Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 338 of 707

plating procedures SELECTIVE PLATING PROCESSES (BRUSH PLATING, ANODIZING, AND ELECTROPOLISHING) SIFCO APPLIED SURFACE CONCEPTS, INDEPENDENCE, OH WHAT IS SELECTIVE PLATING? The term "Selective Plating" includes three different processes • Selective (Brush) Electroplating • Selective Anodizing • Selective Electropolishing and Weld Cleanup These processes differ from traditional tank finishing processes because the plating, anodizing, or electropolishing is done out of tank, focusing the opera- tion onto a localized area of a part. Additionally, the processes are portable. They can be carried out in the shop or in the field. Selective plating is a very flex- ible process. Operations can be carried out manually, they can be mechanized, or they can be automated. HOW IT WORKS The plating tools, typically graphite, are wrapped with an absorbent material that both holds and distributes the solutions uniformly over the work area. Solution is supplied to the work area by either dipping the tool into a container, or by pumping the it through the tool and recirculating. The plating tool is then moved over the work area. In the selective plating process there must be movement between the plating tool and the part – move the tool over the part, move the part and hold the tool stationary, or move both the tool and the part. A portable power pack (rectifier) provides a source of direct current for all the processes. The power pack has at least two leads. One lead is connected to the tool and the other is connected to the part being finished. Direct current supplied by the power pack is used in a circuit that is completed when the tool is touching the work surface. The tool is always kept in motion whenever it is in contact with the work surface. Movement is required to ensure a quality finish. Preparation of the area to be processed is accomplished through a series of electrochemical opera- tions. These preparatory steps are performed with the same equip- ment and tool types that are used for the final finishing operation. Good preparation of the work area is as important as movement of the tools to produce an adherent, qual- ity deposit or coating. 337

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