textile yarn manufacturing lap & comb (1).pptx

yarn

1. Chapter Five Lap preparation for combing

2. Slivers are not fed directly to a combing machine since the nipping by nippers would occur only on the high points. This would result in clumps of fibres being pulled out during combing. Therefore, laps are prepared using preparatory machines called lap formers and These laps are feed to the combing machine. Introduction Lap 2

3. It is clear that lap should be prepared in such as way that: Fibres are parallel. Majority of hooks are present as leading hooks. Lap should be uniform in thickness. In addition, the lap preparation should ensure Lap with less number of piecing points Lap without tendency of licking Lap with longer length (bigger laps ) Piecing is an operation that allows the two strip-one combed in previous cycle and the other freshly combed to superimpose on each other partially. Cont… 3

4. Lap Former Functions of Lap Former Machine: Doubling certain number of draw frame slivers (from 16 to 32 ). Imparting slight draft to the fed material. Produce a uniform lap for comber machine. Winding the lap on spools. Doffing out the fully wound lap. Any one of the following two sequences is used for preparing the lap for combing: Sliver lap machine followed by a ribbon lap machine Draw frame followed by a super lap former( also known as sliver doubling ) 4

5. Sliver lap machine Ribbon lap machine Sliver and Ribbon lap machines 5

6. In the first case, a number of slivers are doubled and drafted together to form laps in sliver lap machine . These laps are then again doubled by unrolling them one over the other and then drafted to form the final lap in the ribbon lap machine . The side by side blending of slivers in the first process and overlapping in the second ensure adequate uniformity in the final lap. However, in the ribbon lap machine , whenever a lap is exhausted , a new one is joined to feed the same number of laps resulting in a piecing defect . 6 Sliver and Ribbon lap machines

7. Super lap machine (Sliver blending) Rieter UNIlap machine 7

8. Here, both the operations of side by side blending and overlap blending are carried out in the same machine . Therefore a large number of slivers ( 28 or even more) are used and more draft is provided in a single operation. Any piecing required during breakage of slivers or exhausting a sliver does not result in fault as big as lap piecing. Since the number of processes between the card and the comber should be of even number and more parallel fiber in lap is desired, a draw frame passage is required before feeding the carded sliver into a super lap machine. In modern combing rooms, lap preparation is invariably carried by the super lap machine . 8 Super lap machine (Sliver blending)

9. Operating principle of super lap machine 9

10. Creel Zone : Used as feeding zone. 16 to 32 draw frame slivers passed through guide roller, guide bars and fed to drafting zone . Guide Roller : It guides the passage of feeding slivers. Operating principle of super lap machine 10

11. Calendar rollers & Lap formation : The slivers are fed side by side , passing through rollers and stop motion . The slivers enter the drafting section and then calendar section to produce a compact lap. Finally, the lap is wound on to spool . Doffing of Lap: The Lap former doffs automatically once the desired length of Lap wound on the spools. During doffing empty spools are taken by the machine itself from the reserve holder and next round of winding starts . 11

12. Chapter Six C ombing m achine 12

13. Combing is a process by which the quantity of short fibers and remnant fragments of impurities present in a carded or drawn sliver are minimized to give a clean sliver , Having more of a rectangular staple diagram, with the vast majority of the constituent fibers in a straightened and parallel state. Combing, therefore , makes possible the spinning of yarns of fine counts with low irregularities and a cleaner appearance. Introduction 13

14. Combing is a process employed to perform the following tasks: Elimination of a precisely pre-determined quantity of short fibers . Elimination of the remaining impurities . Elimination of the large proportion of neps (not all can be removed). To form the sliver having the optimal possible quality parameters. After combing, marked improvement of the following properties of yarn is noticed: Yarn Evenness Strength Cleanliness Tasks of combing machine 14 Smoothness Handle and Visual appearance

15. Negative Effects Of Combing Combing by its own action produces two defects in the sliver: Piecing defects : This will be discussed later and as will be seen, that with proper measures, it can be minimized. II. Reduces the inter fibre cohesion : The high degree of parallelization of fibres in the combed sliver may reduce the inter fibre cohesion It may lead to breakages in creels or false drafts in subsequent processes. So, combed sliver should be carefully handled in subsequent operations. 15

