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From: Larry Kent on 7 Mar 2010 05:09
On Sat, 6 Mar 2010 22:17:50 -0800, dplatt(a)radagast.org (Dave Platt)
wrote:

>You can "stretch" epoxy used for potting, and save quite a bit of
>money, by loading it up with a filler before pouring. I've
>encapsulated small circuit boards in TAP Plastics' slow-cure marine
>epoxy, mixed with fine dry sand... cheap and effective, if rather
>heavy and prone to settle out during the curing process. Glass
>microspheres are much lighter, don't form as hard a matrix, and are
>rather more expensive :-(
>

A friend suggested surfboard epoxy, but with the foam powder that they
use for ding repairs mixed in. Lighter than sand, athough not a tough
I suppose. The "give" it provides apparently cushions the parts during
curing.

Does that sound feasible?

Larry Kent
From: Jan Panteltje on 7 Mar 2010 06:50
On a sunny day (Sat, 6 Mar 2010 22:17:50 -0800) it happened
dplatt(a)radagast.org (Dave Platt) wrote in <e1tb67-u51.ln1(a)radagast.org>:

>>Is it possible to use epoxy or polyester surfboard resin for potting
>>audio fequency PCB's?
>>
>>How about the crystal epoxy used for encapsulating insects, etc?
>
>Polyester resins often heat up a lot, and shrink, when curing. That's
>not necessarily a problem when fiberglassing a surfboard, but it can
>put a serious stress on components during encapsulation - might crack
>'em loose from the board in a really severe case. I believe this
>tendency can be reduced somewhat by using a slower curing cycle (less
>catalyst per amount of resin).
>
>Some of these resins remain somewhat sticky when cured, and need a
>topcoating or upper layer containing a surface-hardening agent or wax.
>
>You can "stretch" epoxy used for potting, and save quite a bit of
>money, by loading it up with a filler before pouring. I've
>encapsulated small circuit boards in TAP Plastics' slow-cure marine
>epoxy, mixed with fine dry sand... cheap and effective, if rather
>heavy and prone to settle out during the curing process. Glass
>microspheres are much lighter, don't form as hard a matrix, and are
>rather more expensive :-(


The electronics in my outside located satellte TV dish motor controller
seems to be covered with some wax, parafine perhaps.
It does make it insensitive to moist it seems, been working OK for years,
in spite of the fact that my scope probe pricked holes in the wax at some points
when I was figuring out the circuit ;-)

>--
>Dave Platt <dplatt(a)radagast.org> AE6EO
>Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
> I do _not_ wish to receive unsolicited commercial email, and I will
> boycott any company which has the gall to send me such ads!
>
From: Boris Mohar on 7 Mar 2010 07:28
On Sun, 07 Mar 2010 04:09:22 GMT, larrykent(a)raglands.com (Larry Kent) wrote:

>Is it possible to use epoxy or polyester surfboard resin for potting
>audio fequency PCB's?
>
>How about the crystal epoxy used for encapsulating insects, etc?
>
>Any other low cost alternatives, aside from flexible rubber/silicone?
>
>Many thanks,
>
>Larry Kent
>

Wax.

--
Boris
From: Jim Yanik on 7 Mar 2010 08:39
D from BC <myrealaddress(a)comic.com> wrote in
news:MPG.25fccf14e30ab03e9896c8(a)209.197.12.12:

> In article <4b932620.4739000(a)news.tpg.com.au>, larrykent(a)raglands.com
> says...
>>
>> Is it possible to use epoxy or polyester surfboard resin for potting
>> audio fequency PCB's?
>>
>> How about the crystal epoxy used for encapsulating insects, etc?
>>
>> Any other low cost alternatives, aside from flexible rubber/silicone?
>>
>> Many thanks,
>>
>> Larry Kent
>
>
> I tried a solvent based 2 part epoxy mistint sold for cheap at a paint
> store.
> It only dries in thin film as it's supposed to.
> I tried potting and it was still gooey after 1 week.
> The gooeyness could be from solvent getting trapped by the skin that
> forms. iows.. The epoxy paint self-seals extending the cure time.
> That or the paint was overtinted. Was blue.
> So don't try that.
> Solvent based epoxy paint is different than 100% solids epoxy or the
> type used for glue.
>
> Maybe try 100% solids epoxy for floors??
>
>

epoxy cures by a thermal reaction;it can get pretty hot,especially in thick
applications.
Some folks discovered this when the plastic tub of epoxy they mixed up
melted from the heat of the reaction.

--
Jim Yanik
jyanik
at
localnet
dot com
From: Jim Yanik on 7 Mar 2010 08:41
larrykent(a)raglands.com (Larry Kent) wrote in
news:4b937a9a.413875(a)news.tpg.com.au:

> On Sat, 6 Mar 2010 22:17:50 -0800, dplatt(a)radagast.org (Dave Platt)
> wrote:
>
>>You can "stretch" epoxy used for potting, and save quite a bit of
>>money, by loading it up with a filler before pouring. I've
>>encapsulated small circuit boards in TAP Plastics' slow-cure marine
>>epoxy, mixed with fine dry sand... cheap and effective, if rather
>>heavy and prone to settle out during the curing process. Glass
>>microspheres are much lighter, don't form as hard a matrix, and are
>>rather more expensive :-(
>>
>
> A friend suggested surfboard epoxy, but with the foam powder that they
> use for ding repairs mixed in. Lighter than sand, athough not a tough
> I suppose. The "give" it provides apparently cushions the parts during
> curing.
>
> Does that sound feasible?
>
> Larry Kent
>

you can buy phenolic microballoon fillers at marine stores,where you will
find quality boatbuilding epoxies like West systems.
Lightweight,yet easy to machine.

--
Jim Yanik
jyanik
at
localnet
dot com
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