Powder Coating Questions

[MotoCreations]

So far I've chrome plated, anodized, hard anodized, powdercoated, polished (bare finish) and painted aluminum wheels without problems.

Only cavaet is that within the SSS wheel nut pinch area, I usually tape it off if when powdercoated and paint later.  I've seen powdercoat under compression slowly erode away.  Never a problem with chrome or anodizing or paint though.

[He Man]

did you have to do any special preperations for SSS?

ive hit it with a sander and as RB said, its pretty bare.

[Oldfisti]

did you have to do any special preperations for SSS?

ive hit it with a sander and as RB said, its pretty bare.

Media blast is best because it gets all the nooks and crannies but sanding is fine too. Prep is similar to paint prep with the exception that you can paint over paint (mostly) whereas I would only powdercoat a bare surface.

[He Man]

in that case, would i want to etch up the surface for a better adhesion? id think not right?

[Triple J]

Why are you prepping it yourself? Are you doing your own powder?

I just had my MTS frame, rims, triples, and a few other pieces powdercoated. The bill for media blasting all of it was only $80. No much to not have to hassle with it.  Total price (prep & powder) was $310 for all of it, including tax.

I also had a GT mountain bike frame powdercoated quite a few years ago (very thin wall aluminum tubing  )...the powdercoater media blasted that as well. Prep & Powder was $100.

Powder is cheap.

[Oldfisti]

in that case, would i want to etch up the surface for a better adhesion? id think not right?

I never tried etching because I have the convenience of my own cabinet. Blasting leaves the surface feeling kind of like 1200 grit paper. Nice surface for the finish to bite into.

Suppose it would work though as long as it's neutralized after and doesn't leave a black oxide finish. I'm sure you could test a piece first. Make sure it feels a little rough after.

[He Man]

good to know.  regarding your other post....

I guess more than anything I would respect the wheel mfr. say on this.

BTW I had no idea wheels could be tempered after powdercoating. Assuming this is true could they be re-tempered after you get them back?

Just some food for thought...

Still waiting on Marchensini's response. From what I've read, you can shape the wheel, spray it and temper it. The tempering process is done at around 375-450degrees for 8 hours. Ive heard you could redo the process, but it isnt as good as the first time around (that last part doesnt make much sense to me because these metals are always recycled and go through thousands of heat treatments and end up fine). All of that information is completely unverified because there are so many variations of that story. But hey, it might be true but its on such a small scale it doesnt matter. which is what my guess is. and If it was a huge deal, people wouldnt be PCing wheels at all right?

[Oldfisti]

 and If it was a huge deal, people wouldnt be PCing wheels at all right?

That was my "common sense" take on all this.   

[He Man]

That was my "common sense" take on all this.   

  you still dont get the question. im just gonna about face.

[Oldfisti]

you still dont get the question. im just gonna about face.

I'm sorry. It was 5am and I wasn't quite cognitive yet. Just woke up to let the dog out, no  yet.

You were saying that tempering the wheel can't be a big deal.

The temp range you described is powdercoat baking/curing temp although for much longer than 20min. As long as the finish didn't "overcook" I guess you could leave the wheel in the oven for 8hrs (and whatever controlled cooling is required) after coating to re-temper. The longest I ever left a part in was 25min so I don't know how the finish (we use corvel brand) reacts to an extended heat cycle.

[RB]

snip...
 As long as the finish didn't "overcook" I guess you could leave the wheel in the oven for 8hrs (and whatever controlled cooling is required) after coating to re-temper.

i have done this, and it will trash the powder coating, but you should test this before you take my word for it.

[Speeddog]

First off, heat treatment of aluminum is a different process than that used for steels.

Here's a primer on heat treating aluminum:
http://www.keytometals.com/Article7.htm

Here's an eng-tips forum thread that's directly on point:
http://www.eng-tips.com/viewthread.cfm?qid=151053&page=10

Regarding this:

I am hypothesizing that it is the structure of the wheel itself that prevents you from seeing the effects of baking the alloy at 400degrees and the fact that wheels are built to withstand a lot of force that pretty much negates the fact that PCing the wheel will cause the wheel to fail.

I still think there is some truth in the weakening of Aluminum alloys at powder coat temps. I will find out soon. The piece has been cooling down in the oven for about 40 minutes and i just lowered it to 100 degrees and im gonna let it cool in the oven for another 20 minutes then take it out to air cool.


test results : inconclusive, both samples took 75lbs to begin deflecting. I will try to seriously anneal a piece later this weekend...400degrees for a a few hours then slowly cool it over the course of a few hours and retest.

You need to check load vs. deflection up to where the sample *fails*.
Failure, in this case, would be a permanent bend in the sample.
Unless you're pushing hard enough on the sample to get a permanent bend in it, or break it, you're just checking the Modulus of Elasticity.
Modulus of Elasticity is the 'spring rate' of the material.
Heat treatment generally does not change the Modulus of Elasticity of a metal.

[Airborne]

powdercoating should have a negligible effect. Im a metallurgist.

[ducpainter]

Whether you are powder coating or painting don't handle the bare aluminum with bare hands or it will need to be etched to remove skin oil. If not you will have a corrosion/adhesion/fish eye issue in that area.

[MotoCreations]

Had a conversation today with the ceramic thermal coater.  Great for exhausts, steel frames, etc.  But keep it away from your aluminum rims.  Ceramic coating heats 525-550 degrees for a few hours to bake the surface.  He did a set of rims and they went "soft" -- ie: the heat process changed the aluminum characteristics.  He only made it a few miles before starting to bend the outer flange edges.

Also the higher temps of ceramic coating cause metal to relieve stress and move about some due to the heating/cooling cycle.  Thus sometimes dimensions might change a bit ala an exhaust system in radius bends. (good thing to know)

I know powdercoaters go to 400 degrees.  Wheels I've had done in the past were "low temp" powdercoating with lower temps specified.  I called them today and asked them the specifics they had done wheels for myself and customers in the past. 

So I definitely wouldn't go above 400+ for extended periods of time.