Oxidation

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Postby russell » Tue Aug 16, 2005 9:38 am

I am trying to stop some oxidation and not having too good of luck. I have removed the oxidation with abrasive pads and the like, treated it with a solution called "alumiprep" (phosphoric acid and potassium fluoride) and finally a wipe down with alodyne. In a weeks time the oxidation is beginning to show once more. I was under the impression that alodyne would kill it. What can I do to stop it? Any suggestions would be greatly appreciated.
Thanks,
Russell Rewis
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Postby Guest » Tue Aug 16, 2005 10:03 am

Best thing to do is remove all surface corrosion, clean with alumiprep, rinse with soap and water, prime with zinc chromate primer, then paint the aluminum.
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Postby Chappy » Wed Aug 17, 2005 1:17 am

You can paint (semi-permanent), polish with a good grade product (temporary), or get anodized (expensive but permanent, but not practical for large pieces like wings). I have all the tubing anodized on my series 1, and they have no corrosion on them ON THE OUTSIDE, as only the outside is usually treated unless you pay a lot more when having it done.

Paint is probably the best option, but it does tend to mask any cracks that might develope in the future.

Chappy

Hey Shannon, how come you never sign in, or sign, your posts anymore?
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Postby Guest » Thu Aug 18, 2005 7:27 am

You can't polish rust off an old car............ ? Cracks ? Cracks develop when corroded aluminum hits the ground too fast !
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Postby Guest » Thu Aug 18, 2005 10:57 am

One guy used "Mothers" polish and his plane looks nice. Over time the oxidation and corrosion will come back if you have a severe case. "Pitted" deep corrosion will come back quickly obviously.
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Postby Guest » Thu Aug 18, 2005 2:40 pm

Okay, as bad as I hate to loose the bare aluminum apeal of the Lazair I'm forced to take drastic measures so I've decided (with the help of all the responses to this post that I have received) to paint the D-cells.

Thanks for all the suggestions,
R.Rewis
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Postby Chappy » Wed Aug 24, 2005 7:43 am

Shannon @ Aug 22 2005, 08:47 PM wrote: Yeah, I made the post ! Forgot to sign in ! My Bad ? Painting Semi-Permanent ? Huh ? Come on, Dales dad painted his wings. Read "Memories" on the Lazair Force site by C. Kramer.


Well, Shannon, I guess you is!

Compared to Anodizing, I would consider paint semi-permanent. Paint can chip/flak off, especially if surface preparation isn't good, and if a good priming job wasn't done. Corrosion can start and spread under paint. Paint can just wear out in the sun/elements. Sure, if everything is done correctly, and you give it great care, paint can last a long, long time. I have nothing against painting a Lazair.

Anodizing, on the other hand, is a very hard, almost ceramic like finish obtained by using a chemical conversion process that actually penetrates into the surface of the aluminum. You can actually tell how deep by careful measurement, as the amount of penetration is usually about equal to the amount of material that builds up on the surface. It can be dyed colors. When you see old, faded anodized aluminum, it's the dye that's deteriorated, not the actual anodizing. The treated surface coating can get stained, and can be very hard to clean up. The only way I know to even remove the coating is to grind it off, but there may be a chemical process to do it. Anyway, IMHO, it's much more permanent than paint. I wasn't trying to say paint is no good, I was attempting to just compare polishing, painting, and anodizing, from an educational point of view.

BTW, if you plan to bend tubing, do it before it's anodized (same as with paint). Bending the tubing after anodizing will cause the surface to craze (lots of little surface cracks).

Chappy
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Postby jb88ci » Wed Aug 24, 2005 8:04 am

Maybe I'm misreading but unless you are getting serious pitting, the surface oxidation of aluminum is normal. In fact, it's that thin coating of corrosion that makes aluminum corrosion resistant, so to speak. Unlike steel, when aluminum corrodes the layer of oxidation essentially seals the metal surface and prevents further oxidation. It isn't until you get a scratch or some form of stress that breaks the layer of oxidation that further corrosion will form.

Steel will just corrode away until nothing is left.
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Postby flyalaz » Thu Aug 25, 2005 11:08 am

Anodizing is an electro-chemical process, best done by plating companies that have the facilities. I doubt that it would be economical to do it at home.

Karl
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Postby flyalaz » Fri Aug 26, 2005 2:24 pm

Check this out for small parts:

http://www.focuser.com/atm/anodize/anodize99.html
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