(noil) is low, the overall micronaire of the sliver after combing is high. Because of combing, fibre parallelisation increases. Please note that this is a side effect which is not an advantage always. The high degree of parallelisation might reduce inter-fibre adhesion in the sliver to such an extent that the fibres slide apart while pulled out of the can. This may lead to sliver breaks or false draft. SEQUENCE OF OPERATION IN A COMBER Feeding, lap is fed by feed roller fed lap gripped by the nipper gripped lap is combed by circular comb detaching roller grips the combed lap and moves forward while the detaching roller delivers the material, top comb comes into action to further clean the lap While going back,nipper opens and receives a new bit of lap The rawmaterial delivered by the carding machine can not be fed directly to the comber. Lap preparation is a must A good lap fed to the comber should have Highest degree of evenness so that lap is gripped uniformly by the nipper a good parallel disposition of fibres so that long fibres will not be lost in the noil trailing hooks from carding should be fed as leading hooks to reduce long fibre loss in the noil Degree of parallelisation of lap fed to the combers should be optimum. If fibres are over parallelised lap licking will be a major problem. Because of fibre to fibre adhesion, mutual separation of layers within the sheet is very poor.Moreover the retaining power of the sheet can be strongly reduced that it is no longer able to hold back the neps as it usually does. Some of these neps also pass thro the top comb. Neppiness of the web is increased. Retaining power of the fibres results in self cleaning of the lap during combing operation. A thick sheet always exerts a greater retaining power than a thin one.To certain extent, the bite of the nipper is more effective with a higher sheet volume.On the negative side , a thick sheet always applies a strong load to the comb and this can lead to uncontrolled combing.A compromise should be struck between quality and productivity. If the sheet is more even across the width, clamping effect at the bite of the nipper will be better. Evenness of the lap is therefore of considerable significance. The most effective method of obtaining a high degree of evenness of the sheet is through more number of doublings in the web form. (as it is done in RIBBON LAP) Fibres must be presented to the comber so that leading hooks predominate in the feedstock. This influences not only the opening out of the hooks themselves, but also the cleanliness of the web.If the sheet is fed to the comber in the wrong direction, the number of neps rises markedly. Both quantity and form of fibre hooks depend mainly upon the stiffness of the fibres. This rises to the second or third power with fine fibres. Fine and long fibres will always exhibit more and longer hooks than short and coarse fibres. Accordingly, the role of fibre hooks in the spinning process becomes more significant as fibres become finer. There are two types of feeds in COMBER Forward feed (concurrent feed):Feed of the sheet into the nippers occurs while the nippers move towards the detaching roller Backward feed (counter-feed) : Feed of the sheet occurs during return of the nippers Higher Noil % always improves the imperfections in the final yarn. But the strength and other quality parameters improve upto certain noil %, further increase in noil results in quality detrioration. In backward feed, the cylinder comb combs through the fibres more often than in forward feed Therefore, the elimination of impurities and neps is always good. However the difference is usually undetectable in modern high performance combers of the latest generation. COMBER – Page 2 The FEED LENGTH has a direct influence on production rate, noil %, and the quality of combing. High feed length increases the production rate but cause deterioration in quality. Higher the quality requirement, feed length should be lower. To some extent , the feed length may be decided by the length of the fibre also. Detaching length is the distance between the bite of hte nippers and the nip of the detaching rollers. This distance direectly affects the noil %. More the detaching distance, higher the elimination of noil. Needles of the top comb have a flattened cross section and are used with a point density in the range of 22 to 32 needles per centimeter. More the needles, more the noil%. The Depth of Penetration of top comb also affects the Noil %. If the comb depth is increased by 0.5mm, approximately 2% increase in noil will occur. When the depth is increased , the main improvement in quality is seen in Neps.Over deep penetration of top comb disturbs fibre movement during piecing which will deteriorate the quality. Since the web from detaching roller is intermittent because of the intermittent functions like feeding, combing and detaching, to have a continuous web from the comber,fibre fringes are laid on the top of each other in the same way as roofting tiles. This process is called Piecing. This is a distinct source of fault in the operation of Rectinlinear Combing. The sliver produced in this way exhibits a periodic variation. As large a lap as possible with adapted lap weight which is as high and as uniform as possible must be positioned in front of the comber. The better the comber lap is prepared, the heavier the lap weight can be set on the comber and the less the resultant noil waste with the same degree of cleanliness of the yarn. The higher degree of combing out are used in order to permit final spinning of ultra-fine yarns or to increase the strength of a yarn. Reducing the lint content improves the medium staple. However, not all cottons meet these requirements. Low degree of combing out , on the other hand, frequently serve to improve purity. When the card sliver is pulled through the needle bars, these separate off foreign bodies, large neps and torn fibres. Light combing out has also been introduced to a greater extent owing to the impairments in cotton purity influenced by mechanical harvesting. Even when combing with minimum noil percentages, there is a noticeable improvement in fibre parallelsim in the sliver. Even the smoothness and shine of the yarn are improved. It must thus be anticipated that this method will become more and more popular in the future. Production of the comber is dependent upon the following N- Nips per min S- feed in mm/nip G- lap weight in g/m K- Noil percentage A- tension draft between lap and feed roller(from 1.05 to 1.1) E- efficiency Production = (E * N * S * G * (100-K) * 60 * 8) / (1000 * 1000 * A *100) ROVING FRAME Roving machine is complicated, liable to faults, causes defects, adds to production costs and delivers a product that is sensitive in both winding and unwinding. This machine is forced to use by the spinner for the following two reasons. Sliver is thick, untwisted strand that tends to be hairy and to create fly. The draft needed to convert this is around 300 to 500. Drafting arrangements of ringframes are not capable of processing this strand in a single drafting operation to create a yarn that meets all the normal demands on such yarns. Drawframe cans represent the worst conceivable mode of transport and presentation of feed material to the ring spinning frame. · TASKS OF ROVING FRAME: 1. Attenuation- drafting the sliver into roving 2. twisting the drafted strand 3. winding the twisted roving on a bobbin Fibre to fibre cohesion is less for combed slivers. Rollers in the creel can easily create false drafts. Care must be taken to ensure that the slivers are passed to the drafting arrangement without disturbance. Therefore, a perfect drive to the creel rollers is very important. · The drafting arrangement drafts the material with a draft between 5 and 15.The delivered strand is too thin to hold itself together at the exit of the front bottom roller. · Bobbin and flyer are driven separately, so that winding of the twisted strand is carried out by running the bobbin at a higher peripheral speed than the flyer. · The bobbin rail is moving up and down continuously, so that the coils must be wound closely and parallel to one another to ensure that as much as material is wound on the bobbin. · Since the diameter of the packages increases with each layer, the length of the roving per coil also will increase. Therefore the speed of movement of bobbin rail must be reduced by a small amount after each completed layer · Length delivered by the front roller is always constant. Owing to the increase in the diameter of the package for every up and down movement, the peripheral speed of package should keep on changing , to maintain the same difference in peripheral speeds between pakcage and flyer. · There are two types of drafting systems. 1. 3/3 drafting system 2. 4/4 drafting system In general 3/3 drafting system is used, but for higher draft applications 4/4 drafting system is used. · The draft often has limits not only at the upper limit (15 to 20), but also at lower limit. It is around 5 for cotton and 6 for synthetic fibres. If drafts below these lower limits are attempted, then the fibre masses to be moved are too large, the drafting resistance becomes too high and the drafting operation is difficult to control. It is advisable to keep the break draft(predarft) as low as possible, because lower breakdraft always improves roving evenness. · In general two condensers are used in the drafting arrangement. The purpose of this condensers is to bring the fibre strands together. It is difficult to control, Spread fibre masses in the drafting zone and they cause unevenness. In addion, a widely spread strand leaving the drafting arrangement leads to high fly levels and to high hairiness in the roving. The size of condensers should be selected according to the volume of the fibre sliver. · Flyer inserts twist. Each flyer rotaion creates one turn in the roving. Twist per unit length of roving depends upon the delivery rate. Turns per metre = (flyer rpm)/(delivery speed (m/min)) Higher levels of roving twist, therefore, always represent production losses in Roving frame and possible draft problems in the ring spinning machine. But very low twist levels will cause false drafts and roving breaks in the roving frame. · · Centrifugal tension is created at the bobbin surface as the layers are being wound and is created by the rotation of the package. Each coil of roving can be considered as a high-speed rotating hool of roving on which centrifugal tension increases with increasing diameter of the package. · centrifugal tension in the roving is proportional to the square of the winding surface velocity.In this context, ccentrifugal force acts in such a manner as to lift the top roving strand from the surface of the package so that the radial forces within the strand that hold the fibres together are reduced and the roving can be stressed to the point of rupture. · Breaks of this type may occur at the winding-on Point of the presser or in strands that have just been wound on the top surface of the package. This phenomenon is known as “bobbin-bursting”. This phenomenon will be prominent if the twist per inch is less or the spindle speed is extremely high when the bobbin is big. · Apart from inserting twist, the flyer has to lead the very sensitive strand from the flyer top to the package without introducing false drafts. Latest flyers have a very smooth guide tube set into one flyer leg and the other flyer leg serves to balance the flyer. The strand is completely protected against air flows and the roving is no longer pressed with considerable force against the metal of the leg, as it is in the previous designs. Frictional resistance is considerably reduced, so that the strand can be pulled through with much less force. · False twisters are used on the flyers to add false twist when the roving is being twisted between the front roller and the flyer.Because of this additional twist, the roving is strongly twisted and this reduces the breakage rate. Spinning triangle is also reduced which will reduce the fibre fly and lap formation on the front bottom roller. · Because of the false twister, the roving becomes compact which helps to increase the length wound on the bobbin. This compactness helps to increase the flyer speed also. · Roving strength is a major factor in determining winding limitations. It must be high enough for the fibres to hold together in a cohesive strand and low enough for satisfactory drafting at the spinning machine. The factors affecting roving strength are as follows: o the length, fineness, and parallelisation of fibres o the amount of twist and compactness of the roving o the uniformity of twist and linear density. · BUILDER MOTION: This device has to perform the following tasks 0. to shift the belt according to the bobbin diameter increase 1. to reverse the bobbin rail direction at top and bottom 2. to shorten the lift after each layer to form tapered ends · Shifting of the belt is under the control of the ratchet wheel. The ratchet wheel is permitted to rotate by a half tooth. The bobbin diameter increases more or less rapidly depending upon roving hank. The belt must be shifted through corresponding steps. · · The amount of shifting, which depends upon the thickness of the roving, is modified by replacement of the ratchet wheel or by other gears.If a ratchet wheel with fewer teeth is inserted, then the belt is shifted through larger steps, i.e. it moves more rapidly, and vice versa. · To form a package, the layer must be laid next to its neighbours. For that the lay-on point must continually be moved. The shift of the winding point is effected by moving the bobbin rail. This raising and lowering is done by rails.Since the package diamter is steadily increasing, the lift speed must be reduced by a small amount after each completed layer. · During winding of a package, the ratchet is rotated at every change-over.Reversal of the bobbin layer occurs little earlier for every reversal.This gives a conitnuous reduction in the lift of the rail . Thus bobbins are built with taper. FIBRE TESTING IMPORTANCE OF RAWMATERIAL IN YARN MANUFACTURING: Raw material represents about 50 to 70% of the production cost of a short-staple yarn. This fact is sufficient to indicate the significance of the rawmaterial for the yarn producer. It is not possible to use a problem-free raw material always , because cotton is a natural fibre and there are many properties which will affect the performance. If all the properties have to be good for the cotton, the rawmaterial would be too expensive. To produce a good yarn with this difficulties, an intimate knowledge of the raw material and its behaviour in processing is a must. Fibre characteristics must be classified according to a certain sequence of importance with respect to the end product and the spinning process. Moreover, such quantified characteristics must also be assessed with reference to the following · what is the ideal value? · what amount of variation is acceptable in the bale material? · what amount of variation is acceptable in the final blend Such valuable experience, which allows one to determine the most suitable use for the raw material, can only be obtained by means of a long, intensified and direct association with the raw material, the spinning process and the end product. Low cost yarn manufacture, fulfilling of all quality requirements and a controlled fibre feed with known fibre properties are necessary in order to compete on the world’s textile markets. Yarn prodcution begins with the rawmaterial in bales, whereby success or failure is determined by the fibre quality, its price and availability. Successful yarn producers optimise profits by a process oriented selection and mixing of the rawmaterial, followed by optimisation of the machine settings, production rates, operating elements, etc. Simultaneously, quality is ensured by means of a closed loop control system, which requires the application of supervisory system at spinning and spinning preparation, as well as a means of selecting the most sutable bale mix. BASIC FIBRE CHARACTERISTICS: A textile fibre is a peculiar object. It has not truly fixed length, width, thickness, shape and cross-section. Growth of natural fibres or prodction factors of manmade fibres are responsible for this situation. An individual fibre, if examined carefully, will be seen to vary in cross-sectional area along it length. This may be the result of variations in growth rate, caused by dietary, metabolic, nutrient-supply, seasonal, weather, or other factors influencing the rate of cell development in natural fibres. Surface characteristics also play some part in increasing the variablity of fibre shape. The scales of wool, the twisted arrangement of cotton, the nodes appearing at intervals along the cellulosic natural fibres etc. Following are the basic chareteristics of cotton fibre · fibre length · fineness · strength · maturity · Rigidity · fibre friction · structural features STANDARD ATMOSPHERE FOR TESTING: The atmosphere in which physical tests on textile materials are performed. It has a relative humidity of 65 + 2 per cent and a temperature of 20 + 2° C. In tropical and sub-tropical countries, an alternative standard atmosphere for testing with a relative humidity of 65 + 2 per cent and a temperature of 27 + 2° C, may be used. FIBRE LENGTH: The “length” of cotton fibres is a property of commercial value as the price is generally based on this character. To some extent it is true, as other factors being equal, longer cottons give better spinning performance than shorter ones. But the length of a cotton is an indefinite quantity, as the fibres, even in a small random bunch of a cotton, vary enormously in length. Following are the various measures of length in use in different countries · mean length · upper quartile · effective length · Modal length · 2.5% span length · 50% span length Mean length: It is the estimated quantity which theoretically signifies the arithmetic mean of the length of all the fibres present in a small but representative sample of the cotton. This quantity can be an average according to either number or weight. Upper quartile length: It is that value of length for which 75% of all the observed values are lower, and 25% higher. Effective length: It is difficult to give a clear scientific definition. It may be defined as the upper quartile of a numerical length distribution eliminated by an arbitrary construction. The fibres eliminated are shorter than half the effective length. Modal length: It is the most frequently occurring length of the fibres in the sample and it is related to mean and median for skew distributions, as exhibited by fibre length, in the follwing way. (Mode-Mean) = 3(Median-Mean) where, Median is the particular value of length above and below which exactly 50% of the fibres lie. 2.5% Span length: It is defined as the distance spanned by 2.5% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using “DIGITAL FIBROGRAPH”. 50% Span length: It is defined as the distance spanned by 50% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using “DIGITAL FIBROGRAPH”. The South India Textile Research Association (SITRA) gives the following empirical relationships to estimate the Effective Length and Mean Length from the Span Lengths. Effective length = 1.013 x 2.5% Span length + 4.39 Mean length = 1.242 x 50% Span length + 9.78 FIBRE LENGTH VARIATION: Eventhough, the long and short fibres both contribute towards the length irregularity of cotton, the short fibres are particularly responsible for increasing the waste losses, and cause unevenness and reduction in strength in the yarn spun. The relative proportions of short fibres are usually different in cottons having different mean lengths; they may even differ in two cottons having nearly the same mean fibre length, rendering one cotton more irregular than the other.It is therefore important that in addition to the fibre length of a cotton, the degree of irregularity of its length should also be known. Variability is denoted by any one of the following attributes 1. Co-efficient of variation of length (by weight or number) 2. irregularity percentage 3. Dispersion percentage and percentage of short fibres 4. Uniformity ratio Uniformity ratio is defined as the ratio of 50% span length to 2.5% span length expressed as a percentage. Several instruments and methods are available for determination of length. Following are some · shirley comb sorter · Baer sorter · A.N. Stapling apparatus · Fibrograph uniformity ration = (50% span length / 2.5% span length) x 100 uniformity index = (mean length / upper half mean length) x 100 FIBRE TESTING – 2 SHORT FIBRES: The negative effects of the presence of a high proportion of short fibres is well known. A high percentage of short fibres is usually associated with, – Increased yarn irregularity and ends dddown which reduce quality and increase processing costs – Increased number of neps and slubs whiiich is detrimental to the yarn appearance – Higher fly liberation and machine contttamination in spinning, weaving and knitting operations. – Higher wastage in combing and other oppperations. While the detrimental effects of short fibres have been well established, there is still considerable debate on what constitutes a ‘short fibre’. In the simplest way, short fibres are defined as those fibres which are less than 12 mm long. Initially, an estimate of the short fibres was made from the staple diagram obtained in the Baer Sorter method Short fibre content = (UB/OB) x 100 While such a simple definition of short fibres is perhaps adequate for characterising raw cotton samples, it is too simple a definition to use with regard to the spinning process. The setting of all spinning machines is based on either the staple length of fibres or its equivalent which does not take into account the effect of short fibres. In this regard, the concept of ‘Floating Fibre Index’ defined by Hertel (1962) can be considered to be a better parameter to consider the effect of short fibres on spinning performance. Floating fibres are defined as those fibres which are not clamped by either pair of rollers in a drafting zone. Floating Fibre Index (FFI) was defined as FFI = ((2.5% span length/mean length)-1)x(100) The proportion of short fibres has an extremely great impact on yarn quality and production. The proportion of short fibres has increased substantially in recent years due to mechanical picking and hard ginning. In most of the cases the absolute short fibre proportion is specified today as the percentage of fibres shorter than 12mm. Fibrograph is the most widely used instrument in the textile industry , some information regarding fibrograph is given below. FIBROGRAPH: Fibrograph measurements provide a relatively fast method for determining the length uniformity of the fibres in a sample of cotton in a reproducible manner. Results of fibrograph length test do not necessarily agree with those obtained by other methods for measuring lengths of cotton fibres because of the effect of fibre crimp and other factors. Fibrograph tests are more objective than commercial staple length classifications and also provide additional information on fibre length uniformity of cotoon fibres. The cotton quality information provided by these results is used in research studies and quality surveys, in checking commercial staple length classifications, in assembling bales of cotton into uniform lots, and for other purposes. Fibrograph measurements are based on the assumptions that a fibre is caught on the comb in proportion to its length as compared to toal length of all fibres in the sample and that the point of catch for a fibre is at random along its length. FIBRE FINENESS: Fibre fineness is another important quality characteristic which plays a prominent part in determining the spinning value of cottons. If the same count of yarn is spun from two varieties of cotton, the yarn spun from the variety having finer fibres will have a larger number of fibres in its cross-section and hence it will be more even and strong than that spun from the sample with coarser fibres. Fineness denotes the size of the cross-section dimensions of the fibre. AS the cross-sectional features of cotton fibres are irregular, direct determination of the area of croo-section is difficult and laborious. The Index of fineness which is more commonly used is the linear density or weight per unit length of the fibre. The unit in which this quantity is expressed varies in different parts of the world. The common unit used by many countries for cotton is microgrammes per inch and the various air-flow instruments developed for measuring fibre fineness are calibrated in this unit. Following are some methods of determining fibre fineness. · gravimetric or dimensional measurements · air-flow method · vibrating string method Some of the above methods are applicable to single fibres while the majority of them deal with a mass of fibres. As there is considerable variation in the linear density from fibre to fibre, even amongst fibres of the same seed, single fibre methods are time-consuming and laborious as a large number of fibres have to be tested to get a fairly reliable average value. It should be pointed out here that most of the fineness determinations are likely to be affected by fibre maturity, which is an another important characteristic of cotton fibres. FIBRE TESTING FIBRE ELONGATION: There are three types of elongation · Permanent elongation: the length which extended during loading did not recover during relaxation · Elastic elongation:The extensions through which the fibres does return · Breaking elongation:the maximum extension at which the yarn breaks i.e.permanent and elastic elongation together Elongation is specified as a percentage of the starting length. The elastic elongation is of deceisive importance, since textile products without elasticity would hardly be usable. They must be able to deforme, In order to withstand high loading, but they must also return to shatpe. The greater resistance to crease for wool compared to cotton arises, from the difference in their elongation. For cotton it is 6 -10% and for wool it is aroun 25 – 45%. For normal textile goods, higher elongation are neither necessary nor desirable. They make processing in the spinning mill more difficult, especially in drawing operations. FIBRE RIGIDITY: The Torsional rigidity of a fibre may be defined as the torque or twisting force required to twist 1 cm length of the fibre through 360 degrees and is proportional to the product of the modulus of rigidity and square of the area of cross-section, the constant of proportionality being dependent upon the shape of the cross-section of the fibre. The torsional rigidity of cotton has therefore been found to be very much dependent upon the gravimetric fineness of the fibres. As the rigidity of fibres is sensitive to the relative humidity of the surrounding atmosphere, it is essential that the tests are carried out in a conditional room where the relative humidity is kept constant. THE SLENDERNESS RATIO: Fibre stiffness plays a significant role mainly when rolling, revolving, twisting movements are involved. A fibre which is too stiff has difficulty adapting to the movements. It is difficult to get bound into the yarn, which results in higher hairiness. Fibres which are not stiff enough have too little springiness. They do not return to shape after deformation. They have no longitudinal resistance. In most cases this leads to formation of neps. Fibre stiffness is dependent upon fibre substance and also upon the relationship between fibre length and fibre fineness. Fibres having the same structure will be stiffer, the shorter they are. The slendernesss ratio can serve as a measure of stiffness, slender ratio = fibre length /fibre diameter Since the fibres must wind as they are bound-in during yarn formation in the ring spinning machine, the slenderness ratio also determines to some extent where the fibres will finish up.fine and/or long fibres in the middle coarse and/or short fibres at the yarn periphery. TRASH CONTENT: In additon to usuable fibres, cotton stock contains foreign matter of various kinds. This foreign material can lead to extreme disturbances during processing. Trash affects yarn and fabric quality. Cottons with two different trash contents should not be mixed together, as it will lead to processing difficulties. Optimising process paramters will be of great difficulty under this situation, therefore it is a must to know the amount of trash and the type of trash before deciding the mixing. SHIRLEY TRASH ANLAYSER: A popular trash measuring device is the Shirley Analyser, which separates trash and foreign matter from lint by mechanical methods. The result is an expression of trash as a percentage of the combined weight of trash and lint of a sample. This instrument is used · to give the exact value of waste figures and also the proportion of clean cotton and trash in the material · to select the proper processing sequence based upon the trash content · to assess the cleaning efficiency of each machine · to determine the loss of good fibre in the sequence of opening and cleaning. Stricter sliver quality requirements led to the gradual evolution of opening and cleaning machinery leading to a situation where blow room and carding machinery were designed to remove exclusively certain specific types of trash particles. This necessitated the segregation of the trash in the cotton sample to different grades determined by their size. This was achieved in the instruments like the Trash Separator and the Micro Dust Trash Analyser which could be considered as modified versions of the Shirley Analyser. The high volume instruments introduced the concept of optical methods of trash measurement which utilised video scanning trash-meters to identify areas darker than normal on a cotton sample surface. Here, the trash content was expressed as the percentage area covered by the trash particles. However in such methods, comparability with the conventional method could not be established in view of the non-uniform distribution of trash in a given cotton sample and the relatively smaller sample size to determine such a parameter. Consequently, it is yet to establish any significant name in the industry. RAW MATERIAL AS A FACTOR AFFECTING SPINNING: Fineness determines how many fibres are present in the cross-section of a yarn of particular linear density. 30 to 50 fibres are needed minimum to produce a yarn fibre fineness influences · spinning limit · yarn strength · yarn evenness · yarn fullness · drape of the fabric · lustre · handle · productivity productivity is influenced by the end breakage rate and twist per inch required in the yarn Immature fibres(unripe fibres) have neither adequate strength nor adequate longitudinal siffness. They therefore lead to the following, · loss of yarn strength · neppiness · high proportion of short fibres · varying dyeability · processing difficulties at the card and blowroom Fibre length is one among the most important characteristics. It influences · spinning limit · yarn strength · handle of the product · lustre of the product · yarn hairiness · productivity It can be assumed that fibres of under 4 – 5 mm will be lost in processing(as waste and fly). fibres upto about 12 – 15 mm do not contribute to strength but only to fullness of the yarn. But fibres above these lengths produce the other positive characteristics in the yarn. The proportion of short fibres has extremely great influence on the following parameters · spinning limit · yarn strength · handle of the product · lustre of the product · yarn hairiness · productivity FIBRE TESTING – 2 A large proportion of short fibre leads to strong fly contamination, strain on personnel, on the machines, on the work room and on the air-conditioning, and also to extreme drafting difficulties. A uniform yarn would have the same no of fibres in the cross-section, at all points along it. If the fibres themeselves have variations within themselves, then the yarn will be more irregular. If 2.5% span length of the fibre increases, the yarn strength also icreases due to the fact that there is a greater contribution by the fibre strength for the yarn strength in the case of longer fibres. Neps are small entanglements or knots of fibres. There are two types of neps. They are 1.fibre neps and 2.seed-coat neps.In general fibre neps predominate, the core of the nep consists of unripe and dead fibres. Thus it is clear that there is a relationship between neppiness and maturity index. Neppiness is also dependent on the fibre fineness, because fine fibres have less longitudinal stiffness than coarser fibres. Nature produces countless fibres, most of which are not usable for textiles because of inadequate strength. The minimum strength for a textile fibre is approximately 6gms/tex ( about 6 kn breaking length). Since blending of the fibres into the yarn is achieved mainly by twisting, and can exploit 30 to 70% of the strength of the material, a lower limit of about 3 gms/tex is finally obtained for the yarn strength, which varies linearly with the fibre strength. Low micronaire value of cotton results in higher yarn tenacity.In coarser counts the influence of micronaire to increase yarn tenacity is not as significant as fine count. Fibre strength is moisture dependent. i.e. It depends strongly upon the climatic conditions and upon the time of exposure. Strength of cotton,linen etc. increases with increasing moisture content. The most important property inflencing yarn elongation is fibre elongation.Fibre strength ranks seconds in importance as a contributor to yarn elongation. Fibre fineness influences yarn elongation only after fibre elongation and strength. Other characters such as span length, uniformity ratio, maturity etc, do not contribute significantly to the yarn elongation.Yarn elongation increases with increasing twist. Coarser yarn has higher elongation than finer yarn. Yarn elongation decreases with increasing spinning tension. Yarn elongation is also influenced by traveller weight and high variation in twist insertion. For ring yarns the number of thin places increases, as the trash content and uniformity ratio increased For rotor yarns 50%span length and bundle strength has an influence on thin places. Thick places in ringyarn is mainly affected by 50%span length, trash content and shor fibre content. The following expression helps to obtain the yarn CSP achievable at optimum twist multiplier with the available fibre properties. Lea CSP for Karded count = 280 x SQRT(FQI) + 700 – 13C Lea CSP for combed count = (280 x SQRT(FQI) + 700 – 13C)x(1+W)/100 where, FQI = LSM/F L = 50% span length(mm) S = bundle strength (g/tex) M = Maturity ratio measured by shirly FMT F = Fibre fineness (micrograms/inch) C = yarn count W = comber waste% Higher FQI values are associated with higher yarn strength in the case of carded counts but in combed count such a relationship is not noticed due to the effect of combing Higher 2.5 % span length, uniformity ratio, maturity ratio and lower trash content results in lower imperfection. FQI does not show any significant influence on the imperfection. The unevenness of carded hosiery yarn does not show any significant relationships with any of the fibre properties except the micronaire value. As the micronaire value increases, U% also increases. Increase in FQI however shows a reduction in U%. Honey-dew is the best known sticky substance on cotton fibres. This is a secretion of the cotton louse. There are other types of sticky substances also. They are given below. · honey dew – secretions · fungus and bacteria – decomposition products · vegetable substances – sugars from plant juices, leaf nectar, overprodcution of wax, · fats, oils – seed oil from ginning · pathogens · synthetic substances – defoliants, insecticides, fertilizers, oil from harvesting machines In the great majority of cases, the substance is one of a group of sugars of the most variable composition, primarily but not exclusively, fructose, glucose, saccharose, melezitose, as found, for example on sudan cotton. These saccharides are mostly, but not always, prodced by insects or the plants themselves, depending upon the influence on the plants prior to plucking. Whether or not a fibre will stick depends, not only on the quantity of the sticky coating and it composition, but also on the degree of saturation as a solution. Sugars are broken down by fermentation and by microorganisms during storage of the cotton. This occurs more quickly the higher the moisture content. During spinning of sticky cotton, the R.H.% of the air in the production are should be held as low as possible. The following table shows the degree of correlation between the various cotton fibre quality characteristics and those of the yarns into which these fibres are spun – RING SPUN YARNS yarn evenness imperfection and classimat faults breaking tenacity breaking elongation hairiness fibre length micronaire value nep, trash, leaf, microdust, fibre fragments 1/8″ breaking strength 1/8″ elongation colot/reflectance significant correlation good correlation little or no correlation The following table shows the degree of correlation between the various cotton fibre quality characteristics and those of the yarns into which these fibres are spun – ROTOR SPUUN YARNS. yarn evenness imperfections and classimat faults breaking tenacity breaking elongation hairiness fibre length micronaire value nep, leaf, trash,microdust, fibre fragments 1/8″ breaking strength 1/8″ breaking elongation color/ reflectance significant correlation good correlation little or no correlation COTTON FIBRE COTTON FIBRE GROWTH: Improvements in cotton fiber properties for textiles depend on changes in the growth and development of the fiber. · Manipulation of fiber perimeter has a potential to impact the length, micronaire, and strength of cotton fibers. The perimeter of the fiber is regulated by biological mechanisms that control the expansion characteristic of the cell wall and establish cell diameter. · Improvements in fiber quality can take many different forms. Changes in length, strength, uniformity, and fineness In one recent analysis, fiber perimeter was shown to be the single quantitative trait of the fiber that affects all other traits . Fiber perimeter is the variable that has the greatest affect on fiber elongation and strength properties. While mature dead fibers have an elliptical morphology, living fibers have a cylindrical morphology during growth and development. Geometrically, perimeter is directly determined by diameter (perimeter = diameter × p). Thus, fiber diameter is the only variable that directly affects perimeter. For this reason, understanding the biological mechanisms that regulate fiber diameter is important for the long-term improvement of cotton. · A review of the literature indicates that many researchers believe diameter is established at fiber initiation and is maintained throughout the duration of fiber development . A few studies have examined, either directly or indirectly, changes in fiber diameter during development. Some studies indicate that diameter remains constant ; while others indicate that fiber diameter increases as the fiber develops. · The first three stages occur while the fiber is alive and actively growing. Fiber initiation involves the initial isodiametric expansion of the epidermal cell above the surface of the ovule. This stage may last only a day or so for each fiber. Because there are several waves of fiber initiation across the surface of the ovule , one may find fiber initials at any time during the first 5 or 6 d post anthesis. The elongation phase encompasses the major expansion growth phase of the fiber. Depending on genotype, this stage may last for several weeks post anthesis. During this stage of development the fiber deposits a thin, expandable primary cell wall composed of a variety of carbohydrate polymers . As the fiber approaches the end of elongation, the major phase of secondary wall synthesis starts. In cotton fiber, the secondary cell wall is composed almost exclusively of cellulose. During this stage, which lasts until the boll opens (50 to 60 d post anthesis), the cell wall becomes progressively thicker and the living protoplast decreases in volume. There is a significant overlap in the timing of the elongation and secondary wall synthesis stages. Thus, fibers are simultaneously elongating and depositing secondary cell wall. · The establishment of fiber diameter is a complex process that is governed, to a certain extent, by the overall mechanism by which fibers expand. The expansion of fiber cells is governed by the same related mechanisms occurring in other walled plant cells. Most cells exhibit diffuse cell growth, in which new wall and membrane materials are added throughout the surface area of the cell. Specialized, highly elongated cells, such as root hairs and pollen tubes, expand via tip synthesis where new wall and membrane materials are added only at a specific location that becomes the growing tip of the cell. While the growth mechanisms for cotton fiber have not been fully documented, recent evidence indicates that throughout the initiation and early elongation phases of development, cotton fiber expands primarily via diffuse growth . Later in fiber development, late in cell elongation, and well into secondary cell wall synthesis (35 d post anthesis), the organization of cellular organelles is consistent with continued diffuse growth . Many cells that expand via diffuse growth exhibit increases in both cell length and diameter; but cells that exhibit tip synthesis do not exhibit increases in cell diameter . If cotton fiber expands by diffuse growth, then it is reasonable to suggest that cell diameter might increase during the cell elongation phase of development. · · Cell expansion is also regulated by the extensibility of the cell wall. For this reason, cell expansion most commonly occurs in cells that have only a primary cell wall . Primary cell walls contain low levels of cellulose. Production of the more rigid secondary cell wall usually signals the cessation of cell expansion. Secondary cell wall formation is often indicated by the development of wall birefringence. · Analyses of fiber diameter and cell wall birefringence show that fiber diameter significantly increased as fibers grew and developed secondary cell walls. Both cotton species and all the genotypes tested exhibited similar increases in diameter; however, the specific rates of change differed. Fibers continued to increase in diameter during the secondary wall synthesis stage of development, indicating that the synthesis of secondary cell wall does not coincide with the cessation of cell expansion. GINNING · The generally recommended machinery sequence at gins for spindle-picked cotton is rock and green-boll trap, feed control, tower drier, cylinder cleaner, stick machine, tower drier, cylinder cleaner, extractor feeder, gin stand, lint cleaner, lint cleaner, and press. · Cylinder cleaners use rotating spiked drums that open and clean the seedcotton by scrubbing it across a grid-rod or wire mesh screen that allows the trash to sift through. The stick machine utilizes the sling-off action of channel-type saw cylinders to extract foreign matter from the seedcotton by centrifugal force. In addition to feeding seedcotton to the gin stand, the extractor feeder cleans the cotton using the stick machine’s sling-off principle. · In some cases the extractor-feeder is a combination of a cylinder cleaner