Preload of Angular Contact Bearings

 

Definition: Preloading bearings is the process of removing the internal clearance of the bearing by applying a permanent thrust load. This applied force makes the rolling elements run in a single “track” and it removes any axial play in the bearing assembly.

Reasons for preloading bearings:

1. Eliminate radial and axial play in the bearings
2. Increase the spindles rigidity
3. Eliminates non-repetitive run out caused by bearing looseness
4. Prevents skidding of the rolling elements

If done incorrectly:

1. Excessive preload causes heat in the bearing drastically reducing its lifespan
2. Excessive preload increases the energy required to rotate the spindle
3. Under preloaded bearings cause the rolling elements to skid. This damages the raceways and the rolling elements causing premature failure
4. Under preloaded bearings cause looseness of the shaft resulting in poor part finish and the inability to hold tolerances.
5. Under preloaded bearings will often generate noise while the spindle is running

Methods of spindle repair bearing preload:

1. Install a duplex bearing set with previously adjusted stand-out dimensions and axial clearance
2. Use a spacer to obtain the correct offset
3. Use a force generated by spring tension
4. Use nuts to adjust axial preload by torque (This is a poor design for spindle applications)