Hardgrove Grindability Index - WikipediaHardgrove Grindability Index (short HGI) is a measure for the grindability of coal. Grindability is an index, therefore it has no unit. The smaller the HGI, the harder and less grindable is the coal. Grindability is an important factor for the design a coal mill. . are filled into the sample mill and a weight is put on the mill's grinding stone.hardgrove grinding mill coal,hardgrove grinding mill coal,Hardgrove Grindability Index (HGI) | Mining | SGSGrinding studies, and the resulting HGI, allow many different types of coal users to evaluate how coals will perform in their mills, allowing them to estimate.
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