Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 231 of 707

ful technology that contin- ues 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 conven- tional sulfamate) are given in Table III. Nickel sulfamate solutions are the most popu- lar 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 solu- tions. 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. Fig. 5. Effect of temperature on the tensile strength, yield strength, and elongation of electrodeposited nickel. A concentrated nickel sulfa- mate solution has been rec- High-Speed, Low-Stress Process ommended 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 concentra- tion of 5 to 15 g/L, and a boric acid concentration of 30 to 40 g/L. It is operated at a pH of 4.0, a temperature of 140 to 160° as high as 800 A/ft2 F (60 to 71° C) and at current densities . The high rates of plating are made possible by the high nick- el concentration. When the bath is properly conditioned and operated, it is pos- sible to control internal stress at or close to zero because of the interrelations of stress, current density, and solution temperature (Table VI). After purification with carbon to remove all organic contaminants, the con- centrated solution is given a preliminary electrolytic conditioning treatment consisting of (1) electrolysis at 0.5 A/dm2 A-hr/L; (2) electrolysis at 0.5 A/dm2 on both anode and cathode for up to 10 on the anode and at 4.0 A/dm2 and at 60O on the cath- ode for up to 30 A-hr/L of solution. For this conditioning treatment, the anode must be nonactivated (sulfur-free). A corrugated steel sheet may be used as the cath- ode. When the solution has been conditioned, a deposit at a current density of 5 A/dm2 C should be lustrous and the internal stress as determined with a spiral contractometer or other device should be 48 ± 14 MPa (7,000 ± 2,000 230

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