carguy123
carguy123 SuperDork
1/2/12 1:23 p.m.

I have a set of rims that I would like to powdercoat.

They came to me with one wheel sandblasted(?) to a satin finish which means the texture doesn't match the texture of the other 3.

I am presuming I will need the texture of all 4 to match or they won't look the same once they are powdercoated, correct?

The other 3 rims have some sort of clear coat on them and at the moment I am presuming that is clear powdercoating, but it needs to come off.

I am looking for glass beads so that I can bead blast the other, but so far no one has any in stock.

So other than texture I am wondering about how far up the lip should I blast and powder coat? It seems that going all the way to the edge is likely to get scratched when they are mounting new tires.

I can protect the 3 with tape(?) while I blast them, but the other rim is blasted all the way to the edge and all the way across the barrel so, presuming I shouldn't powder coat to the edge and that I need to match textures, how do I smooth the edge of the rim that's already blasted?

And is that going to take me weeks and weeks of polishing to get it looking good? And how do I get a hard line finish between the polish and the satiny finish?

This was to wait till spring time, but I just noticed that I've corded the tires currently on the car and I see no sense in putting an interim set of tires on since I intend to replace both the tires and the rims (they are different diameters than the powdercoated rims).

How much bead blasting material would you think I'd need for 3 rims? It comes in 50 lb bags. Is 1 enough?

Conquest351
Conquest351 HalfDork
1/2/12 2:06 p.m.

I'd blast all the wheels. The sand blasting will leave them with a matte finish. As long as there's no obvious pits or scratches, the powdercoat will make them nice and smooth and shiny. Spray them off with non clorinated brake cleaner or mineral spirits. Put them in the oven for about 10 mins and let them outgas. Pull them out (carefully) and hang them up with wire on something. Spray them off with non clorinated brake cleaner or mineral spirits. This will make sure the aluminum is clean and free of debris and gas (keeps the powdercoating from bubbling). If you're only going to do part of the wheel, then regular masking tape will work. Use cork to plug up the bolt holes! Most important! Different powdercoatings will have different finishes. Check with Eastwood for whatever colors or finishes you want.

If you're only going to blast part of the wheels, then a piece of aluminum/steel/wood/anything will be your best bet to protect the other parts against the all removing blasting media.

carguy123
carguy123 SuperDork
1/2/12 2:15 p.m.

You'd blast ALL OF THE WHEEL or ALL of the wheels to get the same texture? I presumed you would be able to tell the difference between the sand/bead blasted rim and others that weren't

I hadn't actually thought of powdercoating the rims myself. I don't have an oven to do it in, but buying an old oven might be cheaper than paying someone to powdercoat them.

z31maniac
z31maniac SuperDork
1/2/12 2:44 p.m.

Wasn't there some discussion about blasting and microfractures?

AutoXR
AutoXR Reader
1/2/12 2:49 p.m.

There's quite a few threads by PCA guys about Powdercoating rims and it not being a great idea. (re heating metal)

Keith
Keith SuperDork
1/2/12 2:56 p.m.

Yup, look into the heat treating involved in T6, and then look at the heat ranges of powdercoating. For a set of street wheels, I'd do it. For a set of wheels in a critical or race application, I would not.

carguy123
carguy123 SuperDork
1/2/12 2:57 p.m.

I didn't know you could dissolve the old paint or powdercoat clear coat. http://www.eastwood.com/ew-powdercoat-and-paint-dissolver-quart.html

carguy123
carguy123 SuperDork
1/2/12 3:01 p.m.

Since many wheels come from the factory with powder coating I'm not worried. These will be my street rims.

Wheels get a lot of heat cycles and those 1100 degree brake temps bleed over in the rims with no deleterious effects so I'm not really worried even if they were race rims.

It's the prep, how far out toward the rim is it a good idea and would the satin texture be noticeable vs. the stock glossy texture or do I need to rough up all of the rims?

And if wheel texture matters that much and I shouldn't carry the powdercoat all the way to the edge, what's an easy way to polish up the lip of the rim that's already been blasted? And keep a good clean edge between polished (smoother) and the textured area?

Conquest351
Conquest351 HalfDork
1/2/12 4:22 p.m.

When I worked for Motion Dynamics, we powdercoated just about everything. Pistons, rods, engine blocks, etc. Anything we could get our hands on, we'd try it. No we didn't put the powdercoated parts back together (engine, pistons, rods) and try to run them. LOL Wheels are no biggy. If you have a local company who specializes in powdercoating. They'll usually do everything for you but blast the wheels. It's pretty affordable too if you do all the hard prep work. When we had larger pieces such as wheels, we'd sublet them. Our oven would do 4 & 8 cyl valve covers and most intake manifolds, but the larger more extravigant things we'd have to take down the street.

