Metal Finishing Guide Book

2013

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plating processes, procedures & solutions GOLD PLATING BY ALFRED M. WEISBERG TECHNIC INC., PROVIDENCE, R.I.; WWW.TECHNIC.COM All types of gold and gold alloy electroplates are used for many different applications by many different industries; however, there are eight general classes that may be listed that include much of present-day gold plating: Class A—Decorative 24K gold flash (2-4 millionths of an in.), rack and barrel. Class B—Decorative gold alloy (2-4 millionths of an in.), rack and barrel. Class C—Decorative gold alloy, heavy (20-over 400 millionths of an in.), rack. These deposits may be either C-1 karat color or C-2 karat assay. Class D—Industrial/electronic high-purity soft gold (20-200 millionths of an in.), rack, barrel, and selective. Class E—Industrial/electronic hard, bright, heavy 99.5% gold (20-200 millionths of an in.), rack, barrel, and selective. Class F—Industrial/electronic gold alloy, heavy (20-over 400 millionths of an in.), rack and selective. Class G—Refinishing, repair and general, pure, and bright alloy (5-40 millionths of an in.), rack and selective brush. Class H—Miscellaneous, including electroforming of gold and gold alloys, statuary and architectural, etc. To further simplify an enormous and diverse subject, gold and gold alloy plating solutions may be considered to belong to five general groups: Group 1—Alkaline gold cyanide for gold and gold alloy plating; Classes A-D and occasionally F-H. Group 2—Neutral gold cyanide for high-purity gold plating; Classes D and G. Group 3—Acid gold cyanide for bright, hard gold and gold alloy plating; occasionally Classes B, C, E-G. Group 4—Noncyanide, generally sulfite, for gold and gold alloy plating; occasionally Classes A-D and F-H. Group 5—Miscellaneous. There are literally hundreds of formulations within these five classes of gold plating solutions. Physical, engineering, or aesthetic considerations will determine which of these groups should be considered for a particular job, but economics will usually be the determining factor in selecting a specific formulation and plating method. The price of gold per troy ounce is only one aspect of the economics that must be considered in deciding among rack, barrel, brush, continuous, or selective plating. For any individual applications it is necessary to balance and optimize the following variables: 1. Cost of the bath. This includes the volume necessary for a particular method and the gold concentration. 2. Speed of plating.(This determines the size of the equipment) and the bath and the cost for a given desired production. 3. Cost of drag-out loss. This will depend on the gold concentration used; the shape of the part; whether it is rack, barrel, continuously, or selectively plated; and must include the probable recovery of dragged-out gold by electrolytic or ion-exchange recovery. 283

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