Bearings must be properly lubricated for optimal performance and long service life. The consistency of grease lubricants has a significant impact on both. Understanding the difference between the worked and unworked consistency is important for proper lubrication.
Consistency is measured by how deeply a cone-like device sinks into worked and unworked grease. Predictably, the penetration level will be higher for unworked than worked grease, which tends to thin out during operation.
It is important to know the spread between these penetration levels. For example, there is little difference between the worked and unworked consistency of a typical non-channeling grease for instrument bearings. This indicates the grease is fairly light to begin with, and maintains its consistency over its service life.
Heavy channeling greases typically have low penetration levels with little difference between their worked and unworked consistency. These greases are used in high-speed applications, where they move to one side of the interface, leaving a thin film of lubrication.
Another small group of greases with large spreads in penetration levels are used to minimize fretting corrosion. Large differences in their worked and unworked states mean these greases start out quite thick, thin to the consistency of heavy oil, and revert to their original unworked consistency.