Tech Tips

 

The following BelleFlex® “Tech Tips” address the most frequently asked questions by our customers about Belleville disc springs and their applications.

While these Tech Tips have been provided for your ease and convenience, we encourage you to contact our engineering team to discuss the specific requirements of your application. Our staff includes metallurgical engineers as well as mechanical engineers with Licensed Professional Engineer credentials.

With more than 20 years of engineering experience, the BelleFlex® team brings an expert level of mechanical and metallurgical skill to the design of your Belleville disc spring application. We provide 24/7 engineering support with members of our engineering team always available to assist our customers with their applications.

What is a Belleville Disc Spring

A Belleville 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. Belleville disc springs are ideal for cushioning heavy loads with short motion. The load/deflection ratio can be changed by using more than one Belleville disc spring, stacked either in series or in parallel.

A Belleville disc spring is characterized by four dimensions: outside diameter (De), inside diameter (Di), material thickness (t), and deflection-to-flat (ho).

Belleville 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 springs needed to meet the requirements of your specific application. Well-designed springs contribute to increased efficiency and prolonged service life for your equipment.


What is the difference between Belleville springs and coiled springs?

A Belleville disc spring is a conical-shaped spring shaped like a washer.

Compared to a coiled spring, a Belleville spring is much smaller and can bear a much larger load relative to its deflection rate.

Knowing which type of spring to use—and in which combination—is a precise science. Our engineers can help you determine the best configurations and materials to meet your specific requirements.

 

 

 

 

 


What is the spring rate?

The spring rate is the amount of force associated with the deflection of a spring 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 and inside diameters, height, and thickness of the specific Belleville spring. Our engineers use these variables to determine the spring you need, based on your specific parameters.


What is the relationship between torque and flat load?

Torque is the rotational force applied to a bolt to tighten a Belleville disc spring. Flat load is the amount of axial force required to flatten a Belleville disc spring.

Flat loading a Belleville disc spring helps to ensure that bolts do not loosen while machinery is in use. Flat loading will help prolong the life of your equipment and ensure proper functioning.

Different springs require different amounts of torque to be flat loaded, depending on the design and material. As with all Belleville disc springs, the design depends on the application.


What is the load/deflection relationship of a Belleville disc spring?

Like all springs, a Belleville disc spring will deflect in response to a load. Belleville 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 disc springs well-suited to areas with constant thrust that must stand up to heavy wear.

The load/deflection relationship can be further altered by using more than one Belleville disc spring in series or in parallel.


What is the purpose of stacking Belleville disc springs?

Stacking Belleville disc springs allows for precise customization of the load and/or deflection of the springs.

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 disc springs depends on the requirements of the application. Our engineers can provide assistance in determining the configuration that best meets your needs.

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Why are flat washers sometimes used with Belleville disc springs?

Belleville disc springs help preserve bolt integrity, particularly in areas that must bear a heavy load. In some instances, the addition of a flat washer increases the effectiveness of a Belleville disc spring by helping to spread the load.

In other applications, a flat washer can prevent a Belleville 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 provide assistance in determining whether flat washers are needed for your specific application.


Why does a bolt loosen?

From the moment it is preloaded, a bolt almost always loosens. Several factors inherent to industrial processes can cause bolts to loosen: changes in temperature, vibration, relaxation of bolts, over-tightening and under-tightening, to name a few. In applications with extreme temperature requirements, such as cryogenic applications, thermal expansion/contraction is a significant cause of bolt loosening.

Well-designed Belleville disc springs protect bolt integrity and ensure that bolt joints remain tight.


What are load and deflection in a joint?

A bolted joint stretches in response to a given load. Over time, this can cause the bolt to loosen.

Deflection is the motion that occurs in response to the application or removal of a load or a stress. It is the “spring” in a spring. As force is applied to a joint, deflection counteracts the force by absorbing it. The greater the deflection in a joint, the more load and stress it can withstand, which increases the longevity of the joint.

Belleville springs, used singly or stacked in series, increase deflection. Increasing the deflection means a greater load or stress can be applied to the jointed system without significant losses in the original tension of the joint.


What is preload, and how much should be applied?

“Preload” is the amount of tension in a bolt or joint when it is first tightened. To ensure the integrity of the joint during operation, the amount of preload must exceed the expected external load that will be applied to it.

In other words, the joint has to be stronger than the force that will act on it.

Adding a spring to a bolt will increase the preload of the bolt. Since Belleville disc springs are flat conical springs, they are ideal for adding preload to bolts in limited spaces. Added in series, Bellevilles will increase preload, while requiring only minimal space.

Inevitably, bolts and joints loosen during the course of mechanical operation. Properly designed and installed, Belleville disc springs can increase preload to maintain joint integrity and endurance.


What causes movement in a flanged joint?

All joints move, or loosen, in the course of typical operation – and a flanged joint is no different. Typically, a flanged joint includes a gasket or some other elastic material between the two sections of the joint. While this gasket is designed to cushion the joint, it also can move (or “creep”) during operation, causing movement in the joint.

Another frequent cause of movement in a flanged joint is differential thermal expansion. Many common industrial materials expand when heated. Often, they expand at different rates. When two or more pieces of the flanged joint expand at different rates, the joint no longer fits together as well as it previously did. Often, a gap or a leak will occur.

