Rieter

Unevenness over different lengths

Index

A length of yarn, for example of 10 mm, contains only few fibers. Every irregular arrangement of only some of these fibers has a strong influence on the unevenness. In a length of yarn of 10 m, incorrect arrangement of the same fibers would hardly be noticed against the background of the large number of such fibers in the total length. Accordingly, the CV value of the same yarn can be, for example, 14% based on 8 mm length, and only 2% based on 100 m length. The degree of irregularity is dependent upon the reference length. Unevenness is therefore discussed in terms of short lengths (Uster Tester); medium lengths (seldom used); long lengths (count variation). If the coefficients of variation are arranged in a co-ordinate system in accordance with their reference lengths, then the well-known length-variation curve is obtained (shown here in simplified form in Fig. 38). If continual variations of mass over short lengths are involved, then an uneven appearance of the product will result. Mass variations over medium (to long) lengths lead to stripiness in the product, and variations over long lengths lead to bars in knitted and woven fabrics.

Fig. 38 – Length variation curve (CVL%)