What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
In the existing life, repair parts are often used to repair the cassettes with damaged screw holes, and the screw holes on the repair parts are used instead of the original damaged cassette screw holes. However, in the prior art (application number: 201520948368.3), the restoration is fixed by rotating the support of the restoration, which is often inconvenient due to the small space of the cassette. In addition, the set screw in the prior art mainly fastens the object through the end of the screw without threaded holes, which makes it difficult to install external screws. Based on this, a method of extruding the support through a set screw with screw installation holes and tightening the repair piece, and then installing the screw on the set screw, will facilitate the quick installation and use of the repair piece.
At present, most of the cylindrical pin press-fitting is to put the product into the positioning position of the lower die first, and then take a cylindrical pin and put it into a cylindrical pin positioning hole that is concentric and perpendicular to the hole in which the product is pressed, or put it on the product. , the pin needs to have a positioning guide; or it is fixed on the top of the indenter so that it will not fall, and then the press is completed. In fact, it is difficult to press the small cylindrical pins. To ensure the good quality of the product, it is required to locate accurately, to ensure that the cylindrical pins are concentric and vertical, and to put the cylindrical pins one by one. It is very easy for workers to produce. Fatigue and low efficiency, product quality control is affected by many human factors, resulting in unstable product quality and certain safety hazards in work. On the other hand, in some production lines, the cost of the press-in cylindrical pins is relatively expensive, such as finger cylinders and moving mechanisms, which will put a lot of cost pressure on the equipment investment of small and micro enterprises.
The drawing process has two purposes, one is to modify the size of the raw materials; the other is to obtain basic mechanical properties of the fasteners through deformation and strengthening. For medium carbon steel, medium carbon alloy steel also has another purpose, that is, to make the wire rod. The flaky cementite obtained after controlled cooling is cracked as much as possible during the drawing process to prepare for the subsequent spheroidization (softening) annealing to obtain granular cementite. However, some manufacturers arbitrarily reduce the drawing in order to reduce costs. The excessive reduction rate increases the work hardening tendency of the wire rod, which directly affects the cold heading performance of the wire rod. If the distribution of the reduction ratio of each pass is not appropriate, it will also cause torsional cracks in the wire rod during the drawing process. In addition, if the lubrication is not good during the drawing process, it can also cause regular transverse cracks in the cold drawn wire rod. The tangential direction of the wire rod and the wire drawing die is not concentric at the same time when the wire rod is rolled out of the die, which will cause the wear of the unilateral hole pattern of the wire drawing die to aggravate, make the inner hole out of round, and cause uneven drawing deformation in the circumferential direction of the wire. The roundness of the steel wire is out of tolerance, and the cross-sectional stress of the steel wire is not uniform during the cold heading process, which affects the cold heading pass rate. During the drawing process of the wire rod, the excessive surface reduction ratio will deteriorate the surface quality of the steel wire, while the too low surface reduction ratio is not conducive to the crushing of the flaky cementite, and it is difficult to obtain as much granular cementite as possible. , that is, the spheroidization rate of cementite is low, which is extremely unfavorable to the cold heading performance of the steel wire. For the bar and wire rod produced by the drawing method, the partial surface reduction rate is directly controlled within the range of 10%-15%.
In order to achieve this purpose, the rivet nut is cold extruded from low carbon steel, the brim is cold forged, the deformed skirt is extruded in the die, and the threaded hole is extruded at the lower end of the deformed skirt. It is characterized in that it consists of a brim, a deformed skirt and a threaded hole. There are fish teeth below the brim; the outer side of the lower end of the threaded hole has a lead angle; the cross section of the thread on the inner wall of the threaded hole is an isosceles trapezoid, and the upper bottom of the trapezoid is a concave arc. Thus, the riveted object is tightly connected with the rivet nut.
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