Mixing different greases, even those with similar thickener types, can sometimes lead to ineffective lubrication resulting in damage of the lubricated components. If not spotted soon enough this may lead to equipment failure.
Many rolling element bearings require relubrication of small quantities of grease between grease flushing intervals. This is best done with a low-pressure grease gun. If seals are in good condition, the quantity of grease needed may be small and infrequent.
- Check the amount of grease in the bearing – remove fitting or grease plug to allow excess grease to come out.
- Check bearings and seals for excess leakage.
- Apply a few “shots” of grease at a time.
Ahead of applying a new grease, thoroughly clean – or flush out – the previous grease from the bearing. This avoids compatibility issues and helps ensure that the new grease can perform at an optimum level.
If this cannot be carried out, mitigating actions should focus on minimizing the amount of the displaced grease remaining in the application, such as by increasing relubrication frequency to facilitate a purge of old grease in a timely manner.
Where bearings are subject to contamination, more frequent relubrication may be necessary.
Contamination will lead to unusual operation such as hot, noisy, vibrating or leaking bearings. Be sure to spot, report and act on those.
Be sure to clean up all excess grease and dirt from the bearing and surrounding areas. Excess grease and dirt on external surfaces acts as an insulator and prevents heat dissipation. Additionally, excess grease on the external surfaces and floors can introduce a safety hazard to personnel.
Bearing manufacturers frequently recommend the amount of grease to apply to a bearing by weight or volume. The grease gun can be calibrated by counting the number of shots to dispense a known amount of grease.
Unfortunately, there's no one single answer, because there's a long list of factors that influence relubrication frequency.
Generally, the smaller the bearing and faster the speed, the less frequent the interval for relubrication with grease. Larger, slower bearings require more frequent relubrication.
Different types of bearings require different relubrication frequencies:
- Radial ball = base interval
- Cylindrical roller = 5 times as frequent
- Thrust-ball and roller = 10 times as frequent
Follow these steps for bearings equipped with fitting and drain:
- Remove lower drain plug; clean out any hardened grease.
- Wipe the grease fitting clean.
- Pump grease into the fitting until old grease is purged and new grease appears. If it is safe and practical, it is preferable to run the machine while performing this task.
- While the drain plug is removed, allow the machine to run at operating temperature. This allows the grease to expand and forces the excess out the drain orifice, thus relieving the internal pressure. The excess grease will cease draining when normal pressure in the bearing housing is reached (approximately 10 to 30 minutes).
- Clean and replace the drain plug.
Follow these steps for bearings equipped with fitting and no drain:
- If safe, remove fitting while equipment is running at operating temperature to allow any purging of excess grease in the bearing.
- Clean and replace fitting. Pump a limited quantity of grease into the bearing to avoid rupturing the grease seal.
- Remove the fitting and allow the equipment to run at its operating temperature for several minutes to purge excessive grease. If no grease purges, the bearing was most likely very dry; this requires repeating steps 2 and 3 until excess grease purges.
- Replace the grease fitting.
Follow these steps for bearings equipped with relief-type fitting and no drain:
- Clean the fitting and pump grease into the bearing until grease relieves from the relief fitting.
- If, after considerable grease pumping, grease does not come out of the relief fitting, the relief slot may be plugged. Remove the relief fitting and clean the relief slot or replace with a new fitting. Repeat step 1 after the fitting has been cleaned or replaced.
- Run the equipment at operating temperature and check for excess grease at the relief fitting.
An insufficient amount of grease could lead to bearing failure due to lack of lubrication. On the other hand, over-lubrication can also lead to bearing failure and cause problems due to migration of the lubricant into the windings.
Higher temperatures increase a grease oxidation rate, typically doubling it for every 10°C (18°F) rise above 65°C (150°F). Grease softens as temperatures increase and may become fluid enough to leak out of housings. And oil separation and volatility also increase with temperature.
Therefore, high temperature operation requires relubrication more often; high-temperature greases that have the capability to maintain structural stability, oil separation, volatility and oxidation under control can help extend that frequency.
Intervention on machinery requires a prior risk analysis to identify potential mishaps during or as a consequence of the maintenance, and therefore determine a safe sequence of events and required protective gears.Beware in particular of high pressure buildup in the dispensing devices or in the bearing when conducting regreasing operations.
During application, first check the amount of grease in the bearing by removing the fitting or grease plug and see if any grease is released. Then check the bearings and seals for any excess leakages.
Yes, with the following conditions:
- If the amount of oil is small, covering only low spots in the surface of the grease.
- The grease readily absorbs the oil upon stirring.
A bearing should never be greased more than two-thirds full – leaving one-third air space – to allow for optimal operation.Refer to the bearing builder manual to determine the exact grease quantity required.
Store your bearings in their original packaging. The best ways to store bearings is horizontally in a dry place and in their original, unopened package. Never place bearings on a dirty surface.
Rotate your bearings while they’re in storage. For greased bearings, periodically turn over sealed and shielded bearings to prevent the grease from settling on one side.
Use identical bearings for replacements. If needed, contact your authorized bearing distributor or manufacturer for interchange information.
Never wash new bearings before installation. The bearing manufacturers take great care to package and ship bearings that are dirt-free and ready for lubrication. There’s really no need to wash them or remove protective slushing compound.For more information please consult the Technical Topic titled “Electric motors – care & maintenance.”
Excessive noise, vibration and temperatures. Assuring proper vigilance for these signs will go a long way in maintaining your operations. Condition monitoring instrumentation is available to help you spot bearings in poor operating condition.For more information please consult the Technical Topic titled “Electric motors – care & maintenance.”