ENGINEERING
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LOAD RATINGS, EQUIVALENT LOADS AND BEARING LIFE
The basic dynamic load rating and the static load rating are commonly used for bearing selection. The basic dynamic load rating is used to estimate the life of a rotating bearing. Static load ratings are used to determine the maximum permissible load that can be applied to a non-rotating bearing.The basic philosophy of Timken is to provide the most realistic bearing rating to assist our customers in the bearing selection process. Published ratings for Timken bearings include the basic dynamic radial load rating C
MAXIMUM CONTACT STRESS
For all spherical roller bearings, the maximum contact stress can be approximated using the static equivalent load and the static rating.
C 1 . This value is based on a basic rating life of one million revolutions. The basic static radial load rating is C
( )( )
000 C .
STATIC EQUIVALENT LOADS
Where: = maximum contact stress
= radial equivalent load = static load rating The static equivalent load rating is based on an assumed nominal clearance in both rows of rollers within the bearing, which equates to a load zone of approximately 130º. The static equivalent load is the radial load that will result in the same maximum contact stress as the applied bearing load. The load factors X
P C and Y
are used with the following equation to estimate the static radial equivalent load. The values of X
(always equal to 1 for SRBs) and Y
The basic dynamic radial load rating, C , is assumed to be the radial load carrying capacity with a 180º load zone in the bearing. The dynamic equivalent radial load is defi ned as a single radial load that, if applied to the bearing, will result in the same life as the combined loading under which the bearing operates.To calculate the L
r )
are listed in the bearing tables.
1 0r = X
F
r + Y
F
a STATIC LOAD RATING
The basic static radial load rating and thrust load rating for Timken bearings are based on a maximum contact stress within a non-rotating bearing of 4000 Mpa (580 ksi) at the center of contact on the most heavily loaded roller.The 4000 Mpa (580 ksi) stress levels may cause visible light Brinell marks on the bearing raceways. This degree of marking will not have a measurable effect on fatigue life when the bearing is subsequently rotating under a lower application load. If sound, vibration or torque is critical, or if a pronounced shock load is present, a lower load limit should be applied. For more information on selecting a bearing for static load conditions, consult your Timken representative.
P
10 life, it is necessary to calculate a dynamic equivalent radial load, designated by P
r . P
r = XF
r + YF
a Where: P
r = Dynamic Equivalent Radial Load F
r = Applied Radial Load F
a = Applied Axial Load X = Dynamic Radial Load Factor
Y = Dynamic Axial Load FactorFor spherical roller bearings, the values of X and Y are dependent on the amount of the axial load. Calculate the ratio of the axial load to the radial load. Compare this ratio to the e value for the bearing. Note that values for e, X, and Y are available in the bearing tables.
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SPHERICAL ROLLER BEARING CATALOG 179761_003-19028 7/19/079:17:35PM