Bolt, as a common tool in fixture, is widely used, but it will also bring many problems, such as loose connection, insufficient clamping force, bolt rust and so on. When parts are processed and produced, the loose bolt connection will affect the quality and efficiency of processing. So how to prevent bolts from loosening?

There are three commonly used locking methods: friction locking, mechanical locking and permanent locking.

Anti-loosening purpose: it can work more effectively for a long time; Improve the reliability of related workpieces.

1. Double nuts

Anti-top locking principle of nuts: When double nuts are locked, two friction surfaces are generated, the first friction surface is between nuts and fasteners, and the second friction surface is between nuts. When installed, the pre-tightening force of the first friction surface is 80% of that of the second friction surface. Under the impact and vibration load, the friction of the first friction surface will decrease and disappear, but at the same time, the first nut will be compressed, which will further increase the friction of the second friction surface. Nut loosening must overcome the first friction and the second friction, because the first friction decreases and the second friction increases. This locking effect will be better.

Down's thread locking principle: Down's thread fasteners are also locked by double nuts, but the two nuts rotate in opposite directions. Under the impact and vibration load, the friction force of the first friction surface will decrease and disappear.

The first nut (the right hand in the picture) tends to loosen, that is, the nut rotates to the left. However, the rotation direction of the second nut (left-handed in the figure) is opposite to that of the first nut, so the loosening force of the first nut is directly converted into the tightening force of the second nut. In this way, the nut will never loosen.

2.30 Wedge Thread Locking Technology

There is a 30-degree wedge bevel at the bottom of the 30-degree wedge female thread. When the bolt and nut are tightened with each other, the tip of the bolt tightly abuts against the wedge-shaped inclined plane of the female thread, thus generating a great locking force.

Due to the change of tooth angle, the normal force generated by the contact between threads makes an angle of 60 with the bolt shaft, instead of 30 like ordinary threads. Obviously, the normal pressure of 30 wedge thread is much greater than the fastening pressure, so the anti-loosening friction force will inevitably increase greatly.

Spielberg thread structure diagram

As can be seen from the following figure, the forces indicated by the two arrows are both p ι, and the normal pressure of the traditional 60 angle thread is p =1.15p ι; However, the angle and magnitude of the normal pressure of the 30 wedge thread change, because there is a 30-degree wedge bevel at the bottom of the tooth, and the normal pressure p = 2p.