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Vapor Transmission Rates Question
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Posted by: bilbat

11/09/2003, 10:26:14

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Does anyone have any experience calculating vapor transmission rates? I have an outdoor electronic enclosure that is sealed from the environment with Buna N gaskets. The repeatability & reliability of the electronics is very dependant upon humidity. There are two pcb's in the assembly. One is fully potted and the other is conformally coated. Futhermore there is a desiccant block inside the enclosure to take care of any humidity left in the enclosure during assembly & any subsequent openings (such as repair work). As a cost reduction effort, I am looking into cure in place silicone. I am concerned about the vapor transmission of silicone apposed to Buna N. This product has a 20 year life. 

Thanks all.


I have seen the evils of procrastination and plan to change my ways tomorrow! Bill

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Re: Vapor Transmission Rates
Re: Vapor Transmission Rates -- bilbat Post Reply Top of thread Forum
Posted by: mechdesigneng

11/28/2003, 11:38:08

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Hello Bill,

Not sure what is the main concern.  You could approach the problem with reducing the amount of gasketting (silicone) and/or increasing the protection of the electronics (potting, protective coating, using an inert gass etc)


A couple of concerns that silicon still outgasses about 1 month after cure.  The manuf could tell you more specific time.  Alot of outgassing occurs after 3 days and petters out from there.  You could also get a composition for the solvent in the silicon and knowing the total weight of silicon you could get a total solvent.  Knowing temp you could calculate any condensation that would occur also (not likely)

Good luck

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