RonCT

We had our CVR PCA meeting last night and the Northeast regional BBS representative gave a presentation. Of particular note was the damage that powder coating does to a wheel if it's done outside of the initial manufacturing process. In other words, if adding clear coat, anodizing, or even powder coating is factored in when the wheel is made such that the chemistry is planned out, then it's not a problem. But people that take delivery of a wheel and then send it out for powder coating are going to see a 30% degradation in the structural integrity of the wheel. The way I understood what he said - it was like heat treating something in the manufacture and then "undoing" it by baking on the powder coat. I didn't quite understand how that differs from heat cycling the wheel on the track - I just don't know much about the powder coating process.

Anyway - I had never before heard of negatives of powder coating metal and even wonder if this applies to things like roll bars. Just a heads-up to all...

P.S. He rolled his eyes and said "Honestly, I don't know why anyone wants black wheels in the first place - if it's to make the car look racy, it isn't working because all race cars have silver / aluminum colored wheels..."

eclou

Powdercoating involve the application of pigment through electrospray followed by baking the material at 350-500F. Depending on the quality of the alloy, that would cause thermal expansion and contraction that could weaken the wheel, especially if it has been repaired in the past. I think most wheel refinishers now have gone to a process baking at the lower end of the heat range to avoid it. Cages are usually constructed of steel which tolerates thermal cycles well.

CWay27

I wouldn't bet my paycheck on everything he said. He might be right for powedercoating but like eclou is saying, the baking temperature have gone down quite a bit (I think it ranges from 250 to 350 degrees).

RonCT

Yah - as I said in the post, I'm not sure how different powder coating is from regular track-use heat cycling. I was curious and did a search and the top site for wheels explained the process - they use 400 degrees of baking. I guess overall the point is why do something for aesthetics that is expensive, can damage wheels, etc.

Oh, another point he made that I forgot - he said the reason race teams leave wheels silver / raw is so they can detect cracks. On a silver colored wheel if a crack forms, you can see a black line from brake dust collecting in the crack. If you have black powder coated wheels you will never be able to tell.

whakiewes

On another board I post on quite a bit, there was a huge discussion about powdercoating wheels, and the negative side effects. There was quite a bit of varying information so I called around to get a better idea (since I get quite a few wheels refinished every year). I called BBS direct, Tire Rack, and HRE; the companies I knew someone personally who could advise me without a bias. The general conclusion as said by all three is exactly what was posted in the first post. The process of powdercoating involves essentially attaching the paint to the wheels, versus painting where it is just lightly adhered. The baking process furthers the problem by just what was said, expanding and contracting the metals.

There was a 'but' though that every single person I spoke with told me. The above only really applies to cast wheels, which the molecules are so tightly packed. They expand and contract causing what Ron said, about a 30% decrease in structural integrity. Forged wheels, as offered by HRE, BBS, and of course TireRack are manufactured differently, also at different temperatures. They can withstand the temperatures of powdercoating much better.

The downside is painted wheels chip. I have gone through tons of them. There is no way to make the paint stick really well to the alloy wheels. Powdercoating is the proper way to do it so the paint sticks, but the downside is what was posted.

Now I just order my wheels finished how I want them. Generally wheels are all either black, silver, and antracite for my cars, so they are readily available. The occasional red or yellow wheels I just have painted.

Wes

mooty

paint and powedercoating.
anyone care to elaborate on annodizing? how that is stronger or weaker than other finishing techniques on forged wheels?

whakiewes

Annodizing is very expensive when doing things the size of wheels. I was quoted a tad over $1000 to have my Champions annodized antracite, so I didn't even care to continue. Thus I never asked the question.

Wes

normank

Anodizing is an electrolytic process for coating and coloring aluminum (and other metals) for the the purpose of reducing corrosion. The metal is given a positive charge and the bath (chemical, color or both) is given a negative charge which produces a chemical reaction, magnetic attraction and a strong bond. Most often used for small products. Hope this helps.

mooty

thanx for the response, i did realize it is an electronic process. but i am wondering if it weakens the wheel?

mooty

when i spoke with CCW, i believe they told me they can anno black (as opposed to powdercoating) and the upcharge was very small. to the tune of $300-400 per set of wheels.

normank

I don't know for sure, but it is a low temperature process and is only adding a fine coating to the metal. It probably has no serious effect on strength.

RTP356

I am in the aluminum business and we also powder coat. When heat treating aluminum it takes 4 to 6 hours at around 450F to reach the typical hardness required. Powder coating is cured at around 300F for about 15 to 20 minutes. We have never seen a change in hardness of the metal when it has been powder coated. Hardness is created by heat and time. The heat and time used to cure powder coating is insignificant. In the past we powder coated aluminum and steel wheels and never had a problem. The only problem I would be concerned about would be the thickness of the powder coating vs. solvent based paint. Because powder coating is about 3 times thicker and becuase of that it is possible for a wheel to develop a crack and not be visible.

I am no expert, but that is real life experience of over 25 years in the business.

frayed

Aluminum alloys used in wheel manufacture are precipitation hardened, that is, undergo a particular heat treatment schedule to manipulate the microstructure and stengthen the material. These temperatures are within the range of powdercoating process temps. The hardening mechanism has to do with intermetallics formed from the alloying elements in the Al base material.

So, the microstructure could possibly be damaged at powdercoating temps. This damage has little to do with thermal expansion/contraction of the material.

While my technical background is in high performance materials, I'm not a metalurgist and have no idea if the particular aluminum alloys used in wheel manufacture can successfully withstand powdercoating temps.

I know that probably doesn't help a whole lot, but there's certainly validity to the claim of potential harm to your wheels.

Dave 86 930 Fl

Fikse anodizes their forged wheels.

Regards, Dave

LastGT3

As for the black wheel colour worry...did PAG get it wrong with black GT3RS wheels?