Hardgrove Grindability measures relative ease of pulverization of coals compared to standard coals. The resulting Hardgrove Grindability Index (HGI) provides a measure of energy required in a grinding process or a measure of yield for a given energy input. A prepared 50g sample of No.16—No.30 sieve size coal and eight 1in (25.4mm) diameter polished steel grinding balls are placed in a stationary bowl having a machined circular track. An upper grinding ring with matching track is rotated at 20rpm to drive the balls while a fixed load of 64lb (29kg) is maintained by weighting the motor-driven spindle attached to the upper ring. A counter/switch assembly automatically stops the tester after 60 revolutions, and amount of grinding is determined by sieving on a No.200 sieve. Model LC-100 is made from durable quality materials throughout to assure reliable, maintenance-free operation. The LC-82 Motorized Disk Mill (listed separately) meets ASTM requirements for sample preparation for the LC-100.
New Hardgrove machines must be user-calibrated with a set of four special coal reference samples having approximately 40, 60, 80, and 100 HGI. Order separately as LCA-30.