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Composite Coil Springs
2

Composite Coil Springs

Composite Coil Springs

(OP)
I am looking for coil springs made of fiber reinforced plastic. Does anybody know, where I could get such springs?

Thanks a lot for every hint,
ulrich

RE: Composite Coil Springs

Try Heli-cal Corp. They machine springs from any type of bar stock.
http://www.heli-cal.com/

RE: Composite Coil Springs

vti

Before jumping to the state of the art and most expensive spring manufacturing process, a normal standard wire coiled spring has to be checked. Anyway, ulrichAT is looking for springs made of composite materials and I assume he has good reasons for it.

RE: Composite Coil Springs

(OP)
Thank you all for the input. israelkk is right, I need a composite spring, because steel springs are to heavy for our application. Titanium is too expensive.

TVP, thanks for your link, this is quite what I'm looking for. But this company is located in France. Do you know something similar in the US?

RE: Composite Coil Springs

ulrichAT,

I do not know of any company other than Sardou that makes helical springs from fiber-reinforced polymer matrix composites.  I know Hexcel was working on composite leaf springs, so you may try them.  Have you discussed your application with TIMET?  They have worked on some solutions that can lower the cost of titanium, including the new alloy TIMET LCB.

RE: Composite Coil Springs

ulrichAT

Can you provide the weight, size, force, deflection etc. that are required from the springs.

May be an optimize metal spring can do the job or get close?

RE: Composite Coil Springs

(OP)
@israelkk: No, a steel spring cannot do the job, we know that for sure.

@TVP: Thanks for the hints, I will check that.

Both of you thanks again for your help,
ulrichAT

RE: Composite Coil Springs

ulrichAT

Did you try a preset (scaragged) spring? It can take up to 70% more stress then non-preset spring.

RE: Composite Coil Springs

(OP)
Ok. israelkk, I need a coil spring, which has a working travel of approx. 2 1/2" and a spring rate of approx. 400 lb./in. The weight of the spring must be lower than 450g. The spring has to make about 100000 strokes in a highly dynamic mode.

If you can give me a steel spring which meets these requirements you will make me very happy!

Regards,
ulrichAT

RE: Composite Coil Springs

You need to specify the maximum and minimum loads as well.

Also, what friction (or damping) is acceptable.

I suspect that nothing short of a diamond will meet that spec, due to the weight requirement. That in itself looks rather arbitrary, since it is almost exactly one pound in the old money.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Composite Coil Springs

(OP)
GregLocock, these values are not arbitrary at all, but of course the values are rounded.

But you are right, we also believe that you cannot meet this specification with a steel spring. What we try to find out is, whether it is possible with a fiber reinforced material or not.

What do you think? Is it possible to reach this goal with FRP? If yes, do you know a company which could build this spring?

Best regards,
ulrichAT

RE: Composite Coil Springs

After investing some time I am convinced that a helical compression spring made from a metal wire can be designed to deflect approx. 2.5" from free position to give the ~1000 lb force and 100000 cycles and weigh 1 lb.

http://israelkk.googlepages.com/home

RE: Composite Coil Springs

Hmm, I can't design one to weigh that little with a stress range of less than 1000 N mm-2, which is not going to last for 10^5 cyles.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Composite Coil Springs

Israelkk,

What "metal wire" type did you use for your analysis?

RE: Composite Coil Springs

As sugested by vti the use of a machined spring should be looked at, especially the multistart variety. Since I lost my spring (smarts and step) some time ago I can't offer any particular direction.   

Aside from the aformention Helical Springs here are two other manufacturers of machined springs.

http://www.abssac.com/product.asp?productnum=9&catnum=2

http://www.taylordevices.com/MachinedSprings.htm

This information is from my buddy who works with weird science and engineering secret stuff.

RE: Composite Coil Springs

(OP)
Israelkk, you make me curious. Can you give me a little bit more information about this spring? What metal did you use? Titanium?

ulrichAT

RE: Composite Coil Springs

(OP)
unclesyd and vti, I will investigate the machined spring option. Thanks for the hint.

ulrichAT

RE: Composite Coil Springs

Air bag.

RE: Composite Coil Springs

(OP)
Fabrico, I don't understand. Can you explain what you mean?

RE: Composite Coil Springs

Actually, they were called that until the blow-up-in-your face safety devices showed up. Now they're called air springs. Pound for pound they hold up many times what a steel spring will. They are used on everything from bicycles freight trains. They will easily achieve the 100,000 cycle requirement. The larger have steel or aluminum end pieces, some smaller have plastic ends. Aside form being light, they are also adjustable. Check out www.Firestoneindustrial.com

RE: Composite Coil Springs

Why is the mass constrained? Is it an overall limitation or to avoid certain natural frequencies? If a mechanical spring will not work, I like the suggestions of air springs (used for many years in racing engines) and the silicone fluid spring.

Best regards,

Matthew Ian Loew


Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Composite Coil Springs

Damn I thought israelkk had limited himself to steel. Titanium alloy is a better bet.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Composite Coil Springs

found this interesting formula* which is appropo of this discussion. It gives the volume efficiency of any spring system according to
U/V=k(max working stress)^2/G for a torsional system.
where
U= energy stored
V= volume of spring material
k=facor depending on spring configuration
To convert this to weight efficiency we get
U/W=U/Vd
d= density
It turns out that a helical spring with a k value of 1/5.4 (I assumed a  spring index of 4) is the most efficient for weight efficiency. I calculated values for alloy steel and berrylium copper to test this formula with the following results:
Steel : 1/5.4(70000)^2/(11.5*10^6*.287)=275 in lb/lb
Berrylium copper: 1/5.4(50000)^2/(6.5*10^6*.297)= 239 in lb/lb
According to these figures (I guessed at the fatigue stresses), for steel you would need
1000*2.5/2/275 = 4.5 lbs steel (U=1000lb*2.5"/2)
and even more for Berrylium bronze. So as everybody has said these metals aren't even close to the requirement of 1 pound.
The key to getting a material is to maximize the
allowable stress^2/density. I don't think that titanium will do it but it is off the table anyway because of the cost.

* Rothbart, Mechanical Design and Systems Handbook, McGraw Hill, 1st and 2nd editions

RE: Composite Coil Springs

I disagree that Titanium would be too costly - if it solves a problem that is unsolvable any other way. I've seen Ti used in some fairly mundane applications - typically the cost of machining a part exceeds the cost of the Ti, so if it is the best material then it can often be cost effective.

That's why I questioned the fixed mass requirement of the spring, the only time the mass of a component is fixed is when mass is the raison d'etre of the component. In ANY other system there is a compromise - for instance, if the spring were 10% heavier, could something else be lightened to compensate? There must be a tradeoff.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

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