Grindability Methods

Chandler [Bull. Br Coal Util. Re.s. A.s.soc., 29(10), 333 (11), 371 (1965)] finds no good correlation of grindabihty measured on 11 coals with roh crushing and attrition, and so these methods should be used with caution. The Bond grindability method is described in the subsection Capacity and Power Consumption. ... 

Grindability index number that indicates the ease of pulverizing a coal in comparison to a reference coal. This index is helpful in estimating mill capacity. The two most common methods for determining this index are the Hardgrove grindability method and ball mill grindability method. Coals with a low index are more difficult to pulverize. 

Several methods of estimating relative strength or friability or grindability utilize a porcelain jar mill in which each coal may be ground for, say, revolutions, and the amount of new surface is estimated from screen analyses of the feed and of the ground product. Coals are then rated in grindability by comparing the amount of new surface found in the test with that obtained for a standard coal. 

ASTM D-5003. Standard Test Method for the Hardgrove Grindability Index (HGI) of Petroleum Coke. 

D 408 - 37 T. Tentative method of test for grindability of coal by the ball-mill method. Part III, pp. 562-565. 

Crindability Methods Laboratory experiments on single particles have been used to correlate grindability. In the past it has usually... 

Some of the drum tests stress the materials much more severely. Methods 1 and 2 particularly are grindability tests producing abrasion values of up to 70%. On the other hand, methods 3 and 4 are so gentle that the results hardly differentiate between samples of different quality. Method 5 differentiates well but the relative measures of quality of materials A, B, and rock salt are switched. 

Unlike fracturing, this approach should cause only moderate disruption of the coal matrix and might not lead to complete comminution, but this method could be envisioned as a prelude to coal grinding. Removal of material from structural boundaries would yield a more friable, "soft" coal structure. The leaching of fine mineral particles from the coal matrix results in a more porous structure and should also improve the coal s grindability. The prior removal of some mineral matter would also reduce the coal s abrasiveness. 

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