Abrasive weels

Abrasive materials, substances of high hardness for mechanical processing of metals, ceramic materials, rocks, minerals, glass, wood, leather, rubber, etc. From the end of 19th century applied artificial A. m. (aluminium oxide, silicon carbide, boron carbide, mono corund, synthetic diamond, etc.), the previously used only natural A. m. (flint, emery, grenades, pumice-stone, aluminium oxide, diamond). The main characteristics of A. m.: hardness, durability and viscosity; form of the abrasive grain; abrasive ability, grit. The hardness of the A. M. determined (Mn/m2) method of compression diamond pyramid in the surface area of the material (for example, for quartz 11 000-11 300, electrocorundum 18 000-24 000, diamond 84 250-100 000). Common definition of hardness in kgf/mm2 (1 kgf/mm2 "10 Mn/m2). With the increase in the strength of A. M. improves the resistance of the cutting efforts. Resistance A. M. compression in several times more than the resistance of a stretch and bend. The strength of the A. M. tensile and compression decreases with the increase of temperature grinding. Abrasive grain - crystal shard (crystal), less monocrystal or unit consisting of many small crystals (поликристалл). The cutting edge of grain - edge, formed by any pair of intersecting crystallographic planes. The grain can be of approximately equal size in height, width and thickness (isometric form) or have and leaf form, which is determined by the generation A. M. and degree of comminution of the original grain. Rational isometric or close to it a form of grain, because each grain is a tool. The least profitable form - pin. The grain has several facets, forming the top with the angles of 30 to 130? and with a radius of roundings in grains from 200 up to 4 microns. The grains of synthetic diamonds corners and radii of roundings less than the natural, so it is possible to shoot thin chips. Abrasive ability is characterized by mass shooting in the grinding material up to the blunting of grains. The abrasive ability A. M. are arranged in the following order: diamond, cubic boron nitride, silicon carbide, monocorund, electrocorundum, emery, flint. Abrasive ability depends on the type of grinded materials, mode of operation, toughness and strength of grain. The smaller the A. M. impurities, the above abrasive ability. Grain size determines the size and homogeneity of the grains A. m.; it is determined by the classification of the grains of the linear size of the method of sieve analysis, the deposition in the liquid or others. The number of grain are determined in accordance with the linear dimensions of the grain of the main faction. The more uniform in shape and size of the grains A. m., the higher the performance of the. The grain A. M. regulated by the standard. Processing with the help of A. M. is characterized by the participation in cutting at the same time a large number of randomly located cutting edges grains. The hardness of the abrasive tool allows you to apply a high cutting speed, that in connection with a large number of simultaneously working blades provides a sufficient volume of the material. On the other hand, with the help of A. M. achieved the most delicate handling, for example finish. A. m. used in the form of grains, sealed in a bunch of different shapes and purposes abrasive tools, or drawn on a flexible basis (cloth, paper, etc.) in the form of sandpaper, as well as in uncombined state in the form of powders, pastes and suspensions. Lit.: Kamencev M.V., Artificial abrasives, M., 1950; N.YE., Filonenko IGOR Lavrov., Abrasive tools and their operation, M., 1959. Mr.. M. Ippolitov.