Bolt anti loosening is by eliminating (or limiting) the relative movement between the thread pair, or increasing the difficulty of relative movement, to prevent the connection loose, to ensure the safety and reliability of the connection. There are various measures to prevent looseness. The following are some commonly used measures to prevent looseness.
2.1 Anti-loosening with additional friction force
There are three main ways to prevent loosening of the attachment: double nut tightening structure, spring washer tightening structure and self-locking nut tightening structure. The double-nut tightening structure is designed to increase the anti-loosening effect by adding a nut and squeezing the original tightening nut, so that it is subjected to additional pressure and friction, as shown in Figure 6.
The spring washer tightening structure is based on the elastic reaction force produced by the washer flattening so that the compression between the screw threads, while the tip of the washer diagonal against the bolt or nut and the supporting surface of the connecting piece, also has anti-loosening effect. However, this structure has poor anti-loosening effect under vibration and impact load, and is generally used for non-critical connections, as shown in Figure 7.
There are two types of self-locking nut tightening structures: all-metal self-locking gold nut and non-metal insert locking nut. The two types of nuts produce locking effect through their own deformation during use and are widely used in key parts of chassis, as shown in Figure 8.
2.2 Mechanical looseness prevention
Mechanical anti - loosening mainly has hexagonal slotted nuts with cotter pins, round nuts and stop gaskets and other structures. The hexagon slotted nut with cotter pin is to pass the cotter pin through the groove of the nut and the pin hole at the end of the bolt. Then, the tail of the cotter pin is separated and held close to the side of the nut, and the nut and bolt are locked, as shown in Figure 9.
This structure is reliable and can be used for intense impact and vibration parts. The round nut and the stop gasket are used to bend the single or double ear stop gasket to the side of the nut and the connecting piece respectively, as shown in Figure 10.
2.3 Other Methods
Chemical anti-loose: add anaerobic glue and other sealing materials between the threads, tighten the nuts, the anaerobic glue can be cured after a certain time, so as to reliably bond the threads and prevent the relative movement of the threads. Permanent anti-loose: through end riveting, punching point, spot welding and other ways on the contact surface of bolt and nut, the bolt and nut form a rigid connection to prevent their relative movement. In addition to the above anti-loose measures, the anti-loose effect of bolts can also be improved by replacing fine-tooth bolts, increasing the preload force (in the feasible range), improving the operation skills of employees, and improving the manufacturing accuracy of bolts and connectors.
