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Differences between black ox and black zinc trivalent


I have a customer that I am looking to switch from a black oxide coated screw to a black zinc trivalent, but they did to see some sort of data sheet that shows the difference between the 2 finishes. Also, they are asking if black zinc trivalent will react negatively with plastic, as this is the material these screws are being placed into. Can someone point me in the right direction to locate some information?

best regards,

Gary Davis
sales person for a fastener distributor - Norcross, Georgia, USA


Black oxide has little if any corrosion resistance and the only protection is provided by the oil that is on it. Black trivalent chrome is in reality black zinc plating so you have lots more corrosion protection and very little chance for reaction with plastic. If anything to watch for it would be the build-up of the zinc plating - it's substantiallly more than black oxide which is nearly nil. Also, my experience with black trivalents products is that by themselves they are blotchy and not very eye appealing. To overcome this applicators of black trivalent typically apply an organic sealer - wax or lacquer based - which if you have electrical requirements (not likely if this is going into plastic) you've now lost conductivity. Bottom line - black trivalent is better and you should charge more! At least make your customer aware of upgrading their value without a cost impact.

Milt Stevenson, Jr.
Syracuse, New York

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