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"Hazy" finish on burnished surface after electropolish

(-----) January 29, 2008

Hello, and thanks in advance for any help or suggestions.

I am having a problem with the finish on some of our parts coming out of the electropolish bath looking hazy. It's not an entire surface, just parts of it.

The parts are made out of 316L SSTL, and the parts that look hazy after happened to be parts that were burnished before the EP.

We are using a purchased EP solution that contains sulfuric and phosphoric mix in water.

Currently the parts are only processed in batches of four and the parts are only about the size of a small lego block (about 1 inch x 1/2 inch x 1/4 inch).

Our EP tank contains 50 gallons of solution and the parts are run on 24 volts and 380 Amps for 6 seconds.

I know that the way we clean the parts needs to involve a better rinsing practice, but could this be contributing to the haziness problem?

We are thinking another possible reason for the haziness could be the burnishing pushing over small peaks and then stretching them out (making them extremely brittle), then in the EP process those brittle peaks are being totally processed off exposing the not burnished area. Could this be a factor?

Thanks again!

Angie Wicklund
- Sauk Rapids, MN, USA

February 1, 2008

Your amperage is extraordinarily high, and your time exceptionally short. Most folks using a sulfuric-phosphoric EP solution use parameters something like these -

Temp, 90-120F, 100-150 amps/sq.ft, 1 to 10 minutes.

There is a common problem with electropolishing T316 wherein you get micro etching on the "end" surfaces, i.e., on the surfaces which are cut across the rolling direction of the bar stock. If this is the case, expect to see the condition on two opposite faces, and not on the other four faces. The only solution to this problem is to mimize the amount of electropolishing - shorter time, lower amperage.

The problem may come and go as you change from one lot (or supplier) of raw material to another.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

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