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What is the best way to remove slight superficial rust from transformer laminations? I am reviving a couple of Croft EL84 stereo amps, and the exposed transformers are looking a bit scruffy after years of storage.Alex
Edits: 03/26/15Follow Ups:
Thanks, all. I will try a wire brush this weekend, followed by cleaning with alcohol.
Alex
I had a Scott 299 with rust on the tranny. Naval jelly was recommended to remove rust. Never got to try it, sold the amp before I could try.
Dave
don't like liquids on my transformers. The lams simply wick the liquid up. Scares the sh#t out of me as you can't see the effect.
I prefer dry mechanical removal: sandpaper, wire brush.etc. but only moving in the direction of the lams
If the lams are painted, will it hinder heat dissipation?
Would some gently-applied fine steel wool or scotchbrite be out of the question to clean off the rust? I suppose you'd still have to coat it, after.
Thanks.
Peter
Heat dissipation is not really affected. I use Rust o leum paint for patio grills and it works great (I like the satin finish)I also lightly SAND the lams. I know its supposed to be a big no no, but if you use one of those sanding blocks you can keep the block square to the edge. In dissecting some transformers, the so called insulation is minimal and at the most seems to a lacquered finish or non existent. I really doubt that there is any insulation between the lams.
Here is the key. You do not want the lams jump across each other. The lams are directing the magnetic fields in the direction of their orientation. If you were, say, file the lams and have the edges over lap each other, that would be very bad for the magnetic fields. Definitely, do not use a circular sander, as the flash will cross lams with the orbital action.
Hand sanding with FINE grain sandpaper in the direction of the lams only, will remove most of the rust from the lams( silicon steel and very prone to rusting). Wipe clean and carefully examine the lams . You should be able to clearly see the demarcation between the lams. I use a bit of alcohol or acetone to degrease and then paint.
Actually the tighter the lams are aligned next to each other the better the magnetic control. Keep the lams tightly bolted together when sanding. This keeps any particles from falling between the lams.
I once visited the Golden Tube factory. They were assembling the outputs when I entered. Cores had been inserted and then the worker took a 2 by 4 and hammer an whacked the lams to align them !!!!!
Just my experience
Edits: 03/27/15
Very interesting, thanks!
I've refreshed a metric carload of rusty transformers.
As Eli pointed out, don't get medieval on the lams. If you have huge rust that's flaking or loose, you may have to *lightly* hit it with a fine wire brush, but that's it and go easy.
I've always used Rustoleum brand spray paint, usually gloss black. This paint will supress rust from continuing to form underneath. I've got some transformers I used this treatment on over 15 years ago and they still look like new.
I am going to check out the rust conversion product Eli mentioneded. That sounds like a good extra step.
Mechanical means are OUT. The last thing you want is removing insulating material from the laminations.
Perhaps a chemical conversion, like Duro "Extend", that turns rust into black plastic is OK. Follow with some kind of paint, perhaps "RustOleum" brand.
Eli D.
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