How to Prevent Motor Shaft Breakage?

How to Prevent Motor Shaft Breakage? We have conducted numerous discussions on the cause analysis of shaft breakage combined with fault cases. The principle for preventing shaft breakage is to reduce and eliminate stress points and exclude external force factors. From the perspective of the shaft's structural characteristics, efforts should be made to avoid sudden diameter changes and slender shafts of large-diameter rotors during the design stage. In the manufacturing process, necessary measures should be taken to remove stress.

(1) Control of Machining Stress

For motor products, most are processed using cylindrical blanks. Due to the structural characteristics of the shaft, it basically has a stepped structure that is thick in the middle and thin at both ends. The positions where the shaft diameter changes are areas with relatively concentrated stress. Therefore, it is necessary to reduce the chance of stress concentration by processing in multiple steps, and reduce machining stress by processing transition fillets at these positions. In actual processing, transition fillets may be understood as a means of surface quality control, but their most essential role is one of the measures to avoid stress.

(2) Elimination of Welding Stress

Welding stress only involves shafts with webs, that is, welding webs of a certain height on the basis of cylindrical blanks to achieve a matching effect with the rotor core. Shaft breakage occurs relatively frequently in such shafts.

According to the welding execution process, welding stress is divided into instantaneous welding stress and residual stress. Controlling the welding stress of web shafts should be carried out during the welding process and the finished product stage. To reduce instantaneous welding stress, preheating the shaft before welding is particularly important. To reduce the residual welding stress of the shaft, the welded shaft should undergo stress relief treatment, which can be performed by ultrasonic vibration or heating.

Fractures of welded shafts generally occur at the butt end of the web and the main shaft, and some are longitudinal cracks extending inward along the weld direction. The early stage of such problems is severe motor noise and rotor rubbing. It is difficult to detect minor cracks, which need to be analyzed and judged through radial runout testing.

(3) Control of Motor Installation and Transmission

For motors with relatively large power, pulley transmission is not recommended, because this transmission method causes the motor shaft to be subjected to bending moment, which may lead to shaft breakage in severe cases.

Requirements in this regard are specified in the product technical conditions of motors and explained in the operation and maintenance manuals of standard motor manufacturers, but these requirements may not be implemented in specific use. For motors that must use pulley transmission, especially those with relatively large specifications, it is recommended to use cylindrical roller bearings at the drive end.

(4) Reliability of Motor Installation Datum

From actual usage, it can be found that the installation datum of some motors does not directly contact the ground, but is raised in height through a frame. Special attention should be paid to the reliability of the datum in such cases. If the datum is unbalanced, it is very easy to cause shaft breakage due to the positional relationship between the motor and the driven equipment.

(5) Daily Monitoring and Measurement During Motor Operation

During motor operation, the placement of the motor itself and the relative position of the equipment have a great impact on the operation quality. Periodic inspections and daily monitoring should be carried out to detect and correct problems, so as to prevent quality accidents.