with the mill is described by the relation [6] 20 15 2 8 40 40 16 Ψ− = Ψ⋅ = − = n D ncr D ϕ (6) where D is the inside diameter of the drum, and n represents mill speed measured in ncr = D 30 ⋅ 2 critical speed of the drum, (D expressed in m.). For φ = – relation (6) leads to the