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Old 03-26-2007, 12:24 PM   #1
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The dangers of powdercoating rims

I read this and thought it was kind of intresting

I'm trying to get a set of my ASA IS6's repaired and have been reading up on powdercoating aluminum alloy rims. For those who aren't familiar with powdercoating, it involves baking the item in an oven for 400 F for 20 minutes. I was concerned about this heat process affecting the hardness of the wheel's alloy. After some research, I found that my fears are not unwarranted. There are a few threads on the NASIOC Subaru forums about cracked, bent and broken rims that many feel were the result of the powdercoating process softening up the rim. One forum member even contacted BBS (who makes the forged STi wheels) and they responded:
"The heat involved with stripping the finish and powder coating process will compromise the structural integrity of your wheel. If you change the color, paint it like you would paint your car. Thanks for asking first!!

Thanks again,
Michael Cox

BBS of America"

There's more:

"We always prefer the wheels not to be powder coated because of the heat involved. They're heat treated during the manufacturing process so reheating them isn't the best thing. Another reason is what if the finish doesn't come out right and the people powder coating it does it again to try to get the finish right....heated again....

It's kind of scary what people are doing to wheels out there these days. That's our position. Just be careful. If you have any other questions, please let us know. "

Apparently the issue lies within the heat treatment and the alloy of the rim. Re-heating the alloy hotter than it was heated during the heat treatment stage can apparently soften the rim. Luke at the Tirerack posts on many forums and has also advised strongly against powdercoating for the same reasons. I did contact him and found out that my rims were heat treated, low pressure cast, & shot peened when produced. The exact alloy used was AC4CH-T6 Aluminum alloy.

I understand that some OEM rims are powdercoated (although I'm not sure which ones). My understanding is that the powder is baked during the heat treatment stage and so this isn't an issue.

I know, there are thousands of people who have powdercoated rims without problems but I'm also aware of quite a few failures including a friend of mine who lives a block away. The last time I talked to him, he said something about cracking his BBS CH's. He just had them coated a few weeks ago.

Something to keep in mind, especially after seeing pictures like this (scroll down):
http://www.witchdoctormotorsports.com/wd-news-tde0607mar04.htm

I am sure there are different alloys, maybe lower bake temps and perhaps "safe methods" to coat rims. However, I don't think it's worth the risk. I understand that Tig welding is the approved method for welding damaged wheels because it doesn't transfer much heat to the rim during the repair. If that's an issue, I'm not sure why so many wheel repair places are quick to throw the rims in an oven. Food for thought; I'm interested in comments or opinions. I'm not a metallurgist but the information and the warnings that I've read were enough to sway me for now. I'm going to stick with paint when I repair these ASA's.
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Old 03-26-2007, 12:38 PM   #2
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Chances are those 9 year old rims came of a tracked and ragged out is300 and were powdercoated YEAAARS ago judging by all the swirl marks from cleaning them. bet the cracks were fault of the driver and or shotty powdercoating.

edit: take that back, tracked z06 getting sideways off a track can break rims.... ever seen rally?
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Old 03-26-2007, 12:39 PM   #3
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I wonder if that's the effect of powdercoating, or just typical Chevy junk.

Seriously, that was an interesting read, and just as I was preparing to powdercoat a set of rims.
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Old 03-26-2007, 12:39 PM   #4
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That is interesting. But there are other (safer) ways to change the color of your rims. You can have them painted without going through the POWDER COATING process. Speacial primers and paints must be used. It does not involve a heating process of any kind. This would be the best way to go about doing a wheel color change on an existing alloy wheel.
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Old 03-26-2007, 01:20 PM   #5
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Ironically, you'd probably be safe powdercoating a new set of rims - but I wouldn't do it to an older set.

Yes, the alloy can make a big difference depending upon whether the aluminum used was tempered (T). In all likelihood, however, you aren't going to find rims which aren't tempered since they would then be too maleable to begin with.

I can't think of a single powdercoating method which involves lower temps. An automated line might get it through quicker, but it still has to get up there in temperature. Most people also don't realize that the preferred way to remove powdercoat paint is to "burn it off" in the ovens.

It is absolutely amazing what running aluminum through a powdercoat process multiple times will do. We had a housing that we kept painting over and over (silver sucks to get right during powdercoating). By the 3rd or 4th time this 4' long, 40lb housing could easily be bent by a small child. My co-worker bent it into a pretzel and hung it on his wall.
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Old 03-26-2007, 07:42 PM   #6
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I can't speak from experience for the rim-side of things, but everyone i know of that severely overheated their engines with aluminum heads ended up replacing the heads (not always immediately) due to them being too soft to hold a shape. Most ended up eating head gaskets since they won't seal quite properly anymore.

I'm imagining the same thing can easily happen to aluminum at temps required for powdercoat.

Your mileage may vary, though, and I'm not a metallurgist/etc, I just have seen these things happen
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Old 03-26-2007, 09:05 PM   #7
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Hi,

As Denverpete aluded to, there are simply too many variables for such a Blanket Statement or Warning.

There are literally hundreds of different alloys out there and numerous ones used by Wheel Manufacturers. Then there are at least 35 different Tempering methods. Several can withstand temperatures as high as 279C (535 F)

I have Powdercoated several sets of Alloy Wheels and Tracked several repeatedly with no issues over 15 yrs. of use, including a set of BBS Wheels.

The Shop I use heats their oven to only 320F as they say this is sufficient to get the powder to Flow and it results in a better overall finish than higher temps.

The email from the guy at BBS isn't very specific with it's "We'd always prefer... " He doesn't catagorically condemn it. Sounds more like Risk-Management speak than anything technical.

Alloys, Tempering Methods, Oven Temps and particularly the Wheel design itself are all factors, and all often very different from Wheel to Wheel and Shop to Shop.

The interesting thing is that if there were a high incidence rate of failure of Powdercoated Wheels, I suspect that the major Wheel Refinishers would do one of 3 things, possibly some in combination.

To avoid liability, they's refuse to Powdercoat Alloy Wheels altogether.

Or, they would put a lot of disclaimers and waivers on the process.

Or, the prices would skyrocket to cover the cost of increased Liability Insurance.

The last time I had any Wheels Powdercoated, about 2 yrs. ago, they were $85/wheel which included unmounting the Tires, Media blasting the wheels, coating them, remounting and balancing the Tires. And this is a nationally known Wheel Repair Specialist.

I'm not wholly endorsing the process, but my experience has all been good and I wouldn't hesitate to Powdercoat a Name Brand Alloy Wheel, though some of the cheap knock-offs would make me more hesitant.

If you're really concerned and want more information, check out:

Properties of Aluminum Alloys: Tensile, Creep, and Fatigue Data at High and Low Temperatures - 12-16-02 - Publishers: The Aluminum Association / ASM International

Happy Motoring!... Jim'99

Last edited by MNBoxster; 03-26-2007 at 09:17 PM.
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Old 03-26-2007, 09:10 PM   #8
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Ive seen plastic coated wheels and it looked pretty good. I dont know how they did it, maybe just dipped it in hot plastic and let it dry. Looked kind of like paint, but plastic, lol.
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