long-term stability of elastomer springs

[epierce]

We're looking to replace a steel compression spring with an elastomer one for space and weight savings. The problem is that the spring acts as a force limiter, so that the spring resistance (at a given deflection) needs to stay within a ±15% tolerance over the product's 5-10 year lifespan.

Can anyone comment on the feasibility of this idea or even recommend an elastomer?

Polyurethane seems like an obvious choice for load bearing applications, but NR has the cost advantage.

Thanks,
Eldon.

PS - Some more detail on the spring loading:

Loading on the spring would be fairly high, on the order of 500 psi, but only momentary (~1 sec on min. 10s cycle). Preloading the spring would be nice, but I'm guessing this isn't possible due to creep.

Depending on the height of the elastomer block, deflection could be anywhere between 10 and 30%. I imagine that less deflection would be better for reliability.

Conditions are room temp and dry.

 

[GrahamBennett]

I suggest you google "natural rubber bearings research".

 

[utkk]

You will check working condition before select materials. I think polyurethane have a good properties and it is the first choice for me.

Rubber engineering

 

[epierce]

Thanks for your suggestions, both of you. Apologies GrahamBennet, I somehow missed the notification when you replied a month ago.

I've looked into the research as much as I have time for, as well as a few books that have been recommended in this forum. I haven't found the precise answer to my question, but it has been enough to say that it seems possible.

Due to the critical nature of this component, it's become clear that we'll need to hire a specialist to help with the specific material selection. For now, a bit more work on the rest of the design is necessary to confirm the forces/geometry we're working with.

E

 

[GrahamBennett]

Thanks OK epierce. the company I work for has an engineering design unit that specialises in designing NR bearings. Unfortunately I'm not allowed to post a link.

Graham.

 

[corrosionman]

epierce, if it is of any value, I recently examined some 30 year old rubber mounting blocks from a heavy vibrating machine in a mineral processing works and they had had a pretty tough life - -they were being replaced because all metal parts were severely corroded - - we did Load / Deflection tests and found that the results were the same as new Nat Rubber blocks. Are you in UK ?
Regards.
Corrosionman

 

[epierce]

Hi, I'm in Canada, but thanks for the info all the same. It reminds me to post this publication I found while researching the subject:

http://www.ismithers.net/publishing/wag005/natural-ageing-of-rubber/

An organization called Rapra carried out tests on several elastomer compounds over the course of 40 years. There is also a paper comparing these results to accelerated test results on the same compounds. Pretty interesting.

Eldon.

 

[GrahamBennett]

RAPRA is very good on plastics and packaging but not so good on rubber IMHO.