Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 384 of 707

Fig. 1. Typical antique finishes. the pure copper alloys can offer such as fasteners or other structural members, which must be able to support some weight in service. In addition steel is usually less cost- ly than solid copper, brass, or bronze and is often preferred because of these two fac- tors. Unlike the copper alloys, steel does not form a protective oxide layer on expo- sure to weathering elements. Consequently, a steel article is usually electroplated with copper or brass in order to protect it from corrosion and present a viable brass or copper outer surface for subsequent antiquing operations. Steel is commonly used to make structural hardware such as hinges, fasteners, casket hardware, and other functional items. Additionally, because of its relative- ly low cost, steel is used to make many indoor decorative items such as light fixtures and cabinet hardware. Many of these items are stamped out of sheet stock. Round items can often be formed in a metal spinning operation. This process begins with a flat disk of steel sheet, which is fastened to a shaped mandrel and rotated. The part is formed when a steel roller is pressed down onto the spinning surface, slowly forcing it to conform to the shape of the mandrel beneath it. Common items, such as lamp bases or bezels, are often formed this way, then brass or copper elec- troplated for antique finishing. Zinc Diecastings This third group is often used to make decorative items that have a detailed shape and have low load-bearing requirements. Many items have a design that is too detailed to make easily out of machined or stamped steel, or the value of the item is not high enough to justify the cost of cast bronze. For these lower-cost articles a zinc diecasting is the preferred base metal because it is easy to cast into very intri- cate shapes at relatively low cost, making it ideal for items such as cabinet hardware, 383

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