Bearing Lifetime - Bosch Rexroth MKE Series Project Planning Manual

Project Planning Manual | Rexroth MKE Synchronous Motors
9.10.4

Bearing Lifetime

Mechanical service life of bearings
Mechanical bearing lifetime with in‐
creased radial force
● a shift in the position of the axis if the driving pinions are not defined axially
on the machine side,
● a thermally dependent component of the axial force if the driving pinions
are defined axially on the machine side. This causes the risk of exceeding
the maximum permissible axial force or of the play within the gears in‐
creasing to an impermissible degree.
In such cases, you should therefore preferably use drive elements
with their own bearings which are connected to the motor shaft via
axially compensating couplings.
The bearing lifetime is an important criterion for the availability of MKE motors.
When the lifetime is considered, the "mechanical lifetime" of bearing compo‐
nents and materials is differentiated from the "grease lifetime" of the bearing
lubricant.
If the MKE motors are operated within the limits specified for radial and axial
loads, the nominal service life of the bearings is as follows:
L = 30,000 operating hours
10h
(calculated according to ISO 281, ed. 12/1990)
This applies to all MKE motors based on the following:
● The permitted loads from the corresponding chapter "Technical Data" are
never exceeded.
● The motor is operated under the permitted conditions for use and in the
permitted ambient temperature range of 0 °C to +40 °C.
●
Differing loads can have the following effects:
● Premature failure of the bearing due to increased wear or mechanical
damage.
● Reduction of the grease lifetime leads to premature failure of the bear‐
ing.
● Avoid exceeding the load limits.
In other cases, the bearing lifetime is reduced as follows:
L Bearing lifetime (according to ISO 281, ed. 12/1990)
10h
F Determined permissible radial force in N (Newtons)
radial
F Actually acting radial force in N (Newtons)
radial_ist
Fig.9-20: Calculation of the bearing service life L10h if the permissible radial force
Fradial is exceeded
Under no circumstances may the actually acting radial force F
be higher than the maximum permissible radial force F
al_ist
.
al_max
Electric Drives | Bosch Rexroth AG
and Controls
Operating Conditions and Application Notes
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radi‐
radi‐