What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
At present, there are many kinds of smart terminals on the market. Due to the reduction of the overall volume of the smart terminal and the more compact internal parts, the nuts are generally made of injection-molded nuts. The traditional injection-molded nuts are directly fixed on the equipment. During the process, it is easy to loosen and fall off, which greatly reduces the service life of the injection nut and brings inconvenience to the use of the mobile terminal.
When the countersunk head screws and hexagon socket head bolts are produced by the cold heading process, the original structure of the steel will directly affect the forming ability of the cold heading process. In the process of cold heading, the plastic deformation of the local area can reach 60%-80%, so the steel must have good plasticity. When the chemical composition of the steel is constant, the metallographic structure is the key factor to determine the plasticity. It is generally believed that the coarse flaky pearlite is not conducive to cold heading forming, while the fine spherical pearlite can significantly improve the plastic deformation ability of the steel. For medium carbon steel and medium carbon alloy steel with a large amount of high-strength bolts, spheroidizing (softening) annealing is performed before cold heading, so as to obtain uniform and fine spheroidized pearlite to better meet the actual production needs. For the softening annealing of medium carbon steel wire rods, the heating temperature should be kept above and below the critical point of the steel, and the heating temperature should not be too high, otherwise tertiary cementite will precipitate along the grain boundary, resulting in cold heading cracking. The wire rod of medium carbon alloy steel is annealed by isothermal spheroidization. After heating at AC1+ (20-30%), the furnace is cooled to slightly lower than Ar1, the temperature is about 700 degrees Celsius for an isothermal period, and then the furnace is cooled to about 500 degrees Celsius and air-cooled. The metallographic structure of the steel changes from coarse to fine, from flake to spherical, and the cracking rate of cold heading will be greatly reduced. The general area of softening annealing temperature for 35\45\ML35\SWRCH35K steel is 715-735 degrees Celsius; while the general heating temperature for spheroidizing annealing of SCM435\40Cr\SCR435 steel is 740-770 degrees Celsius, and the isothermal temperature is 680-700 degrees Celsius.
Currently, a screw generally includes a shank body, a threaded portion formed on the outer edge of the shank body, and a conical head formed at the rear end of the shank body. When the current thread is in use, since the thread part is cylindrical, the thread part and the workpiece are vertical, so it is relatively laborious when in use, and it is difficult to locate, lock and unlock.
By adopting the above technical solution, the setting of the pin cap allows the user to conveniently drive the pin into the pin hole of the workpiece by using a hammer and other power-assisted equipment. Pin hole, the plane of the top contact body relative to the pin cap will collide with the plane where the pin hole is located, the convex body and the pin hole are tightly squeezed, and the pin cannot fall off.
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