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January 18, 2013
Q. I am interested in good coatings for sheet metal screws. The application for the screws are to build an electrical unit. The sheet metal parts are then grounded properly. The coating for the screws is black for cosmetic reasons.
What I have been finding is now that everyone has gone RoHS we are having grounding issues.
What is a good conducting coating for this application?
Manfacturing Engineer - Franklin Park, Illinois, USA
A. I think you should check with your supplier to see what they were using before, and what they changed to now.
I think you need to include more information before anyone can give a proper answer.
- Everett, Washington, USA
March 23, 2013
A. Hi. Sameer proposes a good course of action consisting of finding out what changed in detail and relaying it to us, but the general situation is that your problem is not unusual. In an effort to get their trivalent chromates to match the corrosion resistance of hexavalent chromates, many suppliers have added topcoats to the trivalent process which do not exhibit the same surface conductivity as hexavalent chromate. Another possibility is that you were formerly using a silver-bearing black hexavalent chromate. If you are free to change the coating from black to clear, the solution will probably be easier. Alternatives like black nickel plating may have the conductivity you seek, but would be much more expensive and possibly unsatisfactory in other ways.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey