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RE: Water absorbtion of Gray PVC



Original poster: "Jeff W. Parisse" <jparisse-at-teslacoil-dot-com> 

TCML,

I have to back Dr. Rez on this one guys... We use PVC and fiberglass forms.
We have accumulated hundreds of hours of run time on a dozen or more PVC
coils all above 10kW. We have a really burnt PVC form we keep in the shop as
a trophy...

Sand, bake*, seal...

Sanding breaks up the surface. HV arcs love to travel down smooth surfaces.
We use coarse grit and leave the final finish rough. After surface prep and
careful and gradual baking with tungsten strip heater, seal the PVC with
commercial HV varnish. There's more to the process but those are the basic
steps hobbyists should follow.

Will you coil work the same if you don't follow these steps: sure! Same
applies to O-rings and spray-on foam insulation.

* don't over do this step. 20 degrees above ambient for two hours is all
that is necessary IMO. If you use heat lamps, spread them out, put them on a
variac and don't put them too close. "Hydroscopic" doesn't mean it's full of
water and you have to dry it out.

Jeff Parisse
kVA Effects
www.teslacoil-dot-com



snip...

All PVC is hygroscopic especially when used at high frequencies. It's best
to sand interior and exterior, then paint with 3 separate of Glyptal or
other HV insulation. Interior sanding is rapidly accomplished by using a
sanding "flapper" on a dowel (or other extender) on an electric drill.