Aug 11, 2010· Re: MATERIAL RETENTION TIME IN A BALL MILL VRM. You could do that by measuring the material flowrate Q[tons/h] through the mill as well as the quantity M[tons] of material that accumulates within the mill. The retention time, also called residence time, is the ratio (M/Q) [h] .

THE INFLUENCE OF MILL SPEED AND PULP DENSITY ON THE GRINDING EFFICIENCY 89 ... mill (kg) Retention time (min) 61 59 60 60 % < 75 micron Table II ... These data are then used to calculate the total pulp and ball charge angle (see Graph 5).