Metal Finishing Guide Book

2012-2013

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during normal plating operations. Because nickel plating is highly efficient, hydrogen damage is unlikely to occur as a result of nickel plating per se. The pretreatment of steel prior to plating, however, may require exposing the steel to acids and alkalies. During these operations, excessive amounts of hydrogen may evolve which may damage steels susceptible to hydrogen embrittlement. Steels that are susceptible to hydrogen embrittlement should be heat treated to remove hydrogen. The time required may vary from 8 to 24 hr depending on the type of steel and the amount of hydrogen to be removed. The temperature is of the order of 205��C (400��F), and the exact temperature may be alloy dependent. Fig. 5. Effect of temperature on the tensile strength, yield strength, and elongation of electrodeposited nickel. NICKEL ELECTROFORMING Nickel electroforming is electrodeposition applied to the production of metal products. It involves the production or reproduction of products by electroplating onto a mandrel that is subsequently separated from the deposit. It is an extremely useful technology that continues to grow in importance. Conventional Processes The composition, operating conditions, and mechanical properties of deposits from the electrolytes most often used for electroforming (Watts nickel and conventional sulfamate) are given in Table III. Nickel sulfamate solutions are the most popular because the deposits are low in stress, high rates of deposition are possible, and the thickness of the deposit is less affected by variations in current densities than are deposits from Watts solutions. By maintaining the solution as pure as possible and the chloride as low as possible, the internal stress of the nickel sulfamate deposits can be kept close to zero. Watts solutions are very economical. High-Speed, Low-Stress Process A concentrated nickel sulfamate solution has been recommended for electroforming at high rates and at low stress levels in deposits that do not use organic stress reducers, which would introduce sulfur. The solution has a nickel sulfamate concentration of 550 to 650 g/L, a nickel chloride concentration of 5 to 15 g/L, and 343

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