Plastic media and abrasives are used in blasting, tumbling, and other finishing processes. Plastic blast media allows the removal of paints or organic coatings without abrading the underlying metal substrate. Plastic grit is used to clean surfaces, remove powder coatings, and to abrade gel coats and printed circuit boards (PCBs). Product specifications include material type, hardness measurement, and mesh type. Plastic media and abrasives may contain different types of plastic materials, but typical choices include polyester, urea, melamine, and acrylic. Specialty plastic abrasives are also available. Typically, hardness is measured according to the Mohs scale and/or the Barcol scale. For each type of plastic media or plastic abrasive product, there are several standard mesh types.
Most plastic media and abrasives are made of polyester, urea, melamine, or acrylic materials. Polyester media and polyester abrasives are the softest products. Applications include deflashing and deburring electronic circuits, and stripping paints and primers from metal substrates. Urea media and abrasives are heavier and much more aggressive than polyester products. Typically, urea abrasives are used to strip paints and primers from vehicles such as aircraft, cars, rail cars, and ships. Melamine media and melamine abrasives are sometimes used in place of glass beads or other harsh abrasives. These fast-acting, aggressive, plastic media and abrasives are used to clean molds or remove paints and primers from engine components and turbine blades. Acrylic media and acrylic abrasives are also available. They are used to strip aircraft structures, buses, trucks, tractors, and metal frames.
Typically, plastic media and abrasives carry two measurements for material hardness: Mohs and Barcol. Mohs hardness indicates how well a material resists scratching. To provide numeric values for this property, minerals such as diamond and talc are ranked along the Mohs scale. Materials such as those in plastic media and abrasives are then compared to these standard values. Another method for measuring the hardness of plastic media and abrasives, the Barcol method, provides values for resistance to penetration of a sharpened steel point under spring load. ASTM D2583, a standard from the American Society for Testing and Materials (ASTM), is a common test method for determining the hardness of plastics.