THE EQUILIBRIUM OF THE CONVERGENCE POINT IN 2-STRAND YARN PLYING

In this paper the theory of the bending and twisting of thin rods of u niform circular cross-section is used to find the relationships betwee n the ply-helix angle, the strand convergence angle, and the applied t ensions and torques required to hold the plied strands illustrated in Fig. 1 in equilibrium. The solution of this problem is of importance t o the textile yarn manufacturing industry where singles yarns, made fr om long staple fibres, such as wool, are plied together in order to bi nd the surface fibres more effectively into the plied yarn structure. This produces warp yarns that are more abrasive resistant. A formula f or the relationship between the pre-twist in two initially straight st rands, and the helix angle of the plied structure obtained when they a re allowed to twist together into a balanced ply structure is also der ived in Section 4. A balanced two-ply structure is one that will maint ain its configuration without the application of external tension or t orque. Balanced ply structures are also important in textile manufactu ring processes. (C) 1997 Elsevier Science Ltd.