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Basic Rating Life

Dynamically Stressed Bearings

The standardized calculation method for dynamically stressed rolling bearings is defined in ISO 281:2007(E). The lifetime of 90 % of a group of patently identical ball bearings under identical operating conditions is defined as the nominal basic rating life.
For ball bearings:

Formula 1

L10 basic rating life of ball bearings with 90 % reliability [106 revolutions]
C basic dynamic load rating [N]
P dynamic equivalent bearing load (Formula 3) [N]

The dynamic load rating C for our single and double row deep groove radial ball bearings as well as single and double row angular contact ball bearings are listed in our product tables for our bearing types. For the load C an L10 rating life of 106 revolutions is reached. The basic dynamic load ratings, which are listed in our product tables, are based on our standard bearing steel GCr15 and our standard heat treatment with a maximum allowable duration temperature of 150 °C. Dynamic load ratings of alternative materials or alternative heat treatment conditions can be obtained upon request.

When the bearing rotation speed is constant, the bearing life can be also expressed in operating hours.
For ball bearings:

Formula 2

L10h basic rating life in operating hours
n operating speed [revolutions per minute]

Dynamic Equivalent Load

The dynamic equivalent load, with its direction and magnitude to the bearing, is defined as the load which is able to achieve the same life as the actual bearing load and rotation conditions. It is a radial load for radial bearings, or an axial load for axial bearings. The dynamic equivalent load, which as a theoretical parameter can be found by applying the values listed in the Tables 1 and 2 to the Formula 3 functions as a replacement for the actual axial and radial bearing load.

Formula 3

Fr actual radial bearing load [N]
Fa actual axial bearing load [N]
X radial factor taken from Table 1 and 2 depending on the ratio Fa / Fr
Y axial factor taken from Table 1 and 2 depending on the ratio Fa / Fr
e limit value for the ratio Fa / Fr for selecting the factors X and Y

In the following two Tables 1 and 2 the calculation factors X and Y for calculation of the dynamic equivalent load are summarized for single and double row deep groove ball bearings as well as angular contact ball bearings.

The calculation factors depend on the ratio Fa / Fr and the operational radial clearance after assembling the bearing. The values in the following tables are based on common fits for shaft and housing.

Table 1: Calculation factors X and Y for single and double row deep groove ball bearings
Table 1: Calculation factors X and Y for single and double row deep groove ball bearings
* Relevant: The bearing operational clearance in the mounted condition.

Table 2: Calculation factors X and Y for angular contact ball bearings
Table 2: Calculation factors X and Y for angular contact ball bearings

Fa axial bearing load [N]
C0 basic static load rating [N] (Deep Groove Ball Bearings)
h0 relative axial load (Deep Groove Ball Bearings)

The interim values for X and Y, that are not in the above table shall be calculated by linear interpolation. The relative axial load can be taken from the product tables.

For a detailed calculation please ask for our catalogue.

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