The most common reason for bearing failure is improper lubrication. The lubrication mechanism for grease and oil is the same; oil blended with additives perform the actual lubrication by creating a lubrication film and hydrodynamic lubrication. The difference is the lubrication oil for a grease is suspended in a thickener. The lubrication oil in grease will squeeze out of the thickener under operation pressure.
Normally grease lubrication is used or selected if the lubrication requirements of the bearing will allow it. Grease systems are tend to be simpler than oil systems and are less expensive. Often components that move vertically or under heavy loads normally require a grease. Grease works well in bearing applications that operate at moderate speeds where temperatures are not excessively high.
Oil performs better under high speed and extreme friction applications. Also for systems regularly operating at high temperatures an oil circulation systems helps cool the components.
Grease lubrication versus oil lubrication for bearings both have their own specific advantages:
- Does not require a lubrication circulating system; pump, filter, sump, piping
- Better for leakage control
- Provides better seals against contaminants
- Can remain in equipment longer
- Lowers the risk of a dry start
- Worn seals and connectors can retain grease better, which lowers the risk of lubricant starvation and leakage
- Many grease lubricated bearings can operate for years without the need to repack the bearings.
- A better choice where a continuous supply of oil cannot be maintained
- Less consumption of the lubricant over time
- Easier to drain and replace oil lubricants
- Oiled bearing life can last longer than grease lubricated bearings.
- Easier to control the amount of lubricant to use
- Cleaner than grease due to capacity to carry away contaminants
- Better cooling properties
- Larger volume available allows for more available additive performance
- Avoids the problems associated with proper regreasing at proper frequencies
- Less energy consumption during operation
- Better cold start properties
Generally manufacturer equipment design will decide whether grease or oil lubrication will be required. When deciding on new equipment installation for industrial applications consideration can be made on equipment bearing design to best optimize lubrication.
Contact ALS Tribology for more information on grease and bearing lubrication.
David Doyle, CLS, OMA I, OMA II
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