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Old 5th Jul 2019, 8:46 pm   #1
Ian - G4JQT
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Default Rust prevention

What are people's preferred methods of preventing rust? I have a Murphy A46 with a painted chassis - mostly not very rusty, but will clean and respray - but it also has various unpainted steel brackets etc. which are quite rusty.

After the wire brush treatment (and not going to the lengths of zinc plating - although that's not too expensive) what finish do members use? Some light lacquer? Polyurethane seems to thick, but I don't know what else to uses that will adhere and prevent rust.

Thanks.

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Old 5th Jul 2019, 10:58 pm   #2
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Default Re: Rust prevention

It is a waste of time putting any form of paint coating over existing rust crystals, which are embedded in pits in the surface (even after you have manually cleaned a chassis) unless it was very superficial and could be totally removed with fine grade paper.They will return under the paint always and bubble it off. If you have got them all, you can just use standard automotive spray paint which is quick drying, undercoat & top coat.

Where the rust spots remain the better move is to have the chassis re-electroplated +/- fine glass bead blasted first if the pits in the metal are deep.

However, if you don't want to do that (it is a lot of work) the next best move is to treat the surface with organic rust converter (I use Fertan) This way the rust is totally deactivated (it is turned to a blue-black harmless substance) then, paint the chassis or object after that. The best satin silver look is obtained from the automotive spray cans, never a brush and not with enamel paint, with the exception of VHT paint, that is excellent if you can bake the part in your oven. Many other spray enamels are poor at the task, soft and easily scratched, compared to the automotive lacquers.
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Old 6th Jul 2019, 12:22 am   #3
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Default Re: Rust prevention

I also think it is advisable to remove the existing rust before applying any rust preventative measures.

I bought 5 litres of 28% phosphoric acid from a cleaning supplies shop. They use it for descaling stainless steel catering equipment and porcelain.
I regard it as a relatively safe chemical for rust removal.
It is the active component in many rust converters.

What is a 'lacquer'? I have never found a definitive explanation.
Lacquer has a different meaning depending on the country of origin.

I assume that the original paint coating would be a cellulose paint.
What is in an automotive spray paint can nowadays?

If you find a good colour match with the blue paint used by Murphy pre-war, please let us know.
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Old 6th Jul 2019, 7:00 am   #4
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Default Re: Rust prevention

Generally "lacquers" (it is a loose term) have a quick drying very volatile solvent (acetone like at least) and set in minutes to hours. Enamels set in hours to days tend to have a mineral turpentine like, or similar solvent. Holts duplicolor make the automotive paint in touch up spray cans and they supply a solvent for it. You will find this paint quick drying and it will not dissolve in mineral turpentine.
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Old 6th Jul 2019, 10:47 am   #5
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Default Re: Rust prevention

Hammerite make a range of direct to metal quick drying paints and rust prevention products.
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Old 6th Jul 2019, 11:28 am   #6
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Default Re: Rust prevention

Thanks for the input chaps.

I think it was something like Fertan that Argus mentioned that I had in mind. I think any plating that was on the unpainted parts has gone, or will have after my wire brush treatment. But the rust remover on the awkward to get to parts will be useful.

I guess I'll still have to spray the de-rusted metal to prevent future deterioration. I had in the back of my mind some sort of clear spay that's used to prevent tarnish on brass/bronze spray...?

Yes, Hammerrite/Smoothrite is good stuff, but I've seen it used on radio chassis - not always a pretty sight!

