Standard joint with flat washers (blue)
& Belleville washers (green)
A question we often receive is; should I use a flat washer with a Belleville washer? While there are situations when you can use a flat washer with a Belleville washer,
it is important to note that a Belleville washer is not a replacement for a flat washer.
Let's start by going over the basic functions of both fastener elements:
- A Belleville washer functions as a spring, adding elasticity under load. This elasticity acts similarly to bolt stretch, maintaining preload in the event of relaxation or joint expansion.
- A flat washer is used to spread out force of a bolt or nut onto a larger area of the joint surface. This protects the surfaces of the joint from damage and prevents embedment (i.e. the bolt head digs into joint surface). Functionally, embedment of a bolt or nut decreases the load of the joint and can be a cause of loosening.
As you can see, the two fastener elements are designed to solve two different problems.
Why they work well together
As they do not serve the same function, a Belleville washer and a flat washer can work in tandem to improve the joint. A Belleville works best when it has a flat and smooth bearing surface. This is because the contact surface, (the top inside corner and the bottom outside corner), slides/rolls as the washer deforms to flat. The less friction created by this motion, the better. Without a flat washer, the bottom bearing surface is up against the joint surface. The addition of the flat washer provides a better bearing surface, as well as distributing the load. A flat washer is not required on top of the Belleville as the bolt or nut usually provide an adequate bearing surface to limit friction.
When a Belleville washer does not require a flat washer
Given the right set of circumstances, a Belleville washer will work just fine without a flat washer. It all depends on the joint surface. As stated above, a Belleville washer does not distribute the load nearly as well as a flat washer. If the joint surface is relatively soft or is susceptible to embedment, the washer may dig in. If the surface is uneven or rough, the increase in friction may cause a lower load. However, if the joint surface is hard, even and smooth, a Belleville may be used without a flat washer with minimal change in joint performance.
Selecting the right flat washer
There are three factors to consider when selecting the right flat washer.
1. It is important to make sure that the Belleville, bolt, and flat washer used are of a similar material family. Stainless steel should be used with stainless steel, and zinc-plated carbon with zinc-plated carbon. This will help to prevent the problems caused by galvanic corrosion and differential thermal expansion.
2. It is important that the flat washer OD is large enough to accommodate the Belleville's OD. If the washer OD is too small so that the Belleville overhangs, then the loading characteristics will be altered, limiting the defleciton available for preload retention.
3. The thickness of the flat washer should be at least one-third the thickness of the Belleville washer. This will ensure that the washer itself does not deform under the intended load. This assumes that the flat washer is fully supported by the joint. If the flat washer is not fully supported, then a thicker washer may be warranted.
If your application requires both load distribution and the spring action of a Belleville washer, using them together can be effective. Always consider the specific requirements of your assembly to determine if this combination is suitable.
Solon Belleville Springs & washers advantages
Installing Solon Belleville Springs & Washers to the fastening system ensures a proven and reliable connection. Solon Belleville Springs & Washers increase the elasticity of the bolting system by maintaining consistent, and sufficient bolt preload— providing improved bolted joint reliability, preventing unplanned or costly downtime, and protecting your assets.
Solon Manufacturing, an industry leader on engineered solutions for critical applications, can help from design through aftermarket to ensure bolts have the correct mating parts that will effectively support any applications. Often there are standard options already available, though a custom Belleville washer can be engineered around specifications.
Solon Belleville Springs & Washers are used in a variety of applications and industries to maintain bolt preload on bolted joints and connections. Solon Belleville Springs & Washers minimize the effects of differential thermal expansion, vibration, embedment relaxation, bolt yield/creep, and thermal cycling.
Additional information such as calculator tools, videos, case studies and technical white papers can be found in our resource library.
Learn more about the use of Belleville springs & washers in bolting applications:
Application: General Purpose Bolting
Application: Commercial Bolting Applications
Calculator: Bolt Stretch Calculator
Calculator: Infinite Bolt Life Fatigue Calculator
White Paper: Why Increased Elasticity Leads to Reduced Self-Loosening
Video: Solon
Belleville Spring Washers
Product Selection Tools: Application Specific Calculators
Contact Us
Just how do you propose getting several feet of deflection from a belleville washer 3.5 inches in diameter? You are going to have to stack up dozens of them inside a tube or over a rod. You could do the same with a coil spring to control the buckling. Either one is going to have a pretty large amount of friction (energy loss) which is not going to help your "infinite fatigue life" criteria. What is your actual life requirement? Typical S/N curves only go out to about 10^7, that is a long way short of infinite. I've had springs break at 10^8 when my requirement was 10^9. Simply keeping stress below the "fatigue limit" won't get you to "infinite life".
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
Caddelljoey
Energy loss is the same as dissipating energy through heat, friction etc.
Why not tell us exactly what your trying to do in a single post instead of dribbling information over several posts.
Here is a link to belville washers technical handbook
In it you will find towards the end the frictional losses for spring stacks which will be in the order of 2,5,15% of the spring force, however you haven't provided any load information about either a coil spring or a belville spring stack other than diameter, spring life, what about spring stiffness or load at length because it's these parameters that will govern the energy losses that you require.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
Buy a couple dozen Bellevilles and see how high you can stack them on your desk, like a high tech Jenga.
I'm betting the pile will fall over before you run out.
Note also that the inner and outer edges are both rough, so while it is possible to guide them, there will be uncertain friction against the guides.
You might be better off stacking closed and ground coil springs, which at least give you a finite radius on the rubbing surface.
You could also make one really long spring with square-ish coils from a long piece of hollow bar, given a really long lathe and a milling spindle on the slide, or maybe use a wire saw on the slide and make it look like a very long Heli-Cal. ... but cutting springs from hollow bar is normally done for very high force within a limited envelope, not for very high stroke within a limited envelope.
... but no matter how nicely you make it and how perfectly square the ends are, it will still buckle, and need guidance.
Maybe you could line the outer tube with plastic, if you can find one that will take your downhole temperatures.
As israelkk said, providing some more of the spring parameters you actually need would help us eliminate some of the most inappropriate possibilites.
How much 'idle length' do you have available? Could you, for instance, use an extension spring that's ten feet long, plus a two foot stroke, making your assembly's OAL approx 12 feet?
Mike Halloran
Pembroke Pines, FL, USA