belleville vs coil

[caddelljoey]

Im needing a spring with at least a couple feet of deflection. An Infinite fatigue life is desired. Diameter a maximum of about 3.5 inches. Length is not an issue. It seems belleville washers may seem like my viable option. The buckling of compression springs at this length throws them out. Maybe very long extension springs at a small percentage of deflection for infinate cycles? My main question is as long as belleville washers are not stacked parallel is there still a damping effect and thus energy loss?

 

[TVP]

Have you investigated non-metallic options like air springs or elastomers? The diameter is quite small for that kind of travel. Is there a way that you can implement a linkage that would reduce the necessary spring travel?

 

[caddelljoey]

This is down a borehole and prefer a mecanical spring. Does anyone know if dampening of bellevilles causes a significant energy loss?

 

[desertfox]

Hi cadelljoey

Either a spring made with belville washers or coils will absorb energy however the spring will store the energy and return the energy at the first opportunity, if you want to the dissipate the energy then you need a shock absorber using gas or oil.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[dgallup]

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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[caddelljoey]

Im not wanting to dissapate the energy..bellvilles return the same amount of energy as coil springs if stacked alternatlely(in series) or less ?

 

[desertfox]

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

http://schnorr.com/downloads/handbook/16-engineering-a-design-5-15/file.html

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

 

[israelkk]

There is a way to to make a long compression spring guided over a rod or inside a cylinder without buckle and minimal friction as a result. However, as desertfox stated maybe you can provide actual properties expected from the spring. Such as, exact force/s vs deflection, rate, etc.

 

[MikeHalloran]

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

 

[drawoh]

caddelljoey,

A coil spring will not buckle if there is a shaft inside. A shaft inside is absolutely necessary for belleville springs, as noted by MikeHalloran.

Try working out some designs with your various springs. Almost certainly, you have not described all our design parameters to us. I have designed a series of adjustable optics mounts based on an Oriel mount that used rubber springs. I determined that a stack of belleville springs had a lower nominal height for a given deflection, so I switched. Then, I discovered that medium strength die springs, usually painted blue, used less height than the belleville springs, and thus, were more efficient for my application.

Belleville springs are very stiff. If you need stiffness, I don't see similar sized extension springs as an alternative.

--
JHG

 

[btrueblood]

"Belleville springs are very stiff. If you need stiffness, I don't see similar sized extension springs as an alternative."

Well, actually Bellevilles I have used can have a zero, or even negative stiffness, depending on where they were in their load/deflection curve... I think what you mean is "Belleville springs have a high load capacity in a much more compact size than coil springs".

But I'm being pedantical.