The Purpose Of Bolt Preload

The bolt pretightening force is the pretightening force along the direction of the bolt axis generated between the bolt and the connected parts under the action of the tightening torque during the bolt tightening process. For a specific bolt, its pretightening force is related to the tightening torque of the bolt, the friction between the bolt and the nut, and the friction between the nut and the connected parts.

Preload can improve the reliability, anti-loosening ability and fatigue strength of the bolted connection, and enhance the tightness and rigidity of the connection. In fact, a large number of tests and experience have proved that higher preload is beneficial to the reliability of the connection and the life of the connection, especially for the connection with sealing requirements.

Of course, as the saying goes, "everything is reversed", if the preload is too high, if it is not properly controlled or accidentally overloaded, it will often lead to the failure of the connection. Therefore, it is very important to accurately determine the pretightening force of the bolt.