For electric motor products, the bearing system and the collector ring system of wound rotor motors require regular maintenance and servicing because of material wear and consumption.Two very common typical cases are given as examples: Some manufacturers do not take anti-loosening measures for the motor fasteners, resulting in the loosening and falling off of the fastening bolts; some motor manufacturers do not design an oiling device for the bearings without stopping the machine in order to save costs, which leads to the motor seizing and burning out due to lack of oil in the bearings.
Factors affecting the quality of the motor bearing system
From the failure cases of rolling bearings in oil-lubricated motors, it can be seen that the majority of failures are caused by insufficient lubricating oil viscosity. The lower the viscosity of the lubricating oil, the worse the bearing’s load-bearing capacity, and the lubricating oil film is more prone to rupture. The metal materials on the relative moving surfaces inside the rolling bearing will come into direct contact, resulting in increased friction and accelerated wear, and the service life of the rolling bearing will be significantly shortened or it may suffer from burnout or fracture accidents. However, if the viscosity of the lubricating oil is too high, it will increase the friction resistance, generate more heat due to the mixing of the lubricant, and increase the energy consumption of the system. On the other hand, for rolling bearings operating under special conditions such as high speed, high load, and high temperature, there may be special requirements for rust prevention, oxidation resistance, anti-wear, and improving the adsorption capacity of the lubricating oil. Therefore, the selection of lubricating oil mainly involves determining the viscosity grade of the lubricating oil and the types of additives used or choosing different lubricating oil products with certain additives. The following factors have a significant impact on the lubrication of motor bearings.
1.Motor speed
The higher the motor speed, the more it is advisable to choose lubricating oil with a lower viscosity to prevent an increase in frictional resistance and excessive heat generation; conversely, in low-speed conditions, a lubricating oil with a higher viscosity should be used to improve the load-bearing capacity.
2.Operating temperature
The working temperature affects the viscosity change of the lubricating oil and the lubrication effect. Therefore, when the working temperature is low, a lubricating oil with lower viscosity should be selected; when the working temperature is very high, a lubricating oil with high viscosity or one with appropriate additives should be chosen. Depending on the different environmental temperatures, the viscosity of the selected lubricating oil should also change accordingly. For example, when lubricating the same bearing in winter, a lubricating oil with lower viscosity should be selected compared to that in the south or in summer. When the working temperature frequently changes, a lubricating oil with excellent viscosity-temperature characteristics should be chosen, that is, the viscosity of the lubricating oil should not change much with the increase or decrease of the working temperature to ensure that the oil film thickness remains stable within a certain range.
3.Kinetic property
During movement, there are impacts, vibrations, frequent changes in load, speed variations, starts, stops, reversals, and when performing reciprocating or intermittent movements, it is not conducive to the formation of oil films. Therefore, a lubricating oil with a higher viscosity should be selected. Sometimes, grease or even solid lubricants may be used to ensure reliable lubrication.
4.Working load
The greater the load borne by the rolling bearing, the higher the viscosity of the lubricating oil should be selected. The lubricating oil should also have good fluidity and extreme pressure properties to prevent the lubricating oil from being squeezed out of the friction pair or causing direct contact between the metals.
5.Bearing accuracy
When the friction surfaces of the bearing movement are rough, it is generally advisable to use oil with higher viscosity to withstand the local large pressure formed due to poor contact. While when the precision of the friction surfaces during movement is high, low-viscosity lubricating oil should be selected to reduce unnecessary energy loss and temperature rise.
6.Environmental conditions
When the bearings operate under conditions of dampness, presence of corrosive gases, low temperature, dust, and strong radiation, the lubricating oil is prone to be contaminated and deteriorated. At this time, lubricating oil with strong resistance to water, wear resistance, corrosion resistance, cold resistance and radiation resistance should be selected. In areas where there is splashing water, emulsified liquid spraying, humid air or severe dust and debris, lubricating oil is generally not suitable and grease should be used instead.
7.Structural features
The smaller the radial clearance of the rolling bearing is, the higher the machining accuracy of the friction surfaces will be, and the lower the viscosity of the lubricating oil should be.
8.Bearing hardness
When the hardness of the friction surface of the bearing movement is low, high-viscosity lubricating oil should be selected and the oil quantity should be sufficient; conversely, the viscosity of the lubricating oil can be reduced. To fully utilize the effect of the lubricant, it is necessary to choose the appropriate lubrication method and high-quality lubricant for the usage conditions. During the assembly of the motor, the lubricating grease injected into the bearing chamber must be clean. If the lubricating grease is not clean, contains impurities, especially hard impurities, it is easy to cause abnormal wear of the bearing and lead to bearing failure. The filling amount of the lubricating grease should be appropriate. If the addition amount is too little, the bearing will be heated due to intermittent lack of oil and dry grinding, causing bearing failure; if the addition amount is too much, the lubricating grease will be heated by stirring and cause bearing failure, and it will also become thin and splash out to contaminate the interior of the motor.
Post time: Apr-01-2026