Thread breakage of single-needle lockstitch sewing machines can be divided into two categories according to working conditions:
The first type is the backward seam that is completely on the sewing material, the second type is the reverse seam that is not completely on the sewing material and may be empty.
We must firstly understand the main causes of thread breakage during forward stitches. There are many reasons for the broken thread in the forward seam. In summary, the needle used is the main reason. The quality of the suture is poor and the suture does not match the needle, including the presser foot, needle plate, rotary hook, rotary hook positioning hook, and feeder. There are sharp edges or grooves in all thread passing parts of the cloth thread, the quality of the hook positioning hook is not good (the geometric shape is not conducive to the thread take-up lever up), the quality of the hook is not good (some Can not guide the suture smoothly around the bobbin case of the bobbin holder, some hook thread tips are too blunt, and some have high friction resistance when rotating), the timing of the needle bar and the hook is not correct, the needle bar and the teeth are sent The timing of the cloth eccentricity is incorrect, the needle temperature is too high during sewing, etc. After solving the above problems, there is basically no problem with the normal seam.
As for reverse stitches that are not completely on the sewing material (ie, reverse stitches and empty stitches), in order to clarify it, the sewing principle of the single-needle lockstitch machine should be reviewed again. The long needle slot of the lockstitch machine faces the left side of the operator. When working, the machine feeds and retracts the sewing thread to the hook through the long needle slot, and the loop provided for the hook thread is on the right side of the needle Forming. There are two necessary conditions for forming an ideal thread loop at the same time. The first is that the needle rises from the bottom dead center, and the second is that there is enough friction between the suture on the right side of the needle and the sewing material to prevent the suture from moving upward. As it rises when lifting, that is, the suture depends on the sewing material tube bundle. Only when the sewing material tube bundle and the needle rise from the bottom dead center, can the suture form an ideal thread loop. At the same time, only in the case of the sewing material tube bundle will the suture complete its prescribed action; on the contrary, if the sewing material is separated from the tube bundle, the prescribed action of the suture may be irregular. The broken thread of the reverse seam that is not completely on the sewing material sometimes has a good effect by adopting a continuous operation method, that is, the two slip knots are very close, and the two slip knots jointly pipe the suture of the empty seam.
From the above discussion, it is known that the reverse seam completely on the sewing material, through the adjustment and maintenance of the machine, the use of high-quality needles, sutures and an appropriate reduction in speed can meet the requirements of the single needle lockstitch machine on the sewing material; The reverse stitching that is not completely on the sewing material (ie, reverse stitches) should adopt a continuous operation method, which can also meet the requirements of the lockstitch machine for reverse stitching on the sewing material, which can effectively avoid the thread breaks during reverse stitching.
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