Metal Finishing Guide Book

2013

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plating processes, procedures & solutions ZINC PLATING BY CLIFF BIDDULPH AND MICHAEL MARZANO PAVCO INC., CLEVELAND; WWW.PAVCO.COM The electroplater can achieve excellent results from bright zinc plating electrolytes when the baths are operated correctly. This article is designed to give quick reference to all vital data needed for optimum bath performance. Discussion has been kept to a minimum in favor of tables in an effort to convey more useful information in a simplified form. Present data concentrate on acid chloride zinc, alkaline non-cyanide zinc, and cyanide zinc baths. Typical bath compositions are given in Tables I and II. PLATING TANK CONSTRUCTION The choice of plating tank construction material should fit the type of bath. All types of tank linings have advantages and disadvantages ranging from length of wear to economy. Acid Chloride Baths Acid chloride zinc baths may use fiberglass tanks or polypropylene tanks, but steel tanks must be lined with any of the following: fiberglass, polyvinyl chloride (PVC), or polypropylene. Tanks for chloride zinc must not be constructed of unlined steel. Alkaline Non-cyanide Baths Alkaline non-cyanide zinc baths can use tanks constructed from steel, PVC, fiberglass lined with PVC, or polypropylene. Alkaline non-cyanide zinc systems cannot use unlined fiberglass tanks. Cyanide Baths Cyanide zinc baths can use tanks constructed of steel, fiberglass, PVC, or polypropylene. TYPE OF SUBSTRATE TO BE PLATED The selection of a bath to match the substrate characteristics is of major importance to the success of a zinc plating system. Regular steel substrates and leaded steel substrates both are compatible with acid chloride, alkaline non-cyanide, and cyanide zinc systems. In fact, these materials are the only two recommended for alkaline and cyanide plating. Acid chloride zinc is more flexible in compatibility with other substrates. Successful use on malleable, high-carbon, heat-treated, and carburized substrates can be accomplished with acid chloride zinc systems. AUTOMATIC CONTROL EQUIPMENT Automatic control equipment can play an integral role in the operation of a consistent, high-quality plating line. Both acid chloride zinc and alkaline noncyanide zinc systems can benefit from the use of starter, carrier, or refining agent automatic feeder systems. All three zinc baths are suited for the use of brightener feeders connected to rectifiers. An automatic pH controller can simplify and improve the operations of an acid chloride zinc bath. 324

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