Rieter

Technological interrelationships

Index

This ingenious spinning system has been developed in Australia by the CSIRO research center. A fiber strand passed between reciprocating rubbing rollers takes up turns of twist, but in alternating directions (over a short length, in Z and S directions). The untwisting moment releases these turns of twist. However, if two fiber strands with the same twist direction pass through in parallel, closely adjacent to each other, the untwisting moment can no longer act separately on the individual yarns; it acts on both together to twist the yarns around each other. A two-fold thread is obtained with a continuously changing direction of twist: Z twist where S twist is present in the individual yarns, and S twist where the yarns have Z twist (Fig. 13).

However, since the stroke of the rubbing rollers has reversal points, there is always a small length of strand left without twist between each section of Z twist and the adjoining section of S twist. The plied thread will also have no twist in this zone (Fig. 14). Such a thread has no strength. It cannot be wound up or subjected to further processing.

In order to obtain adequate strength despite these twistfree zones, the two yarns cannot be allowed to run in parallel, but instead they must be passed through with a relative phase shift. Then S twist will be generated in the plied yarn wherever one yarn has Z twist (with zero twist in the second yarn) or where both yarns have Z twist. Similarly, the plied yarn will have Z twist wherever at least one yarn has S twist (with zero twist in the other yarn) or where both have S twist. If a yarn section with S twist is combined with a section with Z twist, which cannot be avoided, the torsion forces stabilize each other so that no plying twist results. The two-fold yarn obtained with this process therefore always consists of three successively arranged zones (Fig. 15):

  • folded yarn with S twist arising from two yarns with Z twist, with one of the yarns exhibiting a short twist-free length;
  • two yarn sections lying parallel to each other without plying, one yarn having S and the other Z twist;
  • folded yarn with Z twist, where the yarns have S twist, with one of the yarns again exhibiting a short twist-free length.

Instead of one large weak point (Fig. 14), three smaller weak points have been created. The two-fold yarn has adequate strength to permit winding up but not for further processing. For that purpose, it must be twisted again. However, since the two-fold yarn has alternating turns of twist, a folded yarn with continuously varying sections of different twist is obtained upon further plying (two-for-one twisting process), (Fig. 16).

Fig. 13 – Reciprocating friction of a fiber strand

Fig. 14 – Combining two fiber strands previously strengthened by friction

Fig. 15 – Combining two fiber strands with a phase shift

Fig. 16 – The twist structure in a Repco double thread