25—THE FORM OF YARN TWISTING PART I: IDEAL CYLINDRICAL AND RIBBON-TWISTED FORMS

Abstract

Yarns may twist either as cylindrical bundles of fibres or as flattened ribbons: the former mode has been the basis of most scientific studies. The present paper describes the behaviour of a rubber strip as a model of a yarn ribbon. On twisting the strip, the twisted form that appears initially Is subsequently replaced by a wrapped-ribbon form. The energy relations causing this are discussed, and the theoretical prediction is compared with experimental results. The geometry of the wrapped-ribbon form is analysed, and its consequences oti the expected form of yarns are considered. A wrapped-ribbon yarn may degenerate by collapse into a cylinder, but the relics of the ribbon-twisting are apparent in asymmetry and in a redistribution of the fibres in the yarn.