Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 17 of 707

Applications: Pressure deburring of steel parts, ball burnishing (or ball polishing) of mainly stainless steel parts, occasionally also aluminum parts. ORGANIC MEDIA Material: Mostly corn cob or walnut shell granules. Applications: For drying of parts after vibratory finishing. Also used for high- gloss polishing of metal parts, mainly stainless steel, aluminum, titanium, etc., in combination with a mixed-in polishing paste. SELECTION CRITERIA: MEDIA SHAPE, SIZE, AND ABRASIVE CONTENT Media shape, size, and abrasive content are crucial for achieving the optimum sur- face finish. MEDIA SHAPE The geometry of the parts to be finished generally determines the shape of the media to be used. A simple rule of thumb is: Figure 14: Round and compact media. Round and compact media (Fig. 14): Use for standard appli- cations. There is less danger of media lodging in the part; low- er danger of chipping (in the case of ceramic media); and low- er wear rate. Typical shapes include: cylinder, cone, ball. Media with sharp edges (Fig. 15): For parts with complex geometry and difficult-to-reach surfaces. Danger of chip- ping; higher wear rate. Typical shapes include: tri-star, tri- angle, arrowhead. Figure 15: Media with sharp edges. MEDIA SIZE The required finish usually determines the media size (Fig. 16): Figure 16: Small and large media. Small media size: Produces a smoother surface by having more contact with the part surface; usually requires longer processing times and more gentle processing. Large media size: Faster removal of burs and radiusing of sharp edges on the parts; produces a rougher surface than small media; more aggressive grinding required. ABRASIVE TYPE Silica: For deburring/deflashing of relatively soft metals, such as aluminum, brass, and zinc. Silicon carbide: For aggressive grinding on difficult-to-machine metals. This abrasive produces dark surfaces. Aluminum oxide: Characteristics are similar to silicon carbide. Zirconium: Used in plastic media for adding weight. Mainly used for fine grind- ing of all kinds of metals. HOW DO YOU SELECT THE CORRECT MEDIA? BY ASKING THE RIGHT QUESTIONS! Selecting the right media requires much experience and possibly, as mentioned 16

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