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Old 02-09-2005, 02:51 PM   #1
whitesti04
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Default powdercoated stock sti wheels

just got my stock wheels powdercoated semi gloss black. i was getting tired of seeing all the brake dust all over my wheels.
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Old 02-09-2005, 03:07 PM   #2
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bot any pics
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Old 02-09-2005, 03:19 PM   #3
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tittiwop.

ss
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Old 02-09-2005, 06:03 PM   #4
whitesti04
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ill try to get pics up asap, but right now its kinda dirty from all the rain
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Old 02-09-2005, 06:05 PM   #5
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I Wanna See Pics!
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Old 02-09-2005, 08:33 PM   #6
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Quote:
Originally Posted by subysouth
tittiwop.

ss
And, I know what you mean. I cleaned my wheels the other day and my buddy game me a hard time saying (I thought those wheels were gunmetal).

haha!
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Old 02-10-2005, 01:12 AM   #7
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I got mine painted STi Pink....

but I dont have any pics.
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Old 02-10-2005, 04:15 PM   #8
TubeDriver
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Be careful. The heat of the powdercoat process can mess up the tempering in forged wheels.


Quote:
Originally Posted by whitesti04
just got my stock wheels powdercoated semi gloss black. i was getting tired of seeing all the brake dust all over my wheels.
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Old 02-10-2005, 04:37 PM   #9
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Dewey 8d wants to see pics.
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Old 02-10-2005, 04:55 PM   #10
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Quote:
Originally Posted by TubeDriver
Be careful. The heat of the powdercoat process can mess up the tempering in forged wheels.
TD,

is this for real or internet rumour ? i figure if they can withstand being bolted directly to a 700 or 800 F brake rotor, then the couple o hundred degrees it takes to bake the powder coat should be ok,

no?


G
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Old 02-10-2005, 05:20 PM   #11
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I have a hard time believing powder coating would really damage wheels. powder coating heats to 450 and brakes are about 700. I would hope a forged wheel can hold up to 450.

I know the wheels I had on my street rod where powder coated from the factory.
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Old 02-10-2005, 07:20 PM   #12
subysouth
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I think powder coating can go well below that tempwise too, I seem to recall 375 degrees. I think this is an internet rumor. I cant find any credible evidence of this and I've looked.

Still no pics in this thread? Its a travesty of justice.

ss
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Old 02-10-2005, 07:51 PM   #13
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regarding the powder coating process ruining the temper on wheels, it is a fact that it can happen.

For a typical aluminum alloy, holding it at elevated temperatures for long periods of time "ages" the alloy from it's as-cast or as-forged state. Aging is a process that is used to strengthen alloys but if you age too long or at too high a temperature, the alloy becomes "over-aged" and begins losing strength.

Here's a page from one of my textbooks:

As you can see, the lower temps reach higher ultimate strenghts and take a lot longer to begin over-aging the alloy.

Most powder coating is baked at 400 degrees for about 3-4 hours so follow that line and see how long it takes (in hours) to overage the alloy. You see that only 1 hour at 400 deg F is enough to make the alloy reach full strenght for that temperature, but at 10 hours (notice it's a logarithmic scale), the alloy only loses about 3ksi of its 43 ksi max.

So does powder coating reduce the strength of the metal? Yes. Is it a large amount? Not really.

Now regarding brakes, your brakes don't stay at 700 degrees for long (not nearly enough to over-age the alloy) and there is a significant heat transfer barrier between the steel of the rotors and the aluminum of the wheel: it's called an interface. Even though the wheel is pressed tightly against the rotor, heat doesn't transfer as quickly as it would need to transfer to heat up the wheel significantly. If you don't believe this, go out and do a few highspeed stops at full braking force (enough to make the rotors HOT) and then touch the wheel right around the studs. it's barely warm.
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Old 02-10-2005, 08:20 PM   #14
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The density (thermal mass) of the metals comes into play too, with regard to heat transfer. And the contact area of the dissimilar metals. The rotors will retain more heat than the forged aluminum. Also, the spinning wheel is hitting more air than the rotor is and will stay cooler due to airflow. Maybe the area around the studs is initially warm, but give it a few minutes. Does it really matter ... no. Just adding real world variables.
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Old 02-10-2005, 11:07 PM   #15
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I checked this out and read a lot about it. This one Boeing employee (im pretty sure it was boeing) said that airplanes are NOT powdercoated for a very good reason. He also said that the reason a lot of forged wheels come powercoated from the facotry is because the wheel manufacturer has the right equipment to safely coat the wheels at the right temp. In order to do it right you need some really expensive machinery and most shops would never be able to afford them. So you have to be extra careful.

