In the harsh environment, the amplitude vibration will increase during the excavator operation.At this time, the bolts of some working devices and spare parts on the digging body will be very easy to loosen. The following article mainly describes the inspection and prevention methods of loose bolts of Carter excavator.
Cause Analysis:
The causes of the loosening of the bolts of the Carter excavator are various, and need to be controlled from all aspects at the same time. This paper discusses the causes of bolt loosening from the aspects of stiffness, vibration, thread anti-loosening structure, preload, material, etc., and puts forward preventive measures.
1. Stiffness: including the stiffness of the bolt (fastener) and the stiffness of the frame (fastener). Bolt stiffness When the bolt is subjected to an axial variable load, under the condition of constant tightening force, the smaller the change in stress, the less the possibility of fatigue fracture of the bolt and the higher the reliability of the connection. When the working tensile force is constant, the amplitude of stress change can be reduced by reducing the stiffness of the bolt; when the rigidity of the connected parts and the stiffness of the bolt are unchanged, increasing the working tension by increasing the pretension force can also reduce the stress Variation. Properly increasing the bolt length can reduce the stiffness of the bolt. For example, in the slewing bearing, counterweight, track guard, cab protective net, etc., long bolts can be used to reduce the stiffness of the bolts.
2. Vibration: Carter excavator bolts generally use common threads, and the angle of thread rise is less than the equivalent friction angle of the thread pair to meet the self-locking condition of the thread pair. After the bolt is tightened, the friction between the bolt head and the supporting surface of the nut also has an anti-loosening effect. However, when the bolt is installed on a machine with variable load such as vibration and impact, the friction between the thread pairs may decrease or disappear in an instant. After repeated vibrations and shocks, the bolts will loosen. The excavator vibration part includes the vibration generated by the engine and the vibration generated by the excavator operation.
3. Material: When the fastener bolt 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 fastener being steel, cast iron, and light alloy, the bolt is screwed The depth of penetration should gradually increase. The depth of screwing into the steel should be slightly larger than the nominal diameter of the thread, but when the nominal diameter of the bolt is less than 12mm, and the screwing situation is the battery terminal, pipe clamp, wire clamp, radiator dust screen, bottom seal plate, the screw The penetration depth can be equal to the nominal diameter. The graphite formed in the matrix after the casting of the cast iron has an expansion effect, which can reduce the shrinkage of the casting volume and reduce the internal stress, and can also weaken the transmission of vibration, and has good vibration resistance and vibration absorption performance. For example, the transition block, the engine bracket and the compressor bracket on the walking pilot valve are made of cast iron, and the anti-loosening effect of the fastening bolt is better.
