I would like to know if anyone has experienced a rim failure as a result of powder painting. I have a friend with a 2011 Ford F-350 with forged aluminum factory wheels. These wheels had Michelin tires on them with very low miles. His last set went to 100,000 miles. He had his rims removed and powder painted. He had them remounted and balanced. The rears were supposed to be inflated to 60 PSI and the fronts were supposed to be 75. After he bolted the rims on the truck he checked the tire pressures. They had the front and rear pressures swapped. He took the rears down to 60 psi from 75, and the fronts up to 75. Michelin rates these tires at 80 PSI. But fords sticker in the doorjamb says 75 front, 60 rear. Probably lower in the rear because they are duals. He is a commercial driver and this truck has all the bells and whistles to monitor tire pressures. He drove not more than 20 miles and was slowing to make a turn and enter a freeway. The right front tire blew, he assumed the tire failed. He put on a spare (steel wheel) and did not make it more than another 200 yards and the left front tire blew. After inspecting the tires, they have no holes in them. Both tires came off the back side of the rim. I would add that he checked the other front tire after the first blew. Both of the rims are severely bent, so much than in the few feet he traveled on the second blowout, the egg shaped rim rubbed on the brake calipers. I went to help him on the road, and he moved the one of the inside duals because they are steel to the left front tire because he already used his spare. He was afraid to drive this truck on the freeway with any of these powderpainted rims on the truck. It is now parked and we are looking to get the rims inspected to find the root cause. This could hae been a fatal accident had he been on the highway. He is pulling 23,000 pounds behind this truck. The shop that powderpainted the rims claimed they were at 800 degrees to burn off the old coating, then powder painted. He is not sure what temps were used (vehicle owner) but we are talking to the shop owner tomorrow. I had some alloy rims powderpainted on my Porsche and I am curious as well. I have read exceeding 300 degrees affects the aging of the aluminum.
I've had three sets of wheels powder coated and not had any problems. One set was on a Maserati I just traded in, another was a set of Gallardo wheels mounted on an Audi, and the other was actually on a 2008 F250 that I still own...110K miles on the ford now and probably 70K since the powder coat. After market wheels that I had powder coated on it, not factory. Not sure where you are located but the company that did mine specializes in wheel repair and does all their powder coating in house...they're fantastic. send me a PM if you want the company name and info, they might have some answers for you.
Sounds like it. There's a local wheel repair shop in NJ that does a ton of wheel repairs and powder coats them all day long 365/year. The shop you're talking about is clearly unqualified. Quite scary. I had a LF tire blow on my Suburban once while towing the 7K lb trailer and I used all three lanes to get the truck under control. He's quite lucky.
Well, the 800°F are not neccesarily harmful, actually tempering at higher temperatures (around almost 1000°F) is ONE step in treatment of aluminium alloy components. At this temperature (several hours) alloy components like Mg and Si become dissolved, therby forming homogenous cristallites. This is followed by quenching (rapid cooling) to conserve this (at room temperature metastable phase) condition. At room temperatures the alloy would not form such stable cristallites but by the quenching this condition is established. The result is a comparably soft alloy. For achieving the desired strength, a further tempering ("aging") process is needed at less than about 400°F for a very critical duration (several hours and depending on the specific alloy composition). Heterogenous cristallite composition is generated thereby in a defined way (diffusion controlled), imparting the desired strenght and avoiding too high brittleness at the same time. It seems that those guys simply softened the rims by their paint removal "tempering" and neither quenched nor applied the subsequent and essential low temperature tempering, which establishes the necessary strength. Since they presumably are no material experts, they would anyway not know how to execute the essential following low temperature tempering, so they had better not done the high temperature "annealing" .... That would be my explanation. I may note that although material science is one of my fields of work, a still other cause might be true. But it is worthwhile having the hardness of the damaged rims measured by an independent material science expert to verify or discard my "theory". I would assume that they are way too soft, due to the mistreatment at the shop ... P.S.: Powder coating (the low temp. heating process involved) generally does not (any more) change the heterogenous critallite structure significantly, but I would nevertheless try to keep the temperature as low as possible and the duration as short as possible.
My Gallardo rims I had powdercoated, along with many other rims, never had a failure with a proper shop, following proper procedures...my shop doesnt use heat to remove previous coatings
I've done some powder coating as a hobbyist and the powder I've used flows at about 400 to 425 degrees. Some of the clear coats are even lower at 325-350 degrees. I suspect those reporting no issues with powder coating had their wheels heated to no more than 400 or 450 degrees. What's different about your friend's situation was heating to 800 degrees to remove the old coating. I don't know anything about metallurgy, but 800 degrees is very far above the normal powder coating temp, so it seems quite possible that super heating the wheels to 800 caused the problem.
