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Old 1st Feb 2019, 1:45 pm   #1
Malcolm T
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Default Steel chassis resto How to ?

I have a radio rentals radio in a Bakelite cabinet and the steel components have a rust patina now . Whats the procedure for restoring the metal to new , would it be acid dipping then hot dip galvanizing ?. How was it done back when the radio was made is there any historical archives on this procedure or anyone still alive with the knowledge !.
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Old 14th Mar 2019, 9:49 pm   #2
Uncle Bulgaria
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Default Re: Steel chassis resto How to ?

I don't know what it looked like when new, but if you want to get rid of the rust then oxalic acid, vinegar/salt, abrasives and elbow-grease are all good. You will remove some of the metal, of course, as it has already turned to iron oxide. If it was a painted finish then you'd need to get it back flat to remove the pitting first.

You can't 'restore' the metal, as if it's rusted then it's gone. If you want it shiny then rubbing it down and lacquering it would do. Galvanising is only worthwhile if the object is going to be in a corrosive atmosphere, and I would have thought was an unlikely finish for a radio chassis. No doubt experts here will show I'm wrong though!

Even shinier would be a metal plated finish - zinc or nickel. I had a bicycle electroplated with yellow zinc that got a lot of compliments. Other colours are available...
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Old 14th Mar 2019, 10:17 pm   #3
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Default Re: Steel chassis resto How to ?

I had some some slight rust on the small steel clips that hold the glass dial on a Radio Rentals model 58.

I submerged them in some phosphoric acid that is used by caterers to descale kettles, etc.

After 30 minutes they looked like new, i.e. shiny.

The results you get can vary. Sometimes the rusty steel turns grey.
It may depend on the alloy.
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Old 14th Mar 2019, 10:51 pm   #4
M0FYA Andy
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Default Re: Steel chassis resto How to ?

I'm not aware of any steel chassis being galvanised. My interest and experience is in military equipment, where the chassis were usually electroplated zinc, maybe sometimes cadmium. Modern zinc plating uses 'brighteners', so doesn't replicate the grey appearance of old. A suitable grey paint can be successfully used after cleaning off any rusty patches.

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Old 15th Mar 2019, 1:27 am   #5
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Arrow Re: Steel chassis resto How to ?

Quote:
Originally Posted by Silicon View Post
I submerged them in some phosphoric acid that is used by caterers to descale kettles, etc.
I use citric acid monohydrate to de-scale my kettle: does an excellent job. Citric acid monohydrate is reality available at many pharmacies, it's cheap and should be effective at removing rust from steel, too, although I haven't tried it for that purpose yet.
As for phosphoric acid, I do believe that that is the active ingredient in 'Jenolite' - the favourite for neutralizing rust on car bodywork.

Al.
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Old 15th Mar 2019, 11:01 am   #6
Paul JD
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Default Re: Steel chassis resto How to ?

I have had good success using a commercial rust remover followed by some elbow grease with wire brush and emery paper then spraying with a cold galvanising spray. It may not look exactly the same as the original finish but it is easy to apply (no primer needed) and it gives a good finish that does not look out of place in a vintage radio.

https://www.screwfix.com/p/no-nonsense-zinc-galvanising-spray-paint-silver-400ml/40801#_=p
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Old 15th Mar 2019, 7:50 pm   #7
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Default Re: Steel chassis resto How to ?

Can you remove all the components ftom the chassis?

If so I would do so then 'pickle' it in acid for a few days. You can get "Brick acid" [hydrochloric] in 5-litre plastic bottles from your local builders-suppliers. This will strip the chassis back to bare-metal and remove any rust-pitting.

Then - thoroughly wash it, dry it, and mist-coat it with a Zinc-Chromate etch-primer [Aviation-suppliers/workshops will have this - https://www.aircraftspruce.com/catalog/cspages/zinc.php ]

After that, the only issue is "what colour would you like it?"
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Old 16th Mar 2019, 11:01 pm   #8
mark_in_manc
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Default Re: Steel chassis resto How to ?

Here's a brief post I once put up on electrolytic rust removal.

https://www.vintage-radio.net/forum/...d.php?t=140544

If you use plasterer's mesh for a convenient bendy anode, the zinc comes off it (it's galvanised) and attaches itself to your cathode work piece. I know this as I treated some badly rusted push bike forks, whose thickness I did not want to reduce further by abrasion. When my kids knocked off the paint I had finished the job with, when putting their own bikes in and out for school every day, the forks stayed grey and non-rusty. It is a surprise how well the zinc has stuck.
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Old 17th Mar 2019, 1:30 pm   #9
Silicon
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Default Re: Steel chassis resto How to ?

