Curved Washers

Curved Spring Washers for Compact Axial Preloading

Curved spring washers are axially loaded spring elements with a simple curved profile. When compressed, the washer is progressively flattened and generates an axial spring force.

Due to their low installation height, curved spring washers are particularly suitable for applications with limited axial space. They can reduce axial play, compensate for manufacturing and assembly tolerances and generate a defined preload between two components.

Typical applications include bearing arrangements, electric motors, gearboxes, precision mechanical assemblies, fastening systems, machinery and automotive components.

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

Meaning of the Specifications in the Product Table

The test height L1 and test force F1 must always be considered together. The force F1 only applies at the corresponding height L1.

Spring Travel of a Curved Spring Washer

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 of the unloaded spring washer,

• L = actual installed or working height.

For the test point specified in the product table:

s1 = L0 − L1

Here, s1 is the spring travel at which the spring washer generates the specified force F1.

The load-deflection characteristic is approximately linear over a large part of the available deflection. Close to the completely flat position, however, the spring behaviour may change. The test force F1 specified at the test height L1 is therefore decisive for selection.

How to Select the Right Curved Spring Washer

Proceed in the following order:

1. Determine the radial installation space: Define the maximum permissible outside diameter Da and the required inside diameter Di.

2. Determine the installed height: Establish the height available to the spring washer in the assembled condition.

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

4. Define the required spring force: Select a spring washer whose force F1 at a suitable test height L1 corresponds to the required preload.

5. Consider the tolerances: Check the minimum and maximum installed heights that may result from component tolerances.

6. Assess the type of loading: Distinguish between static preload, occasional movement and frequently cycled loading.

7. Select the material: Consider humidity, corrosion, temperature and contact with surrounding media.

The spring washer should not be selected solely by its inside and outside diameters. The actual installed height and the spring force required at this height are equally important.

Compression to the Flat Position

Due to their simple geometry, curved spring washers can be compressed close to the flat position. When completely flat, the height of the spring washer is approximately equal to its material thickness.

However, the completely flattened position should not automatically be used as the normal working point. High compression may result in high material stresses, settling and a permanent reduction in the free height.

For reliable operation, we therefore recommend compressing the spring washer only as far as required to generate the necessary spring force. The intended working height should preferably be close to the specified test height L1.

Compensating for Axial Play and Tolerances

Curved spring washers are frequently used to reduce axial play within an assembly. The spring washer is installed between two components and preloaded during assembly.

This allows it to:

• compensate for manufacturing and assembly tolerances,

• reduce axial play,

• generate a continuous contact force,

• partially compensate for settling,

• absorb temperature-related changes in length,

• reduce rattling noise and vibration.

The required spring force must be suitable for the application. Insufficient force may not adequately compensate for the available play. Excessive force may increase friction, wear or unwanted loading of the adjacent components.

Use for Bearing Preload

Curved spring washers can be used to axially preload small bearings and other rotating components. They are installed between a bearing ring and a housing or cover surface.

Suitable preload can reduce axial bearing clearance and compensate for dimensional changes within the assembly. However, the spring force must be appropriate for the bearing being used.

Excessive preload may increase bearing friction, heat generation and wear. Depending on the required spring travel and load-deflection characteristic, stamped wave spring washers, coiled wave spring washers or special ball bearing disc springs may be more suitable for demanding bearing applications.

Installation Recommendations

For reliable operation, we recommend:

• providing flat and preferably parallel supporting surfaces,

• loading the spring washer evenly in the axial direction,

• allowing sufficient clearance at the inside and outside diameters,

• avoiding sharp edges and burrs on the supporting surfaces,

• not permanently compressing the washer more than necessary,

• avoiding lateral loads and tilting,

• maintaining an adequate safety margin from the flat position under dynamic loading.

The actual spring force may be influenced by friction, supporting geometry, component tolerances and surface condition. In critical applications, the function should be tested under actual installation conditions.

Similarity to DIN 137

The geometry of the spring washers offered is partly similar to the curved spring washers previously described in DIN 137. However, the designation “similar to DIN 137” does not automatically mean that the individual article has been manufactured or tested fully in accordance with this standard.

DIN 137 has been withdrawn. The spring washers offered should therefore primarily be regarded as axial spring elements for preloading and tolerance compensation.

Materials for Curved Spring Washers

Depending on the dimensions, the curved spring washers in the Febrotec standard range are available in spring steel 1.1248 or stainless spring steel 1.4310.

Spring Steel 1.1248

Spring steel 1.1248 provides high strength and is suitable for many industrial applications in dry or suitably protected environments.

Without a suitable coating or protective treatment, the material is not permanently corrosion-resistant. The spring surface should therefore be protected against humidity and corrosive media.

Stainless Spring Steel 1.4310

Material 1.4310, also known as X10CrNi18-8, provides good corrosion resistance for many industrial applications and humid environments.

It has limited suitability for permanent contact with seawater or media containing high concentrations of chloride. Due to cold forming during manufacture, 1.4310 may be slightly magnetic.

Typical Applications

Curved spring washers are commonly used in:

• bearing arrangements and small electric motors,

• gearboxes and drive components,

• machinery and fixtures,

• automotive components,

• electrical and electronic assemblies,

• precision mechanical devices,

• measuring and control equipment,

• household appliances,

• axially preloaded fastening systems,

• assemblies with manufacturing and installation tolerances.

They are particularly suitable for applications requiring a light to medium axial spring force within a very small installation height.

Custom Curved Spring Washers

In addition to the standard dimensions available from stock, curved spring washers can be manufactured according to individual requirements.

Customisable characteristics include:

• outside and inside diameters,

• material thickness,

• free height,

• working height,

• spring travel and spring force,

• material,

• surface finish and corrosion protection.

For a technical enquiry, please provide information about the available installation space, minimum and maximum installed heights, required spring force, type of loading and operating conditions.

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

Frequently Asked Questions About Curved Spring Washers

What is the difference between free height L0 and test height L1?

L0 is the height of the unloaded spring washer. L1 is the defined compressed height at which the spring force F1 is specified.

Can curved spring washers be compressed completely flat?

Compression close to the flat position is geometrically possible. However, the flat position should not automatically be used as a permanent working point, as high compression may cause settling or permanent deformation.

What is the difference between a curved and a wave spring washer?

A curved spring washer has one continuous curved profile. A wave spring washer has several waves distributed around its circumference, providing several defined contact areas.

Are curved spring washers suitable for bearing preload?

They can be used to axially preload bearings, provided that the spring force, spring travel and installation geometry are suitable for the application. Other types of spring washers may be more suitable where greater spring travel or a more precisely defined load-deflection characteristic is required.

Do curved spring washers prevent screws from loosening?

Not reliably without separate technical verification. Their primary function is to generate an axial spring force and compensate for dimensional changes.