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Parts seem to be getting scratched and pitted during electropolishing

I am having problems after electropolish with the parts looking scratched and pitted. I mechanically polish the parts well under 10 Ra, sometimes as low as 2 or 4 Ra, but they return electropolished visually poor. I have no control over the electro-polish process; is there any thing I can use that wil greatly enhance the visual appearance before electropolish to insure that they look good after electropolish? We are a small shop, and we are polishing 180 degree outleted U-Bends and having trouble at it. Any help would be appreciated. Any sugestions for compounds would be nice as well. I use a slow, non-rigid machine to mechanically polish to 180 degree bend, so any tips on that would be great as well. Thanks.......

Mike Cochara
- Springfield, Missouri
1998

Mike:

There are a number of factors other than the electropolishing bath which could be causing this problem. These factors include the metal substrate, the tube bending method, the mechanical polishing process, and the cleaning/descaling prior to electropolishing.

It sound as though the only one under your direct control is the mechanical grinding. You should be careful how you produce the low Ra readings. Any method which smears the surface and traps contaminants can cause the Ra to appear worse after electropolishing.

Ed Bayha
Metal Coating Process Corporation - Charlotte, North Carolina
1997

In order to eliminate the pitting during electropolishing of stainless steels, it is extremely important to control the chloride content in the bath as low as possible. It is therefore helpful to have D.I. water rinse immediately prior to electropolishing. Temperature and power are also important factors influencing the pitting generation.

Ling Hao
- Grand Rapids, Michigan
1998