spring rate for NBR and CR rubbers

[janagan]

Looking for spring rates for NBR rubber
hardness - 75 shore a
tensile - 2000 psi
100% modulus - 980 psi

for Neoprene

hardness - 75 shore a
tensile - 2710 psi
100% modulus - 650 psi

ultimate goal is to find how much it deflects under a certain load ( rubber thickness .125")

 

[APH]

The spring rate is not constant. If you want to to find load vs deflection, testing is probably the only accurate way to do it. Force gage and dial indicator mounted on the height gage should give you a ball park.

APH

 

[garrity]

I want to second the idea that testing is essential since almost ALL rubber compounds are custom mixed for a particular rubber manufacturer and results can vary widely, even for a 75 durometer (Shoire A) compound with 2700 psi tensile. One rubber company's recipe may have five ingredients; another may have 10 or much more depending on their needs for special properties. It's made even more difficult by companies that use inexpensive an SBR polymer as a filler for CR, up to 45 percent of the polymer in the compound. It's completely different from plastics where we can just jump on the phone and order a bag by stock number. With rubber, testing is almost essential.

 

[craigj]

testing is essential depending on your application. Sometimes testing cost does not pay off! I have done simulations with both fully tested materials and also with a linear approximation and guess what...it didnt matter.

What Im trying to say is that some thought must be given to what you want to accomplish before you go out and spend money for testing. BUT I do agree that understanding and testing is required to acheive accurate material properties for a particular "brand" of practically any polymer, rubber, TPE/TPU alloy, etc...

Craig