What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
In the current plastic matrix, it is common to use self-tapping screws or add copper inserts during injection molding. The former has poor strength, and the threaded hole is easy to crack; the processing cost is high, the injection molding efficiency is low, the labor cost and manufacturing cost are increased, and the insert is easy to slip and crack on the plastic, and the thread strength of the copper insert is not as high as that of the iron nut.
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%.
Blind rivets are a type of rivets for single-sided riveting, but they must be riveted with a special tool - a rivet gun (manual, electric, and moving). This type of rivet is especially suitable for riveting occasions where it is inconvenient to use ordinary rivets (which must be riveted from both sides), so it is widely used in construction, automobiles, ships, aircraft, machinery, electrical appliances, furniture and other products. Among them, the open type oblate head blind rivets are the most widely used, the countersunk head blind rivets are suitable for riveting occasions that require smooth performance, and the closed blind rivets are suitable for riveting occasions that require higher load and certain sealing performance.
The use of the screw is mostly used in plastic molding equipment, such as plastic profile extruders, injection molding machines, etc. Screw and barrel are the core components of plastic molding equipment. It is the part of heating extrusion plasticizing. It is the core of plastic machinery. Screws are widely used in machining centers, CNC machines, CNC lathes, injection molding machines, wire cutting machines, grinding machines, milling machines, slow wire walking, fast wire walking, PCB drilling machines, engraving machines, engraving and milling machines, spark discharge machines, tooth bite machines , planer, large vertical lathe gantry milling, etc.
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