Conquest351
Conquest351 HalfDork
1/2/12 4:31 p.m.
carguy123 wrote: Since many wheels come from the factory with powder coating I'm not worried. These will be my street rims. Wheels get a lot of heat cycles and those 1100 degree brake temps bleed over in the rims with no deleterious effects so I'm not really worried even if they were race rims. It's the prep, how far out toward the rim is it a good idea and would the satin texture be noticeable vs. the stock glossy texture or do I need to rough up all of the rims? And if wheel texture matters that much and I shouldn't carry the powdercoat all the way to the edge, what's an easy way to polish up the lip of the rim that's already been blasted? And keep a good clean edge between polished (smoother) and the textured area?

The sand blasting will rough up the wheel enough for the powdercoating to stick.

Sand blast, don't bead blast. Get a rather fine media to do it too. We used a really abrasive black sand media once... Worked great for cast iron, not so great for aluminum.

Polishing is OK, but if you have someone near by who polishes, it's well worth the cash to have them do it. We had a couple of guys who we'd use, but we'd let them know it was no rush, as long as we got them by the end of the month or so. It cost us MAYBE $20 a wheel at most and they'd be damn near chrome. Check around and get friendly with some people.

OR... If you have a bench grinder, get the polishing kit from Eastwood and get to work.

Keith
Keith SuperDork
1/2/12 5:52 p.m.

I'm not sure many wheels DO come from the factory with powdercoat. I think they're mostly painted. Still, you could work the powdercoat process into the heat treating, as it would meet well with the aging.

When I first came across this, I asked some actual wheel engineers instead of the Internet. They said no. So did 949Racing, who supplied the wheels for the Targa Miata. So mine are painted.

carguy123
carguy123 SuperDork
1/2/12 6:24 p.m.
The sand blasting will rough up the wheel enough for the powdercoating to stick. Sand blast, don't bead blast. Get a rather fine media to do it too. We used a really abrasive black sand media once... Worked great for cast iron, not so great for aluminum.

I thought I would need the smoother surface the beads would give vs. the rougher sand blast. I've got blasting sand, but can't get beads till Friday (no one has any in stock till then- Christmas presents?)

How about powder coating all the way to the lip? Too likely to chip? If not that will save me from polishing.

Conquest351
Conquest351 HalfDork
1/2/12 9:36 p.m.

Not too sure about the chipping. Most wheel mounting shops have plastic boots they put on the machines to keep this from happening.

The heat treating guys are making me kinda nervous. LOL If it's a street wheel, I don't really see the harm in it. You're going to be putting a marginal load on it, not near the loads you're going to inflict during racing, but you have to think about the longevity. I know that during the powdercoating process you heat it to about 400 degrees (I can't remember exactly) for about 30 mins or so. I don't think that'll destroy the integrity of a set of wheels. Of course, I've been wrong before...

carguy123
carguy123 SuperDork
1/2/12 9:45 p.m.

And how hot do you think the rims get under hard braking on a track?

Hal
Hal Dork
1/2/12 9:45 p.m.

<---- My wheels are powdercoated. I had them done 10 years ago and have had no problems. I had them done by a local company that makes decorative railings and fencing. They did everything from sandblating thru powdercoating for $50 a wheel. They didn't have any problems since they do stuff like this every day. Actually their oven is big enough to do car frames.

Keith
Keith SuperDork
1/2/12 10:27 p.m.

It's the aging of the material that will be affected by the powdercoating process. The aging part of the T6 process involves holding the wheels at 350F for 10 hours. Since powdercoating takes the wheels up to around 400F for another 30 minutes or more, you're over-aging the alloy. Aging is a function of temperature and time, not just temperature.

You don't get your wheels up to 400F and hold them there on a track. I've done enough wheel changes on cars in endurance races to know that they're below the boiling point of water when the cars come in for a tire change.

Is it a definite no-no to powdercoat wheels? Nope. The temperatures are borderline and it may even come down to the sort of powder being used and the temperature ranges for it. There's a lot of disagreement on internet forums with posts such as "i had mine done 10 years ago and they're fine" and "a guy in our club had it done and all four wheels cracked". You know the saying, the plural of anecdote is not data. But based on my investigations and conversations with people in the wheel business as opposed to the powdercoat business, it's something I'd recommend avoiding if possible.

Painting will not hurt your wheels. Powdercoating may not - but it might. On a set of lightweight wheels that will be supporting my race tires as I peel into a 100 mph corner, I'm going to go with the safe option.

z31maniac
z31maniac SuperDork
1/3/12 1:27 a.m.

Again, I can't say for certain..........but I know Mike an engineer at BBS told me specifically not to powdercoat their wheels or do a low-temp powdercoat (below 200 ° and takes longer) because of the heat treatment issue.

You can discount/ignore me if you like, I personally don't care.

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