Metal finishing Q&As since 1989

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Critical cosmetic finish

2005

Having issues with a 6061 aluminum spacer. The customer is concerned with the finish. We had the parts black anodized the first time and they were returned to us because of water marks. We returned them to the anodizer stating that they needed to be cosistant and require a critical cosmetic finish. They stated that this would not be an issue in the future. I received the parts back today and the water marks are still there. They appear to be different then the water marks that we observed on the parts previously.

Is there something that we need to do on our end to ensure that the parts get a solid jet black finish or do we need to find a different anodizer?

What is causing this to happen? How can we elinimate this issue?

Patrick Carr
Machine shop - Winona, Minnesota

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First of two simultaneous responses --

Uniform color on 6061 should not be a problem. It appears that your anodizer is either disinterested, incompetent, or both.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
2005

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Second of two simultaneous responses -- 2005

Patrick

If your supplier knows that the 'water spots' are unacceptable, and he continues to ship you 'water spots', look for another finisher.

If you are practicing process control, and your supplier can produce acceptable results sometimes, then he needs to be on the same page. Can you imagine buying food that was produced without process control? You may be getting your anodize done by a grill cook when you need a chef;).

Willie Alexander
- Colorado Springs, Colorado

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For a metal finisher's site, we seem awful quick to blame the anodizer. It takes a lot of faith in some unknown person's troubleshooting ability to assume that "water marks" are really caused by an anodizer's process or even by water. It could be grain structure in the metal which results in uneven appearance. It could be dried oil or die lubricant which resulted in uneven etching. It could be etching from an in-process acid or caustic cleaner or stains or corrosion from parts left to dry during fabrication. It could be remains of the metal marking or machinists ink. Or it could be that the anodizer did not do a good job rinsing and drying the parts. Many things outside of the anodizer's control can contribute to cosmetic problems. I do not think we have enough information to recommend switching vendors.

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.

Wadsworth, Ohio

2005

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That's an excellent point, Chris. While we certainly don't want to be apologists for poor metal finishing practice, there may be more to the story that we are able to infer from this posting. Pictures might not tell the whole story, but they might help.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005