Effect of Needle Thread Slipped out of Rotating Hook on TighteningTension of an Industrial Single-Needle Lockstitch Sewing Machine

Part 2. Drawing Out of Needle Thread from Tension Disk

Abstract

To find out the cause of decrease in tightening tension and increase in the variation of the tension whichoccurs frequently during the high-speed sewing operation on an industrial single-needle lockstitch sewingmachine, this paper aims, in succesion to the previous paper (1) to investigate experimentally the relation betweenthe length of needle thread drawn out of a tension disk when the needle thread disengages from rotatinghook and tightening tension, and to discuss about the elongation properties of sewing thread with respect tothe length of needle thread when the needle thread disengages from rotating hook.
For this purpose two measuring systems were developed. One is a system, which was improved system usedin the previous paper (1), to observe photographically needle thread behaviors when the needle thread isgoing to disengage from rotating hook and to measure the tension of the thread generated at the same time.
The other is a system to measure the length of needle thread tension.
The results obtained are as follows :
(1) It was confirmed experimentally that the needle thread was drawn out of a tension disc not only whenthe thread tightened a stitch but also when the thread was disengaged from rotating hook, and thatthe more the drawn length was long, the more tightening tension was decreased.
(2) It was supposed that disengagement behaviors of needle thread from rotating hook were decided bythe length of the needle thread, and that the length depends entirely on the elongation recovery propertyof the sewing thread.