Rubber Consistency 1

[Sodboa]

In our business we use a number of silicon diaphragms, both gum rubber and Liquid injection Molded (LIM). We have had at times had parts that were under cured (we believe) and were extremely sticky especially when exposed to heat and humidity (I realise silicone is inherently sticky). Does anyone know of a simple testing procedure for checking that parts remain consistent?

We have experimented with Shore M durometer, but this is a very subjective test IRHD appears better. Hexane swell, but this is 24+ hour test and is limited in quantities that can be done. NMR (Nuclear Magnetic Resonance), but the equipment is expensive and not very robust.
TGA and DMA, but in both cases these seem to be quite vague in thier result, also these are somewhat expensive pieces of equipment.

Any suggestion please.

 

[ElastomerXpert]

I realize you wrote your question long ago, but will offer what I can in any case.

If the rubber parts are small enough, you will probably reach equilibrium swell in 8 hrs (overnight) and that is a reasonably valid and precise measure of crosslink density. You can also dry out the specimens after they've swelled, and check final weight against original weight, which will tell you about the % extractables, which should also be consistent if the rubber is consistent.

Silicone slightly undercured is often slick, almost oily, rather than sticky. Stickiness can come, oddly enough, from overcure.

R J Del Vecchio
Technical Consulting Services
(consultant in Applied Rubber Technology)

 

[jajal]

I want to know abaout rubber belting process, can you help me?