Since the number of stitches and the principle of forming stitches on the sewing material, sewing machine stitches can be divided into lock stitches, chain stitches, overlock stitches, and covered chain stitches. Due to the limitation of the manufacturing process specifications of flexible container bags.
This passage introduces the double-thread lock stitch sewing machine. The basic feature of this stitch is that the upper thread passes around the bottom thread to form an interlacing, and then the bottom thread is tightened to hide the suture in the seam material layer. There are three ways to obtain lock stitches, namely shuttle, swing shuttle, and rotary shuttle. Here is the method of forming the lock stitch with the most widely used hook-type hook thread mechanism. From a dynamic point of view, the hook-hook mechanism does not have an inertial load that changes in speed. Therefore, under high-speed rotation, all the movements of double-thread lock stitch sewing machine are stable.
The process of forming the hook stitch by the hook thread mechanism can be summarized into three basic links about double-thread lock stitch sewing machine.
(1) Lead the upper thread through the sewing material to form the upper thread loop. In this step, the needle moves downward, pierces the sewing material, and passes the upper thread through the sewing material. When the movement reaches the lowest point, it starts to rise upward. Due to the resistance between the thread and the needle and the sewing material, the thread exit is blocked. As a result, the upper thread accumulates at the bottom of the pinhole of the machine, and gradually forms a loop, as shown in Figure. The purpose of forming the loop is to make the hook tip smoothly lead the bottom thread through.
(2) The upper thread passes around the bobbin case, forming an interweaving with the bottom thread. After the upper thread loop is formed, the hook tip of the hook case hooks the loop. During the movement, the loop loops the thread over the bobbin case that stores the bottom thread. At this time, the thread take-up lever is raised to lift the loop from the tip of the shuttle. Pull it out and take off the hook around the upper thread loop.
(3) Basic link three: Tighten the bottom and upper threads and hide the threads in the sewing material. After the upper thread loop and the lower thread form an intertwined knot, it continues to shrink and retracts in the sewing material. At the same time, the threading hole of the thread take-up lever is raised, and the upper thread is drawn from the threader to supplement the consumption of the upper thread.
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