The importance of bearing lubrication in electric motors.

Maintaining lubrication in electric motors is important as it:

• Reduces bearing friction.
• Helps prevent undue temperature rises and dissipate some of the heat generated.
• Helps prevent corrosion.

While most lubrication applications are ambient temperature based there are also extremities.  For instance, lubrication choice differs for electric motors at the top of Mount Ruapehu to a high heat application or the food industry.  As well as being application-based, lubrication also depends on:

• operating temperature
• motor shaft speed
• bearing size
• bearing load
• hours of operation
• environmental conditions/ contaminants
• vibration levels

It is also important the correct lubrication and/or mix of lubricants are used for application and relubrication.  Mixing incompatible lubrications will result in rapid bearing failure. The only sure way to prevent incompatibility issues is use the same lubrication, unless BOTH lubricant manufacturers state BOTH lubricants are compatible.  If in doubt, purge it out!

Lubrication levels for ball and roller bearings differ for horizontal and vertical shaft applications.

• Horizontal shaft applications the oil level should be maintained at approximate centre of lowest rolling element when motor is not operating.
• Vertical shaft applications the oil level should be maintained at approximately 50% submergence of rolling elements.

Relubrication frequency depends on the operating conditions, type and quantity of lubrication.  As a guide operating temperatures 50°C or less replace lubrication once a year.  For temperatures 80°C to 100°C replace at least quarterly.  For critical equipment, test lubrication at least quarterly to determine when lubrication replacement is required. Over and under lubricating can cause bearing failures.  Always use calibrated grease guns! 

Procedure for ball and roller bearings lubrication

1. Relubricate with shaft stationary & warm motor (near operating temperature).
2. Locate lubrication inlet and clean around it. Replace pipe plugs at inlets with lubricant fittings.
3. Remove relief plug and clean off any caked lubricant.
4. Add recommended volume of recommended lubricant.
5. Use a calibrated hand operated grease gun.
6. Run motor for 1/2 hour with relief plug removed.
7. Replace pipe plugs and wipe off excess lubricant.

If the motor manufacturer instructions/data sheet are not available, determine the appropriate lubricant through sample testing and lubrication intervals under the motors normal operating conditions. 

Please note sealed bearings do not require relubrication.

References

EASA BearingLubricationFreqQty_0119

EASA Electric Motor Bearing Lubrication_webinar_220406