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Dimensioning
Bearings under dynamic load
The standardized calculation method (DIN ISO 281) for dynamically stressed rolling bearings considers material fatigue
(pitting) as the cause of failure. The service life formula is:
C
L10 = L = [10 6 10
revolutions]
P
where
C p
L 10 = L nominal rating life [10 6 revolutions]
C dynamic load rating [kN]
P equivalent dynamic load [kN]
p life exponent
L 10 is the nominal rating life in millions of revolutions which is reached or exceeded by at least 90% of a large group
of identical bearings.
The dynamic load rating C [kN] is indicated in the tables of all the bearings. This load ensures an L10 rating life of
10 6
The dynamic load rating C [kN] is indicated in the tables of all the bearings. This load ensures an L
6
revolutions.
The equivalent dynamic load P [kN] is a theoretical value. It is a radial load for radial bearings or axial load for axial
bearings which is constant in size and direction. P results in the same service life as the actual load combination.
P = X · F r + Y · F a [kN]
where
P equivalent dynamic load [kN]
F r radial load [kN]
F a Axialbelastung [kN]
X axial load
Y thrust factor
The life exponent p differs for ball bearings and roller bearings.
p = 3 for ball bearings
10
p = ––– ––
3
for roller bearingsr
If bearing speed is constant, service life can be expressed in hours.
L · 10 6
L h10 = L h = ––––––– [h]
n · 60
where
L h10 = L h nominal service life [h]
L nominal service life [10 6 revolutions]
n speed (frequency of rotation) [rpm]
A service life of 10 6 revolutions is equivalent to 500 operating hours at a speed of 33 1
3 rpm. The speed of 331 / 3 rpm
is defined as reference speed, the service life of 500 hours as reference service life. The service life equation is.
For the specification of the service life required in traffic engineering, in [km], the wheel diameter [DR] should be introduced,
so the following applies:
L km = L · D R · π
L km mean nominal rating life [km]
L nominal service life [h]
D R wheel diameter [mm]