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Best cleaning method for aluminum to be anodized


We have some aluminum parts that we machine here at our factory and then clean and ship off to get black anodized. Some recent batches of these parts have been coming back with the anodizing flaking off. My question is this - what is the best method for us to use to clean these parts post-machining to avoid this flaking problem? Or could this be a problem with the platers, and not our cleaning?

Brendan Bagwell
- Tucson, Arizona

First of two simultaneous responses -- 2002

You should not have sharp corners on your parts because anodizing will not be able to protect sharp corners--it will break off. That having been said, it is the anodizer's responsibility that the anodizing not flake off. Certainly the anodizer has every right and reason to be curious about your precleaning process though, and to insist on stability in it.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Second of two simultaneous responses -- 2002

The problem is at the "platers". It is his responsibility to (1) remove the organic soil burned on by your machining operations, (2) remove the inorganic oxides left on the surface, and (3) anodize in a 15%/wt (12 fl oz/gal)of 66 degree baumé sulfuric acid clean contamination free anodizing solution containing less than 12 gm/L of dissolved aluminum at the proper voltage and current for the particular alloy ! If he cannot do it, then get another anodizer.? Set up your own?

robert probert

Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina



You say: "Some recent batches of these parts have been coming back with the anodizing flaking off". If I do understand well, that means that the problem just arose recently. In this case you should first find out if you have introduced any changes to your process (ex. Coolant, machining oil, etc). If not, then, and if you were using the same vendor, ask the anodizer if he made any changes to his process (ex. Vapor degreaser, Cleaner, etc). It might just be that you have changed your coolant but neglected to change the cleaner (degreaser) in your shop. Even though, I agree with Robert, that it is the anodizer's responsibility to clean the parts, it is your duty to report to the finisher any changes of coolant so that he can choose the appropriate cleaner or elect to not do the job.

Hocine Djellab
anodizing shop - Verdun, Quebec, Canada

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