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No powder coating for aluminum?



 
 
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  #1  
Old March 8th 18, 12:52 AM posted to rec.bicycles.tech
Frank Krygowski[_4_]
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Posts: 6,163
Default No powder coating for aluminum?

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?

--
- Frank Krygowski
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  #2  
Old March 8th 18, 01:12 AM posted to rec.bicycles.tech
AMuzi
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Posts: 9,644
Default No powder coating for aluminum?

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?


Right you are. The T-6 state will be lost between 350 and
400F. Retempering is not feasible because you're up in the
950F range where the powder finish will be lost and the
quenching from that process is very likely to warp or crack
your closed-figure frame. Krylon maybe?

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


  #3  
Old March 8th 18, 01:13 AM posted to rec.bicycles.tech
JBeattie
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Posts: 3,300
Default No powder coating for aluminum?

On Wednesday, March 7, 2018 at 4:52:45 PM UTC-8, 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?


From some interweb poster:

"Powdercoating is a process where a power is electrostatically stuck to metal then baked on. The baking procedure is done at around 390°F, the melting temperature for 6061 is 985°F and the annealing temperature for 6061 is 775°F for 2-3 hours. Unless you drastically mess up the cure cycle on powdercoat, you're not going to even touch the temperature where the aluminum structure changes. You might get into a precipitation hardening temperature, but you'd need to hold 320°F for 12 hours or more to see a difference.

Anyway, most every bike manufacturer uses powdercoat on some of their bikes.. If it was detrimental to the structure they certainly wouldn't use it so extensively. Plus, you're getting a bike from a manufacturer so they would be the one liable for the job they do. Annodizing produces a harder surface of metal, but powdercoat does not hurt aluminum in any way I know of."


Who knows if that's right. I've also seen reports and pictures of powder coated Cannondales. People do it.

-- Jay Beattie.
  #4  
Old March 8th 18, 01:53 AM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,644
Default No powder coating for aluminum?

On 3/7/2018 7:13 PM, jbeattie wrote:
On Wednesday, March 7, 2018 at 4:52:45 PM UTC-8, 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?


From some interweb poster:

"Powdercoating is a process where a power is electrostatically stuck to metal then baked on. The baking procedure is done at around 390°F, the melting temperature for 6061 is 985°F and the annealing temperature for 6061 is 775°F for 2-3 hours. Unless you drastically mess up the cure cycle on powdercoat, you're not going to even touch the temperature where the aluminum structure changes. You might get into a precipitation hardening temperature, but you'd need to hold 320°F for 12 hours or more to see a difference.

Anyway, most every bike manufacturer uses powdercoat on some of their bikes. If it was detrimental to the structure they certainly wouldn't use it so extensively. Plus, you're getting a bike from a manufacturer so they would be the one liable for the job they do. Annodizing produces a harder surface of metal, but powdercoat does not hurt aluminum in any way I know of."


Who knows if that's right. I've also seen reports and pictures of powder coated Cannondales. People do it.



Yeah I could be very wrong too.
Here's more from someone who either knows something or fakes
it very well:

https://www.pinkbike.com/news/To-the...um-Frames.html

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


  #5  
Old March 8th 18, 02:05 AM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,644
Default No powder coating for aluminum?

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."






--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


  #6  
Old March 8th 18, 05:08 AM posted to rec.bicycles.tech
John B.[_3_]
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Posts: 3,967
Default No powder coating for aluminum?

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.

  #7  
Old March 8th 18, 02:36 PM posted to rec.bicycles.tech
[email protected]
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Posts: 259
Default No powder coating for aluminum?

"Yeah I could be very wrong too."

OMG Andrew, that's a heavy-duty breach of internet etiquette. No one EVER admits they're wrong on an internet forum!

  #8  
Old March 8th 18, 05:04 PM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 2,833
Default No powder coating for aluminum?

On Wed, 7 Mar 2018 19:52:41 -0500, Frank Krygowski
wrote:

Is there something I'm missing?


Maybe take a look at UV curable powder coatings:
https://www.pcimag.com/articles/85628-uv-curable-powder-coatings-benefits-and-performance
See Table 2 for temperatures. 176-285F (80-140C)
http://www.fusionuv.com/ApplicationSolutions.aspx?id=278
Sorry, but no personal experience with the technology.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 




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