Metal Finishing Guide Book

2012-2013

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Fig. 3. Typical mechanical plating layout. 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. EQUIPMENT Mechanical plating equipment is a specially designed plating and material handling system. The plating takes place in stainless steel variable-speed tumbling barrels (Fig. 1). Because the entire process operates at an acidic pH of 1 to 2, the barrels must be lined with an inert, abrasion-resistant protective coating, such as urethane, neoprene, or polypropylene, to a thickness of 19 to 25 mm (0.75-1 in.). Typical plating barrels have capacities of 0.04 to 1.13 m3 (1.5-40 ft3), where capacity is defined as the total available working volume, typically 30 to 35% of the total volume. For example, a 0.57 m3 (20 ft3) plating barrel will hold approximately 910 kg (2,000 lb) of 25-mm- (1-in.)-long threaded fasteners and 1,000 kg (2,200 lb) of glass bead mix. See barrel loading capacity chart (Fig. 2). In Fig. 3, parts to be mechanically plated are brought to the barrel loading hoist (1). Glass media are transferred from an overhead media reservoir tank (2) into the plating barrel (3). The operator���s platform and control panels serve as the stag450

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