Bearings are the most important supporting components of motors. In general, when the temperature of the motor bearing exceeds 95 ℃ for the rolling bearing and 80 ℃ for the sliding bearing, it indicates overheating of the bearing.

Overheating of bearings during motor operation is a common fault with various causes, sometimes difficult to accurately diagnose. Therefore, in many cases, if not handled in a timely manner, the result is often greater damage to the motor, shortening its lifespan, and affecting work and production. Summarize the specific situation, causes, and treatment methods of motor bearing overheating.

1、 Reasons and treatment methods for overheating of motor bearings:

1. Incorrect installation of rolling bearings, tight or loose fit tolerances.

Solution: The working performance of rolling bearings not only depends on the manufacturing accuracy of the bearing itself, but also on the dimensional accuracy, form and position tolerance, surface roughness, selected fit, and whether the installation is correct or not.

In general horizontal motors, well assembled rolling bearings only bear 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, the clearance between the bearings becomes too small after assembly, sometimes even close to zero. This makes the rotation inflexible and generates heat during operation.

If the fit between the inner race of the bearing and the shaft is too loose, or if the fit between the outer race of the bearing and the end cover is too loose, the inner race of the bearing and the shaft, or the outer race of the bearing and the end cover, will rotate relative to each other, generating friction and heat, causing overheating of the bearing. Usually, the tolerance zone for the inner diameter of the bearing inner race, which serves as the reference part, is moved below the zero line in the standard. This is much tighter for the fit between the tolerance zone of the same shaft and the bearing inner race than for the fit formed between it and the general reference hole.

2. Improper selection or maintenance of lubricating grease, poor quality or deterioration of lubricating grease, or mixing with dust and impurities can cause bearing heating.

Solution: Adding too much or too little lubricating grease can also cause bearing heating, because when there is too much lubricating grease, there will be significant friction between the rotating part of the bearing and the grease, while when there is too little lubricating grease added, dry friction may occur and heating may occur. Therefore, it is necessary to adjust the amount of lubricating grease to approximately 1/2-2/3 of the volume of the bearing chamber space. Unsuitable or deteriorated lubricating grease should be cleaned and replaced with suitable and clean lubricating grease.

3. The axial clearance between the outer bearing cover of the motor and the outer circle of the rolling bearing is too small.

Solution: Large and medium-sized motors generally use ball bearings on the non shaft extension end. The shaft extension end adopts roller bearings, so that when the rotor expands under heat, it can freely extend. Due to the use of ball bearings on both ends of small motors, there should be an appropriate gap between the outer bearing cover and the outer ring of the bearing. Otherwise, the bearing may generate heat due to excessive axial thermal elongation. When this phenomenon occurs, the front or rear bearing covers should be removed slightly, or a thin paper pad should be added between the bearing cover and the end cover to form a sufficient gap between one end of the outer bearing cover and the bearing outer ring.

4. The end covers or bearing covers on both sides of the motor are not installed properly.

Solution: If the end covers or bearing covers on both sides of the motor are not installed parallel or the joints are not tightly secured, it will cause the ball to deviate from the track and rotate, resulting in heat generation. It is necessary to reinstall the end caps or bearing caps on both sides and tighten them evenly with bolts.

5. Severe wear or metal peeling of the balls, rollers, inner and outer rings, and ball racks.

Solution: At this point, the bearings should be updated.

6. Poor connection with load machinery.

The main reasons are: poor coupling assembly, excessive belt tension, inconsistent shaft center with the load machinery, small pulley diameter, too far away from the bearing, and excessive axial or radial load.

Solution: Correct incorrect connections and avoid bearings bearing abnormal forces.

7. The shaft has bent.

Solution: At this point, the force on the shaft is no longer purely radial, causing the bearing to heat up. Try to straighten or replace the bent shaft with a new one.

2、 How to protect motor bearings from overheating?

It can be considered to embed temperature measuring elements near the bearings, and then protect the bearings through control circuits. Generally, electric motors are equipped with temperature measuring components (such as thermistors) inside the motor, and two wires are connected to a dedicated protector. The protector sends a constant 24V voltage, and when the motor bearing overheats beyond the set value of the protector, it trips to provide protection.