First of all and quite crucially – and a significant point in favor of the economics of rotor spinning – a rewinding process can be dispensed with entirely for rotor-spun yarn. In contrast to the initial generations of machines, the rotor spinning machine delivers cylindrical or conical packages ready for sale, which can immediately be processed further. Modern quality monitoring systems enable yarn defects, extraneous matter or deviations from quality parameters to be detected and eliminated directly at the spinning position. Yarns for knitting are waxed directly at the spinning position and supplied in different package formats (cylindrical, 2°, 3°51 and 4°20). Dyeing packages with appropriately reduced package density also at the outer edges permit direct processing in high-pressure dyeing equipment (refer to section Winding helix and delivery speed).
Every rewinding process with guides, yarn tensioners, etc. on the winder results in neppy fiber shifting, however small, in ring-spun yarn. Since this can contribute to a more unsettled fabric appearance, dispensing with subsequent rewinding is certainly also a qualitative advantage for rotor-spun yarn.
The running properties of rotor-spun yarns in downstream processing are usually better than comparable conventional ring-spun yarns. The number of yarn-induced ends down in weaving preparation (beamer, sizing machine) are as much as 75% lower than with ring-spun yarns. The reasons for this are the greater regularity of rotor-spun yarns, the smaller number of imperfections and their lower hairiness, as well as the significantly longer lengths of knot-free yarn. Not only the much smaller number of yarn joins, but also the quality of the piecings precisely produced by the operating robots on the rotor spinning machine make a major contribution to the good processability of rotor-spun yarns. Piecings in rotor-spun yarns are virtually identical to the original yarn in appearance but display about 90% of its tenacity. Piecings produced by operating robots are the cause of stoppages in downstream processing only in exceptional cases. Added to this are the advantages of package weights of up to 6 kg, which enable up to 4 warp beams to be produced from one full warping creel, for example.
Fiber fly on and between the operating units of weaving and knitting machines is frequently the cause of ends down in downstream processing and of defects in the fabric structure (if accumulated fiber fly has not already caused an end down). A typical defect on circular knitting machines are holes in the fabric caused by fiber fly. The fiber fly carried along by the yarn prevents the formation of the loop on the needle. Rotor-spun yarns produce much less fiber fly and thus have a very favorable influence on running properties in downstream processing. Yarn-induced ends down are up to 50% lower in weaving and up to 40% lower in circular knitting than for comparable ring-spun yarns.
The conical package formats required for circular knitting machines with overhead creels are supplied by rotor spinning machines with package tapers of 2° to 4°20’. Wider tapers are now only required for older knitting machines with overhead creels and no yarn storage devices (although they are not always absolutely necessary!), and are not produced on rotor spinning machines. However, these circular knitting machines are steadily disappearing from the market.
On the other hand, increasing numbers of circular knitting machines with lateral creels are coming into use, with the economic advantage that cylindrical packages up to 340 mm in diameter weighing some 5 kg can be accommodated on these creels instead of conical packages. The running time of these packages is almost twice that of conical packages with a maximum diameter of approx. 270 - 280 mm and a maximum package weight of approx. 2.5 to 3 kg. Not only is operator effort in creeling and joining the packages reduced by up to 40%, the number of knots joining two packages is reduced proportionally on the same scale, and thus also the number of knots in the knitted fabric.
Table 18 rates the properties of rotor-spun yarn compared to ring-spun yarn in downstream processing, with the rating (lower, higher, etc.) relating to rotor-spun yarn.