16. Noil is the material removed by comber, which includes fibres, trash and neps. The amount of noil can be expressed in two different ways: % Noil = Tear ratio = : 1 Tear ratio = The tear ratio is mostly used in the worsted sector , whereas % noil is used in cotton spinning process. The amount in combing noil depends on the type of yarn to be spun and also on the quality of fibre. In cotton industry the range is 5-30%.   Amount of Noil in Combing 16

17. Classification of combing mills Combing mills can be divided in to the following groups based on the type of combing: Long staple combing factories :- These factories produce fine to superfine yarn and also use high grade fibre having long staple and low trash . Percentage noil in combing is kept high . Production in combing is low. 17

18. II. Medium staple combing factories :- Yarns spun are medium to fine in count. Medium staple and middle grade fibres are used. Noil level is moderate . Such mills tend to produce high grade yarn and combing production also is maintained at high level . However, it requires good technology and practices to maintain both quality and production and also medium level of noil at the same time. Cont… 18

19. III. Short to medium staple combing factories :- Raw material used here is the same as that for the production of carded yarn . Yarn count range is medium and sometimes, low to medium . Percentage noil is kept low ( 6 - 14%). Production in combing is high . Light combing is also introduced to a greater extent owing to the impairments in cotton quality influenced by mechanical harvesting. Even when minimum noil is removed, there is a noticeable improvement in the fibre parallisation in sliver; Smoothness and shining of the yarn is improved. Cont… 19

20. 20 Combing efficiency B ased on the % improvement in 50% span length over noil removed Combing efficiency = Where; S = 50% span length of combed fibre L = 50% span length of uncombed fibre W = % noil

21. Types Of Comber Quite number of different types of comber are available, including: Rectilinear comber (with stationary or oscillating nippers, for cotton); Circular combers(English worsted process); Rotary combers (production of Schapper-spun yarns): Hackling machines (bast fiber). Short-staple spinning mills use only the rectilinear comber with swinging nippers and stationary detaching rollers . 21

22. Sequence of operations in a Rectilinear comber Feed rollers (S) move lap sheet (W) forward by small amount ( 4.3 – 6.7 mm ), while nippers (Zo/Zu) are held open ( feed ) Upper nipper plate Zo is lowered onto cushion plated (Zu) so that the fibers are clamped between them( nipping ) Combing segment (K), mounted on rotating cylinder (Z) sweeps saw teeth through fiber fringe (B) and carries away anything not held by nippers ( rotary combing ). 22

23. (d) The nippers open again and move toward detaching rollers (A) ( nippers forward ) (e) Detaching rollers (A) have returned part of previously draw-off stock (web V) by means of a (partial) reverse rotation , So that the web protrudes from the back of the detaching devices( web return ). Cont… 23

24. (f) In the case of the forward movement of the nippers the projecting fiber fringe (B) is placed on the returned web (V) ( piecing ). (g) The detaching rollers being to rotate in the forward direction again and draw the clamped fibers out of web (W) held fast by feed rollers( S) (inside the nippers) ( detaching ). Cont… 24

25. (h) Before the start of the detaching operation, top comb (F) has thrust its single row teeth into the fiber fringe. As the fibers are pulled through the teeth of the top comb during detaching, the trailing part of the fringe is combed, thus making up for the inability of the circular combs to reach this part of the fringe ( passive combing by the top comb ) Cont… 25

26. ( i ) As the nipper assembly is retracted , the nippers open for the next feeding step . The top comb is withdraw a new combing cycle begins. (k) Contrary to the movements of the other parts, the combing cylinder rotates continuously. During this rotation and at a certain instant the combing segment is brought into the vicinity of a rapidly revolving brush (K) mounted blow the combing cylinder. Cont… 26

27. This brush removes the imperfections from the combing segment , and ejects them into an extractor that carries the noil away to a collecting filter system . All these mechanically very demanding processing steps are carried out on 8 combing heads simultaneously at speeds of up to 500 mm times per minute. Cont… 27

