Zamak finishes

rimcanyon · Jan 19, 2016

Is Zamak finishing available as a service similar to plating? I would like to restore the original finish on some Zamak carburetors. but I have not found anyone that does it. I am not sure of the process, because the color is gold, but does not appear to be a urethane. i.e. 50 year old carburetors still retain some of the gold color, but not much. I have read that chromic acid was used to impart a green finish on Zamak, so maybe that is what was used. Here are a couple of photos that show a 50 year old Solex carburetor that still retains most of the finish, and one where the finish is mostly gone. I'm going to soda blast the bodies which need refinishing, and either leave them as is, or refinish them if I can find a place to do it. Is there any way I could brighten the carburetor on the right with a chemical dip rather than soda blasting? This is what it looks like after it comes out of Berryman's 905.

Perry Harrington · Jan 19, 2016

Looks like Zinc Chromate to me.

rimcanyon · Jan 19, 2016

Yes I think it is Zinc chromate. And most likely it was done using chemicals that the EPA would regulate heavily, e.g. hexavalent chromium. Will trivalent chromium give as durable a finish?

First I need a way to brighten the carburetors before dipping in yellow chromate, to clean off all the dark oxide. I have some aluminum cleaner that contains oxalic acid, and although it removes oxides from aluminum, it does not work on Zamac. The next step I will try is some dilute sulfuric acid.

JST · Jan 19, 2016

Zamak is an alloy, and some constituents are nearly always going to etch off preferentially, so there could be an issue with any dip etch cleaning.

There are so-called organic chromate finishes, that the military now prefers. That's likely what you refer to. They do NOT have the nice yellow color, you often can barely tell they were processed, even with an unprocessed next to a processed part.

The durability is fine, and the electrical conductivity is a little different, I forget which way, but that won't bother you.

If you look up the MIL standard on "conversion coatings" you should find the info.

Monarchist · Jan 19, 2016

rimcanyon said:
Is Zamak finishing available as a service similar to plating? I would like to restore the original finish on some Zamak carburetors. but I have not found anyone that does it. I am not sure of the process, because the color is gold, but does not appear to be a urethane. i.e. 50 year old carburetors still retain some of the gold color, but not much. I have read that chromic acid was used to impart a green finish on Zamak, so maybe that is what was used. Here are a couple of photos that show a 50 year old Solex carburetor that still retains most of the finish, and one where the finish is mostly gone. I'm going to soda blast the bodies which need refinishing, and either leave them as is, or refinish them if I can find a place to do it. Is there any way I could brighten the carburetor on the right with a chemical dip rather than soda blasting? This is what it looks like after it comes out of Berryman's 905.

View attachment 160415 View attachment 160416

Mostly Zinc? See if this source from a few years back is any help. It has further links & sources:

RE-COLORING / REFINISHING ZAMAK

Bill

rimcanyon · Jan 20, 2016

Monarchist said:
Mostly Zinc? See if this source from a few years back is any help. It has further links & sources:

RE-COLORING / REFINISHING ZAMAK

Bill

Yes, I saw that when I was searching for info. I found one reference that said H2SO4 solutions will brighten Zamak. Caswells suggested HCl. I'll try both to see which gives the best result, then follow with a yellow chromate dip and see if I get good results.

swall · Jan 20, 2016

Be careful with HCl. It can go really quick.

bloomautomatic · Jan 20, 2016

rimcanyon said:
Yes, I saw that when I was searching for info. I found one reference that said H2SO4 solutions will brighten Zamak. Caswells suggested HCl. I'll try both to see which gives the best result, then follow with a yellow chromate dip and see if I get good results.

I would be VERY cautious about putting anything zinc in any acid. Before I dipped an important part, I would try it on another piece of zamak and see what it does. Matchbox cars were cast from zamak. Try one of those. Most cast zinc parts are some grade of zamak, 3, 5 or 7.

I used HCl to test the zinc coating thickness on galvanized steel. It would take about 30 seconds to completely remove the zinc from a piece galvanized sheet metal.

If you're just looking for the color, try eastwood. They have a yellow cad finish that imitates the original. As stated before, the cadmium chromate finish is not feasible due to the environmental restrictions on the chemicals.

