Rieter

Denim fabrics

Index

Another range of application dominated by rotor-spun yarns are denim fabrics, usually in 3/1 or 2/1 twill weave. Rotor spun yarns are used both in the warp and in the weft. Depending on fashion trends, the rotor-spun yarn content can be up to 70% of the total yarn volume, although the proportion of ring-spun yarns can increase to meet fashion requirements. The incredible variety of denim fabrics, differing in terms of raw material, color, final treatment, fabric weight and a host of other parameters, can be divided into two main groups. On the one hand there is the so-called „authentic look“, where „irregular“ and rustic yarn characteristics are called for primarily in the warp yarn.  Ring-spun yarns are outstandingly suitable for this type of fabric and also contribute to the soft hand of the finished product. Rotor-spun yarns are too regular for this type of fabric. Special spinning elements or fancy yarn devices have to be used in order to reproduce the more irregular character of ring-spun yarns and simulate this type of yarn (refer to section  Components for manufacturing fancy yarns). The second main group consists of yarns that have to be very regular in order to produce a clearly defined fabric structure in warp and weft. Denim yarns are clearly dominant in this type of fabric due to their outstanding regularity and the significantly lower level of imperfections. Ring-spun yarns have virtually disappeared from this application.

Rotor-spun yarns are used in both warp and weft as well as in combination with ring-spun yarns – in this case mostly as weft yarns. The demands imposed on warp and weft yarns are very different. Weft yarns are usually coarser than the warp yarns (Ne 5 - 7), have medium hairiness and are spun with medium to high twist multiplyers in order to withstand the high loads of the weft insertion systems on modern high-performance automatic weaving machines. For the finer warp yarns (Ne 8 - 12), which are always dyed, there are two dyeing methods, with which the yarn characteristics must be coordinated. Beam-dyed yarns (the ends are guided through the dye bath parallel with each other) display low to medium hairiness and are spun with medium twist multiplyers in order to prevent an excessively high tendency to snarl in the yarns. By contrast, rope-dyed yarns may only display a very low tendency to snarl in order not to obstruct the opening of the dyed rope and rebeaming. Yarns for this application must therefore display high hairiness (hairs act as spacers between the ends) and be spun with the lowest possible twist multiplyers (yarn tenacity must not fall below a certain minimum in the process).