Why does the motor shaft turn blue?

For most readers, the term “bluing” is not unfamiliar. Bluing is a process where steel or steel parts are heated to an appropriate temperature in air, water vapor or chemical agents to form a blue or black oxide film on the surface. However, for motor components, it is often not due to a dedicated bluing treatment process, but rather a physical phenomenon that occurs during the production and processing of the motor or during its operation.

Why does the motor shaft turn blue?

During the processing of the motor shaft itself, there will be no bluing factors. However, during the assembly process of the motor shaft with other components or subsequent processing, bluing may occur. The cage-type motor shaft and the rotor core have a typical interference fit relationship. When the rotor core is assembled with the shaft in the hot state after casting, the heat of the cast aluminum rotor is sufficient to cause local bluing (at the mating position of the rotor core and the shaft, and extending to both ends to varying degrees) on the motor shaft. In some cases, it may also appear black.

Why do the rotors of some faulty motors turn blue?

Under normal circumstances, whether during the production and processing stage or the operation of the motor, the rotor surface of the motor is the original color after metal turning. However, in some faulty motors, the rotor surface may show local bluing or overall bluing. Analyzing from the physical phenomenon of metal bluing, this is due to the problem caused by excessively high temperature during the motor operation. Generally, the local bluing of the motor rotor is caused by casting defects such as broken or thin strips in the rotor itself. During the testing of such motors, a serious imbalance in the stator current will be observed, and in severe cases, the rotor may experience aluminum leakage. If the entire rotor is in a bluing state, one possible reason is that the temperature of the stator winding is too high. At this time, the stator winding may already show an insulation aging state similar to overload. Of course, if the rotor aluminum strips are too thin, similar problems may occur, but this possibility is relatively smaller.