What is the difference between a Solon Flange Washer and a Solon Belleville Spring?
Flange washers are a type of Belleville spring. The main distinction of a flange washer is that the OD/ID ratio is small (about 1.75) relative to most Belleville designs. This allows the flange washers to be used in applications where bolts are in close proximity and where spot-faces may exist. In general, the OD of these parts is about the same as the points on a standard nut. In addition, the flat loads for flange washers are generally high to meet the demands of many flange live loading applications. <top>

How many times can a Belleville Spring be used?
Belleville spring can be used indefinitely as long as it is not damaged in some way. 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 failure if they have been compromised in some way. Parts can be damaged by excessive cycling, corrosion, exposure to temperatures beyond the material ratings, and mechanical damage
such as galling. <top>

What do you consider a cyclical application?
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, if the change in load is less than 20%, then the calculated cycle life will be nearly infinite. <top>

Should one or two Solon Belleville Springs be used on a bolt?
The answer to this question depends on the application. The most common bolting arrangement is to have one Solon Belleville Spring on each side of the joint. This is what is suggested in 80% to 90% of all cases. There are many applications where a single spring adds enough elasticity to the system. Conversely, there are other situations where three or more springs may be needed for a sound design. Solon engineers can suggest how many Belleville springs should be used for a given application. <top>

What does preset mean?
Presetting is part of the manufacturing process for most of Solon Manufacturing's Belleville Springs. This simply involves taking the parts to the flat position momentarily. Since the parts are typically formed higher than their maximum deflection, they will yield (or take a set) to their design height. The variation in free height is reduced by this process. In addition cycle life and performance of the part is improved. <top>

Some Belleville springs are not prestressed since it is often impractical and costly to prestress springs that are very small or thin. Machined flange washers are not often prestressed since very close tolerances are already maintained and they are rarely subjected to mechanical cyclical loading. <top>

Should a Belleville Spring be bolted down until it is flat?
The answer to this question depends on the application. There are many situations where this is appropriate and others where it is not. In general, Solon Belleville Springs are designed to be loaded to flat without damaging them. This does not mean that they should be bolted to flat in every case. There are many applications where a spring should be employed at a load considerably lower than the flat load. 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. <top>

How do I know when a Belleville Spring is flat?
It is very difficult to determine when a Belleville spring is in its flat position. Some technicians claim that they can "feel" when the Belleville becomes flat as they are tightening the bolt. This is probably true for small bolts (under 1/2") but it is more difficult as bolts become larger. This is risky because it is very easy to exceed the loading limits of the joint or bolt. <top>

Another method that is employed by some technicians is to place a straight-edge against one of the flats on the nut and then try to rock it on the top of the Belleville spring. When the straight-edge no longer rocks, then the part is flat. This is also risky because the technician may not know to what extent the flat load of the spring has been exceeded. <top>

In general, Solon Manufacturing Company suggests that torque be used to determine the bolt load. Remember that the torque values listed in Solon's Belleville Spring catalog are based on a nut factor of 0.2 for dry steel on steel. If lubricant is used on the joint, then the torque should be reduced. Conversely, if the bolts and nuts are stainless, then the torque may need to be increased. Contact the engineering department at Solon Manufacturing for help in determining the appropriate torque for a given application. <top>

What load should be used on a Belleville Spring?
This is a very common question. At Solon Manufacturing Company, we consider the application to determine the proper load. The correct approach for live loading a bolted joint is to:
1. Decide what load or torque should be used for a sound joint design. If the joint is a flange, then the gasket manufacturer should provide this value. If the joint is a bus (electrical) connection, then the designer of the system should provide this.
2. Decide which material the Belleville Spring should be. Generally, we at Solon Manufacturing Company would suggest a material that is similar to the bolt material

3. If it is determined that the spring may be used at its flat load, then we find 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. This does not have to be exact for bolting applications. Ideally, the design preload will be 90% to 100% of the flat load.
4. Check to ensure that the spring arrangement fits into the space constraints of the application. <top>

Why do other Belleville manufacturers have different flat loads listed for the same size spring?
Almost all Belleville spring manufacturers employ a calculation derived by Almen and Lazlo. This derivation makes several assumptions such as sharp corners and that the parts are loaded at the corners. However, in most bolting applications, the springs are loaded between a flat surface (the joint) and a nut (or bolt head). As the spring is loaded close to its flat position, it begins to 'bottom out.' In other words, the contact points are no longer at the corners. As a result, load increases non-linearly as the flat load is approached. The loads listed in Solon's catalog take this phenomenon into account. <top>

Shouldn't the deflection plus the thickness of a Belleville equal the overall height (OH)?
Actually, thickness plus deflection is not equal to the OH. This is because the 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 OH. <top>

Why are stainless steel springs magnetic?
All stainless steels are magnetic with the exception of the austenitic group (300 series). Even the austenitic group can be made more magnetic by cold working. Solon Belleville
301 Springs are manufactured using cold worked material, and hence are slightly magnetic. <top>

Should I use a Solon Belleville Spring in 301 Stainless or 17-7 Stainless?
301 stainless is the less costly of the two materials and offers a slightly better corrosion resistance. 17-7PH stainless springs have better mechanical and high temperature properties. In addition, since 301 stainless springs are stamped from work hardened material, the size range of this product line is much more limited. <top>

Does Solon Manufacturing Co. offer any non-magnetic springs?
718 Inconel and 510 Phosphor Bronze are non-magnetic and are standard Solon stock materials. <top>

Can you offer a Belleville spring made from non-magnetic 18-8 stainless?

Note that the 18-8 designation relates to the nominal amount of chromium (18%) and nickel (8%) in the material. There are several grades of stainless steel that may fall under this category. These are most commonly 302 and 304 stainless steels.

18-8 stainless can be slightly magnetic. It would be possible to manufacture springs from 302 or 304. However, we would manufacture from a work-hardened grade of these materials. The work-hardening increases the strength and spring properties of the material which allows the material to pick up a slight amount of magnetism.

It would be possible to make Bellevilles from non-magnetic (annealed) 18-8 stainless. However, the low strength of the material would make the parts useless as springs. After one cycle, the parts would essentially become flat washers.

Solon offers Belleville springs made from 301 stainless rather than 302 or 304. The corrosion and magnetic properties of all of these grades are very similar. However, 301 offers superior spring properties in the work-hardened state. Our 301 springs are only slightly magnetic.

Solon offers Belleville springs made from 17-7PH stainless. These are precipitation hardened and highly magnetic springs<top>

What types of plating/corrosion protection does Solon Manufacturing offer on Solon Belleville Springs?

Aside from zinc plating, Solon offers other methods to protect parts such as nickel plating, yellow chromate, black oxide, oil coating, etc. Contact Solon for pricing and availability of optional coatings. <top>

What does mechanically zinc plated mean?
Mechanical plating is the method that Solon Manufacturing employs to apply zinc to our parts. The process involves rotating the parts with a mixture of zinc particles and glass beads. The beads essentially cold-weld the zinc to the substrate of Solon Belleville Springs. This provides corrosion protection for steel parts and all but eliminates the risk of hydrogen embrittlement that is common for electroplated parts. <top>

George P. Davet, BSME has been with Solon Manufacturing Company since 1993. He currently holds the position of Vice President and Chief Engineer. His responsibilities include overseeing new product design, R&D testing programs, and application assistance for all Solon Manufacturing's products. George has written and published numerous articles on the application of Solon Belleville Springs. He can be reached at gdavet@solonmfg.com or 800-323-9717.