In a harsh environment, the amplitude vibration of the excavator will increase during operation. At this time, the bolts of some working devices and spare parts on the excavator will be very easy to loosen. Therefore, it is necessary to check the bolts at key parts at intervals. The following article mainly describes the inspection and prevention methods for bolt looseness of Caterpillar excavator.
Cause analysis:
There are many reasons for bolt looseness of Caterpillar excavator, which need to be controlled from all aspects at the same time. Based on the typical cases of bolt looseness of excavator, this paper discusses the causes of bolt looseness from the aspects of stiffness, vibration, thread anti looseness structure, pre tightening force and materials, and puts forward preventive measures.
1. Rigidity: including the rigidity of bolts (fasteners) and frame (fasteners). Bolt stiffness when the bolt is subjected to axial variable load and the fastening force remains unchanged, the smaller the stress change amplitude, the less likely the bolt will have fatigue fracture, and the higher the reliability of the connection. When the working tension is constant, the change range of stress can be reduced by reducing the bolt stiffness; When the stiffness of the connected part and the stiffness of the bolt are unchanged, the working tension can be increased by increasing the preload, and the range of stress change can also be reduced. The bolt stiffness can be reduced by increasing the bolt length appropriately. For example, long bolts can be used at slewing bearings, counterweights, track guards, cab protective nets, etc. to reduce the bolt stiffness.
2. Vibration: the bolt of Caterpillar excavator generally adopts ordinary thread, and its thread rise angle is less than the equivalent friction angle of the thread pair, so as to meet the self-locking conditions of the thread pair. After the bolt is tightened, the friction between the bolt head and the nut support surface also has an anti loosening effect. However, when the bolts are installed on the parts with variable loads such as vibration and impact, the friction between the thread pairs may decrease or disappear instantly. After repeated reciprocating action of vibration and impact, bolts will become loose. The vibration part of excavator includes the vibration generated by engine and the vibration generated by excavator operation.
3. Material: when the fastener bolt is screwed into the fastener, the fastener material is different, and the screw in depth of the fastener bolt is also different. According to the arrangement order of the fastener as steel, cast iron and light alloy, the screw in depth of the bolt should gradually increase. The screw depth of the bolt into the steel shall be slightly greater than the nominal diameter of the thread. However, when the nominal diameter of the bolt is less than 12mm and the bolt is screwed into the battery terminal, pipe clamp, wire clamp, radiator dust screen and bottom sealing plate, the screw depth can be equal to the nominal diameter. The graphite formed in the matrix of cast iron after casting can expand, which can reduce the shrinkage of the casting volume, reduce the internal stress, weaken the transmission of vibration, and have good anti vibration and vibration absorption properties. For example, the transition block, engine support and compressor support on the travel pilot valve are made of cast iron, and their fastening bolts have good anti loosening effect.
