Analysis of The Causes and Serious Consequences of Overheating of Cast Aluminum Rotors

Compared with the winding rotor motor, the safety performance of the cast aluminum rotor motor is better, and the theoretical electrical failure rate is half that of the winding rotor motor. However, some motors with special working conditions and specific purposes are particularly sensitive to some manufacturing process defects, and the probability of electrical failure of the cast aluminum rotor overheating and the cage fuse is also very high.

Whether it is high-pressure aluminum casting, low-pressure aluminum casting, or centrifugal aluminum casting process, there are some inherent defects, such as the quality of the casting process is relatively difficult to monitor, the process parameters are difficult to quantify, and the operator tends to rely on experience to set the parameters; pores, trachoma and other manufacturing defects are very hidden, most of them occur internally, and the preliminary inspection and testing cannot be found. Only in the actual operation of the motor, the impact of the defect is exposed. Especially in some applications with large load variation range and high speed, there are often problems such as aluminum rejection, softening and distortion of rotor wind blades due to overheating, and blueness of rotor overheating.

During the operation of the motor, the heating of the rotor itself and the thermal radiation of the stator part may cause the rotor to overheat and turn blue locally or as a whole. When the rotors are all blue, the temperature rise of the motor is generally very high. When the rotor is partially overheated, it is more due to the casting quality of the rotor itself. For example, it is more typical to have problems such as thin strips and broken strips. In severe cases, the phenomenon of aluminum flowing will occur due to overheating, that is, part of the rotor guide strip melts due to high temperature and flows out of the notch, and the quality of the broom is associated with failure.

For most cast aluminum rotors, due to many factors such as the aluminum casting process, ventilation and heat dissipation, and late balance, the aluminum end ring of the rotor has a balance column and wind blades. When the temperature of the motor rotor is high, the aluminum in the rotor will undergo varying degrees of fluidized deformation, especially the rotor end, unlike the guide strip, which is restricted by the rotor groove, serious distortion and deformation are very likely to occur at high speeds. The final state is similar to the package rejection failure of the winding rotor. After all the blades are thrown out, they rub against the stator winding, causing the entire motor to burn down instantly.