Where the
world gathers for metal finishing
Q&As since 1989


-----

Loss of material from stripping anodized coating

I had some aluminum (2024-t4) anodized and the parts came back dis-colored. They we sent back and stripped and anodized again. Now the parts are undersize and the holes are oversize. Are parts sent for re-anodizing stripped in an acid bath again? and could this cause loss of aluminum?

Thanks in advance,

James Kelly
Packaging equipment - RANDOLPH, Massachusetts
2003

---

Anodizing can be a great finish, but the problem you observed is inherent in the process. In a painting or plating process, a coating is added on top of the substrate, which can subsequently be stripped if necessary. But in anodizing, the aluminum in the aluminum oxide coating comes from the substrate. If you want the anodizing to be .002" thick, about .001" of aluminum is consumed in building the coating; when you strip the anodized coating, the part is smaller by that .001".

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

---

So.. just to answer your question, yes, the parts were stripped in either a caustic solution, or a chromic/nitric acid solution. If they were stripped in a caustic solution, you would most likely see more loss on your substrate. When I worked in a job shop, it was our policy to ask the customers about the tolerancing of their parts prior to stripping/reworking, to prevent the issue that you have encountered.

Marc Green
anodizer - Boise, Idaho
2003