On Wed, 7 Mar 2018 19:52:41 -0500, 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?

I powder coated an aluminum bike a couple of years ago. I checked the
annealing temperature for the (assumed) 6061 and then checked with the
shop and their "cooking" temperature was somewhat lower then that, so
went ahead and coated it. To date no problems what so ever.

I'm not saying that you should immediately run out and powder coat
your frame but I'm sure that a little research might prove
enlightening.

It's been a couple of years but I think that the solution treating
temperature for 6061 was in the 450 - 570 degree (C) range and the
cooking temperature for powder was in the 200 degree (C) region. But
do check yourself.

As an aside, the front forks that I have on that bike are "Hell for
strong". They are about the diameter of the original telescoping forks
and same diameter top to bottom (Ugly!).

Another point is that powder coating shops have very noticeable
different levels of skill and I'd advise that you try to see something
made of tubes and similar to a bike frame before you decide.

I used to just have a frame "powder coated" and they held up very
well, better then paint. I'm now having two colors used and apply the
first and second color and then "clear coat" the whole shebang, which
looks better :-) The "clear coating" is just powder coating powder
without any pigment.
--
Cheers,

John B.