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Old 06-27-2009, 08:03 PM   #1
cpunlamd
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Default Powder coat vs Painting wheels

Its obvious that powder coat is much more durable and the finish is much more brilliant than paint. But the question is, why are some wheel retailers suggesting NOT to powder coat? They imply something about the 400 degree temps used to powder coat, will weaken the wheel and can cause it to fail.

Isnt that weird? A true race wheel (or any decent wheel for that matter) could take 24 hours of red hot glowing brakes at the race track (im sure thats WAY over 400 degrees). But the wheels cant take 400 degrees in the powder booth for 1 hour? WTF?
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Old 06-28-2009, 02:16 AM   #2
VR62STI
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Your brakes may glow red, but your wheel does not. The issue with powder coating is they require baking between 400 and 700 degrees. Many little shops can't afford expensive ovens, so they use ovens that aren't accurate with cooking temps. So the wheel may get baked at 400, or it may get baked at 700, who knows. Forged wheels are heat-treated at around 700. Any heat approaching that temp will undo the heat treating and your wheel will literally crumble. I have seen this first hand. I don't think cast wheels are this fragile with temps. In any case I would not risk it - use a quality urethane (PPG) and sleep better.
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Old 06-28-2009, 03:02 AM   #3
Web Foot STi
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Wheels, cast, or forged are typically made of aluminum alloys that are solution heat treated then artificially aged. Typically to a T6 condition.

The solution temperature is in the 900-1000 deg F range for about 8 hours. At this point the aluminum (Al) is fully annealed, dead soft and easy to bend (straighten). With time the Al age and become harder. After about 4 hours forget about straightening.

For a T6 condition the Al parts are put in an oven at about 300 degrees F for 4 hours. Now the parts are strong, hard, and ductile. That's not a contradiction.

Powder coating requires a 300-400 degree F bake. When you do this to a T6 part you run the risk of over aging the Al and if you do you wind up with a stronger, harder part with little, or no ductility. i.e. brittle.

The part/Wheel manufacture can allow for and combine the paint cure with his aging and not suffer any detrimental effects and lower his overall cost as there is only one bake.

Search is also your friend. This is a repeat...

Edit: The manufacture may have age the part/wheel some before machining and spaying so the Al isn't to gummy. Then do the final age/paint cure.

Last edited by Web Foot STi; 06-28-2009 at 10:41 PM.
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Old 06-28-2009, 10:20 PM   #4
cpunlamd
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Im hoping that if I do bring my wheels to a body shop, the paint they use wont flake off when I tighten the lug nuts with the air gun. I know the factory paint wouldnt flake off, but I have seen aftermarket paint flake in the past.
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Old 06-29-2009, 09:01 AM   #5
cpunlamd
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Just so I get this straight. I went through the other threads regarding the pros and cons of powder coating wheels. It is basically the excessive temps and quenching that could cause the wheel to become weaker (hence fail under load). But the other threads specify that these pros and cons differ depending in the whether the wheel was CAST or FORGED. Since forged wheels were created under 400 degrees, it would weaken due to the fact that some powder coaters heat up to 700 degrees. But this ONLY applies to forged wheels. And that since the cast wheels were made under much higher temps, powder coating it and heating it from 400-700 degrees would pose no harm to a cast wheel. Is this correct?

1. Powder coating CAST is ok?
2. Powder coating FORGED is a no no?
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Old 06-29-2009, 11:30 AM   #6
Web Foot STi
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No. Similar alloys are heat treated to similar temperatures. It is the additional ageing that the can make a wheel brittle. Cast, or Forged makes no difference on the subject of powder coating.

Since most wheel makers don't share their alloy and manufacturing details there are a lot of can's, may's, and could's. "Do you feel Lucky?"

I have an old 5086 Al bike frame. It's not a heat treatable alloy and I could toss it into a powder coating oven and if the paint cam out looking good I'd be happy. I'd be very scared to do that with beer can thin down tube 6061 T6 frame.

PS Some forgings start out as cast blanks...
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