Be careful with Hydrochloric acid, it is very 'aggressive'.

It will discolour Chrome plating if you try to descale taps, etc.
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Old 17th Mar 2019, 1:56 pm   #10
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Default Re: Steel chassis resto How to ?

I de-rust small parts using a rotary wire brush mounted on a bench grinder, followed by kurrust (now marketed under tthe Hammerite brand) as a primer if the part needs painting. I think kurrust is phosphate-based.
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Old 17th Mar 2019, 4:08 pm   #11
Bazz4CQJ
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Default Re: Steel chassis resto How to ?

In the OP, the comment was that there is a ‘rust patina’, which I take to mean a very light degree of rusting. That being so, I too think that I’d start and see if it can be removed by a wire brush or even iron wool and perhaps follow that by oxalic acid (probably just wiping). Hydrochloric acid seems like the nuclear option. I wouldn’t go within 20ft of any restoration project with any chemical containing chloride ions, which includes numerous domestic cleaning products. Phosphoric acid will create a layer of iron phosphate on the steel, which is potentially a problem at any grounding points.

The link to zinc chromate paint in post#7 actually takes you to a page selling zinc phosphate. All chromates are now regarded with deep suspicion from a H&S standpoint (especially in aerosol form), hardly anyone still supplies the consumer market and zinc phosphate is a very good paint.

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Old 19th Mar 2019, 7:26 pm   #12
ColinTheAmpMan1
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Default Re: Steel chassis resto How to ?

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Originally Posted by Bazz4CQJ View Post
I wouldn’t go within 20ft of any restoration project with any chemical containing chloride ions, which includes numerous domestic cleaning products.B
I am probably misunderstanding you here, but if you don't like chloride ions then your chips won't taste too good. Table salt is sodium chloride. Admittedly, table salt isn't too great for iron and steel items.
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Old 19th Mar 2019, 8:10 pm   #13
Bazz4CQJ
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Default Re: Steel chassis resto How to ?

Yes, Colin, sodium chloride plus iron and steel (and any other metal for that matter) bad, my tongue OK . IIRC, you're a professional chemist...

In the days when felt-tipped pens usually had ink based on chloro-carbon solvents, the company I worked for went to great lengths to find pens which were chloro-free (for writing on piece-parts), out of concern about corrosion.

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Old 20th Mar 2019, 12:57 pm   #14
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Default Re: Steel chassis resto How to ?

Quote:
Originally Posted by Bazz4CQJ View Post
Yes, Colin, sodium chloride plus iron and steel (and any other metal for that matter) bad, my tongue OK . IIRC, you're a professional chemist...

In the days when felt-tipped pens usually had ink based on chloro-carbon solvents, the company I worked for went to great lengths to find pens which were chloro-free (for writing on piece-parts), out of concern about corrosion.

B
Yes, you are quite right about me being a research chemist - before I retired. I would have thought that chloro-carbon solvents wouldn't release chloride ions, more likely chlorine radicals. But I suppose it is possible that chloride ions could be generated by some mechanism and be nasty to the metal.....Better safe than sorry.
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Old 20th Mar 2019, 5:22 pm   #15
David G4EBT
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Default Re: Steel chassis resto How to ?

I'm surprised that no-one has mentioned the electrolysis method of rust removal for iron and steel objects which can be immersed in water. The equipment called for is basic - a plastic tub of sufficient size, some 'rebar' steel bar for electrodes, a 12V battery charger, water, and washing soda. It's been extensively covered on internet and is especially useful for de-rusing irrregular shaped objects, which other methods such as wire brushes can't access.

A couple of youtube examples are here, though the second one calls for much higher current than a battery charger could provide:

https://www.youtube.com/watch?v=qi8qIxK4IlA

https://www.youtube.com/watch?v=HN590K81D5c

I haven't tried the method myself - I've only fully stripped down and de-rusted one chassis - an Ekco AC77. I removed all the components, used a small belt sander (AKA 'electric file') to remove the rust, then treated the chassis with Jenolite. To finish the chassis I sprayed it with acid etch primer, and Halfords brand Ford 'Dove Grey' gloss, which Gary Tempest advised me was a good match for 1930s Ekco chassis, as indeed it proved to be.

First pic below shows the rusted chassis with all components removed.
Second pic shows the chassis half de-rusted with the electric file.
Third pic is after treatment with Jenolite.
Fourth pic is after re-spray.
Last pic is after main components had been re-fitted.

Hope that's of interest.
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