Composite Coil Springs 2

[ulrichAT]

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

 

[ulrichAT]

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

 

[Fabrico]

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

http://www.Firestoneindustrial.com

 

[unclesyd]

Another possibility is a liquid die spring. This is from the the above mentioned Taylor Devices website. I would give them a call and discuss you requirements.

http://www.thomasregister.com/olc/63970008/liquid.htm

 

[mloew]

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.

 

[GregLocock]

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.

 

[zekeman]

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

 

[GregLocock]

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.