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Eliminate bulk anodize burns/voids

We bulk anodize small aluminum parts, as small as 1/8 x 2 inch. We use bulk titanium baskets with lids that compress the load. Packing the baskets involves both tapping the basket and a vibratory unit. Our problem is that we still get about 1% of the parts that fail to make adequate contact and turn black (burnt) or do not anodize. These parts must be sorted out of the order. Management has tasked me with eliminating these burnt part. We anodize 7075, 2xxx alloys at about 16-17 volts, 45 minutes in type 2 process. We have used both the donut basket and plain cylindrical titanium basket with equal success. Does anyone have any ideas, short of racking, on how to maintain 100% electrical contact on 100% of the parts in bulk anodizing?

Brad Walters
plating shop engineer - Orange County, California, USA
November 3, 2008

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1% is GOOD !, Cap the top of the inner cylinder and pump fresh solution into the bottom. Raise free acid. Experiment with higher voltage. Take temperature up to 75 °F.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

November 5, 2008

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Bob is on the right tract but 100% is a pipe dream. Some % will always be reject until someone figures out how to change the basic facts of anodizing.

Drew Nosti, CEF
Anodize USA

Ladson, South Carolina

November 15, 2008