This has been discussed at length in a previous thread; including a lengthy materials discussion. BJJ is on the right track, the problem with powder coating is that you don't know the exact material and it can respond very poorly to heat (or well) depending on how it is treated. Most powder coating shops don't have the kind of thermal control required to execute this without some changes. Plus, they really don't know the exact alloy that is used so there is no way to know the impact of their treatment. Sure, many have had no problems and some have. BUT anecdotal evidence doesn't make fact. Pretty much every wheel manufacturer says in their warranty that it is void if you powder coat the wheels. They do that for liability but they have liability because of the above. No way to assure that things are done right. With all of that considered, I would say paint wheels and forget powder coating.
This seems like a really good approach because (at least the clears I used) flow at lower temp than the colored powder so risk it minimizes the risk.
Whether or not 800 F. will harm a wheel, I don't know. I'm no metallurgy expert. 6 years ago, I had two sets of aluminium wheels powdered at a place in Sweden who specialized in this sort of thing. Anyway, when I handed in the wheels and discussed the process, I was told that they NEVER worked with powders which needed to be heated above 275 c. which equals 527 degrees F. I think mine was done at around 235 c.
You may want to get your hands on the current (Oct.'14) issue of the Porsche Club magazine. There is an well written article on the failure of both forged and cast wheels and they state that powder coating at anything greater than 400 degrees will compromise the strength of a wheel. They also show a three piece forged wheel that came apart on a GT-3 at a DE due to the paint melting under the rim bolts. Best to paint wheels and stay away from PC for safety sake. Keep in mind that at the stated heating of 800 degrees they were 2/3 of the way to turning those wheels into liquid blobs (alum. melts at 1200 degrees).
Agreed 100% wheels should never be powdercoated. Even some media blasting can cause issues with the heat generated on the surface
There is some hyperbole and absurdity being posted in this thread. Media blasting causing issues with heat generated on the surface? You got a scientific lab that's going to back that one up with research? I think the OP has a pretty good idea about what probably went wrong here by now. It started with a bad selection of a vendor for the work.
Media annealing alum is a common occurrence on thinner aluminum which I should have stated not heavy alloy. Either way alum should always be chemical etched and conversion coated before refinishing. You see I am not a fan of powder coating on aluminum, magnesium at all. I have actually media blasted alum sheet and annealed it for a test in our shop years ago to show why its not the correct way to strip and refinish aluminum Heraeus - Precious metals and technology Group They can supply you with all the info needed on the subject at a fair cost. Jersey ehh? that explains a lot LOL Wait I am from Alpine NJ
There shouldn't be any paint between the surfaces in those locations. I just finished doing a set of 3 piece wheels with powder coated centers and had to make certain the powder coating either never got in those spots via proper masking or remove any that had. I've seen wheels come off a car at the track because they had powder coat in the lug nut areas. The problem isn't with powder coating but with the powdercoater.
I've not used powder coating on two sets of magnesium alloy wheels I've restored for a variety of reasons. Those got a conversion coating teatment, followed with a zinc chromate primer and then a good enamel. But the guys who manufactured my race wheels, Forgeline, powdercoat their forged aluminum center sections.
Cool, thats the correct procedure Unfortunately too many companies are using powdercoating instead of painting due to cost and environmental issues. Powdercoating bare metals allows for oxidizing to start before the paint is even applied and continue. Almost anyone can powdercoat but not many folks can paint
Hill Engineering sell wheel masking bungs specifically for this reason. "Time and time again we are seeing wheels being finished with a huge build up of paint on the conical surface of the wheel insert. We can not begin to explain how dangerous this can be as the layer(s) of paint on the insert surface seriously affects the integrity of the bolted joint. The paint basically begins to get squashed and is soft enough to slowly move out of the bolted joint thus the bolt becoming loose. This pattern is accelerated when temperatures rise above normal driving conditions:-" WMB-01 - Wheel Masking Bungs by: Hill Engineering - Hill Engineering
Hey those are nice. I've seen that happen with a wheel coming off at the track. I just finished up a thread on here about 3pc wheel restoration. I asked the painter to mask these and half of them were not! It was pretty easy to clear out though. I used a small brush with paint remover and went carefully from the back side. Very slick. But they also did not mask the countersunk holes (20 on each wheel center) that receive the cap screws for securing the center section to the two piece rims! Not so easy. Now these wheels originally were painted with a very thin paint that worked quite well for 25+ years. Some of that WAS under the heads of the socket headed cap screws too! But that won't work with powder. So I had to use the drill press and very carefully clean the bottom of each hole out without damaging the sides. Not so slick ... But it worked!
Whether paint or powder coat, all wheel/wheel and wheel/hub surfaces bearing load should always be in blank metall contact with each other with no coating therebetween. When I bought my Jarama (center lock wheels, "miura style") a rear wheel came loose soon after. The reason was quite simple, the conical faces centering the wheels on the hub had also been painted and this layer naturally did not carry the load of tightening the wheel nut all too long. Was on all wheels and I scratched it carefully off, no issues since then. Luckily I had noticed before the wheel came off.
