Broken wire is the most common fault encountered in sewing. The quality of the thread is not satisfactory. The machine is not properly adjusted. The threaded parts have sharp mouth, the operation method is problematic, the needle cooling is insufficient, etc., which will lead to wire breakage. When a product with uneven thickness is sewn with a lock stitch sewing machine, in addition to the above-mentioned various reasons, it is also necessary to pay attention to the disconnection caused by the two hook lines.

It is well known in the sewing machine industry that the transmission ratio of the upper shaft of the lock stitch sewing machine to the hook is 1:2 due to the design of the distribution of the action cycle. That is, the upper shaft rotates one revolution, and the rotary shaft rotates for two weeks. Therefore, during the sewing process, the needle rotates for one rotation for each rotation of the needle for two weeks, and the hook-expanding loop is completed in one week, and the needle is idling for one week. If the hook hooks the upper thread every week, the needle is punctured once, and the needle is rotated. If the hook line is twice, it will conflict with the retraction of the upper thread, which will cause the suture to be broken. This situation is likely to occur when sewing thick and uneven sewing materials: the reason for this is from the formation of the lock stitch:

1. Brief description of the formation process of the lock stitch The lock stitch is formed by interlacing the upper thread and the lower thread in the sewing material.

When the sewing machine is working, the needle thread of the needle passes through the sewing material, and after reaching the lower limit position, it is lifted upwards: due to the friction between the sewing material and the suture, the upper thread fails to be synchronously lifted, but stays Under the sewing material, both sides of the needle are swelled under the action of elasticity to form a ring shape.

Then, the tip of the hook reaches the needle during the movement, passes through the upper loop, and in the continuous rotation movement, the hooked loop is continuously enlarged. After winding around its own radius, it jumps over the enlarged loop like a skipping rope.

The next action is to take the thread take-up line, feed the cloth feed so that these actions have enough time to go smoothly, the hook still rotates at the original speed for one week, but no longer hooks the line, just idling one turn. Due to the take-up action of the thread take-up rod, the upper thread loop which was originally expanded and "jumped" by the hook is rapidly reduced until the bottom thread drawn from the bobbin bobbin is pulled into the sewing material to form an interlace.

After the needle reaches the upper limit position, when the lower lead is stabbed again, the sewing machine repeats the above-mentioned action process, thereby forming a continuous and regular lock stitch on the sewing material.