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Best non-cyanide plating bath for steel bolts: acid zinc
Q. I'm looking for a cyanide free bath in order to plate steel bolts and nuts (actually I use NaCN bath). Could somebody help me with composition and operating parameters in order to do this?
Thank a lot in advance.
Victor Mendoza- Lima, Peru
A. Hi Victor. Acid zinc processes are by far the most widely used for barrel plating of hardware. You could use a bright zinc chloride process operating at room temperature, or an ammoniated one which could operate 10-15 °C higher than room temperature. But the thing is, here in the USA no one that I know of attempts to formulate their own acid zinc plating solutions; they buy a proprietary process. I'm not sure if things are different in Peru. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. Absolutely. Acid Zinc Chloride is the way to go with a chromate conversion at the end. Actually, the electrolyte itself can be easily formulated yourself: Zinc Chloride, Potassium Chloride, HCl; but the brighteners & wetters are all proprietary and need to be purchased from outside suppliers. These compounds take a lot of R&D to come up with, so its hardly worth it to try to formulate them yourself. Also, the Acid Zinc Chloride bath doesn't like heat much, so you may need to cool the bath.
Dave Kinghorn
Chemical Engineer
SUNNYvale, California
A. The new generation acid zincs are made of zinc chloride, potassium chloride and boric acid. This allows you to run the temperature up to 45 °C (about 120 °F) without losing too much of the solution efficiency. You will have to make sure that you purchase a brightener system, which works with potassium chloride. Coventya is the one we use.
All the best,
Trudy Kastner
electroplating service - Durban, KZN, South Africa
A. Acidic zinc is out, alkaline non cyanide zinc is in. Not that acidic zinc is no good, it gives great results but if you are looking for a new installation, go for the alkaline.
And of course Ted is right, you cannot formulate your own additives. A plating solution requires additives that you will have to purchase from a supply house.
Sara Michaeli
Tel-Aviv-Yafo, Israel
Hi Sara. Agreed that alkaline zinc is better for full coverage and deep recesses, but why do you say acid zinc is out for barrel plating of nuts and bolts?
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted,
The results of alkaline zinc for barrel are great, also for bolts and nuts. For an existing installation I would not say that it has to be switched to alkaline but this question was related to a new installation. For a new one I would certainly recommend an alkaline barrel process.
Sara Michaeli
Tel-Aviv-Yafo, Israel
A. Hi.
Go for the ammonium chloride mixed potassium baths.They work at higher temp.
Mustafa Shakir- Kolkata, INDIA
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