From: RWolf99@aol.com
Message-ID: <a4.f65843f.27a9c6b8@aol.com>
Date: Wed, 31 Jan 2001 14:51:20 EST
Subject: Paint, Anodize and Alodine
To: lancair.list@olsusa.com
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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I tried to etch and alodine an already anodized part and it didn't work.  The 
part in question was an aluminum piano hinge -- I hadn't realized that it was 
already clear anodized.  The only place the etching and chromium conversion 
(that's alodine, folks) occured was where I had drilled holes through it.  
The hole edges are now golden.  What a waste of time.  If the anodize coating 
protected the aluminum against the phosphoric acid etching, it should be 
plenty good in operational service.  

This is why I state that anodize is a perfectly adequate anti-corrosion 
coating as far as I'm concerned.  Painting is not required, but if you must 
paint it for aesthetic reasons, just clean it thoroughly (acetone or MC) and 
paint directly on it.  Be aware that many colors are available for anodize, 
such as gold, red, black, clear, and probably green as well.

Having said that, I had the opportunity to have some large aluminum pieces 
professionally painted with a polyurethane paint prior to flying them on the 
Space Shuttle in 1985.  The paint shop told me that alodine (more accurately, 
a MIL-C-5541C chromium conversion coating, of which alodine is merely one 
trade name) is the single most important thing you can do for promoting paint 
adhesion to aluminum.  However, scraping off an anodize coating to get the 
alodine would be pointless, IMHO.

- Rob Wolf
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