Disc Springs for Ball Bearings

Bearing Preload Disc Springs for Axial Preloading of Ball Bearings

Bearing preload disc springs are specially designed disc springs used to apply axial preload to ball bearings. They are mainly used in combination with deep-groove ball bearings and act on either the inner or outer bearing ring, depending on the design.

The spring generates a defined axial force and keeps the bearing components under preload even when dimensional deviations or temperature-related changes in length occur. This can reduce axial bearing clearance, vibrations and running noise while allowing a compact and mechanically simple bearing arrangement.

Typical applications include electric motors, fans, pumps, gearboxes, household appliances and other rotating assemblies where smooth running and consistent bearing preload are required.

The Febrotec range includes slotted and non-slotted bearing preload disc springs made from spring steel. Use the product table above to select the appropriate version by outside diameter, inside diameter, material thickness, free height, compressed height, preload force and design.

Meaning of the Specifications in the Product Table

The values L1 and F1 must always be considered together. The specified spring force applies only at the corresponding compressed height.

The spring travel to this operating point is calculated as follows:

s1 = L0 − L1

L0 is the free height and L1 is the compressed installation height.

Why Are Ball Bearings Axially Preloaded?

Small axial gaps can occur within a bearing arrangement due to manufacturing, housing and assembly tolerances. Different rates of thermal expansion in the shaft, housing and adjacent components may also change the position of the bearing rings.

A bearing preload disc spring compensates for these variations elastically while maintaining a defined axial preload.

This can provide the following advantages:

• reduced axial bearing clearance,

• lower vibration and running noise,

• smoother operation of the bearing arrangement,

• compensation for dimensional and assembly tolerances,

• compensation for temperature-related changes in length,

• more even loading of the rolling elements.

However, the preload force must not exceed the permissible value for the ball bearing used. Excessive preload can increase friction, bearing temperature and wear, thereby reducing bearing service life.

The required preload force should therefore be determined on the basis of the bearing data, rotational speed, lubrication, operating temperature and external loads.

Slotted and Non-Slotted Designs

Non-Slotted Bearing Preload Disc Springs

Non-slotted versions have a closed conical ring. They generate an evenly distributed axial force and provide a continuous annular contact surface.

This design is particularly suitable where:

• a compact spring is required,

• a closed contact surface is needed,

• only limited dimensional deviations must be compensated,

• a defined preload force is required over a short spring travel.

The non-slotted bearing preload disc springs offered on this page are designed so that they can be compressed to a flat position without permanent setting when used as intended.

Slotted Bearing Preload Disc Springs

Slotted bearing preload disc springs contain several radial slots. This geometry makes the spring softer in the initial part of its travel.

As a result, a larger spring travel can be accommodated without an excessive increase in preload force. Slotted versions are therefore particularly suitable for compensating for larger manufacturing, assembly or temperature-related deviations.

They are useful where:

• a softer spring characteristic is required,

• larger axial movements must be compensated,

• the preload force should remain as constant as possible over a greater travel,

• the bearing arrangement is sensitive to large changes in force.

The choice between a slotted and non-slotted version should not be based solely on dimensions. The available spring travel, required preload force and permissible change in force throughout the operating range are decisive.

How to Select the Right Bearing Preload Disc Spring

Proceed in the following order:

1. Identify the ball bearing: Determine the bearing type, bearing size and permissible axial preload.

2. Define the bearing ring to be preloaded: Decide whether the spring is to act on the inner or outer ring.

3. Check the installation space: Determine the maximum possible outside diameter Da, required inside diameter Di and available axial installation height.

4. Define the preload force: Determine the required axial force from the bearing and application data.

5. Calculate the operating height: Establish the height to which the spring will be compressed in the installed condition.

6. Compare L1 and F1: Select a spring whose test point is as close as possible to the planned installation height and preload force.

7. Consider tolerance compensation: Check which dimensional deviations and temperature-related movements must be accommodated.

8. Select the design: Use a slotted version for a softer characteristic or a non-slotted version where a continuous contact surface is required.

Bearing preload disc springs have significantly different proportions from standard disc springs to DIN EN 16983. The force and dimensional tolerances of standard disc springs cannot therefore be transferred directly to bearing preload disc springs.

Installation on the Outer Ring

In many bearing arrangements, the bearing preload disc spring is installed between a housing shoulder or housing cover and the outer ring of the ball bearing.

The spring presses the outer ring against an opposing contact surface. To allow the spring to compensate for axial movement, the preloaded outer ring must remain sufficiently movable within the housing. An excessively tight fit may prevent the intended spring compensation.

The spring must be dimensioned so that it acts only on the outer ring. Contact with the inner ring, seal, shield or bearing cage must be avoided.

Installation on the Inner Ring

Depending on the design, the bearing inner ring can also be preloaded. In this case, the spring is guided on the shaft or a suitable sleeve and acts axially on the inner ring.

The inside and outside diameters must be selected carefully. The spring must not unintentionally contact the outer ring or other rotating or stationary bearing components.

For reliable operation, we recommend:

• flat and parallel contact surfaces,

• even axial loading,

• sufficient radial guidance without jamming,

• avoiding lateral forces and misalignment,

• sufficient installation space for the intended spring travel,

• clean contact surfaces without chips, burrs or dirt,

• testing at the minimum and maximum operating temperatures.

The bearing preload disc spring must not rub between components rotating relative to each other during operation.

Material and Operating Conditions

The standard versions are manufactured from cold-rolled spring steel 1.1231, also known as C67S or Ck67. This material is suitable for many general applications involving disc, leaf and wave springs.

A temperature range of −40 to +80 °C is specified on this page for the standard material. Actual suitability nevertheless depends on the load, operating duration, preload and environmental conditions.

In the presence of humidity, condensation, aggressive media or increased corrosion requirements, it must be determined whether a special surface treatment or alternative material is required.

Frequently Asked Questions About Bearing Preload Disc Springs

What is the difference from standard disc springs?

Bearing preload disc springs have a geometry specifically designed for bearing applications. Their degressive spring characteristic allows a comparatively constant preload force over a greater spring travel.

Where is the spring installed?

It is usually installed between a housing component and the outer ring of the ball bearing. Depending on the design, the inner ring may also be preloaded.

What does spring force F1 mean?

F1 is the axial spring force at the specified compressed height L1. Both values must always be considered together.

When is a slotted version recommended?

Slotted springs are suitable where larger dimensional deviations or axial movements must be accommodated with the smallest possible increase in preload force.

Can a bearing preload disc spring compensate for any amount of bearing clearance?

No. The spring can compensate only for movement within its available spring travel. The permissible axial load of the ball bearing must also not be exceeded.

Further information on function and selection can be found in our Disc Spring FAQ.