Material whose modulus changes minimally with temperature

[trauba]

I'm running into a problem where I need to make a spring out of a material whose modulus doesn't change much with temperature (up to ~130C). I have a part suspended between two springs, so the spring preloads are not important, only the spring rate (and the spring rate is directly related to the modulus).

The problem is that the force required to move the part decreases as temperature increases.

My original material was Ph17-7 stainless steel, which has ~5% decrease in modulus from 20C to 120C.

I've investigated some other materials including Inconel, Monel 400, Monel K-500. Monel 400 has ~1.5-2% decrease in modulus from 20C to 120C.

Does anyone know of any other materials that would minimize the problem? Thanks.

 

[israelkk]

Iso elastic, Ni-Span C

 

[patprimmer]

I don;t know if it's possible, but can you use thermal expansion to change mechanical advantage to correct fot change of modulus or change of force required.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[MikeHalloran]

It might be easier to just control the temperature of the spring, e.g. by passing an electric current through it, with a thermostat to keep it at a constant temperature, say 135C. ... or by controlling the temperature of a stream of air ducted over the spring.








Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

Some scientific instruments use fused quartz as a precision spring material.

 

[EdStainless]

If these are leaf springs look at using SiC.

For metals you need an alloy with minimal thermal expansion also.
Look at the various Invar and Nilo alloys.

Also remember that steel would half the variation of your 17-7.

Using the spring as a resistance heating element with a precision current controller would give you the best results. You don't need temp sensors since the resistance of the metal itself can be used for control feedback.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[metman]

Elgiloy and Nitronic(N?)come to mind

Design for RELIABILITY, manufacturability, and maintainability

 

[trauba]

Hey all,

I solved the problem by picking two different springs of different material. This way, at high temperatures, the difference in spring rate change between the two compensates for the overall decrease in spring rate. Thanks.