How to choose the loosening prevention method of threaded fasteners

Update:14 Feb 2020
Summary:

There are four ways to prevent loosening of threaded fa […]

There are four ways to prevent loosening of threaded fasteners
The first is friction and loosening. This is the most widely used anti-loosening method. This method generates a positive pressure between the screw pairs that does not change with external forces, so as to generate a friction force that can prevent the relative rotation of the screw pairs. This positive pressure can be achieved by pressing the screw pair axially or simultaneously. Such as the use of elastic washers, double nuts, self-locking nuts and nylon insert lock nuts. This anti-loosening method is more convenient for the disassembly of the nut, but in the case of impact, vibration and variable load, the bolt will initially reduce the pre-tension due to slack. As the number of vibrations increases, the pre-tension lost will slowly increase. , Will eventually cause the nut to loosen and the threaded connection to fail.

The second method is mechanical anti-loosening. The relative rotation of the screw pair is directly restricted by the stopper. Such as the use of split pins, series wire and stop washer. Because the stopper has no pre-tightening force, the anti-loosening stopper can work only when the nut is loosened to the stop position, so this method actually does not prevent loosening but prevents it from falling off.

The third method is riveting, punching and preventing loosening. After tightening, punching points, welding, bonding and other methods are used to make the thread pair lose the characteristics of the motion pair and the connection becomes an inseparable connection. The disadvantage of this method is that the bolt can only be used once, and the removal is very difficult, and the bolt pair must be destroyed before it can be removed.

The fourth way is to prevent the structure from loosening. It uses the thread pair's own structure, namely the Down's thread anti-loosening method.

The first three types of anti-loosing methods rely on the force of a third party to advance anti-loosing, which mainly refers to frictional force. The effectiveness of the anti-loosing effect depends on the magnitude of the third party's force. The structural anti-loosing does not rely on the third party force, but only on its own structure. Structural anti-loosening method is Down's thread anti-loosening method, which is also the most advanced and effective anti-loosening method, but it is not known to most people.