Rieter

Influence of combing operation on quality

Index

Combing can be applied to a wide range of spinning processes and the range of improvement in quality is correspondingly wide. Accordingly, quality classes must be differentiated in combed yarns:

  • semi-combed (upgrading) with a noil percentage below 12%;
  • normally combed, with a noil percentage between 12 and 18%;
  • highly combed, 18 - 22%;
  • super combed, with noil percentages above 22%.

Combing with a noil percentage below 12% is also referred to as upgrading, since this type of combing enables cotton stock to be moved up one or two classes, with the additional advantage of elimination of short fibers. Combing with a noil percentage above 22% is rare and is generally used only where superfine yarns are to be spun.

Besides the removal of impurities, combing serves mainly to eliminate short fibers. The effect is shown in a simple example in Fig. 11: a is the original staple, b the staple diagram after combing and c the diagram of the noil.

Fig. 12 shows the effect of combing at different noil percentages for a certain type of cotton. What can be generally noticed is that with increasing noil percentages the important quality parameters of strength and evenness improve, but not as much as may be expected. A far bigger improvement can be achieved in imperfections, and the big leap up to 10% of noil is remarkable here. This is exactly the range of upgrading. A further improvement is noticeable with regard to the ends-down rate in downstream processing. Compared with carded material, the ends-down rate in spinning combed cotton is generally lower, but the improvement does not continue with the increase in noil percentage; on the contrary, the ends-down rate can start to increase again as the noil percentage rises above 20%.

Fig. 11 – Staple diagram: a, cotton before combing; b, cotton after combing; c, noil

Fig. 12 – Dependence of various quality parameters on noil elimination; A, improvement of yarn quality in %; B, noil elimination in %; a, yarn strength; b, yarn evenness; c, yarn imperfections; (M. Frey, Rieter Machine Works, presented at a Colloquium in Reutlingen, Germany)