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Preload: parameters
to take into account
Preload levels
SNR has defined 3 preload levels which correspond
to a level of contact pressure suitable for operating
conditions:
- Light preload (code 7):
High-speed, light load applications.
- Medium preload (code 8):
Best balance between speed and load.
- Heavy preload (code 9):
Large load, reduced speed applications.
- SNR can supply specific preloads on request
(code X) to meet spindle operation optimization
requirements.
Should a specific preload be required, it can be
achieved using bearings preloaded as standard
assembled with different length spacers.
The following formula is used to calculate the space
required between two spacers to alter the bearing
assembly preload:
2/3 2/3
a = 2K(Pr i – Pr S )
a: difference in length between the 2 spacers (µm)
K: deflection constant (see page 44)
Pr i : initial preload (daN)
Pr s : preload required (daN)
See also page 15, axial deflection
of an angular contact ball bearing.
Factors influencing preload
The following factors can influence the preload
value:
- assembly interference (fits),
- rotation speed,
- temperature, possibly associated with shaft and
housing materials,
- geometry of the surrounding parts.
Make sure these parameters are fully taken into
account when a spindle is designed. Contact
SNR's design office for any further information.
They are always prepared to share their expertise in
this area.
Increase factor
25
20
15
10
7012CV/HV
CH7012CV/HV
ML7012CV
MLCH7012CV
ML7012HV
MLCH7012HV
Preload increase
factor according
to rotation speed:
comparison between
7012 and ML7012
bearings, versions
with steel
or ceramic balls.
5
0
0,0 0,5 1,0 10 6 N.Dm 1,5 2,0 2,5
14