Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 16 of 707

such as pressure deburring, ball burnishing, drying, and dry polishing. Whereas in the case of ceramic media the carrier is clay, in the case of plastic media the carrier is either polyester or urea resin. The most common abrasives used in ceramic and plastic media are: • Silica (sand) • Brown and white fused alumina (aluminum oxide) • Silicon carbide • Zirconium Depending on the application, mesh sizes can vary between 40 and 400. The different types of media, how they are made, and for what applications they are generally used, are subsequently described. Figure 11: Ceramic media CERAMIC MEDIA (Fig. 11) Density: 95–110 lbs/ft3. Production method: extruded or pressed. Firing temperatures: 2,100–2,400°F. Available shapes: triangle, star, ellipse, cylinder, arrowhead, tri-star, pyramid, cone, rhomboid, para- bolic, ball. Applications: Due to their relative high density, ceramic media are generally used for aggressive grinding on "tough" metals, such as steel, stainless steel, titanium, and so on. However, certain ceramic media can also be used for fine grinding—producing low Ra values on the part surface. Porcelain media, made from pure alumina, can be used for polishing, producing a high-gloss surface. Limitations: Ceramic media can chip, and chips may lodge in bore holes and undercuts. Figure 12: Plastic media PLASTIC MEDIA (Fig. 12) Density: 60–85 lbs/ft3 Production method: Abrasive/liquid resin mix is poured into molds at room temperature; mix hard- ens within 15–20 minutes. Available shapes: triangle, tri-star, double wedge, cone, pyramids of different shapes, parabolic. Applications: Due to their somewhat lower densi- ty, plastic media are generally used on softer metals, such as aluminum, zinc, and brass. Applications range from relatively aggressive deburring/radiusing to pre-plate surface finishes. Figure 13: Steel media STEEL MEDIA (Fig. 13) Density: 210–250 lbs/ft3 (depending on size) Material: hardened carbon steel, standard carbon steel, stainless steel. Production method: Cut to length from wire/round bar and then forged. Available shapes: Sphere (ball), satellite, oval, angle- cut cylinder, etc. 15

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