Strength reduction in and damage to fibres during high-speed sewing in an industrial lockstitch machine

The reduction in the tensile strength of polyester fibres on sewing is studied for threads with different yarn and fibre linear density and tenacity. The strength loss ranges between 4.8% and 8.9% and is much less than that of the sewn threads. The initial modulus of the fibre and the extent of loading during sewing influence the strength reduction. A scanning-electron-microscope (SEM) study of sewn threads and of the constituent fibres shows that the damage is mostly concentrated at the interlacing point of the needle thread in the stitch. Among the various stresses acting on the fibres, bending and surface abrasion are found to be more dominant in causing damage to the fibre.