Metal Finishing Guide Book


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Platinum anodes, although more expensive, are used in some cases. These anodes may be made from pure platinum or from either niobium or columbium clad with platinum. The use of platinum anodes is generally reserved for brush plating applications that are long term, repetitive or that require thick brush plated deposits. Platinum anodes are also an excellent choice when brush plating bores as small as one-sixteenth of an inch diameter. Graphite anodes this small in diameter are brittle and are easily broken. Since selective plating occurs only where the tool touches the part, it is best to select a tool that covers the largest practical surface area of the part. Selecting the correct tool also ensures uniformity of the finish. Manufacturers offer a wide selection of standard selective plating tools. These tools are available in a variety of sizes and shapes to accommodate different surface shapes. However, special tools are frequently made to accommodate special shapes or large areas. Proper design of these tools is critical to successful finishing operations. An equally important aspect of selective plating processes is the selection of an anode cover. Anode covers perform several important functions. They form an insulated barrier between the anode and the part being finished. This prevents a short circuit, which might damage the work surface. Absorbent anode covers also hold and uniformly distribute a supply of finishing solution across the work surface. The solution held in the anode covers provides a path for the direct current supplied by the power pack. This is required for all selective plating processes. Anode covers also mechanically scrub the surface being finished. All anode cover materials sold by manufacturers are screened for possible contaminants. Many materials, that seem similar, contain binders, stiffening agents and lubricants that will contaminate finishing solutions. Testing has shown that these contaminants have a significant impact on finish quality and adhesion of deposited materials. Anode covers suitable for selective plating should be obtained from solution manufacturers to avoid contamination. Auxiliary Equipment: When a finishing operation is required on a large work surface or a deposit is applied in a high thickness, best results are obtained by continuously recirculating the finishing solution with a simple pump or a flow system. This method will reduce the time required for the finishing process by eliminating lost time from dipping the anode and by supplying fresh solution to cool the work surface so that higher current densities can be used. Submersible and peristaltic pumps are used when operating in the 1 to 100 A range, and when the finishing solution does not have to be preheated. Flow systems, which include specially fabricated tanks ranging in size from 1 to 10 gallons and heavy duty magnetic drive pumps and a filter, are used when operating in the 100 to 500 A range, and when the solution has to be preheated. The most sophisticated flow systems are used with 384

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