Vince

Porschefix · Jan 20, 2016

rimcanyon said:
Is Zamak finishing available as a service similar to plating? I would like to restore the original finish on some Zamak carburetors. but I have not found anyone that does it. I am not sure of the process, because the color is gold, but does not appear to be a urethane. i.e. 50 year old carburetors still retain some of the gold color, but not much. I have read that chromic acid was used to impart a green finish on Zamak, so maybe that is what was used. Here are a couple of photos that show a 50 year old Solex carburetor that still retains most of the finish, and one where the finish is mostly gone. I'm going to soda blast the bodies which need refinishing, and either leave them as is, or refinish them if I can find a place to do it. Is there any way I could brighten the carburetor on the right with a chemical dip rather than soda blasting? This is what it looks like after it comes out of Berryman's 905.

View attachment 160415 View attachment 160416

I have a set of Solex's I have been asked to recondition and I have exactly the same problems mentioned in this thread. Rimcanyon, please keep me posted as to the results and processes you use to get finished results. I find soda blasting barely touches the surface. Thanks for all the other comments.
Ron

WizardOfBoz · Jan 20, 2016

My first thought was that zinc will be attacked by either HCl or H2S04. I wouldn't use HCl anywhere around Zamac (Zinc, Aluminum, Magnesium, Copper)

HCl and Zinc: Zn + 2 HCl --> 2 ZnCl2 + H2 https://www.youtube.com/watch?v=ft82C6jQq30
HCl and Aluminum: 2 Al + 6 HCl --> 2 AlCl3 + 3 H2 https://www.youtube.com/watch?v=LaaORZ0ofCY
HCl and Magnesium: Mg + 2 HCl --> 2 MgCl2 + H2 https://www.youtube.com/watch?v=cpy_Zh-8sKA
HCl and Copper: Copper is not too reactive with HCl

I'd probably be very careful with sulfuric as well, as similar reactions occur. https://www.youtube.com/watch?v=O1MpQv-P-24

The examples are with strong HCl and H2SO4, and dilute stuff will not be as agressive. So a short dip in dilute may just affect the surface and clean it off. But soaking your part for any length of time may have nasty effects.

Bruce Griffing · Jan 20, 2016

You can still buy fasteners with a zinc chromate finish. Someone must be able to do it.

tdmidget · Jan 20, 2016

Let me google that for you

rimcanyon · Jan 27, 2016

bosleyjr said:
My first thought was that zinc will be attacked by either HCl or H2S04. I wouldn't use HCl anywhere around Zamac (Zinc, Aluminum, Magnesium, Copper)

HCl and Zinc: Zn + 2 HCl --> 2 ZnCl2 + H2 https://www.youtube.com/watch?v=ft82C6jQq30
HCl and Aluminum: 2 Al + 6 HCl --> 2 AlCl3 + 3 H2 https://www.youtube.com/watch?v=LaaORZ0ofCY
HCl and Magnesium: Mg + 2 HCl --> 2 MgCl2 + H2 https://www.youtube.com/watch?v=cpy_Zh-8sKA
HCl and Copper: Copper is not too reactive with HCl

I'd probably be very careful with sulfuric as well, as similar reactions occur. https://www.youtube.com/watch?v=O1MpQv-P-24

The examples are with strong HCl and H2SO4, and dilute stuff will not be as agressive. So a short dip in dilute may just affect the surface and clean it off. But soaking your part for any length of time may have nasty effects.

I agree 100%. Plan is to try dilute solutions of various acids: oxalic, citric, HCL (muriatic) & H2SO4 , since those are what I have available. I have several junk carburetor bodies to experiment with. I'll neutralize with sodium carbonate or sodium bicarbonate solutions.

-Dave

rimcanyon · Jan 27, 2016

Porschefix said:
I have a set of Solex's I have been asked to recondition and I have exactly the same problems mentioned in this thread. Rimcanyon, please keep me posted as to the results and processes you use to get finished results. I find soda blasting barely touches the surface. Thanks for all the other comments.
Ron

Ron, I'll post my results here, also on the 356 Registry site.

I will also try soda blasting, since I just bought a compressor that can handle it (I replaced my 1955 3HP Quincy with a 10HP rotary Atlas Copco). I need to buy a new blast gun too, the Harbor Freight unit I have is pretty miserable. I have been looking at Clemco guns.

-Dave

henrya · Jan 27, 2016

I cleaned a cast fuel tap in my ultrasonic cleaner with some citric acid and it came super clean in about 10 minutes but was pretty dull and a little dark looking when done.

rbjscott · Jan 27, 2016

Call Holey's tech line and ask what they use. They have a rebuild shop that re-colors the carbs.

rimcanyon · Jan 27, 2016

rbjscott said:
Call Holey's tech line and ask what they use. They have a rebuild shop that re-colors the carbs.

Good idea. I hope they will share info.

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