Accelerated life testing of EPDM diaphragm

[twizel]

Hello,

Im working on a small high flow dump valve that uses a small round ( 14mm dia) diaphragm as the valve. The diaphragm seals around the perimeter using a circular x-section bead design.
The exhaust port of the valve is an annulus with an ID of 6mm and an OD of 8mm. The annulus is concentric with the diaphragm. The valve housing is injection moulded PA66, the Diaphragm is a Nordel 4570, hardness 60Shore A,
The working pressure is 450Kpa - 65Psi. pressure in the exhaust port is atmospheric.
While at working pressure, the diaphragm has to bridge across the 1mm wide exhaust port. both edges of the port are radiused to 0.25mm.
The thickness of the diaphragm is 2mm in the area that bridges the exhaust port.
service life is 10 yrs.

I am wanting to test the parts resistance to extrusion or creep down into the exhaust port. Some research indicates that by raising both pressure and temperature I can test the parts long term performance and resistance to extrusion and creep?

Can anyone give me any guidance on what pressures, temperatures and time of test would be required to run such a test?

thanks for your help,

regards,,

twizel

 

[btrueblood]

I don't think there are any "rules of thumb" for rubber creep rates that would allow you to predict the effect of temperature a priori. Further, I don't think standard tensile and/or compression test methods would yield data to help you predict the extrusion you are looking for. I think you really are stuck with doing the test at (at least) two temperatures and two pressures, in order to gain both data on relative extrusion rates, and possibly to guide you in determining the temp/pressure limits for the design.

 

[btrueblood]

Also, is this a reinforced diaphragm? Either way, another damage mechanism to worry about is the stretching/relaxation and subsequent wear of the diaphragm (and/or fatigue) as it seats to, and flexes into/over the annulus. This implies that an open/close cycle test should also be run.

 

[twizel]

thanks btrueblood
diaphragm is not reinforced.
annual cycles of the diaphragm are less than 100 so cycle testing should be a quick test.