Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 613 of 707

guiding pulleys. With this sys- tem, stripe width cannot be as closely controlled. The somewhat higher cost of equipment and the fact that specially fabricated belts are required for each family of parts being plated are the two most often-voiced objections to the moving belt selective plating system. Belt and Drum A rubber covered drum masks Fig. 3. Drum and mask selective plating. the back of the strip being plat- ed and two rubber belts are used to produce the selectively plated stripe as shown in Fig. 3. The width and location of the stripe are controlled by the placement of the belts. This system may also be used for tip plating by allowing the material to protrude laterally from between the drum and a masking belt. Belt and drum selective plating compares technically with the moving belt sys- tem; however, it may lack some of its versatility and precision. Also, when used for spot plating, it is very difficult to precisely synchronize belt, drum, and strip speed. Tape Masking This is a novel technique, pictured in Figure 4, in which a thin Mylar tape is "tooled" by prepunching where plating is required. The tape is then compressed against the strip, which must be solid, as it passes over the plating cell. Strip widths as narrow as approximately 0.010 in. and spots 0.020 in. in diam- eter can be produced with tolerances of approximately ±0.005 in. The process is not widely used because it doesn't lend itself to large scale production and Fig. 4. Tape masking. Thin Mylar (or equivalent material) is prepunched with slots or holes. It is then held firmly against the strip being plated as it passes over the plating cell. 612

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