The mechanism by which the needle guides the thread through the sewing material is called the needle bar mechanism. The task of the needle bar mechanism is to drive the needle and guide the thread through the fabric to form a thread loop in preparation for the interweaving of the threads.
The role of the needle bar mechanism is ultimately realized by the needle. In order to sew the material together when the sewing machine is in operation, the needle has to make a piercing movement. The movement of the needle to pierce the material is vertical, horizontal, straight or curved. Sewing machine for different purposes, the type of needle bar mechanism is not the same, most of the sewing machine is for vertical reciprocating linear movement, and some specialized machines, such as lockstitch machines, buttonholing machines, embroidery machines, etc. not only to vertical reciprocating linear movement, but also to make the lateral swing, but this lateral swing time must occur in the machine needle to leave the material after the beginning of the end of the material before the end of the needle into the sewing material.
The height positioning of the needle bar is an important parameter in the use and maintenance of sewing equipment. The height of double or multiple straight needles is not the same, and the height positioning is generally based on the long needle.
The distance between the upper and lower dead center of the needle bar movement is called the needle bar stroke. Needle bar stroke is an important parameter of sewing equipment. Needle bar stroke and the effective working stroke of the needle are two different things. The effective needle stroke is the distance from the instant of stabbing the cloth until the needle reaches its lowest point.
To try to achieve the choice of straight needle and the thickness of the material, thread thickness, sewing product quality of the process of unity, so that the straight needle in the puncture of the sewing material to ensure that the sewing material and sewing thread is not damaged, and is conducive to the formation of the thread ring.
1.1 Needle feed
The process of piercing the sewing material with the needle is called needle feed. The needle is one of the key parts of the sewing machine through which the various actions of the needle bar mechanism and its mechanism are realized. When feeding the needle, the needle has to overcome the friction from the positive resistance of the sewing material and the side of the sewing material, and the tension reaches its highest point due to the change in the interaction force between the thread, the needle and the sewing material.
Reducing the friction between the needle and the material can be achieved by precision manufacturing of the needle (especially the needle tip), coating the needle and softening the material, or adding silicone oil to the needle and thread.
Factors affecting the smoothness of the needle feed in addition to the friction between the needle and the sewing material, as well as the pressure of the presser foot pressure and the size of the hole in the needle plate and so on. If the needle is improperly selected, or poorly manufactured, or the hole in the needle plate is too large, it will form a hole in the sewing material, causing damage to the sewing material, which affects the aesthetics and makes the firmness of the bottom. Therefore, in the case of meeting the sewing strength needs, should try to use a smaller diameter needle, special sewing materials should choose a special needle, in order to reduce friction, to achieve good sewing results.
1.2 Thread insertion
The process by which the needle brings the thread to the opposite side of the fabric is called thread insertion. The thread insertion phase starts when the needle is lowered to the point where the needle eye comes into contact with the sewing material, and ends when the desired stitch length is formed (needle bar is in the lower dead center position).
The thread entry length is not equal to the stitch length required to form the stitch. It is an important parameter to satisfy the need to form a thread loop that can be accurately entered by the bobbin point and hook of the sewing machine to prevent thread breakage and skipped stitches. The amount of thread introduced into the overlock sewing machine and the actual amount of thread used is about 6 times, so each section of thread has to repeatedly puncture the sewing material many times, and the increase in the number of friction times affects the strength of the sewing thread, which is prone to cause the occurrence of thread breakage.
In the process of entering the thread, due to the twisting direction of the thread and the different orientation of the thread will cause the loose twist or twisting of the thread, and the size of the angle of the thread is an important factor affecting the change of the force of the thread, so the angle of the thread should be reduced as much as possible. Changes in the interaction forces of the thread, material and needle depend mainly on changes in the characteristics and thickness of the thread and material, so the quality of the thread and the correct selection of the needle are very important.
