Rieter

The straightening-out operation

Index

A disadvantage of web formation at the card that has already been mentioned is the formation of hooks. According to investigations by Morton and Yen in Manchester, UK, and others, it can be assumed that the fibers in the web show the following hooks:

  • more than 50% have trailing hooks;
  • about 15% have leading hooks;
  • about 15% have doubled hooks,
  • and less than 20% have no hooks.

Such fiber hooks, which effectively convert longer fibers to short fibers, cannot be permitted in the yarn. They must therefore be removed before yarn formation. This is done by the draft or by combing as the following description shows:

In the drafting arrangement, the fiber hooks may be bedded in the body of fibers either as leading or as trailing hooks (Fig. 23 and Fig. 24). Consider first a trailing hook (S): it will be seen that for a certain period it moves with the remainder of the fiber strand at the speed of the back roller towards the front roller. If the fiber tip passes into the nip region of the drawing roller, the fiber is accelerated. However, since the trailing end is moving with a relatively thick body of slowly moving fibers, the fiber is straightened before the whole fiber can reach the drawing speed — the hook is eliminated. On the other hand, leading hooks (K) are immediately caught bodily by the front roller and carried along unchanged (Fig. 24). The comber however mainly straightens out leading hooks, because the needles of the circular comb can grasp only these (Fig. 25).

Fig. 23 – Trailing hooks in the drafting arrangement

Fig. 24 – Leading hooks in the drafting arrangement

Fig. 25 – Leading hooks in the comber