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How to Analyze the Quality of Cast Aluminum Rotors
source：未知 time：2024-09-02 09:06
The quality of cast aluminum rotors affects the efficiency, power factor, and starting and running performance of motors. In order to comprehensively improve the quality of rotors, it is necessary not only to analyze the defects of cast aluminum rotors, but also to study the various factors affecting the quality of cast aluminum rotors, so as to propose improvement measures. This article briefly introduces the rotor casting method and analyzes the broken bar problem.
Casting aluminum rotors is a secret project. The quality control of rotors depends on process parameters. In a sense, the performance and quality of cast aluminum rotors focus on the casting of the rotors. Casting aluminum method and rotor quality After the squirrel cage rotor is changed from copper bar to casting method, the stray loss of the motor increases by 2 to 6 times. Different casting methods of the rotors have different stray losses. When pressure cast aluminum rotors are used, the stray loss of the motor is the largest. Although centrifugal cast aluminum and vibration cast aluminum are affected by various factors and are prone to defects, the stray loss of the rotor is small. Further research found that the density of the aluminum cage of the die-cast rotor is about 8% lower than that of the centrifugal cast aluminum rotor, and the average resistivity is 13% higher. This makes the main technical and economic indicators of the asynchronous motor with die-cast rotors worse, the core loss, slip rate, and temperature rise all increase, while the minimum torque and efficiency decrease.
The density of die-cast rotor aluminum decreases and the resistance increases because the gas mixed into the aluminum water during die-casting is densely distributed in the rotor cage bars, end rings, fan blades, etc. in the shape of "pinholes". Also, due to the strong pressure, the cage bars and the iron core are in very close contact (even aluminum conductors are scattered between the iron core laminations), and the transverse current greatly increases the stray loss of the motor. The aluminum water of low-pressure cast aluminum comes from the inside of the crucible, and a relatively "slow" low-pressure pouring is adopted, the exhaust is better, and the quality of the cast aluminum rotor is good. The quality of low-pressure cast aluminum rotors is the best, followed by centrifugal cast aluminum, and the worst is pressure cast aluminum.
The density of die-cast rotor aluminum decreases and the resistance increases because the gas mixed into the aluminum water during die-casting is densely distributed in the rotor cage bars, end rings, fan blades, etc. in the shape of "pinholes". Also, due to the strong pressure, the cage bars and the iron core are in very close contact (even aluminum conductors are scattered between the iron core laminations), and the transverse current greatly increases the stray loss of the motor. The aluminum water of low-pressure cast aluminum comes from the inside of the crucible, and a relatively "slow" low-pressure pouring is adopted, the exhaust is better, and the quality of the cast aluminum rotor is good. The quality of low-pressure cast aluminum rotors is the best, followed by centrifugal cast aluminum, and the worst is pressure cast aluminum.
There are many defects in cast aluminum rotors, and the reasons for their occurrence are also complicated. Domestic motor factories mostly use centrifugal aluminum. The following mainly analyzes the quality problems of centrifugal cast aluminum rotors. Some quality problems of other aluminum casting methods will be briefly introduced.
Why do cast aluminum rotors break?
(1) The core slot is misaligned or blocked. The misalignment reduces the cross-section of the slot hole and causes blockage; individual punching slot holes are missed and inclusions brought in during preheating can block the slot hole, so that the aluminum liquid is blocked during pouring.
(2) The rotor cage bars are broken. When the rotor core is stacked too tightly, after the dummy shaft is withdrawn, the cage bars may be broken when the core expands outward: if the aluminum liquid has not completely solidified during demolding, the cage bars will also break due to premature knocking on the mold. When vibrating aluminum casting, the cage bars are often broken due to excessive vibration time.
(2) The rotor cage bars are broken. When the rotor core is stacked too tightly, after the dummy shaft is withdrawn, the cage bars may be broken when the core expands outward: if the aluminum liquid has not completely solidified during demolding, the cage bars will also break due to premature knocking on the mold. When vibrating aluminum casting, the cage bars are often broken due to excessive vibration time.
(3) Pause during pouring. Since aluminum is very easy to oxidize, the aluminum liquid poured in after the pause cannot be melted into one with the previous aluminum liquid, causing the cage bars to break.
(4) The air holes in the slots cause the cage bars to break.
(5) The core temperature is too low, which affects the fluidity of the aluminum liquid, which is particularly important for gravity cast aluminum.
Measures to prevent rotor bar breakage
(1) Strengthen the inspection before pouring to eliminate the misalignment and blockage of the slot holes.
(2) When stacking the rotor core, control the stacking pressure so that it is no more than 4 MN/m2. After casting aluminum, wait until the aluminum liquid is completely solidified before demolding.
(3) Pour all the water at once during pouring, and do not pause in the middle.
(4) Appropriately increase the core preheating temperature.
electric motor price, Ex motor, Motor manufacturers in China, three phase induction motor, Wolong Nanyang Explosion Protection
electric motor price, Ex motor, Motor manufacturers in China, three phase induction motor, Wolong Nanyang Explosion Protection
