Rieter

Parallelization of the fibers in the batt

Index

From the viewpoint of both economics and quality, the degree of parallelization has a very great influence on the result of the combing operation. It is necessary to seek an optimum level, since a maximum is just as unfavorable as a minimum. Lack of longitudinal orientation, i.e. noticeable fiber disorder, leads, as already explained, to elimination of longer fibers together with the  noil. Loss of good fibers owing to fiber disorder is reinforced to the extent that the  circular combs are overloaded during passage through a disordered batt, so that they pluck and tear at the stock, thereby carrying away bunches of fibers. The same happens with an excessively thick batt. With constant machine settings, the quantity of noil decreases linearly with increased parallelization of the fibers (Fig. 7) and with a decrease in batt thickness (below the optimum, of course). It therefore does not always follow that more noil is automatically associated with better yarn quality. The correct goal is always a predetermined waste elimination level.

On the other hand, an understanding of the disadvantages of excessive longitudinal fiber orientation requires a clear picture of the combing process and in particular the detaching stage.  

In this operation, between 1/5 and 1/6 of the fibers presented to the detaching rollers are drawn out of the batt, i.e. only few fibers are drawn out of a thick layer of feedstock. During this stage, impurities, neps and so on are held back in the sheet because of the retaining power of the thick layer. This retaining power, and hence the so-called self-cleaning effect of the batt, will be all the greater the higher the disorder of the fibers within the sheet. If the fibers have an excessively high degree of parallelization, the retaining power of the batt can be so severely reduced that it is no longer able to hold back the neps as it usually does. Some of these neps also pass through the  top comb. Neppiness of the product is increased.

A second disadvantage is that if the fibers are too highly ordered, the single layers of the lap do not hold together well (it lacks cohesive strength of the layers compared with that of the fiber-to-fiber adhesion at the surface of the lap layers) and mutual separation layer from layer is disturbed. A high degree of parallelization always leads to considerable hairiness of the lap. Furthermore, the lap weight must be kept low.

The degree of parallelization depends on the total draft between the  card and the comber. Fig. 8 shows the relationship between fiber parallelism (draft) and yarn strength/yarn cleanliness.

Fig. 7 – Dependence of noil elimination on the degree of parallelization of the fibers in the feedstock. (Degree of parallelization corresponding to the draft). A: noil percentage. B: draft between the card and the comber. (M. Frey, Rieter Machine Works Ltd., presented at a Colloquium in Reutlingen; Germany.)

Fig. 8 – Dependence of yarn strength and cleanliness on the degree of parallelization of the fibers in the feed lap. (Degree of parallelization corresponding to the draft). A, improvement or deterioration in %; B, draft between the card and the comber based on classical system. (M. Frey, Rieter Machine Works Ltd., presented at a Colloquium in Reutlingen, Germany.)