Design greasing systems

Design greasing systems for electric motors

COMMON PROBLEM: Overheating due to excess grease – The balls of a bearing act as tiny viscosity pumps which roll on a small amount of oil film between the balls and the race. Too much volume will cause the elements to churn the grease, resulting in parasitic energy losses and high operating temperatures, which in turn increase risk of bearing failure. Hence you need to be very careful when design proper greasing system.

How Should the Grease Be Added?

Because the bearing balls act as tiny viscosity pumps, and the grease is less viscous when hot, a bearing should be regreased while the motor is running. If this is not practical, then perform regreasing immediately after the motor is removed from service while the grease is still hot. The steps listed below will help minimize overgreasing-related failures. The following steps should be performed in the sequence listed:

1. Ensure the grease gun contains the appropriate lubricant for the bearings to be regreased.

2. Clean the areas around the fill and drain fittings.

3. Remove the drain fitting and if possible, run a spiral bottle brush into the grease cavity and remove a small amount of grease to form an exit path. If the plunger-type drain plugs are used, this step can be eliminated.

4. Grease the bearing with the proper amount of grease. Add grease slowly to minimize excessive pressure buildup in the grease cavity.

5. If regreasing is performed with the motor out of service, operate the motor until bearing temperature stabilizes to allow thermal expansion of the grease. Ensure the drain plug is left out during this run unless the plunger-type is used.

6. After excessive grease has been purged, reinstall the drain plug and clean excessive grease from the drain area