According to the force of the whole vehicle and the way of flange connection, the connecting bolt of the lower part of the electric wheel is subjected to the pulling force, and the connecting bolt of the upper part of the electric wheel is subjected to the tension of the pre-tightening force under the normal condition after the connection. In addition, it is not affected by any force, and as the bolt is mounted upwardly, the tensile force is gradually reduced, theoretically higher than the axial position becomes zero. Of course, there is also the effect of shear stress, but due to the pre-tightening force of the coupling bolt, the joint surface of the electric wheel and the rear axle housing of the truck does not have relative motion during truck operation, so the effect of shear stress is almost non-existent. Then how does the electric wheel coupling bolt break? For the 630E electric dump truck, the self-weight is 108.8t, and the total weight at the normal load is 281.1t. Based on the design idea, the weight of each rear wheel is 93.7. t. According to the force analysis, these static loads can not break the bolt anyway. However, during the operation of the truck, the impact load is quite large due to road, speed and loading. It can be inferred from the mv=Ft momentum formula that the impact load is several times or even ten times that of the static load, and the coupling is a bolt. Due to the structure and manufacturing precision of the bolt itself, stress concentration is easily generated at the bottom of the thread. . From the damage characterization and force analysis, during the operation of the 630E truck, due to its own movement and the bumps of the road, the truck generates and impacts. Although there are buffers for oil and gas shock absorbers, it cannot be completely eliminated and offset. This impact load causes stress concentration in the coupling bolt. During a certain period of operation, the stress concentration caused by this impact will cause fatigue cracks in the bottommost joint bolt. Once the fatigue crack is generated and gradually expanded, the connection between the electric wheel and the vehicle body is changed on the one hand. It is more unreliable; on the other hand, the maximum force position is gradually moved up, which deteriorates the stress of the joint bolt and increases the speed of fatigue cracking. When the fatigue cracking extends to a certain extent, especially when the 7 joint bolts at the same level of the lowermost part are mostly fatigue cracked and subjected to the impact of strong vibration, the electric wheel coupling bolt can no longer withstand such a huge impact. The load is broken all at once, causing the electric wheel to separate from the truck, and the lower connecting bolt is fatigue fracture. The upper connecting bolt is tensile fracture and the upper edge of the electric wheel is inclined outward. In summary, the cause of the breakage of the electric wheel coupling bolt is the insufficient fatigue strength of the coupling bolt and the vibration during the operation of the truck. Measures to prevent breakage of joint bolts, strengthen the management of bolts and check the bolts of important parts are the key components of the equipment. They should be purchased and stored in strict accordance with technical requirements, creating the necessary conditions for the safe operation of electric wheels. Before the installation of the electric wheel, the maintenance personnel should carefully check each connecting bolt. For bolts with deformation, cracks and thread damage, they must never be used again to ensure the quality of the coupling bolt. Make sure the pre-tightening torque is 2007Nm during installation. Determine the use period of the coupling bolt. After the joint bolt has been used for a certain period of time or after a certain cycle, although the surface looks good, the internal structure may be generated due to the slight fatigue crack or plastic deformation under the action of stress. With the change, it is impossible to confirm the state by the inspection of the naked eye. If it continues to be used, it will bring unsafe risks to the operation of the truck, which provides conditions for stress concentration. Therefore, determining the service life of the bolt is an important means to ensure the safe and reliable operation of the truck.
Research and prevention of cracking of wheel connecting bolt