In batch production, we often encounter this situation: sometimes different defects appear due to seemingly the same cause, and sometimes the same defect occurs due to different causes. This shows that rotor defects are often the result of the combined effect of multiple unfavorable factors. Of course, there must be a main cause. When conditions change, even if the same defect occurs, the main cause of the defect will change.
For example, rotor pores are often caused by poor mold exhaust or mold exhaust slot blockage. However, sometimes, even if the exhaust slot is unobstructed, the residual gas cannot be discharged in time due to the high pouring speed, which will also cause pores in the rotor. At this time, the main reason for the rotor pores is no longer the mold exhaust problem, but the pouring speed problem. Therefore, when analyzing the quality problems of cast aluminum rotors, it is necessary to conduct a comprehensive analysis based on the location and characteristics of the rotor defects and various conditions in order to more accurately find the main causes of the quality problems and take corresponding measures to effectively prevent the occurrence of cast aluminum rotor defects.
Combined with the defects of thin rotor bars, broken bars, shrinkage holes, cracks, etc. mentioned above, Ms. San will focus on the cold shut and rotor conformity issues of cast aluminum rotors with Baowei today. The failure of molten aluminum to completely fill the mold cavity is called "incomplete pouring". The places where the rotor is not poured or the edges are unclear are mainly the fan blades and balance columns. Cold shut refers to the joints or pits where the molten aluminum is not completely fused. The intersection edge is smooth and is most obvious at the fan blades.
Causes of cold shut defects
● The temperature of the molten aluminum is too low during pouring; the pouring speed is too slow or there is a flow interruption phenomenon. ● The temperature of the mold and the core is low. ● Aluminum leakage or insufficient molten aluminum. ● Insufficient rotation speed. ● The cross section of the inner gate is too small or the mold is not vented smoothly. ● Separated by oxide scale or other inclusions. Cold shut defect control measures ● The temperature of the molten aluminum should meet the specified value, and the pouring speed should be correctly controlled. It must be poured in one time. ● Appropriately increase the core temperature and the temperature of the mold, especially the upper root temperature (for low-pressure products, increase the lower mold ● Eliminate aluminum leakage. When pouring aluminum, use 10~20% more than the actual rotor. ● Control the speed. If the speed is too high at the beginning of overflow,
it will cause ground voids. (5) Keep the exhaust unobstructed and the pouring day can be appropriately enlarged. ● Keep the mold and the core clean and free of debris. Pay attention to the stimulation and cleaning of the corresponding water. Rotor resistance exceeds the tolerance (1) Analysis of the reasons for the rotor resistance exceeding the tolerance ● The core is too long, or the slot slope is greater than the allowable value, which increases the cage bar resistance. ● The rotor is misaligned and serrated, which reduces the effective area of the aluminum bar. ● Aluminum water The cleaning or slag cleaning is not good, and contains a large number of pinholes and impurities. ●The quality of the rotor aluminum casting is poor, with defects such as pores, shrinkage cavities, shrinkage, slag inclusions, cracks or cold shuts. ●The wrong grade of aluminum ingot is used or the quality is poor, and the conductivity is low. (2) The rotor resistance is small, which mainly occurs in aluminum alloy rotors. It may be that high-purity aluminum ingots are used incorrectly, or the slot slope is less than the value, which reduces the cage bar resistance. Control measures for rotor resistance out-of-tolerance problems ●Before pressing and pouring the core, pay attention to check the core length and slot slope, which should meet the requirements of the drawing. ●Do a good job of cleaning and slag removal of the aluminum liquid. ●Eliminate the rotor's casting defects such as pores and shrinkage cavities. ●Use aluminum ingots of the specified grade.
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