Imperfections (thin places, thick places, neps)


Rotor-spun yarns are also characterized, among other things, by the fact that the number of so-called yarn defects – stated as the number of thick places, thin places and neps per 1 000 m of yarn – also referred to in the literature as imperfections, is much lower than for comparable ringspun yarns. Imperfections can both be the cause of ends down in downstream processing and also make a disturbing appearance in the fabric. According to the latest Uster Statistics, the number of thick places and neps per 1 000 m of yarn are up to 60% and 80% lower in rotor-spun yarn than in  ring-spun yarn.

However, if the number of imperfections rises above the usual level, this can be attributable to both raw material and machine-related causes. For example, immature cottons are very inclined to produce neps during processing. However, thick places and neps also occur when spinning elements or other fiber-guiding machine components are worn or damaged. Bent, broken or notched clothing teeth on the opening roller in particular can cause steep increases in the numbers of neps and thick places. Wear or deposits in the fiber guide channel also result in fibers accumulating at these points and being fed uncontrolled to the rotor as larger or smaller clumps of fiber. Depending on their mass, these clumps result either in ends down or – if spun in – in defects in the yarn and the final fabric.