Metal Finishing Guide Book


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bottom of the tank. The other common mistake is not taking into consideration obstructions on the top of the tanks when the racks are moved from tank to tank. The length is the useable left-to-right dimension. This is important on both a return and hoist line. For a return line, typically one rack will be set into a single tank for rinsing. If the width of the rack is too wide, then rack and parts can be damaged from hitting or scraping the walls of the tank. On a hoist line, racks with the wrong width will not allow the maximum number of racks on a flight bar, resulting in lower overall production. WEIGHT RESTRICTIONS The manufacturer has designed the machine hoists systems to handle specific weights which will include the racks and the parts. This information must be known and may restrict the number of parts that can be processed on a work bar. This is not typically a problem, but it can be if particularly heavy parts are being processed. Also important is the human weight restrictions in the loading/ unloading segment of the process. With racks that are to be handled off line, the rack designer will need to know what the weight limits will be as required by the customer's safety and health administrator. Many situations require parts to be loaded onto the rack and then hand carried to the plating line. The rack supplier must ensure that the total weight of the rack and parts do not exceed the maximum restrictions. Keeping the weight manageable will avoid possible lost time, injuries and worker compensation claims. The use of aluminum in the framework of the rack will eliminate the weight that copper adds. (This will be discussed later.) PART PRESENTATION AND SPACING Most plating processes are reliant on proper positioning of the parts, particularly during the plating process. Consideration of the part configuration is vital when planning how it is placed on the rack contacts. If a part is cup-shaped, the part would not rack with the cup facing up or down. The desired positioning would be such that the solutions flow freely in and out of the part when being moved from tank to tank. Maximum exposure to the anodes must be achieved. For the same cup-shaped part, the open end of the part must face toward the anodes, especially when plating inside of the recessed area is a requirement. When plating wheels, one would not face the outside diameter of the wheel toward the anodes. It is preferable to position the face of the wheel toward the anodes and configure the rack to locate the rim as close as possible to the anode to allow for proper thickness and plating distribution. Even with these design concerns, some recesses might not plate properly. In these cases, an auxiliary anode must be considered. AUXILIARY ANODES Plating inside of recessed areas, such as wheels and step bumpers, is difficult and sometimes impossible to do without the use of an auxiliary anode. The determination is at times easy to make and at other times not so simple. Experience and knowledge of the process is normally adequate to make the decision. At times it is necessary to use an auxiliary anode due the part simply not plating 718

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