October 17, 2017

Nickel Plating Maintenance

In nickel plating maintenance of a steady, but very slight acidity is most important. Satisfactory nickel plate can only be obtained in the pH 5.2 to 5.8. The pH value of the nickel plating solution tends to rise slowly in use, due to a small proportion of current discharging hydrogen ions rather than nickel ions, especially at lower pH values of the solution, and must be adjusted from time to time by adding sulfuric acid, or alternatively, if it has become too acid, by adding nickel carbonate. The presence of the boric acid in the solution ensures that these changes of pH value are less sudden than would otherwise be the case.

The nickel plating solution is held in an open topped, lead lined or hard rubber lined tank. The solution is heated by immersed steam coils or electric heaters, or in some other way. A temperature of at least 35 oC is usual, but because higher current densities, and hence faster electroplating, can be achieved at higher temperatures, the bath are often operated at temperature up to 65 oC or 70 oC. The plating solution is stirred or agitated, usually by compressed air, which is blown in through a perforated pipe on the floor of the tank.

The tank is provided with a central metal rod at the top, from which the articles to be plated can be hung by the wires or jigs on to which they were fixed prior to de-greasing. This rod is connected to the negative side of the low voltage direct current supply. Similar rods are arrange a long two opposite sides of the tank, and are connected to the positive side of the current supply. On these the nickel anodes are hung by metal hooks. Nickel anodes are usually cast with some care from metal containing oxide and other trace elements to facilitate their dissolution, and these are called depolarized anodes. Nickel (and other electroplating) anodes are therefore enclosed in heavy cotton twill bags. The electric current and the solution can percolate through the fabric, but the particles are retained. It is nevertheless quite common for nickel plating solutions to be filtered continuously, or from time to time.

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