Issues in processing unstable twisted fibre assemblies

Abstract

During yarn formation by ring spinning, fibres are bent into approximately helical shapes and an unbalanced torque or twist-liveliness is created. Generally, the torque depends on yarn geometric factors such as the yarn twist and linear density and the fibre properties. In order to prevent the instability of yarn (e.g., snarling), twist-liveliness must be controlled. A practical solution to the problem of twist-liveliness is the formation of a two-fold yarn. This twisting or plying process produces a yarn structure where the energy of the system is determined by purely geometrical constraints of the plied structure and consequently when an energy minimum is reached the plied yarn obtained from the process is torsionally balanced and torque-free. In the present paper, the instability of twisted textile yarns will be interpreted using the Topological Conservation Law (Fuller, 1971) which has been developed to study the dynamics of twisted rods by Van der Heijden et al. (2003). The present work considers the equilibrium configuration of a series of multi-ply twisted yarns (2, 4, 8, and 16 strands) of finite length. The influence of structural properties (the number of strands, the diameter and twist of each strand) on the parameters of a balanced multi-ply yarn (writhe and twist) using a topological invariant of the twisted yarn (link) is established and investigated using experimental results obtained at CSIRO.