FAQs About Belleville Springs & Washers

The term "live loading" means using a Belleville spring to maintain load on a seal. Many valves utilitze studs or bolts to exert load on to the gland follower, which applies stress to the packing. As the valve is operated, the seal material consolidates during each operation. High temperature and thermal cycling can accelerate this loss. As this occurs, preload is lost on the seal, and once the preload falls below a certain threshold, a leak will occur. Since the stretch in the stud is small, loss of preload and packing stress can occur quickly.

Flange live loading with Solon Flange Washers manufactured with precipitation-hardened stainless steel are ideal in cryogenic applications where cold temperature and corrosion are factors in process leaks and fugitive emissions. 

The widely accepted forumal for torque calculation is: T=K*F*D, where K = estimated nut factor, T = bolt torque, D = nominal bolt diameter. Find more Belleville Spring Specifications. 
 

Things to consider when choosing material are bolt material, temperature, environment, application, cost, availability. Our Material Guide will ensure your Belleville washers hold up to your specific application requirements.

The maximum deflection should normally be calculated as follows: MAX Deflection = MAX Overall Heigh - MIN Thickness

Read our Technical Service Bulletin to learn more.
 

Download our technical white paper, Why Bolts Work (and Why Some don't), which discusses the three main important points to remember when bolting and why it is important to understand why factors such as embedment relaxation, differential thermal expansion (DTE), elastic interactions, vibration loosening, bolt creep, and component yielding cause bolts to lose load and how to counteract these phenomena. 
 

Download our technical white paper, Using Belleville Springs to Prevent Bolt Fatigue Failures, to learn how changes to a bolt, such as stiffness, will influence the cyclical load on the fastener. This paper takes a closer look at the science behind the elements of preventing bolting malfunctions, and explains how using Solon Belleville Springs & Washers increases the elasticity of the bolting system and maintains bolt preload. 
 

A Belleville spring can be used indefinitely as long as it is not damaged. It is perfectly acceptable to reuse the springs many times in bolted applications. However, it is important to note that as highly stressed parts, Belleville springs can be prone to failures if they have been compromised in some way, as outlined in Belleville Spring Washer Products. Parts can be damaged by excessive cycling, corrosion, exposure to temperatures beyond the material ratings, and mechanical damage such as galling. 

Load on a Belleville spring changes (or cycles) to some extent in all applications. We consider an application to be cyclical when these changes in load will eventually result in the failure of the part. If this is the case, we must then determine if the number of calculated cycles provides adequate life of the product. Cycle life is calculated by considering the maximum load (and resultant stress) for each cycle and the change in load. Generally, the calculated cycle life in a bolting application will be nearly infinite. 

In general, Solon Belleville Springs are designed to be loaded to flat without damaging them. However, this does not mean they should be bolted to flat in every case. There are some applications where a spring should be employed at a load considerably lower than the flat load, as outlined in Design & Tech Support. For instance, when elevated temperatures may damage the springs, it may be necessary to use a heavier spring in order to keep the stresses below a certain threshold. In addition, in some elevated temperature applications it may be desirable to allow the spring to partially “absorb” the differential expansion to prevent excessive loading. 

In general, Solon Manufacturing Co. suggests that the following torque calculation be used to determine the bolt load. For detailed calculation tools, see Washer Calculator & Tools.

• Imperial: (ft. – lbs.) - .2 X Bolt Diameter (in.) X Load (lbs.) / 12

• Metric: (N-m) = .2 X Bolt Diameter (mm) X Load (N) / 1000

• If lubricant is used on the joint, then the torque should be reduced.

• If the nuts and bolts are stainless, then torque may need to be increased. Your Solon application engineer can help determine the appropriate torque value for your requirement. 

The application will determine proper load. The following factors are important for live loading a bolted joint:

• Decide what load or torque should be used for a sound joint design. If the joint is a flange, the gasket manufacturer should provide this value. If the joint is a bus (electrical) connection, the designer of the system should provide this value.

• Decide which material the Belleville spring should be. We generally suggest a material that is similar to the bolt material.

• If the Belleville spring may be used at its flat load, use a spring whose flat load is close to the design preload. It may be necessary to use multiple Belleville springs in parallel in order to achieve the requisite flat load. Ideally, the design preload will be 70%-100% of the flat load.

• Confirm the spring arrangement fits into the space constraints of the application. 

Actually, thickness plus deflection is not equal to H. This is because thickness is measured on an angle with respect to the deflection. However, since this angle is typically very small, the thickness plus deflection is approximately equal to H. In addition, if a spring is not prestressed, the H will usually be greater than the thickness plus deflection. For detailed calculation guidance, see Washer Calculator & Tools.

• Flat Load: How much load (force) will be required to elastically deflect the Belleville spring completely. Load is measured in lbs (Imperial) or Newtons (Metric).

• Flat Torque: Bolt torque required to produce the flat load assuming a k factor of 0.2. See Solon Belleville Springs Catalog for calculations.