Metal Finishing Guide Book


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nickel sulfamate brush plating solutions because they require preheating and constant filtering. These units have reservoirs of several sizes, pumps designed for high temperature operation, provision for filtering and the capability of changing filters while plating. In addition, they include a heater and heater control that preheats and maintains the solution at the proper temperature. Flow systems also can be equipped with cooling units for anodizing and high current brush plating operations. Turning equipment is frequently used to speed up and simplify finishing operations. Specially designed turning heads are used for small parts, i.e. a diameter less than approximately 6ʺ, a length less than 2 ft, and a weight less than 50 lb. Lathes are often used to rotate large parts while brush plating inside or outside diameters. When a part cannot be rotated, special equipment can be used to rotate anodes. For bores up to 1 1/2ʺ in diameter, small rotary units are used. These units have a variable speed motor, flexible cable and a special handle with rotating anode and stationary hand-held housing. For bores in the 1ʺ to 6ʺ diameter range, larger rotary units are required. These units are similar to the smaller ones but include heavy duty components, and they have provisions for pumping solution through the anode. The largest turning units are used for bore sizes in the 4ʺ to 36ʺ diameter range. These units have two opposing solution-fed anodes which are rotated by a variable speed motor. The anodes are mounted on leaf springs which apply the correct amount of pressure and also compensate for cover wear. These devices are used at up to 150 A. They are not hand-held, but mounted on a supporting table instead. Traversing Arms are used to supply either a mechanical oscillation or a back and forth "traversing" motion for an otherwise manual selective plating operation. ADVANTAGES AND DISADVANTAGES Selective plating processes are used approximately 50% of the time because they offer a superior alternative to tank finishing processes and 50% of the time because they are, in general, better repair methods for worn, mismachined or damaged parts. For example, the decision to use brush plating rather than tank plating, welding or metal spraying, depends on the specific application. There are distinct advantages and disadvantages that should be considered. Some advantages of brush plating over other repair methods are: • The equipment is compact and portable. It can be taken to the work site so that large or complicated equipment does not have to be disassembled or moved. • No special surface preparation such as knurling, grit blasting or undercutting is required. The only requirement is that the surface be reasonably clean. Often solvent cleaning or sanding the work surface is sufficient. • Brush plating does not significantly heat the part or work surface. Only 385

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