Impact of Positive Thread Feeding for High-Speed Industrial Lockstitch Sewing Machines: Part I Development of Device

Abstract

During high-speed industrial lockstitch sewing, repeated stresses and strains on the needle thread adversely influence its sewing performance. The sewing performance of threads is affected by reduction in its tensile strength. For maximum strength retention of needle thread, a positive thread feeding device is developed, which is independent of the fabric feed mechanism as in conventional sewing, where sewing thread is pulled from the cone directly wherein the thread feed is controlled by spring disc tensioner and needle movement. The dynamic needle thread tension is measured above the needle bar using strain gauge load cell. The load cell converts force or weight into electrical signal. The highest thread tension (stitch tightening tension) occurs when the take-up lever pulls the required thread amount through the spring disc tensioner. Positive thread feeding of needle thread lowers the tightening tension (peak tension), and hence, strength retention of needle thread is observed. In this paper, the breaking force of mercerized cotton needle thread at various sewing variables, viz. fabric density, number of fabric layers, and stitch length, is studied during conventional sewing and also by using positive thread feeding device. The loss in breaking force increases with the increase in fabric density, whereas it decreases as the number of fabric layers and stitch length increased.