Metal Finishing Guide Book

2013

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BURR REMOVAL The removal of burrs is a breaking of sharp edges. Burr removal is done by the following methods: hand filing, polishing, flexible polishing, satin finishing, brushing, and tumbling. Functional parts do not necessarily need a decorative finish and usually deburring becomes the final mechanical finish. Burrs can be removed by hand methods such as filing, which is very laborintensive making mechanical means preferred in most cases. Parts that contain restricted areas can be processed using set-up polishing wheels and muslin buffs coated with a greaseless compound. See the discussion on polishing wheels (above) and buffing. Processing methods will be determined by the configuration of the part. If a part contains a heavy burr yet the edges are straight, a rigid set-up wheel is needed. Where the contours are irregular and the burrs not excessive, a sewn or loose cotton buff with a greaseless compound works more efficiently. If extreme flexibility is required, a string wheel with greaseless compound or a tampico wheel with aluminum oxide, grease-based material is required. BUFFING Buffing is the processing of a metal surface to give a desired finish. Depending on the desired finish, buffing has four basic categories: satin finishing, cutdown buffing, cut-and-color buffing, and luster buffing. Satin finishing produces a satin or directional lined finish; other types of satin finishing are brushed or Butler finishing. Cutdown buffing produces an initial smoothness; cut-and-color buffing produces an intermediate luster; and luster buffing (color buffing) produces high reflectivity or mirror finish. TYPES OF BUFFING COMPOUND COMPOSITIONS Greaseless compound is used to produce a satin finish or a directional lined finish. Greaseless compound contains water, glue, and abrasive. As its name implies, it retains the abrasive on the buffing wheel in a grease-free environment, leaving the surface of the finished part clean and free of greasy residue. The principal uses of greaseless compound are for satin finishing or flexible deburring. Generally, the abrasive contained in such compounds is silicon carbide or fused aluminum oxide. Grades are available in abrasive sizing from 80 grit to finer depending on the degree of dullness required on a particular base metal. Silicon carbide abrasives are used for the finishing of stainless steel and aluminum. Aluminum oxide grades are used for brass and other nonferrous metals, as well as for carbon steel prior to plating. To produce a finer satin finish on nonferrous materials, fine emery and hard silica are used. For Butler finishes on silver plate and sterling, fine buffing powders of unfused aluminum oxide and soft silica are used. Greaseless compounds are applied to a revolving buff by frictional transfer. The buff speed is 4,000 to 6,000 surface feet per minute (sfm). The material then melts on the cotton buff, adheres to the peripheral surface, and dries in a short period of time. This produces a dry, abrasive-coated wheel with a flexible surface. The buffing wheels on which greaseless compounds can be applied are sewn muslin buffs, pocketed buffs, full disk loose buffs, and string wheels. The coarser the abrasive particle, the duller the satin finish; the finer the abrasive particle, the brighter will be the satin finish. BAR COMPOUNDS Bar compounds contain two types of ingredients; binder and abrasive. The binder can consist of one or more materials taken from animal or vegetable fats as well as petroleum and similarly derived products. Animal fats are such materi22

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