and an extractor. Sometimes an impact or revolving screen cleaner is used in addition to the second cylinder cleaner. In the impact cleaner, seedcotton is conveyed across a series of revolving, serrated disks instead of the grid-rod or wire mesh screen. · Lint cleaners at gins are mostly of the controlled-batt, saw type. In this cleaner a saw cylinder combs the fibers and extracts trash from the lint cotton by a combination of centrifugal force, scrubbing action between saw cylinder and grid bars, and gravity assisted by an air current · Seedcotton-type cleaners extract the large trash components from cotton. However, they have only a small influence on the cotton’s grade index, visible liint foreign-matter content, and fiber length distribution when compared with the lint cleaning effects. Also, the number of neps created by the entire seedcotton cleaning process is about the same as the increase caused by one saw-cylinder lint cleaner. · Most cotton gins today use one or two stages of saw-type lint cleaners. The use of too many stages of lint cleaning can reduce the market value of the bale, because the weight loss may offset any gain from grade improvement. Increasing the number of saw lint cleaners at gins, in addition to increasing the nep count and short-fiber content of the raw lint, causes problems at the spinning mill. These show up as more neps in the card web and reduced yarn strength and appearance . · Pima cotton, extra-long-staple cotton, is roller ginned to preserve its length and to minimize neps. To maintain the highest possible quality bale of pima cotton, mill-type lint cleaners were for a long time the predominant cleaner used by the roller-ginning industry. Today, various combinations of impacts, incline, and pneumatic cleaners are used in most roller-ginning plants to increase lint-cleaning capacity. COTTON FIBER QUALITY: · Two simple words, fiber quality, mean quite different things to cotton growers and to cotton processors. No after-harvest mechanisms are available to either growers or processors that can improve intrinsic fiber quality. Most cotton production research by physiologists and agronomists has been directed toward improving yields, so the few cultural-input strategies suggested for improving fiber quality during the production season are of limited validity. Thus, producers have limited alternatives in production practices that might result in fibers of acceptable quality and yield without increased production costs. Fiber processors seek to acquire the highest quality cotton at the lowest price, and attempt to meet processing requirements by blending bales with different average fiber properties. Of course, bale averages for fiber properties do not describe the fiber-quality ranges that can occur within the bales or the resulting blends. Further, the natural variability among cotton fibers unpredictably reduces the processing success for blends made up of low-priced, lower-quality fibers and high-priced, higher-quality fibers. · Blends that fail to meet processing specifications show marked increases in processing disruptions and product defects that cut into the profits of the yarn and textile manufacturers. Mill owners do not have sufficient knowledge of the role classing-office fiber properties play in determining the outcome of cotton spinning and dyeing processes. Even when a processor is able to make the connection between yarn and fabric defects and increased proportions of low-quality fibers, producers have no way of explaining why the rejected bales failed to meet processing specifications when the bale averages for important fiber properties fell within the acceptable ranges. If, on the other hand, the causes of a processing defect are unknown, neither the producer nor the processor will be able to prevent or avoid that defect in the future. Any future research that is designed to predict, prevent, or avoid low-quality cotton fibers that cause processing defects in yarn and fabric must address the interface between cotton production and cotton processing. Every bale of cotton produced in the USA crosses that interface via the USDA-AMS classing offices, which report bale averages of quantified fiber properties. Indeed, fiber-quality data reports from classing offices are designed as a common quantitative language that can be interpreted and understood by both producers and processors. But the meaning and utility of classing-office reports can vary, depending on the instrument used to evaluate. · COTTON FIBRE – 2 · · Fiber maturity is a composite of factors, including inherent genetic fineness compared with the perimeter or cross section achieved under prevailing growing conditions and the relative fiber cell-wall thickness and the primary -to- secondary fiber cell-wall ratio, and the time elapsed between flowering and boll opening or harvest. While all the above traits are important to varying degrees in determining processing success, none of them appear in classing-office reports. · Micronaire, which is often treated as the fiber maturity measurement in classing-office data, provides an empirical composite of fiber cross section and relative wall thickening. But laydown blends that are based solely on bale-average micronaire will vary greatly in processing properties and outcomes. Cotton physiologists who follow fiber development can discuss fiber chronological maturity in terms of days after floral anthesis. But, they must quantify the corresponding fiber physical maturity as micronaire readings for samples pooled across several plants, because valid micronaire determinations require at least 10 g of individualized fiber. · Some fiber properties, like length and single fiber strength, appear to be simple and easily understood terms. But the bale average length reported by the classing office does not describe the range or variability of fiber lengths that must be handled by the spinning equipment processing each individual fiber from the highly variable fiber population found in that bale. Even when a processing problem can be linked directly to a substandard fiber property, surprisingly little is known about the causes of variability in fiber shape and maturity. For example: · Spinners can see the results of excessive variability in fiber length or strength when manifested as yarn breaks and production halts.Knitters and weavers can see the knots and slubs or holes that reduce the value of fabrics made from defective yarns that were spun from poor-quality fibre · Inspectors of dyed fabrics can see the unacceptable color streaks and specks associated with variations in fiber maturity and the relative dye-uptake success. · The grower, ginner, and buyer can see variations in color or trash content of ginned and baled cotton. But there are no inspectors or instruments that can see or predict any of the above quality traits of fibers while they are developing in the boll. There is no definitive reference source, model, or database to which a producer can turn for information on how cultural inputs could be adapted to the prevailing growth conditions of soil fertility, water availability, and weather (temperature, for example) to produce higher quality fiber. The scattered research publications that address fiber quality, usually in conjunction with yield improvement, are confusing because their measurement protocols are not standardized and results are not reported in terms that are meaningful to either producers or processors. Thus, physiological and agronomic studies of fiber quality frequently widen, rather than bridge, the communication gap between cotton producers and processors. This overview assembles and assesses current literature citations regarding the quantitation of fiber quality and the manner in which irrigation, soil fertility, weather, and cotton genetic potential interact to modulate fiber quality. The ultimate goal is to provide access to the best answers currently available to the question of what causes the annual and regional fiber quality variations From the physiologist’s perspective, the fiber quality of a specific cotton genotype is a composite of fiber shape and maturity properties that depend on complex interactions among the genetics and physiology of the plants producing the fibers and the growth environment prevailing during the cotton production season. Fiber shape properties, particularly length and diameter, are largely dependent on genetics. Fiber maturity properties, which are dependent on deposition of photosynthate in the fiber cell wall, are more sensitive to changes in the growth environment. The effects of the growth environment on the genetic potential of a genotype modulate both shape and maturity properties to varying degrees. Anatomically, a cotton fiber is a seed hair, a single hyperelongated cell arising from the protodermal cells of the outer integument layer of the seed coat. Like all living plant cells, developing cotton fibers respond individually to fluctuations in the macro- and microenvironments. Thus, the fibers on a single seed constitute continua of fiber length, shape, cell-wall thickness, and physical maturity . Environmental variations within the plant canopy, among the individual plants, and within and among fields ensure that the fiber population in each boll, indeed on each seed, encompasses a broad range of fiber properties and that every bale of cotton contains a highly variable population of fibers. Successful processing of cotton lint depends on appropriate management during and after harvest of those highly variable fiber properties that have been shown to affect finished-product quality and manufacturing efficiency . If fiber-blending strategies and subsequent spinning and dyeing processes are to be optimized for specific end-uses and profitability, production managers in textile mills need accurate and effective descriptive and predictive quantitative measures of both the means and the ranges of these highly variable fiber properties . In the USA, the components of cotton fiber quality are usually defined as those properties reported for every bale by the classing offices of the USDA-AMS, which currently include length, length uniformity index, strength, micronaire, color as reflectance (Rd) and yellowness (+b), and trash content, all quantified by the High Volume Instrument (HVI) line. The classing offices also provide each bale with the more qualitative classers’ color and leaf grades and with estimates of preparation (degree of roughness of ginned lint) and content of extraneous matter. The naturally wide variations in fiber quality, in combination with differences in end-use requirements, result in significant variability in the value of the cotton lint to the processor. Therefore, a system of premiums and discounts has been established to denote a specified base quality. In general, cotton fiber value increases as the bulk-averaged fibers increase in whiteness (+Rd), length, strength, and micronaire; and discounts are made for both low mike (micronaire less than 3.5) and high mike (micronaire more than 4.9). Ideal fiber-quality specifications favored by processors traditionally have been summarized thusly: “as white as snow, as long as wool, as strong as steel, as fine as silk, and as cheap as hell.” These specifications are extremely difficult to incorporate into a breeding program or to set as goals for cotton producers. Fiber-classing technologies in use and being tested allow quantitation of fiber properties, improvement of standards for end-product quality, and, perhaps most importantly, creation of a fiber-quality language and system of fiber-quality measurements that can be meaningful and useful to producers and processors alike. GENE AND ENVIRONMENTAL VARIABILITY: Improvements in textile processing, particularly advances in spinning technology, have led to increased emphasis on breeding cotton for both improved yield and improved fiber properties Studies of gene action suggest that, within upland cotton genotypes there is little non-additive gene action in fiber length, strength, and fineness ; that is, genes determine those fiber properties. However, large interactions between combined annual environmental factors (primarily weather) and fiber strength suggest that environmental variability can prevent full realization of the fiber-quality potential of a cotton genotype. More recently, statistical comparisons of the relative genetic and environmental influences upon fiber strength suggest that fiber strength is determined by a few major genes, rather than by variations in the growth environment . Indeed, spatial variations of single fertility factors in the edaphic environment were found to be unrelated to fiber strength and only weakly correlated with fiber length . Genetic potential of a specific genotype is defined as the level of fiber yield or quality that could be attained under optimal growing conditions. The degree to which genetic potential is realized changes in response to environmental fluctuations such as application of water or fertilizer and the inevitable seasonal shifts such as temperature, day length, and insolation. In addition to environment-related modulations of fiber quality at the crop and whole-plant levels, significant differences in fiber properties also can be traced to variations among the shapes and maturities of fibers on a single seed and, consequently, within a given boll. EFFECT ON FIBER LENGTH: Comparisons of the fiber-length arrays from different regions on a single seed have revealed that markedly different patterns in fiber length can be found in the micropylar, middle, and chalazal regions of a cotton seed – at either end and around the middle . Mean fiber lengths were shortest at the micropylar (upper, pointed end of the seed) . The most mature fibers and the fibers having the largest perimeters also were found in the micropylar region of the seed. After hand ginning, the percentage of short fibers less than 0.5 inch or 12.7 mm long on a cotton seed was extremely low. It has been reported that, in ginned and baled cotton, the short fibers with small perimeters did not originate in the micropylar region of the seed . MEasurements of fibers from micropylar and chalazal regions of seeds revealed that the location of a seed within the boll was related to the magnitude of the differences in the properties of fibers from the micropylar and chalazal regions. Significant variations in fiber maturity also can be related to the seed position (apical, medial, or due to the variability inherent in cotton fiber, there is no absolute value for fiber length within a genotype or within a test sample . Even on a single seed, fiber lengths vary significantly because the longer fibers occur at the chalazal (cup-shaped, lower) end of the seed and the shorter fibers are found at the micropylar (pointed) end. Coefficients of fiber-length variation, which also vary significantly from sample to sample, are on the order of 40% for upland cotton. Variations in fiber length attributable to genotype and fiber location on the seed are modulated by factors in the micro- and macroenvironment . Environmental changes occurring around the time of floral anthesis may limit fiber initiation or retard the onset of fiber elongation. Suboptimal environmental conditions during the fiber elongation phase may decrease the rate of elongation or shorten the elongation period so that the genotypic potential for fiber length is not fully realized . Further, the results of environmental stresses and the corresponding physiological responses to the growth environment may become evident at a stage in fiber development that is offset in time from the occurrence of the stressful conditions. Fiber lengths on individual seeds can be determined while the fibers are still attached to the seed , by hand stapling or by photoelectric measurement after ginning. Traditionally, staple lengths have been measured and reported to the nearest 32nd of an inch or to the nearest millimeter. The four upland staple classes are: short (<21 mm), medium (22-25 mm), medium-long (26-28 mm) and long (29-34 mm). Pima staple length is classed as long (29-34 mm) and extra-long (>34 mm). Additionally, short fiber content is defined as the percentage of fiber less than 12.7 mm. Cotton buyers and processors used the term staple length long before development of quantitative methods for measuring fiber properties. Consequently, staple length has never been formally defined in terms of a statistically valid length distribution. In Fibrograph testing, fibers are randomly caught on combs, and the beard formed by the captured fibers is scanned photoelectrically from base to tip . The amount of light passing through the beard is a measure of the number of fibers that extend various distances from the combs. Data are recorded as span length (the distance spanned by a specific percentage of fibers in the test beard). Span lengths are usually reported as 2.5 and 50%. The 2.5% span length is the basis for machine settings at various stages during fiber processing. The uniformity ratio is the ratio between the two span lengths expressed as a percentage of the longer length. The Fibrograph provides a relatively fast method for reproducibility in measuring the length and length uniformity of fiber samples. Fibrograph test data are used in research studies, in qualitative surveys such as those checking commercial staple-length classifications, and in assembling cotton bales into uniform lots. Since 1980, USDA-AMS classing offices have relied almost entirely on high-volume instrumentation (HVI) for measuring fiber length and other fiber properties (Moore, 1996). The HVI length analyzer determines length parameters by photoelectrically scanning a test beard that is selected by a specimen loader and prepared by a comber/brusher attachment The fibers in the test beard are assumed to be uniform in cross-section, but this is a false assumption because the cross section of each individual fiber in the beard varies significantly from tip to tip. The HVI fiber-length data are converted into the percentage of the total number of fibers present at each length value and into other length parameters, such as mean length, upper-half mean length, and length uniformity . This test method for determining cotton fiber length is considered acceptable for testing commercial shipments when the testing services use the same reference standard cotton samples. All fiber-length methods discussed above require a minimum of 5 g of ginned fibers and were developed for rapid classing of relatively large, bulk fiber samples. For analyses of small fiber samples , fiber property measurements with an electron-optical particle-sizer, the Zellweger Uster AFIS-A2 have been found to be acceptably sensitive, rapid, and reproducible. The AFIS-A2 Length and Diameter module generates values for mean fiber length by weight and mean fiber length by number, fiber length histograms, and values for upper quartile length, and for short-fiber contents by weight and by number (the percentages of fibers shorter than 12.7 mm). The AFIS-A2 Length and Diameter module also quantifies mean fiber diameter by number . Although short-fiber content is not currently included in official USDA-AMS classing office reports, short-fiber content is increasingly recognized as a fiber property comparable in importance to fiber fineness, strength, and length . The importance of short-fiber content in determining fiber-processing success, yarn properties, and fabric performance has led the post-harvest sector of the U.S. cotton industry to assign top priority to minimizing short-fiber content, whatever the causes . The perceived importance of short-fiber content to processors has led to increased demands for development and approval of a standard short-fiber content measurement that would be added to classing office HVI systems . This accepted classing office-measurement would allow inclusion of short-fiber content in the cotton valuation system. Documentation of post-ginning short-fiber content at the bale level is expected to reduce the cost of textile processing and to increase the value of the raw fiber . However, modulation of short-fiber content before harvest cannot be accomplished until the causes of increased short-fiber content are better understood. Fiber length is primarily a genetic trait, but short-fiber content is dependent upon genotype, growing conditions, and harvesting, ginning, and processing methods. Further, little is known about the levels or sources of pre-harvest short-fiber content . It is essential that geneticists and physiologists understand the underlying concepts and the practical limitations of the methods for measuring fiber length and short-fiber content so that the strong genetic component in fiber length can be separated from environmental components introduced by excessive temperatures and water or nutrient deficiencies. Genetic improvement of fiber length is fruitless if the responses of the new genotypes to the growth environment prevent full realization of the enhanced genetic potential or if the fibers produced by the new genotypes break more easily during harvesting or processing. The reported effects of several environmental factors on fiber length and short-fiber content, which are assumed to be primarily genotype-dependent, are discussed in the subsections that follow. COTTON FIBRE – 3 FIBER LENGTH AND TEMPERATURE: Maximum cotton fiber lengths were reached when night temperatures were around 19 to 20 °C, depending on the genotype . Early-stage fiber elongation was highly temperature dependent; late fiber elongation was temperature independent . Fiber length (upper-half mean length) was negatively correlated with the difference between maximum and minimum temperature. Modifications of fiber length by growth temperatures also have been observed in planting-date studies in which the later planting dates were associated with small increases in 2.5 and 50% span lengths . If the growing season is long enough and other inhibitory factors do not interfere with fiber development, early-season delays in fiber initiation and elongation may be counteracted by an extension of the elongation period . Variations in fiber length and the elongation period also were associated with relative heat-unit accumulations. Regression analyses showed that genotypes that produced longer fibers were more responsive to heat-unit accumulation levels than were genotypes that produced shorter fibers . However, the earliness of the genotype was also a factor in the relationship between fiber length (and short-fiber content by weight) and accumulated heat units . As temperature increased, the number of small motes per boll also increased. Fertilization efficiency, which was negatively correlated with small-mote frequency, also decreased. Although fiber length did not change significantly with increasing temperature, the percentage of short-fibers was lower when temperatures were higher. The apparent improvement in fiber length uniformity may be related to increased assimilate availability to the fibers because there were fewer seeds per boll. FIBER LENGTH AND WATER: Cotton water relationships and irrigation traditionally have been studied with respect to yield . Fiber length was not affected unless the water deficit was great enough to lower the yield to 700 kg ha-1. Fiber elongation was inhibited when the midday water potential was -2.5 to -2.8 mPa. Occurrence of moisture deficits during the early flowering period did not alter fiber length. However, when drought occurred later in the flowering period, fiber length was decreased . Severe water deficits during the fiber elongation stage reduce fiber length , apparently due simply to the direct mechanical and physiological processes of cell expansion. However, water availability and the duration and timing of flowering and boll set can result in complex physiological interactions between water deficits and fiber properties including length. FIBRE LENGTH AND LIGHT: Changes in the growth environment also alter canopy structure and the photon flux environment within the canopy. For example, loss of leaves and bolls from unfavorable weather (wind, hail), disease, or herbivory and compensatory regrowth can greatly affect both fiber yield and quality . The amount of light within the crop canopy is an important determinant of photosynthetic activity and, therefore, of the source-to-sink relationships that allocate photoassimilate within the canopy . Eaton and Ergle (1954) observed that reduced-light treatments increased fiber length. Shading during the first 7 d after floral anthesis resulted in a 2% increase in the 2.5% span length . Shading (or prolonged periods of cloudy weather) and seasonal shifts in day length also modulate temperature, which modifies fiber properties, including length. Commercial cotton genotypes are considered to be day-length neutral with respect to both flowering and fruiting . However, incorporation of day-length data in upland and pima fiber-quality models, based on accumulated heat units, increased the coefficients of determination for the length predictors from 30 to 54% for the upland model and from 44 to 57% for the pima model . It was found that the light wavelengths reflected from red and green mulches increased fiber length, even though plants grown under those mulches received less reflected photosynthetic flux than did plants grown with white mulches. The longest fiber was harvested from plants that received the highest far red/red ratios. FIBER LENGTH AND MINERAL NUTRITION: Studies of the mineral nutrition of cotton and the related soil chemistry usually have emphasized increased yield and fruiting efficiency . More recently, the effects of nutrient stress on boll shedding have been examined . Also, several mineral-nutrition studies have been extended to include fiber quality . Reports of fiber property trends following nutrient additions are often contradictory due to the interactive effects of genotype, climate, and soil conditions. Potassium added at the rate of 112 kg K ha-1yr-1 did not affect the 2.5% span length , when genotype was a significant factor in determining both 2.5 and 50% span lengths . Genotype was not a significant factor in Acala fiber length, but an additional 480 kg K ha-1yr-1 increased the mean fiber length . K ha-1yr-1 increased the length uniformity ratio and increased 50%, but not 2.5% span length. Genotype and the interaction, genotype-by-environment, determined the 2.5% span length. As mentioned above, fiber length is assumed to be genotype-dependent, but growth-environment fluctuations – both those resulting from seasonal and annual variability in weather conditions and those induced by cultural practices and inputs – modulate the range and mean of the fiber length population at the test sample, bale, and crop levels. Quantitation of fiber length is relatively straightforward and reproducible, and fiber length (along with micronaire) is one of the most likely fiber properties to be included when cotton production research is extended beyond yield determinations. Other fiber properties are less readily quantified, and the resulting data are not so easily understood or analyzed statistically. This is particularly true of fiber-breaking strength, which has become a crucial fiber property due to changes in spinning techniques. FIBER STRENGTH: The inherent breaking strength of individual cotton fibers is considered to be the most important factor in determining the strength of the yarn spun from those fibers . Recent developments in high-speed yarn spinning technology, specifically open-end rotor spinning systems, have shifted the fiber-quality requirements of the textile industry toward higher-strength fibers that can compensate for the decrease in yarn strength associated with open-end rotor spinning techniques. Compared with conventional ring spinning, open-end rotor-spun yarn production capacity is five times greater and, consequently, more economical. Rotor-spun yarn is more even than the ring-spun, but is 15 to 20% weaker than ring-spun yarn of the same thickness. Thus, mills using open-end rotor and friction spinning have given improved fiber strength highest priority. Length and length uniformity, followed by fiber strength and fineness, remain the most important fiber properties in determining ring-spun yarn strength. Historically, two instruments have been used to measure fiber tensile strength, the Pressley apparatus and the Stelometer . In both of these flat-bundle methods, a bundle of fibers is combed parallel and secured between two clamps. A force to try to separate the clamps is applied and gradually increased until the fiber bundle breaks. Fiber tensile strength is calculated from the ratio of the breaking load to bundle mass. Due to the natural lack of homogeneity within a population of cotton fibers, bundle fiber selection, bundle construction and, therefore, bundle mass measurements, are subject to considerable experimental error . Fiber strength, that is, the force required to break a fiber, varies along the length of the fiber, as does fiber fineness measured as perimeter, diameter, or cross section Further, the inherent variability within and among cotton fibers ensures that two fiber bundles of the same weight will not contain the same number of fibers. Also, the within-sample variability guarantees that the clamps of the strength testing apparatus will not grasp the various fibers in the bundle at precisely equivalent positions along the lengths. Thus, a normalizing length-weight factor is included in bundle strength calculations. In the textile literature, fiber strength is reported as breaking tenacity or grams of breaking load per tex, where tex is the fiber linear density in grams per kilometer . Both Pressley and stelometer breaking tenacities are reported as 1/8 in. gauge tests, the 1/8 in. (or 3.2 mm) referring to the distance between the two Pressley clamps. Flat-bundle measurements of fiber strength are considered satisfactory for acceptance testing and for research studies of the influence of genotype, environment, and processing on fiber (bundle) strength and elongation. The relationships between fiber strength and elongation and processing success also have been examined using flat-bundle strength testing methods . However cotton fiber testing today requires that procedures be rapid, reproducible, automated, and without significant operator bias. Consequently, the HVI systems used for length measurements in USDA-AMS classing offices are also used to measure the breaking strength of the same fiber bundles (beards) formed during length measurement. Originally, HVI strength tests were calibrated against the 1/8-in. gauge Pressley measurement, but the bundle-strengths of reference cottons are now established by Stelometer tests that also provide bundle elongation-percent data. Fiber bundle elongation is measured directly from the displacement of the jaws during the bundle-breaking process, and the fiber bundle strength and elongation data usually are reported together (ASTM, 1994, D 4604-86). The HVI bundle-strength measurements are reported in grams-force tex-1 and can range from 30 and above (very strong) to 20 or below (very weak). In agronomic papers, fiber strengths are normally reported as kN m kg-1, where one Newton equals 9.81 kg-force . The HVI bundle-strength and elongation-percent testing methods are satisfactory for acceptance testing and research studies when 3.0 to 3.3 g of blended fibers are available and the relative humidity of the testing room is adequately controlled. A 1% increase in relative humidity and the accompanying increase in fiber moisture content will increase the strength value by 0.2 to 0.3 g tex-1, depending on the fiber genotype and maturity. Further, classing-office HVI measurements of fiber strength do not adequately describe the variations of fiber strength along the length of the individual fibers or within the test bundle. Thus, predictions of yarn strength based on HVI bundle-strength data can be inadequate and misleading . The problem of fiber-strength variability is being addressed by improved HVI calibration methods and by computer simulations of bundle-break tests in which the simulations are based on large single-fiber strength databases of more than 20 000 single fiber long-elongation curves obtained with MANTIS . COTTON FIBRE – 4 Fiber Strength, Environment, and Genotype: Reports of stelometer measurements of fiber bundle strength are relatively rare in the refereed agronomic literature. Consequently, the interactions of environment and genotype in determining fiber strength are not as well documented as the corresponding interactions that modulate fiber length. Growth environment, and genotype response to that environment, play a part in determining fiber strength and strength variability . Early studies showed fiber strength to be significantly and positively correlated with maximum or mean growth temperature, maximum minus minimum growth temperature, and potential insolation . Increased strength was correlated with a decrease in precipitation. Minimum temperature did not affect fiber strength. All environmental variables were interrelated, and a close general association between fiber strength and environment was interpreted as indicating that fiber strength is more responsive to the growth environment than are fiber length and fineness. Other investigators reported that fiber strength was correlated with genotype only. Square removal did not affect either fiber elongation or fiber strength . Shading, leaf-pruning, and partial fruit removal decreased fiber strength . Selective square removal had no effect on fiber strength in bolls at the first, second, or third position on a fruiting branch . Fiber strength was slightly greater in bolls from the first 4 to 6 wk of flowering, compared with fibers from bolls produced by flowers opening during the last 2 wk of the flowering period . In that study, fiber strength was positively correlated with heat unit accumulation during boll development, but genotype, competition among bolls, assimilatory capacity, and variations in light environment also helped determine fiber strength. Early defoliation, at 20% open bolls, increased fiber strength and length, but the yield loss due to earlier defoliation offset any potential improvement in fiber quality . FIBER MATURITY: Of the fiber properties reported by USDA-AMS classing offices for use by the textile industry, fiber maturity is probably the least well-defined and most misunderstood. The term, fiber maturity, used in cotton marketing and processing is not an estimate of the time elapsed between floral anthesis and fiber harvest . However, such chronological maturity can be a useful concept in studies that follow fiber development and maturation with time . On the physiological and the physical bases, fiber maturity is generally accepted to be the degree (amount) of fiber cell-wall thickening relative to the diameter or fineness of the fiber . Classically, a mature fiber is a fiber in which two times the cell wall thickness equals or exceeds the diameter of the fiber cell lumen, the space enclosed by the fiber cell walls . However, this simple definition of fiber maturity is complicated by the fact that the cross section of a cotton fiber is never a perfect circle; the fiber diameter is primarily a genetic characteristic. Further, both the fiber diameter and the cell-wall thickness vary significantly along the length of the fiber. Thus, attempting to differentiate, on the basis of wall thickness, between naturally thin-walled or genetically fine fibers and truly immature fibers with thin walls greatly complicates maturity comparisons among and within genotypes. Within a single fiber sample examined by image analysis, cell-wall thickness ranged from 3.4 to 4.9 µm when lumen diameters ranged from 2.4 to 5.2 µm . Based on the cited definition of a mature fiber having a cell-wall thickness two times the lumen diameter, 90% of the 40 fibers in that sample were mature, assuming that here had been no fiber-selection bias in the measurements. Unfortunately, none of the available methods for quantifying cell-wall thickness is sufficiently rapid and reproducible to be used by agronomists, the classing offices, or fiber processors. Fiber diameter can be quantified, but diameter data are of limited use in determining fiber maturity without estimates of the relationship between lumen width and wall thickness. Instead, processors have attempted to relate fiber fineness to processing outcome. Estimating Fiber Fineness: Fiber fineness has long been recognized as an important factor in yarn strength and uniformity, properties that depend largely on the average number of fibers in the yarn cross section. Spinning larger numbers of finer fibers together results in stronger, more uniform yarns than if they had been made up of fewer, thicker fibers . However, direct determinations of biological fineness in terms of fiber or lumen diameter and cell-wall thickness are precluded by the high costs in both time and labor, the noncircular cross sections of dry cotton fibers, and the high degree of variation in fiber fineness. Advances in image analysis have improved determinations of fiber biological fineness and maturity , but fiber image analyses remain too slow and limited with respect to sample size for inclusion in the HVI-based cotton-classing process. Originally, the textile industry adopted gravimetric fiber fineness or linear density as an indicator of the fiber-spinning properties that depend on fiber fineness and maturity combined . This gravimetric fineness testing method was discontinued in 1989, but the textile linear density unit of tex persists. Tex is measured as grams per kilometer of fiber or yarn, and fiber fineness is usually expressed as millitex or micrograms per meter . Earlier, direct measurements of fiber fineness (either biological or gravimetric) subsequently were replaced by indirect fineness measurements based on the resistance of a bundle of fibers to airflow. The first indirect test method approved by ASTM for measurement of fiber maturity, lineardensity, and maturity index was the causticaire method. In that test, the resistance of a plug of cotton to airflow was measured before and after a cell-wall swelling treatment with an 18% (4.5 M) solution of NaOH (ASTM, 1991, D 2480-82). The ratio between the rate of airflow through an untreated and then treated fiber plug was taken as indication of the degree of fiber wall development. The airflow reading for the treated sample was squared and corrected for maturity to serve as an indirect estimate of linear density. Causticaire method results were found to be highly variable among laboratories, and the method never was recommended for acceptance testing before it was discontinued in 1992. The arealometer was the first dual-compression airflow instrument for estimating both fiber fineness and fiber maturity from airflow rates through untreated raw cotton (ASTM, 1976, D 1449-58; Lord and Heap, 1988). The arealometer provides an indirect measurement of the specific surface area of loose cotton fibers, that is, the external area of fibers per unit volume (approximately 200-mg samples in four to five replicates). Empirical formulae were developed for calculating the approximate maturity ratio and the average perimeter, wall thickness, and weight per inch from the specific surface area data. The precision and accuracy of arealometer determinations were sensitive to variations in sample preparation, to repeated sample handling, and to previous mechanical treatment of the fibers, e.g., conditions during harvesting, blending, and opening. The arealometer was never approved for acceptance testing, and the ASTM method was withdrawn in 1977 without replacement. The variations in biological fineness and relative maturity of cotton fibers that were described earlier cause the porous plugs used in air-compression measurements to respond differently to compression and, consequently, to airflow . The IIC-Shirley Fineness/Maturity Tester (Shirley FMT), a dual-compression instrument, was developed to compensate for this plug-variation effect (ASTM, 1994, D 3818-92). The Shirley FMT is considered suitable for research, but is not used for acceptance testing due to low precision and accuracy. Instead, micronaire has become the standard estimate of both fineness and maturity in the USDA-AMS classing offices. Fiber Maturity and Environment: Whatever the direct or indirect method used for estimating fiber maturity, the fiber property being as sayed remains the thickness of the cell wall. The primary cell wall and cuticle (together »0.1 µm thick) make up about 2.4% of the total wall thickness ( »4.1 µm of the cotton fiber thickness at harvest) . The rest of the fiber cell wall (»98%) is the cellulosic secondary wall, which thickens significantly as polymerized photosynthate is deposited during fiber maturation. Therefore, any environmental factor that affects photosynthetic C fixation and cellulose synthesis will also modulate cotton fiber wall thickening and, consequently, fiber physiological maturation Fiber Maturity and Temperature and Planting Date: The dilution, on a weight basis, of the chemically complex primary cell wall by secondary-wall cellulose has been followed with X-ray fluorescence spectroscopy. This technique determines the decrease, with time, in the relative weight ratio of the Ca associated with the pectin-rich primary wall . Growth-environment differences between the two years of the studies cited significantly altered maturation rates, which were quantified as rate of Ca weight-dilution, of both upland and pima genotypes. The rates of secondary wall deposition in both upland and pima genotypes were closely correlated with growth temperature; that is, heat-unit accumulation . Micronaire (micronAFIS) also was found to increase linearly with time for upland and pima genotypes . The rates of micronaire increase were correlated with heat-unit accumulations . Rates of increase in fiber cross-sectional area were less linear than the corresponding micronaire-increase rates, and rates of upland and pima fiber cell-wall thickening were linear and without significant genotypic effect . Environmental modulation of fiber maturity (micronaire) by temperature was most often identified in planting- and flowering-date studies . The effects of planting date on micronaire, Shirley FMT fiber maturity ratio, and fiber fineness (in millitex) were highly significant in a South African study (Greef and Human, 1983). Although genotypic differences were detected among the three years of that study, delayed planting generally resulted in lower micronaire. The effect on fiber maturity of late planting was repeated in the Shirley FMT maturity ratio and fiber fineness data. Planting date significantly modified degree of thickening, immature fiber fraction, cross-sectional area, and micronaire (micronAFIS) of four upland genotypes that also were grown in South Carolina . In general, micronaire decreased with later planting, but early planting also reduced micronaire of Deltapine 5490, a long-season genotype, in a year when temperatures were suboptimal during the early part of the season. Harvest dates in this study also were staggered so that the length of the growing season was held constant within each year. Therefore, season-length should not have been an important factor in the relationships found between planting date and fiber maturity. COTTON FIBRE – 5 Fiber Maturity and Source-Sink Manipulation: Variations