Rieter

Yarn irregularity (CVm%)

Index

The positive influence of back-doubling in the rotor has already been described several times in this paper. The result of this, compared with other yarns, is the more uniform distribution of the fiber mass along the yarn, as expressed in the regularity of the weight per unit of length. The best possible regularity of a fiber bundle in the spinning process would be achieved if the fibers were distributed at random along the yarn. However, this ideal distribution cannot be achieved in practice, neither in ring-spun, rotor-spun nor in any other staple fiber yarn. Deficiencies in machine operation or the drafting system are the cause of more or less pronounced cross-section variations. The size of the crosssection variations is expressed in mean linear irregularity (U%) or – more correctly and customarily in terms of physical textile properties – in mean square irregularity (CVm%).

Only the rotor spinning system is able to offset this process- related deterioration in cross-section variations to some degree by back-doubling the fiber layers in the rotor. The mass uniformity of the rotor-spun yarn is therefore better than for  ring-spun yarn (given equal machine conditions).

According to Brunk/Trommer (see references), the irregularity limit (CVlim) of a rotor-spun yarn is some 75% of the irregularity limit of a comparable ring-spun yarn. The CVm% values that can actually be achieved with rotor-spun yarns are therefore usually better than with yarns from other spinning processes.