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grinding,process by which surface material is removed from an object, usually metal, by the abrasive action of a rotating wheel or a moving belt that contains abrasive grains. A grinding wheel can be made by mixing a bonding material, usually clay, with abrasive grains of such substances as silicon carbide or aluminum oxide. The mixture is then shaped into a wheel and hardened. A grindstone is a grinding wheel made by shaping naturally occurring sandstone, which contains abrasive quartz grains. Grinding is used in many manufacturing processes to produce a fine surface finish on an object and to bring the size of an object to within very fine tolerances. A grinding machine has devices that hold an unfinished object and move it past the machine's abrasive wheel or belt, which is driven by a motor. For less exacting work, such as sharpening cutting tools, objects can be hand held and ground by a machine consisting mainly of an abrasive wheel or belt. For many products grinding is only one step in a finishing process that involves additional similar operations such as honing, lapping, polishing, and buffing.
(1) In metalworking, the machining of surfaces of workpieces with an abrasive tool. It is performed on grinding machines and other types of meal-cutting machine tools by means of special attachments (such as grinding heads), as well as by hand. A distinction is made between grinding in which the peripheral speed of the tool is approximately 20 m/sec and high-speed grinding, in which the peripheral speed is greater than 50 m/sec. Grinding makes it possible to fabricate metal parts having a precision of class 1 and a surface roughness of class 10. It is widely used to machine external and internal flat, cylindrical, conical, and irregularly shaped surfaces of workpieces made from metals, plastics, ceramics, ferrites, stone, and wood. Rough grinding is also used to some extent to remove large machining allowances from cast pig iron and steel workpieces.
The various types of grinding include external and internal cylindrical grinding, grinding with a planetary motion, external and internal centerless grinding, surface grinding, and grinding of special shapes.
Electrochemical grinding is used to work metals that are difficult to machine. Current-conducting grinding wheels are fed with a DC current, and an electrolyte is supplied to the cutting zone. Grinding can also be performed by means of vibration machining with an abrasive powder suspended in a liquid.
A carborundum abrasive tool is usually used to grind stone. The process may be accomplished by grinders or by hand.
(2) In groats production, grinding removes the germ and the outer parts of the kernel, thereby imparting a definite shape and uniformity to the crushed grains.
REFERENCESMaslov, E. N. Teoriia shlifovaniia materialov. Moscow, 1974.
Vul’f, A. M. Rezanie metallov, 2nd ed. Leningrad, 1973.
A. A. SHISHKIN