in fiber maturity were linked with source-sink modulations related to flowering date , and seed position within the bolls . However, manipulation of source-sink relationships by early-season square (floral bud) removal had no consistently significant effect on upland cotton micronaire in one study . However, selective square removal at the first, second, and third fruiting sites along the branches increased micronaire, compared with controls from which no squares had been removed beyond natural square shedding . The increases in micronaire after selective square removals were associated with increased fiber wall thickness, but not with increased strength of elongation percent. Early-season square removal did not affect fiber perimeter or wall thickness (measured by arealometer) . Partial defruiting increased micronaire and had no consistent effect on upland fiber perimeter in bolls from August flowers. Fiber Maturity and Water: Generous water availability can delay fiber maturation (cellulose deposition) by stimulating competition for assimilates between early-season bolls and vegetative growth . Adequate water also can increase the maturity of fibers from mid-season flowers by supporting photosynthetic C fixation. In a year with insufficient rainfall, initiating irrigation when the first-set bolls were 20-d old increased micronaire, but irrigation initiation at first bloom had no effect on fiber maturity. Irrigation and water-conservation effects on fiber fineness (millitex) were inconsistent between years, but both added water and mulching tended to increase fiber fineness. Aberrations in cell-wall synthesis that were correlated with drought stress have been detected and characterized by glycoconjugate analysis . An adequate water supply during the growing season allowed maturation of more bolls at upper and outer fruiting positions, but the mote counts tended to be higher in those extra bolls and the fibers within those bolls tended to be less mature . Rainfall and the associated reduction in insolation levels during the blooming period resulted in reduced fiber maturity . Irrigation method also modified micronaire levels and distributions among fruiting sites. Early-season drought resulted in fibers of greater maturity and higher micronaire in bolls at branch positions 1 and 2 on the lower branches of rainfed plants. However, reduced insolation and heavy rain reduced micronaire and increased immature fiber fractions in bolls from flowers that opened during the prolonged rain incident. Soil water deficit as well as excess may reduce micronaire if the water stress is severe or prolonged . Fiber Maturity and Genetic Improvement: Micronaire or maturity data now appear in most cotton improvement reports . In a five-parent half-diallel mating design, environment had no effect on HVI micronaire . However, a significant genotypic effect was found to be associated with differences between parents and the F1 generation and with differences among the F1 generation. The micronaire means for the parents were not significantly different, although HVI micronaire means were significantly different for the F1 generation as a group. The HVI was judged to be insufficiently sensitive for detection of the small difference in fiber maturity resulting from the crosses. In another study, F2 hybrids had finer fibers (lower micronaire) than did the parents, but the improvements were deemed too small to be of commercial value. Unlike the effects of environment on the genetic components of other fiber properties, variance in micronaire due to the genotype-by-environment interaction can reach levels expected for genetic variance in length and strength . Significant interactions were found between genetic additive variance and environmental variability for micronaire, strength, and span length in a study of 64 F2 hybrids . The strong environmental components in micronaire and fiber maturity limit the usefulness of these fiber properties in studies of genotypic differences in response to growth environment. Based on micronaire, fiber maturity, cell-wall thickness, fiber perimeter, or fiber fineness data, row spacing had either no or minimal effect on okra-leaf or normal-leaf genotypes . Early planting reduced micronaire, wall-thickness, and fiber fineness of the okra-leaf genotype in one year of that study. In another study of leaf pubescence, nectaried vs. no nectaries, and leaf shape, interactions with environment were significant but of much smaller magnitude than the interactions among traits . Micronaire means for Bt transgenic lines were higher than the micronaire means of Coker 312 and MD51ne when those genotypes were grown in Arizona . In two years out of three, micronaire means of all genotypes in this study, including the controls, exceeded 4.9; in other words, were penalty grade. This apparent undesirable environmental effect on micronaire may have been caused by a change in fiber testing methods in the one year of the three for which micronaire readings were below the upper penalty limit. Genotypic differences in bulk micronaire may either be emphasized or minimized, depending on the measurement method used . GRADE: In U.S. cotton classing, nonmandatory grade standards were first established in 1909, but compulsory upland grade standards were not set until 1915 . Official pima standards were first set in 1918. Grade is a composite assessment of three factors – color, leaf, and preparation . Color and trash (leaf and stem residues) can be quantified instrumentally, but traditional, manual cotton grade classification is still provided by USDA-AMS in addition to the instrumental HVI trash and color values. Thus, cotton grade reports are still made in terms of traditional color and leaf grades; for example, light spotted, tinged, strict low middling. Preparation: There is no approved instrumental measure of preparation – the degree of roughness/smoothness of the ginned lint. Methods of harvesting, handling, and ginning the cotton fibers produce differences in roughness that are apparent during manual inspection; but no clear correlations have been found between degree of preparation and spinning success. The frequency of tangled knots or mats of fiber (neps) may be higher in high-prep lint, and both the growth and processing environments can modulate nep frequency . However, abnormal preparation occurs in less than 0.5% of the U.S. crop during harvesting and ginning. Trash or Leaf Grade: Even under ideal field conditions, cotton lint becomes contaminated with leaf residues and other trash . Although most foreign matter is removed by cleaning processes during ginning, total trash extraction is impractical and can lower the quality of ginned fiber. In HVI cotton classing, a video scanner measures trash in raw cotton, and the trash data are reported in terms of the total trash area and trash particle counts (ASTM, D 4604-86, D 4605-86). Trash content data may be used for acceptance testing. In 1993, classer’s grade was split into color grade and leaf grade . Other factors being equal, cotton fibers mixed with the smallest amount of foreign matter have the highest value. Therefore, recent research efforts have been directed toward the development of a computer vision system that measures detailed trash and color attributes of raw cotton . The term leaf includes dried, broken plant foliage, bark, and stem particles and can be divided into two general categories: large-leaf and pin or pepper trash . Pepper trash significantly lowers the value of the cotton to the manufacturer, and is more difficult and expensive to remove than the larger pieces of trash.Other trash found in ginned cotton can include stems, burs, bark, whole seeds, seed fragments, motes (underdeveloped seeds), grass, sand, oil, and dust. The growth environment obviously affects the amount of wind-borne contaminants trapped among the fibers. Environmental factors that affect pollination and seed development determine the frequency of undersized seeds and motes. Reductions in the frequencies of motes and small-leaf trash also have been correlated with semi-smooth and super-okra leaf traits . Environment (crop year), harvest system, genotype, and second order interactions between those factors all had significant effects on leaf grade . Delayed harvest resulted in lower-grade fiber. The presence of trash particles also may affect negatively the color grade. Fiber Color: Raw fiber stock color measurements are used in controlling the color of manufactured gray, bleached, or dyed yarns and fabrics . Of the three components of cotton grade, fiber color is most directly linked to growth environment. Color measurements also are correlated with overall fiber quality so that bright (reflective, high Rd), creamy-white fibers are more mature and of higher quality than the dull, gray or yellowish fibers associated with field weathering and generally lower fiber quality . Although upland cotton fibers are naturally white to creamy-white, pre-harvest exposure to weathering and microbial action can cause fibers to darken and to lose brightness. Premature termination of fiber maturation by applications of growth regulators, frost, or drought characteristically increases the saturation of the yellow (+b) fiber-color component. Other conditions, including insect damage and foreign matter contamination, also modify fiber color. The ultimate acceptance test for fiber color, as well as for finished yarns and fabrics, is the human eye. Therefore, instrumental color measurements must be correlated closely with visual judgment. In the HVI classing system, color is quantified as the degrees of reflectance (Rd) and yellowness (+b), two of the three tri-stimulus color scales of the Nickerson-Hunter colorimeter. Fiber maturity has been associated with dye-uptake variability in finished yarn and fabric, but the color grades of raw fibers seldom have been linked to environmental factors or agronomic practices during production. Other Environmental Effects on Cotton Fiber Quality: Although not yet included in the USDA-AMS cotton fiber classing system, cotton stickiness is becoming an increasingly important problem . Two major causes of cotton stickiness are insect honeydew from whiteflies and aphids and abnormally high levels of natural plant sugars, which are often related to premature crop termination by frost or drought. Insect honeydew contamination is randomly deposited on the lint in heavy droplets and has a devastating production-halting effect on fiber processing. The cost of clearing and cleaning processing equipment halted by sticky cotton is so high that buyers have included honeydew free clauses in purchase contracts and have refused cotton from regions known to have insect-control problems. Rapid methods for instrumental detection of honeydew are under development for use in classing offices and mills . FIBER QUALITY OR FIBER YIELD? Like all agricultural commodities, the value of cotton lint responds to fluctuations in the supply-and-demand forces of the marketplace. In addition, pressure toward specific improvements in cotton fiber quality – for example, the higher fiber strength needed for today’s high-speed spinning – has been intensified as a result of technological advances in textile production and imposition of increasingly stringent quality standards for finished cotton products. Changes in fiber-quality requirements and increases in economic competition on the domestic and international levels have resulted in fiber quality becoming a value determinant equal to fiber yield . Indeed, it is the quality, not the quantity, of fibers ginned from the cotton seeds that decides the end use and economic value of a cotton crop and, consequently, determines the profit returned to both the producers and processors. Wide differences in cotton fiber quality and shifts in demand for particular fiber properties, based on end-use processing requirements, have resulted in the creation of a price schedule, specific to each crop year, that includes premiums and discounts for grade, staple length, micronaire, and strength . This price schedule is made possible by the development of rapid, quantitative methods for measuring those fiber properties considered most important for successful textile production . With the wide availability of fiber-quality data from HVI, predictive models for ginning, bale-mix selection, and fiber-processing success could be developed for textile mills . Price-analysis systems based on HVI fiber-quality data also became feasible . Quantitation, predictive modeling, and statistical analyses of what had been subjective and qualitative fiber properties are now both practical and common in textile processing and marketing. Field-production and breeding researchers, for various reasons, have failed to take full advantage of the fiber-quality quantitation methods developed for the textile industry. Most field and genetic improvement studies still focus on yield improvement while devoting little attention to fiber quality beyond obtaining bulk fiber length, strength, and micronaire averages for each treatment . Indeed, cotton crop simulation and mapping models of the effects of growth environment on cotton have been limited almost entirely to yield prediction and cultural-input management. Plant physiological studies and textile-processing models suggest that bulk fiber-property averages at the bale, module, or crop level do not describe fiber quality with sufficient precision for use in a vertical integration of cotton production and processing. More importantly, bulk fiber-property means do not adequately and quantitatively describe the variation in the fiber populations or plant metabolic responses to environmental factors during the growing season. Such pooled or averaged descriptors cannot accurately predict how the highly variable fiber populations might perform during processing. Meaningful descriptors of the effects of environment on cotton fiber quality await high-resolution examinations of the variabilities, induced and natural, in fiber-quality averages. Only then can the genetic and environmental sources of fiber-quality variability be quantified, predicted, and modulated to produce the high-quality cotton lint demanded by today’s textile industry and, ultimately, the consumer. Increased understanding of the physiological responses to the environment that interactively determine cotton fiber quality is essential. Only with such knowledge can real progress be made toward producing high yields of cotton fibers that are white as snow, as strong as steel, as fine as silk, and as uniform as genotypic responses to the environment will allow. COTTON WHAT IS COTTON?: COTTON is defined as white fibrous substance covering seeds harvested from Cotton Plant. SEED COTTON (called Kapas in India – Paruthi in Tamil)harvested from Cotton Plant. LINT COTTON (RUIA in Hindi, PANJU in Tamil) is obtained by removing the seeds in a ginning machine. LINT COTTON is spun into Yarn, which is woven or knitted into a Fabric. Researchers have found that cotton was grown more than 9000 years ago. However large scale cultivation commenced during middle of 17th Century AD. Many varieties of Cotton are cultivated mainly from 3 important genetic species of Gossipium. G. HIRSUTUM – 87% Grown in America, Africa, Asia, Australia Plant grows to a height of 2 Meters. G. BARBADENSE- 8% Grown in America, Africa & Asia. Plant grows to a height of 2.5 Meters with yellow flowers, long fibers with good quality, fibers with long staple and fineness G. Arboreum – 5% Perennial plant grows up to 2 meters with red flowers, poor quality fibers in East Africa and South East Asia. There are four other species grown in very negligible quantities. Cotton harvested from the Plant by hand – picking or machine picking is ginned to remove seeds and the lint is pressed into Bales for delivery to Spinning Mills. Cotton is Roller Ginned (RG) or Saw Ginned (SG) depending varieties and ginning practices. Cotton is cultivated in 75 Countries with an area of 32 Million Hectares. Cultivation period varies from 175 days to 225 days depending on variety. Cotton is harvested in two seasons, summer and winter seasons. Saw ginned cotton is more uniform and cleaner than Roller Ginned Cotton. But fibers quality is retained better quality in Roller Ginning than Saw Ginning which has high productivity. Cotton Fiber is having a tubular structure in twisted form. Now. researchers have developed coloured cotton also. As on date, percentage of Cotton fiber use is more than synthetic fibers. But, its share is gradually reducing. Cotton is preferred for under garments due its comfort to body skin. Synthetics have more versatile uses and advantage for Industrial purposes. PROPERTIES OF COTTON No other material is quite like cotton. It is the most important of all natural fibres, accounting for half of all the fibres used by the world’s textile industry. Cotton has many qualities that make it the best choice for countless uses: Cotton fibres have a natural twist that makes them so suitable for spinning into a very strong yarn. The ability of water to penetrate right to the core of the fibre makes it easy to remove dirt from the cotton garments, and creases are easily removed by ironing. Cotton fabric is soft and comfortable to wear close to skin because of its good moisture absorption qualities. Charges of static electricity do not build up readily on the clothes. HISTORY OF COTTON Nobody seems to know exactly when people first began to use cotton, but there is evidence that it was cultivated in India and Pakistan and in Mexico and Peru 5000 years ago. In these two widely separated parts of the world, cotton must have grown wild. Then people learned to cultivate cotton plants in their fields. In Europe, wool was the only fiber used to make clothing. Then from the Far East came tales of plants that grew “wool”. Traders claimed that cotton was the wool of tiny animals called Scythian lambs, that grew on the stalks of a plant. The stalks, each with a lamb as its flower, were said to bend over so the small sheep could graze on the grass around the plant. These fantastic stories were shown to be untrue when Arabs brought the cotton plant to Spain in Middle Ages. In the fourteenth century cotton was grown in Mediterranean countries and shipped from there to mills in the Netherlands in western Europe for spinning and weaving. Until the mid eighteenth century, cotton was not manufactured in England, because the wool manufacturers there did not want it to compete with their own product. They had managed to pass a law in 1720 making the manufacture or sale of cotton cloth illegal. When the law was finally repealed in 1736, cotton mills grew in number. In the United States though, cotton mills could not be established, as the English would not allow any of the machinery to leave the country because they feared the colonies would compete with them. But a man named Samuel Slater, who had worked in a mill in England, was able to build an American cotton mill from memory in 1790. GROWING THE COTTON Cotton plant’s leaves resemble maple leaves and flowers look very much like pink mallow flowers that grow in swampy areas. They are relatives and belong in the same plant family. Cotton is grown in about 80 countries, in a band that stretches around the world between latitudes 45 North to 30 South. For a good crop of cotton a long, sunny growing season with at least 160 frost-free days and ample water are required. Well drained, crumbly soils that can keep moisture well are the best. In most regions extra water must be supplied by irrigation. Because of it’s long growing season it is best to plant early but not before the sun has warmed the soil enough. Seedlings appear about 5 days after planting the seeds. Weeds have to be removed because they compete with seedlings for water, light and minerals and also encourage pests and diseases. The first flower buds appear after 5-6 weeks, and in another 3-5 weeks these buds become flowers. Each flower falls after only 3 days leaving behind a small seed pot, known as the boll. Children in cotton-growing areas in the South sometimes sing this song about the flowers: First day white, next day red, third day from my birth – I’m dead. Each boll contains about 30 seeds, and up to 500 000 fibres of cotton. Each fibre grows its full length in 3 weeks and for the following 4-7 weeks each fiber gets thicker as layers of cellulose build up the cell walls. While this is happening the boll matures and in about 10 weeks after flowering it splits open. The raw cotton fibres burst out to dry in the sun. As they lose water and die, each fibre collapses into what looks like a twisted ribbon. Now is time for harvesting. Most cotton is hand-picked. This is the best method of obtaining fully grown cotton because unwanted material, called “trash”, like leaves and the remains of the boll are left behind. Also the cotton that is too young to harvest is left for a second and third picking. A crop can be picked over a period of two months as the bolls ripen. Countries that are wealthy and where the land is flat enough usually pick cotton with machines – cotton harvesters. GLOBAL COTTON – VATIETIES – PLANTING AND HARVESTING PERIODS SNo Country Planting Period Harvesting Staple-mm Mike Variety 1 AFGHANISTAN APRIL-MAY OCT-DEC 26-28 4.0 ACALA 2 ARGENTINA SEPT-OCT FEB-JUNE 24-28 3.9-4.1 TOBA 3 AUSTRALIA SEPT-NOV MAR-JUNE 24-29 3.2-4.9 DPL 4 BRAZIL OCT-NOV MAR-JUNE 26-28 3.2-4.0 IAC BRAZIL PERENNIAL 32-35 3.2-4.8 MOCO 5 BURKIN JUNE-JULY NOV-DEC 25-28 3.6-4.8 ALLEN 6 CAMERRON JUNE NOV-DEC 25-28 3.8-4.3 ALLEN 7 CENTRAL AFRICA JUN-JULY NOV-DEC 25-28 3.8-4.2 ALLEN 8 CHAD JUNE NOV-DEC 25-28 3.8-4.4 ALLEN 9 CHINA APRIL-JUNE SEP-OCT 22-28 3.5-4.7 SHANDONG XINJIANG MNH-93 10 COTED IVORIE JUN-AUG OCT-JAN 24-28 2.6-4.6 ALLEN 11 EGYPT MARCH SEP-OCT 31-40 3.24.6 GIZA 12 GREECE APRIL SEPT-OCT 26-28 3.8-4.2 4S 13 INDIA APRIL-NOV SEP-NOV 16-38 2.8-7.9 SEPARATE LIST INDIA SEPT-NOV FEB-APR 14 IRAN MAR-APR SEP-NOV 26-28 3.9-4.5 COKER 15 ISRAEL APRIL SEP-OCT 26-37 3.5-4.3 ACALA PIMA 16 KAZAKSTAN APR-MAY SEP-NOV 17 MALI JUN-JUL OCT-NOV 26-27 3.7-4.5 BJA 18 MEXICO MAR-JUNE AUG-DEC 26-29 3.5-4.5 DELTAPINE 19 MOZAMBIQUE NOV-DEC APR-MAY 25-29 3.6-4.2 A637 20 NIGARIA JUL-AUG DEC-FEB 24-26 2.5-4.0 SAMARU 21 PAKISTAN APR-JUN SEP-DEC 12-33 3.5-6.0 22 PARAGUAY OCT-DEC MAR-APR 26-28 3.3-4.2 EMPIRE 23 PERU JUL-NOV FEB-AUG 29-.8 3.3-4.2 TANGUIS PIMA 24 SPAIN APR-MAY SEP-NOV 25-28 3.3-4.9 CAROLINA 25 SUDAN AUG JUN-APR 27-E0 3.8-4.2 BARAKAT ACALA 26 SYRIA APR-MAY SEP-NOV 25-29 3.8-4.8 ALEPPO 27 TAZIKSTAN APR-MAY SEP-NOV 28 TOGO JUN-JUL NOV-DEC 28-29 4.3-5.5 ALLEN 29 TURKMENISTAN APR-MAY SEP-NOV 24-29 3.5-5.5 DELTAPINE COKER 30 TURKEY APR-MAY SEP-NOV 24-28 3.5-5.5 DELTAPINE 31 UGANDA APR-JUN NOV-FEB 26-28 3.3-4.8 BAP-SATU 32 UZBEKISTAN APR-MAY SEP-NOV 24-41 3.5-4.7 33 USA APR-MAY SEP-DEC 26-40 3.8-4.5 VARIETIES 28-30 3.0-4.0 ACALA 151T 28-29 3.8-4.6 DELTAPINENC 25-28 3.2-4.6 PAYMASTER 280 27-28 3.7-4.7 STONOVILLE ST 35-40 3.5-4.5 PIMA S7 34 YEMEN AUG-SEP JUN-APR 36-40 3.5-4.9 K4 COTTON 2 Page 1 2 3 4 COTTON AND YARN QUALITY CO-RELATION: Instead of buying any cotton available at lowest price, spinning it to produce yarn of highest count possible and selling Yam at any market in random, it is advisable to locate a good market where Yarn can be sold at highest price and select a Cotton which has characteristics to spin Yarn of desired specifications for that market. ESSENTIAL CHARACTERISTICS of cotton quality and characteristics of Yarn quality of Yarn are given from detailed experimental investigations. Some of the important conclusions which help to find co-relation between Yarn quality and Cotton quality are given below · STAPLE LENGTH: If the length of fiber is longer, it can be spun into finer counts of Yarn which can fetch higher prices. It also gives stronger Yarn. · STRENGTH : Stronger fibers give stronger Yarns. Further, processing speeds can be higher so that higher productivity can be achieved with less end-breakages. · FIBER FINENESS: Finer Fibers produce finer count of Yarn and it also helps to produce stronger Yarns. · FIBER MATURITY : Mature fibers give better evenness of Yarn. There will be less end – breakages . Better dyes’ absorbency is additional benefit. · UNIFORMITY RATIO: If the ratio is higher. Yam is more even and there is reduced end-breakages. · ELONGATION :A better value of elongation will help to reduce end-breakages in spinning and hence higher productivity with low wastage of raw material. · NON-LINT CONTENT: Low percentage of Trash will reduce the process waste in Blow Room and cards. There will be less chances of Yarn defects. · SUGAR CONTENT: Higher Sugar Content will .create stickiness of fiber and create processing problem of licking in the machines. · MOISTURE CONTENT : If Moisture Content is more than standard value of 8.5%, there will be more invisable loss. If moisture is less than 8.5%, then there will be tendency for brittleness of fiber resulting in frequent Yarn breakages. · FEEL : If the feel of the Cotton is smooth, it will be produce more smooth yarn which has potential for weaving better fabric. · CLASS : Cotton having better grade in classing will produce less process waste and Yarn will have better appearance. · GREY VALUE: Rd. of calorimeter is higher it means it can reflect light better and Yam will give better appearance. · YELLOWNESS : When value of yellowness is more, the grade becomes lower and lower grades produce weaker & inferior yarns. · NEPPINESS : Neppiness may be due to entanglement of fibers in ginning process or immature fibers. Entangled fibers can be sorted out by careful processing But, Neps due to immature fiber will stay on in the end product and cause the level of Yarndefects to go higher. · An analysis can be made of Yarn properties which can be directly attributed to cotton quality. 1. YARN COUNT: Higher Count of Yarn .can be produced by longer, finer and stronger fibers. 2. C.V. of COUNT: Higher Fiber Uniformity and lower level of short fiber percentage will be beneficial to keep C.V.(Co-efficient of Variation) at lowest. 3. TENSILE STRENGTH : This is directly related to fiber strength. Longer Length of fiber will also help to produce stronger yarns. 4. C.V. OF STRENGTH : is directly related CV of fiber strength. 5. ELONGATION : Yam elongation will be beneficial for weaving efficiently. Fiber with better elongation have positive co-relation with Yarn elongation. 6. C.V. OF ELONGATION: C.V. of Yarn Elongation can be low when C.V. of fiber elongation is also low. 7. MARS VARIATION : This property directly related to fiber maturity and fiber uniformity. 8. HAIRINESS : is due to faster processing speeds and high level of very short fibers, 9. DYEING QUALITY : will defend on Evenness of Yarn and marketing of cotton fibers. 10. BRIGHTNESS : Yarn will give brighter appearance if cotton grade is higher. COTTON QUALITY SPECIFICATIONS: The most important fiber quality is Fiber Length Length Stapleclassification Length mm Length inches Spinning Count Short Less than 24 15/16 -1 Coarse Below 20 Medium 24- 28 1.1/132-1.3/32 Medium Count 20s-34s Long 28 -34 1.3/32 -1.3/8 Fine Count 34s – 60s Extra Long 34- 40 1.3/8 -1.9/16 Superfine Count 80s – 140s Notes: · Spinning Count does not depend on staple length only. It also depends on fineness and processing machinery. · Length is measured by hand stapling or Fibrograph for 2.5% Span Length · 2.5%SL (Spun Length) means at least 2.5% of total fibers have length exceeding this value. · 50% SL means at least 50% of total fibers have length exceeding this value. COTTON 3 Page 1 2 3 4 LENGTH UNIFORMITY Length Uniformity is Calculated by 50SL x 100 / 2.5 SL Significance of UR (Uniformity Radio) is given below: UR% Classification 50-55 Very Good 45-50 Good 40-45 Satisfactory 35-40 Poor Below 30 Unusable M= 50% SL UHM SL – Average value of length of Longest of 50% of Fibers UI Uniformity Index UI M/UHM Interpretation of Uniformity Index U.INDEX CLASSIFICATION UHM CLASSIFICATION Below 77 Very low Below 0.99 Short 77-99 Low 0.99-1.10 Medium 80-82 Average 1.11-1.26 Long 83-85 High Above 1.26 Extra Long Above 85 Very High Now Uniformity is measured by HVI Fiber Strength Fiber Strength, next important quality is tested using Pressley instrument and the value is given in Thousands of Pounds per Square inch. (1000 psi) For better accuracy, Stelometer is used and results are given in grams / Tex. Lately, strength is measured in HVI (High Value Instrument) and result is given in terms of grams/tex. Interpretation of Strength value is given below G/tex Classification Below 23 Weak 24-25 Medium 26-28 Average 29-30 Strong Above 31 Very Strong Strength is essential for stronger yarns and higher processing speeds. · Fiber Fineness Fiber Fineness and maturity are tested in a conjunction using Micronaire Instrument. · Finer Fibers give stronger yarns but amenable for more neppiness of Yarn due to lower maturity. · Micronaire values vary from 2.6 to 7.5 in various varieties. FINENESS AND MATURITY Usually Micronaire value is referred to evaluate fineness of Cotton and its suitability for spinning particular count of Yarn. As the value is a combined result of fineness and maturity of Cotton fiber, it cannot be interpreted, property for ascertaining its spinning Value. This value should be taken in conjunction with standard value of Calibrated Cotton value. The following table will explain that micronaire value goes up along with maturity but declines with thickness of fiber. An Egyptian variety of Cotton, three samples of High maturity. Low maturity and Medium maturity were taken and tested. Test results are given below, Maturity Micronaire Perimeter Maturity Maturity Ratio High 4.3 52.9 85.1 1.02 Medium 4.0 54.4 80.1 0.96 Low 3.9 54.7 79.3 0.95 Here, Micronaire Value of 4.3 is higher than 3.9 of low maturity cotton Another Greek Cotton was tested and results are give below High 3.8 57.0 75.1 0.88 Medium 3.5 54.9 70.7 0.84 Low 3.2 55.2 65.8 0.80 Micronaire Value of 3.8 is higher than 3.2 of low maturity cotton. Another American Cotton was tested and results are as follows High 4.1 64.4 75.9 0.87 Medium 3.4 62.1 68.0 0.80 Low 2.7 59.8 56.1 0.67 Hence, it is essential to know what Micronaire value is good for each variety of Cotton. Maturity Ratio Classification 1.00 and above Very Mature 0.95 – 1.0 Above Average 0.85 – 0.95 Mature 0.80 – 0.85 Below Average Less than 0.80 immature COTTON GRADE Cotton grade is determined by evaluating colour, leaf and ginning preparation. Higher grade cottons provide better yarn appearance and reduced process waste. Colour is determined by using Nickerson-Hunter Calorimeter. This gives values Rd (Light or Dark) and +b (Yellowness). AMERICAN UPLAND COTTONS ARE CLASSIFIED ACCORDING TO GRADES AS GIVEN BELOW WHITE COLOUR S.NO GRADE SYMBOL CODE 1 GOOD MIDDLING GM 11 2 STRICT MIDDLING SM 21 3 MIDDLING M 31 4 STRICT LOW MIDDLING SLM 41 5 LOW MIDDLING LM 51 6 STRICT GOOD ORDINARY SGO 61 7 GOOD ORDINARY GO 71 8 BELOW GRADE Similar grading is done for Light Spotted, Spotted, Tinged and Yellow Stained Cottons. PIMA cottons are graded I to 9 HOW TO BUY COTTON? COTTON BUYING is the most important function that will contribute to optimum profit of a Spinning Mill. EVALUATION of cotton quality is generally based more on experience rather than scientific testing of characteristics only. TIMING of purchase depends on comprehensive knowledge about various factors which affect the prices. CHOOSING the supplier for reliability of delivery schedules and ability to supply cotton within the prescribed range of various parameters which define the quality of Cotton. BARGAINING for lowest price depends on the buyer’s reputation for prompt payment and accept delivery without dispute irrespective of price fluctuations. ORGANISING the logistics for transportation of goods and payment for value of goods will improve the benefits arising out of the transaction. PROFIT depends on producting high quality Yarn to fetch high prices. Influence of quality of raw material is very important in producing quality Yarn. But, quality of yam is a compound effect of quality of raw material, skills of work-force, performance of machines,- process know-how of Technicians and management expertise. A good spinner is one who produces reasonably priced yarn of acceptable quality from reasonably priced fiber. Buying a high quality, high priced cotton does not necessarily result in high quality Yarn or high profits. GUIDELINES FOR COTTON CONTRACTS: Buyer and seller should clearly reach correct understanding on the following factors. 1. Country of Origin, Area of Growth, Variety, Crop year 2. Quality – Based on sample or Description of grade as per ASTM standard or sample For grade only and specifying range of staple length, Range of Micronaire, range of Pressley value, uniformity, Percentage of short fiber, percentage of non-lint content, Tolerable level of stickiness 3. Percentage of Sampling at destination 4. Procedure for settling disputes on quality or fulfillment of contract obligations. 5. Responsibility regarding contamination or stickiness. 6. Price in terms of currency, Weight and place of delivery. 7. Shipment periods 8. Certified shipment weights or landing Weights 9. Tolerances for Weights and Specifications 10. Port of Shipment and port of destination, partial shipments allowed or not, transshipment allowed or not, shipments in containers or Break-bulk carriers 11. Specifications regarding age of vessels used for shipment, freight payment in advance or on delivery 12. Responsibility regarding Import & Export duties 13. Terms of Insurance cover 14. Accurate details of Seller, Buyer and Broker 15. Terms of Letter of. Credit regarding bank .negotiation, reimbursement and special conditions, if any COTTON 4 Page 1 2 3 4 Choose Correct Supplier or Agent: Apart from ensuring correct terms of Contract, Buyer should ensure that purchase is made from Reliable Supplier or through a Reliable Agent. Some suppliers evade supplies under some pretext if the market goes up. Otherwise, they supply inferior quality Either way buyer suffers. By establishing long term relationship will reliable Suppliers, Buyers can have satisfaction of getting correct quality, timely deliveries and fair prices. CHOOSING SUPPLIER: It is good to establish long term relationship with a few Agents who represent reputed Trading Companies in various Cotton Exporting Countries. They usually give reliable market information on quality, prices and market trends so that buyer can take intelligent decision. As cotton is not a manufactured Commodity, it is good to buy from dependable suppliers, who will ensure supply of correct quality with a variation within acceptable limits at correct price and also deliver on due date. CHOOSING QUALITY: In a market with varying market demand situation. Buyers should decide which counts of Yarn to spin. Buyer can call for samples suitable for spinning Yarn counts programmed for production. Many spinners plan to do under-spinning. For Example, cotton suitable for 44s is used for spinning 40s. Some spinners do over-spinning. They buy cotton suitable for 40s and spin 44s count. But, is advisable to spin optimum count to ensure quality and also keep cost of raw material at minimum level as for as possible. Some spinners also buy 2 or more varieties and blend them for optimum spinning. For’ this purpose, a good knowledge to evaluate cotton quality and co-relate with yarn properties of required specifications. Cotton buyer should develop expertise in assessing cotton quality. Machine tests must be done only to confirm manual evaluation. TAKING RIGHT OPTION: It is not advisable just to look at price quoted by supplier. Correct costing should be done to work out actual cost when the cotton arrives at Mills. Further lowest price does not always mean highest profit for buying. Profitability may be affected by anyone or more of the following factors. · If the trash is higher, more waste will be produced reducing the Yarn out- turn and hence profit. · If the uniformity is less, end – breakages will be more reducing productivity and profitability. · If grade is poor or more immature fibers are found in cotton, the yarn appearance will be affected and Yarn will fetch lesser price in the market. · If the transit period for transport of cotton is longer, then also profitability will be reduced due blocking of funds for a longer period and increased cost of Interest. · Rate of Sales Tax varies from State to State. This must be taken in to account. · Hence, thorough costing should be worked out before deciding on the quoted pnce onlv The margin of profit in spinning cotton should be calculated before deciding on The various options available depending on market conditions should be studied. The factors to be considered for taking options are as follows. · Count for which demand is good in market · Prices for various counts for which demand exists. · Cost of manufacturing various counts. · Adequacy of machinery for the selected count. · Various varieties of cotton available for spinning the selected count. · Profit margin for each count using different varieties. · Price quoted by different Agents for same variety of selected cotton. · Reliability of supplier for quality and timely delivery. Cost Consideration: Apart from the price quoted by the seller, other incidental costs must be taken into consideration before buying. a) Duration for goods to reach Buyer’s godown from the seller’s Warehouse. If the duration is longer, buyer will incur higher interest charges. b) Cost of Transportation and taxes. Resolution of differences If any discrepancy arises in the quality, weight and delivery periods, sellers should be willing to resolve the differences amicably and quickly. In case the matter is referred to Arbitrator, the award of the Arbitrator must be immediately enforced. Bench Marks for Easy Reference It is better if quality bench marks are established for different varieties so that buying decisions are easy for buyers Following standards have been found to be appropriate for Strict Middling Grade Cotton of staple 1.3/32″. 