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The Basics of Bearing Life



The downtime associated with bearing failure can be devastating, but understanding the basics of bearing life can provide valuable insight into preventing extended periods of downtime and improving application efficiency. The most common form of rolling-element bearing failure mode is fatigue spalling of a bearing race or rolling element which occurs when a region of maximum shear stress below the contact surface grows into a crack network. Failures other than those caused by classical rolling element fatigue can be drastically reduced if the bearing is properly designed, handled, installed and lubricated.

The term bearing life, defines the fatigue life that is exceeded by 90 percent of the bearings at the point which 10 percent of the bearings fail. Also known as bearing L10 Life this data is calculated and plotted on a Weibull plot to show the amount of failures based on bearing revolutions. L10 life is critical in a number of industrial applications where the time between removals or overhauls of the equipment is dictated by the system bearing life, although, in some noncritical applications bearings can sometimes run twice as long as the L10 life if faced with raceway spalling. Typically most suppliers refer to the L10 life as the standard selection criteria but others do take into account the median life or L50 at which 50 percent of the bearings have failed, although it is not recommended.

Because of changes in the global supply chain, bearings produced by the same manufacturer can vary considerably in L10 life. The same bearing, produced by the same manufacturer, may have completely different L10 lives if one was made in the United States plant and the other in their overseas facility. This presents a real issue for bearing manufacturers who want to ensure their product is consistent across all facilities, and for OEMs who need a reliable product that will perform consistently to their customer’s expectations. Napoleon Engineering Services dynamic test rigs can aid in the process of ensuring product consistency, qualifying new sources of supply and evaluating bearing design by determining L10 life. Each test rig is customized to specific application demands including speeds and loads which provides data consistent with bearing life in the actual application. Understanding L10 life and bearing performance is a major step that can help bearings and applications perform consistently and efficiently.

Additional Testing Links
Bearing Testing – Life (Dynamic) Testing
Bearing Testing – Environmental
Bearing Testing – Impact/Static Load
Bearing Testing- Bearing Test Rig Manufacturing
Bearing Failure and The Basics of Bearing Life