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 Post subject: Rusty Power Transformer
PostPosted: Sep Tue 21, 2021 1:59 pm 
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Joined: Feb Sat 15, 2020 5:12 pm
Posts: 58
Hello,

I have an amplifier that has a very rusty power transformer. I would like to clean it and then spray paint it black. The transformer has what I think are cooling fins that are pretty close to each other. I have no idea how I am going to get to the rust. I thought about trying to take it apart to clean it but not so sure how to go about doing that. I suppose I would have to remove each plate. Does anyone have a solution. I thought about sand blasting it directing the air away from where the wires enter. Thank you.


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 Post subject: Re: Rusty Power Transformer
PostPosted: Sep Tue 21, 2021 2:32 pm 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 4023
Location: Austin, Texas
You could use a wire brush to clean out the loose rust and then paint it with a rust converter like Reformer.
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Jay


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 Post subject: Re: Rusty Power Transformer
PostPosted: Sep Tue 21, 2021 2:42 pm 
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Joined: Jul Tue 15, 2008 6:13 pm
Posts: 9522
Location: Gretna, Nebraska
I think I would try and remove the end bells. It appears you could pull the four end bell bolts so each side could be removed, leaving the rest of the transformer wired and in place on the chassis.

With the end bells removed, you would be able to do a much more thorough job of sanding and prepping the sheet metal. After prep, spray paint the end bells and they should look pretty good.

If you felt the need, you could paint the exposed laminations on the transformer while still on the chassis. Mask as needed to keep paint off of other surfaces.

Personally, I would avoid sandblasting anywhere near an open transformer like that one.

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 Post subject: Re: Rusty Power Transformer
PostPosted: Sep Tue 21, 2021 8:57 pm 
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Joined: Dec Sat 24, 2011 9:17 pm
Posts: 8349
Location: Vancouver Island, Canada
Unless you're handy, don't try to pry anything apart. I think the bells are connected to the chassis with bolts from below. If what you are wanting is cosmetic, start with a good cleaning by hand with a toothbrush and a bit of soapy water, letting no water seep away into the chassis. Use a bamboo skewer and small paint brushes to clean narrow places.
Clean off the rust with a stiff brush but I wouldn't use a wire brush. You can damage things by getting particles of rust and wire between the plates.
The plates can be sealed with varnish to keep moisture out.

If a lot of original paint is still good, you can wipe your fresh paint off with a cloth. Fresh paint will stay only on the rusted patches. In that case, you can apply paint by brush, then wipe the bells clean.

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 Post subject: Re: Rusty Power Transformer
PostPosted: Sep Tue 21, 2021 10:30 pm 
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Joined: Jan Thu 16, 2020 12:29 am
Posts: 1563
It depends on how far you are prepared to go with the restoration, or preservation.

Generally for the rusty lamination stack, I clean off the surface rust with 600 grade paper, treat it with organic rust converter (Fertan) which mostly deactivates the rust and turns the metal edges a dark blue to black. Then I paint over that with black paint.

But for the transformer covers, it is a different ball game, if you want a good long term result.

By far and away the better method is to send these to the electroplater. The rust gets completely removed, every last crystal of it and have them Zinc plated. This solves the rust issue, so it will not return. Then for mine I have them Satin black powder coated. Because this resembles the original low gloss appearance of the cover and it is super hard, scratch resistant and will not flake off even with temperature cycling. If you have a look at this chassis on the Early Television Foundation site, this is how the brackets on the large power transformer on that chassis were treated:

https://www.earlytelevision.org/holden_621.html


If you want to do the brackets yourself, the next best method, but not quite as good, is to remove as much of the rust as possible with 400 grade then 600 grade paper. Then treat the surface with Fertan. Then spray it black with VHT enamel spray paint and bake it in your home oven. If you don't get permission from the boss to do that, you can use Dupli-color auto spray quick drying paint. However, with the level of rust that you have, the Fertan likely won't get to it in the very deep pits in the metal, so possibly it could come back, after a time, under the paint.

It is surprising when the rust is completely removed, electro-chemically or by fine glass bead blasting, how deep some of the pits in the metal are and these mostly get neglected in "restorations" in favor of a quick cosmetic result vs a long lasting result. So restoration and preservation are two different things.

One golden rule, never put paint over untreated rust.


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 Post subject: Re: Rusty Power Transformer
PostPosted: Sep Wed 22, 2021 12:49 pm 
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Joined: Feb Sat 15, 2020 5:12 pm
Posts: 58
Thank you for the tips. Lot of nice ideas.


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 Post subject: Re: Rusty Power Transformer
PostPosted: Sep Wed 22, 2021 2:52 pm 
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Joined: May Mon 25, 2020 7:37 pm
Posts: 857
Location: Greater Boston, MA
I have also used POR-15 directly on rusted areas (after removing loose rust and de-greasing). It is designed for this. Once dry, it can be sanded and topcoated with the rattle can of your choice.

Have used POR-15 many times for car restoration with good results.


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