Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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4. Cost of control and maintenance. Some high-speed and high-efficiency baths require almost constant attendance and analysis. 5. Cost of longevity of the bath. High-speed and especially high-purity baths with good drag-out recovery must be changed periodically to maintain puri- ty. This results in a certain loss on changeover. 6.Cost of money (interest) to keep the bath. 7. Initial cost of the equipment. 8. Overhead cost of the equipment (whether it is operating or not operating), that is, the interest cost per hour or per day. Sometimes, a simple manual rack or barrel method will be cost-effective; at other times, a high-speed fully automated plant is justified. Gold today is a freely traded commodity with a different price every day. To plate suc- cessfully it is necessary to watch and control costs. DECORATIVE GOLD PLATING (CLASSES A-C AND, SOMETIMES, G) Much, but not all, decorative plating is applied to jewelry, watch attachments, and other items of personal use and adornment. The thicknesses of gold or gold alloy are usually 0.000002 to 0.000005 in. and the time of plating is 5 to 30 sec. The rec- ommended trade practice rules for the jewelry industry require that this deposit be called gold flash or gold wash. (To be called gold electroplate it is necessary to have a minimum of 0.000007 in.) These deposits are usually applied over a bright nick- el underplate and are bright as plated. They do not require any brightening or grain-refining agents. There are hundreds of different colors and hues, but the Class A and B baths, shown in Table I, will give a representative sample of colors. All of the "coloring" baths in Table I should use 316 stainless steel anodes. The ratio of anode to cathode area is best at 1:1 or 3:1. Very high ratios, when the tank is used as an anode, tend to give an uneven color and thickness of deposit, and the end pieces will frequently burn. No agitation should be used to ensure a uniform color. Sliding or tapping on the cathode bar will increase the deposition of gold and make each color richer but will quickly deplete gold and unbalance the bath. Gold and alloying metals should be added periodically, based on ampere-hour (A-hr) meter readings. The baths, with the exception of the white, green, and rose solutions, should operate at approximately 6% cathode current efficiency. Every 11 A-hr of oper- ation 5 g of gold should be added, together with the proper amount of alloy. All operating conditions should be controlled as closely as possible. Any variation of the conditions will affect the cathode current efficiency of the gold or the alloy, or both. Changes in the amount of the metals deposited will change the color of the deposit. Other factors that will alter the color of the deposit are the following: 1. Surface finish. The surface finish of the basis metal will change the appar- ent color of the deposit. This is particularly noticeable when a single item has both bright and textured areas. Plated in the same bath, they will appear to be two different colors. 2. Color of basis metal. The color of the basis metal alters the color of the gold deposit by adding its color to the gold until the deposit is sufficiently thick to obscure the base. Most gold alloy deposits, if properly applied, will obscure the base after 2 millionths of an in. have been applied. Proprietary additives will allow the gold to obscure the base with as lit- tle as 1 ½ millionth of an in. to allow richer colors with the use of less gold. 212

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