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Q&As since 1989


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Wishing to know about the anodizing process

2001

I would like to set-up an aluminum anodizing company. Is anodized coloring a purely electrical process--I don't wish to get into an EPA chemical nightmare, just wish to have a small shop. Most of my pieces will be aluminum, but some casting.

Is sulfuric acid used for ALL colors, and what are the colors made from (or, added to a solution?) Are they a powder, or a liquid?

What's all involved? Have $, so that's no problem.

Thanks for helping!

Scott Kennedy
- Gainesville, Georgia, United States

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In sulfuric acid anodizing of aluminum, the electrochemical process builds a honeycomb-like structure of aluminum oxide on the surface. If the anodized part is then immersed in a dye tank, the dye will be absorbed. The dyes are usually organic dyes, rather similar to fabric dyes. Then a "sealing" process swells the honeycomb walls, locking the dye permanently in place.

Castings are more problematic than wrought material because the alloy contains other materials besides aluminum, and these cannot be anodized, often leaving a grey or black coloration.

Robert Probert's "Aluminum How-To" is a great intro. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007