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yarn

1. College of Engineering and Technology Textile Engineering Program Yarn Manufacturing-I Wolkite University

2. Yarn is a generic term for a twisted continuous strand of textile fibers, filaments or material in a form suitable for knitting , weaving or otherwise intertwining to form textile fabric. Yarn: Introductio n Refers to the conversion of a large quantity of individual unordered fibers of relatively short length into a linear, ordered product of very great length by using suitable machines. It is also called as spinning. Yarn Manufacturing: 2

3. Cotton Harvesting and Spinning Cotton was used as cloth raw material in the  old world at least 7,000 years ago . 3 Ginning is A machine that removes the cotton from the boll without damaging the cotton plant. Cotton continues to be picked by hand in  developing countries .

4. Cotton Grading The term cotton classification or cotton grading refers to; The application of standardized procedures developed by USDA for measuring those physical attributes of raw cotton that affect the quality of the finished product and/or manufacturing efficiency. Essential quality parameters for cotton grading are: Fibre length Length Uniformity Index (UI %) Fibre strength (g/ tex ) Micronaire ( HVI micronaire) Color (HVI color Rd, +b) Trash (HVI trash area %) 4

5. Each cotton fruits consists of seeds, leaf and about 3000 to 5000 fibers. The process of separating seeds from the lint cotton in order to produce two marketable products, fiber and seed is called cotton ginning. Cotton Ginning The objective of cotton ginning is; To reduce moisture content and to remove foreign matter. These operations facilitate processing and improve fiber quality. 5

6. Types of cotton ginning I. Saw ginning: The cotton lint is removed from the seed by pulling it with saw teeth through metallic ribs. It used for medium and short staple varieties. Has higher extraction of fibers from seed but also higher damage of fibers. 6

7. II. Roller ginning: Roller ginning is the most primitive way of removing lint from seeds. Separation is by means of roller & knife. It is used for long and extra long fibers. Has lower extraction of fibers from seed but also lower harm of fibers than saw ginning. Cont… 7

8. Cleaned cotton fibers are collected into a hopper of a machine called bale press machine. The fibers are converted into a compressed bale, weighing 180 to 225 Kg each, with the help of hydraulic pressure . Each bale is wrapped with cloth or plastic, tied with iron or plastic strips . Cotton Bale Cotton Bales 8

9. Cotton Spinning Cotton is a hygroscopic material and easily adopts to the atmospheric humidity. S o, air temperature inside blow-room area should be more than 25ºC , and T he relative humidity ( RH% ) should be around 45 to 60 %. B ecause , high moisture in the fiber leads; To poor cleaning , and D ryness in the fiber leads to fiber damages which ultimately reduces the spinnability of cotton . Standard atmospheric conditions: Relative humidity = 65 ± 2% RH Temperature = 27 ± 2ºC (tropical) Conditioning time = 24 hours (cotton) 9

10. The variation of the following properties are worth considering during cotton spinning: Fiber micronaire Fiber length Fiber strength Variations in these properties result in dye absorption variation. Therefore, it’s a good practice; To check the properties of all the bales, and To maintain good bale management principles. To avoid dye pick-up variation and barrier in the finished fabric. Cont… Fiber color Fiber maturity and trash 10

11. Bale management (Engineered fiber selection system) Bale Management : It is defined as the process of sorting, mixing, and testing of bales according to characteristics of the fibers to produce good quality of yarn at low production cost . The main objectives of bale management are: To compensate for the variation in properties of the raw materials To obtain required and uniform quality of yarn To reduce shade variation of the finished fabric To meet the functional and end use requirements. 11

12. Bale management process has done by following the below steps: Selection of Raw cotton, Testing moisture percentage in bales, Collecting sample from each bale, Testing of sample, 5. Classification of Bales, 6. Bale law down, 8. Mixing. In a particular lot; Not to blend cotton type differing in staple length more than 1/16". Micronaire range and average of the cotton used should be same for all the mixings of a lot. Range and average of color of cotton used should be same for all the mixings of a lot. Cont… 12

