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What are the preventive measures for loosening of excavator bolts?

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What are the preventive measures for loosening of excavator bolts?

The working environment of the bucket chain excavator is relatively harsh, and the excavator generates a lot of vibration during the working process, which will cause the bolt pin locks to loosen. In daily maintenance, the operator should check frequently, find out and deal with it in time.



1. Stiffness


(1) Bolt stiffness

A moderate increase in the length of the pin bolt lock can reduce the stiffness of the bolt. For example, long hitch bolt locks can be used in slewing bearings, counterweights, track guards, and cab protection nets to reduce bolt rigidity.


(2) Rack stiffness

The rigidity of the frame (fastened by fasteners) can be improved by eliminating gaskets and using gaskets with greater rigidity. When the whole machine of a small excavator is upgraded from 5t to 7t, its engine, cab and frame are all used 5t, its vibration isolation effect becomes worse, the vibration of the whole machine increases, and the bolt lock hitch pins are loose. By unilaterally adjusting the shock absorber, the effect is not obvious. Later, the problem was solved by strengthening the frame.



2. Vibration


Generally, the natural vibration frequency can be reduced by reducing the axial stiffness of the shock absorber to obtain a better vibration isolation effect. However, if the axial stiffness of the shock absorber is reduced too much, when the engine is impacted, there will be a gap between the shock absorber and the frame plate, and the shock absorber will be damaged due to friction. It will also affect the radial stiffness of the shock absorber, causing the engine to oscillate.


61-2-bolt pin lock 

3. Thread anti-loosening structure


(1) Anti-loose friction

Anti-loose friction includes methods such as double nut tightening, spring washer, and self-locking nut.


(2) Mechanical anti-loosening

Mechanical anti-loosening is generally used for top link pins of engine shock absorbers. Weld the nut on a bent bracket, and achieve the purpose of preventing looseness through the limit of the bent edge of the bracket.


(3) Destroy the anti-loosening thread

Before the thread pair is screwed together, apply thread fastening glue on the thread, which is to destroy the anti-loosening of the thread pair. Thread fastening glue is used for rv hitch locks in important parts.



4. Preload


(1) The joint surface should meet the requirements

Damaged or corroded threads should be trimmed with taps or dies (commonly known as "return wire") before tightening, and then use a cleaning agent to clean the remaining paint and stains on the inside of the screw hole, the surface of the trailer hitch lock and the joint surface.


(2) The pre-tightening force should be appropriate

This is because too much pre-tightening force will cause the bolt strength to reach the yield point.


(3) Disposal after tightening

After the pin key locks are tightened as required, color marks should be painted on the bolt head (or nut) and the surface of the fastener. Once the bolt 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.



5. Material


(1) Fastened item

The hitch key locks are made of cast iron, and the tightening bolts have a better anti-loosening effect. This is because the graphite formed in the matrix after casting of the cast iron has an expansion effect, which can reduce the shrinkage of the casting volume, reduce the internal stress, and also weaken the transmission of vibration.


(2) Threaded seat

The material selection of the threaded seat is particularly important. The threaded seat steel in the key position is generally selected as Q345B, and the threaded seat steel in the ordinary position is generally selected as Q235B.


(3) Self-made enlarged gasket

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.


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