Process of Controlling Waste in Combing

Control of Comber Waste

Eshan Bansal
Dept. of Textile Engineering
Punjab Technical University
Giani Zail Singh Campus, Bathinda, Punjab, India.
Email: eshanbansal@live.com





CONTROL OF COMBER WASTE
The primary function of a comber are three: to remove fiber hooks and parallelise the fibers, to bring about fiber-to-fiber separation, and to remove short fibers. Of these short fiber removal has to be done through removal of waste. The comber waste also contains a large number of neps and some foreign matter particles. Combing, therefore, results in a considerable reduction of nep content and in some cleaning of cotton also. However, a higher percentage of waste need not always mean more removal of short fibers and neps, and therefore may not always be advantageous for yarn quality and/or performance. The high cost of removing even one percent extra comber waste makes it imperative that a mill should carefully choose the optimum level of comber waste for each mixing and then exercise a strict control on all combers to maintain the waste at the desired level.

TECHNOLOGICAL CONSIDERATIONS
For an effective control of short fibers, retention of long fibers and removal of neps, the following considerations are important.
  1. The card trailing hooks are longer and more numerous than the leading hooks. They are removed when fed as leading hooks by keeping an even number of reversals between card and comber.
  2. The waste at comber can be reduced by increasing precomber draft upto certain limit without effecting the resultant yarn quality.
  3. The proper place for controlling neps is carding and not combing. It is often more economical to run card at somewhat low production rate than to take out extra comber waste.
OPTIMUM LEVEL OF COMBER WASTE
The minimum level of comber waste which gives the desired yarn quality, yarn appearance and end breaks at ring frame depend on nature of fiber length distribution in the cotton or mixing. Experience based information obtained by ATIRA in this regard is summarized as under:

Table: Guidelines for optimum levels of comber waste.
Nature of fiber length distributionof mixing
Short fiber %
(by number)

Mean length
Approximate level of comber waste %
(by weight)
Triangular
>20%
26mm
No optimum
(waste%~quality)
Flat
<18%
26mm
0.5*S.F%
 
An increase in comber waste results in improvement in yarn quality till most fibers below 15mm length are removed. As a starting point, one can take comber waste level at S.F/2 around which actual experiments can be conducted to find out the optimum level in regard to yarn quality and breakage rate at ring frame. For e.g. for a cotton with short fiber content of 22%, one can take trials with 10%, 11% and 12%. The minimum level which gives the desired yarn quality and minimum end breakage rate in spinning gives should be adopted for large scale production.

EVALUATION OF COMBER AS A FRACTIONATING DEVICE
The level of waste removal should always be weighed against reduction in short fiber content or improvement in fiber length. As is well known the comber is not a perfect fractionating device, in other words, some short fibers find their way into the comber sliver and long fibers get into the waste. There are two methods which can be used to express fractionating efficiency. The first one, is based on the short fiber content in the comber lap and the comber sliver while the other consists simply of finding out the improvement in mean length.

In view of the large variability associated with the determination of short fiber content and because of the poor correlation between the values of short fibers determined by different methods, any index of fractionation based on estimation of short fibers could not be reliable. The methods of expressing fractionating efficiency in terms of mean length has been found to be quite reliable.

Table: Norms for improvement in mean length and levels of comber waste

Count
Fiber length(mm)


Waste %
Expected increase in length (mm)
Effective length
Mean length
28-34
26-27
21-23
7-9
1.0-1.2

28-30
21-23
10-12
1.2-1.8
35-44
31-34
24-26
11-13
2.0-2.8
46-60
34-36
25-27
12-14
2.5-3.0
 
ROUTINE CHECK OF COMBER WASTE
The waste at comber need to be checked and controlled due to the following reasons.
  1. More waste than the nominal means financial loss.
  2. Less waste than the nominal could lead to unacceptable yarn quality performance.
  3. Between comber waste variation could contribute to between lea count variation.
The numerous experiments conducted in the industry have brought out the following facts.
  1. Head waste CV exceeding 6% calls for attention.
  2. Comber waste CV in excess of 4% calls for attention.
  3. For a well set and maintained comber , the difference in the level of comber should not exceed 3% from the average.
PROCEDURE FOR DETERMINING COMBER WASTE
Remove noil from the back of each head and break the sliver just beyond the coiler. Collect headwise noils and comber sliver from the can by breaking just after the coiler. The overall comber waste and headwise waste are then calculated as follows:  
 
                                                                Wt. of noils from all heads * 100 
1. Overall comber waste (%) = ...............................................................................
                                                           (Wt. of sliver+Wt. of noil from all heads)

 
                                                   Wt. of noil from a head *100
2. Head wise waste (%) =......................................................................
                                             1/n (Wt.of sliver+Wt.of noil from all heads)

The waste levels and their CV should be determined by taking ten readings of five minutes each over a period of 10-15 days and compare with the norms.

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