Metal finishing Q&As since 1989

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Electropolishing

2000

Regarding electropolishing, can anybody tell me if its the configuration of parts within an electrolyte, and the configuration of the part itself(shape/dimension) can have an impact on the current density seen by the part, and the results?

Reason for asking is that in electropolishing type 416 parts in the hardened and tempered condition, some areas looked pitted or frosted, and others look perfect.

Thanks

Mike Gootman
- Colmar, Pennsylvania, USA

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First of two simultaneous responses--

Mike:

Faraday's Law of Electrolysis, as usual, is inviolate. The problem is with your electropolisher. 400 series, with its low chromium content, will EP, but must be done carefully at lower voltage and time than 300 series alloys. It will have a matte, uniform appearance when done correctly. Dan Weaver

Dan Weaver
- Toccoa, Georgia
2000

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Second of two simultaneous responses-- 2000

Yeap!

Electropolishing, is basically the same as electroplating in reverse.

If your part is irregularly shaped it will have uneven current density. Edges closer to the electrode will get current concentration effects, and resses further away from the electrode will have less current per area.

That's the generalities for specific info' you need an expert in your area.

Ian Brooke
university - Glasgow, Scotland

Hello, Mike:

The above comments about current density and Michael Faraday are essentially true, but the problem may be elsewhere if the pitting comes and goes for no apparent reason. The cause may be in the heat treating or in one of the other mechanical or chemical processing steps. There are specific electrolytes for 400 series alloys, and there are also specific control procedures that must be maintained for best results.

Our company offers a complete consulting/trouble-shooting service for electropolishing. You can contact us via our listing in the Supplier Guide on this web site.

Ed Bayha
Metal Coating Process Corporation - Charlotte, North Carolina
2000

Mike

Ep is the same as electroplating. as with most reverse type of processes (parts are anodes) it seems to be more forgiving, In my experience, if the pitting is in the HCD or at top or bottom of rack is sometimes too high current but by the same token (400 type materials)one rack looks great and the next is not could be a variance of the material, as mention earlier 400 sst is more tricker,

Also found that the "brightener", type of "cathode" and amount of contaminates, really makes a difference it the way the bath will attact the material

Chris Snyder
plater - Charlotte, North Carolina
2000