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. :confused: 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

[chevynut]

PRC wasn't much help. He said they tell guys to pay the $150 they charge to polish them....it's probably a good deal. I was disappointed that he wouldn't even let me talk to their polishing guy. I had no idea it would be this much of a PITA to polish it.

[chevynut]

Here's some pics of what I'm dealing with. I still can't make it work and it's getting pretty frustrating that nobody has an answer. I wet sanded this tank with 1200 followed by 3000 grit on a DA. It's pretty satiny shiny after the 3000 grit paper but not a mirror finish. This is what it looks like:

http://www.trifivechevys.com/attachment.php?attachmentid=5846&stc=1

Then I hit it with a die grinder with a cotton buff and white compound and this is what it does. The second picture is of the other tank, buffing for the first time after sanding to 3000 grit. I can clean it over and over, and buff it over and over, and it doesn't change. I've tried cleaning with acetone and PPG oil and wax remover, both of which take the black off, but then it's dull underneath.

http://www.trifivechevys.com/attachment.php?attachmentid=5847&stc=1

http://www.trifivechevys.com/attachment.php?attachmentid=5848&stc=1


It's not nearly as bad as it was before the 3000 sanding, but it still leaves a slick black deposit that prevents the compound from cutting. You can smear it with your finger. I also noticed that even with wet sanding, the paper clogs with aluminum. It seems like this 3003 crap is too soft to polish for some reason, and it just coats itself with some sort of slick aluminum-filled wax from the compound making it impossible to buff. :(

One other thing I noticed, and you can see in the pic is that I sanded the HAZ next to the weld and it buffs out pretty good as you can see in the second pic. Until sanding, it's a lot rougher and leaves even a darker band that you can see in the last pic. Not sure why the HAZ polishes better, but it's probably a clue as to what the problem is.

I'm going to try using Mother's polish with a foam pad now. Not sure what else to do. :confused: :cry:

[Bitchin'57]

I've heard that with aluminum, you should polish in the direction of the grain, and use a liquid polish.

[Kswartz]

Hey chevynut, go get some Autosol, just there plain metal polish is fine. Amazon has it. And be done with it.

How ya doing
Out kevin.

[chevynut]

Guys, I think the stuff you're recommending, all the liquids and pastes, are for polishing PRE-POLISHED aluminum like wheels, billet, etc. I'm working on an UN-POLISHED radiator and I'm trying to get it to polish. The metal has a mill finish. To polish that you need to use a buffing compound with abrasive in it, after sanding the surface to remove scratches and irregularities. The liquid polishes might make it shiny, but they won't make it smooth and give it a mirror finish.

I think I came up with a process yesterday that seems to work on this 3003 aluminum. It sure seems different than the 6061 that my suspension parts are made of.

[chevynut]

This stuff is still giving me fits. I polished the condenser frame with a coarser compound, then went to a finer compound with a different wheel. In places, the finer compound leaves some of the black residue and it won't polish out. The wheel loads up with aluminum and it needs to be raked constantly. Some of it polished up nicely, but some of it just won't. It's possible they used two different aluminum alloys on this frame, or at least it acts like it. The sides of the frame polish to a mirror finish, but the top and bottom won't. I decided to try finishing it up with Mother's aluminum polish and it actually DULLED the finish and it looks milky. WTH?? :mad:

[55 Rescue Dog]

At that point, I would just paint it black. On some cars a shiny radiator looks good, but on some cars, it sticks out like a sore thumb behind the grill. Plus, I think black dissipates heat better, than a thermos polished surface does.

[chevynut]

At that point, I would just paint it black. On some cars a shiny radiator looks good, but on some cars, it sticks out like a sore thumb behind the grill. Plus, I think black dissipates heat better, than a thermos polished surface does.

Painting it black would hurt heat transfer more than you'd gain from from the higher emissivity of the black surface imo. Most of the heat transfer is by conduction and convection anyhow, and radiation heat transfer is a small component. A very thin layer of black paint might not hurt. My radiator will be covered, but you can see it through the grille. I don't think I want it black but I may change my mind later. Thanks for the suggestion though.

[DocHarley]

Chevynut, I was having the same issue on a few of my parts I was polishing. Not saying this is your problem, I'm no expert by far, but I found on a few of my parts were softer or cheaper aluminum? if I applied too much pressure the part would get hot as hell and cause a blotchy look, even cause what appeared to be deep groves. I discovered using a lot less pressure took longer to achieve satisfactory results but excessive pressure during polishing was the cause for "my" issue.

[chevynut]

Doc, I think you're right about that. I have been having trouble getting a mirror finish on my aluminum and stainless parts. I've been using a spiral sewn buff, and I think a loose buff would bring out that final luster I want. However, I was using a loose cotton buff on this radiator and still having problems. Even the Mother's aluminum polish didn't work.

The PRC radiators are made out of 3003 aluminum which is softer than most aluminum I've been polishing.

[NickP]

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.

When I was QAM at the Kirby Vacuum Cleaner Company, all of the Gen III was polished to a high luster. They never sanded by hand but rather used a belt of an unknown grit (they treated it first). The compound, was black. It would take less than 2 minutes for any one part to be polished. They did use a compound rake to remove the excess from the wheels. I'll try to contact a friend there to see what exact compound, grit and wheel material they used if he is still there.