During the production process of sack bags, a common issue that can arise during stitching is thread breakage. How should this problem be addressed?
During the sewing process, the needle thread passes through the fabric, advancing upwards after reaching the lower limit position due to the friction between the fabric and thread, failing to move synchronously with the needle. Instead, it remains below the fabric, expanding to either side of the needle under elastic force, forming a loop. As the bobbin needle reaches the needle, it passes through the loop of the thread, continuously expanding the loop during its spinning motion. After wrapping around its own radius, it jumps over the expanded loop, and the subsequent action is for the take-up lever to gather the thread and the feed dog to feed the fabric. To ensure these actions have sufficient time for smooth, intermittent operation, the bobbin continues to spin at the original speed, but without catching any thread, simply completing a full rotation.
After the needle reaches the uppermost position, as it retracts to pierce the fabric again, the weaving bag sewing machine repeats this action, creating a regular, intermittent lockstitch pattern on the seam.