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Old 1st Apr 2019, 11:47 am   #1
Steve G4WCS
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Default Zinc plate and passivate? Restoration.

Picked up a "linear" amplifier.

Front panel looks OK and it needs a good de-dusting. but the back panel could do with a light restoration.

Is it zinc plated and passivated and is there a receommended method of restoration? I'm thinking alng the lines of some sort of coloured lacquer ( I'm sure you could get something similar for restoring the finish on carburettors ) rather than completely dismantling the unit and getting the panel re-plated.
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Old 1st Apr 2019, 5:07 pm   #2
Bazz4CQJ
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Default Re: Zinc plate and passivate? Restoration.

I'm not sure that I've heard of a passivation process being applied to a zinc coating. Perhaps more likely, the platers had some tricks up their sleeve to get a zinc plating with a specific look.

Most carburettors are made of aluminium alloys; I don't think I've seen one with zinc plating.

There are kits on the market to carry out plating by means of a cotton swab on the end of a graphite rod, that is dipped in a plating solution and then used to do electroplating. I've seen quite good results from them, especially when the area is small as in your case. They may well be worth a try.

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Old 1st Apr 2019, 7:58 pm   #3
Steve G4WCS
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Default Re: Zinc plate and passivate? Restoration.

This was the stuff I was thinking of. Supposed to replicate zinc chromate

https://www.frost.co.uk/eastwood-bro...SABEgJfvPD_BwE
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Old 1st Apr 2019, 8:57 pm   #4
Bazz4CQJ
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Default Re: Zinc plate and passivate? Restoration.

So, the Eastwood stuff is an acrylic paint which looks like zinc chromate. I wonder how closely it will match?

If you are going to remove the existing zinc with carbide paper or whatever, I guess that will get you down to to plain steel. As you don't have endure the under-bonnet conditions of temperature and petrol, I wonder if you could find something cheaper than 16, perhaps something from the model paint people like Humbrol (who have a metallic bronze).

I'm not too sure that any paint will give a really close match to real zinc plate, but guess it depends on how demanding you are .

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Old 1st Apr 2019, 11:40 pm   #5
alanworland
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Default Re: Zinc plate and passivate? Restoration.

Unless things have changed I thought a zinc plated finish could either have a clear or coloured passivated finish applied?
Might be worth asking a platers

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Old 2nd Apr 2019, 3:26 am   #6
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Default Re: Zinc plate and passivate? Restoration.

Quote:
Originally Posted by alanworland View Post
Unless things have changed I thought a zinc plated finish could either have a clear or coloured passivated finish applied?
Might be worth asking a platers. Alan
A couple of moments on Google reveals that zinc platers do indeed use the term "passivation" to describe the addition of a chromate layer on top of the zinc layer.

The terminology is a bit loose; a more formal description of passivation is as per Wiki https://en.wikipedia.org/wiki/Passivation_(chemistry) but we start to get in to splitting hairs over passivation and inhibition.

For an object which lives in a environment which is not very corrosive, I think you'd expect standard zinc coating to be satisfactory.

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Old 4th Apr 2019, 8:47 pm   #7
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Default Re: Zinc plate and passivate? Restoration.

Linear arrived tonight. Opted for citric acit derust (lemon juice), Brasso, and hard paste wax.
Will do a restoration post in success stories if 80s kit is deemed vintage / interesting enough
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Old 4th Apr 2019, 11:05 pm   #8
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Default Re: Zinc plate and passivate? Restoration.

That looks really good. A re-visit with the wax every blue-moon might well keep it that way!

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Old 6th Apr 2019, 8:21 pm   #9
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Default Re: Zinc plate and passivate? Restoration.

That's made a real difference - it's easy to see where the tissues were (I assume soaked in lemon juice?)
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Old 6th Apr 2019, 8:42 pm   #10
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Default Re: Zinc plate and passivate? Restoration.

Yes, an hour in lemon juice, brought the rust pits back to grey steel
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Old 7th Apr 2019, 12:28 am   #11
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Default Re: Zinc plate and passivate? Restoration.

Quote:
Originally Posted by Steve G4WCS View Post
Yes, an hour in lemon juice, brought the rust pits back to grey steel
And by "lemon juice" we really mean...citric acid, as I mention... occasionally

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Old 24th Apr 2019, 7:01 pm   #12
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Default Re: Zinc plate and passivate? Restoration.

My mother had great difficulty getting citric acid a few years ago for some preserves. The shopkeeper said that apparently there was some control of it because of its propensity to get cut with cocaine!
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Old 24th Apr 2019, 8:00 pm   #13
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Default Re: Zinc plate and passivate? Restoration.

Never had any problems, either on the High Street or ebay.

Used some citric yesterday to clean up a small mild steel bracket which was rusty in some places and covered with zinc plate in others. Cooked it up to about 50C, and after about an hour, both the rust and the zinc were gone leaving a very a really nice surface to paint with primer.

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Old 24th Apr 2019, 8:40 pm   #14
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Default Re: Zinc plate and passivate? Restoration.

That's a good Linear I have one of those, very clean output and the preamps a boon
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