Finger Spring Washers

Finger Spring Washers for Axial Ball Bearing Preload

Finger spring washers are ring-shaped spring elements with several radially arranged spring fingers. When compressed axially, the fingers deflect elastically and generate a defined preload. Because the individual fingers can move largely independently of one another, they can compensate for small dimensional variations within an assembly.

Finger spring washers are mainly used for the axial preloading of ball bearings. A correctly designed preload can reduce axial clearance as well as vibration and operating noise. However, the preload must be suitable for the bearing and the application, as excessive force can increase friction, heat generation and wear.

Use the product table above to select a suitable finger spring washer by outside diameter, inside diameter, material thickness, free height, test height, force range, bearing seat and material.

Meaning of the Specifications in the Product Table

The test height L1 and the force range F1min to F1max must always be considered together. The stated forces only apply at the corresponding height L1.

Determining Spring Travel and Force Range

The spring travel is calculated from the difference between the free height L0 and the installed height L:

s = L0 − L

where:

• s = spring travel in mm,

• L0 = free height,

• L = actual installed or working height.

For the values specified in the product table:

s1 = L0 − L1

At this deflection, the generated force lies between F1min and F1max. A permissible force range is stated because of material, geometry and manufacturing tolerances.

When selecting a spring washer, both limits must be suitable for the application. F1min must be high enough to reduce the required clearance, while F1max must not place an excessive load on the bearing or adjacent components.

How to Select the Right Finger Spring Washer

Proceed in the following order:

1. Determine the bearing and installation space: Check the bearing size, bearing seat B, outside diameter Da and inside diameter Di.

2. Determine the working height: Establish the axial height available in the assembled condition.

3. Calculate the spring travel: Subtract the working height from the free height L0.

4. Check the force range: Select a version whose F1min to F1max values at a suitable test height L1 match the required bearing preload.

5. Consider the tolerances: Determine the minimum and maximum possible installed heights.

6. Assess the operating conditions: Consider speed, temperature, loading and lubrication.

7. Check the installation: The spring fingers must not be blocked by edges, grooves or adjacent components.

The finger spring washer should not be selected solely by the bearing seat B. The actual installed height and the resulting force range are equally important.

Use for Bearing Preload

With spring preloading, a continuous axial force acts on one bearing ring. The finger spring washer is normally installed between the stationary bearing ring and a housing or cover surface.

Suitable preload can:

• reduce axial bearing clearance,

• compensate for dimensional and assembly tolerances,

• absorb temperature-related changes in length,

• reduce vibration and operating noise,

• stabilise the position of the bearing.

The highest possible preload is not automatically the best choice. If the bearing is loaded too heavily, friction, operating temperature and wear may increase. The permissible axial load and the recommendations of the bearing manufacturer must therefore be taken into account.

Installation Recommendations

For reliable operation, we recommend:

• providing flat and preferably parallel supporting surfaces,

• applying the load evenly in the axial direction,

• allowing sufficient clearance at the outside and inside diameters,

• using burr-free edges and clean supporting surfaces,

• ensuring secure centring within the bearing seat,

• providing sufficient spring travel for dimensional and temperature changes,

• avoiding excessive compression.

The spring fingers must not catch on adjacent components during compression. Uneven support or tilting may lead to unequal forces. In demanding applications, the preload should be verified under actual installation conditions.

Material and Surface Finish

The standard versions are manufactured from hardened spring steel 1.1231, also known as C67S. The material provides high strength and is suitable for applications in dry or protected environments.

The surface is oiled. The oil film provides limited protection during storage and transport but does not replace permanent corrosion protection. Suitability must be assessed separately where humidity or corrosive media are present.

The operating temperature range stated on the product page is:

−40°C to +80°C

The actual suitability also depends on the load, operating duration and environmental conditions.

Typical Applications and Custom Versions

Finger spring washers are commonly used in:

• electric motors and generators,

• gearboxes and drive units,

• fans and blowers,

• pumps,

• household and electrical appliances,

• precision mechanical assemblies,

• measuring and control devices.

In addition to the standard dimensions available from stock, finger spring washers can be manufactured according to individual requirements. Customisable characteristics include the outside and inside diameters, material thickness, free height, test height, force range, finger geometry, material and surface finish.

For a technical enquiry, please provide information about the bearing, housing seat, minimum and maximum installed heights, required preload, rotational speed and operating conditions.

Further information on selection and design can be found in our Spring Washer FAQ.

Frequently Asked Questions About Finger Spring Washers

What is a finger spring washer?

A finger spring washer is a ring-shaped spring element with radially arranged spring fingers. The fingers deflect under axial load and generate a preload.

What do F1min and F1max mean?

These values describe the permissible force range at the test height L1. The actual force of an individual article may lie anywhere within this range.

What does bearing seat B mean?

B is the nominal dimension of the intended bearing or housing seat. The outside diameter, inside diameter and installed height must also be checked when selecting the spring washer.

Does a finger spring washer always extend the service life of a ball bearing?

No. Suitable preload can reduce clearance, vibration and noise. Excessive preload, however, may increase friction, heat generation and wear.

Can the finger spring washer be compressed below the test height L1?

Further compression changes the force range and increases the material stress. Compression significantly below L1 should therefore only be carried out after technical assessment.