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Old 24th Oct 2017, 4:03 pm   #1
MrBungle
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Default How can I clean up a rusty transformer laminated core?

I have an HP bench power supply here which has seen better days. The transformer has a lot of surface rust where moisture has got into it. The rest of it is repairable by the looks which is good.

I'd like to clean up the transformer to prevent further problems down the line.

How should I go about doing this without making anything worse?

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Old 24th Oct 2017, 4:11 pm   #2
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Default Re: How can I clean up a rusty transformer laminated core?

A good scrub with a wire brush and a smear of silicone grease. The iron of transformers isn't designed for looks or rust prevention, There will be no problem with a bit of surface rust damp windings are more of a problem.
 
Old 24th Oct 2017, 4:13 pm   #3
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Default Re: How can I clean up a rusty transformer laminated core?

Doesn't look too bad. I'd clean off as much rust as you can with a wire brush, or abrasive and the paint it with Screwfix's 'Red Oxide Primer'. That stuff is fabulous paint (good to apply, very effective and nicely priced) and actually made by Johnstone's and is based on zinc phosphate. Haven't used anything else for a very long time.

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Old 25th Oct 2017, 1:07 am   #4
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Default Re: How can I clean up a rusty transformer laminated core?

Thanks all. I found that I could get 99% of it off with a kitchen scourer and have applied some silicone grease as per merlinmaxwell's suggestion. Looks perfectly new now!

Found a metric ton of rust in the rest of the unit and fittings which have cleaned up nicely. It was thick with dust when I got it and not working at all. I've posted this item elsewhere but the clean up is going really well, it's working and this is looking like a nice restoration so far!
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Old 25th Oct 2017, 8:00 am   #5
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Default Re: How can I clean up a rusty transformer laminated core?

To get a good result with this I would clean off the rust as you have. Don't put any oil or grease near it though. Use a small paint brush to paint the lamination edges with Fertan, which is an organic rust converter (prob there is this, or similar product in the UK) and it will deactivate the residual rust and turn it into a dark blue-black organic compound. Also it will soak into the lamination stack and help deactivate the rust you can't see. Once that is done then paint the lamination edges with semi gloss black enamel paint, it will look like new and stay that way. Even if you didn't paint it, the Fertan treatment will prevent recurrent rust.
Many transformers benefit from the bare cut lamination edges painted with Fertan before they rust and before the transformer is varnished. I always do this to prevent any of the laminations edges rusting on my home wound transformers, because I find rust very unpleasant and try to nail it down one way or another whenever I see it.
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Old 25th Oct 2017, 8:53 am   #6
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Default Re: How can I clean up a rusty transformer laminated core?

Turned out what was above was mainly rust which had come off other stuff and the lamination was intact including the varnish. There was one corner which had some genuine rust. Definitely not as bad as it looked.
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Old 25th Oct 2017, 9:28 am   #7
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Default Re: How can I clean up a rusty transformer laminated core?

Mr Bungle,

Sometimes transformers require a combination of treatments. I have attached two photos showing what the transformers in the power supply section looked like pre- restoration in my HMV904, and after.

For the ones that had pitch coatings, that had to be dissolved off first by putting the transformer in a mineral turps bath. After that the rust got treated with fertan (you can see the now dark color of the lams where they were once rusted) then they needed varnishing and along the way the brackets got re-electroplated.

It can be quite a long job to restore transformers to a good finish and have them electrically sound too.

On another thread there is a discussion about LOPTYS with pitch giving trouble. With those I dissolve off all the pitch and build up a thick coat of varnish instead by dipping it. I got onto this idea after looking at an overwind in a vintage Marconi TV monitor that used multiple layers of varnish (rather than pitch) to insulate it, works really well.
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Old 25th Oct 2017, 11:30 am   #8
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Default Re: How can I clean up a rusty transformer laminated core?

Quote:
Originally Posted by Argus25 View Post
To get a good result with this I would clean off the rust as you have. Don't put any oil or grease near it though. Use a small paint brush to paint the lamination edges with Fertan, which is an organic rust converter (prob there is this, or similar product in the UK) and it will deactivate the residual rust and turn it into a dark blue-black organic compound. Also it will soak into the lamination stack and help deactivate the rust you can't see. Once that is done then paint the lamination edges with semi gloss black enamel paint, it will look like new and stay that way. Even if you didn't paint it, the Fertan treatment will prevent recurrent rust.
Many transformers benefit from the bare cut lamination edges painted with Fertan before they rust and before the transformer is varnished. I always do this to prevent any of the laminations edges rusting on my home wound transformers, because I find rust very unpleasant and try to nail it down one way or another whenever I see it.
Re the rust coming back, it's not generally an issue as once restored most such items are then kept indoors. The rust generally comes about in the first place through stuff having been confined to garden sheds and garages for decades. I'm not against using rust killer products per se, but basically after a good wire brushing, a smearing of oil or grease will do the job and maintain a more original look rather than a coat of 'new paint'. I do the same with rust spots on chassis, wire brush em down them rub with an oily rag until it changes from browny-orange to bluey-grey. The rust won't come back indoors.

Cracking job you've done on those trannies BTW! it's just that for me personally, I would not go that far in a normal restoration; a nice, clean(ish), albeit 'aged' look is what I go for, not a return to (better than?) new.
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Old 25th Oct 2017, 11:44 am   #9
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Default Re: How can I clean up a rusty transformer laminated core?

