Sunday, February 23, 2020

WORKING PROCEDURE OF COMBING MACHINE AND FEED STOCK PREPARATION METHOD


WORKING PROCEDURE OF COMBING MACHINE:

The working procedure of a combing machine can be understood in the following steps:



First of all the lap roller is mounted onto the roller stand.

The lap feed, first of all, passes under the feed roller. The feed roller helps to move forward the lap sheet by a small amount of 4.3 – 6.7 mm. When the lap sheet moves forward the nippers are opened and get ready to receive the feed.

As soon as feeding action gets completed, the upper nipper plate starts to lower on the bottom nipper plate. These nipper plates help to grip the lap sheet firmly during the combing action.

Now combing action gets started. The lap sheet comes into contact with the bottom comb mounted on the rotating cylinder. The saw teeth of comb sweep the lap sheet.  It carries away the material which is not gripped by nipper plates (rotary comber).

The nipper plates get opened again and move toward detaching rollers meanwhile detaching rollers have returned part of the previously drawn-off stock ( web) by means of reverse rotation so that the web protrudes from the back of the detaching device (web return). In the course of the forward movement of the nippers, the projecting fibre fringe is placed on the returned web (piecing).

The detaching rollers start to rotate in the forward direction again and draw the gripped fibres out of the web held fast by feed rollers.

Now upper comb comes into action and combs the trailing part of the fibres fringe.

The detaching rollers acts and nipper plates open again to receive the next feeding. The upper comb goes back in its idle position and a new combing cycle gets started

The brush cylinder helps to remove the impurities from the bottom comb 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 times per minute (in Rieter‘s current E 66 comber generation).


PREPARATION OF STOCK FOR COMBING:

The carded sliver cannot be used directly in the combing process due to its form and fibre arrangement in the carded sliver. If carded sliver gets fed to the comber, the nipper plates grip only high points of the sliver. There is always a risk of improper nipping of the less strongly compressed edge zones of the slivers. When combing action takes place, these fibres are pulled out as clumps by the bottom comb (cylinder comb).

This problem necessitates a cotton sheet with the highest possible degree of uniformity as a feed to the combing machine. The feed material requires the best fibre arrangement (fibre parallel to the length of the feed material). If the fibre arrangement in the feed material is not proper, unnecessary loss of long-staple fibres occurs too. Therefore a fibre sheet having a high degree of uniformity with the best parallel arrangement of fibres is used as feedstock in the combing process.

Methods of preparation: 

A machine having three pairs of drafting rollers and two pairs of calender rolls is used to form a suitable lap for the combing machine. 
In the conventional method of sliver lap/ribbon lap preparation, sixteen to thirty-two number of carded slivers are fed together to the lap preparation machine. This machine forms a lap having a linear density of 50 – 70 grams per metre and 230 – 300 mm. width. This lap is wrapped onto the lap roll. The diameter of the lap roll is around 500 mm. and its weight is 27.0 kg. A draft of 1.5 to 2.5 is used in the sliver lap machine.



Now, these prepared sliver laps are passed through the "ribbon lap machine". Normally ribbon lap machine consists of four heads. Each head processes a single sliver lap. Every thin sheet is led down over a curved plate. All the four thin sheets lead down together. This turns at right angles, inverts them and superimpose one upon the others. "The drafts used in the ribbon lapper are about four, so the weight per meter of the ribbon lap is about the same as that of the sliver lap". 

THE SUPER LAP PREPARATION MACHINE:

 This machine consists of 2/3 vertical drafting systems. In this machine around 20 drawing slivers are fed. The fed material is drafted three to five times. Three such types of units convert the drawn slivers into three thin sheets of fibres. These sheets are superimposed one over the other. Calander rolls press the final lap sheet.

This machine is only used in the manufacturing of a very fine count of yarn from extra-long staple fibres.

THE BREAKER DRAWING/LAP FORMING METHOD:

The breaker drawing/lap-forming method is very common for most combing operations. This method of lap preparation is useful to process the fibre length from medium to long-staple fibre. The whole process of lap preparation in this method completes in two steps:

Drawing process: 

A standard drawing process is used in this method of lap preparation. 20 – 24 number of carded slivers are fed together. After drafting a drawn sheet of sliver results.

Lap winding process:

 Now, this drawn sheet is wound onto the lap roller. The linear density of the lap varies between 50 to 70 grams per metre.

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