Metal Finishing Guide Book


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Fig. 2. Removable side bars protected inside the crossbar. be repositioned as close as possible to eliminate wasted horizontal space between parts (see Fig. 2). The overall width of a rack should be determined by maximizing the number of pieces on the rack in relation to the distance between conveyor pendants and the degree of incline related to any hills in the system. Most racks are designed to be 20 in. wide and to be center hung on 24-in. centers, assuming a 30�� maximum incline/decline. Proper Grounding for Electrostatic Applications Nearly all part hooks eventually lose their ground between the part and the hook as they are used through the finishing system. The ground may be lost within as little as 2���3 cycles or as many as10���12 cycles, depending on the amount of paint being applied and whether the same kind of part is hung. A loss of ground causes loss of paint wrap, uneven paint distribution, blemishes, rejects, scrap, and wasted paint, particularly if there is no recovery system. When loss of ground occurs, it is necessary to either clean the hook or, if possible, remove it and replace it with a clean one. In most cases cleaning requires either burning or chemically stripping the entire rack or burning or grinding just the hook end. The other option,replacing the hook, may be faster depending on the design of the rack and hook connection. There is a rack available that uses spring steel hooks that can be quickly and easily removed even after many cycles (see Fig. 3). The contact to the rack is shielded from paint and always remains clean for grounding. Rack Maintenance Optimizing rack density automatically reduces rack maintenance. Fewer cycles automatically means less cleaning. A common problem with welded racks is the hook breakage that occurs due to the annealing at the weld point of the hook to the rack. This problem causes less product to be painted and gives an inaccurate count of finished parts. Hooks that can be removed and easily replaced are desirable. Part hooks made of stainless steel will retain strength for a longer period of time, particularly if cleaned in a burn-off oven. Stainless steel is also a requirement if spring steel is used to avoid annealing. Most burn-off ovens operate at approximately 800��F, whereas the annealing temperature of stainless steel is approximately 1,900��F. Flexibility Flexibility in racking is very important in any finishing job, large or small. The flexibility achieved with modular racking gives one the ability to concentrate on density and obtain it quickly. Moving part hooks around is not the important part of flexibility. It is having the ability to put a rack together quickly, without 845

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