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#71
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Preserving polished aluminum
On 8/14/2017 12:30 PM, Doug Landau wrote:
On Sunday, July 30, 2017 at 10:44:58 AM UTC-7, Ian Field wrote: "John B." wrote in message ... I've got quite a few aluminum bits and pieces from older bikes that are pretty shoddy looking with nicks and dents and corrosion. I can clean them up with a "flap" wheel and then polish then with the usually buffing wheels and decreasing compound grits until they have a high polish but once back on a bicycle again they seem to corrode rather rapidly and in a few months end up looking sort of "splotched" and dull, which of course is exactly what bare aluminum does in contact with air. I've tried a number of schemes to preserve the polish such as heavy paste wax and even a coat of clear lacquer or in one case thinned epoxy resin. This wasn't exactly successful as the wax disappears quickly and the lacquer tends to chip and even the thinned epoxy tends to flaked off in places. Shimano seems to coat much of their aluminum bits with some sort of "silver paint" which obviously isn't just that as it seems to last for years. I would prefer the look of highly polished aluminum (without the corrosion) but that obviously will take considerable and continued labour the way I am doing it at present. Does anyone have any suggestions on how, or with what, to coat highly polished aluminum to, at least, reduce the corrosion to a reasonable level? Say a once a year polish? Polished aluminium forms an oxide layer instantly, you need a polish that leaves a film in place of what it takes off. So are these things clearcoated or something? https://www.google.com/search?q=amer...HYcgRqdh8K0qM: Planes' skins are made of Alclad aluminum. It's a metallurgical sandwich with 7071 alloy as the meat, and very thin layers of nearly pure aluminum as the bread or skin. The pure stuff oxidizes in contact with the air but the oxide layer prevents further corrosion. That stuff stays shiny just as aluminum foil does. Alloys of aluminum corrode differently and much more than pure aluminum. -- - Frank Krygowski |
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#72
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Preserving polished aluminum
On Mon, 14 Aug 2017 09:30:40 -0700 (PDT), Doug Landau
wrote: On Sunday, July 30, 2017 at 10:44:58 AM UTC-7, Ian Field wrote: "John B." wrote in message ... I've got quite a few aluminum bits and pieces from older bikes that are pretty shoddy looking with nicks and dents and corrosion. I can clean them up with a "flap" wheel and then polish then with the usually buffing wheels and decreasing compound grits until they have a high polish but once back on a bicycle again they seem to corrode rather rapidly and in a few months end up looking sort of "splotched" and dull, which of course is exactly what bare aluminum does in contact with air. I've tried a number of schemes to preserve the polish such as heavy paste wax and even a coat of clear lacquer or in one case thinned epoxy resin. This wasn't exactly successful as the wax disappears quickly and the lacquer tends to chip and even the thinned epoxy tends to flaked off in places. Shimano seems to coat much of their aluminum bits with some sort of "silver paint" which obviously isn't just that as it seems to last for years. I would prefer the look of highly polished aluminum (without the corrosion) but that obviously will take considerable and continued labour the way I am doing it at present. Does anyone have any suggestions on how, or with what, to coat highly polished aluminum to, at least, reduce the corrosion to a reasonable level? Say a once a year polish? Polished aluminium forms an oxide layer instantly, you need a polish that leaves a film in place of what it takes off. So are these things clearcoated or something? https://www.google.com/search?q=amer...HYcgRqdh8K0qM: Most airplanes are built of what is called "alclad" which is an aluminum alloy, often 2024 which is an aluminum copper alloy, which is coated with pure aluminum which is, as has been noted, forms an aluminum oxide coating when exposed to air, which, in turn, protects it from further corrosion. So, yes, any shiny aluminum airplanes you see have been polished and clear coated. However, as alclad coating is approximately 5% of the sheet thickness per side you are talking about, perhaps, a coating that is -.001" thick it is probable that there is very little actual buffing going on. See https://www.youtube.com/watch?v=u0AHap8993U -- Cheers, John B. |
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