13. Raw material as a factor influencing spinning Both natural and man-made fibers are used for spinning to produce yarn of desired quality. The annual world fiber consumption in 2004 approximately 70 million tons; Synthetics: 38 mill tons, Cotton: 22 mill tons, About one third of the man-made fibers is processed as endless filament, still two thirds or 67% come in staple fiber form. And, the greater part of the staple fiber is used in the production of yarn. The major raw materials used in a spinning mill are cotton, viscose and polyester. Characteristics of Raw Material: Cellulose fiber: 2.5 mill tons and Others: 7.5 mill tons. 13

14. Understanding the influence of raw material is important both from the technological as well as economic point of view. Raw material has significant effect on the yarn producer, because; Raw material accounts for about 80% to 90% of the yarn quality and 50% to 70% of the total production cost of a short-staple yarn. Cont… Therefore, it’s very important to have a thorough understanding of; The quality parameters of the fibers and Their influence on the spinning process and yarn quality. 14

15. The optimal choice of cotton for producing yarns of desired property is rendered difficult, because of two reasons: R aw material quality is determined by the interaction of several physical properties of the fibers, and I nherent variation existing in all the properties among the fibers. Cont… Therefore, the spinner should know those aspects of fiber quality which will enable him to choose, The material most suited for the intended purpose from a wide range of cottons that differ in their physical properties. The three major fiber characteristics that influence the compatibility are: The Fiber Length, Fiber fineness and Fiber strength . 15

16. Fiber Fineness: Fiber fineness is an important quality characteristic which plays a prominent part in determining the spinning value of cottons. It determines how many fibers are present in the cross-section of a yarn of given thickness. A multitude of fibers in the cross-section provide not only high strength , but also better distribution in the yarn. Fiber fineness influences primarily: Spinning limit; Yarn strength ; Yarn evenness Luster; Handle ; and Productivity of the process. 16

17. There are lower limits to the number of fibers in the cross-section, as follows (for normal conditions). About 30 fibers are needed at the minimum in the yarn cross-section, but there are usually over 100. Fibers on yarn cross-section of ring and rotor spun yarn   Cotton yarns Ring-spun yarn Combed 33 fibers Carded 75 fibers Rotor-spun yarn Carded 100 fibers Synthetic fiber yarns Ring-spun yarn Carded 50 fibers Rotor-spun yarn Carded 100 fibers The number of fiber can be calculated approximately by; Cont… 17

18. Blends of fine cotton fibers with coarse synthetic fibers would produce a yarn with an externally synthetic fiber character. Specification of fineness: With the exception of wool & hair fibers , fiber fineness can not be specified by reference to diameter. Because, the cross-section is seldom circular and is not easily measurable. Usually specified by the relation of mass(weight) to length. Tex = or Dtex =   Where as for man made fibers, dtex is used almost exclusively, The micronaire value is used worldwide for cotton. Cont… 18

19. Micronaire: This is a measure of fiber fineness and maturity . Low micronaire values indicate fine and/or immature fibers ; High micronaire values indicate coarse and/or mature fibers . Conversion factor:  dtex = Mic × 0.394 Micronaire value Fineness Up to 3.1 Very fine 3.1- 3.9 fine 4.0 – 4.9 Medium(premum range) 5.0 – 5.9 Slightly coarse Above 6 coarse The fineness scale is as follows: Cont… 19

20. Example : A cotton yarn of 30s English cotton count (Ne) consists of cotton with a micronaire value of 4 C alculate ח F Micronaire value does not always represent the actual fineness. Also it is dependent on the degree of maturity. In practice, maturity of cotton has a greater effect on micronaire than the fineness for the same variety; Because , variation in fineness within variety is usually 5% Whereas, variation in maturity can be +10% and –20 %. Cont… 20

21. Maturity: Cotton fiber consists of cell wall and lumen . The maturity index is dependent upon the thickness of the cell wall. Fiber maturity influences both the processing of cotton and quality of yarn in terms of strength , evenness and appearance. A fiber is to be considered as: Mature: cell wall of the moisture-swollen fibre represents 50 - 80% of the round x-section. Immature : when it represents 30 - 45%, and Dead: when it represents less than 25%. Since some 5% immature fibers are present even in a fully matured boll. Cotton stock without immature fibers is unimaginable. 21

