Metal finishing Q&As since 1989

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Trying electropolishing but nothing happens

2003

Sir,

We are looking to manufacture Stainless steel fasteners from grade 304 SS. We tried the electropolishing process whereby we made an electrolyte of sulfuric acid and phosphoric acid with anode as the sample piece and cathode as a copper conductor. We subjected it to 12 v DC current but nothing happened even after 20 mins of process.

Kindly suggest as to what should be done.

Shashank Jain
Manufacturers - Meerut, UP, India

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2003

Most of the "must have" metal finishing books include a chapter on electropolishing, including ASM Metals Handbook, The Metal Finishing Guidebook, and the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon] . As a starting position to point you in the right direction, do you have any of these?

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

One item to consider is that you are operating in the correct cathode current density range. We electropolish 300 series stainless steel and operate at a current density range of 50-100 ASF (amps per square foot). If the current density falls below 50 ASF, the finish is dull and etched appearing. Hope this helps.

Thomas Kemp
- Erie, Pennsylvania, USA
2003

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2003

20 minutes of EP should show an extreme eat-away of your workpiece. Do the anodes & cathodes even gas during your process? They should gas like H@#!. A rough, rough, very rough estimate for 316SS EP bath electrical characteristics is that 7 square inches of polishing surface is equivalent to a 1 OHM resistor for a room temperature, anhydrous, standard bath @ 300 ASF steady state. So 15 volts get you (very roughly)15 amps and lots of gassing. Run this experiment and report back your results. When you run this test, make a 7 square inch workpiece by masking off a larger piece, then you can compare the polished surface to the unpolished. And be sure to clamp it hard, because contact resistance between the workpiece & wire can be substantial.

Dave Kinghorn
Chemical Engineer
SUNNYvale, California