Improving Neoprene Compression Set

[jrdynamic]

Is there any way to improve the compression set of molded neoprene parts? Any production methods that will improve compression set? The samples for compression set testing are taken from the molded parts. The neoprene itself passes compression set testing when the testing is done on molded "buttons" as per the applicable ASTM testing procedure - but the neoprene fails when samples are taken from the production part.

 

[GrahamBennett]

Compression set in a compound depends on the state of cure, which is why this test is always carried out on buttons of a specified size. If the part you are making is thicker than the button then the state of cure throughout the part will be different to that in the button. Therefore the resulting compression set will be different. The only way I can think of improving this property is to post-cure the parts for a given time at a given temperature (determined from the cure traces of your compound(s) to increase the state of cure and, thus, the compression set resistance.

 

[jrdynamic]

Thank you for your reply!!

If we post-cure at the temperature and time recommended by our Custom Mixer, will this adversly affect tensile and elongation properties? How about Shear Modulus?

Any help is appreciated.

 

[Elastomatt]

Post curing will affect the tensile and elongation, but how depends on the initial state of cure. Increases in hardness, tensile and drops in elongation are common when postcuring)

Be aware that post curing may change dimensions as well.

If you can't increase cure time/processing time or raise moulding temp slightly then you may want to ask the material supplier if they can speed the material up a bit.

Do you cut your product down for testing?
We use a splitting machne similar to the following (look up PMF fortuna splitting machines) quite expensive but excellent for cutting down rubber products for testing.