22. Immature fibers have neither adequate strength nor adequate longitudinal stiffness . Instead, they leads to : Loss of yarn strength. Nepinness. A high proportion of short fibers. Varying dyeability. Process difficulties mainly at the card Maturity Percent (Coefficient): Maturity Coefficient = (M + 0.6H + 0.4 I)/100 W here; M is percentage of matured fibers, H is percentage of Half matured fibers and, I is percentage of Immatured fibers. Classification of maturity Coefficient Maturity coefficient Category above 0.9 Mature 0.7- 0.9 Half mature Below 0.7 immature Cont… 22

23. Cont… Classification of maturity ratio Maturity Ratio Category 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 Maturity ratio = [(N – D)/200] + 0.70 . Where; N is percentage of normal (matured) fibers and, D is percentage of dead ( immature ) fibers. Maturity Ratio: Example : For the chosen standard, N = 67% D or I = 7% and H = 26%. Mc = ( 67 + 0.6 (26) + 0.4 (7) ) / 100 = 0.85, Calculate maturity ratio(M.r)??? 23

24. Fiber length: The "length" of cotton fibers is a property of commercial value as the price is generally based on this character. If other factors being equal, longer cottons give better spinning performance than shorter ones. The fiber length influences: Spinning limit Yarn strength Yarn evenness Handle of the product Lustre of the product Yarn hairiness Productivity 24

25. Productivity is influenced through: The end breakage rate The quantity of waste Fibers of under 4 - 5 mm will be lost in processing (as waste and fly) Fibers up to 12 - 15mm do not contribute to strength But, only to fullness of the yarn. Fibers above these lengths produce the other positive characteristics in the yarn. But, noticeable shortening of many fibers arises before the spinning process owing to mechanical working, for example ginning and cleaning . The effect is such that fiber length exhibits the greatest irregularity of all the fiber characteristics. Cont… The required turns of twist(which affects handle) General spinning conditions. 25

26. Cont… Fig: The staple diagram by number Fig: The staple diagram by weight Staple Length (classers’ staple) Staple length is length of clamped fiber, that exceed certain distance. It is measured by personal judgment of the appearance of a hand prepared sample. A sample of cotton contains fiber absolute minimum (2mm) up to absolute maximum b/n 30 and 60 mm, 26

27. The length of cotton fiber can be determined by expert classers and measuring instruments. The staple length (classer‘s staple) groupings for cotton: Short staple: 1’’ or less Medium staple: 1 1/32” - 1 1/8” Long staple: 1 5/32” - 1 3/8” Extra-long staple: 1 13/32” and above. In order to reduce the various errors and difficulties associated with personal judgment , laboratory tests are desired. With the development of HVI, digital fibrograph and other instrument, possible to measure important fiber characteristics easily. 27

28. Various staple Diagram Forms I. Rectangular Staple Fig: Rectangular staple Achievable and Imaginable for synthetic (manmade ) fibers. Since the fibers are all equally long; No length variation are present. However, the length evenness cannot be maintained into the yarn. Because, fibers are shortened during processing, mainly at the card . Spinning machines are not suited to processing of fibers having all the same length. In the drafting arrangement, such fibers are not moved individually , but in bunches, resulting a high degree of unevenness . 28

29. Fig: Triangular staple This permits better processing than the rectangular staple. But, contains too many short fibers . During movement, for example in the drafting arrangement the fibers cannot be maintained under control . They move freely and produce substantial unevenness . They cannot always be bound into the body of fibers, so that some of them are lost as waste and fly . If a short fiber is bound-in , however, one end often projects and results in a hairy yarn . II. Triangular staple Cont… 29

30. III. Trapezoid staple IV.Stepped staple This is the ideal staple for processing and more suitable the flatter the curve. However, a flat curve often means a high price. This diagram is typically for cotton . The stepped staple curve can arise; When fiber materials of very different lengths are mixed in the wrong proportions. As with a rectangular staple, the fibers can be moved only in groups. Cont… 30

31. Fibrogram In addition to the staple diagram, the fibrogram is available. In the staple diagram  the  fibers are aligned at one end. In the fibrogram they are arranged by clamping randomly distributed fibers of a cotton sample. The fibers protruding from the clamps are straightened by a brushing process and measured optically. It gives a good representation of the drafting operation and of the arrangement of the fibers in the yarn. The lengths are stated as span-lengths , that is lengths which span a certain distance. 31

