32—FACTORS AFFECTING THE STABLE DIMENSIONS OF DOUBLE-JERSEY STRUCTURES

Abstract

An account is given of a study in which the dimensional properties of five popular double-jersey structures, made from shrink-resist-treated worsted yarns and knitted under very different machine conditions at the optimum tightness factor (K = approximately 15), were investigated in various relaxed states, including the fully laundered condition, or the ‘completely relaxed’ stable state. In the initial experiment, the machine variables chosen—take-down tension, stretcher-board width, and dial height—were altered selectively to give the maximum distortion to the structural knitted cell (SKC) at the knitting stage. This experimental procedure was repeated in the second experiment at a variety of run-in ratios (but at the same average K value) for three structures: Punto-di-Roma and Swiss and French double piqué. Whereas the machine variables markedly influence the linear (i.e., length and width) dimensions of all structures off the machine, and noticeably after steam relaxation, linear dimensions after further relaxation and laundering, although affected by the processing history of the fabric, are close to being equal within a structure. Thus, machine variables only temporarily distort the SKC: after correct relaxation, this distortion is, for all practical purposes, lost. However, the variable run-in ratio does affect the stable linear dimensions, even at a constant fabric tightness, although the magnitude of the effect of the run-in ratio on linear dimensions depends entirely on the structure. Consequently, the stable linear dimensions of double-jersey structures appear to be determined by two parameters: the structural-cell stitch length (l u) and the run-in ratio. Speculations as to why the run-in ratio affects the stable linear dimensions are presented.