# Rieter

### Count-related yarn tenacity (cN/tex)

#### Index

The less pronounced – less frictional – parallelization of fibers in the yarn surface compared to ring-spun yarn is also the reason for its lower count-related yarn tenacity (cN/tex). In particular the optimization of rotor grooves (e.g. tighter groove radii) and draw-off nozzles (e.g. smaller contact surfaces, smaller surface radii), as well as optimized fiber guidance in the spinning box, have enabled the strength of rotor-spun yarns to be improved continuously and the gap relative to ring-spun yarns to be narrowed. However, differences still exist. On the other hand, the coefficient of variation in yarn tenacity (CV% cN/tex), i.e. the variation in tenacity along the yarn, is better in rotorspun yarn, i.e. lower than in ring-spun yarn. This is due to the smaller range of short-wave mass variations in rotor-spun yarn, and results from back-doubling in the rotor.

The potential tenacity of a yarn can best be described by the substance utilization of the fiber tenacity, i.e. what percentage of the fiber tenacity can be transferred to the yarn tenacity. The substance utilization of the fibers in ring-spun yarn is between approx. 50 and 65%*, that for rotor-spun yarns between 45 and 55%*. The count-related tenacity (cN/tex) of rotor-spun yarn is therefore usually 10% - 20% lower than that of ring-spun yarn (see Uster Statistics).

$cN/tex\ yarn = \frac {cN/tex\ fiber \times substance\ utilization \%}{100}$

For example, if a medium-grade cotton with a count-related fiber tenacity of 24 cN/tex is processed, the following values result for the count-related yarn tenacity (cN/tex) of rotor- spun and ring-spun yarns:

rotor-spun yarn = 24 cN/tex fiber x 45 (%) / 100 or
24 cN/tex fiber x 55 (%) / 100
= 10.8 - 13.2 (cN/tex)

ring-spun yarn = 24 cN/tex fiber x 50 (%) / 100 or
24 cN/tex fiber x 65 (%) / 100
= 12.0 - 15.6 (cN/tex)

* The absolute value for substance utilization depends essentially on the twist multiplyer selected (αm/αe), for both rotor-spun and ring-spun yarn. If substance utilization is below the stated range, setting-related causes usually have an adverse impact on yarn tenacity, e.g. fiber damage due to excessive take-off roller speed or inadequate fiber integration due soiled rotor grooves.