On 3/7/2018 6:52 PM, Frank Krygowski wrote:
Our ancient (1986) Cannondales could use some refinishing.
The paint has bubbled and chipped in places, exposing the
aluminum. The bikes aren't grossly ugly, but they're far
from pristine. I think the original paint is DuPont Imron,
or some similar catalyzing paint.

I was given information about a local place that does a good
job with powder coating, and is not very expensive.

But I got to thinking: The bikes are 6061-T6 if I remember
right. And I think powder coating gets baked at a higher
temperature than the aluminum did. I'm finding that T6 heat
treatment involves about 350 degrees Fahrenheit, but powder
coating uses about 400F. That makes this sound like a bad idea.

Is there something I'm missing?


Seems complex maybe there's no simple yes/no answer.

http://www.practicalmachinist.com/vb...luminum-79102/

discussing aluminum motorcycle wheels:

"If the wheels are cast, they're probably 356-T6 or
something real close to that. It's basically the standard
for cast aluminum wheels, and has been for many years.
Powder curing temps are above the T6 tempering range, but
this evidently is not a problem since many OEM cast wheels
are powdered. Ideally the wheels should be kept near the
lower end of the acceptable curing range, and the cure time
should be kept toward the minimum too, as the artificial
again of aluminum is both time and temperature dependent.

If the wheels were aftermarket "billet" wheels made from
6061, then the powder curing temps can have a definite
effect on the strength because it doesn't take nearly as
long to over age 6061 as it does 356 casting alloy. That's a
major reason why billet wheels are color anodized instead of
powdered if some special effect is desired."






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Andrew Muzi
www.yellowjersey.org/
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