Electropolishing and Rinsing

Q. Our company specializes in the electropolishing of stainless steel. We continually have a problem with staining after the final rinse step. Our rinsing does not seem to remove the entire residue from the electropolishing process. The sequence we are currently using is as follows: electropolish, recovery rinse tank, power rinse at approximately 125 psi. Do you have any suggestions as to what we should do to eliminate the staining? P. C.

 

A. Your problem is a classic example of not having adequate rinsing available after your process step. The electropolishing solution is quite viscous and because of this, additional rinsing is required. I would recommend a sequence as follows:

1. A recovery rinse
2. An immersion rinse
3. A neutralization rinse (3–5 ounces per gallon of sodium carbonate in water)
4. A power rinse

 

Step 3 should neutralize any of the viscous acid mixture remaining on the surface.

In a PF Plating Clinic column written by Larry Durney a number of years ago, two other suggestions were discussed. One uses a dilute nitric acid dip instead of the sodium carbonate rinse. The other was to turn off the current a few minutes before taking the parts out of the electropolishing tank.

I am sure one of these suggestions will solve your problem.