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"Question About Vertical Anodizing"


Q. Dear Sirs, We are a Chemical products supplier for finishing industry in MedellÌn, Colombia. One of our customers has started his new vertical Aluminium Anodizing plant since four months ago. They have had several problems, but the most important has been non uniform colour along the profiles. The upper part appear darker than the lower part for all colours they produce (clear bronze to black). The actual composition of the bath is as follows: Sulphuric acid=40 g/l, Tin(II) Sulphate= 15 g/l and Stabiliser Additive=35 ml/l. We would really thank you any recommendation that you can give us to solve this critical problem. Thanking you

Juan JosÈ PavÛn Palacio
- Colombia

A. Sorry, Juan, I'm not familiar with the term "vertical anodizing". Are you describing something different than conventional anodizing, or are you simply noting that the parts hang with the longest dimension up-and-down rather than left-to-right?

I guess that I would have expected the opposite result to what you are getting, i.e., I would have expected the bottom of the parts to be exposed to the dye longest and consequently be darker. Since that is not the case, my guesses would include the possibilities that

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


A. Dear Sir

Ted's response was dealing specifically with the use of organic dyes. Your question is dealing with what is now an old system (But the best, especially if the app' is out-doors - U/Violet light-fast required) O.K with tin sulphate light scattering approaches it is very important to have an anode (TIN) equal to the work area (The aluminium work that has been anodized)- The Cathode and space it equally from the work for uniform deposition. Also of importance is the A.C.,Voltage & Current waveform shapes during this process to be equal on positive and negative cycles. Get the Book from BRACE...The Technology of Anodizing Aluminum [affil. link to book on Amazon ... or on AbeBooks]

Robert Fyfe
- Gosford, NSW, Australia

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