The reasons for the looseness of the external hexagon screws in practice are: the product material itself or the fact that the screws may not be tightened at that time and eventually lead to the looseness of the screws. The methods to solve the looseness of the external hexagon screws are as follows:
1. Anti-loosening of riveting punching: adopt punching point, welding, bonding and other methods after tightening, so that the threaded pair loses the characteristics of the movable pair and the connection becomes a non-removable connection. The disadvantage of this method is that the bolt can only be used once, and it is difficult to disassemble , the screw must be crushed before it can be disassembled.
2. Structural anti-loosening: It does not rely on outside manpower but only on its own structure. The structural anti-loosening method is the Down's thread anti-loosening method. How to prevent the loosening of the outer hexagon screw
3. Mechanical anti-loosening: use split pins, stop gaskets and string wire ropes, etc. The mechanical anti-loosening method is more reliable, and the mechanical anti-loosening method should be used for important connections.
4. Anti-loosening by friction: a positive pressure that is not isolated by external force is generated between the thread pairs, restraining the frictional force of the relative rotation of the thread pair, which is realized by pressing the thread pair axially or in two directions at the same time, such as using elastic washers , double nuts, self-locking nuts and nylon insert lock nuts, etc.
This anti-loosening method is more convenient for the disassembly of the nut, but in the environment of shock, vibration and variable load, the preload force of the bolt will drop due to relaxation at the beginning. As the number of vibrations increases, the lost preload force becomes dull If it increases, it will lead to the loosening of the nut and the failure of the threaded connection.
