Question

Calculate the critical speed, in revolutions per minute, for a ball mill 1600 mm in diameter charged with 100 mm balls......

a) 149

b) 276

c) 321

d) 419

c) NONE

Answer 1

Critical speed for a ball mill

$N_c = \dfrac{1}{2π} (\dfrac{\sqrt{2g}}{(D-d)})$

$N_c = \dfrac1{2π}(\dfrac{\sqrt{2× 9.81}}{{1.6-0.1}})= 4.64\text{ rps}= 278.3\text{ rpm}$

b