Grinding INDEX

The development of a continuous grinding index was the focus of work in the late 1970s (59). The laboratory test equipment used is similar to that for the Hardgrove test but permits classifying the product and recycling the oversize material. An improved correlation is obtained that may, however, need to be corrected for the relative sizes of the test grinding balls versus those used in commercial-scale equipment. The continuous grinding index is especially useful for lower rank coals. 

Moisture content affects a number of appHcations. The grindabiUty index, ASTM D409, measures the relative ease of pulverising coals and theoretically helps determine the capacity of pulverizers. In practice, low values of grindabiUty occur at moisture extremes and maximal grindabiUty occurs at intermediate moisture content. A small pulverizer to test grinding conditions for design purposes has been developed (20). 

Workers in the metals treatment industry are exposed to fumes, dusts, and mists containing metals and metal compounds, as well as to various chemicals from sources such as grinding wheels and lubricants. Exposure can be by inhalation, ingestion, or skin contact. Historically, metal toxicology was concerned with overt effects such as abdominal coHc from lead toxicity. Because of the occupational health and safety standards of the 1990s such effects are rare. Subtie, chronic, or long-term effects of metals treatment exposure are under study. An index to safety precautions for various metal treatment processes is available (6). As additional information is gained, standards are adjusted. 

The work index may be round experimentally from laboratoiy crushing and grinding tests or from commercial miU operations. Some rules of thumb for extrapolating the work index to conditions different from those measured are that for dry grinding the index must be increased by a factor of 1.34 over that measured in wet grinding for open-circuit operations another factor of 1.34 is required over that measured in closed circuit if the product size Xp is extrapolated below 70 [Lm, an additional correction factor is (10.3 + Xp)/l.l45X . Also for a jaw or gyratory crusher the work index may be estimated from... 

Diamond Precious-stone grinding and polishing Pure carbon High refractive index hardest material on earth... 

Index Entries Distiller s grain corn dry-grind pretreatment enzymatic hydrolysis ethanol animal feed. 

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