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Old 6th Jul 2019, 11:37 am   #7
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Default Re: Rust prevention

The Holts clear is part DS117 (or PS117 in the bigger can) perfect also for coating polished brass or copper or aluminium, it adheres very well. DS110 is the fine metallic silver.The brass escutcheons on this Grebe radio were sprayed with the clear DS117 about 15 years ago, they still look good today:

http://worldphaco.com/uploads/THE_GREBE_MU-1.pdf
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Old 6th Jul 2019, 12:02 pm   #8
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Default Re: Rust prevention

This doesn't really answer your question, but I know from experience that rust-resisting finishes do exist. When at secondary school, I was quite good at metalwork and had finished all of the required stuff. The metalwork teacher asked me if I'd like to make something using the forge and gave me a catalogue of items. I chose a particularly complex table-lamp. After it was all made, the teacher gave me some satin-finish black paint to complete it. Don't forger that this had been in and out of the forge several times and I don't remember wire-brushing it at all. This was over 50 years ago and I still have it as a bedside lamp.The paint is still fine and there is no sign of rust. I wonder what that paint was and if it is still available? Maybe for forge-made items?

I vaguely recall recently seeing a programme on TV about painting and maintenance of the Firth of Forth (I am often tempted to add "of Fifth of Sixth") railway bridge with some new-fangled paint. There was always the comment that as soon as the team of painters had got to the end, they had to go back to start the job all over again, but this new paint is supposedly going to last much longer. Bear in mind that the bridge is in a particularly salty water environment, too.
Colin.

Last edited by ColinTheAmpMan1; 6th Jul 2019 at 12:09 pm. Reason: Firth of Forth of Fifth of Sixth railway bridge info.
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Old 6th Jul 2019, 1:39 pm   #9
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Default Re: Rust prevention

There are of course chromate and zinc based primers for steel with rust inhibiting qualities that I have never been too impressed with. These are nowhere near as good as having the item zinc plated and putting a proper baked coat of paint or a powder coating over that.

Have a look at the transformer covers and black painted rear brackets and EHT cage on this TV chassis:

http://worldphaco.com/uploads/621TSARTICLE.pdf

Also, one advantage of power coating is that it can be made of a custom mix, if you look at the EHT cage on the TV chassis, it is a subtle dark metallic brown. This was done to replicate the original finish of the cage which had rusted. Powder coating is extremely scratch resistant and very long lasting, provided not exposed to direct sunlight. It needs to be applied by an experienced operator so that the applied coat is not too thick.

Last edited by Argus25; 6th Jul 2019 at 1:48 pm. Reason: typo
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Old 6th Jul 2019, 3:05 pm   #10
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Default Re: Rust prevention

Quote:
Originally Posted by ColinTheAmpMan1 View Post
The paint is still fine and there is no sign of rust. I wonder what that paint was and if it is still available? Maybe for forge-made items?
Pure iron is much more rust resistant than steel. Quite possibly the heat treatment also bestowed additional protection.
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Old 6th Jul 2019, 5:12 pm   #11
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Default Re: Rust prevention

Quote:
Originally Posted by Argus25 View Post
There are of course chromate and zinc based primers for steel with rust inhibiting qualities that I have never been too impressed with. These are nowhere near as good as having the item zinc plated and putting a proper baked coat of paint or a powder coating over that.

Have a look at the transformer covers and black painted rear brackets and EHT cage on this TV chassis:

http://worldphaco.com/uploads/621TSARTICLE.pdf

Also, one advantage of power coating is that it can be made of a custom mix, if you look at the EHT cage on the TV chassis, it is a subtle dark metallic brown. This was done to replicate the original finish of the cage which had rusted. Powder coating is extremely scratch resistant and very long lasting, provided not exposed to direct sunlight. It needs to be applied by an experienced operator so that the applied coat is not too thick.
Absolutely excellent job on that TV Argus! An absolute labour of love. I try to get close to that level, but completely dismantling variable capacitors, mains transformers and loudspeakers puts me off. Although I did come very close with an Ekco A22 I restored last year. I even rebuilt the IF cans, re-dipped the coils in hot wax and transformers/choke in varnish. Performance-wise almost certainly completely unnecessary...

