How to calculate bearing’s rating life?

There’s many reasons can affect bearing’s rating life, such as temperature, grease or other external factors, but we can still get bearing’s rating life through a formula,

the calculate result will have 90% credibility, if we multiply coefficient, the result can have 99% credibility.

The formula is as below,

L_h=(C/P)^KX(10⁶/60n), L_h means bearing’s rating life, C means basic dynamic load rating, P means equivalent load, K means coefficient, it’s 3 when calculating ball bearing, it’s 10/3 when calculating roller bearing, n means rotational speed.

Here’s equivalent load P’s formula, P=XF_r+YF_a, F_r means radial load, F_a means axial load, the following chart is used for calculating P,

Coefficient f₀, basic static load rating C_or, judge coefficient e, radial load coefficient X and axial load coefficient Y need table lookup, as radial load F_r (kn), F_a axial load (kn) and rotational speed are based with usage status.

Take 6800 bearing as sample, set F_a=0.05kn, F_r=0.1kn, rotational speed 10000rpm,

as table, C_or=0.84, f₀=14.8, so f₀F_a/C_or為14.8x0.05 / 0.84 ≈0.88, so we choose the closet number, when f₀F_a/C_or=1.03, e=0.28，0.5>0.28, then we’ll choose 0.56 as X, 1.55 as Y to calculate P, P=0.56X0.1+1.55X0.05=0.1335, according to the formula

L_h=(C/P)^KX(10⁶/60n), as table know the C of 6800 bearing is 1.72, K is 3 cause 6800 bearing is deep groove ball bearing, so L_h=(1.72 / 0.1335)³x(10⁶/60x10000) ≈3564 hr