BelleFlex® TechTips

What is a Belleville Washer or Disc Spring?

The Basics
Flat Washers
Spring Rate and Stacking
Understanding Load, Stress, and Fatigue Life
Belleville Spring Specifications
Presetting

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The Basics

A Belleville washer or disc spring is a conical-shaped spring with an open center. It is shaped much like a washer and is typically smaller than a coiled spring. Because Belleville washers can bear a much larger load relative to its deflection rate than a coiled spring, they are ideal for cushioning heavy loads with short motion.

Like all springs, a Belleville disc spring will deflect in response to a load. Belleville washers and disc springs exhibit low deflections relative to high loads. The relationship between the load and deflection is non-linear, particularly as load increases. This quality makes Belleville washers and disc springs well-suited to areas with constant thrust that must stand up to heavy wear.

Belleville washers and disc springs provide the following advantages:

• Conserve space
• Offer a long service life
• Can be used in conjunction with coiled springs
• Offer great versatility when stacked in series or in parallel
• Increase the reliability of machinery
• Prevent bolt failures
• Maintain the positioning accuracy of ball bearings
• Minimize thermal expansion
• Are self-damping
• Distribute loads evenly
• Absorb shocks

Our engineers can help you determine the washers or springs needed to meet the requirements of your specific application.
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Flat Washers

In some instances that must bear a heavy load, the addition of a flat washer increases the effectiveness of a Belleville washer or disc spring by helping to spread the load. In other applications, a flat washer can prevent a Belleville washer or disc spring from biting into softer metals. This is particularly important in preserving the integrity of bus bars, which are typically made from aluminum to withstand conditions of high current loading.

BelleFlex® engineers can help you to determine whether flat washers are needed for your specific application.
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Spring Rate and Stacking

The spring rate of a Belleville washer or disc spring is the amount of force associated with a given deflection measured in lb/in or N/mm. Every spring has its own spring rate, depending on its geometry and material. The formula to determine the load at a specific deflection uses Poisson's ratio, Young's modulus, as well as the outside diameter (De), inside diameter (Di), material thickness (t), and deflection-to-flat (ho).

The load/deflection ratio of a specific outer and inner diameter can be changed by using more than one Belleville washer or disc spring, stacked either in series or in parallel. Stacking Belleville washers and disc springs allows for precise customization of the load and/or deflection.

• Stacking in parallel (same direction) will increase load.
• Stacking in series (opposite directions) will increase deflection.
• Belleville disc springs can also be stacked as a combination of the two alignments.

The exact configuration of Belleville washers or disc springs depends on the requirements and limitations of the application. Our engineers can provide assistance in determining the configuration that best meets your needs.
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Understanding Load, Stress, and Fatigue Life

It is also important to know the limits of a given Belleville washer or disc spring before it is put into service in an industrial environment. Calculating load and stress is a way to determine the point of failure for a spring, including Belleville washers and disc springs. Simply put, it's a way to determine how much force (load) and how much stretch (stress) the spring can bear before it fails.

Fatigue life refers to the number of cycles a spring can withstand before it fails in a particular application. The fatigue life is based on the dimensions of the spring or spring stack, the preload, the final load, the deflection, and the frequency. The goal of determining the fatigue life is to ensure that your Belleville washer or disc spring solution will be able to withstand the stress to which it will be exposed. In situations in which a single Belleville cannot withstand the level of stress, a well-designed stack of Bellevilles can alter the load and stress performance and increase the fatigue life.

Well-designed springs contribute to increased efficiency and prolonged service life for your equipment. Our engineers are always available to provide assistance with all facets of Belleville washer and disc spring design, including load and stress calculations.
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Belleville spring specifications

The term 'tolerance' refers to the amount of deviation from specification that may occur in a disc spring without compromising its performance. For Belleville disc springs, allowable tolerances for diameter, thickness, height, and load are provided in the DIN specification. Deutsches Institut für Normung (DIN) is an international standards organization, based in Germany that governs specifications of many industrial and technical materials.

For more metric belleville disc springsinformation, please contact us. We will provide professional answers.

BelleFlex® utilizes the following DIN specifications to guide our design and manufacturing process:

• Our engineers employ the calculations of DIN to create Belleville disc springs with predictable deflection for a given load and a determinable minimum life cycle.
• BelleFlex® adheres to DIN for the type, dimensions, material, permissible stress, permissible set, guide clearance, and testing of Bellevilles. Although DIN applies only to specific limited applications and sizes, all disc springs produced by BelleFlex® are manufactured in accordance with the quality and testing requirements contained in this specification.
• BelleFlex® utilizes DIN in the manufacturing of heavy-duty Belleville washers.

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Presetting

Presetting takes place during the manufacturing process of a Belleville washer or disc spring when it is momentarily flattened. The process reduces the original unloaded height of the spring, as a result of the residual tensile stresses.

Disc Springs, with all of their variations, are among the most widely used tension generating washers. They are used for spanning alignment holes, distributing bearing loads and for generating and sustaining the tension needed to hold assemblies together.

Belleville washers provide a very high spring force for short movement and have a high energy storage capacity. In a true Belleville washer, the ratio of material thickness to rim width is held to about one in five. Crown height actually should not exceed 40% of material thickness. In application, yield strength is not exceeded and the washer returns to its full crown height when compression force is removed.

Commercial Disc Springs are not held to the specific O.D./crown height/thickness ratios required of the true Belleville Disc Spring washers. Traditionally, the crown height to thickness ratio is considerably greater for commercial Disc Springs. When loaded to flat, their yield point may be exceeded. These washers, however, are often used in appli­cations where they function entirely within their elastic range. In applications where they are loaded beyond their yield point they will act in a consistent manner over a reduced crown height. Such washers have, in effect, become re­formed.

By varying thickness and crown height relationships, design engineers meet a wide range of load/deflection require­ment with Disc Spring washers. A crown height to thickness ratio ranging from 0.4 to 0.8, for example, produces a fair­ly constant spring rate (Figure 1).

With a crown height to thickness ratio up to 1.4, the washer will show a positive rate of increase in the load up to 100% deflection (Figure 2).

At a crown height to thickness ratio of 1.4, the Disc Spring shows a constant load over a fairly large deflection, mak­ing it useful in applications where extreme wear conditions must be absorbed (Figure 3).

Where the ratio of crown height to thickness exceeds 1.4, yielding will occur and, possibly, oil canning or inverting (Figure 4).

Slotted Disc Springs

Often referred to as a diaphragm spring, the Slotted Disc Spring is used in clutch applications and other applications requiring high travel consistent within acceptable stress limits. The characteristics curve, as shown in figure 6, indicates a rela­tively constant load over a wide range of deflection.

Stacking

Disc Springs are often stacked to enhance performance characteristics. By stacking them in parallel, load bear­ing characteristics are enhanced (Figure 7). when stacked in series, greater deflection or travel is achieved (Figure 8).

Combination stacking, in parallel and in series, increases both load bearing and deflection (Figure 9). Disc Springs of varying thicknesses can also be stacked to achieve specific performance objectives (Figure 10).

Comparing Disc Spring Stack To Coil Spring

Figure 11 clearly shows how Disc Springs, stacked in series, support the same load as a coiled spring with a substantial reduction in space required. Disc stacks may be designed for extremely high loads where coil springs are not feasible at all.

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