28. Parameters influencing the combing operation The main parameters influencing combing are: 1. Raw material : Fiber type; Fiber fineness (Micronaire); Fiber length; Uniformity of fiber length (CV); Fiber stiffness; Moisture content;  Foreign material associated with the fibers. 28

29. 2. Material preparation: Parallelization of the fibers in the sheet (batt); Batt thickness; 3. Machine settings: Feed distance; Type of feed; Detachment setting; Point density of the combs; Circular comb clothing (angles of teeth, density of teeth, etc); Depth of penetration of the top comb  Draft; Drafting arrangement settings. Batt evenness; Orientation of the hooks. Cont… 29

30. 4. Factors associated with the machine: Condition of the machine and combs; Speeds and operational performance of combs ; Type of sliver forming element (diagonal  shift of the piecings); Accuracy of the settings; Drafting arrangement; Movement of the elements; Weight of the elements; Type of withdrawal of the combed web  ( either straightforward or oblique). Cont… 30

31. Influence of the feed stock on combing 1) Parallelization of the fibers in the batt Lack of longitudinal orientation, i.e. noticeable fiber disorder , leads to elimination of longer fibers together with the noil. Loss of good fibers owing to fiber disorder is reinforced to the extent that the circular combs are overloaded during passage through a disordered batt, so that they pluck and tear at the stock, thereby carrying away bunches of fibers . The same happens with a excessively thick batt. With contrast machine settings, the quantity of noil decreases linearly with increased parallelization of the fibers and with a decrease in batt thickness (below the optimum). 31

32. 2) Batt thickness (weight)  This effect arises from the  retaining power  of the fibers relative to impurities, which depends  not  only   on the  disorder of the fibers  but also on their  quantity .  A thick batt always exerts greater  retaining   power  than a thin one.  At least up to a certain level, the clamping effect of the nippers is also better with a higher batt volume.  Adversely, a  thick batt  always exerts a heavy load on the comb  and this can  lead to  uncontrolled combing .  In this case, the fiber farthest from the circular combs (upper side of the nipped web) may  escape the combing operation , Cont… 32

33. 3) Evenness of the batt sheet  The more even the batt sheet (web) is across its width, the better the clamping effect at the nipper clamping line. It is very important that the slivers are arranged neatly relative to one another and evenly over the entire working width at the lap machine. The most effective method of obtaining a high degree of evenness of the sheet is high doubling in sheet form, However, nowadays, the disadvantage far exceed the advantages, E.g. the very high fiber parallelization caused by the high draft in two stages, resulting in insufficient cohesion of the sheet . Cont… 33

34. 4) The disposition of the hooks As previously mentioned, fibers must be presented to the comber in leading hooks predominated in the feedstock. This influences not only the opening out of the hooks themselves, but also the cleanliness of the web . These hooks are then removed by the circular comb. If the hooks are feed as trailing hooks , then comber will assume as short fibers, and Released by nippers and as a result, % noil will increase. Cont… 34

35. The influence of machine components and settings on combing 1. The feed amount moved per cycle  This has a noticeable influence on Noil percentage, The quality of the combing operation, and The production rate. A high feed amount  increases the production rate  but causes deterioration  in quality, especially in the cleanliness of the web.  Hence, the feed amount per cycle must be set lower , the higher the quality requirements, and this correlates not exactly but approximately with the fiber length . 35

36. 2) Type of feed Feeding can take place when the nippers move backwards to the detaching rollers (known as backward feed or counter-feed ), and Is used when better quality of product is required at the loss of more noil ( 12-25% ). Feeding can take place when the nippers move forward to the detaching rollers (known as forward feed or concurrent feed ) during a combing cycle. Is preferred when higher production rate with less noil desired ( 5-12% ). Forward feed is mostly used over all staple ranges for achieving noil levels from 8 to 18% . Cont… 36

