Causes of gear shaft fracture of helical gear reducer with hardened tooth surface

The reasons for the fracture of the gear shaft are briefly introduced:

1. In terms of gear shaft material selection of helical gear hardened face reducer, for the shaft mainly transmitting power, the higher hardenability and superior quenched and tempered steel should be selected according to the size of the torque transmitted and the size of the corresponding journal. However, from the metallographic analysis, it can be seen that the material of the pinion shaft has loose structure and super inclusions, which reduces the impact toughness, and under the action of high variable load, the crack rapidly expands, leading to fracture.

2. In terms of structural design, there is almost no transition fillet at the shaft shoulder after surfacing repair, resulting in severe stress concentration and fatigue cracks under the effect of bending stress, which is the main reason for shaft fracture.

3. In terms of heat treatment, the preheating treatment was not carried out as required before the surfacing repair, resulting in the difference in the structure around the welding area. This difference exists in the narrow area, which will generate high internal stress. Due to the effect of this internal stress, cracks will occur immediately after the phase transformation, which will eventually lead to fracture. Secondly, after the surfacing repair of the shaft, the appropriate heat treatment was not taken, and the welding residual stress is large, which will reduce the shaft anti alternating stress, Once encountering vibration, it is very easy to produce cracks, resulting in fracture.

4. In terms of processing technology, it is detected that the processing deviation at<160 journal is large, which makes the fitting between shaft and bearing inner race loose, resulting in relative rotation of shaft and bearing inner race, that is, running the inner race, which causes the bearing inner race to slide on the shaft and wear the shaft, which is another major factor leading to shaft wear and fracture.

5. In terms of load bearing, it can be seen from the force analysis of the gear shaft that the gear shaft bears large bending moments and torques. The bending moments generate normal stresses on the shaft, and the torques generate shear stresses. These stresses change constantly during the operation of the shaft. They belong to symmetrical cyclic alternating stresses. At the same time, there are additional dynamic loads. Once encountering vibration, overload, sudden start, braking and multiple heavy load impacts, the shaft is prone to crack and fracture.

After understanding the cause of the gear shaft fracture of the helical gear hard face reducer, I believe that it will provide greater help in the future use, which is also more conducive to our use.