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Colorants (Polymer Additives)

An advantage of many polymers over metal or ceramics is that the material itself can be obtained in most any color. This eliminates the need for secondary coating operations. Colorants for polymers are of two types: pigments and dies. Pigments are finely powdered materials that are insoluble in and must be uniformly distributed throughout the polymer in very low concentrations, usually less than %1. They often add opacity as well as color to the plastic. Dies are chemicals, usually supplied in liquid form that is generally soluble in the polymer. They are normally used to color transparent plastics such as styrene and acrylics. (Mikell P. Groover; Fundamentals of Modern Manufacturing Materials, Processes, and Systems 3rd Edition; pg.156)

Flame Retardants(Polymer Additives)

Flame Retardants are chemical added to polymers to reduce flammability by any or a combination of the following mechanisms: (1) interfering with flame propagation, (2) producing large amounts of incombustible gases and/or (3) increasing the combustion temperature of the material. The chemicals may also function to (4) reduce the emission of noxious or toxic gases generated during combustion. (Mikell P. Groover; Fundamentals of Modern Manufacturing Materials, Processes, and Systems 3rd Edition; pg.156)

Centerless grinding

Centerless grinding is an alternative process for grinding external and internal cylindrical surfaces. As its name suggests, the workpiece is not held between centers. This results in a reduction in work handling time; hence, centerless grinding is often used for high-production work. The setup for external centerless grinding consists of two wheels: the grinding wheel and a regulating wheel. The workparts, which may be many individual short pieces or long rods (e.g., 3-4 m long), are supported by a rest blade and fed through between the two wheels. The grinding wheel does the cutting, rotating at surface speeds of 1200-1800m/min. The regulating wheel rotates at much lower speeds and is inclined at a slight angle I to control throughfeed of the work.

With internal centerless grinding, in place of the rest blade, two support rolls are used to maintain the position of the work. The regulating wheel is tilted at a small inclination angle to control the feed of the work past the grinding wheel. Because of the need to support the grinding wheel, throughfeed of the work as in external centerless grinding is not possible. Therefore this grinding operation cannot achieve the same high-production rates as in the external centerless process. Its advantage is that it is capable of providing very close concentricity between internal and external diameters on tubular part such as a roller bearing race. (Mikell P. Groover; Fundamentals of Modern Manufacturing Materials, Processes, and Systems 3rd Edition; pg.608-609)

Creep Feed Grinding

In creep feed grinding developed in the late 1950's, the wheel depth of cut, d, is as much as 6 mm and the work piece is low. The wheels are mostly softer-grade resin bonded, and with open structure to keep temperatures low and improve surface finish. That way grinding can be used for large-scale metal removal operations similar to milling, broaching, and planing. (Kalpakjian, Smith; Manufacturing Engineering and Technology 4th Edition; pg. 726)