HOWEVER, I dont think I have ever heard any horror stories of wheels falling apart after being powercoated. Like nhulhr said, yes in theory it does weaken the wheel, but will it actually effect the wheel in a practical sense? Probably not.

ps-tittywop
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Old 02-11-2005, 11:20 AM   #16
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Interesting data. I only threw it out because I have talked to some engineer types who have mentioned this and because it may be hard to find out exactly how hot and how long your wheels will be cooked.

I have run a set of powder coated cast Al wheels for two seasons of autoX/HPDE with no problems but I am thinking about getting a new set and was deciding whether to get them painted or powdercoated. it sound like I would PROBABLY be alright with powdercoating again.....
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Old 02-11-2005, 02:43 PM   #17
subysouth
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Quote:
Originally Posted by nhluhr
regarding the powder coating process ruining the temper on wheels, it is a fact that it can happen.

For a typical aluminum alloy, holding it at elevated temperatures for long periods of time "ages" the alloy from it's as-cast or as-forged state. Aging is a process that is used to strengthen alloys but if you age too long or at too high a temperature, the alloy becomes "over-aged" and begins losing strength.

Here's a page from one of my textbooks:

As you can see, the lower temps reach higher ultimate strenghts and take a lot longer to begin over-aging the alloy.

Most powder coating is baked at 400 degrees for about 3-4 hours so follow that line and see how long it takes (in hours) to overage the alloy. You see that only 1 hour at 400 deg F is enough to make the alloy reach full strenght for that temperature, but at 10 hours (notice it's a logarithmic scale), the alloy only loses about 3ksi of its 43 ksi max.

So does powder coating reduce the strength of the metal? Yes. Is it a large amount? Not really.

Now regarding brakes, your brakes don't stay at 700 degrees for long (not nearly enough to over-age the alloy) and there is a significant heat transfer barrier between the steel of the rotors and the aluminum of the wheel: it's called an interface. Even though the wheel is pressed tightly against the rotor, heat doesn't transfer as quickly as it would need to transfer to heat up the wheel significantly. If you don't believe this, go out and do a few highspeed stops at full braking force (enough to make the rotors HOT) and then touch the wheel right around the studs. it's barely warm.
To add a bit further, that info is for sheet aluminum not forged aluminum(I am pretty sure they have different heat effectance) and the baking temps for powdercoating can be as low as 350 degrees with a duration as short as 15 minutes. 3-4 hours bake time seems extreme.

ss
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Old 02-11-2005, 04:01 PM   #18
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Most Powder Coating lines that I see run in the heat for about 15-30 min before cooling. 3-4 hours of powdercoating at a "recommended temp" would probably burn then bake off the powder again.

from HBfuller.com: A powder coating company that I have used to spec from-

Dark Taupe Metallic Polyester (a nice weatherable Metallic Fleck Bronze Color)

Dark Taupe Metallic Polyester - Gloss 65-85 Cure 15@350F. Film 2-3

15mins at 350-
[IMG][/IMG]

Last edited by draggin wagon04; 02-11-2005 at 04:13 PM. Reason: ttiwwop
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Old 02-11-2005, 04:20 PM   #19
BillJC
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I've witnessed a set of powdercoated wheels crack through 4 of the 5 spokes in each wheel during a track event.
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Old 02-11-2005, 04:29 PM   #20
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Stopped by the powder coating place in Manassas today and asked them how long they heat wheels when powder coating. According to them its 350 for 15-20 minutes. When I asked why so short they said because they dont want to damage the aluminum.

food for thought.
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Old 02-11-2005, 05:13 PM   #21
subysouth
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Quote:
Originally Posted by BryanH
Stopped by the powder coating place in Manassas today and asked them how long they heat wheels when powder coating. According to them its 350 for 15-20 minutes. When I asked why so short they said because they dont want to damage the aluminum.

food for thought.
Hehe, that kinda covers it all.

