Reliability and maintenance engineers are often given the task of improving the reliability of bearing arrangements in a variety of applications. Lubrication is a key area to explore for improvement opportunities. Improper greasing of bearings, particularly motor bearings, would be at or near the top of anyone's list of machinery in need of correction.
The term bearing refers to any mechanism intended to regulate the movement of and support a turning part. Grease is by far the most popular lubricant for rolling element bearings in electric motors.
Studies shave shown that 42% of all electric motor failures are due to bearing failure and experts have estimated that a striking 91% of electric motor bearing failures are premature. Almost every industrial facility has a large population of electric motors and other applications where rolling element bearings are employed.
Evidence of lack of precision in greasing can be quite easily found in almost any industrial facility:
- Hot running bearings
- Grease contaminated motor winding
- Piles of grease around machine mounting components
- Overgreasing, by far the most prevalent greasing problem
Bearings can not simply achieve their design life if they are not provided with a sufficient supply of fresh, stable lubricant.
There are several types of grease related bearing failures:
- Loss of lubricant - The grease cavity is not packed with the proper amount of grease during installation, the bearing is not re-greased or the oils is removed from the base by bearing overheating
- Grease Incompatibility - Not all greases are compatible with each other, therefore it is important to stay with the same grease
- Wrong Grease - the correct grease has to be used for the correct application. Some bearing design and applications only need General Purpose (GP) grease, others need Extreme Pressure (EP) grease
- Overheating due to too much grease - too much grease between the balls and the races will cause the balls to slide instead of roll, which will result in a hot running bearing and possible premature failure.
Other failure modes for rolling element bearings can be installing the incorrect bearing or excessive thrust loads.
Smart Lubrication Tip:
Problem: You see bearing failure due to the lubricant failure in aggressive environment under extreme temperatures from -55 deg C to up to +250 deg C.
Solution: Under these extreme conditions you should use Molykote HP-300, which is synthetic PFPE grease, especially designed for high temperatures.
This information has been sourced, reviewed and adapted from materials provided by Dow Corning.
For more information on this source, please visit Dow Corning.