removing aluminum anodizing
Thanks Joe for the details.
Have you worked in the plating industry.
I worked for a electronics connector company and all our parts were plated to mil spec. Usually electroless nickel over a beryllium copper or brass part. Are parts were machined to a "pre plated" spec. Especially threads. We did see variance in plating thickness. And also the hardness or resistance to flaking when are part was swaged or rolled crimped after plating for assembly.
Yeah, I worked in anodizing in college. We did mil-spec anodizing, but we were mostly a job shop.
Anodizing has good "throwing" power so it tends to build quite evenly. I can't remember exactly how far into a hole anodizing will throw, I think it was 1/2 the diameter but don't quote me. It does throw a LOT farther than chrome though. Since anodize is a dielectric, as the coating builds the current is always looking for the easiest path, thus the part that build the fastest builds resistance to current and the current has to go to an area of the part farther from the cathode. Thus, even with intricately machined parts you get a pretty uniform coating. This compares to Hard Chrome, as the chrome builds it just keeps conducting electricity, this forces some parts to be chromed to a ridiculous thickness and then machined down. With metal plating were you are placing a conductive coating on a part it is much harder to get a uniform plating thickness.
If the anodizer knows what they are doing they can accurately predict the build and keep the part within spec. I had a customer who was complaining about the thickness of our hard anodize on a part that was to receive a pressed in bushing. We were holding our thickness to about 2/10,000 of an inch. But some parts were loose and some too tight. Turned out his machining was off and his boring bar couldn't hold the tolerance, or I should say his machinists couldn't bore to the correct diameter. He was cool about it and apologized and thanked me for helping him find the problem. On parts with male threads anodize is typically not a problem since the coating is so uniform, assuming the machinist allows for the build up of around 2 thousandths of an inch. For anything larger than 3/8 it typically wasn't a problem. Now for screw holes especially small ones we might have to mask the threads because although it throws well it only throws well to about 1/2 the diameter of the hole. So small deep screw holes would need to be masked with nylon screws.
As far as hardness, anodize, especially hard anodize is VERY hard, it is harder than case hardened steel, but it is generally only a couple of thousandths of an inch thick. We had a bunch of tests that parts were subjected to in order to meet the hardness standard but I can't remember exactly what they were.
Anodize is a great coating. Just look at your shower door, those things last forever. Sure you might be rocking a 70s era shower door but as long as you don't use toilet bowl cleaner on it, it probably looks great.
Regards,
Joe Dokes