Letter 3067

yellow fingerprint stains on zinc + clear chromate 

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A question about plating zinc + clear chromate on mild steel... Our plater ships us parts with zinc + clear chromate. If we handle them with bare hands, we leave yellow fingerprint stains. Our customer will not accept this condition. The plater doesn't know what he is doing wrong. Can anyone explain how to correct this problem. thank-you mda

mark d. anderson
- mequon, wi

The plater isn't doing anything wrong. Wear light cotton gloves when handling the parts and this will prevent the sweat attacking the surface. If your supplier can't answer this it you have to ask if he really understands his process and that should start some alarm bells ringing in your head.

Dougie Lightfoot
- Fife, Scotland

Sweat and finger oils are quite corrosive. Your plater is not necessarily doing anything wrong. We found out that one kind of hand lotion would strip yellow or OD chromate which are a lot more resistant than clear by at least an order of magnitude.(in seconds)

I would contact the American Zinc Assn in Washington DC to see what their thoughts were for improving the situation. Alternative would be to contact a major supplier of zinc plating /chromating materials. The chromate is really a gell for up to 24 hours. Any contact prior to that is begging for trouble. One answer is to have your people wear clean gloves until you find a cure or at least an improvement.

James Watts
- FL

There is apparently some anecdotal evidence that people who handle chromated parts are subject to an increased incidence of skin cancer. I have no information to offer either in support of this hypothesis or in refutation of it. However, considering this possibility, plus the very evident reaction between their skin and the chromated surface, and the fact that it is causing rejects, it indeed seems only reasonable that the handlers should wear cotton gloves.

 
Ted Mooney - finishing.com - Brick, NJ

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