1. Staple Length ( 2.5% Spun Length) – Minimum 1.08″ or 27.4 mm 2. Micronaire : Minimum 3.8, Maximum-4.6 Variation within bulk sample should not be more than _ 0.1 3. Colour : Rd not less than 75 not more than 10 4. Nep Content: Less than 150 per gram 5. Strength : More than 30 grams/tex 6. Length Uniformity Ratio: Not less than 85% 7. Elongation : More than 8% 8. Short Fiber Content: Less than 5% 9. Seed Count Fragments : Less than 15 per grams 1. Commercial Bench marks can be given as follows: 1. Price Competitiveness 2. Price Stability 3. Easy Availability throughout year 4. Uniform Classing and Grading system 5. Even- running Cotton in all Characteristics 6. Reliable deliveries òr Respect for sanctity of contract. QUALITY EVALUATION: The need for quality evaluation is for following purposes a) To get optimum quality at lowest price. b) To decide whether cotton bought will can be processed to spin Yarn of desired specifications. c) To check the quality of sample cotton with quality of delivered cotton. d) To decide about correct machine settings and speeds for processing the cotton e) To estimate profitability of purchase decisions. Knowing the cotton properties is only half the battle for profits. It needs expertise to know how to get best of its value. Currently popular instrument called HVI gives ready information on various parameters to make correct purchase decisions. If may not be possible to get all the desired qualities in one variety or one lot of Cotton. In such case, an intelligent decision to select best combination of different varieties or lots to get desired Yam quality is necessary to get optimum yarn quality at optimum cost. If correct evaluation is made, profits are large. Hence, evaluation of quality is essential for optimum profit making and also make the customers happy with supply of correct quality of Yarn. Expert classers can manage to achieve reasonable level of correct evaluation. Now, with availability of better instruments, it is better to check qualities to make sure that desired quality of cotton is procured. These details should give cotton buyer reasonable guidance to make correct evaluation of cotton quality and ensure its suitability for producing required quality of yarn. QUALITY EVALUATION CHARACTERISTICS CO-RELATION TO YARN 1. Staple Length Spinning Potential 2. Fiber Strength Yarn strength, less Breakages 3. Fineness Finer Spinning Potential 4. Maturity Yarn Strength and even ness, better dyeing 5. Non-Lint.content (Trash) Reduced Waste 6, Uniformity Ratio Better productivity and Evenness 7. Elongation Less end Breakages 8, Friction Cohesiveness 9. Class Yarn Appearance 10.Stickiness Spinning problem by lapping & Dyeing quality 11. Grey Value Yarn lustre 12. Yellowness Yarn Appearance 13.Neppiness Yarn neppiness 14. Moisture Content 8.5% moisture content optimum for spinning at 65% QUALITY TESTING INSTRUMENTS: Instrument Measurements Fibrogaph Length Pressley Apparatres Fiber Bundle Strength HV I Instrument Length, Strength, Uniformity, Elongation, Micronaire, Color and Trash Stelometer Instrument Strength, Elongation Micronaire Combined test of fineness & maturity Shirley Trash Analyser Trash Content Manual Test Class & staple length Moisture Meter Moisture Colorimeter Grey value & yellow ness. Brightness Polarised light Microscope orCasricaire test Maturity Photographic film Neppiness EFFECT OF COTTON PREPARATION ON AFIS AND HVI MEASUREMENTS J.L. Simonton, W.D. Cole and P. Williams International Textile Center Texas Tech University Lubbock, TXv INTORDUCTION: The basic purpose of this study is to examine the use of the AFIS and the HVI to improve performance of the spinning process. Since the various mechanical processes modify the state of the fibers, we must first determine the effects of fiber preparation on instrument readings. Cotton processing machines that mechanically work the cotton fiber from bale to yarn are designed with the intent of minimizing fiber damage. Nevertheless, opening, cleaning and blending equipment shorten the staple length while increasing short fiber content and neps. Carding and combing reverse this by removing a percentage of the short fibers and neps. Drawing is thought to have a minimal effect on fiber physicals, its purpose being to improve sliver evenness and fiber orientation. With machine settings and speeds optimized, a comparison of the fiber properties of stock-in compared with stock-out provides valuable information for achieving further optimization. PROCEDURE: · Instrument used: Uster AFIS and HVI Spinlab 900B · No. of bale samples: 10 bales with different mic and length were used · No. of processing method : 12 different processing combinations · Machineries used: Blow room: hunter hopper feeder Rieter Mono cylinder (750 rpm) Rieter ERM B5/5(850 rpm) Rieter ERM B5/5(950 rpm) Carding : Rieter C4 card with Hollingsworth Trashmaster TM2000 (100 pounds per hour, with 60 grains per yard sliver) Drawframe: Rieter RSB-851 Speed frame: Saco Lowell Rovematic FC-1B Ring spinning: Saco Lowell SF-3H Open end machine: Schlafhorst Autocoro Predrawframe for comber: Saco-Lowell DE-7C Lap former : Rieter Unilap E5/3 Comber : Rieter E7/6 DETAILS OF THE FINDINGS: · There are slight AFIS variations in the apparent fiber diameter when going from a processing stage to another. It seems that the ERMII results in a slight increase, which could be due to the removal of dead fibers in the opening line. Certainly the card also removes neps and dead fibers; however, the diameter appears to decrease slightly (Figure ) There is also a significant decrease due to the drawing. These mechanical processes cannot modify the diameter. The only logical explanation is an artifact effect. In the card sliver and the drawing slivers the fibers are oriented and paralleled, this removes the crimp. The length of the electronic signal and its height are then modified giving higher length readings and lower diameter readings. · The HVI micronaire values (Figure 1) vary slightly in the opening line, perhaps due to the removal of some dead fibers. The carding seems to reduce the micronaire, which is not explainable. Then the drawing leads to an increase in micronaire. The theory of the micronaire instruments is based on airflow passing through a sample constituted of randomly oriented fibers. In the drawing process the fibers are made parallel, which probably leads to an easier flow of air through the cotton sample and results in an apparent higher micronaire. · FIG:1 EFFECT OF COTTON PREPARATION ON AFIS AND HVI MEASUREMENTS – 2 Page 1 2 · As the micronaire is used to calculate the beard mass (function of optical density and micronaire) for the strength test, any positive micronaire bias will lead to a negative HVI strength bias (Figure 2). In addition, the drawing process is similar in effect to an increase in the brushing time (or force) on the HVI combs. Taylor (TRJ, 1986, 93-102) has shown the effect of increasing brushing force on HVI strength readings. In his experiment two sample preparations were tested, hand brushing and HVI brushing (harder brushing than by hand). The results show an increase by 1.9 g/tex when using the HVI brushing device. In our case, we think that the drawing sliver samples have a lower optic density (for a given number of fibers in the comb) than the raw cotton. This results in a lower calculated mass of the sample to be broken. As the HVI strength is calculated by dividing the force applied to break the sample by the FIG:2 · · As expected, the AFIS nep counts (Figure 3) increase with passage of the fibers through the opening line. The Mono- cylinder increases the average nep count by 75, then the first ERM (operating at 850 rpm) by 136 and the second ERM (operating at 950 rpm) by 240; that is 451 neps in total. The card removes 540 neps and the drawing frames have no effect. FIG:3 · The HVI reflectance (Figure 4) increases slightly after each cleaning stage. The drawing seems to also have an effect on the reflectance readings. This is not due to trash removal but more likely to an artifact because the paralleled fibers are not reflecting the light the same way as the randomly oriented fibers. FIG:4 · The changes in yellowness (Figure 5) are quite small but significant. The most important change is due to the drawing. This is, as for the reflectance, probably due to an artifact. · FIG:5 Combed Process: · Combing affects AFIS Upper Quartile Length, Mean Length, Short Fiber Content and HVI Upper Half Mean Length and Uniformity Ratio. As expected the fiber length parameters all increase when the cotton is combed, with the exception of the Short Fiber Content. The drawing also affects the length parameters; as discussed before, it is probably an artifact. It is interesting to note that combing increases the length by 0.006 inch (minimum noil settings) and that the first drawing increases it by 0.027, i.e. nearly five times more. The artifact effect seems to be much more important than the real mechanical effect. The combing process seems to have no effect on the fiber diameter (Figure 6). The drawing, as discussed before, decreases the diameter (artifact). The HVI micronaire (Figure 7) increases when combing is applied, mainly because the removal of short, weak and immature fibers during the combing process increases the average maturity level. As discussed before the drawing has a positive effect on micronaire (artifact effect). FIG:6 AFIS-DIAMETER FIG:7 HVI STRENGTH: · The HVI strength (Figure 8) also increases with combing, because of the removal of short fibers. The drawing, as discussed before, increases the apparent HVI strength (artifact effect). FIG:8 HVI STRENGTH · The AFIS neps (Figure 9) are removed during the combing process as expected (-62% for the minimum noil setting to -91% for the normal noil setting). FIG:9 · The combing also removes trash and dust. The decrease in trash is (Figure 10) nearly 60% for both types of settings. The decrease in dust (Figure 11) is about 40% for the minimum noil setting and 60% for the normal noil setting. As these are removed the HVI reflectance increases as expected and the yellowness decreases. The drawing effect on both parameters is an artifact, as discussed before. FIG:10 AFIS-TRASH: FIG:11 AFIS DUST IGH VOLUME INSTRUMENT SYSTEM The testing of fibres was always of importance to the spinner. It has been known for a long time that the fibre characteristics have a decisive impact on the running behaviour of the production machines, as well as on the yarn quality and manufacturing costs. In spite of the fact that fibre characteristics are very important for yarn yarn proudction, the sample size for testing fibre characteristics is not big enough. This is due to the following · The labour and time involvement for the testing of a representativesample was too expensive. The results were often available much too late to take corective action. · The results often depended on the operator and / or the instrument, and could therefore not be considered objective · one failed in trying to rationally administer the flood of the rawmaterial data, to evaluate such data and to introduce the necessary corrective measures. Only recently technical achievements have made possible the development of automatic computer-controlled testing equipment. With their use, it is possible to quickly determine the more important fibre characteristics. Recent developments in HVI technology are the result of requests made by textile manufacturers for additional and more precise fibre property information. Worldwide competitive pressure on product price and product quality dictates close control of all resources used in the manufacturing process. Following are the advantages of HVI testing · the results are practically independent of the operator · the results are based on large volume samples, and are therefore more significant · the respective fibre data are immediately available · the data are clearly arranged in summerised reports · they make possible the best utilisation of rawmaterial data · problems as a result of fibre material can be predicted, and corrective measures instituted before such problems can occur Cotton classification does not only mean how fine or clean, or how long a fibre is, but rather whether it meets the requirements of the finished product. To be more precise, the fibre characteristics must be classified according to a certain sequence of importance with respect to the end product and the spinning process. The ability to obtain complete information with single operator HVI systems further underscores the economic and useful nature of HVI testing. Two instrument companies located in the US manufacture these HVI systems. Both the systems include instruments to measure micronaire, length, length uniformity, strength, colour, trash, maturity, sugar content etc. LENGTH: The length measure by HVI systems used by the USDA is called upper-half-mean length. This is the average or mean length of the longest one-half of the fibres in the sample. The spinlab system uses the fibrosampler device to load the fibres on needles, the motion control system uses the Specimen Loader to capture the fibres in a pinch clamp. However the preparation of the length specimen for both systems includes combin to straighten and parallel the fibres, and brushing to remove fibre crimp. The length measurement is then made by the instrument scanning along the length of the specimen to determine the length data. The insturments are calibrated to to read in staple length. Length measurements obtained from the instrument are considerably more repeatable than the staple length determination by the classer. In one experiment the instrument repeated the same staple length determination 44% of the time while the classer repeated this determination only 29% of the time. Similarly, the instrument repeated to 1/32″ on 76% of the samples, while the classer agreed on 71% of the samples to within 1/31″. The precision of the HVI length measurement has been improved over the last few years. If we take the same bale of cotton used in the earlier example and repeatedly measure length with an HVI system, over two-thirds of measurements will be in a range of only about 1/32 nd of an inch: 95% of the individual readings will be within 1/32nd of an inch of the bale average. In the 77000 bales tested, the length readings were repeated within 0.02″ on 71% of the bales between laboratories. LENGTH UNIFORMITY: The HVI system gives an indication of the fibre length distribution in the bale by use of a length uniformity index. This uniformity index is obtained by dividing the mean fibre length by the upper-half-mean length and expressing the ratio as a percent. A reading of 80% is considered average length uniformity. Higher numbers mean better length uniformity and lower numbers poorer length uniformity. A cotton with a length uniformity index of 83 and above is considered to have good length uniformity, a length uniformity index below 78 is considered to show poor length uniformity. Repeated measurements on a single bale of cotton show the length uniformity index measurement to have relatively low precision. About two-thirds of the measurements will occur within one unit of length uniformity; thus a bale with an average length uniformity index of 80 would have 68% of the readings occuring between 79 and 81, and 95% of hte readings occuring between 78 and 82. This does not seem too bad until one considers that most US upland cottons will have a length uniformity reading between 75 and 85. Most organizations operate their HVI systems to use an average of 2 or 4 readings per bale for the length uniformity index. Using that number tests per bale, the USDA test of 77000 bales showed that laboratoriesat different locations agreed 68% of the time to within one length uniformity index unit. In some cases low length uniformity has correlated with high short fibre content. However, in general the correlations between length uniformity index and short fibre content have not been very good. One important reason why the length uniformity index is a not a very good indicator of the short fibre content has to do with the fact that the HVI systems do not measure the length of any fibres shorter than about 4mm. Another reason for the poor correlations between length uniformity index and short fibre content is that the short fibre content is related to staple length while the length uniformity index is fairly independent of staple length. As an example, the shorter staple cottons tend to contain higher amounts of short fibre than the longer staple cottons. Howeer, many short staple cottons have length uniformity index readings above 80. MICRONAIRE: The micronaire reading given by the HVI systems is the same as has been used in the commercial marketing of cotton for almost 25 years. The repeatability of the data and the operator ease of performing the test have been improved slightly in the HVI micronaire measurement over the original instruments by elimination of the requirement of exactly weighing the test specimen. The micronaire instruments available today use microcomputers to adjust the reading for a range of test specimen sizes. The micronaire reading is considered both precise and reperable. For example, if we have a bale of cotton that has an average micronaire of 4.2 and repeatedly test samples from that bale, over two-thirds of thet micronaire readings will be between 4.1 and 4.3 and 95 %of the readings between and 4.0 and 4.4. Thus, with only one or two tests per bale we can get a very precise measure of the average micronaire of the bale. This reading is also very repeatable from laboratory to laboratory. In USDA approx 77000 bales were tested per day in each laboratory, micronaire measurements made in different laboratories agreed with each other within 0.1 micronaire units on 77% of the bales. The reading is influenced by both fibre maturity and fibre fineness. For a given growing area, the cotton variety generally sets the fibre fineness, and the environmental factors control or influence the fibre maturity. Thus , within a growing area the micronaire value is usually highly related to the maturity value. However, on an international scale, it cannot be known from the micronaire readings alone if cottons with different micronaire are of different fineness or if they have different maturity levels. COTTON LENGTH RELATED PROPERTIES The “length” of cotton fibres is a property of commercial value as the price is generally based on this character. To some extent it is true, as other factors being equal, longer cottons give better spinning performance than shorter ones. But the length of a cotton is an indefinite quantity, as the fibres, even in a small random bunch of a cotton, vary enormously in length. Cotton is the shortest of the common textile fibers, hence, other things being equal, it makes the most irregular yarns and fabrics. Accordingly the market pays a premium for good length. The various methods of measuring length may be classified according to whether they · measure the staple length only, or other parameters · work by aligning the fiber ends, e.g comb sorters, · measure only length, or use the tuft for other measurements, such as strength etc The importance of fiber length to textile processing is significant. Longer fibers produce stronger yarns by allowing fibers to twist around each other more times. Longer fibers can produce finer yarns to allow for more valuable end products. Longer fibers also enable higher spinning speeds by reducing the amount of twist necessary to produce yarn. The variability in fiber length can be explained 70-80 percent by genetics , so variety selection is very important. Fiber elongation begins at bloom and continues for about 21 days. Moisture stress during the fiber elongation period will reduce fiber length in all varieties. Starting with a variety that has better genetic potential for fiber length will minimize the probability of producing fiber length in the discount range. Severe weathering after bolls have opened can reduce fiber length because more breakage can be expected in the ginning process. Besides variety, water management and maintaining good plant-water relations is probably the most important factor affecting fiber length Length Uniformity and Short Fiber Content. Length uniformity is now part of the premium/discount valuation of cotton. Short fibers within a process mix of cotton cannot wrap around each other and contribute little or nothing to yarn strength. Short fibers are virtually uncontrolled in the manufacturing process, indirectly causing product defaults and directly contributing to higher waste and lower manufacturing efficiency. Since short fiber content and length uniformity are derived from length, they are influenced by the same factors as length.. Length uniformity can be more influenced by environment than effective length because temperature is involved in the regulation of genes, which cause epidermal cells to differentiate into fibers. Crop management practices that influence where bolls are located on the plant can impact short fiber content levels. Uniform fruit retention patterns encourage better length uniformity. Disruption to the natural length distribution is most often caused by mechanical damage, so maintaining recommended moisture levels at the gin is important. SHORT FIBER The original theory of the fibrogram as developed by Hertel more than fifty years ago has served as the basis of all subsequent cotton length measurements. The major assumptions Hertel made in deriving the theory of the fibrogram are embodied in the statement “The fiber is to be selected at random and every point on every fiber is equally probable.” This statement translates to: · A sampled fiber is held at a random point along its length. · The probability of sampling a particular fiber is proportional to its length. Since the longer fibers have a greater probability of being sampled, this results in the length distribution in the fiber beard becoming biased toward the longer fibers.. Using Suter-Webb data and assuming uniform fiber fineness, it is possible to calculate the distributions for the length biased samples. To investigate the validity of the second assumption, we measured the length distribution of a few fiber samples in their original forms and of fiber beards made from these samples. The selected samples for the experiment were two staple standard cotton samples (SS28 and SS40). Length measurements were performed on the samples in their original forms using standard Suter-Webb Array (SWA) methods and the Advanced Fiber Information System Length and Diameter module (AFIS-L/D) made by Zellweger Uster, Inc. In addition, the AFIS was used to measure the length distributions of fiber beards prepared using a model 192 fibrosampler with and without allowing the beards to pass over the carding section of the fibrosampler. All AFIS-L/D results are the averages of three repetitions with three thousands fibers were measured in each repetition. The experimental results along with the calculated results based on a length biased sample are listed in Table 1.. Table I. Suter-Webb Array (SWA) and AFIS Length data. Sample: Staple Standard 28 SWARaw SWAExpected AFIS Raw AFIS Uncarded AFISCarded By Weight Mean Length in. 1.19 1.27 1.10 1.09 1.08 Length CV% 29.9 23.7 32.7 31.5 29.9 Short Fiber % 14.2 6.6 13.6 13.6 13.3 Upper Quartile in. 0.92 0.96 0.89 0.89 0.88 By Number Mean Length in. 0.63 0.75 0.64 0.64 0.65 Length CV% 44.7 29.9 43.1 41.8 39.3 Short Fiber % 31.6 14.2 28.7 28.3 26.7 Upper Quartile in. 0.84 0.92 0.81 0.81 0.81 Sample: Staple Standard 40 SWA Raw SWA Expected AFIS Raw AFIS Uncarded AFISCarded By Weight Mean Length in. 1.19 1.27 1.10 1.09 1.08 Length CV% 25.7 19.5 31.2 31.4 31.2 Short Fiber % 4.0 1.1 4.6 4.9 4.6 Upper Quartile in. 1.41 1.44 1.31 1.31 1.3 By Number Mean Length in. 1.0 1.2 0.9 0.9 0.9 Length CV% 44.0 25.7 40.3 40.3 38.9 Short Fiber % 17.3 4.0 14.0 14.3 13.0 Upper Quartile in. 1.34 1.41 1.22 1.21 1.19 A comparison of the Suter-Webb array data and the AFIS data for the raw stock show good agreement between the methods with small differences characteristic of this version of AFIS. Of more importance is a comparison of the AFIS data between the raw, uncarded and carded samples. The mean lengths and length distributions as indicated by the coefficient of variation are almost identical to those in their original forms. Even if some fiber damage occurs in the AFIS, the damage would be very similar for a given sample and allow us to detect differences in the samples due to the sampling or carding process. Since the differences of the length distributions and the calculated mean lengths between fiber beards and the original fiber samples are small, this would indicate that the second assumption should be modified such that each fiber in the original sample has equal probability to be caught in forming the fiber beard. This in turn would indicate fibers are sampled in clumps rather than individually. Thus the fibrogram theory derived by Hertel should not be applied to the fiber beards prepared from the fibrosampler. However, his theory appears to apply to those fiber beards prepared from sliver by using sliver clamp. EFFECT OF COTTON FIBER LENGTH DITSTRIBUTION ON YARN QUALITY International Textile Center, Texas Tech University Eric Hequet and Dean Ethridge Lubbock, TX The prediction of yarn quality based on the technological characteristics of the raw material has been improved by the use of the AFIS. Unfortunately, information about distributions of fiber properties that are measured by the AFIS is generally not used. The studies carried out at the ITC show that the AFIS length distribution is variety related. In addition, the percentages of both the shortest and the longest fibers have an important impact on yarn quality. Introduction During recent years, the Uster AFIS (Advanced Fiber Information System) has been increasingly used in the research projects carried out at the International Textile Center (ITC), Texas Tech University. The prediction of yarn quality based on the technological characteristics of the raw material has been improved by the use of the AFIS. The ITC has shown in the past few months the value of AFIS measurements such as the short fiber content or the standard fineness (Ethridge et. al., 1998; Hequet, 1999). Unfortunately, information about distributions of fiber properties that are measured by the AFIS are generally not used, because the data are not available in an electronic file. This makes the use of these data extremely unfriendly. Nevertheless, we decided to investigate the value of the distribution information with a focus on the influence of the fiber length distribution on the yarn quality. Procedures First Experiment Fourteen USDA (United States Department of Agriculture) standards cottons were used in this first experiment. The following measurements were performed on fiber: . AFIS with 5 replications of 3,000 fibers, . Sutter Web Fiber Array with 3 replications per technician and two technicians, . Peyer AL 101 with 6 replications Second Experiment Variety evaluation tests were performed at the ITC during the 1998-99 crop year. Eighteen U.S. Upland cotton varieties were represented. Each variety was grown in three locations and two replicated samples were taken at each location. Therefore, a total of 108 cotton samples were collected (18 x 3 x 2). The cotton fibers from each variety were processed through the Short Staple Spinning Laboratory at the ITC and were made into both ring-spun (36 and 50 Ne carded, 50 Ne combed) and rotor-spun yarns (36 Ne carded). The following measurements were performed on fiber and yarn: Fiber Tests: . Zellweger Uster HVI 900A: 4 mike measurements, 4 color-grade measurements, 10 length and strength measurements. . Zellweger Uster AFIS Multidata: 5 replications of 3,000 fibers Yarn Tests: . Zellweger Uster Tensorapid: 10 breaks per bobbin and 10 bobbins . Zellweger Uster UT3: 400 yards per bobbin and 10 bobbins The printout from the AFIS provides us with a distribution of the length by weight. The histogram is built based upon the percentage of fibers in each of the 40 length categories, from 0 to 2.5 inches with an increment of 1/16th of an inch. In order to get a first look at the data provided on those 108 cotton samples, we limited the number of length categories to 10 by aggregating 4 categories together; therefore, the length category increment became 0.25 inch. A brief statistical summary of fiber properties is given in Tables 2 and 3, showing the mean, minimum and maximum values for each characteristic. An examination of this data reveals that all of the cottons exhibit relatively good fiber properties, with a low short fiber content, good length and maturity and high strength levels. The percentages in the last two AFIS length categories are very low, for this reason they have been aggregated for all the following analysis. Third Experiment Two commercial cotton bales were selected. A very low amount of ELS cotton was added (2% and 5%) in order to check if the addition of a very small amount of long fibers would increase significantly the CSP. The same measurements used in the second experiment were taken on the fibers and yarns. Results and Discussion The first experiment grew out of an anomaly with AFIS measurements. Figure 1 shows a typical AFIS length distribution by weight for Acala- type cotton. EFFECT OF COTTON FIBER LENGTH DITSTRIBUTION ON YARN QUALITY – 2 During the past few years, thousands of cotton samples have been analyzed at the ITC using the AFIS. Results for most of the cottons indicate a very small percentage of fibers in the length categories of 2 inches and longer. We can postulate either that those very long fibers really exist or that the AFIS over- estimates the length of the longest fibers. To investigate this, 14 USDA standard cottons were tested on the AFIS, Sutter Web Fiber Array and Peyer AL 101. Results showed that the instruments correlate very well for the shortest fiber percentages (Figures 2 and 3), although the levels are different. For the very short-staple cotton (staple 26), the length distributions obtained are very similar (Figure 4). For the short-staple cotton (staple 32), AFIS and Peyer are in good agreement, but the Array method tends to get higher percentages for the longest fibers (Figure 5). For the medium (staple 35) and long (staple 40) fibers, the discrepancy between instruments is clear (Figures 6 and 7). Neither the Peyer nor the Array showed any fibers to the longer than 2 inches, but the AFIS did indicate some of these for most of the samples. This suggests that the AFIS tends to over- estimate the length of the longest fibers. One hypothesis to explain this result is that the speed of the fibers passing trough the sensing device is not constant; i.e., the longer the fiber, the higher the friction forces for the air-to-fiber interface. This could lower the speed, resulting in a longer electronic signal. Given this anomalous result with the AFIS, the question arises whether it is a useless artifact or if it has predictive power. This led to the second experiment involving 18 upland varieties grown in 3 locations with 2 field replications per location. Using the AFIS multidata, for each length category, defined, an analysis of variance was done. Figures 8, 9 and 10 give the variety and location effects for the three length categories. For the length category [0.25; 0.50], the variety effect is highly significant, but the location effect and the interaction effect × are not statistically significant. For the length category [1.25; 1.50] both the variety and the location effects are highly significant, but the interaction effect location*variety is not. For the fibers longer than 2 inches, the variety effect is highly significant, the location effect significant and the interaction effect location*variety non- significant. These results suggest at least two very important things. First the length distribution by weight is variety related; this implies that breeders could modify the length distribution. Second, the longest fibers measured with the AFIS, although a very small percentage of total fibers, are also variety related. This means that the fibers measured as too long by the AFIS cannot be dismissed as meaningless. To investigate further, we calculated the coefficients of correlation between major yarn characteristics and the percentages of fibers in the different length categories. For Count Strength Product (CSP), these correlations are quite similar for all the types of yarns.ring or rotor, carded or combed (Figure 11). Page 1 2 3 EFFECT OF COTTON FIBER LENGTH DITSTRIBUTION ON YARN QUALITY – 3 For the fibers shorter than one inch the correlation coefficients are negative in all cases; therefore, the larger the share of these length categories, the lower the CSP. For fibers in the 1.00-to-1.25 category the correlation coefficients are still negative but are near zero. As the length categories increase above this level, the correlations become positive and large. The category longer than 2 inches exhibits the highest positive correlation of all. The calculation of the correlation coefficients between the CSP and the various fiber properties used for prediction is given in Table 4. It shows that the AFIS percent of fibers longer than 2 inches is the best length parameter to predict CSP. In fact, it performs better than the HVI strength and the AFIS standard fineness. This is even more startling given that the percentage of fibers longer than 2 inches averages only 1 percent on the 108 samples tested . Figure 12 shows the coefficients of correlation between the UT3 non-uniformity (CV%) and the percentages of fiber in the different length categories. Note the following: . The carded ring spun yarns exhibit very similar behavior. The length categories giving the best correlation coefficients with the yarn uniformity are: [0.00;0.25], [0.25;0.50] and [>2.00], with a positive correlation for the shorter fibers and a negative correlation for the longer fibers. Therefore, the higher the short fiber content, the higher is the yarn CV%; and the higher the long fiber content, the lower is the yarn CV%. . The UT3 CV% of the combed ring-spun yarn exhibits a very good correlation with the percentage of fibers longer than 2 inches and a quite poor correlation with the shorter fibers. This is logical because a large part of the shorter fibers has been removed during the combing operation. . For the rotor spun yarn, the negative effect on the yarn uniformity of the shorter fibers is limited. But the fibers between 1.75 and 2 inches exhibit the highest correlation with the yarn CV%. The fibers longer than two inches give a lower correlation, probably because a part of them (the extremely long fibers) wrap around the yarn and create imperfections. This is likely related to the rotor diameter and it will be necessary to test different rotor diameters to confirm this hypothesis. Figures 13 and 14 show the coefficient of correlation between the UT3 thin and thick places, respectively, and the percentages of fiber in the different length categories. The figures look very similar to the UT3 CV% and similar conclusions can be made. Figure 15 shows the correlation coefficients between the UT3 neps and the percentages of fiber in the different length categories. The correlation levels are generally lower than were exhibited for the previous parameters. However, for the carded ring-spun yarns of 36 Ne and 50 Ne, correlations of neps with the length category [1.00;1.25] are fairly high. We currently have no coherent hypothesis to explain this. Figure 16 shows the correlation coefficients between the UT3 hairiness and the percentages of fiber in the different length categories. The shapes of the curves are quite similar for all the types of yarns.ring vs. rotor and carded vs. combed. For the fibers shorter than 1/4 inch, the correlation coefficients have positive signs and are very high in all cases. Therefore, these very short fibers are important contributors toward increased yarn hairiness. Conversely, correlation coefficients for the fibers longer than two inches are also high but with negative signs; therefore, these fibers, which measure very long, are important contributors toward decreased yarn hairiness. Figure 17 shows the correlation coefficients between levels of the combing noils and the percentages of fiber in the different length categories. As expected, the correlation coefficients very high for the three shortest length categories but low for the other length categories. Table 5 shows the multiple regression coefficients between the fiber and yarn parameters and the percentages of fiber in the different length categories (Forward Stepwise regression with Sigma-restricted parameterization). These results reveal that the only statistically significant length parameter related to the CSP is the percent of the fibers longer than 2 inches. For the yarn regularity (CV%, thin places and thick places) the important parameters are the very short fibers (shorter than ¼ inch) and the very long fibers (longer than 2 inches). The third experiment was done to obtain some confirmation of effects of the longest fibers on the yarn strength. Using two commercial bales of Upland cotton, ring-spun 30 Ne yarns were made. Then very small amounts (2% and 5%) of ELS cotton fibers were mixed with the Upland cotton and also ring spun into 30 Ne yarns. Figure 18 gives results on CSP and Figure 19 gives results on tenacity. They both show a tendency for increased strength with small additions of ELS. On average for the two bales, adding 2% ELS increased the CSP 3.8% and the tenacity 7.7%. Adding 5% ELS results in average increases of 7.3% in CSP and 8.5% in tenacity. These limited results give encouragement to design a more complete study using larger samples and optimizing the spinning parameters for each mix tested. Conclusions The length distribution data available with the AFIS appears to contain information that is useful to both the cotton breeders and the spinners. Since the length distribution clearly appears to be variety related, it may provide a new tool for cotton breeders in their efforts to reduce short fiber content. The causes for the AFIS measuring some fibers as longer than 2 inches are not understood; nevertheless, this measurement exhibits the highest correlation with the yarn CSP. For the carded ring-spun yarns, the shortest fibers and the longest fibers exhibit the highest correlation with the yarn CV%, the number of thin places, and the number of thick places. For the combed ring-spun yarns and the rotor-spun yarns, the longest fibers exhibit the highest correlation with the yarn CV%, the thin places, and the thick places. The correlation coefficients between the different length categories and the number of neps are generally low. The shortest and the longest fibers are highly correlated with the hairiness for all the types of yarns. The shortest fibers increase hairiness and the longest fibers decrease hairiness. The three shortest length categories are highly correlated with increased combing noils. PROCESSING STICKY COTTTON The following article was published in Journal of Cotton Science volume 2002. By Mr.Eric Hequet and Mr.Noureddine Abidi, Ph.D. In spinning mills, sticky cotton can cause serious problems. It contaminates the textile machineries like blow room , card, drawing, roving, and spinning frames. These contaminants are mainly sugar deposits produced either by the cotton plant itself (physiological sugars) or by feeding insects (entomological sugars), the latter being the most common source of stickiness. Seventeen mixes having a moderate level of stickiness were evaluated in both ring and rotor spinning. High-performance liquid chromatography tests were performed on residues collected from the textile machinery to identify the types of sugars present. It was shown that among the sugars identified on raw fiber, only trehalulose exhibits higher percentages in the residues than on the fiber. During the fibers-to-yarn transformation, the flow of lint is submitted to different friction forces; consequently, the temperature of some mechanical elements may increase significantly and affect the thermal properties of the contaminated lint. After a sugar becomes sticky, the other sugars present on the lint, as well as other substances such as dusts, silica, etc., will stick to the lint and could cause unevenness in the flow of lint being drawn, such as lapping up on the rolls, nep-like structures, and ends-down. Therefore, the thermal properties of the five sugars identified on the contaminated fiber and on the residues collected on the textile equipment were investigated. Among the sugars tested, trehalulose is the only one having a low melting point, around 48degre C. In addition, trehalulose is highly hygroscopic. After passive conditioning of dehydrated trehalulose at 65% ± 2% relative humidity and 21 degree C ± 1degree C for 24 h, the quantity of adsorbed water at equilibrium was found to be approximately 17.5%. This corresponds to three molecules of water adsorbed for each molecule of trehalulose. The combination of low melting point and high hygroscopicity could be the cause of the selective accumulation of this sugar on the textile equipment. Stickiness is primarily due to sugar deposits produced either by the cotton plant itself(physiological sugars) or by feeding insects(entomological sugars) .Insects have been documented as the most common source of contamination in some studies . The analysis of honeydew from thecotton aphid and cottonwhitefly has shown that aphid honeydew contains 138.3% melezitose(C18H32O16) plus 1.1% trehalulose (C12H22O11),whereas whitefly honeydew contains 43.8%trehalulose plus 16.8% melezitose . Otherrelative percentages may occur, depending on the environmental or feeding conditions. Furthermore, stickiness is related to the type of sugars present on the lint. The authors showed that trehalulose and sucrose(C12H22O11),bothdisaccharides, were the stickiest sugars when added to clean cotton, while melezitose(trisaccharide), glucose (C6H12O6), and fructose(C6H12O6) (both monosaccharides) were relatively non-sticky. Previous investigations wereconducted to elucidate the factors affecting the behavior of cotton contaminated with stickiness. In textile mills, the method mainly used to reduce the impact of stickiness is blending sticky cotton with non-stickycotton . Stickiness caused by honeydew depends on the relative humidity, which is a function of both water content and air temperature, in which the contaminated cotton is processed. Stickiness measured with the thermodetector is dependent on the relative humidity.Sticky cotton (with 1.2% reducing sugarcontent), when stored in high relative humidity(70degree F, 80% relative humidity, caused moreproblems during processing than the same stickycotton stored at low relative humidity 75degree F, 55% relative humidity. However, at low relativehumidity, the fibers are more rigid and will increase the friction forces creating static electricity . . Therefore, it will require more energy to draw the lint. Stickiness has been reported to cause a build-up of residues on textile machinery, which may result in irregularities or excessive yarn breakage . When processing low to moderately contaminated cotton blends, residues will slowly build up, decreasing productivity and quality, and forcing the spinner to increase the cleaning schedule. Consequently, we decided to study the origin of the residues collected on the textile equipment after processing sticky cotton blends with low to moderate levels of contamination. MATERIALS AND METHODS Materials We selected 12 commercial bales contaminated with insect honeydew on the basis of their insect sugar (trehalulose and melezitose) content and their stickiness as measured with the high-speed stickiness detector . In addition, five non-sticky bales from one module were purchased for mixing with the contaminated cotton, so that alternative stickiness levels in the mixes could be obtained. The 12 contaminated bales were broken and layered. Ten samples per bale were taken. Each sample was tested with a high-volume instrument (Model 900 Automatic, Zellweger Uster, ) and high-performance liquid chromatography High-Speed Stickiness Detector The high-speed stickiness detector is derived from the sticky cotton thermodetector , which was approved as a reference test by the International Textile Manufacturers Federation in 1994 . This thermomechanical method combines the effect of heat and pressure applied to a sample of cotton placed between two pieces of aluminum foil. When the temperature increases, moisture in the cotton vaporizes and is absorbed by the sticky spots, making them stick to the foil. The high-speed stickiness detector is an automated version of the sticky cotton thermodetector . Three replications were performed on each sample (10 samples per bale x three replications = 30 readings per bale). Spinning Trials The mechanical process used in this study is described in Fig. 1. Opening, carding, drawing, roving, ring spinning, and rotor spinning machines used were all industrial equipment. In the ring spinning trial, the yarns were spun to a 19.68 x 10-6 kg m-1 (19.68-tex or 30 English number) count. Fourteen spindles were used for each mix spun, and each mix was run for 72 h. For the open-end spinning trials, the yarn produced was 26.84 x 10-6 kg m-1 (26.84-tex or 22 English number); 10 positions were used, and each mix was run for 20 h. We ran preliminary tests on ring spinning before testing the mixes. A 13.6 kg sample of lint from each bale was carded and drawn. If noticeable problems occurred at the draw frame, the process was stopped. If not, the drawing slivers were transformed into roving. If noticeable problems occurred at the roving frame, the process was stopped. If not, the roving was transformed into yarn at the ring spinning frame. If noticeable problems occurred at the ring spinning frame, the process was stopped. If not, 45.4 kg of lint was processed for the large-scale test. If noticeable problems occurred at any step of the process, the cotton was mixed with 50% non-sticky cotton and the process was repeated. This procedure was used for 17 large-scale tests. Four bales were spun without mixing the lint with the non-sticky cotton. Four bales were spun after mixing the lint with 50% non-sticky cotton. Four bales were spun after mixing the lint with 75% nonsticky cotton. Three bales were spun after mixing the lint with 87.5% non-sticky cotton. Finally, two baleswere spun after mixing the lint with 93.75% nonsticky cotton. Card slivers, flat wastes, draw frame residues, and sticky deposits collected at the end of each test on the rotor spinning and ring spinning frames were analyzed by high-performance liquid chromatography. These tests quantify the amount of sugars, expressed as a percentage of total sugars present. In addition, high-speed stickiness detector measurements were made on card slivers. After each spinning test was completed, the opening line and the card were purged by processing a non-contaminated cotton, then all the equipment was washed with wet fabric and thoroughly dried. PROCESSING STICKY COTTTON – 2 Page 1 2 3 4 High-Performance Liquid Chromatography on Sticky Deposits Residues on textile equipment were collected using wet wipes . Each wipe was identified, placed into a plastic bag, and frozen. After the spinning trials, sugars were extracted from the wipes using 20 mL of 18.2- megohm water. High-performance liquid chromatography tests were performed following the same procedure used for the bale samples. Three replications were performed on each sample. The results for each sugar were expressed as a percentage of total sugars identified. Dust Test Dust was collected from 20 rotors after a 4-h run. The spinning equipment for this test was an Elitex BD200M , because it has no auto-cleaning devices to remove dust. Collected dust was frozen. We extracted the sugars from the dust using 20 mL of 18.2-megohm water. High-performance liquid chromatography tests were performed following the same procedure used for the bale samples. Three replications were performed on each sample. The results for each sugar were expressed as a percentage of total sugars identified. Water Adsorption The selected sugars were fructose, glucose, sucrose, trehalulose, and melezitose. Trehalulose was obtained from Cornell University; the other sugars were from Sigma Chemical Company (St. Louis, MO). The sugars first were dehydrated at room temperature under vacuum for 48 h. They were weighed immediately in tightly closed weighing containers in a controlled atmosphere (65% ± 2% relative humidity, 21degreeC ± 1degreeC. Recorded weight, m0 (dry weight), at time, t0 = 0, was used for calculation of weight-gain. Since the stickiness tests were done at 65% ± 2% relative humidity and 21degree C ± 1degreeC, the open containers containing sugar samples were stored at these conditions and weighed (weight mt) over