Bearing life refers to the expected operating life of a bearing before it reaches a predefined level of wear or damage. It is typically defined as the number of revolutions (or operating hours) that a group of bearings can endure before a certain percentage of them will develop signs of fatigue damage.
Rating life, on the other hand, is an estimation of the average or median life expectancy of a specific group of bearings under ideal operating conditions. It is expressed as a standardized L10 life, which represents the number of revolutions (or operating hours) that 90% of a group of identical bearings are expected to complete or exceed before the first signs of fatigue occur.
The bearing life calculation is based on the ISO 281 standard, which takes into account the load, speed, and basic dynamic load rating (C) of the bearing. The basic dynamic load rating represents the load at which a bearing has a calculated rating life of one million revolutions.
To calculate the bearing life, you can use the following formula:
L10=(C/P)^p
Where:
L10 = Rating life in millions of revolutions
C = Basic dynamic load rating of the bearing
P = Equivalent dynamic load acting on the bearing
p = Exponent based on the type of bearing (p = 3 for ball bearings, p = 10/3 for roller bearings)
The equivalent dynamic load (P) is determined by considering the actual loads acting on the bearing, like radial load, axial load, and moment load. If multiple loads are present, they should be combined into an equivalent load.
It's important to note that the bearing life calculated using this formula is an estimation, and actual operating conditions, such as external factors, lubrication, and maintenance practices, may influence the actual bearing life.
Manufacturers often provide bearing catalogs with load and speed ratings, and specific formulas or calculation tools for bearing life may be available from the manufacturer or industry standards organizations. Consulting these resources and considering the specific bearing type and application is recommended for accurate bearing life calculations.