Heavy hex bolts are used for the connection of important machinery. Repeated disassembly or various installation torque methods require extremely high requirements for high-strength bolts. Therefore, the surface condition and thread accuracy will directly affect the service life and safety of the host. In order to improve the coefficient of friction and avoid corrosion, seizure or jamming during use, the technical requirements stipulate that the surface should be treated with nickel-phosphorus plating.

In high-strength bolt connections, the friction coefficient has a great influence on the bearing capacity. Tests show that the friction coefficient is mainly affected by the form of the contact surface and the material of the component. In order to increase the friction coefficient of the contact surface, methods such as sandblasting and wire brush cleaning are often used to treat the contact surface of the components within the connection range.

The heavy hex bolt is used to tighten the nut with a special wrench, so that the bolt generates a huge and controlled pretension. Through the nut and the backing plate, the same amount of pretension is generated on the connected parts. Under the action of preload, a relatively large friction force will be generated along the surface of the connected part. Obviously, as long as the axial force is less than this friction force, the component will not slip and the connection will not be damaged. This is a high-strength bolt connection The principle.

Therefore, if the bolts factory wants to produce high-quality high-strength fasteners, it must have advanced heat treatment technology and equipment. Because high-strength bolts are produced in large quantities, low in price, and the threaded part has a relatively fine and relatively precise structure, the heat treatment equipment must have a large production capacity, a high degree of automation, and a good heat treatment quality.