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A New Economic Two-Step Coloring Process For Bronze And "Stainless Steel" Colors

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A New Economic Two-Step Coloring Process For Bronze And "Stainless Steel" Colors

Walter Dalla Barba, Italtecno
Fabio Vincenzi, Italtecno


ABSTRACT --- This new technology for anodized aluminum two-step coloring is
based on the possibility of obtaining traditional bronze colors, including the color
black, with a lower stannous sulphate concentration. The most important
advantages are: economical, ecological (tin is a heavy metal), and aesthetic
(possibility to create new “stainless steel” colors). On the other hand, a more dilute
solution could give problems for darker and black colors. Therefore, preventive
methods have been studied in order to avoid this inconvenience. In particular, by
using a special power supply which delivers unidirectional pulsating current followed
by bi-directional current in the same color tank, it is possible to obtain darker and
black colors in the same way as in tanks with a higher concentration of stannous
sulphate. Advantages have also been introduced with the use of bi-directional
current with adjustable asymmetry of the positive and the negative semiwave.
Various types of counter-electrodes such as tin electrodes and stainless steel
electrodes have also been studied. The combination of the more dilute solution with
the new power supply makes it possible to easily obtain a new fashion color called
"stainless steel".

© Extrusion Technology for Aluminum Profiles Foundation (ET Foundation). All rights reserved. No part of The Proceedings may be reproduced in any form without the express written permission of the ET Foundation.