chris walrod

From this weekend in Houston -- Yep, all black --

chris walrod

and another since several of our Atlantic teams powdercoast their BBS wheels--
Note: a 40G impact with the wall did this damage, not the powdercoating

Geo

Damn, I stopped by the Swift trailer on Sunday but it was a ghost town. Wish I had stopped by on Saturday.

chris walrod

****, your kidding. What time? I was there ALL week, just about..

RonCT

The guy from BBS was there to sell his product and from what I could see 99% of what they sell is silver (unless a special order black from the factory). When he said what he did about silver being a more logical color I couldn't help but agree. In the case of special orders, even BBS obviously must use black paint instead of silver if a team or OEM supplier wants a black wheel. Again, his point was that it is not a good idea to take a finished alloy wheel and send it out for powder coating.

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.

The quenching process described above is only for alloy 6061 and only if a T6 temper is required.

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

Geo

Damn. It was about 1:30. It was between the Atlantic race and the Champ Car race. Damn damn damn!

I didn't get around to finding Chad either this year.

RonCT

It is an interesting debate for sure. One thing that I'm sure of is that if you took a wheel and powder coated it, you would be voiding the warranty (BBS said it was something like 3 years). So if you did coat and then cracked a wheel, you'd be on your own.

complexx

Can you measure hardness of a wheel without breaking it?

RTP356

I am not in the wheel business, so I do not know for sure. We manufacture aluminum extrusions and we test the hardness without destroying the product.

500

Hardness can be measured without noticeably damaging the product.

Yes the process I described before was for 6061-T6, a wrought alloy, not a cast alloy. I had mentioned I was using it only as an example. Every type of alloy and temper has different parameters for quenching, re-heating etc.

BUT, I do agree that subsequent re-heats in the 350-400 degree F temperature range for short durations CAN have an impact on strength (and other factors such as intergranular corrosion). It is very dependent on the alloy.

Right now I am looking at the ASM Aluminum Handbook at a table that gives maximum permissable re-heating times for a number of different 2XXX, 6XXX and 7XXX alloys (pg. 318). These times are that for which the particular alloy will not lose more than 5% of it its strength. At the 400 degree F level, the times range from 5 minutes to one half hour (6061-T6 which has a bake time of 8 hours to peak conditions is listed as having a max re-heat time of 1/2 hour on this table). Yes, these are all wrought alloys, not the same as the cast wheels, but I think it is illustrative in that it does show that even short re-heats can have measurable effects. 5% may not be significant most of the time.

Our company has had product extruded by Alcoa, Aluminum Shapes, Indalex, Bon-L and Kaiser (plus a few others) and through lots of testing and investigation we have come to learn that factors such as wait time (between quenching and subsequent baking) and bake time have considerable impact on final properties.

I would expect a good wheel casting company would consider the powder coating re-heat cycle as part of the total perciptiation hardening time. However, they are "just" wheels and it is likely that the process paramaters are not super-tight anyway...

complexx

Interesting information.

I found that a two cans of spray paint from the hardware store did the trick when i was trying to make a silver BBS wheel into a gold BBS wheel.

911pcars

"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."

Thanks for that comment. Isn't this enough to be wary of applying any thick coating to a stressed component?

Paul Jongbloed (sp) of racing wheel fame also warned about this in an article in Victory Lane mag (vintage racing).

Sherwood