Re: Coil Coatings

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Kevin,

At 10:18 AM 12/1/2001 -0500, you wrote:
>Hi Guys,
>I just got done coating an 8" coil with epoxy.
>While it was curing, large bubbles would form and if I blew on them, they
>would go away.
>When everything was said and done, it looks beautiful and I know it is hard
>because my coil took a fall to the basement floor and I can not tell where
>there is even a scratch.

WOW! :-))

>But when I look real real close, it looks like there are very very tiny
>bubbles at the level of the wire coating, not in the middle of it, or near
>the surface that you touch, just deep in it.
>What causes this? The big bubbles, which I don't really care about because
>they disappear, and the tiny ones? I used a slow hardener. This is epoxy
>used for boats, Westco brand.

They may have gotten in there if you stirred the epoxy (two part?) too much
so that air got mixed in.  Otherwise, it is some kind of gas that is either
from the epoxy or was trapped in the coil, perhaps beneath the windings.

I am sure they will do absolutely no harm, so just forget them.

>I know my next question has been gone over in the past, but I am wondering
>what everyone's favorite coating is as of now?

I have always liked polyurethane...  Fortunately, almost any of the clear
or even nonconductive colored paint coatings made these days work well, so
whatever you want is fine.  One may wish to test unproven coatings first.
Always a good idea to test old or unproven coatings to be sure they dry
right and will work on the coil as you want before risking messing up the
whole coil.

>I hate polyurethane and acrylic turns out to be brittle and these epoxy
>bubbles drive me crazy but it seems the hardest and prettiest. I did use
>Behr build 50 on one of my 4" coil years ago and really can't remember how
>that compares to these now and what exactly that coating was.
>I am practicing coatings on a couple 8" coils for a small TC and want to get
>things perfect before I go on to coating my 18" coil. So I would like to
>hear other peoples input before I coat the next 8"er.

I would do some testing.  Try little batches and see if the bubbles are
getting stirred in or if it is out gassing.  One could put the two parts
under vacuum to remove the air or maybe even high temperature to drive off
water.  Always keep the cans well sealed and use fairly new product.
Heating the coil first may drive off water vapor if that is the cause.  You
just have to do some testing or perhaps call the place that makes the epoxy
and ask them for hints.  If you can find what causes the bubbles, you are
probably 90% on your way to a perfect coating.  If worst comes to worst,
just don't look so hard :o))

Cheers,

	Terry


>Kevin
>