time until the weight stabilized (14 wk). The percentage of adsorbed water on each sugar was then calculated as [(mt - m0)/m0] x 100 and plotted against time. Differential Scanning Calorimetry The differential scanning calorimetry technique is widely used to examine and characterize substances. The principle of this method is based on measuring the heat flux between the sample and a reference while the temperature is rising. The sample and the reference are deposited into two different pans and heated at the same rate. In this work, the reference was an empty pan. The analysis of the differential scanning calorimetry profiles indicates the thermal properties of the substances being tested; specific values such as melting point and decomposition point are obtained. The differential scanning calorimetry profiles were recorded by heating at the rate of 5degreeeC min-1 between 25degreeC and 250degreeC. Scanning Electron Microscope Following the processing of the 17 mixes, yarn neps were identified and collected. The samples were mounted in the stub and coated with a layer of gold by means of thermal evaporation in a vacuum coating unit. They were then examined in the scanning electron microscope using an accelerating voltage of 20 KV. RESULTS AND DISCUSSION Sucrose is virtually the only sugar in the phloem sap of the cotton plant . Insects produce trehalulose and melezitose by isomerization and polymerization of sucrose; neither of these sugars occurs in the cotton plant . Therefore, their presence on cotton lint demonstrates honeydew contamination. Stickiness can cause a build-up of residues on the textile machinery, which may result in irregularities or excessive yarn breakage. When cotton is very sticky, it cannot be processed through the card; however, with low to moderate stickiness levels, yarn can generally be produced. For this reason we decided to work with mixes having a very moderate level of stickiness so that residue would build-up slowly on the textile equipment. Performing the spinning test this way is more representative of industrial practice. Indeed, a spinner will not run a very, or even moderately, sticky blend. Rather, the spinner will mix the sticky cotton in such a way that no short-term effect will be noticed. Nevertheless, residues will build up over time and translate into a slow decrease in productivity and quality, forcing the spinner to increase the cleaning schedule. In this article, we present only the results of the study on the composition of residues found on the textile equipment after processing of sticky cotton blends. The productivity and yarn quality analysis will be presented in a future article. With trehalulose content ranging from 0.003% to 0.188% and melezitose content ranging from 0.025% to 0.227% (Table 1), the 12 commercial bales selected were all contaminated with insect honeydew to some degree. This was confirmed by the high-speed stickiness detector readings ranging from 1.9 to 69.9 sticky points. The fiber properties of the 12 contaminated bales and of the non-sticky control are presented in Table 2. The range of fiber properties is fairly typical for upland cottons. From the 12 contaminated and the five nonsticky bales, 17 mixes were evaluated. The spinning trials were performed using the protocol outlined in Fig. 1. The high-performance liquid chromatography and high-speed stickiness detector results obtained on the card slivers are presented in Table 3. Testing was performed on card slivers because of the intimate blend between the two bales composing the mix at this stage. As expected, sugar contents and highspeed stickiness detector readings on the mixes indicated slight to moderate stickiness. PROCESSING STICKY COTTTON – 3 Page 1 2 3 4 During the processing of the 17 mixes, sticky deposits were noticed on the textile equipment, as shown in Figs. 2 to 4. Figure 5a shows average high-performance liquid chromatography results obtained on the 17 mixes for the fiber, the flat waste, and the residues collected on the draw frame and the drawing zone of the ring spinning frame. In this figure, the high performance liquid chromatography results are normalized, the base being the high-performance liquid chromatography results on the fiber. It shows that trehalulose content is always higher in the residues collected than on the original fiber while the other sugars are not. The same behavior was observed in rotor spinning (Fig. 5b). Fig. 5. Normalized high-performance liquid chromatography (HPLC) results averaged for fiber and flat waste on 17 mixes and residues collected from the draw frame and drawing zone of the ring spinning frame (a) and from the draw frame of the rotor spinning frame (b). Base used for normalization was HPLC results from fiber. A, card flat; B, draw frame – drafting zone; C, ring spinning frame – back rubber rolls; D, ring spinning frame – back steel rolls; E, ring spinning frame – belt; F, ring spinning frame – center rubber rolls; G, ring spinning frame – front rubber rolls; H, ring spinning frame – front steel rolls; I, rotor spinning frame – face plate; J, rotor spinning frame – feed table; K, rotor spinning frame – rotor groove; L, rotor spinning frame – rotor housing; M, rotor spinning frame – rotor ledge; N, dust test. Among the sugars identified in contaminated cotton, only trehalulose exhibits higher concentration in the residues. Coefficients of correlation between the logarithms of the percentage of each individual sugar, expressed as a percentage of total sugars identified on the fiber, and the percentage of each individual sugar, expressed as a percentage of the total sugars on the flat strips and residues collected, are shown in Table 4. Table 4. Coefficients of correlation (r)between the logarithms of sugar content on the fiber and on the flat strips and residues collected on textile equipment. Specific sugars (fructose, glucose, melezitose, sucrose, and trehalulose) are expressed as a percentage of total sugars. Codes denote: A) card flat; B) draw frame – drafting zone; C) ring spinning frame – back rubber rolls; D) ring spinning frame – back steel rolls; E) ring spinning frame – belt; F) ring spinning frame – center rubber rolls; G ) ring spinning frame – front rubber rolls; H) ring spinning frame – front steel rolls; I) rotor spinning fframe – face plate; J) rotor spinning frame – feed table; K) rotor spinning frame – rotor groove; L) rotor spinning frame – rotor housing; M) rotor spinning frame – rotor ledge; N) dust test. The logarithm transformation was chosen because of the clear nonlinearrelationship between the variables. The percentage of each individual sugar identified, expressed as a percentage of the total sugars, is calculated as follows: % Individual Sugar = [Individual Sugar/*(Fructose + Glucose + Melezitose + Sucrose + Trehalulose)] x 100 PROCESSING STICKY COTTTON – 4 Page 1 2 3 4 The correlations between fiber and flat strips are significant for all sugars except sucrose, showing that the individual sugar contents in the flat strips increase when the sugar content on the fibers increases. Trehalulose is the only sugar having a higher percentage in the flat strips than in the fibers, as shown in Fig 5a. . For the residues collected, only glucose and trehalulose have significant correlations with fiber. Nevertheless, Figs. 5a and b show that the percentages of glucose in the residues are equal or lower than the percentages of glucose on the fiber, while there is a marked increase in trehalulose content on the residues when compared with fiber. Figures 6a to show the nonlinear relationship between trehalulose on the fibers and trehalulose on the residues for some selected locations on the textile equipment. This figure shows that during the processing of mixes having trehalulose content above 5% of the total sugars, trehalulose content has a clear tendency to increase in the residues collected. Consequently, we decided to investigate the sugars’properties to understand why trehalulose content increases in the residues collected while the others sugars do not. The temperature of the textile equipment increases during processing. Therefore, the temperatures on carding, drawing, roving, ring spinning, and rotor spinning frames were recorded after machine warming in a controlled environment (Table 5). The temperature readings were all above 25degree C. The highest temperature range was recorded on the drawing frame( from 38degree C to 53degreeC) and the rotor spinning frame( from 31degree C to 38degree C). The lowest temperature was recorded on the ring spinning frame (from 25degreeC to 28degreeC). The effects of these temperatures should vary according to the thermal properties of the sugars. Therefore, we decided to investigate the thermal properties of the five sugars identified on the contaminated fiber and on the residues collected on the textile equipment. Differential scanning calorimetry was chosen to study the thermal properties of the following sugars: fructose, glucose, trehalulose, sucrose, and melezitose. The differential scanning calorimetry profiles were recorded between 25degree C and 250degree C with a heat rate of 5degree C min-1. Figures 7 a through c show the differential scanning calorimetry profiles.Each sugar has two characteristic peaks corresponding to melting points and decomposition (or carbonization) points (Table 6). Among the selected sugars, trehalulose has the lowest melting point (48degrees C). It begins to melt immediately when the temperature starts rising. The other sugars remain stable when the temperature rises to 116 degree C (melting point of fructose). Therefore, any increase in the temperature of the textile processing equipment will first affect trehalulose, causing it to either stick to the mechanical parts or become the precursor of nep formation. Figure 8 shows one example of a sticky nep. Resulsts showed an excellent relationship between ring-spun yarn neps and stickiness measurements on the raw material using the manual thermodetector. In this study, the authors showed that, on average, each sticky spot counted on the thermodetector translated into 2.8 additional neps on ring spun yarn (20 x 10-6 kg m-1 or 20-tex). The build-up of residues on the textile equipment may have long-term effects, first sticking to surfaces, then catching dust, silica etc., increasing the friction forces within the machinery and leading to excessive wear and temperature increase.Sugars are carbohydrates that are hydrophilic because of several hydroxyl groups (OH-) that interact with water molecules, allowing many hydrogen bonds to be established. Therefore, several authors investigated the relationship between stickiness and relative humidity. It was generally reported that contaminated cottons are less sticky at low relative humidity than at high relative were investigated. The stickiness tests (thermodetector or high-speed stickiness detector) were always performed in a standard textilelaboratory atmosphere,Thus, the quantity of water adsorbed on each sugar was evaluated at 65% ± 2% relative humidity and 21degrees C± 1degreesC. Fig. 9. (a) Hydration kinetic of selected sugars at 65% ± 2% relative humidity and 21(C ± 1(C from 0 to 12.6 h. (b) Hydration kinetic of selected sugars at 65% ± 2% relative humidity and 21(C ± 1(C from 0 to 650 h. Figure 9a shows the percentage weight gain during the first 12 h of hydration. No sugar showed any significant variation within this time period except trehalulose, which picked up about 12% of moisture – corresponding to two molecules of water per molecule of trehalulose. The weight gain of the sugar samples was recorded until plateaus were reached. Trehalulose continued to pick up moisture, while fructose began to pick up moisture after 12 h of exposure to the laboratory conditions (Fig. 9b). The hydration kinetic was very fast for trehalulose – equilibrium was reached after 80 h, but slow for fructose – the plateau was reached after 500 h. The total amount of weight gain corresponds to three molecules of water per molecule of trehalulose and three molecules of water per molecule of fructose. If we assume that trehalulose accumulates more on the spinning equipment than other sugars because of its hygroscopicity, then fructose should accumulate in a similar way, but this was not the case. The high performance liquid chromatography tests performed on the residues collected on the textile equipment did not show any increase in fructose content, even if fructose content was high in some mixes. In the 17mixes tested, the fructose content, expressed as a percentage of the fiber weight, ranged from 0.012% to 0.101%, which corresponds to 10.6% to 33.6% when expressed in the percentage of the total sugars identified. Thus, the fact that trehalulose is highly hygroscopic does not explain why this sugar has the tendency to accumulate more on the textile equipment than other sugars. The combination of trehalulose renders it stickier than the other sugars, allowing its higher concentration on the textile equipment. CONCLUSIONS Stickiness caused by honeydew contamination has been reported to cause residue build-up on textile machinery, which may cause subsequent irregularities or yarn breakage. We evaluated 17 mixes having a moderate level of stickiness. In both ring and rotor spinning, trehalulose content had the tendency to increase in the residues collected on the equipment while the other sugars did not. The study of the thermal properties of the identified sugars present on contaminated lint shows that among the selected sugars, trehalulose has the lowest melting point 48 degree C . It begins to melt as soon as the temperature starts rising. Therefore, any increase in the temperature of the textile processing equipment will first affect trehalulose. In addition, trehalulose is highly hygroscopic. The combination of high hygroscopicity and low melting point could explain the higher concentration of trehalulose in the residues collected on the textile equipment than on the original fiber. REFERENCES American Society for Testing and Materials. 2001. D1776- Practice for conditioning textiles for testing. ASTM, West Conshohocken, PA. Budavari, A. (ed.) 1989. Merck Index, 11th ed. Merck & Co., Rahway, NJ. Frydrych, R., E. Goze, and E. Hequet. 1993. Effet de l’humidite relative sur les resultats obtenus au thermodetecteur. Cotton et Fibres Trop. 48(4):305-311. Frydrych, R., and E. Hequet. 1998. Standardization proposal: The thermodetector and its methodology. p. 97-102. In Proc. Int. Comm. Cotton Testing Methods, Bremen, Germany. Int. Textile Manuf. Fed. Zurich, Switzerland. Frydrych, R., E. Hequet, and G. Cornuejols. 1994. A high speed instrument for stickiness measurement. p. 83-91. In 22nd Int. Cotton Conference Int. Textile Manufacturers Federation. Bremen, Germany. 3-5 March 1994. Faserinstitut, Bremen, Bermany. Gutknecht, J., J. Fournier, and R. Frydrych. 1986. Influence de la teneur en eau et de la temperature de l’air sur les tests du collage des cottons a la minicarde de laboratoire. Cotton et Fibres Tropicales. 41(3):179-190. POLYESTER FIBRE: Fibre manufacturing process: Today over 70 to 75% of polyester is produced by CP( continuous polymerisation) process using PTA(purified Terephthalic Acid) and MEG. The old process is called Batch process using DMT( Dimethy Terephthalate) and MEG( Mono Ethylene Glycol). Catalysts like 5b3O3 (ANTIMONY TRIOXIDE) are used to start and control the reaction. TiO2 (Titanium di oxide) is added to make the polyester fibre / filament dull. Spin finishes are added at melt spinning and draw machine to provide static protection and have cohesion and certain frictional properties to enable fibre get processed through textile spinning machinery without any problem. PTA which is a white powder is fed by a screw conveyor into hot MEG to dissolve it. Then catalysts and TiO 2 are added. After that Esterification takes place at high temperature. Then monomer is formed . Polymerisation is carried out at high temperature (290 to 300 degree centigrade) and in almost total vacuum. Monomer gets polymerised into the final product, PET (Poly ethylene Terephthalate). This is in the form of thick viscous liquid. This liquid is them pumped to melt spinning machines. These machines may be single sided or double sided and can have 36/48/64 spinning positions. At each position , the polymer is pumped by a metering pump-which discharges an accurate quantity of polymer per revolution ( to control the denier of the fibre) through a pack which has sand or stainless steel particles as filter media and a spinnerette which could be circular or rectangular and will have a specific number of holes depending on the technology used and the final denier being produced. Polymer comes out of each hole of the spinnerette and is instantly solidified by the flow of cool dry air. This process is called quenching. The filaments from each spinnerette are collected together to form a small ribbon, passed over a wheel which rotates in a bath of spin finish: and this ribbon is then mixed with ribbon coming from other spinning positions, this combined ribbon is a tow and is coiled in cans. The material is called undrawn TOW and has no textile properties. At the next machine ( the draw machine), undrawn tows from severl cans are collected in the form of a sheet and passed through a trough of hot water to raise the temperature of polymer to 70 degrees C which is the glass transition temperature of this polymer so that the polymer can be drawn. In the next two zones, the polymer is drawn approximately 4 times and the actual draw or the pull takes place either in a steam chamber or in a hot water trough. After the drawing is complete, each filament has the required denier, and has all its sub microscopic chains aligned parallel to the fibre axis, thereby improving the crystallinity of the fibre structure and imparting certain strength. Next step is to set the strength by annealing the filaments by passing them under tension on several steam heated cylinders at temperatures 180 to 220 degrees C. Also the filaments may be shrunk on the first zone of annealer by over feeding and imparting higher strength by stretching 2% or so on the final zone of the annealer. Next the fibre is quenched in a hot water bath, then passed through a steam chest to again heat up the tow to 100 degree C so that the crimping process which takes place in the stuffer box proceeds smoothly and the crimps have a good stability. Textile spin finish is applied either before crimping by kiss roll technique or after crimping by a bank of hollow cone sprays mounted on both sides of the tow. The next step is to set the crimps and dry the tow fully which is carried out by laying the tow on a lattice which passes through a hot air chamber at 85degree C or so. The two is guided to a cutter and the cut fibres are baled for despatch. The cutter is a reel having slots at intervals equal to the cut length desired 32 or 38 or 44 or 51mm. Each slot has a sharp stainless steel or tungsten carbide blade placed in it. The tow is wound on a cutter reel, at one side of the reel is a presser wheel which presses the tow on to the blades and the tow is cut. The cut fibre falls down by gravity and is usually partially opened by several air jets and finally the fibre is baled. Some, balers have a preweighting arrangement which enables the baler to produce all bales of a pre determined weight. The bale is transported to a ware house where it is “matured” for a minimum of 8/10 days before it is permitted to be despatched to the spinning mill. FIBRE SPECIFICATION: DENIER: Usually the actual denier is a little on the finer side i.e for 1.2 D, it will be 1.16 and for 1.4 , it could be 1.35. The tolerance normally is +- 0.05 and C.V% of denier should be 4 to 5%. Denier specifies the fineness of fibre and in a way controls the spinning limit. Theory tells us that in order to form yarn on ring spinning (and also in air jet) there must be minimum of 60 to 62 ifbres in the yarn cross section. Therefor the safe upper spinning limit with different denier is DENIER COUNT(Ne) 1.0 90 1.2 80 1.4 62 2.0 40 3.0 32 The limit is for 38 mm fibre. The limit rises for a longer fibres. When spinning on open end system, the minimum no of fibres in the yarn cross section is 110. So all the fibre producers recommend finer denier fibres for OE spining . Here the safe upper spinning limit is DENIER COUNT(Ne) 1.0 50 1.2 40 1.4 30 2.0 24 3.0 16 However in actual practice , 30s is an upper limit with OE AND 1.2 Denier is being used, in USA and other countries, even for 10s count in OE. Deniers finer than 1.0 are called micro-denier and commercially the finest polyester stple fibre that can be worked in a mill is 0.7 D. CUT LENGTH: Cut lengths available are 32, 38, 44, 51 and 64mm for cotton type spinning and a blend of 76, 88 and 102 mm – average cut length of 88m for worsted spinning. The most common cut length is 38 mm. For blending with other manmade fibres, spinners preferred 51mm to get higher productivity, because T.M. will be as low as 2.7 to 2.8 as against 3.4 to 3.5 for 38mm fibre. If the fibre legnth is more, the nepping tendency is also more , so a crompromise cutlength is 44 mm. With this cut length the T.M. will be around 2.9 to 3.0 and yarns with 35 to 40% lower imprfections can be achieved compared a to similar yarn with 51 mm fibre. In the future spinners will standardise for 38 mm fibre when the ringspinning speed reaches 25000 rpm for synthetic yarns. For OE spinning , 32 mm fibre is preferred as it enables smaller dia rotor(of 38mm) to be used which can be run at 80000 to 100000 rpm. Air jet system uses 38 mm fibre. TENSILE PROPERTIES: Polyester fibres are available in 4 tenacity levels. · Low pill fibres- usuall in 2.0 / 3.0 D for suiting enduse with tenacities of 3.0 to 3.5 gpd(grams per denier). These fibres are generally used on worsted system and 1.4D for knitting · Medium Tenacity – 4.8 to 5.0 gpd · High tenacity 6.0 to 6.4 gpd range and · Super high tenacity 7.0 gpd and above Both medium and high tenacity fibres are used for apparel enduse. Currently most fibre producers offer only high tenacity fibres. Spinners prefer them since their use enables ring frames to run at high speeds, but then the dyeablity of these fibres is 20 to 25% poorer, also have lower yield on wet processing, have tendency to form pills and generally give harsher feel. The super high tenacity fibres are used essentially for spinning 100% polyester sewing threads and other industrial yarns. The higher tenacities are obtained by using higher draw ratios and higher annealer temperatures upto 225 to 230 degree C and a slight additional pull of 2% or so at the last zone in annealing. Elongation is inversely proportional to tenacity e.g TENACITY ELONGATION AT BREAK T10 VALUES LOW PILL 3.0 – 3.5 45 – 55% 1.0 – 1.5 MEDIUM 4.8 – 5.0 25 – 30% 3.5 – 4.0 HIGH 6.0 – 6.4 16 – 20% 5.2 – 5.5 SUPER HIGH 7.0 plus 12 – 14% 6.0 plus All the above values of single fibre. Testing polyester fiber on Stelometer @ 3mm guage is not recommended. The T10 or tenacity @ 10% elongation is important in blend spinning and is directly related to blend yarn strength. While spinning 100% polyester yarns it has no significance. Tenacity at break is the deciding factor. Polyester Fibre manufacturing process – 2 CRIMP PROPERTIES: Crimps are introduced to give cohesion to the fibre assembly and apart from crimps/cm. Crimp stability is more important criterion and this value should be above 80% to provide trouble free working. A simple check of crimp stability is crimps/inch in finisher drawing sliver. This value should be around 10 to 11, if lower, the fibre will give high fly leading to lappings and higher breaks at winding. Spin finish also gives cohesion, but cohesion due to crimp is far superior to the one obtained by finish. To give a concrete example, one fibre producer was having a serious problem of fly with mill dyed trilobal fibre. Trilobal fibre is difficult to crimp as such, so it was with great difficulty that the plant could put in crimps per inch of 10 to 11. Dyeing at 130 degrees C in HTHP dying machine reduced the cpi to 6 to 8. Mills oversprayed upto 0.8% did not help. Card loading took place yet fly was uncontrolled, ultimately the fibre producer added a steam chest to take the two temperature to 100degrees plus before crimping and then could put in normal cpcm and good crimp stability. Then the dyed fibre ran well with normal 0.15 to 0.18 % added spin finish. SPIN FINISH: Several types of spin finishes are available. There are only few spin finish manufacturers – Takemoto, Matsumoto, Kao from Japan, Henkel, Schill &Scheilacher, Zimmer & Schwarz and Hoechst from Germany and George A.Goulston from USA. It is only by a mill trial that the effectiveness of a spin finish can be established. A spin finish is supposed to give high fibre to fibre friction of 0.4 to 0.45, so as to control fibre movement particularly at selvedges , low fibre-metal friction of 0.2 to 0.15 to enable lower tensions in ring spinning and provide adequate static protection at whatever speed the textile machine are running and provide enough cohesion to control fly and lapping tendencies and lubrication to enable smoother drafting. Spin finish as used normally consists of 2 components – one that gives lubrication / cohesion and other that gives static protection. Each of these components have upto 18 different components to give desired properties plus anti fungus, antibacterial anti foaming and stabilisers. Most fibre producers offer 2 levels of spin finishes. Lower level finish for cotton blends and 100% polyester processing and the higher level finish for viscose blend. The reason being that viscose has a tendecy to rob polyester of its finish. However in most of the mills even lower spin finish works better for low production levels and if the production level is high, high level spin finish is required if it is mixed with viscose. For OE spinning where rotor speeds are around 55000 to 60000 rpm standard spin finish is ok, but if a mill has new OE spinning machines having rotors running @80000 rpm, then a totally different spin finish which has a significantly lower fibre – fibre and fibre – metal friction gave very good results. The need to clean rotors was extended from 8 hours to 24 hours and breaks dropped to 1/3rd. In conclusion it must be stated that though the amount of spin finish on the fibre is only in the range 0.105 to 0.160, it decides the fate of the fibre as the runnability of the fibre is controlled by spin finish, so it is the most important component of the fibre. Effectiveness of spin finish is not easy to measure in a fibre plant. Dupont uses an instrument to measure static behaviour and measures Log R which gives a good idea of static cover. Also, there is s Japanese instrument Honest Staticmeter, where a bundle of well conditioned fibre is rotated at high speed in a static field of 10000 volts. The instrument measures the charge picked up by the fibre sample, when the charge reaches its maximum value, same is recorded and machine switched off. Then the time required for the charge to leak to half of its maximum value is noted. In general with this instrument , for fibre to work well, maximum charge should be around 2000 volts and half life decay time less than 40 sec. If the maximum charge of 5000 and half life decay time of 3 min is used , it would be difficult to card the fibre , especially on a high production card. DRY HEAT SHRINKAGE: Normally measured at 180 degree C for 30 min. Values range from 5 to 8 %. With DHS around 5%, finished fabric realisation will be around 97% of grey fabric fed and with DHS around 8% this value goes down to 95%. Therefore it makes commercial sense to hold DHS around 5%. L and B colour: L colour for most fibres record values between 88 to 92. “b” colour is a measure of yellowness/blueness. b colour for semidull fibre fluctuates between 1 to 2.8 with different fibre producers. Lower the value, less is the chemicals degradation of the polymer. Optically brightened fibres give b colour values around 3 to 3.5. This with 180 ppm of optical brightner. DYE TAKE UP: Each fibre producer has limits of 100 +- 3 to 100+-8. Even with 100+-3 dye limits streaks do occur in knitted fabrics. The only remedy is to blend bales from different days in a despatch and insist on spinning mills taking bales from more than one truck load. FUSED FIBRES: The right way to measure is to card 10 kgs of fibre. Collect all the flat strips(95% of fused fibres get collected in flat strips). Spread it out on a dark plush, pick up fused and undrawn fibres and weigh them. The upper acceptable limit is 30mgm /10kgs. The ideal limit should be around 15mgm/10kgs. DUpont calls fused/undrawn fibres as DDD or Deep Dyeing Defect. LUSTRE: Polyester fibres are available in bright : 0.05 to 0.10 % TiO2 Semil dull : 0.2 to 0.3 % TiO2 dull : 0.5 % TiO2 extra dull : 0.7% TiO2 and in optically brightened with normally 180 ppm of OB, OB is available in reddish , greenish and bluish shades. Semi dull is the most popular lustre followed by OB (100 % in USA) and bright. PHYSICAL AND CHEMICAL PROPERTIES OF POLYESTER FIBRE: 1. DENIER: 0.5 – 15 2. TENACITY : dry 3.5 – 7.0 : wet 3.5 – 7.0 3. %ELONGATION at break : dry 15 – 45 : wet 15 45 4. %MOISTURE REGAIN: 0.4 5. SHRINKAGE IN BOILING WATER: 0 – 3 6. CRIMPS PER INCH: 12 -14 7. %DRY HEAT SHRINKAGE: 5 – 8 (at 180 C for 20 min) 8. SPECIFI GRAVITY: 1.36 – 1.41 9. % ELASTIC RECOVERY; @2% =98 : @5% = 65 10. GLASS TRANSITION TEMP: 80 degree C 11. Softening temp : 230 – 240 degree C 12. Melting point : 260 – 270 degree C 13. Effect of Sunlight : turns yellow, retains 70 – 80 % tenacity at long exposure 14. RESISTANCE TO WEATHERING: good 15. ROT RESISTENCE: high 16. ALKALI RESISTENCE: damaged by CON alkali 17. ACID RESISTENCE: excellent 18. ORGANIC CHEMICAL RESISTENCE: good PROBLEMS WHICH OCCUR DURING MANUFACTURE OF POLYESTER STAPLE FIBRE: The manufacture of polyester fibre consists of 4 stps: · Polymerisation:Using PTA/DMT and MEG on either batch or continuous polymerisation (cp_ – forming final polymer · Melt spinning :Here molten polymer is forced thorough spinnerette holes to form undrawn filaments, to which spin finish is applied and coiled in can · Drawings: in which several million undrawn filaments are drawn or pulled approximately 4 times in 2 steps, annealed, quenched, crimped and crimp set and final textile spin finish applied and · Cutting: in which the drawn crimped tow is cut to a desired 32/38/44/51 mm length and then baled to be transported to a blend spinning mill. 1.PROBLEMS FACED IN POLYMERISATION: properties of Polymer: The polymer formed is tested mainly for intrinsic viscosity (i.v), DEG content, % oligeomers and L and b colours. Intrinsic viscosity is an indirect measure of degree of polymerisation and this value is around 0.63 for polymer meant for apparel fibres. DEG or Di Ethylene Glycol gets formed during polymerisation and varies from 1.2 to 1.8%. Oligomers are polymers of lower molecular weight and vary in quantity from 1.2 to 1.8 %. L and b are measures of colour. L colour signifies whiteness as a value of 100 for L is a perfect value. Most fibres have L colour values around 88 to 92. b colour denotes yellowness/blueness of polymer. the positive sign for b colour indicates yellowness whilst negative sign shows blueness, only polymer which contain optical brightener has b of 3 – 3.5 whilst all semil dull polymers show b values of 1.0 to 2.4. Higher values indicate more yellowness, which indirectly shows chemical degradation of the polymer. Running a CP @ lower / higher throughput: Every CP is designed for a certain throughput per day. Like say 180 tons/day or 240 tons/day. Sometimes due to commercial constraints like high buildup of fibre stocks etc. , the CP may have to be operated at lower capacityies. In that case the polymer that is produced has a higher “b” colour and a lower DEG content. Higher “b” colour of say 1.5 against normal value of 1.0 will show fibre to be yellowish and has a little more chemical degradation; which gives higher fluorescence under UV light. Most spinning mills have a practice of checking every cone wound under UV lamp to find out whether there has been any mixup. However if a mill is consistently receiving fibre with a “b”colour of say 1.0 and then if one despatch comes of “b”colour of say 1.5 then in winding, ring bobbins of both “b” colours will be received, and when cones are wound and checked under UV lamp, then higher “b” colour material will give higher fluorescence compared to that of lower “b” colour materials, and will cause rings under UV lamp. Fortunately a minor difference in “b” colour of 0.4 to 0.5 does not give variation in dyeability. Polyester Fibre manufacturing process – 3 What can spinning mills do to overcome this problem: One way is to use a Uster Glow meter which measures the reflectance of fibre samples under UV light. We understand that these values lie between 80 and 120 for samples from different bales. so then divide bales with reflectance values of say 80 to 90 , another 91 to 100, third 101 to 110 and fourth 111 to 120. Then while issuing bales to blow room, issue first group say 80 to 90 then issue the enxt group and so on. Bales from different groups should not be mixed. Second is to use bales from each truck separately. Third is to mix up bales from 4/5 trucks to do a blending Changes in DEG: The amount of DEG in fibre is directly proportional to dye pick up or dye ability of the fibre. Higher the DEG, higher is the dye ability, so much so that some filament producers add DEG, but then higher DEG will lower tensile properties. So this practice is not followed for fibre, where tensile properties are critical. So if the CP is run at lower throughout, DEG drops down, so the dyeablity of the fibre goes down. Since fibre production group is keen on maintaining merge, they resort to lowering of annealer temperatures to maintain dye ability but in the process tensile properties suffer, and mills will notice thread strength falling by 5-7% if annealer temperature is lowered from say 210 degree C to 180 Degree C. If fibre production group does not do this, then they will produce fibre with a different merge – which normally accumulates in the warehouse and so is not appreciated by both marketing and top management. Also when CP is run at higher than rated, then higher temperatures have to be used to compensate lower residence time, here “b” colour actually improves It must be emphasized that the “b”colour changes occur not only due to higher / lower thorugh put but there are several other factors such as air leakags in valves / polymer lines, failure of pumps to remove product from one reaction vessel to another etc. There is yet one more problem in CP. It is a sudden increase in oligomer content. When the amount of oligomers increase, it manifests itself in excessive white powder formation on rings and ring rail. Oligomers cause problems in spinning of dyed fibres. The surface oligomer content almost doubles on dying dark and extra dark shades. The only way to control oligomers is to use LEOMIN OR in 1 – 1.5 gms/litre in reduction clearing bath. All oligomers will go into suspension in reduction clearing liquor and get removed when the liquor is drained. Higher annealer temperature also cause higher surface oligomers 2.PROBLEMS FACED IN MELT SPINNING: Control of C.V% of Denier: A good international value of C.V.% of denier is 4 to 5. However some fibre manufacturers get value as high as 10 to 12. Denier is controlled by having uniform flow of polymer through each spinnerette hole. However if a hole is dirty or has polymer sticking to it, its effective diameter is reduced; and the filament that comes out becomes finer. IF the spinneretters have been used for more than say 6 to 7 years , then some of the holes would be worn out more than others and filament emerging out would be coarser Currently sophisticated instruments are available to check the cleanliness and actual hole diametrs of each and every hole automatically, but few producers have them. Fused Fibres: These are caused mainly at melt spinning either due to breaks of individual filaments or breakages of all the filaments(ribbon break) and polymer and block temperatures are too high. Tying of broken position in the running thread line should be as near to the broken position as possible, failure to do this will result in trailing end leading to fused fibres. Other reasons could be impurities, choking of polymer filters and non-uniform quenching or cooling of filaments. The only way to control is to ensure that breaks at melt spinning are held at the minimum. 3.PROBLEMS FACED AT DRAW LINE: Draw line is the place where the fibre is born. All its major properties denier, tenacity , elongation at break , crimp properties, spin finish, shrinkage and dye ability are all imparted here. For obtaining excellent runnability of the fibre in a blend spinning mill, the two most important properties are – spin finish and crimp. Spin finish: Finish is applied to the undrawn tow at melt spinning stage essentially to provide cohesion and static protection. On the draw line, a major portion of this finish is washed away, and a textile spin finish is put on the tow by either kiss roll or a spray station. This textile finish consists of two components, one that gives cohesion and lubrication and the other confers static protection, usually these 2 components are used in 70/30 ratio. These spin finishes are complex and each may contain some 18 chemicals to not only control inter fibre friction ( should be high at 0.35 to 0.40), fibre metal friction (should be low at 0.15-0.20), anti bacterial components, anti foaming compund etc. Finish is made in hot demineralise water and is sprayed on to tow after the crimper by a series of spray nozzles mounted on both sides of the tow. The finish is pumped to the spray unit by a motor driven metering pump, which is linked to the draw machine such that when the machine stops, the pump motor stops. The percentage of finish on the fibre is based on spin finish manufacturers recommendations and fine tuned by tech service. Once set, the finish and its percentages are normally not changed. The percentage spin finish is decided by the end use of the fibre. Mills blending polyester with viscose need higher amount of spin finish and also mills running their equipment at high speeds. 