Letter 37047

Grounding issues on crs / clear zinc plated power supplies  

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We are having grounding issues on crs / clear zinc plated power supplies.

Our customer is finding issues grounding sheet metal parts that we supply that have been clear zinc plated.
The thicness call out is 200 microinchss or .0002 .0005 thickness

Any ideas why?

Seems an on and off again situation.

Sean Halloran
KAL Tool - Webster, NY

You need a clear and detailed specification for your plating, especially in these days where shops are rapidly getting rid of hexavalent chromates and substituting in their place trivalent chromates that need post treatments to offer similar corrosion resistance. The post treatment may be a wax or a lacquer or another top coat that interferes with conductivity. How do you spec the plating to insure that the plating shop knows your requirements?

Ted Mooney, P.E.  finishing.com Brick, New Jersey

We are using Trivalent.

Grounding Issue:
When using the parts, a formed tin plated copper ground clip is held against the inside of each part. During test it was found that some of the parts grounded very well and some did not ground at all. Further analysis showed that there were two sources of supply for the parts and each used a different zinc plating and chromate. One company used an automated zinc plating system that utilized acidic baths for the zinc plating while the other company utilized a manual alkaline system. We found that the alkaline system parts worked and the acidic process parts did not.

Spec:
FINISH: ZINC PLATE(alkaline process only) per ASTM B-633 [link is to spec at TechStreet], 200 MICROINCHES MIN. With Type III CLEAR TRIVALENT CHROMATE COATING.

Sean Halloran
KAL Tool & Die Co. Inc. - Webster, NY

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