English Views: 327 Author: Site Editor Publish Time: 2022-02-17 Origin: Site
The working condition of the mud bucket excavator is bad, and the vibration is very large during the operation. The bolt pin locks at the working device, pin shaft, baffle, supporting wheel and body accessories are easy to loosen, which has a great potential safety hazard. There are many reasons for pin bolt lock loosening, which need to be controlled from all aspects at the same time. We discuss the causes of bolt loosening from the aspects of stiffness, vibration, thread locking structure, preload and material.
The stiffness mentioned in this article includes two aspects: the stiffness of the hitch bolt lock and the stiffness of the frame.
(1) Bolt stiffness
When the working tension is constant, the stress variation range can be reduced by reducing the bolt stiffness. The smaller the magnitude of the stress change, the less likely the bolt will undergo fatigue fracture, and the higher the reliability of the connection.
(2) Rack stiffness
The smaller the rigidity of the frame, the more easily the vibration will be amplified when the vibration propagates from the excitation source (engine) to the surroundings, and the greater the stress amplitude will be. On the contrary, the greater the rigidity of the frame, the better the stability of the whole machine, and the smaller the stress change amplitude under the same conditions.
Excavator bolt lock hitch pins generally use ordinary threads, and the thread lift angle is smaller than the equivalent friction angle of the thread pair to meet the self-locking condition of the thread pair. After the pin pad lock is tightened, the friction between the bolt head and the nut supporting surface also has an anti-loosening effect. However, when the bolt is installed on a machine with variable load such as vibration or impact, the friction between the thread pairs may decrease or disappear instantly. After repeated reciprocating effects of vibration and shock, the bolts will loosen.
Commonly used anti-loosening methods for threaded connections are: friction anti-loosening, mechanical anti-loosening, and damage screw anti-loosing. Generally speaking, friction prevention is simple and convenient, but not reliable enough. The threaded connection of important parts, especially the threaded connection that is not easy to check inside the excavator, should be mechanically prevented from loosening.
(1) The joint surface should meet the requirements
(2) The pre-tightening force should be appropriate
Increasing the pre-tightening force can reduce the stress variation amplitude. However, the pre-tightening force should not be too large and must be controlled within the specified range. This is because too much pre-tightening force will cause the bolt strength to reach the yield point.
(3) Disposal after tightening
After the trailer ball hitch locks are tightened as required, color marks should be painted on the hitch lock head (or nut) and the surface of the fastener. Once the pin cylinder lock is loose, it can be tightened gradually in the tightening direction until the head of the bolt (or nut) overlaps with the mark on the surface of the fastener again.
(1) Fastened
When the tow hitch lock is screwed into the fastener, the material of the fastener is different, and the depth of the fastening bolt is also different. According to the order of the steel, cast iron, and light alloy of the fastener, the depth of the bolt should be gradually increased.
(2) Threaded seat
The material selection of the threaded seat is particularly important. When the yield strength of the threaded seat is too small, it may cause the bolt to deform after being screwed in, causing early fatigue failure, and the bolt is also easy to loosen.
(3) Self-made enlarged gasket
The enlarged washer used when tightening the bolt is not a standard part and has strict technical requirements, so it can only be made by yourself. The self-made enlarged gasket is generally made of No. 45 steel, the hardness is about HRC39, and the heat treatment method is quenching and tempering at medium temperature.