60 to 65% of problems faced in mills are due to uneven % of spin finish on the fibre. IF a fibre producer desires to put say 0.120% spin finish on fibre, then ideally the %finish should be maintained @ 0.120 +- 0.005 i.e from 0.115 to 0.125 only; then the fibre will run smoothly. If the finish is on the lower side, card web will show high static, web will lap around doffing rolls, sliver will not pass smoothly through coiler tube – causing coiler choking. Sliver could be bulky and will cause high fly generation during drafting. On the other hand if spin finish is on the higher side, fibres will become sticky and lap around the top rollers, slivers will become very compact and could cause undrafted. Thus it is extremely important to hold finish level absolutely constant. The reasons for non uniformity is concentration of spin finish varies; sprayer holes are choked ; the tow path has altered and so the spray does not reach it. Normally fibre producers check spin finish% on the fibre quite frequently- even then in actual practice considerable variations occur. Crimp: It is the most important to spin finish for smooth running of fibre. There are 3 aspects of crimp. · no of crimps per inch or per cm – usually 12 – 14 crimps per inch · crimp stability – be 80% plus and · crimp take up – be 27% on tow crimps per inch can be measured by keeping a fibre in relaxed state next to a foot ruler and counting the no of crimps or arcs. Crimp stability refers to % retention of crimps after subjecting fibre to oscillating straightening and relaxing. We can get an indication on how good crimp stability is in a spinning mill by measuring crimps per inch in fibre from finisher drawing sliver. The crimps per inch of drawing sliver should be atleast 10 to 11, if below this, then the crimps stability is poor , so to compensate may be a cohesive compound like Nopcostatt2151 P or Leomin CH be used in the overspary. Fibres like trilobal and super high tenacity fibres are difficult to crimp. Trilobal because of its shape and super high tenacity due to very high annealer temperature (220 degree C) used which makes the fibre difficult to bend. Also fibre dyeing particularly dark and extra dark shades reduces crimps per inch from 14 to 10 – 11 and in trilobal, as it is crimps per inch in fibre is 11 to 12, after dyeing it goes further down to 8 to 9. In dyed trilobal fibre, crimps per inch in fibre at finisher drawing may be around 6 to 7 so necessitating using almost 50% of cohesive compound in the overspray. Polyester Fibre manufacturing process – 4 Crimp take up is % difference between relaxed length and straightened length of fibre in fibre stage. Normally this difference is around 18 to 20%. If the difference is much smaller, then it means the crimps are shallow and would have lower cohesion. After the tow is crimped , the crimps are set by passing tow through a hot air chamber. If crimp per inch is low, then that could be due to lower stuffer box pressure, but if crimp stability and/or crimp take up is low, it means the steam supply to crimper steam box is low. Undrawn fibre: As the draw line, 1.6 to 3.0 million filaments are drawn or pulled, if a filament had a break at spinning and this is fed as a trailing end to the drawing, then that end cannot be drawn fully, and causes plasticises and fused fibres. Undrawn fibres are generated if the draw point is not uniform i.e not in a straight line. Plasticised fibre: When drawline is running and if some filaments breaks then these broken filaments wrap themselves around a rotating cylinder, since most of these cylinders are steam heated, the wrapped portion solidifes. The operator then cuts out the solid sheet and throws it away as waste but then usually picks up the plastic end and uses it to thread the material and so a small piece of plastic material goes into the cutter and falls into the baler. Tenacity / Dye ability: Both these properties are controlled by acutal draw ratio and annealer temperature. Draw ratio does not change in running, but annealer temperature can fall due to problem of condensate water removal. Most drawlines have temperature indicators – but then some buttons have to be pressed to see the temperatures so if the annealer temperature falls, tenaciy will fall and dye ability will increase which could lead to a change in merge. PROBLEMS FACED IN CUTTING / BALING: Nail Head / Tip Fusion: In the cutting process, a highly tensioned tow is first laid over sharp blades and the pressed down by a Pressure Roll, resulting in filaments being cut. However if some blades become blunt, then the pressing of tow on to those blades creates high temperature and so tips of neighbouring fibres stick to each other and so separating this cluster becomes impossible. If it is not getting removed in Lickerin it will go into the yarn and cause a yarn fault. The tip fusion occurs when the blade is fully blunt. If the blade is not very sharp, it does not give a straight edge, there could be some rounding at the cut edge. Such fibres are called nail heads. Tungsten carbide blades gives sharp cut Opening of fibre cluster after opening: When fibres are cut, they fall down by gravity into the baler. Because of crimping clusters get formed; and so those need to be opened out; otherwise these can cause choking either in blowrrom pipes or in chute feed. This opening is obtained by having a ring of nozzles below the cutter through which high pressure air jets are pointed up; and these jets open up fibre clusters. Over length / Multilength: Over length fibres are those whose length is greater than the cut length plus 10mm and are casued by broken filaments which being broken cannot be straightened by tensioning at the cutter. Multilength are fibre whose length is exactly 2 or 3 times the cut length and are caused by nicks in neighbouring blades. SPECIALITY FIBRES IN POLYESTER: · HIGH/LOW SHRINK FIBRES: The high shrink fibre shrinks upto 50% at 100 degree C while that of low shrinkage is 1%. The high shrink fibre enable fabrics with high density to be produced and is particularly used in artificaial leather and high density felt. Low shrinkage fibre is recommended for air filters used in hot air, furniture, shoes etc. · MICRO DENIER: Available in 0.5/0.7/0.8 deniers in cutlengths 32/38 mm. Ideal for high class shirts, suitings, ladies dress material because of its exceptional soft feel. It is also available in siliconised finish for pillows. To get the best results, it is suggested that the blend be polyester rich and the reed/pick of the fabric be heavy. · FLAME RETARDANT: Has to be used by law in furnishings / curtains, etc where a large number of people gather – like in cinema theatres, buses, cars etc in Europe and USA. It is recommended for curtains, seat covers, car mats, automotive interior, aircraft interiors etc. · CATIONIC DYEABLE: Gives very brilliant shades with acid colours in dyeing / printing. Ideal for ladies wear · EASY DYEABLE: Can be dyed with disperse Dyes @98 degrees C without the need for HTHP equipment. Ideal for village handicrafts etc. · LOW PILL: In 2 and 3 deniers, for suiting end use and knitwear fibre with low tenacity of 3 to 3.5 gm/denier, so that pills which forms during use fall away easily. · ANTIBACTERIAL:It is antibacterial throughout the wear life of the garment inspite repeated washing. Suggested uses are underwears, socks, sports, blankets and air conditioning filters · SUPER HIGH TENACITY: It is above 7 g/denier and it is mainly used for sewing threads. Low dry heat shrinkage is also recommended for this purpose. Standard denier recommended is 1.2 and today 0.8 is also available. · MODIFIED CROSS SECTION: In this there are TRILOBAL, TRIANGULAR, FLAT, DOG BONE and HOLLOW FIBRES with single and multiple hollows. Trilobal fibre gives good feel. Triangular fibre gives excellent lustre. Flat and dog bone fibres are recommended for furnishings, while hollow fibres are used as filling fibres in pillows, quilts, beddings and padding. For pillows silicoised fibres is required. Some fibre producers offer hollow fibre with built in perfumes. · CONDUCTING FIBRE: This fibre has fine powder of stainless steel in it to make fibre conductive. Recommended as carpets for computer rooms. · LOW MELT FIBRE: It is a bi-component fibre with a modified polyester on the surface which softens at low temperature like 110 degree C while the core is standard polyester polymer. This fibre is used for binding non woven webs. REFERENCE: POLYESTER STAPLE FIBRE AND BLEND SPINNING SEMINAR BY MR.S.Y.NANAL M.TEXT, F.T.I YARN TESTING INTRODUCTION:Yarn occupies the intermediate position in the manufacture of fabric from raw material. Yarn results aretherefore essential, both for estimating the quality of rawmaterial and for controlling the quality offabric produced. The important characteristics of yarn being tested are,· yarn twist · linear density · yarn strength · yarn elongation · yarn evenness · yarn hairiness etc.SAMPLING:In order that the results obtained are reproducible and give reliable information about the material,the sampling must be true and representative of the bulk lot. The sampling procedure should be designedto take account of and to minimise the known sources of variability such as the variation betweenspindles, the variation along the length of the bobbin, etc. The procedure for sampling and the number of test carried out are given under each characteristic. AMBIENT CONDITIONS FOR YARN TESTING:Some textile fibres are highly hygroscopic and their properties change notably as a function of the moisturecontent. Moisture content is particularly critical in the case of properties, i.e yarn tenacity, elongation, yarn evenness, imperfections, count etc. Therefore conditioning and testing must be carried outunder constant standard atmospheric conditions. The standard atmosphere for textile testing involves a temperature of 20+-2 degree C, and 65+-2% Rh. In tropical regions, maintaining a temperature of 27+-2 degree C,65+-2%RH is legitimate. Prior to testing, the samples must be conditioned under constant standard atmospheric to attain the moisture equillibrium. To achieve this it requires at least 24 hours. TWIST:”Twist is defined asthe spiral disposition of the components of yarn, which is generally expressedas the number of turns per unit length of yarn, e.g turns per inch, turns per meter, etc. · Twist is essential to keep the component fibres together in a yarn. · The strength, dyeing, finishing properties, the feel of the finished product etc. are all dependenton the twist in the yarn. · With increase in twist, the yarn strength increases first , reaches a maximum and then decreases. · Depending on the end use, two or more single yarns are twisted together to form “plied yarns” or “folded yarns” and a number of plied yarns twisted together to form “cabled yarn”. · Among the plied yarns, the most commonly used are the doubled yarns, wherein two single yarns ofidentical twist are twisted together in a direction opposite to that of the single yarns. · Thus for cabled and plied yarns, the direction of twist and the number of turns per unit length of the resultant yarn as well as of each component have to be determined for a detailed analysis. · Direction of twist is expressed as “S”-Twist or “Z”-Twist. Direction depends upon the direction of rotationof the twisting element. · Twist take up is defined as, “The decrease in length of yarn on twisting, expressed as a percentageof the length of yarn before twisting.- LINEAR DENSITY OR COUNT OF YARN:· The fineness of the yarn is usually expressed in terms of its linear density or count. · There are a number of systems and units for expressing yarn fineness. But they are classified as followsDIRECT SYSTEM:1. English count(Ne) 2. Metric count(Nm) 3. French count(Nf)INDIRECT SYSTEM:4. Tex 5. Denier6. Ne : No of 840 yards yarn weighing in One pound 7. Nm : No of one kilometer yarn weighing in One Kilogram 8. Nf : No of one kilometer yarn weighing in 0.5 kilogram 9. Tex : Weight in grams of 1000 meter(1 kilometer) yarn 10. Denier: Weight in grams of 9000 meter(9 kilometer) yarn· · For the determination of the count of yarn, it is necessary to determine the weight of a known lengthof the yarn. For taking out known lengths of yarns, a wrap-reel is used. The length of yarn reeled off depends upon the count system used. · Another factor which determines the length of yarn taken for testing is the type of balance used.Some balances like quadrant balance, Beesley’s blanace have been specially designed to indicate the yarn count directly from tests on specified short lengths of yarn and are very useful for determining the counts of yarn removed from the fabrics. The minimum accuracy of balance required is 0.001mg · One of the most important requirements for a spinner is to maintain the average count and count variation within control. The term count variation is generally used to express variation in the weight of a lea and this is expressed as C.V.%. This is affected by the number of samples and the length being considered for count checking. While assessing count variation, it is very important to test adequate number of leas.After reeling the appropriate length of yarn, the yarn is conditioned in the standard atmospherefor testing before it’s weight is determined. · The minimum number of sample required per count is 20 and per machine is 2.YARN STRENGTH AND ELONGATION:· Breaking strength, elongation, elastic modulus, resistance abrasion etc are some important factors which will represent the performance of the yarn during actual use or further processing. Strength testing is broadly classified into two methods 1. single end strength testing 2. skein strength or Lea strengthTensile strength of single strands of yarn:· During routine testing, both the breaking load and extension of yarn at break are usually recorded forassessing the yarn quality. Most of the instruments record the load-elongation diagram also. · Various parameters such as initial elastic modulus, the yield point, the tenacity or elongation at any stress or strain, breaking load, breaking extension etc can be obtained from the load-extension diagram.· Two types of strengths can be determined for a yarn1. Tensile strength -load is applied gradually 2. Ballistic strength – applying load under rapid impact conditions· Tensile strength tests are the most common tests and these are carried out using either a single strandor a skein containing a definite number of strands as the test specimen. · · An important factor which affects the test results is the length of the specimen actually used for carrying out the test. The strength of a test specimen is limited by that of the weakest link in it.If the test specimen is longer, it is likely to contain more weak spots, than a shorter test specimen. Hencethe test results will be different for different test lengths due to the weak spots. YARN EVENNESS INTRODUCTION: Non-uniformity in variety of properties exists in yarns. There can be variation twist.,bulk, strength, elongation , fineness etc. Yarn evenness deals with the variation in yarn fineness. This is the property, commonly measured as the variation in mass per unit length along the yarn, is a basic and important one, since it can influence so samy other properties of the yarn and of fabric made from it. Such variations are inevitable, because they arise from the fundamental nature of textile fibres and from their resulting arrangement. The spinner tries to produce a yarn with the highest possible degree of homogeneity. In this connection, the evenness of the yarn mass is of the greatest importance. In order to produce an absolutely regular yarn, all fibre characteristics would have to be uniformly distributed over the whole thread. However, that is ruled out by the inhomogeneity of the fibre material and by the mechanical constraints. Accordingly, there are limits to the achievable yarn eveness. IMPORTANCE OF YARNEVENNESS: Irregularity can adversely affect many of the properties of textile materials. The most obvious consequence of yarn evenness is the variation of strength along the yarn. If the average mass per unitlength of two yarns is equal, but one yarn is less regular than the other, it is clear that the more even yarn will be the stronger of the two.The uneven one should have more thin regions than the even one as a result of irregularity, since the average linear density is the same. Thus, an irregular yarn will tend to break more easily during spinning, winding, weaving, knitting, or any other process where stress is applied. A second quality-related effect of uneven yarn is the presence of visible faults on the surface of fabrics. If a large amount of irregularity is present in the yarn, the variation in fineness can easily be detected in the finished cloth. The problem is particularly serious when a fault(i.e a thick or thin place) appears at precisely regular intervals along the length of the yarn. In such cases, fabric construction geometry ensures that the faults will be located in a pattern that is very clearly apparent to the eye, and defects such as streaks, stripes, barre, or other visual groupings develop in the cloth. Such defects are usually compounded when the fabric is dyed or finished, as a result of the twist variation accompanying them. Twist tends to be higher at thin places in a yarn. Thus , at such locations, the penetration of a dye or finish is likely to be lowe than at the thick regions of lower twist. In consequence, the thicker yarn region will tend to be deeper in shade than the thinner ones and, if a visual fault appears in a pattern on the fabric, the pattern will tend to be emphasized by the presence of colour or by some variation in a visible property, such as crease-resistance controlled by a finish. Other fabric properties, such as abrasion or pill-resistance, soil retention, drape, absorbency, reflectance, or lustre, may also be directly influenced by yarn evenness. Thus, the effects of irregularity are widespread throughout all areas of the production and use of textiles, and the topic is an important one in any areas of the industry. “UNEVENNESS” OR “IRREGULARITY”: The mass per unit length variation due to variation in fibre assembly is generally known as “IRREGULARITY” or “UNEVENNESS”. It is true that the diagram can represent a true relfection of the mass or weight per unit length variation in a fibre assembly. For a complete analysis of the quality, however, the diagram alone is not enough. It is also necessary to have a numerical value which represents the mass variation. The mathematical statistics offer 2 methods · the irregularity U% : It is the percentage mass deviation of unit length of material and is caused by uneven fibre distribution along the length of the strand. · the coefficient of variation C.V.% In handling large quantities of data statistically, the coefficient of variation (C.V.%) is commonly used to define variability and is thus well-suited to the problem of expressing yarn evenness. It is currently probably the most widely accepted way of quantifying irregulariy. It is given by coefficient variation (C.V.%) = (standard deviation/average) x 100 The irregularity U% is proportional to the intensity of the mass variations around the mean value. the U% is independent of the evaluating time or tested material length with homogeneously distributed mass variation. the larger deviations from the mean value are much more intensively taken into consideration in the calculation of the coefficient of variation CV(squaring of the term) C.V.% has received more recognition in the modern statistics than the irregularity value U. The coefficient of variation CV can be determined extremely accurately by electronic means, whereas the calculation of the irregularity U is based on an approximation method. It can be considered that if the fibre assembly required to be tested is normally distributed with respect to its mass variation, a conversion possibility is available between the two types of calculation. C.V.% = 1.25 * U% INDEX OF IRREGULARITY”: Index of irregularity expresses the ratio between the measured irregularity and the so-called limiting irregularity of an ideal yarn. The manner in which irregularity is assessed can lead to different ways of expressing the index. In calculating the limit irregularity, the assumption is made that, in the ideal case, fibre distribution in a yarn is completely random and a practical yarn can never improve upon this situation.Thus, the measured irregularity will be an indication of the extent to which fibre distribution falls short of complete randomness. If all fibres are uniform in cross-sectional size, it can be shown that the limiting irregularity expressed in terms of C.V is given by C.V.(limit) = 100 / sqrt(N) This expression also assumes a POISSON distribution in the values around “N”(the mean number of fibres in the cross section) Let C.V.lim = the calculated limit irregularity C.V. = the actual irreglarity Then, Index of Irregularity (I) = C.V / C.V.lim By calculating the limit irregularity and then measuring the actual irregularity, we can judge the spinning performance. DEVIATION RATE: Deviation rate describes by what percentage a mass deviation exceeds or falls below a certain limit. The cut length factor in m averages out the shorter, higher deviations DR (xy) = (L1+l2..+Ln) x 100 / L tot DR = Total relative length in (%) of all deviations of the mass signal which surpass the limit +/- x% over a total test length of L meters, with the cut length of curve being y meters. FORMULA FOR DR PERCENTAGE: The standard DR used for yarn is 1.5 m cutlength at a +/- 5% limit. The application of DR is similar to that of the CVm values. One has to take in to consideration that the DR is based on threshhold values and changes more significantly than CV values when higher mass deviations over long stretches of test material arise. THe deviation rate is calculated by comparing all the deviations of the positive range with the whole test length Ltot. The same is valid for all deviations in the negative range. As the zero line corresponds to the median , the Deviation Rate (DR) can reach the maximum of 5 0%. YARN EVENNESS – 2 Page 1 2 3 DETERIORATION IN EVENNESS DURING PROCESSING: In processing in the spinning mill, the unevenness of the product increases from stage to stage after drawframe. There are two reasons for this · The number of fibres in the cross section steadily decreases. Uniform arrangement of the fibres becomes more difficult, the smaller their number. · Each drafting operation increases the unevenness Each machine in the spinning process adds a certain amount to the irregularity of finished yarn. The resultant irregularity at the output of any spinning process stage is equal to the square root of the sum of the squares of the irregularities of the material and the irregularity introduced in the process. Let us assume that, CVo – CV of output material CV1 – CV of input material CV – irregularity introduced by machine then, CVo = sqart(CV1 + CV) UNEVENNESS OVER DIFFERENT CUT LENGTHS: A length of yarn, for example of 10mm, contains only few fibres. Every irregular arrangement of only some of these fibres has a strong influence on the unevenness. In a length of yarn of 10m, incorrect arrangement of the same fibres would hardly be noticed against the background of the large number of such fibres. Accordingly, the CV value of the same yarn can be, for example, 14% based on, 8mm, and only 2% based on 100 m. The degree of irregularity is dependent upon the regerence length. Unevenness is therefore discussed in terms of short lengths(uster tester):medium lengths(seldom used):long lengths(count variation). Fabric stripiness and barre have been problematic fabric defects in the textile industry for many years. Though direct quantification has not been possible, the causes for such fabric defects have been studied. It has been shown that raw material quality and yarn mass variations (particularly medium and long term variations) contribute significantly to the guidance of such faults. Of these causes, there has been a general neglect of the control of medium term variations (variations over 1m, 3m,10m, etc). A mill needs to control the cut length variations of the yarn produced in order to ensure a fault free fabric. If the variation of cut length C.V.% of 1 meter, 3 meters, 10 meters is high , when different cops are tested , the fabric appearance will be very badly affected. It will result in fabric defects such as stripiness. IMPERFECTIONS: Yarns spun from staple fibres contain “IMPERFECTIONS” . They are also referred to as frequently occurring yarn faults. They can be subdivided into three groups · Think places · Thick places · Neps The reasons for these different types of faults are due to rawmaterial or improper preparation process. A reliable analysis of these imperfections will provide some reference to the quality of the raw material used. Thick places and thin places, lie in the range of +-100% with respect to the mean value of yarn cross-sectional size.The Neps will overstep +100% limit. Thick places over +100% are analysed by the CLASSIMAT system, are cut by the clearers in winding depending upon the end use of the yarn. Imperfection indicator record imperfections at different sensitive levels. · Thin place o -30% : yarn cross section is only 70% of yarn mean value o -40% : yarn cross section is only 60% of yarn mean value o -50% : yarn cross section is only 50% of yarn mean value o -60% : yarn cross section is only 40% of yarn mean value · Thick place o +35% : the cross section at thick place is 135% of yarn mean value o +50% : the cross section at thick place is 150% of yarn mean value o +70% : the cross section at thick place is 170% of yarn mean value o +100%: the cross section at thick place is 200% of yarn mean value · Neps o 400%: the cross section at the nep is 500% of the yarn mean value o 280%: the cross section at the nep is 380% of the yarn mean value o 200%: the cross section at the nep is 200% of the yarn mean value o 140%: the cross section at the nep is 140% of the yarn mean value Thick places and thin places which overstep teh minimum actuating sensitivity of +35% and -30% , respectively, correspond to their length to approximately the mean fibre length. Medium length or long thick and thin places are to be considred as mean value variations and are not counted by the instrument. The standard sensitive levels are as follows · Thin place : -50% · Thick place : +50% · Neps : 200% ( 280% for open-end yarns) The reason for reducing the sensitivity of nep counting in rotor spun yarns is due to the fact that with these yarns, the neps tend to be spun into the core of the yarn and therefore are less visible to the human eye in the finished product. With ring spun yarns, on the other hand, the neps, in general tend to remain on the surface of the yarn. Due to the above reasons, while a nep is considered serious for a ring spun yarn even if its size exceeds +200%, it becomes serious only after its size exceeds +280% for open end yarns. It is however worth mentioning here that, though the imperfection values at standard sensitiviy levels i.e. +50% for thick places and -50% for thin places indicate the acceptable quality levels in terms of fabric appearance, the quality of processing in terms of optimization of process parameters will be better indicated by imperfections at higher sensitivity levels. It is commonly observed that while the thin places may be ‘0’ for any two mills at the standard sensitivity level of -50%, the thin places at -40% sensitivity may show a big difference. Thin places and thick places in a yarn can, on the one hand, quite consdierably affect the appearance of a woven or knitted fabric. Furthermore, an increase in the number of thin places and thick places refer to a particularly valuable indication that the raw material or the method of processing has become worse. On the other hand, it cannot be concluded from the increased number of thin place faults that this yarn, the downtime of weaving or knitting machines will be increased to a similar degree. Thin places usually exhibit a higher yarn twist, because of fewer fibres in the cross-section resulting in less resistance to torsion. The yarn tension does not become smaller proportionally with a reduced number of fibres. With thick plalce faults the contrary is the case. More fibres in the cross-section result in a higher resistance to torsion. Thic places have therefore, in many cases, a yarn twist which is lower than the average. The yarn tension in the yarn at the position of the thick place is only in very few cases proportional to the number of fibres. These considerations are valid primarily for ring-spun yarns. YARN EVENNESS – 3 Page 1 2 3 · Neps can influence the appearance of woven or knitted fabrics quite considerably. Furthermore neps of a certain size can lead to processing difficulties, particularly in the knitting machines. Therefore the avoidance of neps in the production of spun yarns is a fundamental textile technological problem. Neps can be divided, fundamentally , into two catergories: -raw material neps -processing neps The rawmaterial neps in cotton yarn are primarily the result of vegetable matter and immature fibres in the raw material. The influence of the rawmaterial with wool and synthetic fibres in terms of nep production is negligible. Processing neps are produced at ginning and also in cotton , woollen and worsted carding. Their fabrication is influenced by the type of card clothing, the setting of the card flats, workers and strippers, and by the production speeds used. SPECTROGRAM: “DIAGRAM” is a representation of the mass variations in the time domain. Whereas SPECTROGRAM is a representation of the mass variation in the frequency domain. Spectrogram helps to recognize and analyse the periodic fault in the sliver, roving and yarn. For textile application, the frequency spectrum is not practical. A representaion which makes reference to the wavelength is preferred. Wavelength indicatres directly at which distance the periodic faults repeat. The more correct indication of the curve produced by the spectrograph is the wave-length spectrum. Frequency and wavelength are related as follows frequency = (wavelength)/(material speed) In the SPECTROGRAM, the X-axis represents the wavelength. Inorder to cover a maximum range of wavelengths, a logrithmic scale is used for the wavelength representation. The y-axis is without scale but represents the amplitude of the faults in yarn. The spectrogram consists of shaded and non-shaded areas. If a periodic fault passes through the measuring head for a minimum of 25 times, then it is considered as significant and it is shown in the shaded area. Wavelength ranges which are not statistically significant are not shaded. In this range the faults are displayed but not hatched. This happens when a fault repeats for about 6 to 25 times within the tests length of the material. As far as those faults in the unshaded area is concerned, it is recommended to first confirm the seriousness of the fault before proceeding with the corrective action. This can be done by testing a longer length of yarn. Faults which occur less than 6 times will not appear in the spectrogram. A spectrogram starts at 1.1 cm if the testing speed is 25 to 200 m.min. It starts at 2.0cm if the testing speed is 400 m/min and it starts at 4 cm if the speed is 800 m.min. For spun material the maximum wavelength range is 1.28 km. Maximum number of channels is 80 Depending upon the wavelength of the periodic fault, the mass variations are classified as 1. short-term variation( wavelength ranges from 1 cm to 50cm) 2. medium-term variation( wavlength ranges from 50cm to 5 m) 3. long-term variation(wavelength longer than 5 m) · periodic variations in the range of 1 cm to 50 cm are normally repeated a number of times within the woven or knitted fabric width, which results in the fact periodic thick places or thin places will lie near to each other. This produces, in most cases, a “MOIRE EFFECT”. This effect is particularly intensive for the naked eyes if the finished product is observed at a distance of approx. 50 cm to 1m. · Periodic mass variations in the range of 50cm to 5m are not recognizable in every case. Faults in this range are particularly effective if the single or double weave width, or the length of the stretched out yarn one circumference of the knitted fabric, is an integral number of wave-lengths of the periodic fault, or is near to an integral number of wave-lengths. In such cases, it is to be expected that weft stripes will appear in the woven fabric or rings in the knitted fabric. · Periodic mass variations with wave-lengths longer than 5m can result in quite distinct cross-stripes in woven and knitted fabrics, because the wave-length of the periodic fault will be longer than the width of the woven fabric or the circumference of the knitted fabric. The longer the wavelength, the wider will be the width of the cross-stripes.Such faults are quite easily recognizable in the finished product, particularly when this is observed from distances further away than 1 m. A periodic mass variation in a fibre assembly does not always result in a statistically significant difference in the U/V value. Nevertheless, such a fault will result in a woven or knitted fabric and deteriorate the quality of the fabric. Such patterning in the finished product can become intensified after dyeing. This is particularly the case with uni-coloured products and products consisting of synthetic fibre filament yarns. The degree to which a periodic fault can affect the finished product is not only dependent on its intensity but also on the width and type of the woven or knitted fabric, on the fibre material, on the yarn count, on the dye up-take of the fibre, etc. A considerable number of trials have shown that the height of the peak above the basic spectrum should not overstep 50% of the basic spectrum height at the wavelength position where the peak is available. · CHIMNEY TYPE FAULTS: The eccentricity roller results in a sinusoidal mass variation whereby the periodicity corresponds to full circumference of the roller. With one complete revolution of an OVAL roller, a sinusoidal mass variation also results, but 2 periodic faults are available. Chimney type of faults are mainly due to -mechanical faults -eccentric rollers, gears etc -improper meshing of gears -missing gear teeth -missing teeth in the timing belts -damaged bearings etc · HILL TYPE FAULTS: These faults are due to drafting waves caused by -improper draft zone settings -improper top roller pressure -too many short fibres in the material, etc Numerous measurements of staple-fibre materials have shown that there are rules for the correlation between the appearance of drafting waves in the spectrogram and the mean staple length. It is given below -yarn : 2.75 x fibre length -roving : 3.5 x fibre length -combed sliver : 4.0 x fibre length -drawframe sliver : 4.0 x fibre length A periodic fault which occurs at some stage or another in the spinning process is lengthened by subsequent drafting.If the front roller of the second drawframe is eccentric, then by knowing the various drafts in the further processes, the position of the peak in the spectrogram of the yarn measurement can be calculated. The wavelength of a defective part is calculated by multiplying the circumference of the part and the draft upto that part. The wavelength of a defective part can be calculated if the rotational speed of the defective part and the production speed are known. Doubling is no suitable means of eliminating periodic faults. Elimination is only possible in exceptional cases. In most cases, doubling can, under the best conditions, only reduce the periodic faults. The influence of periodic mass variation is proportional to the draft. Due to the quadratic addition of the partial irregularities, the overall irregularity of staple-fibre yarns increases due to the periodic faults only to an unimportant amount. YARN EVENNESS DIAGRAM The mass variations or weight per unit length variations are recorded and printed as a Diagram by the Evenness tester. The diagram is an extremely important part of evenness testing. It contains a large amount of information which cannot be provided by the wavelength spectrum, U% value, and the imperfections. Diagrams help to understand the following seldom occuring events long wave-length variations periodic mass variations with wave-lengths which are longer than 40m(which can not be confimed by the spectrogram. extreme thick and thin places randomly occurring thick and thin places which tend to be available in batches. slow changes in the mean value step changes in the mean value with periodic faults, it can be determined whether the fault is permanently availabe or occurs only in batches with measurements “within a bobbin”, seldom occurring events can be found and changes in the mean value taking place over a number of kilometers can be confirmed. with unusual measured values, it can be proved in many cases by means of the diagram whether these refer to a faulty or to a correct measurement. RELATIVE COUNT: It is a measure used to calculate the count variations using capacitance method of USTER TESTER. It calucalates a value called “Average Value Factor AF”. This factor is proportional to the mean count of the tested sample length. The relative count describes the variation of count between separate measurements within a sample. The single values are calculated such that they are in direct reference to the mean value of the sample which is always considered to be 100%. The relative count is always estimated with reference to a test length of 100m or 100 yards. From the single-overall report, it is possible to recognize immediately which samples are lying above or below the mean value. The standard deviation provides a reference to the variation in count between samples. As the mean value is always 100%, the standard deviation also provides a reference to the coefficient of variation. If the samples are from the same bobbin this would indicate the “within bobbin” variation and if the samples are from the same bobbin this would indicate the “within bobbin” variation and if the samples are from different bobbins this would indicate “between bobbin” variation. VARIANCE LENGTH CURVE: The variance-length curve is generally regarded as the most useful technique for expressing the yarn irregularity data. Any fibre assembly has a TOTAL IRREGULARITY CV(T), and this coefficient of variation is made up of two terms. These are the coefficient of variation within length ,CV(L) and the coefficient of variation between lengths CB(L). The co-efficient of variation at different cut lengths provided by the evenness testers provide invaluable information with regard to the variations prevalent at the specific cut lengths. Therefore independently, the short, medium and long term variations could be studied by estimating the coefficient of variation of the required length. However, such numerical values, cannot directly provide complete information on the source of faults. The spectrogram provides a possibility of localizing the source of fault but with a spectrogram, only faults of periodic nature could be identified and that too, in most cases, only if proceeded by some other means of identifying the machine / processing stage responsible for the fault. When the variations prevailing at different cut lengths are simultaneously represented graphically, it provides the possibility of segregating cut lengths at which abnormal variations occur and consequently identify the process stage which is most likely to be responsible. This is made possible by the “Variance Length Curve” which is a standard feature of most evenenss testers. A variance-length curve can be set out in quite a simple manner by cutting a fibre assembly into pieces and determining gravimetrically the mass of these pieces. The CV value is then calculated from each of these separate values. If this procedure is repeated for various cut lengths and the CV value drawn out, one obtains the variance-length curve. Uster tester can be used to obtain the curve in a much shorter time than is possible by manual analysis. For constructing the variance length, the measuring field length is taken as the basic cut length at which the CV is calculated and plotted. For variations at other cut lengths, the mass of successive portion of material are added up and the CV calculated. Strictly speaking, the variance-length curve is only a straight line on double logrithmic paper in the medium length range of approx.1 cm to 100m. For cut lengths shorter than 1 cm and longer than 100m, the variance-length curve tends to become flatter. One can easily comprehend that the curve for the same raw material and same ideal processing conditions will always be a straight line with an unchanged angle of inclination. Deviations from the straight line must therefore indicate porblems due to the machine or the raw material. THEORETICAL LIMIT FOR IRREGULARITY: The spinning process is based primarily on a procedure which evenly mixes the fibre, separates each fibre from its neighbour, lays the fibres parallel to each other and draws these out to produce a final count. The mixing leads, however, to the fact that each single fibre has the same probability of appearing in any chosen section of the fibre mass. The fibres are therefore equally distributed in the fibre assemblies. The number of fibres in any section considered is dependent on random variations. The fibres overlap each other and result, even under the best conditions, in a spun material which has a certain minimum irregularity. With the natural fibres, in contrast to the synthetic staple fibres, there is an additional irregularity because the single fibres themselves have differences in their fibre corss sectional size. The theoretical investigations have helped to arrive at a formula which will help us to calculate the limiting irregularity. CV(lim) = 100 /(sqrt(N) where, N = mean number of fibres in the cross section. CALCULATION OF NUMBER OF FIBRES IN THE YARN CROSS-SECTION: The number of fibres in the cross section of a yarn can be calculated if the fibre fineness and yarn count in tex are available, or can be converted into tex(gram per 1000m) N = T/Tf where, N = number of fibres in the cross section T = count of the fibre material in TEX Tf= Fibre fineness in TEX INERT TEST: The uster evenness testing installations offer two possible modes of operation which are referred to as the · Normal test · Inert test With the “NORMAL TEST” , a signal is obtained from the tested masterial which is in reference to the measuring field length of the applied measuring slot. In the operating mode “INERT TEST”, the signal obtained from the test material is passed through an electrical filter arrangement. Normally, the signal from the test material consists of short and long- term variations which are superimposed on each other. By means of this filter procedure, the shorter-term variations are suppressed in a certain manner, so that only the mean value variations, i.e the long-term mass variations, will be traced out in the diagram. This testg serves primarily to provide, · an indication of the random mean value variations in the test material · a means of localizing and indicating long term periodic variations in the test material · a means of facilitating the setting of the mean value at the yarn signal instrument. If medium-term varitaions appear in a diagram, one can make these more distinctive by choosing a suitable diagram feed and suitable material speed and operating with the mode Inert test. YARN HAIRINESS INTRODUCTION Yarn hairiness is a complex concept, which generally cannot be completely defined by a single figure. The effect of yarn hairiness on the textile operations following spinning, especially weaving and knitting, and its influence on the characteristics of the product obtained and on some fabric faults has led to the introduction of measurement of hairiness. FACTS ABOUT YARN HAIRINESS: Hairiness occurs because some fibre ends protrude from the yarn body, some looped fibres arch out from the yarn core and some wild fibres in the yarn. · Pillay proved that there is a high correlation between the number of protruding ends and the number of fibres in the yarn cross-section. · Torsion rigidity of the fibres is the most important single property affecting yarn hairiness. Other factors are flexural rigidity, fibre length and fibre fineness. · Mixing different length cottons-No substantial gain in hairiness. Although the hairiness of a yarn could be reduced to some extent by the addition of a longer and finer cotton to the blend. The extent of reduction is not proportional to the percentage of the longer and finer component. This is probably due to the preferential migration of the coarser and shorter component, which has longer protruding ends, from the yarn body. The addition of wastes to the mixing increases the yarn hairiness; the effect of adding comber waste is greater than that of adding soft waste. · Blending-not a solution to hairiness. The blended yarns are rather more hairy than expected from the hairiness of the components; a result similar to that found in cotton blends. This may be due to the preferential migration of the shorter cotton fibers; a count of the number of protruding ends of both types of fiber shows that there is more cotton fiber ends than expected, although the difference is not very great. · The number of protruding ends is independent of twist, whereas the number of loops decreases when the yarn twist increases because of a greater degreee of binding between hte fibres owing to twist. The number of wild fibres decreases only very slightly with twist because of their position on the yarn periphery. · The proportion of fiber ends that protrude from the yarn surface, counted microscopically · has been found to be about 31% of the actual number of ends present in the yarn. · If the length of the protruding fibre ends as well as that of the loops is considered, the mean value of the hairiness increases as the cross-sectional area increases and decreases with the length of the loops. The hairiness is affected by the yarn twist, since an increase in twist tends to shorten the fibre ends. · Wild fibres are those for which hte head alone is taken by the twist while the tail is still gripped by the front drafting rollers. · Fibre length influences hairiness in the sense that a greater length corresponds to less hairiness. · Cotton yarns are known to be less hairy than yarns spun from man-made fibres. The possible reason for this is the prifile of the two fibres.Because of taper, only one end, the heavier root part of the cotton fibre, tends to come out as a protruding end in a cotton yarn. With man-made fibres, both ends have an equal probability of showing up as protruding ends. · If the width of the fibre web in the drafting field is large, the contact and friction with the bottom roller reduce the ability of the fibres to concentrate themselves and hairiness occurs. This effect is found more in coarse counts with low TPI. This suggests that the collectors in the drafting field will reduce yarn hairiness.