Metal Finishing Guide Book


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Page 403 of 843

Fig. 3. Typical mechanical plating layout. ing, hot-dip galvanizing, painting, or organic finishing are now successfully being mechanically plated or galvanized. Parts now universally accepted for consideration include regular and self-tapping screws, bolts (including A 325), nuts, washers, and stampings; nails; chain and wire forms of all types; pole line and tower hardware for telecommunications; electrical connectors; and automotive, aircraft, and marine fasteners. The suitability of parts considered for mechanical plating or galvanizing is determined by its size, shape, and base metal. Part types that would not withstand the tumbling action of the process are usually not suitable. Parts heavier than 1 to 2 kg (2.2-4.4 lb) or longer than about 300 mm (12 in.) are not normally coated in this manner. Parts that have deep recesses or blind holes may make the part unsuitable, because to obtain a satisfactory deposit, solution and glass beads must flow freely and have sufficient impact energy in all areas of the part surface. This must happen without glass beads permanently lodging in holes or recesses. A variety of substrates are suitable for mechanical plating and galvanizing and include low carbon steel, high carbon heat-treated spring steel, leaded steel, case-hardened and carbonitrided steel, malleable iron, and stainless steel. Powder metallurgy parts can be plated by this process without prior sealing of the surface. Because mechanical plating solutions are usually chemically consumed, little excess is available to get trapped in the pores of the substrate. In addition, the initial copper strike will seal such pores and the metal powder that follows will fill and bridge them. The process can also plate onto brass, copper, lead, and certain other substrates. 396

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