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Question About RTV Silicone & High Voltage

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sparky99

Sat Mar 21 2009, 08:47PM

Registered Member #1159 Joined: Fri Dec 07 2007, 02:10AM
Location: Hudson Valley of NY State
Posts: 84

And so goes to continuing saga of my X-ray transformer. I've got the bushing flanges filed / sanded to the correct diameter so they fit where the federal plugs were. I'm wondering if its ok to use RTV silicone to seal where the bushings sit in the threaded flange. I'd also like to use RTV silicone to seal the tank where the bottom & sides meet. There is one spot that weeps oil. I'm concerned about contaminating the virgin DIALA A transformer oil. Of course, the RTV silicone would be fully cured before the tank was filled.

Can't wait to light this thing up.......should make one helluva Jacobs Ladder. I've got my Miller Thunderbolt welder all set up for current limiting duties.

Here's a few pictures. So, what do you think?

Regards,
bob

aonomus

Sat Mar 21 2009, 09:17PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

I'm pretty sure I read that RTV silicones that aren't platinum cured end up giving off acetic acid which can cause corrosion and maybe some conduction... I believe that 'food grade' silicone is platinum cured but I'm not 100% sure.

Arcstarter

Sat Mar 21 2009, 11:29PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

To test if something contains acetic acid, just put a little bit on some paper or something and let it sit for awhile, then, smell it. If it smells like vinegar, it contains acetic acid.

I saw that somewhere, and i think they where suggesting not to use it if it contains acetic acid. Not sure though :P

Nik

Sun Mar 22 2009, 01:49AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

I used food grade silicone to seal electrical equipment in a meat plant and it all used vinegar (acetic acid) to cure. It also took a fair bit of time to cure if there was any thickness to the silicone more then a few mm. Just keep that in mind.

Herr Zapp

Sun Mar 22 2009, 04:02AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Sparky -

Almost all of the "household sealant" grades of silicone RTV utilize a cure system that is triggered by exposure to atmospheric moisture, and that release acetic acid vapor during the cure cycle. Acetic acid is highly corrosive, and RTV sealants that release acetic acid are not appropriate for ANY electronic application.

General Electric manufactures a line of "electronic grade" silicone RTV sealants that are especially designed for electronic applications, and that release alcohol vapor during curing rather than acetic acid. These are RTV 160, RTV 162, and RTV 167.

Some automotive-grade RTV sealants that are identified as "safe for catalytic converters" may also utilize a cure system that does not release acetic acid.

I would definitely not use ANY grade of RTV sealant that releases acetid acid for your X-ray transformer application.

Regards,
Herr Zapp

...

Sun Mar 22 2009, 08:39PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

You might consider aquarium sealant, although it is acid cure as well (but hey if its good enough for fish it seems like your transformer would be fine, just make sure to rinse the tank well with water before adding oil)

if you are really worried about the acetate ion floating around I would recommend just using polyurethane or silicone sealant (although would stay away from the acrylic). Just take a trip through the sealant section at your hardware store and find something cheep to use

Steve Conner

Mon Mar 23 2009, 01:12PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Dow Corning also make electrical grade silicone.

Having the silicone contaminate the oil with acetic acid is one thing. If you were really worried, you could test the breakdown strength of some transformer oil before and after adding some vinegar. I don't think acetic acid reacts with oil or dissolves in it, though (you're basically making a foul-tasting salad dressing here) so it would just float to the top or sink to the bottom depending on the specific gravity. I very much doubt there would be acetate ions around, because the acetic acid won't be in solution.

I'd be more worried about the opposite problem, the silicone failing to stop the oil weeping out, as it's a lot better at seeping through things than water is. Depending how the tank is constructed, you might have more luck if you soldered the leaky spot with plumbing solder.

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