The rolling element bearing is subject to forces from gears, pulleys, or other components. These forces simultaneously act on the bearing from many different directions. The direction in which force is exerted on the bearing helps identify the type of load on the bearing:
Radial loads are exerted on the bearing on a plane perpendicular (90°) to the shaft.
Axial loads, or thrust loads, are exerted on the bearing on a plane parallel to the center of the shaft.
Combination loads exert both a radial and axial load on the bearing.
The illustration below shows a shaft mounted fan driven by a belt Fan and powered by a motor. Two bearings support the shaft and are subjected to loads as follows:
Radial loads originate from the:
- weight of the shaft
- weight of the pulley
- tension of the belt
- weight of the propeller
- propeller rotation
Note: Radial loads exerted on the ends of the shaft, outside of the two bearings supporting the load (i.e. the belt tension, pulley weight and propeller weight), are compounded by a lever affect and are referred to as overhung loads.
Axial loads originate from the wind induced by the propeller rotation.
Combination loads are the result of both radial load(s) and axial load(s) being combined and exerted on a single bearing.