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Hardgrove Grindability Index (short HGI) is a measure for the grindability of coal. Grindability is indicated using the unit °H, e.g. "40°H" or "55°H". The smaller the HGI, the harder and less grindable is the coal. Grindability is an important factor for the design a coal mill. As grindability depends on many unknown factors, HGI is determined empirically using a sample mill according to the following procedure: == Procedure of measurement == 50 g of air dried coal featuring a grain size in the range between 0.6 and 1.2 mm are filled into the sample mill and a weight is put on the mill's grinding stone. After 60 rounds the grinded coal is put on a sampling sieve. Factor D equals the fraction of the coal passing through the sieve. HGI is calculated from D as follows: : This procedure only results in relative values because the sampling mill is calibrated using a reference coal. The HGI of the reference coal is defined as 100. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hardgrove Grindability Index」の詳細全文を読む スポンサード リンク
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