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Unusually high current while anodizing

Q. We have had some parts in type 2 anodizing that have unusually high current densities. As the current is ramped up to 15 volts the current rises to about 6 times what it should be. In the past, this could be traced to someone leaving in a bushing or other metal part that conducts the current. Lately we haven't been finding any metal that shouldn't be there, but by anodizing in a different tank the same part anodizes at the right current. This effect is sporadic, happening three times in the last month.

The solution is fairly old, and the aluminum levels are getting high (7.46 g/L), but they are still in spec.

Has anyone else seen this before?

Mark Robison
- Ogden, Utah
February 14, 2012

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First of two simultaneous responses -- February 14, 2012

Difficult to read on the basis of the info you sent. How could the aluminum be that low and the solution be "old"?"
What is the "free acid"? Is chloride present?

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

Mark: Sounds like you may have a short in your anodize tank that is intermittent. Your bus bar may be shorting our to the tank; otherwise I would think your workload would be "toast" at the high current levels.

Kent Backus
Fort Worth, Texas, USA
Second of two simultaneous responses -- February 15, 2012