Refinishing Wheels
I have two sets of OZ wheels and a set of BBS wheels that I want to refinish. Once stripped is paint preferred over powder coat???
I would prefer the durability of powder coat but did not know if the heat required to cure the finish would affect the wheels???
DP90
Many do use powder coat, but I have been advised not to to do so based upon the heat. I have used PPG DP-90 primer (flat black) for many years with good success on both wheels and the frame. It is virtually indestructible. There are other colors available in the DP lineup as I recall.
John
I agree with John... the PPG epoxy is the most durable paint I've seen. I've used the flat black, grey (which does have a little sheen to it) and now also the flat white. The white is a very "clean" looking color. There are other colors too.
It takes 400 degs to powder coat, I know I wouldn't. And I was told by BBS not to blast their wheel centers. However, I did chemically strip the paint off my BBS aluminum wheels and polished the rims. They look great !
God is my pilot, I'm just the loose nut behind the wheel !
Thanks for the input...I was planning on a two part paint similar to the PPG that is used on aircraft in lieu of powder coat Durable and available in many colors although a satin black makes the most sense...
I thought that they may have been powder coated from the factory but if its paint I can chemically strip them and avoid the media blast...
I've heard that the temps for cure was 400-450F.
I've always wondered though as that doesn't seem that high.
What is the specific danger? Warpage, restructuring the molecules, issues with trapped gasses within the castings/forgings?
Also I would think certain chemical dips would or could change or corrode the surfaces at least.
Are there different protocols for aluminum and magnesium?
It won't melt the wheel material but it is in the range to anneal the metal.Originally Posted by ChristopherBernard
I was at this crossroads a few years back and chose to have them polished instead.
Drop dead gorgeous! I only have to do 'em twice a year out here in dry, dry California desert. Might be more of a PITA in FLA....
If the OZ's are mag, I'd recommend chromating them instead of just paint. If they're aluminum, paint away.
Ethan Shippert
http://shippertracingservices.com
https://www.norwestff.com
"l'audace, l'audace, toujours l'audace!"
Powder coating can hide cracks....
Its good but not for everything....
FWIW this was what PacWest used on their IRL and Lights cars in the day. They had to blast them annually for inspection as I recall.
John, I had a buddy who worked for PacWest some years ago. His name was Tim Wilson...ever meet/hear of him? He was a fabricator, I think.
jerry
No, I don't recognize the name. I worked with a guy called Fuzzy. He's with C&R at this time.
Short answer: You might weaken the metal by powdercoating the wheels.
Long answer: It depends on the temperature and duration of the bake, and also on the material the wheels are made from.
Magnesium wheels are often die cast from a magnesium alloy called AZ91. The alloying elements are aluminum ("A") and zinc ("Z") in addition to the base magnesium. The heat treatment is very similar to aluminum alloys. The most common aluminum alloy for cast wheels is probably A356. Forged aluminum wheels could be 6061 aluminum.
All of these materials are strengthened by something called solution heat treatment. That involves raising the temperature of the alloy enough that the various constituent elements "dissolve" and form a finer and stronger grain structure, then quenching (cooling quickly) to lock this structure into place.
For example, the wheels we buy from OZ are die cast from AZ91 and heat treated to what's called the T4 condition. This represents the first step in solution heat treatment where the magnesium alloy is heated to just under 800 F then quickly air cooled ("quenched").
By adding what's called a "artificial aging" step, where the temperature is raised just enough for the grain structure to become finer and more uniform, they could be brought to the T6 condition, which is somewhat stronger. That involves raising the temperature to something like 350 F for 16 hours or so (can't recall the exact parameters). It turns out that these alloys will naturally age over time even at room temperature, so the T6 treatment is just accelerating the aging process from years to hours.
The process for aluminum alloys is slightly different, for example, wheels cast from A356 aluminum would be solution heat treated at about 1000 F for 8 hours or more, then quenched in water, then artificially aged at something like 300 F to result in a T6 condition.
Most production aluminum and magnesium wheels are powder coated, so the wheel manufacturer will often shorten the aging time slightly (called underaging) and continue the aging in the powder coating furnace. I believe this is what OZ does with our magnesium wheels as they come powder coated.
When you refinish your wheels they are (in the ideal world) already at the optimum T6 condition, fully aged and at their strongest. If you then powder coat them you are raising the temperature high enough that you will age them further.
In the best case there won't be a significant difference, you might lose 10% strength by baking your wheels at 400 F for an hour or two. In the worst case, if the temperature is higher than that and they are left in the oven for a much longer time, this "overaging" could result in a wheel that is significantly weaker.
They will not be annealed (brought to a dead soft, malleable, and weak condition) unless the powder coater is completely incompetent. To fully anneal aluminum you need to bring it to something like 750 F and cool it very slowly. But the higher the temperature and the longer it is left at that temperature, the weaker your wheel will get.
Medium answer: you are taking a small but real risk in powder coating your wheels. The wheel manufacturer uses a tightly controlled process with strict oven temperatures and times, and compensates for the aging of the powder coating furnace. They also regularly test wheels and sample coupons of material to maintain control of the wheel mechanical properties.
Nathan
and THAT, folks, is why we all hang out here......virtually unlimited shared knowledge.
Hi guys, I just spoke with the owner of National Metal Processing, My company uses them for our Heat Treating needs. He tells me 400 degrees won't bother the hardness of aluminum. That you have to get over 700 degrees to change it's physical properties. However he had no knowledge of magnesium.
Thanks Wes
Mag. refinish
I had KeCo redo 6 Tiga/Gotti centers for my S2. Came out nice, even though treatment (Kephos) won't fill in any corrosion/damaged areas (fine with me...best to see, rather than cover up true condition). About a mil build up for coating. They have facilities in Indy and NC....goggle them for contact info, read detail of services/coatings... I dealt with Marti Humphery...min. charge of 250.
(See my post over in SR classified for rims to see photos of redone rim...lots of hand work on the alum...)
Bob L.
Then you misunderstood him or you should find another heat treater.
Many tempers of aluminum (T6, T7, etc) involve artificial aging at temperatures in the 300-400 F range. The longer you age, the softer the aluminum gets. In some cases you overage the aluminum on purpose to make it softer and more ductile.
Some aluminum castings (like for engine heads) are aged at temperatures in the 400 F range to improve high temperature strength.
Nathan
Another comment of PC of alum.
Way back when powder coating was getting going, several divers refinished their alum. scuba tanks. There were some instances of those coming undone, with catastrophic results, when later filled.....don't recall all details (whether a re-hydro was done after finishing or not..temps, etc.....) but, seemed to be a case of too much heat annealing the aluminum, dropping allowable UTS...
Old rims is an area where you most likely won't KNOW what alloy or treatments were used....suggest you tread lightly...
Bob L.
Last edited by Bob L.; 01.06.15 at 2:43 PM.
Refinishing wheels
Get ahold of Steve Oseth. He repairs/repaints alloy wheels for a living.
I always said heat treating was like being a witch doctor! Half the new wheels on the market look powder coated to me?
Yes, I believe most new wheels are powder coated.
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