Letter 41024

Electropolishing to remove "white layer" [Minnesota] 

June 6, 2006

I have large gears made from maraging steel 250 KSI and using WEDM to cut the teeth. The WEDM process leaves an unacceptable .0004 thick layer of untempered martensite that appears to be approx 60-65 Rc. I have tried different methods to remove this "white layer" but due to not being able to control dimensional changes once the martensite layer is penetrated, have stopped. I'm currently spending hours and hours hand polishing the gear teeth and would like to find a more controlled and less expensive solution.

Will electropolish or other finishing solution do the job?

Bill Moss
- Fridley, MN, USA

Bill, I'm not sure but what about a pickling agent to help clean the gear up?

Kevin W. Gallich
- Freemansburg, PA, USA

.0004" can be quickly and easily removed in an appropriate electropolishing solution composed of phosphoric and chromic acid.

Jeffrey Holmes, CEF - Spartanburg, SC, USA

I have not tried pickling, I didn't think it would penetrate that far. If it were to remove .0004 of the hard material, wouldn't it remove much more of the softer base material. Since this is a precision gear sector, consistent material removal is key. I will look into it though.
I thought of epolish but the problem is I can't find anyone local who will epolish carbon steel, I we don't want to set up tanks in our facility. Thanks,

Bill Moss
- Fridley, MN, USA

I agree, you don't want to set up electropolishing in-house. Too much investment and trouble. There are shops which EP carbon steel. Find a good one, communicate your needs clearly, and you'll solve your problem for a few dollars per part. If you're now spending hours hand polishing, the cost of shipping for electropolishing would be small by comparison. Please don't try acid pickling. You'll likely end up with hydrogen enbrittlement, a serious problem.

Jeffrey Holmes, CEF - Spartanburg, SC, USA

Don't mess with chemical methods, that`s not the way. Have them ground in a special gear grinder. Precise, controllable, able to cut through hard materials and leaves an even and quality looking surface finish.

Guillermo Marrufo
Monterrey, NL, Mexico

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