Howard W Penrose, Ph.D., General Manager, ALL-TEST Pro, writes an article regarding the proper method of greasing electric motors:
The lubrication of electric motors can be a critical maintenance practice for improved motor system reliability. Unfortunately, a significant amount of misinformation is provided within industry. For instance, those with a lack of knowledge of how motors and bearing work will often promote the ‘purging’ of motor grease, frequently. This practice puts undue stress on the motor, reducing its life and increasing the chance for both bearing failure and winding contamination.
Grease purging is the practice of forcing grease completely through the bearing housing and bearing until old grease is removed and new grease shows at the grease relief plug. While this practice is performed in highly contaminated environments, it provides many dangers to the reliability of the motor. There was many a time, as a motor repair journeyman, that I would disassemble or troubleshoot a motor winding or bearing failure in which the motor was full of grease. Some grease additives will react with winding insulation or will just provide a thermal blanket, reducing the life of the winding, when purged grease leaks through the bearing or bearing cap and onto the winding, even when you have the grease relief open.
Dr. Penrose explains how a bearing works, precautions in motor greasing, procedures, and a schedule for greasing. He concludes:
It is recommended that the type of grease used on each motor is recorded in order to avoid premature bearing failure. In many cases, you may be able to standardize the type of grease used in a majority of your motors. It is also good practice to let your motor repair center know the type of grease in case the standard grease used by the repair center conflicts with your standard grease.
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For more information on lubrication schedule, visit our technical reference page.