EPDM Gaskets and Compression

Im finding the torque to be very low (nowhere near yield of bolts), which is worrying me that during the vibration of operation that they will loosen.

I went and calculated the modulus of elasticity in compression from the shore A hardness then I calculated the force required to deflect it 10% hoping that the load would somewhat correspond to the ASME calculated load, but its much smaller

The ASME torque is ~5 lbft, and the gasket compression torque is 0.13 lbft.

The flange is a 16" 150# flange, so 0.13lbft on a 1"-8 bolt... nah

Have you read #1? If you do as suggested there you can tighten to the correct torque for the bolts (to reduce risk of vibrating loose) without overstressing the rubber.

Also consider locknuts.

I will look into the offgassing, our material scientist here recommended butyl and EPDM for my application.

we get down to 1-3 torr range, BUT usually the duration is not very long max 15-30 minutes per test and we test maybe 2-4 times a year

Lyn,

Very nice link to outgassing data. I think I may find this very useful for future projects.

The original poster didn't say what type of vacuum chamber this is. I would be concerned about outgassing, but I would also be concerned about potential sulfur content. Many EPDMs are sulfur cured, and residual sulfur can cause surface corrosion. This is a concern for switches, electronics, etc. Again, this depends on what type of equipment you are dealing with.

Thanks,

GSFC tested many materials for me when I worked on covert satellites.

Satellite optics, thermal control surfaces and mechanical contacts do not like polymer films.

E595 - ASTM International

Amazing that I still remember that ASTM spec. It didn't exist till years after we started testing for outgassing.

[quote]Lyn,

Very nice link to outgassing data. I think I may find this very useful for future projects.

The original poster didn't say what type of vacuum chamber this is. I would be concerned about outgassing, but I would also be concerned about potential sulfur content. Many EPDMs are sulfur cured, and residual sulfur can cause surface corrosion. This is a concern for switches, electronics, etc. Again, this depends on what type of equipment you are dealing with. [/quote]

its an altitude chamber for hot firing rockets/thrusters, most of our essential electronics are in EP boxes. and these windows are on the edges of the chamber which has a radius of about 20 feet

the specific EPDM we spec'd out is sulfur cured to get the higher hardness we wanted to combat leakage and gasket relaxation

Fluoro elastomer like Dupont Viton may be better than EPDM for vacuum seal.