32. 2.5% Span Length (SL): Distance from the clamp on a fiber beard to a point up to which only 2.5% of the fibers extend. Defined as the length of fiber at which only 2.5% of long fibers are excluded . Distance from the clamp on a fiber beard to a point up to which only 50 % of the fibers extend. Defined as the length of fiber at which only 50% of long fibers are excluded. 50% Span Length (SL): Cont… 32

33. This is defined as the mean length of the longer half (50%) of the fiber distribution by weight. Mean length of the fibers is defined as “the average length of all fibers in the test specimen based on weight – length data” Upper-half-mean length (UHML): Length Uniformity Ratio (UR): UR = *100 This is often used by digital fibrograph users.   Cont… 33

34. SFI = 122.56-(12.87UHML) - (1.22 UI) = 90.34- (37.47 2.5% SL) - (0.90 UR) Length uniformity Index (UI): UI = *100, This is commonly preferred by HVI users.   Short Fiber Index (SFI): Cont… 34

35. Fiber Strength: Fiber strength is very often the predominant characteristic. A numerous types of fibers are not usable for textiles, Because of inadequate strength. Minimum strength for a textile fiber is approximately 6 cN /tex . Since binding of the fibers into the yarn is achieved mainly by twisting , and thus can exploit at most 30 - 70% of the strength of the material . A lower limit of about 3 cN /tex is finally obtained for the yarn strength, which varies linearly with the fiber strength. Some significant breaking strengths of fibers are: Polyester fiber…….35-60cN/tex. Cotton……………………..15-40cN/tex. Wool………………………...12-18cN/tex. 35

36. The strength characteristics can be determined either on individual fibers or on bundle of fibers. Some standards of fiber strength Cont… 36

37. Short Fiber Content: Usually percentage of fibers less than 12.7 mm , is referred to as the short fiber content ( SFC) . The negative effect of a high percentage of short fibers are : Extreme drafting difficulties Increased number of neps and yarn irregularity, and Ends down which reduce quality and increase processing costs Higher wastage in combing and other operations. Sources of short fibers are: i . Seed cotton and Variety of cotton There are not much variations in cotton fiber inside the ball. But, variety plays some part as weaker fibres tend to break down in processing. 37

38. II. Growing conditions Growing conditions affect the maturity of cotton. Immature fibers break up easily during harvesting , ginning and other processing. Harvesting Manual harvesting still adopted in developing countries cause less impurities, less harsh treatment in ginning, opening and cleaning. However, mechanical harvesting results the opposite and all cotton balls including unopened balls are collected at a time. As the result more immature fiber , so result for more fiber breakage. Cont… 38

39. IV. Ginning The marketing of cotton emphasizes clean cotton (higher grades) and the higher grades bring higher prices. The requirement of very clean cotton without dust for open-end spinning has resulted in hard ginning , and more intense cleaning in blow room machines. Effect of lint cleaners on short fiber content V. Blow room machines Each operation in the blow room and subsequent machines stresses and breaks fibers increasing short fiber content. Cont… 39

40. Trash Content: Trash is a measure of the amount of non-lint materials in cotton, such as leaf and bark from the cotton plant. Trash affects yarn and fabric quality. Therefore, it is very important to know the amount of trash and the type of trash before deciding the mixing . The scale below represents the degree of contamination : Up to 1.2% Very clean 1.2 – 2.0% Clean 2.0 – 4.0% Medium 4.0 – 7.0% Dirty 7.0 % and above Very dirty 40

41. Therefore , mixing of cottons having a trash content differing by more than 3% is not advisable. The average level of trash in the mixing for producing a card sliver of good quality for a specified count is given below. Ne 20 30 40 60 80 100 Average Trash (%) in mixing 5.0 4.0 3.5 3.0 2.5 2.0 Cont… 41

42. Neps: Neps are small entanglements or knots of fibers. In general , two types of neps can be distinguished. Fiber neps which are small knots that consist only of fibers, and Seed-coat neps which contain foreign particles such as seed or leaf fragments. A large proportion of neps in raw cotton is produced by the processing method such as; Plucking, Hard ginning , and The nep count is substantially increased in the blow room. 42

