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Question about NaOH attack

We have a few work pieces in the shop that NaOH stripper attacks in strange ways. The alloys attacked were 300 and 4340. pH level was fine. The current was the right amount. Any suggestion to improve the process is greatly appreciated.

A. Durmeyer
Plating Shop - Atlanta, GA, USA
2007

You probably posted your inquiry while reviewing a related thread, A., but we are missing some of the context that you were looking at. I'm guessing that you are talking about stripping of hard chrome from a workpiece?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

If you are talking about stripping chrome, the process has to be monitored because when the chrome is gone it starts attacking the base metal, normally pits.

James Watts
- Navarre, Florida
2007

2007

Ted,

Yes, it is for hard chrome stripping. The NaOH attack I am talking about happened like this:
The strip solution leaves a swirly pattern on the work piece while stripping. Tried to brush it off w/ scotchbrite a few spots came off but still have swirly patterns on the work piece.

We didn't have this problem before. I did search thru the archive but couldn't find any thing that relates to the situation we have. We checked the voltage, dumped the solution and prep a new tank. We have been performing weekly analysis as well and found the solution to be within the spec. Normally we mask the areas of the workpiece with high temp wax (Miccro Wax). But we are seeing some workpieces (such as bushing) attacked are not even masked w/ the wax at all.

The alloys attacked are high strength low alloys Fe based wroght alloys (AISI 4340)(Journals, pistons) and CRES Austentic iron base alloys (300 series).

It has been an on-going nuisance for past 6 weeks.
Any thoughts?

James,

yes the process is monitored. As mentioned before we never had this prob. previously.

A. Durmeyer
Engineering - Atlanta, GA, USA

Could you have chloride contamination that crept in somehow? All it takes is a trace.

Dave Wichern
Consultant - The Bronx, New York
2007

David,
Could it be the rack causing the problem? We dumped the bath and refilled the tank up. Still seeing some prob.

A. Durmeyer
- ATL, GA, USA
2007

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