to help thread breakage and skipped aches. The quantum of thread introduced and the factual quantum of thread used in the overlock machine is about 6 times, so each section of thread has to constantly perforate the sewing material numerous times, and the increase in the number of disunion times affects the strength of the sewing thread, which can fluently lead to the miracle of thread breakage.

The needle carries the thread through the sewing material to its smallest point and also rises again, forming a thread circle due to the disunion between the sewing material and the needle. The purpose of forming the thread circle is to enable the confluence ripper( hook) to enter the circle easily and to interweave the bottom thread. The thread circle is formed by the following 2 factors.

1) When the needle reaches the bottom dead center with the topstitching thread, the pressure of the thread is maximum due to the downcast pull of the needle eye and the extrusion of the needle blade and the material at the preface groove. When the needle rises, the pressure at the top of the needle eye disappears and a part of the thread is in a free state( at this point it's only necessary to add a veritably small force to the thread to make it change shape). As the needle rises, the thread itself has a certain adaptability, coupled with the bottom of the eye of the needle on the thread generated by the necklace, which is one of the conditions for the conformation of the thread circle.

2) From the structural point of view of the needle, the needle groove is divided into a long groove and a short groove( or notch), with one side of it being a long groove and the other side being a short groove( or notch). The lead- in groove is a long groove with a periphery larger than the periphery of the thread, and the lead- eschewal groove is a short groove( or notch) structure with a periphery lower than the thread. When the needle out of the sewing material, the preface of the niche away the thread and the sewing material doesn't disunion arbitrary needle rise, while the preface of the niche away the thread and the sewing material squeeze each other disunion occurs, can't rise together with the needle to stay under the sewing material. This disunion is obviously the short side of the groove( gap) is lesser than the long side of the groove, which is the conformation of another condition of the thread circle.

The size and stability of the thread circle is the key to the dependable entry of the confluence-former, the interweaving of the bottom thread and the conformation of the sewing. In order to insure that the sewing thread circle can be easily entered by the sewing machine tip, two conditions should be met originally, the sewing thread circle has a certain range, and secondly, the sewing thread circle must be vertical to the aeroplane of the

The conformation of the thread ring with the needle rise size and different, the needle shouldn't be too large or too small, the quantum of rise is too small thread ring range isn't enough, isn't conducive to the entry of the sewing machine. The needle rise is too large, although it's favorable for the sewing machine to enter, but due to the conformation of the thread ring for a long time caused by the deviation of the thread ring, so that the sewing machine isn't easy to enter. Tests have shown that the ideal stage for the conformation of the thread circle for sewing accoutrements of normal consistence and viscosity should be about 2 to 3 mm when the needle rises.

The needle plate hole periphery is too large or too small will also have a negative impact on the needle, if the needle plate hole is too large, when the needle into the sewing material when the impact will make the sewing material to slack, may form a needle hole, and when the needle back over when the sagging sewing material will be arbitrary needle together with the movement, affecting the normal conformation of the thread ring. In general, the periphery of the needle plate hole is about 1.5 to 2 times the periphery of the needle is applicable, but also to insure that the needle in the center of the needle plate hole.

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