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Zinc metal build up in plating solution
Q. Our zinc metal keeps growing in our rack line. We have tried all the usual fixes. Has anybody tried to use insoluble anodes to drive the metal down without destroying the brightener? This is a chloride zinc bath 16 oz./gal. Hoping for a 21st. century answer. Thanks, --Frank
Frank Z [last name deleted for privacy by Editor]- Paterson, New Jersey
1995
aNo, I've never heard of insoluble anodes for zinc, but you might try elevating the pH a little with potassium hydroxide. See how it works in a Hull cell.
Dave Wichern
Consultant - The Bronx, New York
A. I hope that when you say that "This is a chloride zinc bath 16 oz./gal." that you are referring to the KCl level and not the Zn metal level. Bare titanium will become passive and not conduct current. You could try platinized titanium or iridium oxide coated titanium anodes; it is pretty expensive stuff, though. I have found Cosmos (Mineral Corp.) to be very helpful in obtaining this material on short notice. I'm not sure, though, what will be the relative resistance between this material and standard zinc anodes. If they do not conduct current similarly, you could find the current preferentially going through one or the other anode material. You would have to try and do some experimenting.
Ken Rosenblumfinishing shop - Minneapolis, Minnesota
Q. We have an automatic barrel- acid chloride zinc plating line.Our zinc plating solution is of 2000 USG capacity.We maintain total chloride at 145 g/l and boric acid at 30 g/l.We used to have our metal content at 35 to 37 g/l.But for past few weeks it is at 47 g/l.Ideally we want to maintain it at 30 g/l.( cloud point is at 150 F) Our existing options are to reduce anode baskets without affecting surface area of anodes and / or remove the baskets on weekend.
And I studied in literature about use magnesium and aluminium alloys of zinc which reduces the metal build up.
My questions on that are :
Is it commonly used and is it proved to be successful?
Does it affect the current efficiency and properties of the deposit?
Is the corrosion resistance of the deposit same
Or is there a still better alternative.
Thanks
Venkat Raja- Kitchener, Ontario, Canada
2004
A. Venkat,
We experienced the same problem on our rack acid chloride zinc line (rising [Zn]). I switched to a different brightener system that was compatible at higher pH's (~5.5-6.0). This seemed to help. I also switched from a boric acid/KCl bath to an ammonium chloride/potassium chloride system. It was a quick and easy solution in my application.
Hope this helps.
Trent Kaufman
electroplater - Galva, Illinois
Hi Trent,
Thanks for your response. As mentioned in your reply I do have an option of going for a different brightener system which doesn't oil out in high chloride concentration. But I am still wondering whether there are any other options to prevent metal buildup.
Venkat Raja- Kitchener, Ontario, Canada
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