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Re: Coilforms, sealants/glyptal (fwd)



---------- Forwarded message ----------
Date: Sun, 12 Jul 1998 03:44:55 -0600
From: David Dean <deano-at-corridor-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Coilforms, sealants/glyptal (fwd)


-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Friday, July 10, 1998 11:00 PM
Subject: Coilforms, sealants/glyptal (fwd)


>
>
>---------- Forwarded message ----------
>Date: Fri, 10 Jul 1998 14:26:53 -0500 (CDT)
>From: Larry Bud Melman <gasman-at-althea.a-line-dot-net>
>To: Tesla List <tesla-at-pupman-dot-com>
>Subject: Coilforms, sealants/glyptal
>
> {snip}
>
>> Glyptal is available from two sources I know of.  One is the red
corona dope
>> marketed in the GC line of TV solvents and chemicals.  Most good
electronic
>> jobbers carry the GC line of chemicals.  The other is Aldrich
chemical with
>> still offers it. (expensive in block form)   Glyptal is not as good
as some of
>> the more modern low vapor pressure materials like Inland seal,
vac-tite or
>> others.
>>
>> Richard Hull, TCBOR
>
>
> Richard, and other glyptal advocates:
>
> I'm a little cunfused about glyptal - only heard of it a couple of
posts
>ago.  What is the nature and design purpose of the stuff??
>
> Do you contend that all coilforms should be sealed inside and out with
>it, or just cardboard and other forms with 'poorer' electrical
qualities?
>
> I ask this partially because I'm having trouble finding a coilform as
>large as I want, and I've been considering just doing a 12 inch one out
of
>one of those concrete post pouring forms made of spiral-wound
cardboard.  I
>had been planning, if I used that, to seal the form inside and out with
Bondo
>fiberglass resin (a two-component product with the 'fiberglass' (?!)
resin and
>a hardener which is methyl ethyl ketone peroxide.)  I believe this is
widely
>used for auto body repair.
>
> I don't know anything about the electrical qualities of the material.
>I chose it because it will make the cardboard tube rigid enough.  Any
experience
>with this stuff?  Would you go ahead and use 'glyptal' after sealing
the tube as
>I described??
>
> Thx in advance.
>
> Clay
>
The stuff you are talking about is polyester resin. The mixing ratio is
a few drops
hardener per cupful of resin. (The MEK peroxide is the hardener) This
stuff produces
a very hard, very brittle material that is prone to cracking. Fiberglass
gets its strength
from the glass, all the binder does is hold it together. At any rate, I
don't think that polyester
resin would be a good choice for your proposed application because it
would tend to crack,
although it would seal out moisture very well. A better choice would be
epoxy resin, Bondo
makes this also, they call it marine epoxy resin, it is also a two part
mixture with a ratio
of one to one. It is a little more tricky to work with, but has
excellent electrical characteristics
(after all the pc boards in your PC are made from glass epoxy), is
tougher, and more flexible.
In a thin coat without glass fiber reinforcement, epoxy will do nicely,
polyester won't.

Many people use polyurethane to coat the forms as well as to seal (fix)
the windings.
Polyurethane has the advantage that it does not require any mixing.

I can't tell you anything about glyptal as I have never used the stuff
(except corona dope
as corona dope) but I do have some electric motors around with it in
there, and it is very
tough and very flexible.

All the coils that I have built so far have been on acrylic forms using
acrylic resin as a
sealer and to fix (and insulate) the windings. I use Krylon brand clear
acrylic resin in a
spray can.

I am in the process of building a new coil, much larger than any I've
built before, and am leaning
toward the cardboard tube just like you are talking about for the first
secondary because it is cheap
and if I screw it up it won't be as much of a loss as if I used the
glass epoxy pipe I have. I am going to save
that for a day when I have a little more experience. For the cardboard
tube, I will be using polyurethane
varnish. This decision is based on the experience of others.

Good luck on your endeavor,
deano