Permissible static loads

Very heavy loads or shock loads can permanently deform the raceways or rolling elements. In the case of super-precision bearing arrangements, permanent deformation must not occur. To make sure that static loads do not lead to permanent deformation, the basic static load rating of the bearing and equivalent static bearing load can be compared to determine if a bearing is at risk of permanent deformation. For very heavily loaded super-precision angular contact ball bearings, the contact ellipse truncation should be checked to avoid edge stress, which also could lead to permanent deformation. For additional information, contact the SKF application engineering service.

Basic static load rating

The basic static load rating C0 as defined in ISO 76:2006 corresponds to a calculated contact stress at the centre of the most heavily loaded rolling element / raceway contact. This stress produces a total permanent deformation of the rolling element and raceway, which is approximately 0,0001 of the rolling element diameter. The loads are purely radial for radial bearings and axial, centrically acting for thrust bearings.
Values for basic static load rating C0 are listed in the product tables.

Equivalent static bearing load

To compare actual loads with the basic static load rating, the actual loads must be converted into an equivalent load. The equivalent static bearing load P0 is defined as that hypothetical load (radial for radial bearings and axial for thrust bearings) which, if applied, would cause the same maximum rolling element load in the bearing as the actual loads to which the bearing is subjected.
Information and data required for calculating the equivalent static bearing load are provided in each product section.

Required basic static load rating

The required basic static load rating C0, to protect the bearing from permanent deformation, can be determined from

C0 ≥ s0 P0

C0=basic static load rating [kN]
P0=equivalent static bearing load [kN]
s0=static safety factor
Guidelines for minimum values:
  • 2 for super-precision angular contact ball bearings with steel balls (including thrust ball bearings)
  • 3 for super-precision cylindrical roller bearings with steel rollers
  • 4 for super-precision axial-radial cylindrical roller bearings

For hybrid bearings, the static safety factor should be increased by 10%.
For angular contact thrust ball bearings for screw drives, safety factors down to s0 = 1 can be used.
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