Production of Grinding Balls of High Surface and Normalized Volume Hardness
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PRODUCTION OF GRINDING BALLS OF HIGH SURFACE AND NORMALIZED VOLUME HARDNESS K. N. Shvedov,1 I. K. Galim’yanov,2 and M. A. Kazakovtsev3
UDC 621.771.65
Materials on and the results of testing new types of equipment for producing grinding balls of high surface hardness and normalized volume hardness are presented. The EVRAZ NTMK company has implemented a technology of producing grinding balls of high strength, including of hardness group 5 (high surface hardness and normalized volume hardness), according to GOST 7524–2015. For this purpose, a set of equipment for producing grinding balls and testing them for impact resistance was put into operation. Meeting the requirements allows achieving high service characteristics of grinding balls. Keywords: grinding balls; quenching; tempering; hardness; volume hardness, impact resistance, macrostructure.
The global development of the mining industry constantly toughens the requirements to the processing of mining raw materials. Reduction of the content of extracted elements in ore leads to an increase in the dimensions of ball mills. To process and grind ore raw materials, steel bodies of spherical, cylindrical, and other shapes are usually used all over the world. Grinding balls are used in ball mills intended to grind various ore and nonmetallic minerals and constructional materials of medium hardness. Mills are also used to produce constructional materials (gypsum, silicate brick, dry mixes, etc.), materials for asphaltic concrete (mineral powder), raw materials for paints and varnishes, and paper (micromarble, microcalcite) and in the mining, mining-and-chemical, and other industries. Ball mills are parts of various processes (open or closed cycles) and allow obtaining uniformly sized products using grinding bodies (balls and cylpebs). The output of a mill depends on the properties of ground materials (strength, grindability): feed size (to 50 mm), moisture content (to 0.5%), grinding fineness, feed consistency, degree of filling with grinding bodies and material, quality and hardness of grinding bodies. The hardness and wear resistance of grinding bodies used depend on the strength of ground materials. For example, balls of high hardness are used to grind nonferrous metal ores. The requirements to and the characteristics of steel balls for ball mills can be found in the GOST 7524– 2015 standard. There are five groups of hardness of balls: 1, normal surface hardness; 2, higher-than-normal surface hardness; 3, high surface hardness; 4, high surface hardness and normalized hardness at a depth of 0.5 ball radius; 5, high surface hardness and normalized volume hardness. Volume hardness was determined in two mutually perpendicular directions as the average of the volume hardnesses of reference balls, using templates cut out from a ball: Evraz Nizhniy Tagil Iron and Steel Works, Nizhniy Tagil, Russia. 1 E-mail: [email protected]. 2 3
E-mail: [email protected].
E-mail: [email protected].
Translated from Metallurg, Vol. 64, No. 6, pp. 16–22, Jun
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