Load capacity and lifetime

The resistance to the material strength determines the bearings dynamic load capacity load capacity. It is described by:

• the dynamic load base C
• the nominal lifetimes L and Lh

For continued rotation bearings, the lifetime is determined by the dynamic load C. The C load corresponds to a constant limited load in height, way and direction, for which a definite quantity of bearing sample can reach a million spin lifetime.

The ball bearings lifetime is estimated according DIN ISO 281 as following:

L = (C/P)³
Lh = (16'666 / n) x (C/P)³

L in 10⁶ spins, nominal lifetime in millions spins which was reached and surpassed by 90% of a sufficient quantity of identical bearings before a sign of material weariness would show.

• Lh in h, nominal lifetime in according the L definition
• C in N, bsic dynamic load
• P in N, equivalent load for radial bearings
• n in min-1, rotation speed

Bearings subject to high loads while they are stationary, at a slow rotation speed or in oscilation rotation movement may sustain local plastic deformations. These deformations will cause noise and thus limit the good functioning of the bearing.

The bearings, which do not rotate well, are calculated according to the basic static load CO. The basic static load CO is the load for which the Hertz pressure between rolling body and the bearing ring reaches 4200 N/mm2 in the most loaded place.

The S0 static safety factor is determined by the relation of static load CO and its equivalent P0 static load.

S0 = C0/P0
S0 static safety factor
C0 in N, static load
P0 in N, equivalent static load.

According to the operating conditions and requirements set out to bearings, the following values can be chosen for the SO static safety factor :

• S0 = 0,5 to 0,7 for low requirement applications and an operating without shocks
• S0 = 1,0 to 1,2 for application  known as normaland an operating without shocks
• S0 = 1,5 to 2,0 for high requirement applications and an operating with continuous loads (with shocks)

P = X • Fr + y • Fa [N]

For deep groove ball bearings, values for X and Y depend on the relation Fa/C0 .

Fr [N], radial strengh applying to the bearing.
Fa [N], axial strengh applying to the bearing.

P0 = FR for FA/FR < 0,8
P0 = 0,6 X FR + 0,5 X FA for FA/FR > 0,8

See chart below valid for bearings assembled in standard bore class (J5 and K5 for the bore of the inner ring, j6 for the housing).