Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 389 of 707

recessed areas. The only way to accomplish this task is to mechanically remove the coating from these areas. There is no chemical treatment available to do this job. There are several proven methods that work well. Hand Buffing The buffing wheel is constructed of many disks on cotton fabric, sewn together to form a single buffing wheel about half an inch thick. These can be stacked together on a sin- gle spindle to form a buffing wheel up to 3 or 4 inches wide depending on what is need- ed to cover the part most effectively. Once the wheel is assembled it can be loaded with different compounds, ranging from abrasive to fine polishing compounds, depending on the type of contrast desired on the part's surface. For example some parts have designs, which have well-defined edges to the details or have sharp corners, etc. These parts generally would be highlighted with a fairly abrasive compound in order to clean off the colored coating completely from the highlights and allow the coating to remain almost entirely in the recesses. A dry nonmetallic abrasive flap wheel might also be used to achieve a sharp contrast. On the other hand the part may have a rounder shape with softer curves and no clear-cut, sharp edges. This part may look better with a softer contrast bur- nishing than with sharp contrast abrasive buffing. If so the cotton wheel would be loaded with a less abrasive compound in order to achieve a softer shading or "feathering" of the colors on the part. Some parts go one step further requiring no actual removal of the antique finish but only a softening or burnishing of the coating of blend tones. This type of part might be buffed on a soft, brass wire wheel rather than a cotton wheel and a compound. This softer wire wheel would not really remove any coating, but merely smooth it out a bit or impart a soft directional grain to the surface. An alternative method might be to use a wet burnishing wheel—a brass wire wheel wetted with a slow dribble of water to soften the abrasive action. It is easy to see that the hand-buffing operation is more art than science. Just as cleaning is important to the integrity of the deposit on the surface, buffing is crit- ical to the final appearance of the finish and can even determine the market value of the piece. Since the decorative hardware business is all about appealing to the "the eye of the beholder," it is important to appeal to the eye of the buffer first. Automated Buffing Machines As in many other aspects of the finishing process higher production volumes also produce a need for automatic buffing capabilities in order to reduce labor costs and rely less heavily on the human factor in the buffing operation. Larger volume production lines often use very little hand buffing and have come to rely on auto- matic machines, which can be programmed to follow the shape of almost any part. These machines often take the form of a turntable surrounded by several buff- ing heads, each of which is oriented to buff just one aspect of the part as it passes by. Alternatively, some machines can index the part or rotate it so that a single buff- ing head does the entire job. The shape of the part will determine the type of machine that will be most suitable. Tumbling and Vibratory Methods Just as hand buffing is most often suitable for high value pieces, lower value parts can often be effectively highlighted in bulk. Parts, such as certain cabinet hardware, fasteners, or other small parts, would typically be brass plated or antiqued in bulk handling methods. If so it is desirable to burnish or highlight in bulk as well. To do this the parts can be burnished in a tumbler or in a vibratory mill. 388

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