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From: Joseph Legris
X-Mailer: Mozilla 4.77 [en]C-SYMPA (Win95; U)
Subject: Re: Side effects of potting compound !
Date: Sat, 02 Nov 2002 11:15:14 -0500
NNTP-Posting-Date: Sat, 02 Nov 2002 11:15:25 EST
Organization: Bell Sympatico
Bob Wilson wrote:
> In article <firstname.lastname@example.org>,
> email@example.com says...
> >"Tom Del Rosso" firstname.lastname@example.org wrote:
> >>"Gibbo" wrote in
> >>message news:email@example.com...
> >>> The square ones with a circular element and worm drive. Beats me how
> >>the hell
> >>> it's doing it. All three have moved by roughly the same amount (within
> >>a few
> >>> percent).
> >>> Can't leave it exposed as it'd buried really deep next to some high
> >>> components.
> >>If you did the conformal coating after gluing it with nail polish, then
> >>you could be really confident of it.
> >>It would be neat to have a trimmer remain exposed through a tunnel,
> >>especially if the screw is on top. I'm thinking of a piece of tubing
> >>wide enough to surround the whole trimmer, a little silicone squirted on
> >>the board around the base of the trimmer, and the tube placed over the
> >>trimmer before potting. Just a thought since you don't need it exposed.
> >Yeah that would be the ideal but the time meddling with it kinda kills the
> >Tomorrow is truth day. I did 2 more today. Calibrated them then covered the
> >entire preset with 2 part silicon sealer. Then potted them in polyeurethane
> >(instead of epoxy). If that fails then they're having them unpotted. I'm
> >starting to get bored of it now !
> This may be somewhat pointless. Silicone is completely incompressible. While
> it may SEEM soft and rubbery to the touch, this is only because it DISPLACES
> when you compress one part of it. While this may be great for locally
> applied pressure when unpotted, once it is entirely encapsulated by a
> rock-hard potting compound, there is nowhere for the material to displace
> when presure is applied. Thus, once potted, silicone is effectively as hard
> as a rock.
But it can still flow a little within the fixed volume.
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