What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
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.
There are two grades of hexagonal nuts, one is grade 4.8, ordinary nuts, and the other is grade 8 nuts. For more industry knowledge about nuts, you can read the nut specification table and the national standard specification table of the nut industry. Knowledge of these nut specification sheets and industry standards. Allows us to have a deeper understanding of the nut.
In CN203807560, nails and bolts are used to connect the plates, but the heads of the nails and the bolts are enlarged ends that are wider than the rods, and the heads of the nails and the bolts cannot penetrate into the interior of the door body, so in terms of appearance, the more More nails and bolts will leave more spots on the surface of the door that are not suitable for the door itself. In the prior art, the treatment method for these spots is generally to paint with paint, which can only make the door panel consistent with the head of the nail and the bolt in color, but cannot change the shape of the head of the nail and the bolt, and the appearance is still good. Obvious spots were noticed, which made the door panels connected by nails and bolts to the panels, which could not be used as door panels for household doors.
The slotted nut needs to be fixed with a cotter pin through the slot of the slotted nut, and the cotter pin must pass through the middle of the screw to fix the slotted nut. Usually, both ends of the screw need to be drilled, the diameter of the hole and the size of the slotted nut. The width and depth of the slot determine the size of the cotter pin. When the selected screw, cotter pin and slotted nut are relatively matched, the nut is fixed by the screw, so that the slotted nut does not loosen. This hexagonal slotted nut has the characteristics of high strength and is not easy to loosen when subjected to vibration. It is mainly used in occasions with vibration and shock, such as front and rear axles of automobiles, lifting equipment, presses and die-casting machines.
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