Summary for racking for anodizing Discussion
racking for anodizing of flat aluminum sheets is discussed as a practical question about whether sheets loaded like books on a shelf will be shadowed in the center of a tank. Marc Green says the practical answer is no one can guarantee equal anodizing, because the absolute theoretical answer has not been researched and tabulated; he notes anodizing will wrap around the front side to some extent, but the amount of throw is unknown. He suggests trying the cathodes on the ends of the tank and experimenting with spacing to see how close the load can be before thickness becomes unacceptable. John Peterson agrees shadowing will occur, but says increasing the spacing between parts on the rack can improve results; he cites his own Type III, Class II work on 21" x 30" panels, where outer edges measured about .003 and centers about .0024. The original poster plans to test both cathode placement and shelf-style loading.
Q. We have a large number of flat sheets of .062 by 36″ x 48″ aluminum that need to be clear anodized. In order to get the highest density we would like to rack the parts like books on a shelf running parallel to the cathodes. If the sheets are longer than the narrow width of an anodizing tank and the cathodes run along the long sides of the tank, will the parts racked in the center of the tank be shadowed by the outer sheets or will all parts anodize equally?
G Heath
– Providence, Rhode Island
January 3, 2012
The practical answer is NO. The work for the absolute theoretical answer has not been done. Anodizing will “wrap” around quite a bit after the front side is insulated, but the degree of “throw” or “wrap” has never been researched and tabulated. You may want to put the cathodes on the ENDS of the tank and experiment with just how far apart you can close in and still get acceptable thickness. Come back with more data, maybe a sketch.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
January 4, 2012
Actually, assuming I’m understanding the question and visualizing it properly, the answer is YES, Robert, as the question was, would there be “shadowing”.
The sheets on the outside would definitely shield current from reaching the sheets on the inside.
A work-around would be to develop cathodes that would fit in between the racked sheets.
Marc Green
anodizer – Boise, Idaho
January 12, 2012
Thanks Marc. You have caught me two times no reading the fine print. NOw if you could just hjelop me with tyhping and spelling !!! thanks for cleaning me up.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
January 13, 2012
No worries Robert. The only reason I tend to catch some things is because I’ve misinterpreted several posts myself.
Marc Green
anodizer – Boise, Idaho
January 17, 2012
I agree there will be shadowing but if you increased the space between the parts while on the rack you could get better results. For instance I have been processing panels 21″ X 30″ going Type III, Class II at about 27 parts to a load and have .003 on the outer edge with about .0024 in the center. We run them like books on a shelf so the parts and the cathodes are perpendicular to each other.
John Peterson
– Fridley, Minnesota, USA
January 19, 2012
Thank you for all of your responses. I’ll check on moving the cathodes for one run and running them like books on a shelf for another run.
G. Heath
– Bristol, Rhode Island
January 20, 2012