37. One main reason is better “ self cleaning ” effect during detaching and top combing action by generating higher retaining forces. Fiber rear ends and the hooks are more extended. Disturbing impurities (husk particles, dust and trash, leaf, fiber neps and seed coat fragments) and short (floating) fibers are hold back by the top comb during detaching and are combed out by the next circular combing cycle . Cont… 37

38. 3) The detachment setting  This refers to the distance between the clamping line of the nippers and the nip line of the detaching rollers . The detachment setting provides the chief means for influencing the level of noil elimination ; A wide detachment setting results in a high level of noil elimination ; A closer setting is associated with a lower noil level . The detachment setting normally lies in the range of 15-25 mm. Cont… 38

39. 4) The number of points on the combs Saw tooth clothing is used in circular comb and needles are used in top comb Fineness and point density depend on the raw materials processed. Usually top comb point density falls in the range 23 - 32 needles per centimeter. More needles give more noils. 5) The depth of penetration of the top comb  Noil extraction can also be influenced by the depth of  penetration of the top comb Lowering of the top comb by about 0.5 mm is followed by an increase in noil of about 2% . 39 Cont…

40. The optimum setting must be established, since excessively deep penetration of the top comb disturbs fiber movement during piecing. The result is deterioration in quality . 6) Piecing and detachment timing During piecing fiber are laid on top of each other. By using correct setting ( adjusting the timing of detaching the nip line of the detaching rollers ), It is possible to partly cancel out unevenness part, and Incorrect settings will be increase unevenness from piecing. Cont… 40

41. 41 1.Reserve lap and 2. Lap 3. Lap support roll 4. Eccentric shaft 5. Feed roller 6. Nipper 7. Nipper top plate 8. Spring 9. Top comb 10. Circular comb brush Elements of rectilinear combing machine 11. Circular comb 13. Oscillating nipper shaft 14. Detaching rollers 15. Web plate 16. Lead-off rollers 17. Trumpet 18. Table roller 19. A brush(circular comb clean)

42. Two fluted rollers (3), driven at constant speed, unroll the web from lap (2) An eccentric shaft (4) is fitted between the rollers and feed cylinder (5) The web is fed over this shaft, which is rotated intermediately in time with nipper cycle. Each shaft rotation represents less than a full revolution, first in a forward direction and then in backward feed. This back-and –forth rotation ensures even tension in the web and hence prevents false drafts, Feed of the lap sheet Elements of rectilinear combing machine 42

43. There is no machine drive of the feed rollers as such; they are driven indirectly by the opening and closing of the nipper plates. Forward shift of the web by the feed roller into the opened nippers can be performed: While the nippers moved forward (described above as forward feed); or When the nippers swing back (described as backward feed). The Feed Device Cont… 43

44. The nipper assembly is of enormous importance to the design of a comber. The nipper assembly has to clamp a relatively thick lap batt(up to 80 ktex) firmly and evenly. The upper nipper is mounted so that it can pivot on the lower nipper on pivot axis (a), and can therefore be raised and lowered. The Nipper assembly Cont… 44

45. Two spiring (8), one each to right and left of the nipper assembly, generate the required contact pressure for the nipper closing. The so-called bite . The nose (n) is designed to press the fringe downward during clamping , So that the fringe cannot escape the action of the circular combs. Cont… 45

46. Fig: Circular comb with metallic clothing (teeth) The circular comb: A  cylinder drive shaft (R)  extends through the whole machine, and carries  one combing  cylinder (D) per combing head.  The combing cylinder in turn supports a combing segment (half-lap) (S), which is bolted to the cylinder and is fitted with metallic clothing (K). Since metallic clothing are more robust, they are not liable to get damaged easily. Such clothing's require less maintenance Circumference with wire points are usually 75 , 90 , 110 in different machines. Cont… 46

47. The Top comb Fig: The top comb assembly The replaceable top comb (F) is arranged between nippers (Z) and detaching rollers (A). Top comb plays a major role in waste removal . Out of total comber noil, about 60% is removed by top comb. However, top comb gets damaged soon. Even 4-5 damaged needles affect the quality seriously. So, top comb maintenance is very important in combing. Cont… 47

48. T h e End!!! 48