Combing:
Combing allows the production of very fine, high-quality spun yarns. Combing is an intermittent operation carried out between carding and drawframe. The combing process is normally used to produce smoother, finer, stronger and more uniform yarns. The carded materials (sliver) contain certain amount of short fibers, neps, fine kitty and leaf particles. Short fibers are a hindrance to spinning of finer counts where the number of fiber in the cross section of the yarn is less. The short fibers cause thick and uneven places in the yarn length and the yarn looks hairy. Apart from this, very short fibers do not contribute anything to yarn strength. Short fibers below a certain pre-determined length can be easily separated out by using comber. Therefore, combing is commonly confined to high grade, long staple natural fibers. In recent years, combing has also been utilized for upgrading the quality of medium staple fibers. In this article I will explain combing cycle step by step with diagram.
Fig: Combing process in cotton spinning
Combing Cycle or Sequence of Combing Process: The combing cycle begins with the nipper plates in their backmost position (farthest position from the detaching rollers) and closed so as to nip the sliver fringe. As shown in the below figure, the feed roller is stationary, and the top comb is in the up position, clear of the fringe. During the early stages of the cycle, the pins projecting from the cylinder comb enter the sliver fringe and subsequently remove impurities and fibers not held by the nipper plates. As the pins leave the fringe, the nipper-plate unit begins moving toward the detaching rollers. The nipper plates start opening, the top comb drops into the fringe just in front of the nipper plates and, as the latter becomes fully opened, the feed roller pushes forward a short length of fringe. By the time the nipper plates reach the detachment setting, the detaching rollers will have formed an overlap and begun their clockwise rotation. The leading ends of fibers spanning the detachment setting will then be caught, and these fibers are pulled through the interspaces of the top comb. The top comb prevents neps, impurities, and fibers not spanning the preset distance from being dragged out of the sliver fringe by those being detached. It effectively combs and straightens the trailing ends of fibers being detached. In the following cycle, the cylinder removes, along with any neps and impurities, fibers retained in the sliver fringe that are not held by the nipper plates.
Fig: Combing cycle
Once detachment has taken place, the nipper-plate unit returns to its backmost position and, in so doing, the newly formed length of fringe is nipped and ready for combing. The top comb will have returned to its up position. The combing cycle is then repeated. Since, in each cycle, the nipper plates have to be closed for the cylinder to extract the noil, a cycle may be referred to as a nip. The combing frequency is therefore the number of nips per minute, which is normally stated as the combing speed.
The detachment and piecing of fibers from the sliver fringe results in a thin web of straight and parallel fibers being issued from the delivery rollers. The combed web is then consolidated to make a sliver, which is pulled along a table alongside slivers from other combing heads on the same machines (usually six or eight heads), and the set of doubled slivers are drawn to form a single sliver, termed a combed sliver, by a drafting system at end of the machine. The sliver is then wound into a sliver can, ready for the next process.
Each step of combing cycle is described below with diagram:
a) Lap feeding by feed roller: The feed rollers S move the sheet w (4-6.5mm) forward, while the nipper Zo and Zu are held open.
Fig: Lap feeding by lap Roller
b) Lap nipping by the nipper: The upper nipper plate Zo lowered onto the cushion plate Zu, so that the fibers are clamp between them.
Fig: Lap nipping by the nipper
c) Combing by the cylinder: The fiber fringe B (fiber protruding from the lap beyond nipping point) is combed by the cylinder comber. Cylinder comber rotates and carries away the short fibers, neps and other impurities.
Fig: Combing by the cylinder
d) Nipper opening and forwarding: The nippers open again and move towards the detaching rollers A.
Fig: Nipper opening and forwarding
e) Detaching roller backward movement: Meanwhile, the detaching rollers A have returned part of the previously drawn off stock (web V) by means of a reverse rotation (web return).
Fig: Detaching roller backward movement
f) Piecing: In the course of forward movement of the nippers, the projecting fiber fringe B is placed upon the returned web V.
Fig: Piecing
g) Combing by the top comb: Before the start of detaching roller operation, the top comb F has thrust its single row of needles into the fiber fringe. As the fibers are pulled through the needles of the top comb during detaching, the trailing part of the fringe is combed.
Fig: Combing by the top comb
h) Detaching roller forward movement: The detaching rollers begin to rotates in the forward direction again and draw the clamped fibers out of the sheet W held fast by the feed rollers S.
Fig: Detaching Roller forward movement
i) Starting a new cycle: As the nipper assembly is restarted, the nippers open for the next feeding step. The top comb is withdrawn. A new combing cycle begins.
j) Cleaning of cylinder comb: The combing cylinder rotates continually and the combing segment is therefore brought into the vicinity of a rapidly revolving brush mounted below the cylinder comb. This stripes the combing segment of fiber impurities, neps etc. and eject them into a aspirator that carries the noil away to a collecting filter drum.
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
