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THE COMBING PROCESS.pptx

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THE COMBING PROCESS.pptx

  1. 1. THE COMBING PROCESS Introduction The process of straightening and parallelizing of fibers and the removal of short fibers and impurities by using a comb on combs assisted by brushes and rollers is called combing.  The combing process is carried out in order to improve the quality of the sliver coming out of the card. The process eliminates short fibers, it achieves better parallelization of fibers, it straightens curls, and it removes neps and residue impurities.
  2. 2. Objectives (tasks)of Combing Following are the objectives of combing process:  To remove naps in the carded sliver.  To make the fiber more parallel and straight.  To produce a uniform sliver of required per length.  To remove the fiber shorter than a predetermine length.  To remove remaining impurities in the comber lap. Necessity of Combing The following quality of fibers can only be obtained by combing  Absence of nap  More parallel arrangement of fibers  Straight fibers  Clean finer fiber  Uniformity in length of fiber
  3. 3. FACTOR INFLUENCING THE COMBING PROCESS 1. Machine settings I. Feed distance:- This indicates the distance fed by the feed roller per cycle; high feed distance increases the production rate but, reduces the comber noil and deteriorates the quality. However, % noil and feed rate relationship is different for forward and backward feed systems Feed distance also very much depends upon the staple length. Fig Cm-5 indicates typical values of feed distance for different length of cotton fiber.
  4. 4. Cont.. II. Feed type:- Feeding can take place when the nippers move backwards (known as backward feed or counter-feed) and alternatively, when nippers move forward (known as forward feed or concurrent feed) during a combing cycle. Counter- feed is used when better quality of product is required at the loss of more noil (12-25%). Concurrent feed is preferred when higher production rate with less noil desired (5-12%).
  5. 5. Cont… III. Detachment setting:- This is one of the main settings responsible for the change of noil percentage. This setting refers to the distance between the bite of the nippers and the nip of the detaching rollers when nipper assembly is at the most advance position. A closer setting is associated with lower noil level. Detachment setting normally lies in the range of 15-25 mm. A large setting (more than optimum) does not produce further improvement in quality, but results in more loss of noil. As such, optimum setting has to be found out depending on quality and production level desired for a particular machine and material processed.
  6. 6. Cont… IV. Number of point on comb; Saw tooth clothing is used in circular comb and needles are used in top comb. Fineness and point density depend on the raw material processed. Usually top comb point density falls in the range 23-32 needles per centimeter. More needles give more noils. V. Depth of penetration of top comb:- Lowering of the top comb by about 0.5 mm is followed by an increase in noil of about 2%. The main improvement is seen in elimination of neps. Over deep penetration of the top comb disturbs fiber movement during piecing and so optimum penetration is very important.
  7. 7. Cont… VI. Piecing and detachment timing:- During piecing, fiber fringes are laid on top of each other in the same way as roofing tiles. Sliver produced in this way has a wave like structure due to this piecing having a wavelength of 30-75 cm. This is known as piecing defect. • The combed fiber fringes can be compared with very flat parallelogram although the leading edge is blunter. By using correct setting (by adjusting the timing when detaching begins relative to the instant at which the fringe protruding from the nipper reaches the nip line of the detaching rollers), it is possible to lay the fringes on each other in such a way that unevenness in successive fringes partly cancels out. On the other hand, incorrect settings will cause an increase in unevenness arising from piecing.
  8. 8. 2.Properties of raw material I. Fiber length and its uniformity: These parameters play critical role in deciding the combing performance. If the fiber has high short fiber content, then the improvement in the yarn quality becomes significant only on removal of high amount of noil, which will in turn increase the material cost. II. Fiber stiffness: If the fiber stiffness is high, there is good chance of fiber breakage during the combing operation as the fibers have to go through lot of bending during the combing operation. III. Moisture content: High moisture content is the fibers make the combing operation difficult since the fibers tend to cling to each other making the passage of the combing needles between the fibers rather difficult leading to improper combing and high fiber breakage. If the moisture content is less and the fibers are dry, then the fibers do not move smoothly from one component to another and they tend to fly.
  9. 9. Cont… IV. Fiber fineness: The combing machine parameters like the speeds and settings will be influenced by the micronaire value of the cotton being processed. In case of finer fibres, the total number of fibres in a unit length of the lap of given linear density will be much higher than that for coarser fibres. The finer fibres are also delicate. Hence, the combing machine parameters need to be selected appropriately. V. Foreign material associated with the fibers: The foreign materials and larger trash particles should have been already removed from the fibers at the carding stage itself. If larger trash particles and metallic particles are still left in the feed lap, they can cause damage to the combing needles.
  10. 10. 3.Material preparation: I. Fiber parallelization: The condition of fibres in terms of orientation and parallelization as they are feed to the combing head is a very critical parameter which decides the combing performance. Parallelization of the feed fibres depends upon the draft between card and the combing machine. If the fibres are not oriented (parallelized), then long fibres are presented to the circular comb as if they are short fibres and they are therefore eliminated as noil. At the same time, too high parallelization is also not desired. During detaching, a few fibres reaching the nip of the detaching rollers are drawn out of the thick layer of feedstock.

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