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Dimensioning
Selected f L values
Point of installation Desired f L -value
Motor vehicles 0,9...2,8
Rail vehicles 2,5...5,0
Ships 1,5...6,0
Agricultural machines 1,0...2,0
Construction machines 1,0...2,5
Textile machines 3,0...4,5
Paper processing and printing machines 4,0...6,5
Conveying machines and equipment 2,5...6,0
Pumps. fans. compressors 1,0...4,5
Crushers. grinding mills. classifiers etc. 2,0...5,0
Electric motors 1,5...5,0
Rolling mills. metallurgical plants 1,0...4,5
Tool machines 2,5...5,0
In many publications, you can find the term length of use, which is different from the service life, in that the length
of use describes the actual functionality of the roller bearing, expressed in a time unit.
Whereas the calculations for the nominal service life merely address the fatigue criteria of the material and otherwise,
nearly ideal operating conditions are assumed, the length of use expresses a complex of load and environment
conditions that characterize a reduced length of use of the bearing.
Extended service life calculation
If it can be assumed that all the influences that act to reduce the nominal rating life, can be surmounted or eliminated,
recommendations in the ISO provide the option to increase the length of use of the bearing significantly.
The principles of this are:
• the greatly improved material properties since the development of the service life theory by Lundberg and
Palmgren, e. g. the purity of the bearing steels
• the constructive development of the geometry of the roller bearing parts and their active relationship between
one another among all the leading roller bearing manufacturers
• the maximum possible exploitation of the theory of the lubricant of the roller bearing during operation including
the additive addition of the lubricant
• the use of optimized lubrication systems that facilitate friction-lowering and hence, low-wear operation
of a bearing.
On the basis of quantifiable influences, the theories of Ionnanides and Harris allow the definition of fundamental
quantities of the bearing, which, in the result of the extended modified service life calculation, allow a greater
length of use and sometimes a reduction in size. The calculation of the extended modified service life is standardized
in DIN ISO 281:2001.2004.
The calculation methods and symbols used above correspond to the instructions in DIN ISO 76 and 281. For the sake
of simplification, our equations and tables use the symbols C and C 0 for the dynamic and static load rating of radial
and thrust bearings, and P and P 0 for the dynamic and static equivalent load.
For the extension of the service life, the factor a DIN is decisive. The following applies
L nm = a 1 · a DIN · L 10
L hnm = a 1 · a DIN · L h10
L nm extended service life [10 6 revolutions]
L hnm extended modified service life [h]
a 1
a DIN
coefficient
coefficient
L 10 nominal rating live [10 6 revolutions]
L h10 nominal rating live [h]