Maximising for Longevity: How to Deal with Electric Motor BearingsSeptember 10, 2020
Electric motor bearings play numerous significant roles in electric motors. First, these bearings are intended to support and locate the rotor. They also help in maintaining the air gap small and consistent throughout the motor operations. Ultimately, electric motor bearings are responsible for transferring and moving the loads from the shaft to the motor frame.
Locating bearings that are found on most medium and huge electric motors are deep-groove ball bearings. Non-locating bearings, on the other hand, are comprised of ball bearings, cylindrical-roller bearings, or toroidal-roller bearings. Vertical machines maximise deep-groove ball bearings, angular-contact bearings, or spherical-roller thrust bearings.
For these electric motor bearings to function well, they must be able to sustain both low- and high-speed operations while minimising friction, noise, and power consumption. So, to maximise the functionality and longevity of electric motor bearings, here are some elements that you must look out for.
Bearings found on electric motors must have a minimum load so that their rolling elements can rotate and subsequently form a lubricant film. Without a minimum load, the bearings would skid, which elevates the operating temperatures of the motor and diminishes the lubrication. For roller bearings, its minimum load must be equal to about 0.02 times the dynamic radial-load rating. Ball bearings, on the other hand, must have a minimum load of about 0.01 times the same dynamic radial-load rating.
Related to the load of bearings, the connector or coupling type between the drive and the driven unit can likewise identify the load of motor bearings. If the coupling drives are misaligned, then additional forces like a magnetic pull from unsymmetrical air gaps, out-of-balance forces, pitch errors in gears, vibration, and thrust loads can negatively affect the bearing and motor life. For perfect alignment, the driven equipment must be secured first before installing the coupling.
Another element that affects the life of motor bearings is the operating speed of the motor. Operating speed can easily affect the operating temperature of the motor, which then influences bearing and lubricant life. Ball bearings can easily perform under high-speed applications, while precision or hybrid bearings that are coupled with ceramic rolling elements can work with extremely high-speed operations. As a rule of thumb, the motor speed must be capped within the bearing operating-temperature limits.
Electric motor bearings that are lubricated with grease can generally run at moderate speeds and temperatures. Grease is a lubrication option that simplifies housing and sealing designs, adheres to critical surfaces, and protects the bearings from various contaminants. The use of oil as the lubrication, on the other hand, can only be done if the bearings are used in extremely high rotational speeds or operating temperatures. Huge electric motors can mostly utilise oil for the lubrication of their bearings.
The longevity of electric motor bearings can significantly decline if they are exposed to water and humidity. The heat from running motors can easily evaporate moisture, but the condensation that is created whenever the motor powers down can accumulate and affect the bearings. Lubricants that are enhanced with rust inhibitors can be applied to bearings to prevent getting damaged. Electric arcing can also pose a problem to electric motor bearings since it can melt and retemper bearing surfaces. The use of specialised ceramic coatings can electrically insulate the bearing and help it avoid damages.
The longevity of electric motor bearings can be extended if you consider and check these elements regularly. Maintenance and inspections can also help you prolong the service life of your motor bearings.
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