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topic 805

Bleach cause black anodizing to fade


(1998)

We have trouble with 10% bleach solution causing fading in black anodized parts. I was told that changing from a Nickel Acetate to a Nickel Fluoride rinse would eliminate this problem. We anodize over 5052 H-32 Sheet Metal.

David Polley
Becton Dickinson


(1997)

I really doubt if any organic dye will stand up to a 10% bleach solution. I think that it will gradually attack even clear anodize. Your best shot would be to switch to two step anodize. Since it is inorganic, it will stand up longer, but not forever.

James Watts
- Navarre, Florida


(1997)

It sounds to us like your seal is failing. First of all, the word "rinse" you use concerns me. This is the seal & must be done for an adequate time, not just rinsed in & out.

The nickel acetate seal you are using should be more that adequate if it is being used properly. The Nickel Fluoride, aka COLD RINSE is not nearly as good.

There are tests you can do after sealing to insure the part is fully sealed.

Also, it could be the black dye that your anodizer is using. Different black dyes have different reactions to heat, light & chemicals, like bleach.

We run huge amounts of black anodize here, in our two plants & we use the highest quality dye available. We also test the seal on every load to ensure it is properly done.

David A. Kraft
- Long Island City, New York


(1997)

Dave, I will freely admit to your being more qualified than me on color anodizing. The inquiry stated 10% bleach. I am assuming he meant store bought 3% sodium hypochlorite. What was not stated, was what quantity and for how long in the bleach. If my chemistry serves me correctly, you get some hypochlorous acid and obviously a oxychlorine compound. Regardless of the UV colorfastness of the dye and the quality of the seal, a prolonged exposure is going to attack the dye as the surface is abraded or attacked chemically.

Some are obviously much, much better than others, but not perfect, or you would never have a failure with an anodized salt spray if you left it in for a month. My assumption was a piece of lab equipment or something similar that was cleaned with a bleach solution daily. Put a 3x10 panel with normal processing in a 10% bleach solution and let it set for a month and tell all of us it looked as good as when it started. I will publicly apologize for differing with you when you do.

That said, your dye and seal may give him 10 times the resistance to fade. Not enough data given for perfect answers. Jim

James Watts
- Navarre, Florida


(1997)

The Canning Handbook, page 801, states that architectural anodizing may be lacquered to give increased resistance.

tom pullizzi monitor
Tom Pullizzi
Falls Township,
   Pennsylvania 



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