Brown stains

[jrow Experienced Metal Finisher Find all posts View Profile Close jrow]

Project: 20 year old automotive alternator.

I have followed the proper procedure in bringing the aluminum to the final polishing stage, white compound. I polished with the white compound and can still see stains below the polished aluminum. There like a brownish color.

I am using a loose 10" wheel for the final buffing.

How do I get the stains out prior to doing a final buffing?

Jrow

[mpierich Metal Finishing Guru Find all posts View Profile Close mpierich]

Dunno...got any pix? Sounds like you got to drop back a few steps. Re-work one small area where a stain is, experiment a little - did you do any sanding first?

[jrow Experienced Metal Finisher Find all posts View Profile Close jrow]

I started with 150 grit sandpaper, then went to 220, 320, and 600 grit wet and dry. Wet sanded it, and then went to sisel/emery. I then proceded to polish all the way up to tripoly/spiral. Found the brown spots and started again sanding with 220 grit ETC.

No pic's

John

[fxstcguy98 Amateur Metal Finisher Find all posts View Profile Close fxstcguy98]

ARE THE BROWN STREAKS LEFT THERE FROM THE POLISHING COMPOUNDS? IF SO, YOU NEED TO GET MORE HEAT IN IT WHEN YOUR BUFFING, SOMETIMES YOU MAY NEED TO PREHEAT THE PART TO 150 AND KEEP REHEATING IT AS NEEDED. MOVE SLOWER WITH THE WHEEL TO KEEP THE HEAT IN THE PART AND USE LESS COMPOUND APPLIED MORE OFTEN. A SISAL IS PRETTY AGGRESSIVE FOR ALUMINUM, TRY USING EMORY ON A SPIRAL SEWN.

[mpierich Metal Finishing Guru Find all posts View Profile Close mpierich]

I started with 150 grit sandpaper, then went to 220, 320, and 600 grit wet and dry. Wet sanded it, and then went to sisel/emery. I then proceded to polish all the way up to tripoly/spiral. Found the brown spots and started again sanding with 220 grit ETC.
No pic's
John

Well youcertainly went thru the paces pretty well. Only thing I can see is lke the man says maybe it's compound (try acetone or lacquer thinner as a last resort) - or, slight chance you "burnt" the material while buffing...but it shoulda come ou the 2nd time.

Guess there's a chance it's just a bad piece of metal with contaminates in it.

[jrow Experienced Metal Finisher Find all posts View Profile Close jrow]

I was wondering if it is some kind of chemical stain? I tried using some aluminum cleaner that they use on aircraft. You mix it with water. I may try to mix it a little stronger to see if that will remove the stains.

Anyone got any ideas on a product that will remove chemical stains?

John

[mpierich Metal Finishing Guru Find all posts View Profile Close mpierich]

I was wondering if it is some kind of chemical stain? I tried using some aluminum cleaner that they use on aircraft. You mix it with water. I may try to mix it a little stronger to see if that will remove the stains.
Anyone got any ideas on a product that will remove chemical stains?
John

If it was a surface stain, I feel you would've gotten rid of it with all the sanding and polishing.

I have heard of a set of aluminum S&S engine cases turning brownish/gold color but I forget what they decided caused it.