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Rolling bearing life is defined as the number of revolution carried out by one bearing ring against the other ring, until the first signs of material fatigue occur on one ring or the rolling element.
Great differences in life can occur among bearings of the same type that is why according to the standard STN ISO 281 the basic life is used as the basis for life calculation, i.e. life shown by the operation time attained or exceeded by a bearing group at 90% reliability.

Life Equation

Nominal bearing life is mathematically defined by the life equation valid for all bearing types.

L₁₀ - nominal life  [10⁶ot]

C  - basic dynamic load rating
(values C_r, C_a are given in the dimension tables)  [kN]

P  - equivalent dynamic bearing load (equations for P_r, P_a
calculations are in section 1.1.3 and at each design group of bearings) [kN]

p  - mexponent for ball bearings p  = 3

for cylindrical, needle-, spherical- and tapered roller bearings

Table 1 shows dependence of the life L₁₀in million revolutions and respective ratio C/P. If the rotational speed does not change, the revised life calculation expressing the nominal life in operation hours can be used:

  [h]

L_10h  - nominal life  [h]

n  - rotational speed  [min^-1]

C/P dependence from the nominal life L_10h  and the rotational speed n is shown for ball bearings in Table 2, for cylindrical roller, needle roller, spherical roller and tapered roller bearings in Table 3.

In arrangements of the axles of road and railway vehicles the nominal life can be expressed by a revised relation in the volume of kilometers travelled.

L_10km - nominal life [10⁶km]

D  - wheel diameter    [m]

Reference Nominal Life Values

In cases, where the life for a given arrangement is not specified in advance, the values in tables 4 and 5 can be considered as adequate

Equation of Adjusted Life

Adjust life is a corrected nominal life, where by calculation not only the load but the influence of bearing components, material, physical, mechanical, and chemical qualities of lubricants and the temperature regime of the bearing the operating environment’ are taken into account.

L_na- adjusted life for (100-n)% reliability   and other usual operation conditions [10⁶ot]

a₁ - life factor for other than 90% reliability, see Table 6

a₂₃ - life factor of material, lubricant, production technology 
  and operation conditions, see Pict. 1

L₁₀ - nominal life [10⁶ot]

We can find basic values of a₂₃ by using the diagram in Pict.1.

υ - kinematic lubricant viscosity by operation bearing temperature [mm².s^-1]

υ ₁ - kinematic viscosity for defined rotational speed
  and selected bearing dimensions

[mm².s^-1]

Values υ and υ ₁ are determined according to the diagrams in Pict. 23 or 24.

In the diagram, Pict. 1, the line I is valid for radial ball bearings operating in a very clean environment. In other cases the factor a₂₃ is lower, depending on the environment cleanliness, and the decreasing tendency is dependent on the bearing design group in following order:
- angular contact ball bearings
- tapered roller bearings
- cylindrical roller bearings
- double row self-aligning ball bearings
- spherical roller bearings

Line II can be used when stating the factor a₂₃for spherical roller bearings operating in a dusty environment.