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Contaminant Build up in Anodize Line Rinse Tanks

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"Aluminum How-To" -- Chromating, Anodizing, Hardcoating by Robert Probert (2005)
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"The Metallurgy of Anodizing Aluminum" by Jude Mary Runge (2018)
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"The Surface Treatment & Finishing of Aluminium and Its Alloys" by Wernick, Pinner & Sheasby (1959 - 2001)
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"Surface Treatment and Finishing of Aluminum" by Robert King (1988)
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"Anodic Oxidation of Aluminum and Its Alloys" by V. F. Henley (1982)
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"The Technology of Anodizing Aluminum" by Brace (1979)
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"Aluminum Finishes Process Manual" by Reynolds Aluminum (1973)
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"The Anodic Oxidation of Aluminum" by A. Jenny (1940)
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Anodizing and Coloring of Aluminum Alloys by S. Kawai (2002, VERY RARELY avail)
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Q. Hey there! I have a small anodizing shop where we have decided to modify our line with a cascade counterflow rinse arrangement. We are seeing an interesting build up of contaminants, but I'm unsure if this is affecting our quality further down.

Our tank arrangement leading up to anodize is:
Soap
Soap Rinse
Etch Rinse
Etch
Deox Rinse
Deox
2nd Rinse
Anodize Rinse
Anodize

Our cascades are:
Fresh --> Sulfuric Rinse --> Deox Rinse --> Etch Rinse --> Drain
Fresh --> 2nd Rinse --> Soap Rinse --> Drain

Our line procedure leading up to anodizing is:
--> Soap --> Soap Rinse --> Etch Rinse
--> Etch --> Etch Rinse --> Deox Rinse
--> Deox --> Deox Rinse --> 2nd Rinse --> Anodize Rinse
--> Anodize --> Anodize Rinse --> sealing

With the cascade, we are overall seeing a marked improvement in the quality of our Rinses. However, our Etch Rinse quickly turned a deep tomato orange and developed white "floaties" that easily clump and break apart. They seem to easily rinse off with a sprayer, and they don't seem to be transferring to our Deox Rinse. We knew that the Etch Rinse would look "dirtier" and "cloudy" but this seems extreme. Pictures attached.

61623-1a   61623-1b  

My questions are:
1) I'm assuming the floaties are sodium sulphate, resulting from the weak sulfuric from the anodize rinse and the deox rinse neutralizing the sodium hydroxide getting dragged in from the Etch. Would this be accurate?
2) How much should I worry about the floaties (if they are sodium sulphate) affecting the cleanliness of the aluminum? Is it likely any of it might "stick" to part surfaces that could affect the anodize?

Thank you!

Jeremy Tollefson
- Sacramento CA
December 13, 2023




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