But 15-30 minutes is what I have heard regardless of material. They baked a friend of mines steel deuce frame for 15 minutes at 400. I think the length varies on color and makeup of the poweder but its seldom very long. The reason I heard for the shortness of bake was what draggin wagon said above, too long and it damages the powdercoat. And any longer isnt necessary anyway. All that has to be done is the paint temp elevated to liquify which happens pretty quickly as I understand it.

ss
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Old 02-11-2005, 05:14 PM   #22
subysouth
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Quote:
Originally Posted by BillJC
I've witnessed a set of powdercoated wheels crack through 4 of the 5 spokes in each wheel during a track event.
What kind of wheels out of curiousity? All 4 wheels cracked 4 of 5 spokes?

ss

Last edited by subysouth; 02-11-2005 at 05:25 PM.
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Old 02-11-2005, 07:06 PM   #23
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Quote:
Originally Posted by draggin wagon04
[IMG][/IMG]
that's some pretty bad orange peel there.

Just like there are forums on subarus, there are forums on powder coating. Maybe we should go there and ask someone for sure.
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Old 02-11-2005, 07:19 PM   #24
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Default powder coating...

cold forged wheels are work hardened. baking them at 350 deg. F for even 15 min will relieve some of the grain structure established from the work hardening. the powder coating person will tell you that it's "only 15 min because they don't want to damage the wheel" because he doesn't want to be liable for any rim failure should you track your car. if you only do street driving you'll probably be fine. if you track your car, you might want to at least keep an eye on the spoke roots at both the hub & rim ends of each spoke and look for cracks on both the outer and inner faces. if you take your wheels off and clean them regularly you'll see the formation of any cracks.

brakes get hot but the wheels are turning and being cooled. plus not all the heat can migrate out from the rotor into the wheel and wheel spokes to heat the wheel up to 350 deg. F. if that were the case, our tires would have popped due to escalating tire pressures.

aluminum alloys don't like heat. they lose temper and strength very quickly. this is the reason why planes and race cars that are weight critical and made of aluminum aren't welded but bonded and riveted. if they were welded like motorcycle frames, the joints would have to be way oversized to compensate for the strength lose at the heat affected zones (HAZ).

in the end, it's your wheels and we all hope you the best.

duckboy
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Old 02-11-2005, 07:45 PM   #25
Paulie
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Powder coating wheels...

In my experience, most powder bakes between 375-400 for about 10-15 minutes, with 10 min usually being the standard.

Where most problems arise is when the powder coating company prepares the wheel for powder. Some places will *bake off* the existing finish by heating the wheel up to 600-900 degrees for hours. That gets the current coating to become very brittle. Then they sandblast it off.

This is the absolute worst method to prepare an aluminum wheel for powder coating, and what usually causes horror stories when the subject comes up about changing the properties of the metal with too much heat.

The best method for removing the old coating is to chemically strip them with an aluminum safe, aircraft stripper. Once the old coating is all off, then the wheels are blasted with fine glass beads and then washed to remove the residue.

If the wheel is prepared like that, it should have no problem in the oven at 375-400 for 10 minutes.

The temp times also vary according to ovens. Some ovens are open ended on both ends, allowing a conveyer belt to pass through with the parts on them, and with this method, the time in the oven is almost double, because heat is escaping the oven on both ends.

I've had a lot of experience with this subject lately, and this has been my first hand experience with powder in general, especially regarding wheels.

- Paulie
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