Other causes of movement in a flanged joint include vibration and embedment, and relaxation.

Regardless of the cause, movement in a flanged joint can compromise its effectiveness and lead to joint failure. Adding a Belleville disc spring or a series of Bellevilles reduces the movement in the joint by holding the gasket and flanges in place. BelleFlex® engineers can advise you on how Bellevilles may be used in your application to reduce movement in flanged joints.


What is differential thermal expansion?

Industrial materials can expand when heated. Often, different materials expand at different rates, a condition known as differential thermal expansion.

Differential thermal expansion can cause problems in applications. If two or more parts of an industrial component are made of materials that expand at different rates, the resulting difference in thermal expansion can cause the component to leak or fail. Imagine two halves of a joint that fit together at room temperature, but when heated, one side becomes too large for the other.

Materials also contract when cooled. Different rates of contraction when cooling introduce the same problems as thermal expansion. Cryogenic applications are subject to the effects of intense cooling, which may include component failure.

This engineering problem is further compounded by repeated changes in temperature. Often a single component will be exposed to frequent cycles of heating and cooling. The resulting expansion and contraction not only endangers smooth operation of equipment, it also increases wear and tear on the parts and can accelerate their failure.

Belleville disc springs help compensate for differential thermal expansion. Two common applications are flanged joints and bolted bus conductors.


What is live loading?

“Live loading” is a method of using Belleville disc springs to preserve preload in valves. A Belleville disc spring is added to the gland follower of a packed valve to create a controlled, sustainable amount of stress in the packing set. Properly executed live loading can greatly reduce the likelihood of mechanical failure.

Live loading is used only for packed valves and offers the greatest benefit for valves that are critical, especially those that are governed by Environmental Protection Agency (EPA) rules, located inconveniently for manual maintenance, subjected to high temperatures and pressures, frequently cycled, and/or motor-operated.

Not every joint or valve is a good candidate for live loading. Our engineers can help you determine which parts of your machinery would be best served by live loading.


How do joints work, and when do they fail?

A joint works when it forms a water-tight or gas-tight seal. When pipes are joined, they are often formed with a flange at the end. To create a firm seal, a gasket is positioned between the two flanges. Nuts and bolts—often including Belleville disc springs—secure the pieces in place.

One of the main concerns about joints is their mechanical integrity. They must be designed, installed, and maintained to withstand industrial conditions. A joint can fail for multiple reasons, such as the following.

Gasket set
Gaskets are designed to withstand a certain amount of pressure. If a gasket is operating under too much pressure—due to industrial conditions or perhaps simply over-tightening—it will be crushed. A gasket must be “set” (or pressed) with the appropriate amount of force.

Vibration
The vibration of machines can cause loosening of various parts, including joints. Engineering design must take vibration into account.

Thermal expansion
Materials often expand and contract when exposed to varying temperatures. If different components expand and contract at different rates, gaps can form within the joint.

BelleFlex® engineers provide assistance in the use of Belleville disc springs to protect the mechanical integrity of joints.


What is pre-setting?

Pre-setting takes place during the manufacturing process of a Belleville 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.

Pre-set Belleville disc springs, typically, are used to maintain load or tension in bolted assemblies.

Pre-setting is not always necessary and must be specified at the time the order is placed. Pre-setting is one aspect of creating custom Bellevilles for your application. Our engineers can advise you on whether pre-setting is required for your application and help you determine the amount of pre-setting.


How do you determine working temperatures?

Every metal has a “working temperature” range, or the maximum and minimum temperatures at which it will continue to function in the working environment. Some metals are designed, specifically, to withstand very high or very low temperatures. Others are intended for use in environments where the temperatures are not extreme.

When designing industrial components, it is critically important to know the temperatures at which the equipment must operate. Components must be manufactured from materials that can withstand those temperatures. For example, Belleville disc springs used in cryogenic applications must be made from materials designed to withstand temperatures of -238°F (-150°C) to absolute zero.

Choosing the correct metal is just one part of overall design. BelleFlex® engineers can guide you in the overall design of Belleville disc springs for your application, including the choice of metals.


What does it mean to calculate load and stress?

It is important to know the limits of a given spring before the spring 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 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.

Load and stress performance may be altered by stacking Belleville disc springs. Our engineers provide assistance with Belleville design questions, such as load and stress calculation.


What are DIN specifications?

Deutsches Institut für Normung (DIN) is an international standards organization, based in Germany that governs specifications of many industrial and technical materials.

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

  • Our engineers employ the calculations of DIN 2092 to create Belleville disc springs with predictable deflection for a given load and a determinable minimum life cycle.
  • BelleFlex® adheres to DIN 2093 for the type, dimensions, material, permissible stress, permissible set, guide clearance, and testing of Bellevilles. Although DIN 2093 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 6796 in the manufacturing of heavy-duty Belleville washers.

What are disc spring tolerances?

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 2093 specification.

Although DIN 2093 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.


How do you determine fatigue life?

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 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 increase the fatigue life.

BelleFlex® engineers provide assistance in determining fatigue life for your specific application.