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topic 1245

Anodizing as a pretreatment for powder painting aluminum extrusions.


(1998)

Could anyone tell me his opinion and experience about anodizing without sealing aluminum extrusions as a pretreatment for powder painting in architectural uses?

What about the quality, adhesion, salt spray behaviour, and cost, compared with other pretreatments?

Every answer will be much appreciated.

Jose Castellanos
- Argentina


(1998)

Sir,

We do anodizing & chem film (aka chromating / Iridite / Alodine) on aluminum. We job out lots of paint & powder work & for the most part we chromate all pieces as a base for paint. It greatly enhances adhesion. Anodize is also a great base for paint. It is better than chromate but also much more costly. In my opinion, the chromate, as a base should be sufficient.

David A. Kraft
- Long Island City, New York


(1997)

A good question. most people would seal it first.

Try asking the Aluminum Anodizers Council, or the Aluminum Association, or the American Architectural Manufacturers Association. one of them should be able to give you an answer.

James Watts
- Navarre, Florida


(1997)

We have experience with anodising before painting :

You need a thickness of about 3 - 5 µm.

The anodising bath should be at 25 C with a current density of 1,2 to 1,5 A/dm2.

Rinsing is very important ; I recommend a final rinsing in warm demin water (50C f.i.) painting should be done within 48 hours after anodising. The results are great.

pierre raes
aldurcolor


(1998)

Anodizing of aluminum prior to painting and/or powder coating has shown excellent results in regards to corrosion protection. Our architectural experience in the european powder coating market has shown that anodizing is the new pretreatment of choice for commercial architecture and has even been approved by GSB International, a major commercial architectural specification in Europe. Exact specifications are available through GSB.

Thomas F. Gratz
St. Charles, Illinois


October 9, 2013

A. Regarding anodizing as pretreat I think reason AAMA doesn't recommend is that for best adhesion it would require specific processing conditions. The processing conditions for a good architectural anodize wouldn't be the best for paint adhesion. For a good architectural anodize, you'll want the finish to be as inert as possible. For paint adhesion you'd want it to be as chemically active/receptive as possible.

Therefor the processing conditions for paint adhesion wouldn't result in an optimal architectural anodized finish. Moreover, there are lots of different anodized finishes out there. Folks create a standard 204 anodize with several different seals, not to mention coating densities and pore geometry. It can't be as simple as saying 'anodize makes an acceptable pretreat.'

Penn McClatchey
Southern Aluminum Finishing Co - Atlanta, Georgia
supporting advertiser



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