Causes of motor bearing overheating and solutions

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Bearings are the most important supporting components of motors. Under normal circumstances, the temperature of motor bearings is considered to be too high when the temperature of the rolling bearings exceeds 95°C and the temperature of the sliding bearings exceeds 80°C. Overheating of the bearings when the motor is in operation is a common fault, with various causes. It can sometimes be difficult to diagnose accurately; as a result, if not addressed promptly, it often leads to greater damage to the motor, shortening its lifespan and thereby affecting operations and production. Summarize the specific circumstances, causes, and treatment methods for overheating of motor bearings. I. Causes of overheating in motor bearings and solutions: 1. Improper installation of rolling bearings, or tolerances that are too tight or too loose. Solution: The operational performance of rolling bearings depends not only on the manufacturing precision of the bearings themselves, but also on the dimensional accuracy, form and position tolerances, and surface roughness of the shafts and holes with which they fit together, as well as on the chosen fit and the correctness of installation. In conventional horizontal motors, properly assembled rolling bearings are subjected only to radial stress. However, if the fit between the inner ring of the bearing and the shaft is too tight, or if the fit between the outer ring of the bearing and the end cover is too tight – that is, if the clearance is too large – the bearing clearance will become too small after assembly, sometimes even approaching zero. This makes the rotation inflexible, and it will heat up during operation. If the fit between the inner ring of the bearing and the shaft is too loose, or if the fit between the outer ring of the bearing and the end cover is too loose, then relative rotation will occur between the inner ring and the shaft, or between the outer ring and the end cover, resulting in frictional heat generation and overheating of the bearing. Typically, the standard shifts the tolerance zone for the inner diameter of the bearing inner ring, which serves as the reference part, below zero; this results in a fit between that tolerance zone and the bearing inner ring that is much tighter than the fit with an ordinary reference hole for the same shaft. 2. An inappropriate selection of grease, improper use and maintenance, poor quality of the grease or its deterioration, or the presence of dust and impurities can all cause the bearing to overheat. Solution: Too much or too little grease can also cause the bearing to overheat. When there is too much grease, significant friction occurs between the rotating parts of the bearing and the grease; whereas when too little grease is used, dry friction can occur, leading to overheating. Therefore, the amount of grease must be adjusted so that it is approximately 1/2 to 2/3 of the volume of the bearing housing. Improper or deteriorated grease should be thoroughly cleaned off and replaced with suitable, clean grease. 3. The axial clearance between the external bearing cover of the motor and the outer circumference of the rolling bearing is too small. Solution: Large and medium-sized motors generally use ball bearings at the non-shaft-end. Roller bearings are used at the shaft extension end, allowing it to expand freely when the rotor expands due to heat. In small motors, since ball bearings are used at both ends, there should be an appropriate gap between the outer bearing cover and the outer ring of the bearing; otherwise, the bearing may overheat due to excessive axial thermal expansion. When this phenomenon occurs, the front or rear bearing cover should be removed slightly, or a thin piece of paper should be placed between the bearing cover and the end cover, so as to create a sufficient gap between the outer bearing cover at one end and the outer ring of the bearing. 4. The end caps or bearing covers on both sides of the motor are not properly installed. Solution: If the end caps on either side of the motor or the bearing covers are not installed parallel to each other, or if the seals are not properly in place, this can cause the balls to deviate from their track and rotate, resulting in heating. The flanges on both sides or the bearing cover flanges must be leveled again, and tightened evenly using bolts. 5. Severe wear of the balls, rollers, inner and outer rings, or ball cages, or metal flaking. Solution: The bearing should be replaced at this time. 6. Poor connection to the load mechanism. The main reasons are: poor coupling assembly, excessive belt tension, misalignment with the axis of the driven machinery, too small a pulley diameter, the pulley being too far from the bearings, and excessive axial or radial loads. Solution: Correct the improper connection to prevent the bearings from being subjected to abnormal forces. 7. The shaft has bent. Solution: At this point, the load on the bearing is no longer purely radial, which causes the bearing to overheat. Efforts should be made to straighten the bent shaft or replace it with a new one. II. How to protect motor bearings from overheating? It is possible to embed temperature sensors near the bearings, and then use a control circuit to protect them. Typical electric motors come equipped with temperature sensing elements inside them (such as thermistors), and two wires extend from these elements to a dedicated protector. This protector supplies a constant voltage of 24V; when the motor bearings overheat and exceed the value set by the protector, it triggers a shutdown mechanism to provide protection. At present, **most motor manufacturers use this type of protection method.