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Preserving polished aluminum



 
 
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  #71  
Old August 14th 17, 06:23 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
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Posts: 10,538
Default 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  
Old August 15th 17, 01:59 AM posted to rec.bicycles.tech
John B.[_3_]
external usenet poster
 
Posts: 5,697
Default 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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