Investigation into the applicability of Bond Work Index
15/10/2015#0183;#32;The index varies from 20 to 110, with a lower HGI indicating a coal is harder to grind and more energy will be required to reach the required degree of fineness. The test is conducted on a standardised laboratory scale ballandrace mill and is covered by BS :1995 . A strong, hard coal will often have a high rank and be difficult to