Bearing dynamic load rating, C
The basic dynamic load rating, C, is used for calculating basic rating life that rotate under load.
Basic dynamic load rating expresses a rolling bearing's capacity to support a dynamic load. The basic dynamic load rating is the load under which the basic rating life of the bearing is 1 000 000 revolutions. This is expressed as pure radial load for radial bearings and pure axial load for thrust bearings.
Bearing equivalent dynamic bearing load calculation
When calculating the bearing rating life, a value for equivalent dynamic bearing load is required for basic bearing life.
The loads acting on a bearing are calculated according to the laws of mechanics using the external forces - such as forces from power transmission, work forces, gravitational or inertial forces - that are known or can be calculated.
In real-world circumstances, the loads acting on a bearing may not be constant, can act both radially and axially, and are subject to other factors that require the load calculations to be modified or, in some cases, simplified.
Calculating equivalent dynamic bearing load
The load value, P, used in the bearing rating life equations is the equivalent dynamic bearing load. The equivalent dynamic bearing load is defined as: a hypothetical load, constant in magnitude and direction, that acts radially on radial bearings and axially and centrically on thrust bearings.
This hypothetical load, when applied, would have the same influence on bearing life as the actual loads to which the bearing is subjected.
If a bearing is loaded with simultaneously acting radial load Fr and axial load Fa that are constant in magnitude and direction, the equivalent dynamic bearing load P can be obtained from the general formula
P = X Fr + Y Fa
where,
- P: equivalent dynamic bearing load [kN]
- Fr: actual radial bearing load [kN]
- Fa: actual axial bearing load [kN]
- X: radial load factor for the bearing
- Y: axial load factor for the bearing
An axial load only influences the equivalent dynamic load P for a single row radial bearing if the ratio Fa/Fr exceeds a certain limiting value. With double row bearings, even light axial loads influence the equivalent load and have to be considered.
The same general formula also applies to spherical roller thrust bearings, which can accommodate both axial and radial loads.
Certain thrust bearings, such as thrust ball bearings and cylindrical and needle roller thrust bearings, can only accommodate pure axial loads. For these bearings, provided the load acts centrically, the formula is simplified to
P = Fa