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Analysis of quality problems of cast aluminum rotor

Mar 18, 2019

The quality of the cast aluminum rotor affects the efficiency, power factor, and starting and running performance of the motor. In order to comprehensively improve the quality of the rotor, it is necessary not only to analyze the defects of the cast aluminum rotor, but also to study various factors affecting the quality of the cast aluminum rotor, and propose improvement measures. This paper gives a brief introduction to the rotor cast aluminum method and analyzes the broken strip problem.



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Rotor cast aluminum is a hidden project. The quality control of the rotor depends on the process parameters. In a sense, the performance quality focus of the cast aluminum rotor is concentrated on the cast aluminum of the rotor.



Cast aluminum method and rotor quality


After the squirrel-cage rotor is changed from a copper strip to a casting method, the stray loss of the motor is increased by 2 to 6 times. The cast aluminum method of the rotor is different, and the stray loss is also different. When a pressure cast aluminum rotor is used, the stray loss of the motor is the largest. Centrifugal cast aluminum and vibrating cast aluminum are susceptible to defects due to various factors, but the stray loss of the rotor is small. Further research found that the density of the die-cast rotor is about 8% lower than that of the centrifugal cast aluminum rotor aluminum cage, and the average resistivity is increased by 13%, which makes the main technical and economic indicators of the asynchronous motor of the die-cast rotor deteriorate, core loss, slip rate, The temperature rise is increased, while the minimum torque and efficiency are reduced.

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The density of the aluminum in the die-casting rotor is reduced, and the electric resistance is increased because the gas mixed in the die-casting is densely packed in the shape of a pinhole in the rotor cage, the end ring, the fan blade, and the like. Also due to the strong pressure, the cage and the core are in close contact (even if the aluminum conductor is also scattered between the core laminations), the lateral current greatly increases the stray loss of the motor.


The low-pressure cast aluminum-aluminum water comes from the inside of the crucible and adopts a relatively "slow" low-pressure casting, the exhaust is better, and the quality of the cast aluminum rotor is good. The quality of the low-pressure cast aluminum rotor is the best, followed by centrifugal casting of aluminum, and the worst is pressure-cast aluminum.

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The defects of cast aluminum rotors are varied and the causes are complex. Domestic motor factories mostly use centrifugal aluminum, and the following mainly analyzes the quality problems of centrifugal cast aluminum rotors.



Why is the cast aluminum rotor broken?


(1) The misalignment or clogging of the core slot reduces the cross section of the slot to cause blockage; the leakage of the individual punch slots and the inclusions brought in during the preheating can block the slot, so that the aluminum water is blocked during the pouring. .


(2) The rotor cage is pulled off. When the rotor core is over-tightened and the core is pulled out, the cage may be pulled off when the core is raised outwards. If the aluminum water has not completely solidified during demolding, the cage will also break due to premature knocking of the mold. When the aluminum is vibrated, the cage is often broken due to the long vibration time.

(3) Stopping during the pouring. Since aluminum is extremely oxidizable, the aluminum water poured after the pause cannot be integrated with the aluminum water in front, causing the cage to break.


(4) The air holes in the slot break the cage.


(5) The temperature of the core is too low to affect the fluidity of the aluminum water, which has a great influence on the gravity cast aluminum.



Measures to prevent broken bars


(1) Strengthen the inspection before pouring to eliminate the misalignment and blockage of the slots.


(2) When the rotor core is laminated, the stacking pressure is controlled so as to be no more than 4 MN/m2. After casting the aluminum, the aluminum water is completely solidified and then released.


(3) When pouring once, it must not be stopped in the middle.


(4) Properly increase the core preheating temperature.


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