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Transformer laminations oxidation

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Elerion

Member
2017-09-23 9:04 am
Don't worry, oxidation will take centuries to destroy the core. Only a small film of paint or varnish, and go on!.
Even though it may be true, it is a question of aesthetics too. It looks awful, and it is unconfortable to work with, in case of a repair or rewind.

Get a small can of polyurethane varnish, mix well and brush on a coat. I think satin looks best.
Nice solution. Yes, satin would probably look great.

Or a coating of light oil if you don't want to paint.
Oil? :eek: What kind of oil?
 

Elvee

Member
2006-09-08 2:04 pm
Hi everyone.


One of my transformers is starting to develop oxide in form of tiny brown dots. The laminations are not covered (only the winding is, with a pair of bells). What do you do to stop this from happening? :confused:
Treat with a light (~5%) solution of H3PO4 (phosphoric acid), lightly applied with a soft brush (don't soak the whole laminations).
Leave it to work for ~30 minutes, and wipe the wet residues with dry, absorbing cloth.
If the rust is light, it should do the trick and passivate the metal against further corrosion
 

Dave R

Member
2006-08-09 5:30 am
Treat with a light (~5%) solution of H3PO4 (phosphoric acid), lightly applied with a soft brush (don't soak the whole laminations).
Leave it to work for ~30 minutes, and wipe the wet residues with dry, absorbing cloth.
If the rust is light, it should do the trick and passivate the metal against further corrosion

I have used a product called Ospho, available in US. I don't know if it is available outside US, or if there is an equivalent where you are.
Ospho Rust Treatment - Since 1947

After application, the areas can be touched up with primer and paint to match, if you want.
 
Oil will catch dust like crazy and eventually evaporate or be absorbe; phosphoric acid is, well, an acid, I want none of any kind inside a transformer, even this "protective" kind, it will seep into laminations by capillarity and you will never ever remove it.

Mind you, I use phosphatization a lot: for my speaker frames and iron chassis (even aluminum ones) as a painting pre-treatment, but parts are later rinsed in distilled water (you would need to drop the transformer in a bucket of water to approach that) , oven dried and painted.

Varnish or plain synthetic oil paint works fine, in a "passive" way, just keeping oxygen and water away from iron but for better / more stable results use anti-rust paint (typically brick colour) which *actively* fights rust "walking under the paint" or for better finish, there´s a dual purpose top coat/rust protection paint available everywhere, won´t name brands because it´s Country specific, just ask the paint shop employee for it.
Here in Argentina we like:
skt_4.jpg

"Triple action" here means:
* anti-oxide
* converter (similar to phosphatizing)
* nice shiny topcoat
 

pcan

Member
Paid Member
2015-12-31 4:57 pm
The active ingradient of the product I use is phosforic acid, trapped in a sticky gel suspension. Compared to liquid phosporic acid solutions, this one does not seep into laminations if removed in a short time, and does not drip on nearby painted surfaces, possibly staining them permanently. I apply it with a cotton swab. If the rust is superficial, this treatment removes it completely very fast, almost like an eraser on a pencil. Phosforic acid will easily ruin any paint, I learned this the hard way.
 

Dave R

Member
2006-08-09 5:30 am
I used Ospho on superficial rust spots on the edge of some laminations on my output transformers. (swabbed it on with some Q-tips) It is a light solution, and it turns the rust to a black powder after just a few minutes, which can be wiped off easily.

This was done in 2011 -- no more rust, and no detrimental effects have been noticed up to now in 2019. The touch up paint is still intact over the area.

That being said, if there is a better product available, I'd be willing to try that as well. There is a Sherwin Williams paint store near me. I'll look into the "triple action" paint next time I need something like that.
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
For a different problem, raw iron handrail brackets found in a dump, I have used oil-based wood stain. You can get it near-black to blend with the remains of black paint. It binds-up surface rust and dries (oxidizes) in an hour. 2 or 3 coats is reasonable. I've had these in a semi-damp garage for 7 years and notice no degradation.

As always, try a drop on a hidden edge before you go crazy.
 
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