Discovering the Secrets of Proper Bearing Lubrication

Dave Garner, Dow Corning

At the heart of almost every industrial facility are electric motors, which can render equipment inoperative should their rolling element bearings fail—an occurrence more common than necessary due to strain resulting from improper lubrication. Lubricating your motors properly is easy, but not exactly simple. If you fail to consider all factors involved, your equipment will be predisposed to early failure. Investing in the right tools is a crucial part of maintaining a structured lubrication program and addressing all factors involved. 

Typical Causes of Failure

There are several failure modes to keep in mind when maintaining your electric motors, though statistics show 50% of bearing failures are related to lubrication. Below are a few common lube-related failure modes:  

Loss of Lubricant

If the bearing is not regreased at the appropriate interval with the proper amount of grease, or if the oil separates from the base thickener of the grease by overheating, loss of lubricant and lubrication can occur and contribute to equipment failure. This situation commonly occurs when operators use a time-based regreasing schedule. While regreasing after a certain amount of operating hours is consistent, it usually does more harm than good due to the fact that many variables play a role in when a bearing needs lubrication. Ultrasound monitoring systems assist with detecting the right time to regrease, reducing your chances of oil separation. 

Grease Incompatibility

Not all greases are compatible with each other. It's common to think "grease is grease" and top off a bearing with the first grease you can get your hands on. Using a single-point automatic lubricator ensures there is only one type of grease being used consistently. It is important to stay with the same grease or a compatible substitute for the life of a bearing. 

Incorrect Grease

Be sure to use the correct grease for your application. Some bearing designs and applications need only non-EP or general purpose (GP) grease while others require extreme pressure (EP) grease. If you're unsure of which type of grease to use, consult the OEM. 

Grease Degradation

Grease hardening, chemical breakdown caused by excessive heat, and oil separation from grease base are common types of grease degradation. Of course, excessive heat is caused by friction, which is caused by improper lubrication. Keep a documented list of lubrication tasks and choose condition monitoring tools that will alert you of any potential malfuncition. 

Excess Lubrication

This occurs mainly with open face bearings, when excess grease can cause a temperature increase in the bearings due to churning and also be pushed back into the windings of the motor and can also cause overheating and deterioration of the electrical insulation on the windings. A beneficial switch to make is transitioning from manual regreasing to automatic regreasing. Manual regreasing leaves a lot of room for human error, while automatic regreasing equipment provides the necessary precision to optimally lubricate the bearings. 

Regreasing

If you are choosing manual regreasing methods, procedures play a large role in preventing bearing failure. Following strict regreasing steps in the correct sequence helps to minimize failures:

  1. Regrease a bearing while the motor is running and hot, or after the motor is removed from service and the grease is still hot. Under operational conditions, the grease is less viscous.

  2. Ensure the grease gun contains the right lubricant for the bearings to be regreased.

  3. Clean the areas around the fill and drain fittings to ensure contaminants are not introduced into the bearing cavity.

  4. Remove the drain fitting to allow any excess grease to escape from the bearing.

  5. Leave the drain plug out for the duration of the regreasing process.

  6. With the motor running at operating temperature, add the recommended quantity of grease, or add slowly until it begins to move into the relief tube.

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

Upon installation, monitor motor noise and vibration to establish a baseline. At regular intervals, check these measurements; any sudden or significant change should result in inspection of the bearing lubrication. Motor bearing temperature is also a valuable analysis tool and should be monitored and trended over time. An increasing trend could indicate the need to renew the grease or that the bearings are being overgreased or that a bearing needs to be replaced. Finally, pay attention to any high-frequency (ultrasonic) noise output or vibration level because it may be a sign of bearing lubrication trouble.

 

Regardless of the tools and technology you choose to use, the biggest secret to lubrication success is mindset. Reframing your mindset from reactive to preventive will help you stop problems before they start, which benefits everyone from the operators to plant managers. 

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