- · The yarn hairiness definitely depends on the fibres on the outer layer of the yarn that do not directly adhere to the core. Some of them have an end in the core of the yarn gripped by other fibres, whereas others, because of the mechanical properties of the fibre(rigidity, shape, etc.) emerge to the surface. During the twisting of the yarn, other fibres are further displaced from their central position to the yarn surface. · Greater the fibre parallelization by the drawframe, lower the yarn hairiness. · An increase in roving twist results in lower yarn hairiness, because of smaller width of fibre web in the drafting field. · The number of fiber ends on the yarn surface remains fairly constant; the number of looped fibers reduces in number and length on increasing twist. · Combed yarn will have low yarn hairiness, because of the extraction of shorter fibres by the comber. · Yarn hairiness increases when the roving linear density increases . Yarn spun from double roving will have more hairiness than the yarn spun from single roving. This is due to the increased number of fibres in the web and due to higher draft required to spin the same count. Drafting waves increase hairiness. Irregularity arising from drafting waves increases with increasing draft. Yarn hairiness also may be accepted to increase with yarn irregularity, because fibers protruding from the yarn surface are more numerous at the thickest and least twisted parts of the yarn. · The yarns produced with condernsers in the drafting field, particularsly if these are situated in the principal drafting zone, are less hairy than those spun without the use of condensers. · Higher spindle speed – high hairiness. When yarns are spun at different spindle speed, the centrifugal force acting on fibers in the spinning zone will increase in proportion to the square of the spindle speed, causing the fibers ends as they are emerging from the front rollers to be deflected from the yarn surface to a greater extent. Further, at high spindle speed, the shearing action of the traveller on the yarn is likely to become great enough to partially detach or raise the fibers from the body of the yarn. As against the above factors, at higher spindle speeds the tension in the yarn will increase in proportion to the square of the spindle speed, and consequently more twist will run back to the roller nip, so that it is natural to expect that better binding of the fibers will be achieved. The increase in hairiness noticed in the results suggests that the forces involved in raising fibers from the yarn surface are greater than those tending to incorporate them within the body of the yarn at higher spindle speeds. · Higher draft before ring frame-less hairiness. There is a gradual reduction of hairiness with increase in draft. In other word, as the fiber parallelization increases hairiness decreases. Reversing the card sliver before the first drawing head causes a reduction in hairiness, the effect being similar to that resulting from the inclusion of an extra passage of drawing. · Smaller roving package-less hairiness. Yarn hairiness decreases with decrease in roving (doff) size, and yarn spun from front row of roving bobbins is more hairy and variable as compare to that spun from back row of rowing bobbins. It may be noted that though the trends are consistent yet the differences are non-significant: · The spinning tension has a considerable influence on the yarn hairiness. The smaller the tension, the greater the hairiness. This is the reason why heavier travellers result in low yarn hairiness. If the traveller is too heavy also , yarn hairiness will increase. · Spindle eccentricity leads to an increase in hairiness. Small eccentricities influence hairiness relatively little, but, from 0.5 mm onwards, the hairiness increases almost exponentially with eccentricity. · The increase in hairiness due to spindle eccentricity, will be influenced by the diameter of ring, dia of bobbin, the shape of the traveller,the yarn tension, etc. · Yarn hairiness will increase if the thread guide or lappet hook is not centred properly. Heavier traveler- less hairiness. The reduced hairiness of yarns at higher traveller weights can be explained by the combined effect of tension and twist distribution in the yarn at the time of spinning. The spindle speed remains constant, but the tension in the yarn will increase with increasing traveller weight, and better binding of the fibers would be expected. Parallel fibers-less hairiness. The improvement of yarn quality on combing is mainly ascribed to the reduction in the number of short fiber improvement in length characteristics, and fiber parallelization. There is a marked difference in hairiness of the carded yarn and the combed yarns, even with a comber loss of only 5%, but the effect on hairiness of increasing the percentage of comber waste is less marked. Combing even at low percentage waste causes a marked drop in hairiness relative to that of the carded yarn. In the case of combed cotton yarns the average value of hairiness decreases with increase in count, whereas in the case of polyester/ viscose blend yarns the hairiness increases with increase in count. In the case of polyester/ cotton blend yarns trend is not clear. · Flat and round travellers do not influence yarn hairiness, but a greater degree of hairiness was observed with elliptical travellers and anti-wedge rings. · Traveller wear obviously influences hairiness because of the greater abrasion on the yarn. Yarn hairiness increases with the life of the traveller. · Bigger the ring diameter, lower the yarn hairiness. · Yarn spun in a dry atmosphere is more hairy. · Hairiness variation between spindles is very detrimental. Because these variation can lead to shade or appearance variaion in the cloth. · The variation in hairiness within bobbin can be reduced considerably by the use of heavy travellers alone or by balloon-control rings with travellers of normal weight. In both the cases yarn is prevented from rubbing against the separators. · Yarn hairiness is caused by protruding ends, by the presence of a majority of fibre tails. This suggests that these tails will become heads on unwinding and that friction to which the yarn is subjected will tend to increase their length. It is therefore logical that a yarn should be more hairy after winding. · Repeated windings in the cone widning machine will increase the yarn hairiness and after three or four rewindings, the yarn hairiness remain same for cotton yarns. · Winding speed influences yarn hairiness, but the most important increase in hairiness is produced by the act of winding itself. · Because of winding, the number of short hairs increases more rapidly thatn the number of long hairs. · In two-for-one twisters (TFO), more hairiness is produced because, twist is imparted in two steps. Yarn hairiness also depends upon the TFO speed, because it principally affects the shortest fibre ends. · Hairiness varitions in the weft yarn will result in weft bars. YARN HAIRINESS – 2 Hairiness Testing of Yarns Hairiness of yarns has been discussed for many years, but it always remained a fuzzy subject. With the advent of compact yarns and their low hairiness compared to conventional yarns, the issue of measuring hairiness and the proper interpretation of the values has become important again. Generally speaking, long hairs are undesirable, while short hairs are desirable (see picture ). The picture shown below just give a visual impression of undesirable and desirable hairiness at the edge of a cops. Figure: RING YARN COMPACT YARN There are two major manufacturers of hairiness testing equipment on the market,and both have their advantages and disadvantages. Some detail is given below. USTER USTER is the leading manufacturer of textile testing equipment. The USTER hairiness H is defined as follows . H =total length (measured in centimeters) of all the hairs within one centimeter of yarn . (The hairiness value given by the tester at the end of the test is the average of all these values measured, that is,if 400 m have been measured,it is the average of 40,000 individual values) . The hairiness H is an average value,giving no indication of the distribution of the length of the hairs. Let us see an example 0.1cm 0.2cm 0.3cm 0.4cm 0.5cm 0.6cm 0.7cm 0.8cm 0.9cm 1.0cm total yarn 1 100 50 30 10 5 6 0 2 1 0 398 yarn 2 50 10 11 5 10 0 5 10 0 11 398 Both yarns would have the same hairiness index H, even though yarn is more desirable,as it has more short hairs and less long hairs,compared to yarn 2. This example shows that the hairiness H suppresses information,as all averages do. Two yarns with a similar value H might have vastly different distributions of the length of the individual hairs. The equipment allows to evaluate the variation of the value H along the length of the yarn. The “sh value “is given, but the correlation to the CV of hairiness is somehow not obvious.A spectrogram may be obtained. 2.ZWEIGLE Zweigle is a somewhat less well known manufacturer of yarn testing equipment. Unlike USTER,the Zweigle does not give averages. The number of hairs of different lengths are counted separately, and these values are displayed on the equipment. In addition, the S3 value is given,which is defined as follows: S3 =Sum (number of hairs 3 mm and longer) In the above example,the yarns would have different S3 values: S3yarn 1 =2 . S3yarn 2 =4 . A clear indication that yarn 2 is “more hairy “than yarn 1. The CV value of hairiness is given a histogram (graphical representation of the distribution of the hairiness) is given. The USTER H value only gives an average,which is of limited use when analyzing the hairiness of the yarn.The Zweigle testing equipment gives the complete distributionof the different lengths of the hairs. The S3 value distinguishes between long and short hairiness, which is more informative than the H value. HAIRINESS IN YARN I am very happy to add this article written by Mr.Kamatchi Sundaram , All india Service Manager of VOLTAS LTD. INDIA, in my site. He is one among the good technologists who has indepth knowledge about textile technology and spinning machines. I hope this information is of use to the technical people who browse through this site. Hairiness is a measure of the amount of fibres protruding from the structure of the yarn. In the past, hairiness was not considered so important. But with the advent of high-speed looms and knitting machines, the hairiness has become a very important parameter. In general, yarn spun with Indian cotton show high level of hairiness due to the following reasons. 1. High short fibre content in mixing. 2. Low uniformity ratio. 3. High spindle speeds. Hence most of the Indian yarns have a hairiness index above 50% Uster standards. However, as this parameter is becoming more and more important, Indian spinners are concentrating more on this aspect and try to reach at least 25% standards by conducting lot of trials. He has conducted a lot of such studies on hairiness and he is pleased to share his learning’s with you. Hairiness is measured in two different methods. 1. USTER HAIRINESS INDEX: This is the common method followed in India. The hairiness index H corresponds to the total length of protruding fibres within the measurement field of 1cm length of the yarn. 2. ZWEIGLE HAIRINESS INDEX: This zweigle hairiness measurement (S3) gives the number of protruding fibres more than 3 mm in length in a measurement length of one meter of the yarn. From the above you can infer that Uster hairiness index give the total length of hairs whereas zweigle hairiness testers give the absolute number of fibres. Though the later measurement is more accurate, most of the Indian spinners are still following Uster hairiness index only. The factors effecting hairiness can be sub divided into 3 major components. a) The fibre properties. b) Yarn parameters. c) Process parameters. a)THE FIBRE PROPERTIES: Fibre length, Uniformity ratio, Micronaire and short fibre content are the properties exerting high influence on hairiness. Among the above the length and short fibre content exerting major influence. For a particular count, higher length of fibre leads to lesser hairiness and high short fibre content leads to high hairiness. b)YARN PARAMETER: Hairiness is dependent on the number of fibres present in the cross section of the yarn. Hence coarser yanrs have more hairiness compared to finer yarns. The yarn twist is another major factor and higher twists lead to less hairiness up to a certain extent. This is the main reason while hosiery yarns normally have high hairiness compared to warp yarns. However in a mill condition, the fibre parameters and yarn parameters cannot be adjusted. Hence the next topic, process parameters, assumes very high significance, as this is the only available option at the mill level to reduce the hairiness. C) PROCESS PARAMETER: The preparatory machines do not have a big influence on hairiness. The Speed frame, Ring frame and the Cone winder are the only machines to be attended for reduction in hairiness. I give below the various process parameters that can be attended for reducing the hairiness. a)SPEED FRAME: 1. Roving hank: It plays a major role in the reduction of hairiness. For a particular count, the hairiness of the yarn goes down, as the roving hank is made finer and finer. For example: If 30s yarn is spun with 0.8 and 1.0 hank, yarn made with 1.0 hank will give lesser hairiness than the yarn made with the 0.8 hank. Hence please conduct a trial with finer roving hank to reduce the hairiness. The results of the study conducted recently at a leading mill are given below for your reference on this point. TRIALS ON HAIRINESS EFFECT OF ROVING HANK ON HAIRINESS Ring rail bottom po Ring rail top postion COUNT 24 ch 24 ch 24 ch 24 ch 24 ch 24 ch ROVING HK 1.0 0.9 0.8 1.0 0.9 0.8 SPACER 3.0 3.0 3.0 3.0 3.0 3.0 U% 8.75 8.8 8.72 8.61 8.54 8.68 thin (-50%) 0 0 0 0 0 0 thick (+50%) 10 15 15 9 11 14 Neps (+200%) 12 18 21 12 14 18 Total IPI 22 33 36 21 25 32 Hairiness Index 7.52 7.86 8.45 6.4 6.48 7.09 Sh(-) 1.31 1.3 1.48 1.19 1.27 1.41 You would note from the above that the hairiness as well as imperfections have improved significantly by using finer hank of the roving. 2. Spacer Size: It is the normal tendency of the technicians to use spacer as thin as possible to reduce the U% and imperfections. But thinner spacers lead to higher hairiness. Hence please conduct a trial with a spacer, which is 1.0 to 1.5 mm thicker than existing spacer. b) RING FRAME: 1. Ring Traveller: It is generally opined by many technicians that the traveller plays a major role in hairiness. Though selection of the traveller plays a small role in hairiness (specially with reference to the yarn clearance), it’s effect is quite less. This is because the yarn contact point with the traveller is quite far away from the ring and traveller contact point. Hence even if the traveller is run for a long time, the hairiness will not increase. But the breakage rate will increase. 2. Ring: It is the general opinion of some technicians that imported rings give lesser hairiness than Indian rings. It is also believed by technicians that older rings give more hairiness. Recent studies / trials conducted by us recently at a leading mill indicate this not to be true. Please refer the table below. EFFECT OF RINGS ON HAIRINESS RING COPS TRAIL (TOP POSITION OF THE RING RAIL) PARAMETERS old lmw rings new lmw rings bracker rings NOMINAL COUNT 30s CH 30s CH 30s CH U% 9.37 9.59 9.59 Thin (-50%) 0 0 0 Thick (+50%) 24 28 24 Neps (+200%) 51 52 58 Total IPI 75 80 82 Hairiness Index 5.4 5.26 5.33 Sh(-) 1.18 1.13 1.17 HAIRINESS IN YARN – 2 RING COPS TRAIL (BOTTOM POSITION OF THE RING RAIL) PARAMETERS old lmw rings new lmw rings bracker rings NOMINAL COUNT 30s CH 30s CH 30s CH U% 9.24 9.18 9.24 Thin (-50%) 0 0 0 Thick (+50%) 26 19 27 Neps (+200%) 49 44 46 Total IPI 75 63 73 Hairiness Index 6.11 6.06 6.22 Sh(-) 1.27 1.26 1.29 You would note from the above trials that: a) There is no significant difference in hairiness between Imported & Indian rings. b) There is also no significant difference in hairiness between a new and a one-year-old ring. However if the condition of the ring is highly worn out , it will affect the hairiness. In short the ring and traveller do not play a major role on hairiness compared to other process parameters, which are explained below. 3) SPACER SIZE: Size of the spacer plays significant role in reducing the hairiness. Many technicians have a tendency to use the thinnest spacer for reduction in U% and imperfections. However it leads to significant increase in hairiness. A study conducted recently at a leading mill proves this point. Please refer the table below for the above study. EFFECT SPACER SIZE ON HAIRINESS Ring rail bottom position Ring rail Top position COUNT 24s CH 24s CH 24s CH 24s CH ROVING HK 0.8 0.8 0.8 0.8 SPACER 3.0 4.0 3.0 4.0 U% 8.7 9.06 8.58 8.76 thin (-50%) 0 0 0 0 thick (+50%) 8 15 7 12 Neps (+200%) 14 16 16 19 Total IPI 22 31 23 31 Hairiness Index 7.32 6.72 5.87 5.35 Sh(-) 1.27 1.19 1.07 1.06 You would note from the above that there is a significant reduction in hairiness by using thicker spacer. However the imperfection has also increased. . The spacer should be selected such that optimum results are achieved with respect to imperfections as well as hairiness. We request you to conduct a trial with a spacer, which is 0.5 to 1mm thicker than the existing spacer. It is needless to mention that using thicker spacer will increase the imperfections. However if the reduction in hairiness is more significant than increase in imperfections it can be allowed. 4) TPI IN THE YARN: Increasing the TPI leads to reduction in hairiness and this is more significant in the case hosiery yarn. Hence if the hairiness is a bigger problem faced by mill, trials can be conducted by increasing the TPI up to the allowable limit for achieving reduction in hairiness. 5) LAPPET HEIGHT: Reduction in lappet height leads to direct reduction in hairiness. However care should be taken to ensure that the yarn does not touch the tip of the Empties. Please conduct trials with reduced lappet height (Formula: Lappet height = 2D+5mm). 6) SUCTION TUBE SETTING: The suction tube should be set such that the yarn does not touch the tip of the suction tube in running. If the yarn touches the suction tube due to improper setting, it will lead to increase in hairiness. 7) TRAVELLER SIZE: Usage of heavier traveller leads to reduction in hairiness. For Example: If the breakage rate in 30s carded hosiery count is same with 4/O and 6/O traveller, using 4/O traveller will give lesser hairiness than 6/O traveller. 8) LIFT AND RING DIAMETER: Using lesser lift and lesser ring diameter will lead to direct and significant reduction in hairiness. For Example: If 30s carded hosiery count is spun with 170/38 and 180/40 combination, spindle speeds remaining the same, the former combination will give much lesser hairiness than the later combination because of a reduction in the height and diameter of the yarn balloon while spinning. C) CONE WINDER: There will be a significant difference between the hairiness of the yarn at cop stage and at cone stage. The cone winding process increases the hairiness by 15 to 20%, which is unavoidable. However, if the modern AutoConers are not tuned properly, it will lead to increase in hairiness of much more than 20%. In this case the following points need attention. 1. WINDING SPEED: The speed of winding plays a significant role on increase in hairiness. The increase in winding speed leads to direct increase in the hairiness. The results of the study conducted recently at a leading mill are given below for your reference on this point. EFFECT OF WINDING SPEED ON HAIRINESS PARAMETERS Cop result winding speed 1200 m/min winding speed 1400 m/min winding speed 1600 m/min NOMINAL COUNT 30 s CH 30 s CH 30 s CH 30 s CH U% 9.37 9.59 9.6 9.53 Thin (-50%) 0 0 0 0 Thick (+50%) 16 14 15 17 Neps (+200%) 39 41 41 50 Total IPI 55 55 59 50 Hairiness Index 5.04 7.13 7.47 7.5 Sh(-) 1.08 1.59 1.66 1.73 You would note from the above that the hairiness increases more and more with the increase in the winding speed. However it is not economically feasible to run the AutoConer at slow speed just for achieving lesser hairiness. But all the AutoConers have a provision to adjust the speed of winding according to the stage of the cop and this is called variable speed arrangement. By selecting the right speeds at different stage of the cop the increase in hairiness can be controlled to a great extent. 2. YARN TENSION DURING WINDING: By optimizing the yarn tension the increase in hairiness can be controlled. The results of the study conducted recently at a leading mill are given below for your reference on this point. PARAMETERS tension 25 grams tension 32 grams NOMINAL COUNT 30/1 CH 30/1 CH U% 9.73 9.68 Thin (-50%) 0 0 Thick (+50%) 23 19 Neps (+200%) 52 48 Total IPI 75 67 Hairiness Index 7.41 7.72 Sh(-) 1.74 1.79 You would note from the above that the hairiness can be reduced by optimizing the winding tension. This trial may be conducted at your mills for controlling the hairiness. 3. WAX PICK UP: It is the normal practice of many mills to apply wax on the hosiery yarn during winding. By controlling the wax pick up, the increase in hairiness can be reduced. The detail of the study recently conducted at a leading mill is given below for your reference. EFFECT OF WAX PICK UP ON HAIRINESS PARAMETERS wax pick up 0.8 gms/kg wax pick up 1.2 gms/kg NOMINAL COUNT 30/1 s CH 30/1 s CH U% 9.84 9.91 Thin (-50%) 0 1 Thick (+50%) 32 30 Neps (+200%) 89 112 Total IPI 121 1459 Hairiness Index 8.13 7.89 Sh(-) 1.84 1.87 We request you to conduct a study of this aspect at your mills for control of hairiness. Thus, there are several process parameters that can be optimized for controlling the hairiness. Unless the ring and traveller are in a worn out condition, the role played by the ring and traveller on hairiness is quite negligible on modern ring frames like LG5/1 and LR/6. BARRE IN FABRICS · INTRODUCTION In textile industry, one of the most common and perplexing quality control problems is barre(repetitive yarn direction streaks). The factors which can cause or contribute to barre are varied and diverse. · Barre is defined as “unintentional, repetitive visual pattern of continuous bars or stripes usually parallel to the filling of woven fabric or to the courses of circular knit fabric.” · Barre is sometimes used as a synonym for WARP STREAKS. · Barre can be caused by physical, optical or dye differences in the yarns, geometric differences in the fabric structure or by any combination of these differences. · Barre is basically a visual phenomenon and any property of yarn which makes it ‘look’ different from the adjacent yarn in a fabric would result in this defect. · · Barre can be due to the following · fibre properties · yarn characterisitics · knitting parameters · · In weft knit fabrics Barre is taken to include only those fabric defects charecterised by coursewise (widthwise) repearing bars or stripes. In warp knits, the warp (or length) direction. This is symptomatic of the way in which the fabrics are produced. · CAUSES OF BARRE All barre is the consequence of subtle differences in yarn reflectance between individual yarn in the knit structure. Any mechanism that can change the reflectance of a yarn in a knit structure is a potential barre source. Barre can be caused by physical, optical, or dye differences in the yarns, geometric differences in the fabric structure, or by any combination of these differences. A barre streak can be one course or end wide or it can be several – a “shadow band” · It is not the inadequacy of the raw material property which results in Barre, It is the inconsistency or the variability of the particular property which results in Barre. · · The properties which are the causes of Barre are given below. · · Fibre Micronaire variation · Fibre color variation · Yarn linear density variation · Yarn twist variation · yarn hairiness variation · knitting tension variation · improper mixing of cotton from different origin · improper mixing of cotton from different varieties · improper mixing of cotton grown in different seasons · Zellweger Uster has published the following details regarding Barre · · causes % ge of defect fibre 70 yarn count variation 10 twist variation 10 hairiness 10 · · Micronaire: · The difference in Micronaire average of the mixings of the entire lot should not be more than 0.2 · The range of the Micronaire of the individual bales used in the mixings should be same · the C.V.% of Micronaire of individual bales within the mixing should be less than 12 % · Same micronaire bales should not be placed side by side and a group should be formed with the different micronaire bales and it should be repeated in the bale laydown · David M. Clapp 5 , of Cotton Incorporated demonstrated that as the difference in micronaire value increases, the intensity of the barre effect becomes more serious. In the process, he observed that the cause of barre is not the difference in dye uptake between the thin cell walls of the low micronaire fibres and the thicker cell walls of the high micronaire fibres.He showed that per unit weight, dye exhaustion / fixation is essentially the same for the low micronaire and high micronaire fibres and also illustrated that at high micronairevalues, both the maturity and fineness registered an increase. More importantly, he extended his study and showed that by proper blending of the cottons, the occurrence of barre due to differences of even upto 1.6 micronaire can be eliminated. · · Fluorescence: · The difference in UV reading average of the mixings of the entire lot should be same · Variation in UV readings within the bale should be less · out side storage of cotton should be avoided · UV readings increase over time if it is stored for a long time · should not mix high and low UV bales · · Colour has been one of the primary factors of cotton quality for quite a long time. Colour is particularly important as a measure of how well a yarn or fabric will dye or bleach. Colour in general is expressed in trichromatic terms, such as L, a and b (Reflectance, Redness/greenness and Yellowness / blueness). The significance of these components with regard to cotton has been extensively studied and is generally agreed upon that only reflectance and degree of yellowness are important in assessing cotton colour · · The influence of cotton colour on the dyeability characteristics of fabrics have been studied and reported by the U.S. Department of Agriculture , which revealed that a significant correlation exists between the colour characteristics of raw cotton and the colour of washed and wash-dyed cotton fabrics. Since much of the barre effects are due to the variations in dyeability characteristics within a fabric, difference in colour properties could be expected to influence the seriousness of any barre incidences in the fabric. · Yarn properties: · It has been widely accepted that it is the inconsistency or the variation aspect of the yarn properties which is a prime cause for ‘Barre” · Of the various quality characteristics tested, variation in hairiness count and twist are considered to be three important properties which need proper control to avoid barre. · Slippage of spindle tape is the main reason for the TPI variations. If the TPI is more in yarn then the yarn diameter will reduce adn number of helical angle will increase. If the diameter of the yarn is low then more light will pass through that region of cloth because the gap between the two yarn is more.When more ridges are present, then more light reflects from the surface of the yarn. Hence regions with high TPI yarn appear light coloured after dying. · knitting: · A bar or stripe may be caused by several variables shown below · Tight loops: This may take the form of a shaddow ( several courses involved) or a discreet line ( one course involved). It will normally show up as a dark or dense line or shaddow · Slack loop: Similar to above, but it shows up as a sheer or light line. · improper stich length at a feed · improper tension at a feed · variation in fabric take-up from loose to tight · Worn needles, which generaly produce length direction streaks · Uneven cylinder height needles(wavy barre) · · Uneven loops: In this the “average” stitch length is the same in all cases but the distribution of the length of yarn between the dial and the cylinder of knitting machine is not balanced on a particular course. Thus it will appear as a tight or slack course on one side but analysis will not show up the fault. · Weaving: · Uneven warping tension · Uneven take-up tension · Uneven let-off motion · Uneven tension on filling · Scuffing or filling yarn on the beam · Bent beam gudgeons BARRE IN FABRICS – Page 2 · VISUAL BARRE ANALYSIS: · The first step in Barre investigation is to observe and define the problem. Barre can be the cause of physical causes which can usually be detected, or it can be casued by dyeability differences which may be nearly impossible to isolate in fabric. Barre analysis methods that help to discriminate between physical barre and barre caused by dyeability differences incluede Flat Table Examination, Light source Observation, and the Atlas Streak analyser. · FLAT TABLE EXAMINATION: · For a visual barre analysis, the first step is to lay a full width fabric sample out on a table and view both sides from various angles. Generally, if the streaky lines run in the yarn direction, color differences can be seen by looking down at the fabric in a direct visual line with the yarn direction, and the defect can be positively identified as a barre defect. Viewing the fabric with a light source in the back ground will show if the barre is physical. · LIGHT SOURCE OBSERVATION: · After completing an initial Flat Table Examination, a Light Source Examination may provide further useful information. Full width fabric samples should be examined under two light conditions, fluorescent and ultraviolet (UV) light. Observations that should be made while viewing under lights are: · · frequency and direction of the barre · whether streaks are dark or light and · total length of pattern repeat. · · Ultraviolet light, commonly referred to as a “black light”, allows the presence of mineral iols to be more easily detected, due to their radiant energy (glow). When observed under UV light, fabrics with streaks that exhibit glow suggest improper preparation. A change in composition or content of oil/wax by the spinner or knitter without appropriate adjustments in scouring can create this problem. · · PHYSICAL BARRE ANALYSIS: · When the cause of barre is determined or presumed to be physical in nature, physical fabric analysis should be done. Physical barre causes are generally considered to be those which can be linked to yarn or machine differences. Methods of physical barre analysis include fabric dissection, microscopy, and the Roselon Knit Extension Tester. · FABRIC DISSECTION: · To perform accurate fabric dissection analysis, a fabric sample which contains several barre repetitions is required. First, the barre streak boundaries are marked by the placement of straight pins and/or felt markers. Individual yarns are removed from light and dark streak sections, and twist levels, twist direction, and cut length weight determinations are made and recorded. For reliable mean values to be established, data should be collected from at least two light/dark repeats. After compilation of yarn information, the numbers can be compared individually to adjacent yarns as well as by groupings of light and dark shades. · MICROSCOPY: · Microscopic examination is useful for verifying yarn spinning systems. Yarns from different spinning systems can have different light reflectance and dye absorption properties. Ring spinnning produces yarn that is smooth. Open end spinning produces yarn with wrapper fibres at irregular intervals. Air jet spinning produces yarn with more wrapper fibres than open end and inner fibres are more paralle. Microscopy can also reveal a shift in loop formation in knitted fabrics when twist direction (S and Z) differences are present. · Barre is noticed in a fabric when the visual perception of colour of a particular portion of a fabric is different from that of an adjacent portion. Numerous attempts have been made by research workers to arrive at a mathematical number which gives an equal change when a change in perceptible colour difference exists. · Reflectance differences have been considered by many researches to be indication of barre in fabrics. E.R.Cairns, H.A.Davis and J.W.Coryell 5 hypothesised that double knit barre is caused by textured yarn reflectance differences in the knit structure. Depending on the detailed arrangement of these differences, barre is seen as continuous or random and either as single end streaks or bands. Based on studies made with a research grade spectrophotometer, they also found that yarn reflectance differences are caused by differences in key textured yarn properties like bulk, cross section, loop size etc. · PREVENTION OF BARRE: · As outlined, Barre is caused by INCONSISTENCIES in materials, equipment, or processing. To prevent Barre form occuring, consistency must be maintained through all phases of textile production. Stock yarns should be properly and carefully labelled to avoid mixups. Fugitive tints can be useful for accurate yarn segregation. Inventory should be controlled on a First In/ First Out basis. All equipement should be properly maintained and periodically checked. Before beginning full scale production, sample dyeings can be done to check for Barre. · Salvaging a fabric lot with a Barre problem may be possible through careful dye selection. Color differences can be masked by using shades with very low light reflectance (navy blue, black) or high light reflectance (light yellow, orange, or finished white). Dye suppliers should be able to offer assistance in this area. Also, if the cause of the barre is an uneven distribution of oil or wax, a more thorough preparation of the fabric prior to dyeing may result in more uniform dye coverage. · With close cooperation between production and quality control personnel, barre problems can be successfully analysed and solved. · EXPERIMENT: · The experiments done by Mr.ANBARASAN of PREMIER POLYTRONICS is given below. · FIBRE PROPERTY INFLUENCE ON FABRIC BARRE: · EXPERIMENTAL PROCEDURE It was identified that the incidences of fabric barre was more common in knitted fabrics. So one of the most commonly used hosiery counts – 30s Nec Combed Hosiery was chosen for the study. · Preparation of basic yarn samples: Preparation of samples with different yarn count: The extent of influence of yarn count was studied by taking into consideration three levels of count. To avoid any abnormal conditions of spinning, one of the levels was maintained at the normal level used by mill for regular production. The other two samples were obtained by spinning counts differing by 2 Nec(6.7%) from the normal. The three count samples of 28, 30 and 32 Nec are designated as A, B and C respectively. · The raw material and the process parameters maintained in all departments upto ring spinning were maintained the same for all the three samples. In ring frames, the count change pinion was changed to obtain the required count. All the other process parameters were maintained the same in ring frames as well. Preparation of samples from different micronaire cottons: · The samples for studying the influence of fibre micronaire were prepared by spinning yarn from cottons of micronaire values ranging from 3.8 to 4.32. The micronaire values of the samples are given in Table 1 along with their designations. The cottons were obtained by segregating samples of the same cotton variety to avoid influences of other varietal factors. · Serial No. Sample designation Micronaire 1 P 3.8 2 Q 3.95 3 R 4.14 4 S 4.32 · Table : Micronaire Values of Basic Samples · Cottons with difference in micronaire readings of less than 0.15 were not taken up since 0.15 represented the measurement accuracy of the micronaire instrument. The spinnings were carried out using a miniature spinning system having the following sequential processing stages : · – Carding – Drawing – Sliver to Yarn Spinning About 50gms of cotton was processed from each sample to obtain yarns sufficient for the subsequent knitting process. Barre in Fabrics – Page 3 · Preparation of samples from cotton with different colour levels: For studying the influence of colour, the parameter ‘Degree of yellowness(+b)’ provided by the high volume fibre testers was taken as the reference. Five spinnings were carried out with cottons of different +b values. The values are shown below. · Serial No. Sample Degree of Yellowness (+b) 1 A1 9.2 2 B1 10.5 3 C1 11.6 4 D1 13.5 5 E1 14.7 · Table : Degree of Yellowness (+b) for Basic Samples · The spinnings for these samples were also carried out using the miniature spinning system. Fabric Preparation FFor all the trials to study the influence of count, fibre micronaire and colour, to detect the presence or otherwise of the barre effect, different combination of two levels were selected. The yarn samples were knit into single jersey fabrics on a circular knitting machine with 2.5mm stitch length such that the two different levels of the combination formed alternate portions of the fabric as shown below : · Fabric knitted with a combination of yarn samples. · The fabrics were knitted with 48 cones of each of the two levels feeding the machine. · Dyeing The fabrics for all the combinations were dyed using Procion Blue MR dye of 2.5% concentration. The same batch of dye bath was used to dye all the fabrics pertaining to a particular property in order to eliminate the introduction of any possible errors in the process of dyeing. · RESULTS AND DISCUSSIONS · Influence of Yarn Count The intensity of the barre effect noticed for the various count combinations in terms of the visual grading are represented in the following table. · combination count difference in count average grade 1 2 AB 28 30 2 4.25 BC 30 32 2 4.5 AC 28 32 4 4.75 · Table : Influence of Count on Barre Intensity The table clearly shows that the intensity of barre is more severe as the difference in count levels increases. It can also be noted that even if a count deviation of +2 Nec from the average is present, a grade of more than 4.0 is recorded which indicates a reasonably high amount of barre. · Influence of Fibre Micronaire: The four basic yarn samples obtained from cotton with different micronaire values were used to knit fabrics in a total of 6 combinations with the difference in micronaire values ranging from 0.15 to 0.52. The intensity of barre for these combinations are tabulated below in terms of the average visual grade. · Combination Micronaire value Difference in Micronaire Average grade PQ 3.8 3.95 0.15 3 RS 4.14 4.32 0.18 2 OR 3.95 4.14 0.19 3 PR 3.8 4.14 0.34 2 QS 3.95 4.32 0.37 3 PS 3.8 4.32 0.52 2 · Table : Influence of Micronaire on Barre Intensity · The table shows that, within the range of micronaire taken-up in the present study, the intensity of Barre remains fairly constant. An important observation is that the intensity of Barre is serious even with a micronaire difference of 0.15. Hence when preparing mixings of single cotton variety, it should be ensured that the difference in average micronaire between successive mixings is less than 0.15. · Influence of Fibre Colour: From the basic 5 samples of yarn differing in terms of the ‘Degree of Yellowness (+b)’, a total of 10 combination of fabrics could be obtained, with the colour difference ranging from 1.1 to 5.2. The details of the samples and the intensity of barre noticed in these samples are tabulated below. Micronaire Value Combination · Serial No Combination Degree of Yellowness difference in +b values visual grade 1 B1C1 10.5 11.6 1.1 1 2 D1E1 13.5 14.7 1.2 2 3 A1B1 9.2 10.5 1.3 3 4 C1D1 11.6 13.5 1.9 4 5 A1C1 9.2 11.6 2.4 3 6 B1D1 10.5 13.5 3.0 5 7 C1E1 11.6 14.7 3.1 4 8 B1E1 10.5 14.7 4.2 5 9 A1D1 9.2 13.5 4.3 5 10 A1E1 9.2 14.7 5.5 4 · Table : Influence of Degree of Yellowness on Barre Intensity · The influence of colour on the barre intensity is clearly seen from the last two columns of the table where the visual barre grade shows a direct relationship with the difference in +b values of the cottons used. An exclusive consideration of the +b value gave the following best-fit equation for the Visual Grade (VG). VG = 5.101 – 0.078(+b) – ((4.393 )/square(+b)) A good correlation of 0.90 was obtained between actual and predicted grades. · CONCLUSIONS The influence of three important parameters – yarn count, fibre micronaire and fibre colour – on the intensity of the barre defect iin cotton knitted fabrics are discussed. Of the fibre parameters, the degree of yellowness of cotton seems to have a relatively more significant effect on the Barre intensity in fabrics than the micronaire. However even deviation of micronaire value to the extent of +0.15 results in a visible barre defect. Deviations in yarn count also shows up significantly as Barre defects. Avoidance of the Barre effect, therefore, requires proper control on all these parameters. ON BARRE CAUSED BY RAWMATERIAL The current expansion of the worldwide market for cotton has opened up many possibilities for the spinning mill. Spinning mills now have many options in the raw materials they purchase for producing yarn. This expansion in the availability of raw material has helped in reducing costs and improving yarn quality and spinning efficiency. Unfortunately this situation has also presented some new challenges for the spinning managers and cotton buyers. Traditionally purchased cottons had well established seed varieties and growing regions. This meant that with an average control of micronaire they had few problems with the dying and finishing of cotton fabrics. Over the past two years we have seen a rapid increase of the problems with dying and fabric finishing. This is especially evident in the claims and rejects 100% cotton knitted fabrics for fabric barre’. Claims and rejects can easily wipe out any savings in raw material costs obtained by purchasing cotton from several international sources. Many spinning mills are under the impression that all upland seed varieties mature the same as related to the micronaire. Unfortunately what they discover is that cottons with similar micronaire that have different growing regions and seed varieties dye differently. Controlling some of the basic fiber properties can give the spinning mill the information necessary to reduce and or eliminate the recurring problems of barre’. Mill experience and trials have given us the necessary information to set up guidelines for controlling the fiber properties that influence the dyability of cotton yarns in knitted fabrics. There are several mechanical causes of fabric barre’ that are associated with the spinning and sliver preparation processes in the spinning mill. The following table shows that the major cause of BARRE is due fiber. FABRIC BARRE CAUSE % OF DEFECTS Fibre 70 Yarn count variation 10 Twist variation 10 Hairiness 10 While mechanical differences and variations in yarn count, twist and hairiness can also be a cause of the barre’ effect the single largest cause lies in the variation in fiber properties. Figure 3 shows the fiber properties that have a major influence in the causes of barre’. Micronaire, maturity/fineness and fluorescence all play a major role in the consistent dying and finishing of knitted fabric. Micronaire Most mills have learned over the years that they need to control the average of the micronaire in the bale laydown. Most mills have some type of system to categorize cotton bales into groups in an effort to control the average micronaire. While controlling the average micronaire is a good first step many times this is not enough control to eliminate the barre’ effect, especially in knitted fabric. The causes and controls necessary for eliminating dying problems as they relate to micronaire are given below · difference in micronaire should be less than 0.2 · change in average micronaire from mix to mix should be less than 0.1 · C.V% of micronaire within mix should be within 10% · Bales with same micronaire should not be placed side by side The additional control of the variation or CV% of the micronaire must be added to the overall control of the average in each laydown. It is also necessary to change the average of the laydown over time so that all bales in the warehouse can be processed. The change in average micronaire in the laydown must be changed slowly over time.The maximum bale-to-bale variation ( c.v%)within the mix should be 10%. A variation(c.v%) of micronaire higher than 10% will very likely cause a barre’ effect in the fabric. Maturity & Fineness Micronaire is an indication of the maturity in cotton fiber, although it is not a direct measurement of the fiber maturity. Micronaire can be used successfully to control barre’ if the cotton being processed is from the same seed variety. If cottons from several varieties or growing areas are being blended together, then additional testing and maturity information may be necessary. Causes of Barre due to Maturity · Blending cottons from different growth areas · Blending cottons from different seed varieties · seasonal changes in cotton growth cycle 1. weather 2. insects · Immature fibre cotent % (IFC%) 1.White speck neps 2. carding speeds An example of fabrics made of yarn produced from three (3) different bales of cotton is shown in figure . The cottons all had the same micronaire (4.2) but, as can be seen, the dye uptake on the individual yarns were very different. The above Figure is a good example of how cotton fiber maturity (not micronaire) can cause a barre’ effect in fabric. These bales of cotton were tested on the HVI instrument and the yarn was tested on the Uster Evenness tester. These results are shown in figures 1 , it is not possible to determine any significant differences between these three cottons that would cause a problem in dying and finishing. The cottons are also tested on the new AFIS Length and Maturity to determine if any difference could be found. The results from the AFIS Maturity module are shown in figure 2. FIG:1 STUDY ON BARRE CAUSED BY RAWMATERIAL – Page 2 FIG:2 The AFIS Maturity module is a single fiber measurement of individual fiber maturity. The individual fiber maturity information gives a distribution of fiber maturity as well as the average fiber maturity. The distribution enables us to identify the very immature fibers and it is described by the Immature Fiber Content (IFC%). Figure 2 clearly shows a considerable difference of the three bales in the IFC%. Maturity differences in cotton can also cause defects in fabric such as white speck neps. Fabric in figure 3 was knitted from yarn produced from three different cottons having similar micronaire values. There was a significant difference in the amount of white specks in the three fabric samples. The three cottons were tested on the AFIS Maturity module and the results are given in figure 4. The differences in the AFIS IFC% correlates visually to the amount of white specks in the three fabrics. Interesting is that the overall average maturity ratio from the three cottons was very similar, giving no indication of a potential problem of white specks. FIG 3: FIG 4: Variation of Maturity in Sliver There is a possibility to optimize the carding process to make sure all cards remove as much of the immature fiber as possible. Figure 5 shows the results from testing a line of cards all fed from the same bale laydown. It is interesting that while the card mats all show very similar results the card slivers show quite some variation. The possibility of the influence of carding on the maturity of the sliver was investigated further using the AFIS Maturity module. Several individual cards were analyzed and it was apparent that there was a large variation in the amount of immature fibers removed by the cards. This initial trial indicated that it is possible to change the mechanical setup of a card to influence the removal of immature cotton fibers. These results are shown in figure 6. FIG 5: FIG 6: Fluorescence Another major cause of fabric barre’ is a change in the cotton fiber fluorescence. Fluorescence can be measured by the Uster Fiberglow, which measures the ultraviolet light that is reflected from the cotton sample. Fluorescence (UV) is not cotton color, but the effect of sunlight on the structure of the fibers. Fluorescence can cause BARRE if · the variation in average UV readings between mixings is high · C.V.