Rieter

Wrapper fibers

Index

The rotor, and hence the fiber ring, revolve continuously under the stationary fiber channel – as also does the spun yarn in the binding-in zone. A stream of individual fibers flows from the fiber channel and is deposited in the groove. Normally, incoming fibers land on fibers that have not yet been twisted in, but in the binding-in zone they strike an already-twisted yarn section rotating around its own axis. It cannot always be avoided that fibers arriving here wrap themselves around the yarn core (so-called wrapper fibers). This is a typical characteristic, and simultaneously an identifying feature of rotor-spun yarns. The number of wrapper fibers increases, among other things, the longer the binding- in zone, the shorter the fibers relative to the rotor circumference and the higher the rotor speed.

The wrapper fibers can be wound around the yarn in both the S and Z direction. Together with the lower twist in the outer fiber layers of rotor-spun yarn, this is the reason why the number of twists measured when determining yarn twist in the laboratory is usually lower than the required figure set on the machine.

Since rotor spinning technology was not fully developed when the process was introduced – due mainly to the high twist multiplyers that were still necessary at that time, with the result that the binding-in zones extended far into the rotor groove – rotor yarns were characterized by a large number of wrapper fibers. It is also from those days that the rating of rotor- spun yarns‘ hand as too „hard“ and thus unsuitable for a whole range of end products, especially in the knitwear sector, originates.

The continuous development of rotor profiles in particular and the design of the  draw-off nozzles, as well as optimized fiber and air guidance in the  spinning box zone, have enabled the number of wrapper fibers to be reduced to the extent that modern rotor-spun yarns differ significantly from those of the first generation. Twist multiplyers are now only insignificantly higher than those of ring-spun yarns, so that their hand in the final fabric is much closer to that of ringspun yarns than it was earlier. Knitting yarns now produced on rotor spinning machines have replaced ring-spun yarns to a considerable extent in certain end products, e.g. T-shirts.