A Study of Crushing Brittle Solids

JSGT 1933 V17 T384-T410

Under free crushing conditions, whether the load be applied by simple crushing, shear or impact, it is found that homogeneous brittle solids break down with a constant fracture pattern which is independent of the size of the original specimen. This law must be interpreted statistically, since wide variations will be found in the behaviour of individual particles. It thus appears that the minimum work required to crush a powder depends on the product of:- (1) The constant for the material; (2) The weight of the material crushed; and (3) The logarithm of the total mean reduction (=log(The mean original size/The mean final size). To crush coal and anhydrite through a 10:1 reduction ratio involves an energy consumption of 0·05 and 0·15 kWh/T, respectively. Material of ½ in size crushed to 200 mesh involves a mean reduction ratio of about 100:1 and the work necessary is thus 0·1 kWh/T for coal and 0·3 kWh/T for anhydrite. Values of a similar order have been obtained for other materials, and indicate that industrial crushing requires about 100 times as much energy as that theoretically necessary. This means that the industrial methods of crushing are very wasteful in energy compared with the process adopted by a labourer crushing stones. Industrially this information is perhaps of little value, but it does give a basis on which to define the efficiency of other grinding processes in which the loading conditions of the individual particles are difficult to define.

W. F. Carey & C. H. Bosanquet