Single needle lockstitch sewing machine backstitch broken thread faults is a common phenomenon, which can be divided into two categories according to working conditions. One is the reverse seam that is completely on the workpiece, and the other is backstitch that is not completely on the workpiece with the possibility of an empty seam.
In studying backstitch thread breakage, it is necessary to first understand the main causes of positive seam breakage, which is the basis of backstitching. The causes of thread breakage are manifold, summarized as follows: the use of needles, thread quality is poor; thread and needle mismatch; including the presser foot, needle plate, rotating shuttle, bobbin positioning hook, feed step teeth, including all the parts of the thread over the sharp edges of the burr or the groove by the thread strains; the bobbin positioning hook quality is poor (geometric shape is not conducive to picking up the rod up to the collection of the line); the shuttle quality is poor (some of them cannot guide the needle and thread smoothly around the bobbin bowl bobbin cover, the bobbin bowl, the bobbin cover, the bobbin cover, the needle and thread cannot be guided by the needle and thread, the bobbin cover, the bobbin cover, the bobbin cover is not suitable for the needle and thread. Shuttle bowl bobbin cover, some hook tip fat too rounded, some rotation is not slippery friction resistance); Needle bar and rotating shuttle with the incorrect timing; Needle bar and lifting the teeth to feed the cloth eccentric with the incorrect timing; sewing time needle temperature is too high. These problems are solved after the general sewing basically no problem.
- The biggest difference between backstitch and straight stitch is that the stitch is different. Front seam stitch is a standard lock stitch, like twisting a rope as the upper and lower threads together. The backstitch stitch does not know its official name, and then here tentatively called the fastening stitch, because when backstitching the upper line around the lower line to tie their own deadbolt, like tying a shoelace tied the first dead knot. Obviously, a fastening thread is more demanding, requiring a thread with higher strength, more uniformity, and smoother, softer characteristics.
- The second major difference between backstitch and straight stitch is that the timing of the needle bar and the feed eccentric of the lifting teeth is different. When backward sewing, because in the instantaneous time of pressing down and lifting up the backward sewing wrench, it is possible to catch up with the needle stabbing the cloth, if at this time the cloth feeding teeth are still exposed on the surface of the needle plate, the needle will be with the sewing material instantly swinging which is one of the causes of the backward sewing needle breakage and thread breakage. In order to avoid this situation, it is necessary to adjust the cloth feeding eccentricity of the lifting teeth according to the requirements of the backstitch, so that the needle does not swing instantaneously with the sewing material in the moment of pressing down and lifting up the backstitch wrench. This adjustment avoids the problem of the needle swinging instantly, but it causes another problem, which is that the needle loves to come out of its sockets.
- The third major difference between the backstitch and the straight stitch is that it requires less friction resistance and smoother operation of the bobbin, so that the thread picking lever can overcome the friction resistance of the bobbin operation with minimum force when tightening the upper thread. Only in this way can the pressure on the thread presser be minimized without the sleeve coming out. Because here the frictional resistance is the bobbin bowl (or bobbin frame, bobbin gallon) close to the bobbin positioning hook of the force, the greater the force requires the presser plate on the pressure spring the tighter, the greater the chance of thread breakage.
- The fourth major difference between the backstitch and the straight stitch is that the friction between the sewing thread and the needle is not in the same position, especially below the needle hole. Friction in both directions requires the needle to be smooth in all directions, with no burrs allowed.