It opens the wider issue - just because it looks like new, does it work any better than a more basic rebuild? Almost all the new components will have better performance than the originals, so I like to think such lovingly restored attention to detail has some real effect, especially after a careful alignment. But realistically I'm not sure this is true, especially as most of this work is hidden inside! But it is the feeling of thoroughness I enjoy.
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Old 6th Jul 2019, 11:01 pm   #12
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Default Re: Rust prevention

Quote:
Originally Posted by Ian - G4JQT View Post

It opens the wider issue - just because it looks like new, does it work any better than a more basic rebuild? Almost all the new components will have better performance than the originals, so I like to think such lovingly restored attention to detail has some real effect, especially after a careful alignment.
With my restorations I try to do three basic things:

1) put the set back into a physical condition where it looks new.

2) have a situation though where the surfaces, parts wiring etc are actually much better protected and will last longer than new. For example, the chassis electroplating is coated in lacquer. This requires masking with sticky dots around all the holes where the earths are. Powder coated parts sometimes as noted, wiring that does not degrade with time & heat (silicone rubber covered) re-stuffed waxies with polyester end fills, where the wax has been wiped off and replaced with marine grade varnish that doesn't stick to dust and higher voltage poly caps used. All aluminium parts lacquered too.

Most corrosion is induced from atmospheric dust and moisture settling on the surface, the lacquer prevents this. So as the years roll by, the chassis remains "preserved" rather than rusting again.

3) perfect electrical alignment.

The set of course will only ever work as well as it did when new, but it has to work at least that well or something is amiss.

And it won't necessarily work any better than a more basic rebuilt, but it can help with reliability, especially if corroded valve sockets, mica capacitors and aged resistors have been replaced where indicated. I have come to replace electrolytics with non electrolytics now when I'm able.

I tend to use a lot of 2W metal film resistor in my restorations, because they are about the physical size of vintage 1/4 resistors, but much more stable, reliable and less noisy.


Have a look at the photo of the under-chassis of the TV article on page 6, just below the small transformer on the left, you will see a chassis hole for a screw, notice how it looks different around its perimeter, this is due to lacquer masking by a sticky dot, later removed.

Also I treat rusted transformer laminations with Fertan. Then re-varnish the transformer.

On the topic of fertan, I have in effect being carrying out a 3 or more year experiment with it. I coated the very rusty disc brake hubs with it in my car that drives through a lot of salty road water on the coast. They had no factory coating and just resembled bare cast iron. It turned the surface a dark black-blue hue, Astonishingly not a single rust spot has re-emerged over this time, and it doesn't even have a coat of paint over it. That probably explains why I have had a lot of luck with it in restorations, especially when it is painted over and I don't see rust coming back under the paint.

Last edited by Argus25; 6th Jul 2019 at 11:18 pm. Reason: add remark about Fertan.
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Old 7th Jul 2019, 11:20 am   #13
Ian - G4JQT
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Default Re: Rust prevention

Thanks Argus. Very interesting, particularly your description of the protection apparently provided by Fertan on ferrous components.
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Old 7th Jul 2019, 12:22 pm   #14
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Default Re: Rust prevention

Rust on iron or steel can only form in the prescence of oxygen and water. Unfortunately both are present in our atmosphere. Paints, neutralisers and other coatings work by trying to exclude oxygen and water. For various reasons most, if not all coatings, end up being porous to some degree. Worse still, the seeds of doom are often trapped against the iron/steel. Whatever you do it is ultimately likely to be a losing battle unless the object concerned is placed in a perfect vacuum.

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Old 7th Jul 2019, 1:54 pm   #15
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Default Re: Rust prevention

Quote:
Originally Posted by Ian - G4JQT View Post
Thanks Argus. Very interesting, particularly your description of the protection apparently provided by Fertan on ferrous components.
There are some items that cannot be re-electroplated. This is where Fertan comes in handy. A good example of this were the valve shields on my HMV904, a composite of steel and aluminium. The rust on the steel was treated with Fertan. The aluminium polished and coated with clear Holts lacquer, the body of the shield with the Silver Holts.

There is no evidence at all of any rust activity or expansion of rust Xtals under the paint, I inspected them recently, no deterioration over 17 years now. Have a look at the photo of these shields here:

https://www.earlytelevision.org/hold...storation.html
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