Re: [TCML] sealing coils/Dolph's AC-43

[Joe Mastroianni <joe@xxxxxxxxxxxxxx>]

DC Cox is the expert on this and uses it extensively.
On his advice I procured my own.  I successfully coated 2 secondaries at room temp.  One is 6.5" x 26" and one is 8.5" x 34".   I had zero issues coating the 6.5" coil.  I put on one coat per day for roughly a week and got a great finish.  At the right temps and thicknesses, it dries in 24 hours with no problems.

However, I was doing all my winding and coating in my uninsulated garage, and when I tried to seal my 8.5" secondary the temp dropped below 60 degrees F.   I also was putting on the varnish quite thickly.  Lots of bubbles formed in the AC-3 and the only rationally prescribed method was to use a local heating technnique (hair dryer or heat gun on low setting) only created more bubbles.

Eventually, I was forced to try to lightly wet sand the coating to get to the point I could get past the bubbles, but that rapidly evidenced itself as a futile process.

I have also learned, that at lower temperatures and thicker coats, the varnish not only bubbles but possibly never dries completely.   The top layers may seal in liquid layers below.

Moral of the story - make sure you regulate the temperature wherever you're doing your varnishing, and do it in lots of thin coats.  I have not resorted to using thinner, though I may consider it next time.

Also, I have consulted some coilers who use epoxy (Ultra Glo from Tap Plastics, or Envirotex - available at most local U.S. hardware stores like Home Depot or Ace Hardware) with superior results. The epoxy as well has to be applied in a temperature regulated environment to prevent bubbling, and it is felt by at least one coiler that the thickness of the epoxy prevents it from actually gluing the turns together and to the secondary form.   Rather, it tends to ride on the surface, though forms a reasonably protective and impenetrable bond.  

One coiler used several coats of the AC-3 as a "glue", and then when that dried completely, sealed the secondary with Ultra Glo (available from Tap Plastics).  This coil has been used many times at the Burning Man festival in the desert, where the secondary is exposed to the harsh elements.  So far in 4 seasons, there have been no issues due to the corrosive quality of the sands at Black Rock, nor the abrading action of wind borne sand.

I will use that technique, AC-3 for a couple coats as a "glue", and Envirotex as a sealer, for the 12" secondary I will build next.

Also, Envirotex an Ultra Glo are quite easy to come by from Tap Plastics or Hardware stores.  The AC-3 is a little more difficult to procure, though you used to be able to get it  through Doc Resonance here on TCML.  Maybe you still can.

Cheers,
Joe



On Dec 2, 2010, at 8:26 PM, Rick wrote:

> Hello,
>  
> I am trying to select a sealing compound for my first secondary.  In reading various sources of ideas, I have concluded that any number of different materials would do an effective job (i.e. polyurethane, varnish, polyester and epoxy resins, Behr 50 Super Build, etc.)  The motor rewinding shop where I purchased my wire could supply me with some Dolph's AC-43, but when I inquired about it they reminded me that it is intended for a dip and bake heat curing process.
>  
> Is it possible to use this Dolph's varnish to seal a wound coil without heating it to 350 deg F?  Or will it simply never dry completely if not cured by heat?
>  
> Any advice or anecdotal experience with coil sealers would be appreciated.
>  
> Thanks,
>  
> Rick
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