1.3 Loop formation
The needle passes through the fabric with the topstitching thread, reaches the lowest point and rises again, forming a thread loop due to the friction between the fabric and the needle. The purpose of forming the loop is to enable the seam ripper (hook) to enter the loop and to interweave the bottom thread. The thread loop is formed by the following 2 factors.
(1) When the needle reaches the bottom dead center with the topstitching thread, the tension of the thread is maximum due to the downward pull of the needle eye and the extrusion of the needle blade and the sewing material at the introduction groove. When the needle rises, the tension at the top of the needle eye disappears, and a part of the thread is in a free state (at this point, just add a very small force to the thread to make the thread change shape). As the needle rises the thread itself has a certain resilience, coupled with the bottom of the eye of the needle on the thread generated by the torque, which is the formation of one of the conditions of the thread loop.
(2) From the structure of the needle, the needle groove has a long groove and a short groove (or lack of gear), it is a long groove on one side, while the other side is a short groove (or lack of gear). The lead-in groove is a long groove with a diameter larger than the diameter of the thread, and the lead-out groove is a short groove (or notch) structure with a diameter smaller than the thread. When the needle out of the sewing material, the introduction of the slot aside the thread and the sewing material does not friction random needle rise, while the introduction of the slot aside the thread and the sewing material squeeze each other friction occurs, can not rise with the needle to stay under the sewing material. This friction is obviously the short side of the groove (gap) is greater than the long side of the groove, which is the formation of another condition of the thread ring.
Three threads overlock sewing machine empty sewing, the formation of the thread loop is mainly by bending the needle thread fastening straight needle, so that the thread is embedded in the needle groove, played a similar role in the sewing material, so in the case of no sewing material can still form a seam, which is different from other machines.
The size and stability of the thread loop is crucial to the reliable entry of the seam-former for the interweaving of the bottom thread and the formation of the seam. In order to ensure that the sewing thread loop can be smoothly entered by the sewing machine tip, there should be two conditions: firstly, the sewing thread loop has a certain width, and secondly, the sewing thread loop must be perpendicular to the plane of the sewing machine tip's trajectory when it enters the loop.
The formation of the thread ring and the needle rise size and different, the needle should not be too large or too small, the amount of rise is too small thread ring width is not enough, is not conducive to the entry of the sewing machine. The needle rise is too large, although it is favorable for the sewing machine to enter, but due to the formation of the thread ring for a long time resulting in the deflection of the thread ring, so that the sewing machine is not easy to enter. Tests have shown that the ideal stage of thread loop formation for sewing materials of normal thickness and density should be about 2 to 3 mm when the needle rises.
Needle plate hole diameter 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 of the sewing material will cause the sewing material to sag, the possible formation of needle holes, and when the needle back up when the sagging sewing material will be random needle together with the movement of the normal formation of the thread ring. In general, the diameter of the needle plate hole is about 1.5 to 2 times the diameter of the machine needle is appropriate, but also to ensure that the machine needle in the center of the needle plate hole.
The formation and stability of the thread loop and the specifications of the needle, quality, nature of the material, texture, density, thickness, thread specifications, raw material type, twist, twist direction, and the needle and needle plate, presser foot pressure, press cloth state and other factors.
The role of the needle bar mechanism is ultimately realized by the needle. In order to sew the material together when the sewing machine is in operation, the needle has to make a piercing movement. The movement of the needle to pierce the material is vertical, horizontal, straight or curved. Sewing machine for different purposes, the type of needle bar mechanism is not the same, most of the sewing machine is for vertical reciprocating linear movement, and some specialized machines, such as lockstitch machines, buttonholing machines, embroidery machines, etc. not only to vertical reciprocating linear movement, but also to make the lateral swing, but this lateral swing time must occur in the machine needle to leave the material after the beginning of the end of the material before the end of the needle into the sewing material.
The height positioning of the needle bar is an important parameter in the use and maintenance of sewing equipment. The height of double or multiple straight needles is not the same, and the height positioning is generally based on the long needle.