When to use high-strength bolts

for high strengthboltIn the pair, the strength grade (after heat treatment) is grade 10, and it is used with grade 10.9 bolts.

The mechanical properties and calculation methods of ordinary bolts and high-strength bolts are different. The stress of high-strength bolts is firstly by applying a pre-tension force P inside, and then generating frictional resistance on the contact surface between the connected parts to bear the external load, while ordinary bolts directly bear the external load.

High-strength bolt connection has the advantages of simple construction, good mechanical performance, disassembly and replacement, fatigue resistance, and no loosening under dynamic load. It is a promising connection method.

High-strength bolts use a special wrench to tighten the nut, so that the bolt generates a huge and controlled pre-tension. Under the action of pre-pressure, a large frictional force will be generated along the surface of the connected parts. Obviously, as long as the axial force is less than this frictional force, the components will not slip and the connection will not be damaged. This is the high-strength bolted connection. principle.

The high-strength bolt connection relies on the friction between the contact surfaces of the connectors to prevent them from sliding each other. In order to make the contact surfaces have sufficient friction, it is necessary to increase the clamping force of the components and increase the friction coefficient of the contact surfaces of the components. The clamping force between the components is achieved by applying pre-tension to the bolts, so the bolts must be made of high-strength steel, which is why it is called high-strength bolted connections.

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

There are actually two types of high-strength bolts, friction type and pressure type.

The criterion for the shear force of friction-type high-strength bolts is that the shear force caused by the design load does not exceed the friction force.

The pressure-bearing high-strength bolts are designed based on the principle that the shaft is not sheared or the plate is not crushed.