DODGE
ENGINEERING
B20-9
Plummer Blocks
Sleeve Bearings
SLEEVOIL
Take-Up Frames
Engineering
Part Number Index
Keyword Index
1.4 LIFE ADJUSTMENT FACTOR FOR APPLICATION
CONDITIONS.
Application conditions which affect bearing life
include:
1. Lubrication.
2. Load distribution (including effects of clearance,
misalignment, housing, and shaft stiffness, type of loading
and thermal gradients).
3. Temperature.
Consideration of (1.2) and (1.3) above requires analytical and
experimental techniques beyond the scope of this discussion,
therefore, the user should consult the bearing manufacturer
for evaluations and recommendations.
In most bearing applications, lubrication serves to separate
the rolling surfaces; i.e., rolling elements and raceways; to
reduce retainer-rolling elements and retainer-land friction
and sometimes to act as a coolant to remove frictional heat
generated by the bearing.
If all limitations and qualifications specified by this discussion
are observed, then the life adjustment application factor for
bearings which are adequately lubricated is 1; i.e., a
3
=1.
Operating conditions where a
3
might be less than 1 include:
a)
Exceptionally low values of Ndm (rpm times bore
diameter in mm); e.g., Ndm 1000.
b) Lubricant viscosity less than 20.4 centistokes
(100 SUS) at operating temperature.
c) Excessively high operating temperatures.
When a3 is less than 1, it may not be assumed
that the deficiency in lubrication can be overcome
by using an improved steel.
1.5 FACTOR COMBINATIONS.
A fatigue life formula including
the life adjustment factors is:
Ball Bearings:
L
n
= a
1
x a
2
x a
3
x
Tapered Roller Bearings:
L
n
= a
1
x a
2
x a
3
x
Spherical Roller Bearings:
L
n
= a
1
x a
2
x a
3
x
Indiscriminate application of the life adjustment factors in
this formula may lead to serious over-estimation of bearing
endurance, since fatigue life is only one criterion for bearing
selection.
Care must be exercised to select bearings which are of sufficient
size for the application. Undersizing of shaft and housing
structures by using bearings which appear adequate from a
life standpoint could lead to misalignment and fitting problems
which could invalidate the formulas in this discussion.
*
C = Basic Load Rating computed in accordance with ABMA-ANSI Standards. C90 = C x .259
(
)
(
)
(
)
(16.667)
RPM
(16.667)
RPM
(1,500,000)
RPM
3
10/3
10/3
C*
P
C90*
P
C*
P
Mounted Bearings Life Adjustment Factor