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The concept of bearing life
Bearing life is the most important performance index of an anti-friction bearing, and it is also one of the most complex parameters to be considered when selecting a bearing. Bearing life refers to the number of revolutions or the number of running hours that a bearing can run in a given working environment before it becomes unusable. In practical applications, bearing life is described by the amount of material that a bearing can tolerate before it fails or begins to operate inefficiently. Bearing life is affected by a number of factors, including load, speed, lubrication, environmental conditions, frequency and amplitude of shocks, misalignment, and manufacturing tolerance.
Various calculations can be made to determine bearing life, but the most reliable method is known as the L10 life calculation. This calculation was developed by the American Bearing Manufacturers Association (ABMA) and is the accepted standard for determining bearing life. This calculation takes into account the bearings load, speed and lubrication conditions and predicts the bearing life for a 90 percent reliability rate. The L10 bearing life is often defined as the length of time that 90 percent of a group of identical bearings subjected to the same conditions will run before the first bearing fails.
The formula for calculating L10 bearing life is fairly simple. It takes into account the equivalent dynamic bearing load (Pr), the bearings speed rating (N); the bearing races diameter (D); and the bearing operational life (logarithmic life, t):
Life(L10)in hrs =(P x 106) x (N x 106) / (60 x D3) x t
This formula can be used to calculate the L10 life of any bearing, as long as its load, speed and diameter are known. When the bearing is being lubricated, the L10 life is determined based on the dynamic equivalent bearing load, or Pr. For example, if the dynamic equivalent bearing load is greater than or equal to 200 kN, the bearing is fully loaded, and the L10 life is calculated based on the maximum dynamic equivalent bearing load.
In order to accurately estimate the service life of a bearing, the L10 life calculation should be used in combination with the rating life calculation. The rating life calculation is the ABMAs rating for a bearings life for a given load, speed and lubrication level. For example, a bearings rating life for grease lubrication is calculated based on a Pr of 90% of the static equivalent bearing load, speed at 10 million revolutions, and lubrication with a constant flow of lubricant at the same temperature. The rating life is the length of time that 100 percent of a group of identical bearings under the same conditions will run without the first bearing failing.
The L10 life calculation is a reliable calculation method when it comes to estimating the service life of a bearing. It takes into account a variety of factors that can influence the bearing life, such as load, speed, lubrication conditions, and other environmental conditions. The combination of the L10 life calculation and the rating life calculation helps to ensure that the service life of a bearing is correctly calculated and accurately estimated.
