More Efficient Zinc-Nickel Plating

Zinc-nickel coatings are well-known for their corrosion-protection properties, but the electroplating process typically used to apply them is fairly inefficient, thanks in great part to the breakdown products it produces.

Coventya has come up with a more efficient and “cleaner” zinc-nickel process that minimizes the amount of breakdown. The company’s patented Selective Separative System (3S) includes an inert micro-porous membrane in addition to an alkaline anolyte and a stainless steel anode, and this combination results in reduced cyanide generation and carbonate formation, as well as faster plating speed and less energy consumption.

“The biggest selling point is that you don’t have the cathode efficiency drop because of the anode breakdown products,” says Director of Business Development Greg Terrell.

With conventional zinc-nickel processes, only 50 to 60 percent of the applied current is used for metal deposition, and the rest is consumed in producing hydrogen and heat. With 3S, about 80 to 90 percent of the applied current is used for metal deposition. 

But different applicators have different priorities. “The cool thing about this technology is that there are multiple things it can accomplish and do,” Terrell says.

In the typical combination of electrolyte and anode, a chemical reaction causes cyanide and carbonate breakdown products. “Those breakdown products contribute to the loss of cathode efficiency,” he says, “but they also essentially poison the bath over time.”

A plater in California, for example, might be using zinc-nickel in place of cadmium to plate connectors and doesn’t want cyanide in the effluent. “They don’t care so much about improved efficiency; they just don’t want cyanide,” he says.

Or perhaps a rack applicator has to repeatedly shut down its zinc-nickel lines to freeze out and filter the buildup of carbonates. The 3S configuration eliminates that problem. “Separating the anode from the plating bath with the membrane prevents those breakdown products from forming,” he says. 

The very fine, porous membrane isn’t permeable to large molecules and also prevents the oxidation of organic compounds, therefore minimizing carbonate formation as well as reducing the consumption of organic additives.

“You use about 20 percent less proprietary additives,” Terrell says,” and therefore there’s also less waste treatment.”

In the end, however, all of the benefits circle back to improved cathode efficiency, including increased throughput. “Greater than 80-percent efficiency for the applicator equates to tons per hour,” Terrell points out. “If you’ve got 40 percent more cathode efficiency, you’re going to plate 40 percent more work in the same amount of time.”

The 3S technology has been in use in Europe and Asia for at least six or seven years with 60+ installations, and Coventya now is growing it in the North American market for use with its Performa line of alkaline zinc-nickel products. The company currently has four U.S. installations.

Coventya / Brooklyn Heights, Ohio
216-351-1500 / coventya.com

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