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Chemical polishing of aluminum wheels to reduce mechanical polishing
Q. I operate a one man powder coating shop and I have been getting a lot of requests to polish aluminum car wheels. I have tried manually polishing using a variety of buffers and polishers and I could not figure out a way to do it economically.
I have research automated wheel vibratory polishers and found a few that are offered for sale with an acceptable cycle time of approximately 4 hours total per wheel. However both vibratory polisher manufacturers state that the wheel must be pre sanded down to approximately 400 grit or the cycle time will become extremely long, about 18 hours to do the rough cut if I choose to have the machine do all the work.
My question is, is there a feasible way to chemically etch the wheel down to the 400 grit equivalent before hand. I have researched bright dipping and electropolishing but I cannot find any available information on how to apply these techniques to car wheels.
Would a simple solution of sodium hydroxide work in an immersion tank to smooth the wheel prior to placing in the vibratory system? Is there a more suitable chemical? Maybe using acid instead or alkali? I could really use some help here because my head has been spinning trying to find a way to do this without manually sanding car wheels.
Custom Powder Coater - Queens, New York, USA
March 26, 2012
A. Hi Mat.
Generally, electropolishing, chemical brightening, and indeed all chemical processes on aluminum work only on the aluminum portion, not the alloying materials. I hope someone can offer encouragement, but aluminum wheels are pressure diecastings full of all sorts of non-aluminum garbage, so I think mechanical polishing is more promising :-)
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 5, 2012
A. Usually the wheel is Al-Mg alloy, it can be polishing or etching by chemicals, it is easy to do so.
Denny Lee- Foshan City, China
April 13, 2012
i. Thanks, Denny. If it's easy, please give us a hint what Mat is doing wrong that is so time-consuming in his mechanical polishing, or what kind of process he can apply to do it chemically. Thanks again.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 14, 2012
A. Dear Ted,
Thanks for your reply. Maybe I had misunderstand Mat's meaning. You are right, for pressure castings, it is better to use machine polishing. Using acid is too much fume generating, not environment friendly, and the effect is not good.
- Foshan City, China
April 16, 2012
A. Many Aluminum alloy types electropolished well in "green" electrolytes, like our Universal electrolytes. Other alloy types require some modifications. Only testing can answer this questions. Contact us for test arrangement.
Anna Berkovich
Russamer Lab
Pittsburgh, Pennsylvania
April 16, 2012
A. Hi, Anna. Let us know if you enjoy success. As you say, only testing will answer the question; still, my understanding to date is that mechanical polishing is necessary for aluminum pressure castings.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 16, 2012
A. Ted,
Electropolishing Al-Mg alloy (and very low Si content) is no problem. However we will never achieve the same results as you can see on auto wheels (mechanical buffing).
Al-Cu alloy is indeed impossible for us to electropolish.
Anna Berkovich
Russamer Lab
Pittsburgh, Pennsylvania
April 19, 2012
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