% in UV readings within a mix is high · End of season cotton crop changes · Outside storage of cotton bales is practiced · mixing high and low UV bales is done · UV readings increase over time in the warehose Bale laydowns should be controlled using similar techniques that are used for micronaire. These solutions for controlling fluorescence are given below · UV test every bale before making mix · dont allow more than 10 points difference of UV readings within mix · UV average should be less than 1 point between mixes · category groups should be set up for UV The variation within a single mix should be a maximum of +/- 5 points. The average UV reading of the mix should not change more than +/- 1 point from mix to mix. There is normal change in the UV readings from crop year to crop year. This is due to seasonal changes as well as the difference in UV from cotton stored in a warehouse from 9-12 months. Blending old crop and new crop must be done carefully to reduce the chance of creating fabric barre’. Typically each new year the cotton crop will have a different UV average and range depending on the weather at the time of the harvest. Conclusions At least 70% of the causes of fabric barre’ are due to variations in fiber properties. There are specific solutions available for spinning mills to control the key fiber properties that affect the dyeing and finishing of cotton fabrics. Individual bale measurements of micronaire, maturity and fluorescence will help the spinning mill to control all aspects of fiber barre’ problems. The exact solution will depend greatly on the specifics of end product, spinning system and raw materials used by individual mills. Application guidelines are available for use in selecting bales for mixes and storing bales in the warehouse. Instruments and software programs are available to help the spinning mill monitor and control these specific fiber properties. REFERENCE:USTER APPLIACTION HANDBOOK FOR AFIS PRO COMBED YARN FOR KNITTING Yarn quality requirement is changing everyday. Quality requirement is different for different end uses and it is different for different customers. It is easy to make the highest quality yarn just for the sake of achieving the best yarn results. But it is difficult to produce a good quality yarn with a minimum deviations. Very high fluctuation in yarn quality is an EVIL for any enduse. Some times it is better to keep same level of yarn quality ( around 25% USTER STANDARDS) by strict quality control than achieving 5% USTER STANDARD but without consistency. Consistent quality will be very much appreciated by the clients. “I often say that when you can measure what you are speaking about and express it in numbers, you know something about it. But when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the stage of science, whatever the matter may be” (attributed to Lord Kelvin, 1883). Hence it is advisable to fix the standards for different yarn characteristics for cotton spun yarns for different end uses. The following table gives the quality requirement for KNITTING YARNS. Table: Quality Standard for4 Ringframe Cop Yarn Characteristic required value for 30S Combed other combed counts Average count 30 ( 29.6 to 30.4) nominal count plus or minus 1.3% Count C.V% less than 1.5 less than 1.5% Twist Multiplier 3.5 to 3.6 3.5 to 3.6 TPI C.V% less than 2.5 less than 2.5% U% 9.2 to 9.8 5 to 10 % Uster Stat . value -50% thin place / 1000m less than 4 5 to 10 % Uster Stat . value -30% thin place / 1000m less than 650 5 to 10 % Uster Stat . value +50% thick place / 1000 m less than 30 5 to 10 % Uster Stat . value +200 Neps / 1000m less than 50 5 to 10 % Uster Stat . value Total Imperfection / 1000 m less than 85 5 to 10 % Uster Stat . value RKM ( tenacity) gms /tex more than 16.5 more than 16.5 RKM C.V% less than 7.5 % 5 to 10 % Uster Stat . value Elongation % more than 5.5 more than 5.5 Hairiness H 4.0 to 4.5 < 50% value of Uster Statistics Hairiness Standard Deviation less than 1.5 25% Uster stat value Objectionable classimat faults(both short and long) less than 1 per 100 km less than 1 per 100 km Total classimat faults less than 150 5 to 10 % Uster Stat . value H1- thin faults less than 5 per 100 km 5 to 10 % Uster Stat . value shade variation on cones in UV lamp no shade variation no shade variaition GUIDE LINES TO ACHIEVE THE ABOVE: RAWMATERIAL: Raw material should be selected properly. There is a direct relationship between certain quality characteristics of the fibre and those of the yarn. 70 to 80 % of basic yarn quality is decided by cotton. · Short fibre content is very important for yarn quality. Uniformity Ratio should be more than 47%. Fibres of length 4 to 5 mm will be lost in porcessing (as waste and fly). Fibres upto 12 to 15mm do not contribute to strength but only to fullness of the yarn. Only the fibres above these lengths produce the other positive characteristics in the yarn. · 2.5% span length should be more than 28 mm. Span length affects yarn strength and yarn uniformity. End breakage rate also depends upon the fibre length. Longer the fibre, lower the end breakage rate, better the yarn quality. · Average Microaire should be between 3.8 to 4.3 for counts 24s to 40s (Ne). It can be between 4.1 to 4.7 for counts coarser than 24s. · If the micronaire is coarse, the number of fibres in the yarn cross section will be less. This always results in lower strength and lower elongation. But it is easy to process coarse micronaire fibres in blowroom and cards. · Nepping tendency is less for coarse micronaire fibres. On the contrary, spinnability (in both speed frame and ringframe) is not good with coarser micronaire fibres. · U% is affected by Micronaire. Coarser the micronaire, higher the U%. Coarser the fibre , higher the end breakage rate in spinning. · Uster Thin place( -30%) in the yarn vary depending upon the fibre micronaire. Lower the micronaire, lower the thin places vice versa · Strength of the fibre should be more than 23 grams/tex · Elongation of the fibre should be more than 6%. · No of neps per gram should be less than 250 · should not mix two cottons with wide Reflectance value (Rd value) and yellow ness value (+b) · sticky cotton should not be used. If cotton is sticky, it is better to reduce the percentage of sticky cotton in the mixing. Low humidity and high temperature should be maintained in the departments · cottons with less contamination should be used (cottons like Andy, SJV, alto etc) · PROCESSING REQUIREMENTS: MIXING: · Average Micronaire of the mixing should be same for the entire lot. The difference in average micronaire of different mixings of the same lot should not be more than 0.1 · The micronaire C.V% of a mixing should be less than 10% · The micronaire Range should be same · Cottons with two different origins should not be mixed · Cottons with too wide micronaire range should not be mixed · Cottons with too wide reflectance value(Rd) and Yellowness value(+b) should not be mixed · immature fibre content should be minimum as it will affect dyeiing and will result in white-specks · If automatic bale openers are used, bale laydowns should be done properly, so that different micronaire bales and colors are getting mixed up homogeneously even if small quantity is being checked · · If manual mixing is carried out, bales should be arranged and mixed properly so that different micronaire bales and colors are getting mixed up homogeneously even if small quantity is being chekced · for manual mixing, the tuft size should be as low as 10 grams · If cottons with contamination is used, the best way is to open the bales into small tufts and segregate the contaminants. There are mills who employ around 60 to 80 persons to pick up contamination from a mixing of 20tons. · Japanese insist on mixing atleast 36 bales for one mixing to avoid Barre problem COMBED YARN FOR KNITTING – 2 Page 1 2 3 BLOWROOM: · If the micronaire is low, blowroom process parameters become very critical. · It is better to do a perfect preopening and reduce the beater speeds in fine opening. If required one more fine opener can be used with as low as beater speed, instead of using very high speed in only one fine opener · If the micronaire is lower than 3.8, it is not advisable to use machines like CVT4 or CVT3 · Nep increase in cotton after blowroom process should be less than 80%.(i.e 180 % of rawcotton nep) · If the nep increase is more, then beater speeds should be reduced instead of feed roller to beater setting · If the trash percentage in cotton is less and the neps are more in the sliver, no of beating points can be reduced. 3 beating points should be more than enough. · · variation in feed roller speed should be as low as possible especially in the feeding machine · beater types and specification should be selected properly based on the positions of the beater and the type of raw material (fibre micronaire and trash percentage) · the material pressure in the ducts should be as high as possible to reduce feeding variation to the cards · feed rollers in the chute should work continuously without more speed variation if pressure filling concept is used.(i.e. balancing of the chute should be done properly). For others, the feed roller should work at the maximum speed for a longer time. · material density between different chutes should be same. The difference should not be more than 7% · The difference in duct pressure should not be more than 40 pascals in chute feed system. · air loss should be avoided in the chute feed system, to reduce the fan speed and material velocity · blow room feeding should be set in such a way that the draft in cards is same for all the cards and the variation in feed density is as low as possible · fibre rupture in blowrrom should be less than 2.5% CARDING: · 70% of the quality will be achieved in carding, if the wires are selected properly · following table can be used as a guide line for cylinder wire selection carding production wire height angle of wire(degrees) points per square inch less than 30 kgs/hr 2 mm 30 around 840 more than 30 kgs 2mm 35 to 40 900 to 1050 · Flat tops with 400 to 500 points per square inch should be used · if the micronaire is lower than 3.5, the cylinder speed should be around 350rpm. If the micronaire is between 3.5 to 4.0, it can be around 450 rpm. If the micronaire is more than 4.0, it can be around 500 rpm. · Lower the micronaire, lower the lickerin speed. It should range from 800 to 1150 rpm depending upon the micronaire and proudction rate · pointed wires should be used for cyliner · TSG grinder should be used once in 2 months for consistent quality · Flat tops should be ground frequently (once in 3 months) for better yarn quality. Because, flat tops plays a major role in reducing neps and kitties in the yarn. Emery fillet rollers should be used for flat tops grinding, instead of using grinding roller grinding stone · Licker-in wire should be changed for every 150000 kgs produciton in carding · stationary flats should be changed for every 150000 kgs production in carding · Individual card studies upto yarn stage should be conducted regularly, and if the quality is deteriated by 25% from the average quality. card should be attended (wire mounting, grinding, full-setting etc to be done) · setting between cylinder and flat tops should be as close as possible, depending upon the variation between cylinder and flat tops. Care should be taken so that , wires do not touch each other. · Card autolevellers should be set properly. Nominal draft should be correct. Draft deviation should not be more than 5% during normal working. · card stoppages should be as low as possible · slow speed working of cards should be avoided. slivers produced during slow speed should be removed · 10 meters C.V% of card sliver should be less than 2.0 · Sliver weight difference between cards should not be more than 2.5% · Sliver U% should be less than 3.5 and spectrogram peaks should be attended · cylinder loading should be nil. If cylinder is loaded, wire should be inspected. If required grinding should be done or wire should be changed · sliver diameter difference should be less. Calender roller pressure should be same in all the cards · trash in sliver should be less than 0.1% · uiformity ratio of sliver should be same or better than raw cotton · if kitties or seed coat fragments are more, higher flat speeds should be used and as much as flat waste should be removed to reduce seed coat fragments in the yarn · in general sliver hank varies from 0.12 to 0.14 · individual card studies should be conducted upto yarn stage, if the quality from a particular card is bad, immediate action to be taken to rectify the problem. Lower the variation better the yarn quality. COMBER: · In lap preparation, total draft, fibre parallelisation ,no of doublings, lap weight etc should be decided properly(based on trial) · higher the lap weight(grams /meter) lower the quality. It depends upon the the type of comber and the fibre micronaire · if fine micronaire is used, lap weight can be reduced to imrpove the combing efficiency · if coarse micronaire is used, lap weight can be increased · if fibre parallelisation is too much, lap sheets sticking to each other will be more( It will happen if the micronaire is very low also). If the lap sheets are sticking to each other, the total draft between carding and comber should be reduced · If the draft is less, fibre parallelisation will be less, hence loss of long fibres in the noil will be more · top comb penetration should be maximum for better yarn quality. But care should be taken so that top comb will not get damaged. · damaged top comb will affect the yarn quality very badly · setting between unicomb and top nipper should be same and it should be around 0.4mm to 0.5 mm · feed weight is approximately 50 to 58 grams for combers like E7/4 and is 65 to 75 grams for combers like E62 or E7/6 · lower the feed length, better the yarn quality. Trials to be conducted with different feed lengths and it should be decided based on quality and production requirement · required waste should be removed with the lowest detaching distance setting · for cottons with micronaire upto 3.5, top comb should have 30 needles/cm and for cottons with more than 3.8 micronaire, the top comb should have 26 needles/cm · Trials to be conducted to standardise the waste percentage · · piecing wave should be as low as possible. Piecing index should be decided based upon cotton length and feed length · spectrograms should be attended. Comber sliver uster should be less than 3.5 · head to head waste percentage should be as low as possible · variation in waste percentage between combers should be as low as possible( less than 1.5%) · If cotton with low maturity coefficient is used, it is better to remove more noil to avoid dyeing variation problem COMBED YARN FOR KNITTING – 3 Page 1 2 3 DRAWFRAME: · Drawframe with a short term Autoleveller is a must · no of doubling should not be less than 7 and the total draft also should be more than 7 · U% should be around 1.5 to 1.8 · 1 meter C.V% (from Uster Evenness Testing machine ) should be less than 0.6 · top roller lappings should be almost nil · If group creeling is used, all the sliver piecings from the creel should not enter the tongue and groove roller at the same time · no sliver should be removed from the machine after the tongue and groove roller (which is meant for sensing the feed variation) for any reason. Because, draft correction will be done according to tongue and groove roller sensing and there is a time lag between sensing and correction. · · top rollers should be checked by the operators atleast once in a shift · top rollers should be checked by the operators , whenever there is a lapping · top roller buffing should be done once in 20 days(maximum 30 days) · If the top roller eccentricity is more than 0.05 mm, it should be buffed · top roller eccentricity should be zero after buffing. · diameter variation between top rollers should be less than 0.1mm · sliver test should be conducted atleast once in 15 days and the A% should be less than 0.8 · the delivery speed should be around 400 to 500 meters per minute depending upon the make of the machine · whenever there is a top roller lapping, min 10meters of sliver should be removed from the can · creel breaks should be as low as possible and it need to be piececd properly. Trials should be taken to see the yarn made out of piecing. Piecings should not be too thick and high twisted SPEED FRAME: · Total draft should be around 10 for 4 over 4 drafting system · better to use floating condenser in the front zone to reduce hairiness and the diameter of the roving · cots buffing should be done once in two months. top roller runout to be checked and it should be nil. There should not be any compromise on top roller quality. Top roller cost for speed frame is negligible if it is compared with ringframe · If possible it should be treated with surface treatment like treatment with LIQIMIX or treated with acid to reduce top clearer waste which is caused by top roller surface · Twist Multplier should be high enough to reduce stretch in Ringframe. Higher the T.M lower the classimat “H1″ faults · If single speed for flyer is used, it is advisable to run less than 1000 rpm · When the speed frame bobbin is full, flyer speed should be less than 1000 rpm. Otherwise surface cuts will increase and thin places also will increase · False twisters should be changed once in two years. Variation in false twister will result in high count C.V% · Roving tension should be as low as possible and as uniform as possible. Higher the roving tension, higher the count C.V% and higher the thin places · Density of all roving bobbins should be same. Higher the variation, higher the count C.V% · Break draft should be around 1.18 to 1.24 depending upon the type of drafting system and total draft · Roving hank should be decided in such a way that the ring frame draft is around 20 to 34 for different counts. · no sliver piecing or roving piecing from speedframe should be worked in Ringframe. All sliver piecing and roving piecing will result in thin and thick yarn. Some times it may be cut by the clearer, but all yarn faults created by piecings are not cut by the clearers. RINGFRAME: · Front zone setting should be as close as possible · breakdraft of 1.14 and back zone setting of 60 mm is recommended · 65 degree shore hardness for front top roller · buffing should be carried out once in 45 days · if the top roller diameter is less by 1.5 mm from the standard diamter, top roller should be changed · the gap between front top roller and apron nip should be as low as possible(around 0.5 to 1 mm). If it is more imperfections will be high · bottom and top aprons should be changed atleast once in 1.5 years · It is better to use lighter travellers instead of using heavier travellers. Enough trials should be taken , because traveller size depends upon, speed, micronaire, humidity condition, count, ringdiameter etc · It is advisable to use Eliptical travellers for hosiery counts · ring travellers should be changed before 1.5% of travellers burn out · whenever there is a multiple break, ring travellers should be changed · At any point of time, fluff accumulation on travellers should be less. Ring traveller setting should be close enough to remove the waste accumulation but at the same time it should not disturb the travller running · hariness varition between spindles should not be high. To achieve this, traveller should be changed in time, bad workings (multiple breaks) should be avoided, rings like TITAN rings (from Breaker) should be used, damaged rings should be removed · Ring frame breaks should be as low as possible ( less than 10 breaks per 1000 spindle hours) · Start up breaks after doffing should be less than 3 %. · Overhead cleaners is a must for processing combed cotton · Exhaust trenches should be between machines and for every 200 spindles there should be a trench · ring centering should be perfect. Abc rings and lappet hook centering should also be done perfectly · If ring diameter is more than 40 mm, ring centering plays a major role. If ring centering is not done properly, hairiness variation within the chase will be very high · good quality spindle tapes should be used and changed for every 24 months. Spindle speed variaiton will affect yarn strength, tpi and hairiness WINDING: · Winding speed should be around 1250 meters/ min · machines with tension management is preferred · Clearers settings should be as close as possible. Loephe Yarn master setting is given below N -4.0 (nep) : DS-2.0 (short) : LS-1.6 (short) : DL-1.18 (long) : LL-40 : (long) -DS-14%(thin) : -DL-40(thin) Since loephe has a facility of class clearing. “C”s to be added in such a way that the following faults which are displayed in Loephe class clearing should be cleared. A4,A3,B4,B3, B2(50%),C1,C2,C3,C4,D1,D2,D3,D4,E,F,G,H1(50%),H2,I1,I2 · Count channel setting should be less than 7% · setting for cluster faults should be set such that, if a yarn produced without bottom apron, or damaged rubber cots is fed, it should be cut by the clearer · long thick faults in the cone yarn should be zero · long thin faults should be zero · If the waxing attachment is below the clearers, the clearers should be cleaned once in a day · splice strength should be more than 75% of yarn strength · splice apperance should be good and all the splicers should be checked atleast once in a week · good qulity wax should be used · wax pick up should be around 0.1% · uniform application of wax to ensure uniform coefficient of friction (0.125 to 0.15) · uniform moisture in the cones is important, because coefficient of friction varies as a function of moisture · all wax rollers should rotate properly · repeaters should be as low as possible, because this will affect the package quality · It is advisable to produce cones with 1.8 to 2.4 kgs · yarn tension in winding should not be very high · imperfection increase between ringframe and winding should not be more than 30% for cotton combed yarns GENERAL: · finished garments rejection should be less than 1% · yarn faults contribute to 25% of the rejections. Major yarn faults are contamination thick and thinks Unevenness periodicity Stiff yarn – Higher TPI ( holes) higher friction high hairiness variation mixed properties of yarn – “Barre” Neps white specs(immature fibres) Kitties ( vegetable matters, dust content) Lower elongation and elasticity · · It is better to use cottons with less contaminations like Andy, SJV, Alto, etc · contaminations of length more than 20 mm should be nil in the yarn · as per japanese standard, the no of contamination per Kg of fabric should be less than 5 · If cotton has contamination, it is compulsary to use manual picking on preopener lattice, cotamination detectors at blowroom, visual clearer(siro) at winding. · It is advisable to go to the supplier(cotton ginner) for quality – a concept of Japanese · 10 meter C.V% of yarn should be controlled and it should be as low as possible. This affects the fabric appearance LINEAR PROGRAMMING PRODUCT MIX (USING LINEAR PROGRAMMING): Linear programming is a quantitative tool for optimal allocation of limited resources amongst competing activities. It is perhaps the most popular amongst OPERATIONS RESEARCH techniques and has found application in several functional areas of business- production, finance, marketing, distribution, advertising and so forth. Any resource allocation problem is characterised by specification of an objective such as minimising cost, or maximising profit. The constraints can be of a financial, technological, marketing or anyother nature. Linear programming involves formulating the problem in linear terms and solving it to provide a plan for deploying the resources in an optimal manner. This technique is being used by many managements to maximise the profit or to minimise the cost. In earlier days, fomulating a linear programming model and solving the same was a tedious process. frontsys software company has developed a tool called solver which will be used with MICROSOFT EXCEL SPREADSHEETS to solve LINEAR PROGRAMMING MODELS. This is a very simple tool which can be used by everyone who can use MICROSOFT EXCEL and understand little about formulating the constraints. PRODUCT MIX USING LP FOR A SPINNING MILL Let us assume C1,C2,C3 and C4 are quantities of four counts to be produced in cotton TC1,TC2 and TC3 are quantities of three counts to be prodced in Poly/Cotton blend. CX1,CX2,CX3 and CX4 are Contribution in US$/KG for four cotton counts. TCX1,TCX2 and TCX3 are contribution IN US$/KG for three POLY/COTTON counts correspondigly. HOW TO FORMULATE A LP MODEL: EXAMPLE TARGET FUNCTION: (TO MAXIMISE) (C1*CX1)+(C2*CX2)+(C3*CX3)+(C4*CX4)+(TC1*TCX1)+(TC2*TCX2)+(TC3*TCX3) = CONTBN. MAXIMUM BY CHANGING : ( THE FOLLOWING QUANTITIES) C1,C2,C3,C4,TC1,TC2,TC3 CONSTRAINTS: · C1+C2+C3+C4 less than or equal to 180 tons · TC1+TC2 less than or equal to 100 tons · C1 should be 19.6 tons ( committed to the customer) · TC2 more than 19.6 tons ( committed to the customer) · C1+C2+C3+C4 no of m/cs allotted should not be more than 20 (m/c constraint) · TC1+TC2+TC3 no of m/cs allotted should not be more than 10 (m/c constraint) · C1 less than or equal to 20 · C2 less than or equal to 20 · C3 less than or equal to 20 · C4 less than or equal to 20 · TC1 less than or equal to 10 · TC2 less than or equal to 10 · TC3 less than or equal to 10 HOW TO SOLVE THIS: MICROSOFT EXCELL Spreadsheet has a tool called SOLVER. This can be used to solve any LINEAR AND NON-LINEAR EQUATIONS. · OPEN an EXCEL SHEET · FEED the PARAMETERS in the Excell Sheet · SELECT SOLVER in the Tools Menu, Now Solver parameters are seen · SET the TARGET cell and it should contain the target function · FEED the range of cells to be changed · FEED the constraints · press SOLVE, THE RESULTS ARE ALREADY THERE ISN’T IT SIMPLE? PLEASE TRY THIS. LP IS THE RIGHT SOLUTION FOR PRODUCT MIX OF ANY INDUSTRY. ANALYSIS-PERFORMANCE IMPROVEMENT-Spinning Mill CRITICAL ANALYSIS OF PERFORMANCE IMPROVEMENT OF A Spinning Mill with 32400 spindles working on 100% cotton combed yarns The data given below will help us to understand the impact on overall contribution by 1. Utilisation of the plant 2. Selling price increase 3. Cheaper rawmaterial for coarse counts 4. selling price increase for coarse counts 5. Increased back process production 6. Increased spindleage 7. Increased grams per spindle 8. Working coarses counts 9. working finer counts 10.Raw material price ASSUMPTIONS: The selling prices is the actual net sales price for a reasonably good yarn produced in Indonesia. Product mix is decided by Linear programming which satisfies all the constraints given below Linear programming decides the maximum possible contribution meeting all the constraints. contrubution = Net sales price – clean raw material cost – packing and forwarding cost grams per market constraints spindle 24sc should be less than 60 tons per month 240 utilisation 97% 20sc should be less than 510 tons per month 280 no of RFs 45 30sc should be less than 90 tons per month 170 no spls/RF 720 32sc should be less than 20 tons per month 155 36sc should be less than 20 tons per month 135 40sc should be less than 300 tons per month 120 Total no of ring frames should not be more than 45 utilised total avg count 24sc 20sc 30sc 32sc 36sc 40sc rfs cotrbn count usd sell price 1.96 1.90 2.10 2.14 2.30 2.40 raw mat 1.30 1.30 1.30 1.30 1.30 1.30 packing 0.04 0.04 0.04 0.04 0.04 0.04 contrbn 0.62 0.56 0.76 0.8 0.96 1.06 12. 5 tons 20.5 0 90 20 20 225 44.3 354291 36.09 13.5 tons 60 22.9 77.5 0 20 225 45 366179 34.39 15 tons 60 137 7.99 0 20 225 45 377470 31.4 17 tons 0 303 0 0 0 207 45 389117 28.12 19 tons 0 408 0 0 0 162 45 400217 25.69 21 tons 3.39 510 0 0 0 117 45 411308 23.72 if the utilisation goes up by 1% I.e form 97% to 98% 15 tons 60 127 15.7 0 20 227 45 380179 31.68 17 tons 0 297 0 0 0 213 45 392156 28.36 19 tons 0 402 0 0 0 168 45 403256 25.9 if grams per spindle is increased by 5% 15 tons 60 88.6 45.6 0 20 236 45 390605 32.74 17 tons 60 171 90 0 20 169 45 399811 29.5 19 tons 60 276 90 0 20 124 45 410911 26.92 if the selling price goes up 5% 15 tons 60 137 7.99 0 20 225 45 426494 31.4 17 tons 0 303 0 0 0 207 45 442743 28.12 19 tons 0 408 0 0 0 162 45 458418 25.69 if the raw material price comes down by 3 cents 15 tons 60 137 7.99 0 20 225 45 390970 31.4 17 tons 0 303 0 0 0 207 45 404417 28.12 19 tons 0 408 0 0 0 162 45 417317 25.69 if the rawmaterial for 20s, 24s and 30s is cheaper by 3 cents compared to other counts 15 tons 60 137 7.99 0 20 225 45 383634 31.4 17 tons 60 250 0 0 0 200 45 398281 28.3 19 tons 60 355 0 0 0 155 45 412531 25.84 if grams per spindle comes down by 3% bec of cheaper raw mat for 20s,24s and 30s 15 tons 51.3 154 0 0 20 225 45 381512 31.15 17 tons 0 310 0 0 0 200 45 394824 27.84 19 tons 0 418 0 0 0 152 45 407902 25.35 if grams per spindle comes down by 10% bec of cheaper rawmat for 20s,24s and 30s 15 tons 0 212 0 0 19.8 218 45 375491 30.41 17 tons 0 326 0 0 20 164 45 385255 27.05 19 tons 0 441 0 0 20 109 45 395018 24.39 if 40sc can not be sold more than 180 tons per month 15 tons 60 92.1 90 7.91 20 180 45 373479 31.45 17 tons 60 243 7.14 0 20 180 45 386071 28.3 19 tons 0 408 0 0 0 162 45 400217 25.69 if 20sc can not be sold more than 300 tons per month 15 tons 60 137 7.99 0 20 225 45 377470 31.4 17 tons 3.39 300 0 0 0 207 45 389108 28.13 19 tons 60 300 90 0 20 97 45 395617 26.0 if 20sc can not be sold more than 150 tons per month 15 tons 60 137 7.99 0 20 225 45 377470 31.4 16 tons 60 150 90 0 20 161 45 379760 29.79 17 tons 60 150 90 0 20 161 45 379760 29.79 19 tons 60 150 90 0 20 161 45 379760 29.79 pleease note in this case it has not considerd more than 16 tons , even thought the option upto 19 tons is given to choose if spindle installed is increased by 10% 15 tons 60 35.5 90 20 20 225 49 398660 33.76 17 tons 60 169 36.7 0 20 225 49.5 416621 30.62 19 tons 0 349 0 0 0 221 49.5 429693 27.75 if grams/spl goes up by 5% for 40sc 15 tons 60 109 25.3 0 20 236 45 386556 32.29 17 tons 0 284 0 0 0 226 45 398527 28.86 19 tons 0 393 0 0 0 177 45 407582 26.20 if grams/spl goes up by 5% for 20sc 15 tons 0 170 35.9 0 20 225 45 379457 31.49 17 tons 0 293 0 0 0 217 45 394340 28.53 19 tons 0 394 0 0 0 176 45 407251 26.18 PLEASE NOTE THAT WHATEVER CONCLUSIONS, STATEMENTS, OPINIONS ARRIVED AT BASED ON THE ABOVE DATA IS APPLICABLE ONLY FOR THE SAME DATA. CONCLUSIONS, RESULTS MAY VARY DEPENDING UPON THE PROUDCTIVITY OF DIFFERENT COUNTS, SELLING PRICE COMBINATIONS FOR DIFFERENT COUNTS, OVERALL QUANTITY ETC STUDY ON BARRE CAUSED BY RAWMATERIAL The current expansion of the worldwide market for cotton has opened up many possibilities for the spinning mill. Spinning mills now have many options in the raw materials they purchase for producing yarn. This expansion in the availability of raw material has helped in reducing costs and improving yarn quality and spinning efficiency. Unfortunately this situation has also presented some new challenges for the spinning managers and cotton buyers. Traditionally purchased cottons had well established seed varieties and growing regions. This meant that with an average control of micronaire they had few problems with the dying and finishing of cotton fabrics. Over the past two years we have seen a rapid increase of the problems with dying and fabric finishing. This is especially evident in the claims and rejects 100% cotton knitted fabrics for fabric barre’. Claims and rejects can easily wipe out any savings in raw material costs obtained by purchasing cotton from several international sources. Many spinning mills are under the impression that all upland seed varieties mature the same as related to the micronaire. Unfortunately what they discover is that cottons with similar micronaire that have different growing regions and seed varieties dye differently. Controlling some of the basic fiber properties can give the spinning mill the information necessary to reduce and or eliminate the recurring problems of barre’. Mill experience and trials have given us the necessary information to set up guidelines for controlling the fiber properties that influence the dyability of cotton yarns in knitted fabrics. There are several mechanical causes of fabric barre’ that are associated with the spinning and sliver preparation processes in the spinning mill. The following table shows that the major cause of BARRE is due fiber. FABRIC BARRE CAUSE % OF DEFECTS Fibre 70 Yarn count variation 10 Twist variation 10 Hairiness 10 While mechanical differences and variations in yarn count, twist and hairiness can also be a cause of the barre’ effect the single largest cause lies in the variation in fiber properties. Figure 3 shows the fiber properties that have a major influence in the causes of barre’. Micronaire, maturity/fineness and fluorescence all play a major role in the consistent dying and finishing of knitted fabric. Micronaire Most mills have learned over the years that they need to control the average of the micronaire in the bale laydown. Most mills have some type of system to categorize cotton bales into groups in an effort to control the average micronaire. While controlling the average micronaire is a good first step many times this is not enough control to eliminate the barre’ effect, especially in knitted fabric. The causes and controls necessary for eliminating dying problems as they relate to micronaire are given below · difference in micronaire should be less than 0.2 · change in average micronaire from mix to mix should be less than 0.1 · C.V% of micronaire within mix should be within 10% · Bales with same micronaire should not be placed side by side The additional control of the variation or CV% of the micronaire must be added to the overall control of the average in each laydown. It is also necessary to change the average of the laydown over time so that all bales in the warehouse can be processed. The change in average micronaire in the laydown must be changed slowly over time.The maximum bale-to-bale variation ( c.v%)within the mix should be 10%. A variation(c.v%) of micronaire higher than 10% will very likely cause a barre’ effect in the fabric. Maturity & Fineness Micronaire is an indication of the maturity in cotton fiber, although it is not a direct measurement of the fiber maturity. Micronaire can be used successfully to control barre’ if the cotton being processed is from the same seed variety. If cottons from several varieties or growing areas are being blended together, then additional testing and maturity information may be necessary. Causes of Barre due to Maturity · Blending cottons from different growth areas · Blending cottons from different seed varieties · seasonal changes in cotton growth cycle 1. weather 2. insects · Immature fibre cotent % (IFC%) 1.White speck neps 2. carding speeds An example of fabrics made of yarn produced from three (3) different bales of cotton is shown in figure . The cottons all had the same micronaire (4.2) but, as can be seen, the dye uptake on the individual yarns were very different. The above Figure is a good example of how cotton fiber maturity (not micronaire) can cause a barre’ effect in fabric. These bales of cotton were tested on the HVI instrument and the yarn was tested on the Uster Evenness tester. These results are shown in figures 1 , it is not possible to determine any significant differences between these three cottons that would cause a problem in dying and finishing. The cottons are also tested on the new AFIS Length and Maturity to determine if any difference could be found. The results from the AFIS Maturity module are shown in figure 2. FIG:1 STUDY ON BARRE CAUSED BY RAWMATERIAL – Page 2 FIG:2 The AFIS Maturity module is a single fiber measurement of individual fiber maturity. The individual fiber maturity information gives a distribution of fiber maturity as well as the average fiber maturity. The distribution enables us to identify the very immature fibers and it is described by the Immature Fiber Content (IFC%). Figure 2 clearly shows a considerable difference of the three bales in the IFC%. Maturity differences in cotton can also cause defects in fabric such as white speck neps. Fabric in figure 3 was knitted from yarn produced from three different cottons having similar micronaire values. There was a significant difference in the amount of white specks in the three fabric samples. The three cottons were tested on the AFIS Maturity module and the results are given in figure 4. The differences in the AFIS IFC% correlates visually to the amount of white specks in the three fabrics. Interesting is that the overall average maturity ratio from the three cottons was very similar, giving no indication of a potential problem of white specks. FIG 3: FIG 4: Variation of Maturity in Sliver There is a possibility to optimize the carding process to make sure all cards remove as much of the immature fiber as possible. Figure 5 shows the results from testing a line of cards all fed from the same bale laydown. It is interesting that while the card mats all show very similar results the card slivers show quite some variation. The possibility of the influence of carding on the maturity of the sliver was investigated further using the AFIS Maturity module. Several individual cards were analyzed and it was apparent that there was a large variation in the amount of immature fibers removed by the cards. This initial trial indicated that it is possible to change the mechanical setup of a card to influence the removal of immature cotton fibers. These results are shown in figure 6. FIG 5: FIG 6: Fluorescence Another major cause of fabric barre’ is a change in the cotton fiber fluorescence. Fluorescence can be measured by the Uster Fiberglow, which measures the ultraviolet light that is reflected from the cotton sample. Fluorescence (UV) is not cotton color, but the effect of sunlight on the structure of the fibers. Fluorescence can cause BARRE if · the variation in average UV readings between mixings is high · C.V.% in UV readings within a mix is high · End of season cotton crop changes · Outside storage of cotton bales is practiced · mixing high and low UV bales is done · UV readings increase over time in the warehose Bale laydowns should be controlled using similar techniques that are used for micronaire. These solutions for controlling fluorescence are given below · UV test every bale before making mix · dont allow more than 10 points difference of UV readings within mix · UV average should be less than 1 point between mixes · category groups should be set up for UV The variation within a single mix should be a maximum of +/- 5 points. The average UV reading of the mix should not change more than +/- 1 point from mix to mix. There is normal change in the UV readings from crop year to crop year. This is due to seasonal changes as well as the difference in UV from cotton stored in a warehouse from 9-12 months. Blending old crop and new crop must be done carefully to reduce the chance of creating fabric barre’. Typically each new year the cotton crop will have a different UV average and range depending on the weather at the time of the harvest. Conclusions At least 70% of the causes of fabric barre’ are due to variations in fiber properties. There are specific solutions available for spinning mills to control the key fiber properties that affect the dyeing and finishing of cotton fabrics. Individual bale measurements of micronaire, maturity and fluorescence will help the spinning mill to control all aspects of fiber barre’ problems. The exact solution will depend greatly on the specifics of end product, spinning system and raw materials used by individual mills. Application guidelines are available for use in selecting bales for mixes and storing bales in the warehouse. Instruments and software programs are available to help the spinning mill monitor and control these specific fiber properties. REFERENCE:USTER APPLIACTION HANDBOOK FOR AFIS PRO

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