Cause Analysis & Consequences of Overheating of Cast Aluminum Rotor

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

> Problems in Casting Process
Whether it is high-pressure aluminum casting, low-pressure aluminum casting or centrifugal aluminum casting, there are some inherent defects, such as the monitoring of casting process quality is relatively difficult, the process parameters are difficult to quantify, and the operators tend to set the parameters by experience; Manufacturing defects such as air holes and trachoma are very hidden, most of which occur inside. They can not be found in the preliminary inspection and test. Only in the actual operation of the motor can the influence of the defects be 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 rotor overheating and Bluing.

During the operation of the motor, the heating of the rotor itself and the thermal radiation of the stator may lead to the problem of local or overall overheating and Bluing of the rotor. 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 caused by the casting quality of the rotor itself, such as thin strip, broken strip and other problems. In serious cases, aluminum flow will occur due to overheating, that is, the guide strip of the rotor flows out of the notch due to high-temperature melting, accompanied by chamber sweeping quality failure.
> Rotor End Deformation Problem

For most cast aluminum rotors, due to many factors such as aluminum casting process, ventilation and heat dissipation and later balance, the aluminum end ring of the rotor is equipped with balance column and wind blade. When the temperature of the motor rotor is high, the aluminum in the rotor will undergo fluidization deformation to varying degrees, especially the rotor end, which is not restricted by the rotor slot like the guide bar, Serious distortion and deformation are likely to occur at high speed, and its final state is similar to the package rejection fault of wound rotor. After all blades are thrown out, they rub with the stator winding, resulting in the instantaneous burning of the whole motor.