Metal Finishing Guide Book

2012-2013

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plating processes, procedures & solutions BARREL PLATING BY RAYMUND SINGLETON AND ERIC SINGLETON SINGLETON CORP., CLEVELAND; www.singletoncorp.com Barrel plating typically involves a rotating vessel that tumbles a contained, bulk workload. The barrel is immersed, sequentially, in a series of chemical process tanks, including plating baths, while tumbling the workload. Utilizing interior cathode electrical contacts to polarize the workload, metals are attracted out of solution onto the individual workpieces. Effectively, the workload becomes part of the plating equipment during processing because the individual pieces function as bipolar electrical contacts to the other pieces in the workload. This bipolar contact is a significant contributor to the high efficiencies of barrel plating because the entire surface of the workload, in the current path at any time, is in cathode contact. USES OF BARREL PLATING Barrel plating is used most often for bulk finishing. It is the most efficient method for finishing bulk parts and any pieces that do not require individual handling. According to a Metal Finishing Industry Market Survey published a few years ago, there are approximately 6,750 plating facilities in the U.S. Of these, 37% exclusively provide barrel-plating services, and an additional 32% provide both barrel and rack plating; therefore, approximately 69% of all plating facilities employ the advantages of barrel plating in providing their services. Plated finishes generally provide the following three functions (singly or in combination) for the plated article, or workpiece: (1) corrosion protection, (2) decoration/appearance, and (3) engineering finishes (for wear surfaces or dimensional tolerances). Barrel plating is used most often for corrosion protection of the workpiece. Because of the surface contact of the workpieces with each other inherent in the tumbling action during processing, barrels are not often used to produce decorative or engineering finishes. Advantages Along with the high efficiency already mentioned, in any event, the advantages of barrel plating are many and interrelated: 1. The relatively large cathode contact area yields faster, larger volume production, in the presence of ample current, when compared with rack-type plating. 2. A barrel-plating system occupies less floor space and requires a lower investment for equipment than a rack- or other-type plating line of similar capacity. 3. Barrel plating is labor efficient because it is not necessary to handle, rack, load, or unload individual workpieces. 4. The work usually remains in the same vessel for other operations, including: cleaning, electro-cleaning, rinsing, pickling, chromating and/or sealing. A more recent innovation in barrel plating/processing equipment is drying of the work while it remains in the barrel. This elimination of some 417

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