Timken Super Precision Bearings for Machine Tool Applications

ENGINEERING
Grease Lubrication Factor (C gr )
For grease lubrication, the EHL lubrication film becomes depleted of
oil over time and is reduced in thickness. Consequently, a reduction
factor (C gr) should be used to adjust for this effect.
C gr = 0.79
Misalignment Life Factor (a 3m )
The life of the bearing depends on the magnitude of the angle of
misalignment, on the internal bearing geometry, and on the applied
loads.
Accurate alignment of the shaft relative to the housing is critical for
best performance. The life prediction using the method defined in
this publication is relatively accurate up to the limits listed within,
based on bearing type. The base condition, for which the load rating
of the roller bearing is defined, is 0.0005 radians misalignment.
Performance of all Timken bearings under various levels of
misalignment and radial and axial load can be predicted using
sophisticated computer programs. Using these programs,
Timken engineers can design special bearing-contact profiles
to accommodate the conditions of radial load, axial load and/or
bearing misalignment in your application. Consult your Timken
representative for more information.
a3p
Low Load Life Factor (a 3p )
Bearing life tests at the Timken Technology Center have shown
greatly extended bearing fatigue life performance is achievable
when the bearing contact stresses are low and the lubricant film is
sufficient to fully separate the micro-scale textures of the contacting
surfaces. Mating the test data with sophisticated computer
programs for predicting bearing performance, Timken engineers
developed a low-load factor for use in the catalog to predict the life
increase expected when operating under low-bearing loads. The
following figure shows the low-load factor (a 3p) as a function of the
lubricant life factor (a 3l) and the ratio of bearing dynamic rating to
the bearing equivalent load.
6.5
C 90 /P r =3.50
6
C 90 /P r =2.50 C 90 /P r =2.00 C90/P r =1.75 C 90 /P r =1.50
5.5
5
C90/P r =1.33
4.5
4
C90/P r =1.25
3.5
3
2.5
C 90 /P r =1.10
2
1.5
C 90 /P r =1.00
C
1
90 /P r =.90
C 90 /P r =.80
0.5
0 0.5 1 1.5 2 2.5 3
a 3l
A
Fig. 53. Low load factor (a 3P ) vs. lubricant life factor (a 3l )
and C 90/P r ratio.
TIMKEN MACHINE TOOL CATALOG 51