Metal Finishing Guide Book

2013

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finishing equipment & plant engineering BASIC CONSIDERATIONS AND CONCEPTS FOR RACK DESIGN BY DON BAUER, ASSOCIATED RACK CORPORATION, VERO BEACH, FLA. Historically, metal finishing racks have come a long way in their design. The crudest form of racking is simply a wire twisted onto the part. With the production and quality requirements of today, an expensive piece of copper wire will not suffice. The parts must be presented to the anodes with consistency to ensure visual and measurable quality requirements. For decorative automotive finishes of today, require custom racking. In this paper, I will review some basic concepts for rack design and maintenance. The most important aspect of any rack is the design. Without the proper design, one cannot expect to obtain the optimal productivity that the process is capable of achieving. There are many factors that come into play when designing and building racks. In this paper I will discuss: Equipment Manufacturers, Dimensional Restrictions, Weight Restrictions, Part Presentation and Spacing, Rack Material,  Manufacturing Techniques, Optimized Designs, and Selecting a Supplier. EQUIPMENT MANUFACTURERS There are several automatic equipment manufacturers in the market and each may have distinct methods of attaching or mounting a rack. The two most common lines manufactured are the return line and hoist line. Regardless of the equipment, the first consideration is how the rack will hang on the cathode. Return lines are typically a "Carrousel" design. The racks will travel from station to station in a circular movement. The racks are usually similar in dimensions and will carry, as close as possible, the same surface area. Manufacturers of return-type equipment use brass alloy castings, or hangers, to carry the current to the rack. Hangers are different; what needs to be known to ensure a perfect fit is the center-to-center dimension, the area where the rack hangs on the casting. Castings are mounted on the machine and the racks hang on specific notched areas of the casting. If a rack does not hang properly onto the casting, it cannot be assured of the required current flow, and one runs the risk of the rack not having the appropriate clearance as it moves from station to station. The advantage of a hoist line is the racks can be designed to have varying center-to-center locations and can vary in overall width, allowing several racks to be loaded onto a flight bar. Hoist lines typically do not use castings and the racks are simply hung onto the cathode bar. DIMENSIONAL RESTRICTIONS The primary dimensional restrictions (the work envelope) are the overall height, width and length of the rack and the placement of the parts. These specifics must be known before a useable rack can be fabricated and successfully perform. The overall height is measured where the rack hangs on the hanger or flight bar to the bottom-most useable space in the process tanks. One of the mistakes made when taking these measurements is neglecting unseen any piping in the 717

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