Metal Finishing Guide Book

2012-2013

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Dimension B���Distance from Cathode Hook to Location of First Part This dimension is very critical as it will determine the number of parts per rack. Dimension C���Width On return-type automatics, this width dimension is the direction of travel. Proper dimensions are extremely critical, as each manufacturer may have different width requirements. As in any automated system, this dimension might have some variables and the rack must be designed for the smallest cell. Improper width could result in damaged racks because of machine jam-ups. This dimension on automated hoist lines or manual straight lines determines the number of racks on each work bar. Spacing between the racks is important, as this will ultimately determine production rates. How many racks will effectively fit on a work bar? Look at the design of the work bar to help with proper spacing, especially the location of the pick-up points. Fig. 1. Rack dimensions Dimension D���Thickness The thickness dimension is the direction of travel on an automated hoist line. Relating to plating rack design, this dimension is the most critical. The distance between the anodes and their relationship to the cathode bar will determine how wide the rack will be. The rack must fit between the anodes with ample room for holding the parts (usually 1-3 in.). On a manual line it will be necessary to determine the smallest anode distance so that the rack will fit in all process tanks. Another factor on a hand line is making sure that the plater can easily put the rack in and out of each process tank without knocking parts off. Dimension E This is only for racks that have a double cathode hook and is usually for returntype automatics. This design is also used where additional stability is required or where weight might be a factor. Having developed all the dimensions necessary for design of the spine, special attention must be focused on cathode hook design. What size of work bar will be used? It is important that the hook make clean contact with the bar so that current flows properly. This can be accomplished with the V-hook design, the most commonly used today. (See Fig. 2 for commonly used hook shapes.) Some manufacturers have developed their own hook design. Recent work bars have been rectangular for the primary reasons of stability in relationship to the speed of the machine and quick starts and stops. CONSTRUCTION OF THE PLATING RACK SPINE The plating rack spine (Fig. 3) is the backbone of a rack. It must be capable of carrying the necessary current to each tip, it must have adequate strength to support all the parts, plus be wear resistant, especially for use on an automatic machine. The plating bath in which the rack will be used has a known current density rat746

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