Metal Finishing Guide Book

2013

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handling and some work transfer enhances the overall efficiency of the finishing operations. 5. Barrel plating is very versatile because of the variety of parts that can be processed in the same equipment. It is the predominant method for finishing fasteners, metal stampings, and similar bulk work. It has been said that "if a part can fit through the door of a barrel, it can be barrel plated." This is, of course, an oversimplification. Most often, the part configuration, end use, and finish type help determine the applicability of barrel plating. 6. Conversely to barrel operations, rack plating often requires special part carriers, or fixturing, and other purpose-built equipment. This can include special contacts, such as formed anodes, based on the individual part type and shape. Barrel plating does not usually require these items, although there are special-purpose contacts available for barrel plating when needed. 7. Barrel rotation causes the workload to tumble in a cascading action. This, in addition to the bipolar electrical activity from individually contacting parts, usually produces a more uniform plated finish than rack plating. 8. Agitation of the tank solutions by barrel rotation inherently eliminates stratification and produces homogeneous baths. Additional agitation equipment is usually not required, although certain tanks and operations are equipped with spargers (air agitation manifolds) when needed. Origins Barrel-plating methods originated in the post-Civil War era, with equipment readily adapted from available wooden barrels, kegs, or baskets. Equipment was constructed of wood because it was probably the most economical and available material that was not a conductor of electricity. Subsequent advances in the knowledge of chemistry, electricity, and material sciences enabled the evolution of barrel-type metal-finishing equipment for bulk finishing. This evolution culminated in the third or fourth decade of the 20th century with now-familiar basic designs. Today, the submerged portions of barrel-plating equipment are constructed, as much as possible, of nonconductive, chemically-inert materials that can be utilized in various acid and alkaline solutions. Great advances in plating-barrel performance, capability, and longevity were possible largely as the result of plastic materials newly available after World War II. Prior to that time, plating barrels were known to be constructed of more primitive plastic or phenolic materials and wood. EQUIPMENT TYPES Available barrel equipment varies widely but generally conforms to two major configurations: (1) horizontal barrels and (2) oblique barrels. Horizontal units are the most common, being adaptable to a greater variety and capacity of work (see Fig. 1). Horizontal barrels also vary by size and are grouped into three major categories: (1) production barrels, (2) portable barrels, and (3) miniature barrels. Production barrels, the largest units, usually have a capacity in the range of 1.5 to 17 cubic feet. They handle the majority range of the work. Portable barrel units are so named because of their generally smaller size (capacities range from 0.1 to 1.5 cubic feet) and their ability to be transferred 364

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