The main functions of a rolling bearing are to carry load and provide near frictionless environment to support and guide a rotating shaft. Rolling bearings have four components: outer race, rolling elements, inner race, and a cage to support and guide the rolling elements. The most common rolling bearing is ball bearing.
Every bearing has an expected service lifetime. Research has shown that most bearings fail below their predicted lifetime. These are some reasons why bearings fail prematurely.• Manufacturing errors
• Incorrect bearing selection
• Alignment problems
• Incorrect lubrication problems
• Excessive load
• Environment (heat, humidity, etc)
The actual life span of a bearing is very difficult to predict. In theory, an average life span can be calculated as a function of dynamic load and the nominal load of the bearing. The following formula indicates the connection between the expected life span of a bearing and its operation load.
L10 = (C/P)r
L10 = basic rating life in a million cyclesC = basic dynamic bearing load rating P = equivalent dynamic bearing constant, 3 for ball bearings and 3.33 for roller bearings. r = exponent for the life equation
The equation suggest that bearing load is proportional to the rating life. This means excessive load or vibration can significantly reduce the expected life span of a bearing. Condition monitoring plays a very important role to monitor bearing fault stages. The bearing can then be replaced before it fails to avoid catastrophic failure, which can result in secondary damage.