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Ningbo Tongren Bearing Co., Ltd.
18
2023
-
05
Question: Factors causing high motor bearing temperature
1. Axial movement affects the quality of the motor bearings.
Numerous experiments have shown that if the axial movement of the motor rotor is large, it will inevitably increase bearing wear, and heat generation is unavoidable, requiring more frequent bearing replacements. Axial movement is caused by a variety of factors, directly related to the axial force on the rotor, the selection of the locating ball bearing, the radial fit characteristics, and the axial assembly clearance. Axial movement was more common in the previous YB series of medium-voltage motors, and has been significantly alleviated through proper handling, greatly reducing the incidence of motor bearing heating and damage caused by axial movement.
Some medium-voltage motor bearing structures use axial seals. These seals, through elastic compression contact with the bearing outer cover, improve the bearing structure's protective performance. However, because there are currently no specialized assembly tools for the seals, the axial assembly position is largely controlled manually. Even if the specified position is reached, due to unsuitable seals, high hardness, low elasticity, dimensional deviations, and lack of lubrication on the friction contact surface, friction heat is generated between the seal and the bearing outer cover (or water shield), resulting in high bearing temperatures.
2. Motor bearing lubrication is essential for the reliable and safe operation of motor bearings, but the amount of lubricating grease is limited.
After bearing assembly, lubricating grease must be applied to both sides and inside the bearing. Experiments show that both too much and too little oil are unsuitable. Too much will cause the bearing to overheat, while too little will cause bearing noise and ineffective lubrication, leading to overheating. Therefore, only a moderate amount should be added. The generally prescribed oil quantity is one-half of the bearing chamber for 2P and two-thirds for 4P and above. However, this is often impractical, and most on-site applications rely on actual conditions and experience, sometimes requiring multiple iterations. At the same time, the lubricating oil must be kept clean and free from deterioration or contamination.
During bearing assembly, the assembly process specifications must be strictly followed. Cold hammering, impact, bumping, impurities in the bearing raceway, oil stains on the outer surface, improper positioning, excessive shaft deflection, poor positioning, poor accuracy of the shaft and bearing sleeve, all affect the bearing assembly quality and thus the bearing's service life. Poor alignment of the coupling, rotor imbalance (static and dynamic), poor foundation rigidity, loose footings, rotational stall, and surge. Some rotors, during operation, may experience corrosion from the medium or wear from solid impurities, or shaft bending, causing unbalanced centrifugal force, leading to bearing overheating, vibration, severe raceway wear, and eventual failure.
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