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  for Metal Finishing since 1989
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Work piece geometry that hinders CCC rinsing

I am a mechanical design engineer working at a facility that makes complete flight simulators. We make most structures out of 6061-T6 Al. I have been told by plating technicians that my designs should avoid situations where chromate conversion coating solution can become trapped, such as riveted or welded assemblies with large overlapping surfaces, as the solution itself can cause corrosion in the part if unable to be rinsed. Later, as our organization was creating standard procedures, the engineer researching finishes could not find any official guidance on this topic and apparently deemed it a wives tale. I would appreciate any help you could give me, especially references to documents that cover this situation.

Thank you very much for your time.

Matt Morrison
mechanical engineer - Patuxent River, Maryland, USA
2003

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Any feature which traps water or absorbs it by capillary action is obviously less desirable than if it were possible to design the part without that feature. That will be true regardless of the substrate or the finish, and that is probably half of the source of the confusion. The other half of the confusion probably comes from the fact that an alternative treatment for aluminum -- sulfuric acid anodizing -- must be avoided when good rinsing can't be guaranteed because the sulfuric acid is definitely corrosive.

I am not aware of any similar issue related to chromate conversion coating, but we have several "regular readers" who are in aerospace design and hopefully one will correct me if I'm wrong.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003