Low Creep Elasomer
Low Creep Elasomer
(OP)
I am looking for an elastomer of approximately 70A hardness which exhibits very low creep. I am currently using a thermoset urethane. While testing is not complete, preliminary results do not look good.
What type(s) of elastomers typically exhibit the best creep performance?
The application is similar to a suspension airbag except I don't have air as a restoring force. I need the elastomer structure to be the return spring.
What type(s) of elastomers typically exhibit the best creep performance?
The application is similar to a suspension airbag except I don't have air as a restoring force. I need the elastomer structure to be the return spring.





RE: Low Creep Elasomer
At ambient temperatures natural rubber has good low set properties, especially when cured with an EV system. No elastomer is free of permanent set, however. Set can be minimised by elastomer choice, compounding and cure system
RE: Low Creep Elasomer
Creep and compression set are the same thing in my book. I don't have a good feel for why thermoset urethanes generally have such poor compression set properties. My best guess is that bonds get broken and remade. It would be interesting to run a tesile test after a creep test and to see how much strength is retained.
Another possibility is that there is really very little crosslinking in a typical urethane, so most thermoset urethanes are more akin to thermoplastics than say an epoxy.
RE: Low Creep Elasomer
However elastomers do exhibit stress relaxation under constant load, which IS time dependant. Maybe this is closer to creep than set.
Either way, you are right. The breakdown of crosslinks under compression and new crosslinks forming in the compressed state is the main cause of set.
Neither urethanes nor rubber-like elastomers are heavily crosslinked, especially when compared to epoxies. The ability of elastomers to recover after rapid and short duration deflections is what differentiates them from thermoplastics. This recovery/elasticity is made possibly by the light and rather mobile network of crosslinks.
I'd be interested in seeing your results from the urethane claiming 1% set. ASTM D 395 Method B is about the least demanding compset test (22 hours at 70 deg C) and I've yet to see anything do THAT well.
RE: Low Creep Elasomer
Most Silicones can acheive a low compression set if they are cured for the right amount of time and temperature. By low I mean 5-10%, NOT 1%! That seems impossible to me. What uethane is claiming this?
CJ
RE: Low Creep Elasomer