INFLUENCES OF THE SEWING CONDITIONS OF THE LOCK-STITCH SEWING MACHINE FOR INDUSTRIAL USE ON THE NEEDLE THREAD TENSION

Abstract

The influences of the setting conditions, i. e. sewing machine speed, drawing tension of bobbin thread and stitch length, of the lock-stitch sewing machine for industrial use on the needle thread tension have been investigated under the standard sewing condition of seam balance about 100 percent.Needle thread tension have been measured by the home made stress detector put on between the frame thread guide and the needle bar thread guide of the sewing machine, and stress was changed to the electric signal, amplified by the strain amplifier and recorded by the electro-magnetic oscirograph. It was found the following matters. The needle tension varied remarkably and some tension peaks occurred during one revolution of sewing machine motion. They were distinguished four, the first was peak groups (named “peak A”), the second was the tension passed through the contact point between the rotating hook bobbin case holder and the rotating hook bobbin case holder position bracket (peak B), the third was the tension when the thread was drawn up the thread take-up lever (peak C) and the fourth was peak D. Peak B did not appear at slow speed sewing, but the tension increased as the sewing speed increased and was often larger than peak C at high speed. Peak B appeared in the region of 25-35 degrees of turning angle of arm shaft, and the value of the turning angle of the arm shaft had a tendency to increase with machine speed increasing. As bobbin thread tension increased, peak C increased linearly and peak B decreased. As the stitch length increased, peak C increased, but its increasing ratio was not proportional to increase of the stitch length.