Letter 29013

Cadmium Plating vs. Magnetism  

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We manufacture solenoids for a line of valves for the semiconductor industry. Currently, we are using a black oxide finish on all the magnetic parts. This finish tends to corrode easily in the harsh environments these valves see. Could we use, say, a gold cadmium plate finish to provide better corrosion resistance w/o effecting the magnet properties of the steel parts?

Jeff Schwenk
solenoid mfgr - Laguna Hills, CA, USA

This question is multi-faceted. Yes, you could electroplate the solenoids, although it will add a couple to a few ten-thousandths of an inch to the dimensions. The effect on magnetism should be minimal; i.e., it doesn't change the magnetism, but it does keep other things a few ten-thousandths of an inch away from the magnetic surface.

Some plating baths have filters and some, including cadmium, often don't. But good anode bags and efficient filters are extra important when you put a magnetic object into solution.

Cadmium is no longer commonly and casually plated because it is a cumulative toxin. You probably should be thinking of a zinc alloy plating (zinc-nickel, zinc-iron, zinc-cobalt, tin-zinc) or even electroless nickel.

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

I AGREE WITH TED REGARDING THE MAGNET PROPERTIES. SOME OF THE ZINC ALLOY SYSTEMS THAT TED MENTIONS MAY BE TOO EXPENSIVE OR MAY JUST BE OVERKILL. TODAY THERE IS AVAILABLE TRIVALENT CHROMATES FOR ZINC PLATING BATHS. OUR TESTING ON 1010 PANELS IN ACCORDANCE WITH ASTM B-117 [link is to spec at TechStreet] NEUTRAL SALT SPRAY OFFERED RESISTANT UP TO 150 HRS. TO WHITE RUST (CORROSION) AND 264 HRS. TO RED RUST.THIS WAS AT A THICKNESS OF .0002 MIN. OF ZINC FOLLOWED BY THE BRIGHT BLUE/CLEAR TRIVALENT CHROMATE.THIS CHROMATE ALSO ELIMINATES THE ENVIRONMENTAL CONCERNS ASSOCIATED WITH TOXIC HEXAVALENT CHROMATES, WHILE MEETING THE AUTOMOTIVE AND EUROPEAN DIRECTIVES TO ELIMINATE HEXAVALENT CHROME.

AS AN ASIDE THE HIGH CORROSION RESISTANT IS NOT AFFECTED BY TRADITIONAL BAKING CYCLES IF REQUIRED, AND OTHER EXPOSURES TO HEAT ASSOCIATED WITH CURING PROCESSES TYPICAL IN PAINTS, POWDER COATS AND RUBBER MOLDING, AS WELL AS SERVICE CONDITIONS. THE ONLY QUESTION HERE IS AND TED HAS ADDRESSED THIS BEFORE THE THE COLOR OF THE CHROMATE IS CONSIDERED CLEAR. SOME HEADWAY IS BEING MADE TO PROVIDE A YELLOW TO WORK WITH THE TRIVALENT CHROMATE.

MICHAEL SWASKO
PLATING AND ANODIZING - CICERO, IL, USA

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