Combing is the process which is used to upgrade the raw material. It influences the following yarn quality
In addition to the above, combed cotton needs less twist than a carded yarn.
TASK OF THE COMBER:
To proudce an improvement in yarn quality, the comber must perform the following operation.
elimination of short fibres
elimination of remaining impurities
elimination of neps
The basic operation of the comber is to improve the mean length or staple length by removing the
Since fineness of short fibres(noil) is low, the overall micronaire of the sliver after combing is high.
Because of combing, fibre parallelisation increases. Please note that this is a side effect which
is not an advantage always. The high degree of parallelisation might reduce inter-fibre adhesion in the sliver to such an extent that the fibres slide apart while pulled out of the can. This may lead to sliver breaks or false draft.
SEQUENCE OF OPERATION IN A COMBER
Feeding, lap is fed by feed roller
fed lap gripped by the nipper
gripped lap is combed by circular comb
detaching roller grips the combed lap and moves forward
while the detaching roller delivers the material, top comb comes into action to further clean the lap
While going back,nipper opens and receives a new bit of lap
The rawmaterial delivered by the carding machine can not be fed directly to the comber. Lap preparation is a must
A good lap fed to the comber should have
Highest degree of evenness so that lap is gripped uniformly by the nipper
a good parallel disposition of fibres so that long fibres will not be lost in the noil
trailing hooks from carding should be fed as leading hooks to reduce long fibre loss in the noil
Degree of parallelisation of lap fed to the combers should be optimum.
If fibres are over parallelised lap licking will be a major
problem. Because of fibre to fibre adhesion, mutual separation
of layers within the sheet is very poor.Moreover the retaining
power of the sheet can be strongly reduced that it is no longer
able to hold back the neps as it usually does. Some of these
neps also pass thro the top comb. Neppiness of the web is
Retaining power of the fibres results in self cleaning of the lap during combing operation. A thick sheet always exerts a greater retaining power than a thin one.To certain extent, the bite of the nipper is more effective with a higher sheet volume.On the negative side , a thick sheet always applies a strong load to the comb and this can lead to uncontrolled combing.A compromise should be struck between quality and productivity.
If the sheet is more even across the width, clamping effect at the bite of the nipper will be better.
Evenness of the lap is therefore of considerable significance. The most effective method of obtaining a
high degree of evenness of the sheet is through more number of doublings in the web form.
(as it is done in RIBBON LAP)
Fibres must be presented to the comber so that leading hooks predominate in the feedstock. This influences not only the opening out of the hooks themselves, but also the cleanliness of the web.If the sheet is fed to the comber in the wrong direction, the number of neps rises markedly.
Both quantity and form of fibre hooks depend mainly upon the stiffness of the fibres. This rises to the
second or third power with fine fibres. Fine and long fibres will always exhibit more
and longer hooks than short and coarse fibres. Accordingly, the role of fibre hooks in the spinning process becomes more significant as fibres become finer.
There are two types of feeds in COMBER
Forward feed (concurrent feed):Feed of the sheet into the nippers occurs while the nippers move towards the detaching roller
Backward feed (counter-feed) : Feed of the sheet occurs during return of the nippers
Higher Noil % always improves the imperfections in the final yarn. But the strength and other quality parameters improve upto certain noil %, further increase in noil results in quality detrioration.
In backward feed, the cylinder comb combs through the fibres more often than in forward feed
Therefore, the elimination of impurities and neps is always good. However the difference is usually undetectable in modern high performance combers of the latest generation.
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