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TECHNICAL INSIGHT

TECHNICAL INSIGHT
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TECHNICAL INSIGHT A PUBLICATION OF NSK EUROPE Bearing life – Calculating the basic fatigue life expectancy of rolling bearings Bearing life is essentially the length of time a bearing can be expected to perform as required in predeﬁned operating conditions. It is based primarily on the probable number of rotations a bearing can complete before it starts showing symptoms of fatigue, such as spalling or cracking due to stress. What determines a bearing’s service life? In addition to natural wear and tear, bearings can fail (prematurely) due to other factors such as extreme temperatures, cracks, lack of lubrication, or damage to the seals or cage. Bearing damage of this kind is often the result of choosing the wrong bearings, inaccuracies in the design of the surrounding components, incorrect installation or insufficient maintenance. Typical signs of fatigue: small, ﬂat ﬂakes of the bearing material become detached A standardised formula – also known as the catalogue method (ISO 281) – is the conventional means of calculating a bearing’s life. The parameters are bearing load, rotational speed, dynamic load rating and bearing type. The result is the bearing fatigue life L10 or L10h. › The Dynamic load rating (basic load rating) is defined as the constant load applied on bearings with stationary outer rings that the inner rings can endure for a rating life of one million revolutions (106 rev). The basic load rating of radial bearings is defined as a central radial load of constant direction and magnitude, while the basic load rating of thrust Average Life 1. Basic fatigue life rating L10 A bearing’s basic fatigue life rating is calculated using the number of rotations which 90% of all bearings in a specific group achieve or exceed a calculated time without failure (probability of failure: 10%). Rating Life Failure Probability and Bearing Life TECHNICAL INSIGHT · A publication of NSK Europe · www.nskeurope.com

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bearings is defined as an axial load of constant magnitude in the same direction as the central axis. The load ratings are listed under Cr for radial bearings and Ca for thrust bearings in the dimension tables. > The dynamic equivalent load P is defined as a mathematical radial load for radial bearings or axial load for axial bearings of a constant magnitude and direction which has the same effect on bearing life as the forces actually acting on the component. In the case of combined or constant loads, the value of P is calculated using the following formula: P = X • Fr + Y • Fa. Apart from...

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