grinding efficiency in 826 ball mill feed micrometers 1300 ball mill product micrometers 115 ball mill ratio of reduction 113 power per metric tonne motor input kw 92 calculated operating work index wio 1575 on basis motor output 42 x 0956 92 x 0947 1273 kwtonne 1575 x 1273 134 1496 on basis short ton x 09074 1358.