Causes of Heating and Damage to Motor Bearings

The bearing system is a crucial working system for motor products. When there is a problem with the bearing system, it can cause premature wear, disassembly, and other issues due to heating. Bearings are important components for positioning motor products, and are associated with other components to ensure that the relative position of the rotor in the radial and axial directions of the motor product meets the requirements.

When there is a problem with the bearing system, the precursor symptoms are noise or heat. Mechanical failures generally manifest as noise first, then begin to heat up, and later develop into bearing wear. The specific symptoms are increased noise, and even more serious problems such as bearing disassembly, motor shaft holding, and winding burnout may occur.

What are the causes of bearing heating and damage?

(1) Assembly and usage factors. Anyone who has been to a bearing manufacturing factory knows that the control of the bearing manufacturing process is particularly strict, especially for some better bearing manufacturers. The key processes of bearings are carried out in a very clean environment; However, in the assembly and later use and maintenance of the motor, sometimes it is not satisfactory: for example, during the assembly process, poor environmental conditions can contaminate the bearings themselves, impurities (particles, other oils, water, etc.) can be mixed into the lubricating oil (or grease), collisions with the bearings during the assembly process, abnormal stress during the bearing assembly process, etc., all of which can cause problems with the bearings in a short period of time. In the process of use, if the motor is placed in a damp or more harsh environment, the bearings may rust, which is also a problem for the bearing system.

Regarding the bearing system, another issue is the sealing between the bearing inner cover and the bearing outer cover, which is what we call the standardization of the sealing oil groove processing. If the processing is not standardized or the diameter of the bearing inner and outer covers exceeds the tolerance, it is also easy for foreign objects to enter the bearing and cause malfunctions.

(2) Problems caused by unreasonable radial fit of bearings. For any bearing product, there are initial clearance and working clearance. Once the bearing is installed, especially when the motor is running, the clearance of the bearing is the working clearance. Only within the normal range of the working clearance can the bearing work normally. In practice, the fit between the inner ring of the bearing and the shaft, the fit between the outer ring of the bearing and the end cover (or bearing sleeve) and the bearing chamber, all directly affect the working clearance or relative operation of the bearing: when the bearing is in a tight clamping state, the working clearance will decrease and the bearing will heat up; Similarly, when the fit is too loose, the problem of bearing runout may occur. When the size of the bearing chamber exceeds the positive tolerance, there may be a problem of running out of the outer ring, that is, the outer ring of the bearing and the bearing chamber undergo relative motion in the circumferential direction. When the diameter of the bearing position exceeds the negative tolerance, there may be a problem of running out of the inner ring of the bearing, that is, the inner ring of the bearing and the bearing position undergo relative motion in the circumferential direction.

(3) The problem of misalignment caused by the lack of concentricity between the stator and rotor. In theory, when the stator and rotor of a motor are coaxial, the radial clearance of the bearings should be relatively uniform during motor operation. If the stator and rotor are not concentric, it is equivalent to the center lines of the two not coinciding, but intersecting. Taking a horizontal motor as an example, the rotor will not be parallel to the foot surface, causing the bearings at both ends to be subjected to a radial and axial external force, which will naturally cause the bearings to work abnormally during motor operation.

The influence of lubrication on the operation of motor bearings

(1) The matching relationship between the performance of lubricating grease and the operating conditions of the motor. In the technical conditions of the motor, the standard operating environment of the motor will be specified, such as ambient temperature, altitude, etc. When selecting lubricating grease for standard motors, these conditions will be followed. However, for motors operating in special environments, the operating environment may be harsh, such as high temperature environments, low temperature environments, etc.

For particularly cold climates, lubricating grease must have sufficient low-temperature resistance. After a batch of motors were taken out of the warehouse on a cold day, the manual motor could not rotate, and there was obvious noise during power on operation. The motor sound was normal after running for about 5 minutes. After verification, the lubricating grease used in the motor does not meet the requirements. Similarly, for motors operating in high-temperature environments, such as air compressor motors, especially in the warmer southern regions, most air compressor motors operate in environments with temperatures above 40 degrees Celsius. Coupled with the temperature rise of the motor, the bearing system temperature will be very high, and ordinary lubricating grease will degrade and fail due to excessive temperature, resulting in the loss of bearing grease. The bearings are in a non lubricated state, and in a short period of time, the bearings will heat up and be damaged. In severe cases, the windings may burn out due to high current and temperature.

(2) Excessive lubricating grease causes bearing heating. From the perspective of heat conduction, bearings also generate heat during operation, which is dissipated through related components. When there is too much lubricating grease, it accumulates in the bearing system cavity, which is extremely unfavorable for heat dissipation. Especially for bearing systems with larger inner cavities, this problem is more severe. We once conducted a test using an infrared instrument to measure the temperature of the bearing system. We checked the points with relatively high temperatures and found that there was a lot of grease accumulation in the outer cover of the bearing. After removing it, the temperature naturally decreased.

This involves two issues, one is the filling amount of lubricating grease, and the other is a very important issue in the design of bearing related components, mainly involving the oil baffle and bearing inner and outer covers.

(3) The rationality of the design of bearing system components. Many motor manufacturers have made improvements to the design of bearing system components. In addition to the fitting tolerances we discussed in the previous issue, improvements have been made to the bearing inner cover, bearing outer cover, and oil baffle to ensure the circulation of an appropriate amount of grease during bearing operation, meet the necessary lubrication requirements, and prevent heat resistance problems caused by excessive grease filling.

(4) Regular replacement of lubricating grease. When the motor is running, the lubricating grease should be replaced according to the frequency of use. During the replacement process, the original grease should be cleaned and replaced with the same brand of grease; For this issue, normal manufacturers will indicate the replacement cycle and specific brand of lubricating grease.

HZC-3980 Circuit Breaker Analyzer Testing Equipment