Why care about proper motor bearing lubrication?
According to EASA (Electrical Apparatus Service Association), the motor component with the highest failure rate is the bearing. Of all the different types of motor failures, 51% of these failures are bearing failures. Bearing lubrication is one of the many aspects of motor care and one of major importance to the life of a motor. Getting it correct isn’t as easy as it might seem. It will take some investigating, documentation, and a lot of hard work. Arbitrarily re-lubricating motor bearings will result in one of two things. The bearings will be either over lubricated or under lubricated. Either one will reduce the expected life of the bearing. What needs to happen is to find that happy medium where the bearing is getting the correct amount of lubrication.
Bearing lubrication details
Bearings come in all shapes and sizes. They can be sealed (RS, 2RS) shielded (Z, ZZ) or open. These identifying characters are found in the bearing numbers on the nameplate of the motor. Lubricant compatibility is of major importance. If two incompatible greases/oils are mixed together, they will lose their lubricating abilities very quickly. If in doubt, contact your lubricant provider or the motor manufacturer. Sealed bearings are basically lubricated for life. When determining the frequency of re-lubricating a motor, there are many criteria that need to be addressed.
Some criteria to determine frequency:
- Type of grease,
- Motor operating temperature,
- Motor speed,
- Bearing size,
- Environmental conditions, and
- Duty cycle, to name just a few.
The bearing type and size in conjunction with the motor’s speed need to be considered. Large or small bearings turning at 3600 RPM are working much harder than if they were turning at 900 RPM. Roller bearings require more frequent lubrication than ball bearings because of their heavy radial load. Motors operating 24/7 located in a clean room may not require as frequent lubrication as a motor operating only 8 hours a day in a cement plant. The lubricant not only provides the bearing with grease, it also, to a slight degree, provides the bearing with protection from contaminates.
Eliminating contaminates from the lubrication will definitely have an effect on bearing life. Pumping clean grease into a fitting covered in dirt is defeating the purpose. New grease can be contaminated before it leaves the storage location. Keeping grease containers sealed and the storage locker clean and free of debris, will lower the risks of adding contaminates when re-lubricating bearings.
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