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Pit left on the electropolished surface

Houston, we have a problem. We did electropolishing on 316L Vim/var material (after hand-polish). We even used diamond paste to do manual pre-polishing. After EP, we found pits on the surface. We get darker finish some time. We can change the duration of EP (20 seconds only). Could you give us some clues? The polished surface gets even worse after "diamond" paste - polishing.

Liu Song Yun
Compart manufacturing company - GuangDong, China
2006

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It is very common in electropolishing that the parts will pit or etch if it is not done quite correctly. The parts must be properly clean, there must not be excess water in the solution, and the current density must be high enough to get out of the "etching range" and into the "polishing range", as three quick examples of things that cause problems.

The best readily available book on electropolishing is the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] , but you could try to contact AESF (www.nasf.org) about whether they have any copies left of their "Illustrated Lecture on Electropolishing".

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006