Trouble polishing aluminum

[chevynut]

I ran into a problem that's driving me nuts and I can't figure out what's going on. I'm trying to polish my PRC radiator so I can install it into my radiator support. I cannot get it to polish for some reason.

I just spent weeks polishing all my stainless exhaust, gas tank, plumbing, and a whole bunch of suspension parts with no problem using the same equipment and materials. I took the radiator out of the box it's been sitting in for years, sanded it with 1200 grit to get it smooth. Then I tried to polish it with my die grinder with a cotton wheel on it and thought it might take me an hour or so to finish it. The problem is that the buffing compound just builds up on the radiator, and it won't polish it. I did some research on the problem and it suggested the part was too cold causing the wax-based compound to freeze on it so I heated it with a propane torch. It did the same thing. I tried 3 different compounds (brown white, green) and they all do the same thing. I even took the radiator to my buffer and tried 2 different wheels and 3 different compounds and no go. I tried polishing another aluminum part and it works fine.

What the hell is going on? I spent 3 hours trying to get this to buff and I've gotten virtually nowhere. All that happens is the radiator turns black from the compound and a film of compound builds up preventing any cutting. I don't know what kind of aluminum they use for the radiator frames, but it shouldn't really matter.

[Troy]

Could it be that the aluminum is soft from annealing during welding?

[WagonCrazy]

Did you ask them at PRC?

[chevynut]

I plan to call PRC this morning, but don't expect to get much from them. I suspect they're using 6061 aluminum but imo it shouldn't really matter what it is. I'm not sure why too soft or too hard should keep it from polishing up. But something weird is going on for sure.

[Rick_L]

You need to sand on it until the black stuff quits coming off. Are you wet sanding? You could use either water or kerosene/WD40.

[chevynut]

Just called PRC and they told me they're using 3003 aluminum, which was a bit of a surprise because it's usually used for parts that need a lot of forming.

"3003
This is the most commonly used commercial aluminum alloy. It is alloyed with a small percentage of manganese and has slightly higher strength than 1100. It is very workable and can be easily sheared and brake-formed. This alloy offers good corrosion resistance, but does not always provide the most consistent finish in anodized applications."

Anyhow, the rep told me this is a common problem and they've only found one guy who can do it. He polishes all of their radiators and does it part-time and is a fireman.

I couldn't get any suggestions for the process used, nor would he give me the guy's phone number so I could try to get some help. So I'll search the net.

The black won't quit coming off with more sanding....at least that's been my experience with aluminum of any kind. I tried sanding with 500, then 1200 and it still doesn't help. I wet sanded it.

There must be something peculiar about 3003 as compared to 6061, because I can polish 6061 with no problem.

[chevynut]

Just called Caswell Plating where I bought my buffing compound and wheels, and they don't know what's going on either. He told me I'm either using too much or not enough compound....like that really helps. I tried raking the wheel to remove compound and I've tried adding a lot of compound. I've been able to get one small area shiny with a lot of work....it acts like there's some clear epoxy or something on top of the aluminum, but I'm sure there's not. I might try to post a picture.

[JT56]

I use the Blue Magic polish on mine. I will say dont run the orange anti freeze in it...it will stain it.

[chevynut]

I use the Blue Magic polish on mine. I will say dont run the orange anti freeze in it...it will stain it.

Was yours pre-polished when you got it? Mine isn't. I'm trying to get the initial shine, not maintain it.

[JT56]

Was yours pre-polished when you got it? Mine isn't. I'm trying to get the initial shine, not maintain it.

Yes iit was polished...I assumed your was already...big difference. I have seen some that the frames are painted and look good