This particular power supply was kept in a moist laboratory environment. It's now in a carefully humidity controlled house so should be ok now. I really can't be bothered to do a perfect job of this if I'm honest as this is a functional restoration rather than a cosmetic one. If the outcome is a working supply then it's good..

Got to say that those transformers do indeed look rather good Argus25!
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Old 25th Oct 2017, 11:56 am   #10
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Default Re: How can I clean up a rusty transformer laminated core?

Beautiful work, Argus25!
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Old 25th Oct 2017, 12:36 pm   #11
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Default Re: How can I clean up a rusty transformer laminated core?

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Re the rust coming back, it's not generally an issue as once restored most such items are then kept indoors. The rust generally comes about in the first place through stuff having been confined to garden sheds and garages for decades.
If only this were true . I live in a coastal area about 1km from the ocean, sounds like a way but even the soil salinity is high. Any bare steel here, indoors or outdoors, rusts stat. All the outdoor fixings/fitting have to be stainless steel unless you like the look of the brown oxide.

I'm very careful not to leave bare steel surfaces, if I cut down a steel screw or potentiometer shaft I always paint the ends (red), you can see from the attached photo of my TV22, if you look at the replacement pots/shafts.

One interesting thing about many UK sets is the preponderance of aluminium, but in American sets, hardly any, they were very big on steel.
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Old 25th Oct 2017, 9:17 pm   #12
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Default Re: How can I clean up a rusty transformer laminated core?

My cottage here in the Isle of Man is about half a mile from the sea, but I get no problems. However when I first moved over I was just about 50 yards from it. The wooden garage behind the cottage showed evidence. A steel lock would not last long, anything steel was either very rusty or only outside a few hours.
You may get some much bigger seas than us.
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Old 25th Oct 2017, 10:11 pm   #13
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Default Re: How can I clean up a rusty transformer laminated core?

Quote:
You may get some much bigger seas than us.
Yes, ours is an East coast surf beach with constant breaking waves and we are only about 5 to 10m above sea level. On rough windy days you can easily see a salty haze coming in for at least 300m.
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Old 25th Oct 2017, 11:22 pm   #14
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Default Re: How can I clean up a rusty transformer laminated core?

Do they have concours d'elegance for TV chassis?
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Old 26th Oct 2017, 2:35 pm   #15
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Default Re: How can I clean up a rusty transformer laminated core?

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Quote:
Originally Posted by stevehertz View Post
Re the rust coming back, it's not generally an issue as once restored most such items are then kept indoors. The rust generally comes about in the first place through stuff having been confined to garden sheds and garages for decades.
If only this were true . I live in a coastal area about 1km from the ocean, sounds like a way but even the soil salinity is high. Any bare steel here, indoors or outdoors, rusts stat. All the outdoor fixings/fitting have to be stainless steel unless you like the look of the brown oxide.

I'm very careful not to leave bare steel surfaces, ....
Well, I did say "generally"! Of course if you live by the sea then that's a different issue, things will rust easier. I never advocated leaving bare steel surfaces, the method I described leaves an oil/grease burnished surface that (away from the sea!) protects it from corrosion.
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Old 26th Oct 2017, 2:51 pm   #16
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Default Re: How can I clean up a rusty transformer laminated core?

Not much sea here in London!
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Old 26th Oct 2017, 3:28 pm   #17
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Default Re: How can I clean up a rusty transformer laminated core?

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Do they have concours d'elegance for TV chassis?
Hi,

Thanks for that remark. I have attached a picture of the lower (RF chassis) and the test pattern.

It is not obvious from these photos, but all the transformers and all my restored chassis, including the Bush TV22 have been coated with clear lacquer to prevent future rust and corrosion.

Given the amount of work it takes to restore a chassis I'm very mindful to try to protect them from future damage. And I'm a great believer in the saying rust and corrosion never sleeps. Of course not everybody agrees with these techniques and sees my work as a bit overdone compared to most, but who wants to be normal anyway.

One restored radio I have, an Eddystone 640, I didn't think it was a good idea to lacquer that, since it is nickel plated brass & copper, so with that one I lovingly wipe the chassis down with WD40 every 6 months or so instead and that keeps it maintaining an excellent finish.
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Old 26th Oct 2017, 3:32 pm   #18
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Default Re: How can I clean up a rusty transformer laminated core?

That looks absolutely marvellous. Which lacquer do you use out of interest?
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Old 26th Oct 2017, 4:08 pm   #19
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Default Re: How can I clean up a rusty transformer laminated core?

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That looks absolutely marvellous. Which lacquer do you use out of interest?
I use what was once called Duco automotive lacquer, its called "Holts Dupli-color" now in AU. It is sold in automotive parts stores in small cans as "touch up spray paint", the metallic silver is code DS110 and the clear DS117. But the names of these seems to have changed again recently.

It adheres well, sets very quickly in the hour, but its best not to touch it for 2 or 3 hours. The clear stays clear with time and doesn't yellow like many varnishes. Its good for protecting many metal surfaces like polished brass etc too as it sticks well to polished surfaces.

This sort of quick setting spray is not suitable for some items like transformer windings, so for those I use marine grade spar varnish and apply it with a brush.

The image attached (I recently put on another post) used the DS117 lacquer to coat the polished brass escutcheons on the Grebe MU-1 radio over a decade ago and they show no signs of the lacquer deteriorating, or the brass oxidizing.
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Old 26th Oct 2017, 4:54 pm   #20
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Default Re: How can I clean up a rusty transformer laminated core?

Thanks for the info. It appears you can get this in the UK which is good.

More wonderful restorations! I could look at them all day!
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