Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Anodizing of zinc
Q. What prevents the anodizing of zinc in a process normally used for anodizing aluminum? I am aware of the "zinc anodizing" process (misnomer) but am looking for a "true" oxide coating on zinc alloy parts (Zamak 3 and/or ZA-8).
Thanks.
Brian Brandel- Mequon, Wisconsin
2002
A. The usual aluminum anodizing processes don't work because the voltage must be much, much higher to anodize zinc. Further, I doubt that sulfuric acid attacks zinc in the same way it attacks aluminum, creating the pinhole porosity characteristic of anodized aluminum. Why do you call it a misnomer--educate me please. Thanks!
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. It is a misnomer because with what is described as "zinc anodizing" a layer of oxides, phosphates, and chromates combined, not a simple oxide layer as in aluminum anodizing. In addition, zinc anodizing uses AC current, not DC; therefore, there is no anode and cathode present.
Brian Brandel [returning]- Mequon, Wisconsin
A. Anodizing of Zinc was a process offered by Allied-Kelite but not carried over into the acquisition by Macdermid. The process worked in the lab but never gained commercial acceptance because the equipment set up was prohibitively expensive. If you desire I'll try to dig out some of the old papers and copy for you. However, again, it ain't practical.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Multiple threads merged: please forgive chronology errors :-)
Q. I'm interested in anodizing of zinc. Is it being done, or is it possible -- just not practical?
Thanks,
Brian A. Calver- Grimsby, ON, Canada
2002
A. It may be the most practical, economical, most inexpensive, and longest lasting finish possible for your application. What is that application? :-)
Tom Pullizzi
Falls Township, Pennsylvania
A. It can be done, it has been done, and it's a good finish with phenomenal salt spray resistance. I think one of the biggest impediments is that most job shops, and many captive shops, have an understandable history of being very cavalier about exposed bus bar and worker exposure to electrified tanks because of the low voltages usually required for plating and aluminum anodizing. But considering the voltages required for zinc anodizing, that could be dangerous or fatal.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I did a search in this website in regards to anodizing of zinc, and I found info which says that it can't be done, and why.
I was wondering if anything has changed since the date (2002) of the info?
The color or appearance does not matter at all. We have an electric motor and the housing is a zinc alloy. There is a problem with carbon tracking which causes a very small leakage to ground, which causes ground fault circuit breakers to trip. (4-6 milliamps).
I was interested in anodizing the entire motor housing to prevent the carbon dust from creating a leakage path to ground.
Thank-you for any help that you can provide.
Blackstone Inds. - Bethel, Connecticut, USA
2006
A. Hi Donald. You should not have read on this site that it can't be done because it can :-)
Fred Pearlstein wrote an article on it entitled "Anodic Coatings for Other' Metals, which was printed in Plating and Surface Finishing, Vol. 66, Mar. 1979.
It is not a popular finish and I suspect that one reason is the very high voltages needed for anodizing (over 200 volts, I recall).
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Yes, please it would be great to get some literature on the process.
Thanks a lot!
- Ottawa, Ontario, Canada
December 26, 2011
A. Hi, Irwin.
Fred Pearlstein wrote a good article about it for Plating and Finishing magazine in 1979. Anodized zinc offers fabulous corrosion resistance, but the voltages are probably much too high to safely use in the "open bus bar" fashion of most plating shops.
I bet Frank Goodwin of ILZRO can give you some more current information on the process. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Need to know what coating / finish can be used on ZAMAK to make it less conductive?
Need to replace an Anodized Aluminium with ZAMAK with similar electrical conductivity resistance that Anodizing offers.
Mechanical Engineer - Bangalore, INDIA
September 25, 2014
A. Hi Francis. As Robert Probert notes, zinc anodizing has proved to usually be impractical. How about a UV-cured hard coating as used on auto headlights and such?
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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