Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 223 of 707

Minutes for Obtaining Coating at Various Current Densities, A/ft2 Thickness, in. 0.0001 0.0002 0.0005 0.0008 0.0010 0.0015 0.0020 Thickness m Oz/ft2 2.5 5.1 12.7 20.3 25.4 38.1 50.8 0.0721 0.144 0.360 0.578 0.721 1.082 1.44 G/ft2 2.04 4.08 10.2 16.3 20.4 30.6 40.8 A-hr 1.99 3.98 9.95 15.9 19.9 29.8 39.8 10 20 50 100 12 24 60 96 6 2.5 1.2 12 5 119 60 24 12 179 89 36 18 238 119 48 24 Table I. Data Sheet on Depositing Nickel (Based on 96.5% Cathode Efficiency) imum coating thickness values at specified points on the surface. The amount of met- al that deposits on the surface of any object being plated is proportional to the cur- rent that reaches the surface. Recessed areas on the surface receive less current. The current density and, consequently, the rate of metal deposition in the recessed area are lower than at points that project from the surface. The electrodeposited coat- ing is relatively thin in recessed areas and relatively thick on projecting areas (Fig. 1). The thickness of the deposit at the cathode and the distribution of the coating can be controlled by proper racking and placement of the parts in solution, and by the use of thieves, shields, and auxiliary anodes. Parts can be designed to min- imize problems. It may be necessary to deposit more nickel than is specified to meet a minimum thickness requirement on a specific article. The nickel processes used for decorative, engineering and electroforming purposes have the same electrochemical reaction. The weight of nickel deposited at the cath- ode is controlled by natural laws that make it possible to estimate the thickness of the nickel deposited. These estimates must be adjusted to account for variations in cathode efficiencies for specific processes. Normally, cathode efficiency values are between 93% and 97% for most nickel processes. Some of the so-called "fast" bright nickel-plating processes may have lower efficiencies. The actual thickness at any point on a shaped article depends on current flow. In practice, it is necessary to measure coating thickness on actual parts and make necessary adjustments to racks, thieves, Multiply Wt. of NiSO4 7H2 Wt. of NiSO46H2 Wt. of NiCl2 6H2 Wt. of NiCl26H2 O O O O Wt. of nickel carbonate A-hr/ft2 nickel plating Mil thickness By 21% 22% 25% 30% 50% 1.095 0.0386 0.00086 19.19 1151 0.0226 0.742 To Estimate Wt. of nickel contained Wt. of nickel contained Wt. of nickel contained Wt. of chloride contained Wt. of nickel contained g nickel deposited oz nickel deposited mil. of nickel deposited A-hr/ft2 A-min/ft2 g/cm2 oz/ft2 Table II. Factors Useful in Making Plating Calculations (Assumes 100% Cathode Efficiency) 222 2.4 30 12 6 48 19 9.6

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