43. The card is the first machine to reduce the nep count to a usable level, and Nep-reduction at the card is achieved primarily by disentanglement rather than by elimination . Neps not only create disturbance in themselves as thick places, But , also dye differently from the rest of the yarn and thus become clearly visible in the finished fabric. FIG: Shade variation in dyeing due to the presence of nep in the yarn Cont… 43

44. 44 Dust consists of small and microscopic particles of various substance. Are present as suspended particles in gases and sink only slowly. So that they can be transported in air over substantial distances. Dust Particle size (µm) Trash Above 500 Dust 50 -500 Micro dust 15 - 50 Breathable dust Below 15 Problems created by Dust: i . Additional stress on personnel Dust is unpleasant, e.g. for eyes and nose It can induce allergies It can induce respiratory disease (Byssinosis)

45. 45 2. Environmental problems Dust deposits Dust accumulations which can fall into the machines. loading of the air-conditioning equipment. 3. Effects on the product Quality deterioration directly, or indirectly through machine faults. 4. Stressing of the machines Dust accumulations lead to operational disturbances. Increased yarn unevenness. More end breaks. Rapid wear of machine components. Cont…

46. Color Color grade is determined by the degree of reflectance (Rd) and yellowness (+b) as established by official standards and measured by HVI. Reflectance indicates how bright or dull a sample is, and yellowness indicates the degree of color pigmentation The color of cotton fibers can be affected by rainfall, freezes, insects and fungi, and By staining through contact with soil, grass, or cotton plant's leaf. Color also can be affected by excessive moisture and temperature levels while cotton is being stored, both before and after ginning. 46

47. As cotton used in mixing come from different parts of the country, It may contain different levels of moisture at the time of mixing. Moisture Regain( R): is defined as the mass of water in a material expressed as a percentage of the oven dry weight. R = (W/D) x 100 Moisture content (M): is the mass of water in a material expressed as a percentage of the total weight. M = W x 100 W+D Moisture: W = the weight of absorbed water D = oven-dry weight of the material Where: Example: Let's suppose that a piece of fiber weighs 125.6 grams initially and 109.4 grams after oven-dry weight. 47

48. The measurement of fiber moisture is very important for a spinning factory, because; It helps to decide on correct invoice weight, It is important in controlling count variation by maintaining consistency in moisture content in mixing, and Almost all physical properties are affected by moisture , moisture measurement helps to properly assess other fiber quality parameters. It is the weight of the material at standard moisture regain . Where; D = oven dry mass of the sample R = commercial moisture regain 48

49. Three concepts must be clearly distinguished Permanent elongation: It is the extension of the fiber does not return to its original state upon relaxation ( removal of the load ). Elastic elongation: That part of extension through which the fiber does return to its original state upon relaxation. Breaking elongation: The maximum possible extension of the fiber until it breaks. It is the permanent elongation and the elastic elongation together. Elongation : 49

50. The following scale represents the cotton fiber elongation : Below 5.0% Very low 5.0 – 5.8% Low 5.9 – 6.7% Average 6.8 – 7.6% High And Above 7.6% Very high Man-made fibers have higher elongation. For normal textile goods, higher elongations are neither necessary nor desirable . They make processing in the spinning mill more difficult, especially in drafting operations. But, higher elongations may be needed for sportswear, stretch products and etc. 50

51. Stickiness: The sticky substance ( chemical deposit ) is one of a group of sugars of the most variable composition (saccharides), produced by Insects, or The plants themselves, depending upon the influence on the plants prior to picking. Honeydew secretion of white fly is known sticky substance on cotton fibers. Types of sticky substances are given below: Secretions by whitefly : honeydew Fungus and bacteria : decomposition products Vegetable substances : sugars from plant juices Fats, oils : seed oil from ginning Synthetic substances : insecticides, fertilizers, oil from harvesting machines. 51

52. Dry and mature cotton fibers contain less plant sugar, whereas immature fibers contain more. During spinning of sticky cotton , the relative humidity (RH % ) and ambient temperature should be low as much possible. An effective way to control cotton stickiness in processing is to mix sticky and non-sticky cotton. Sticky cotton percentage in mixing should be less than 25%. 52