I am working in a grinding unit having a vertical roller mill for slag grinding (UBE VRM). Initially this mill is for only slag grinding but we are also able grind clinker. We are getting clinker from various sources. Because of this we are getting different output & power consumption. I want to ask you is this normal to get different output & power consumption? How much influence does the wear rate of table & rollers have on output & power consumption. Also I want to know what are ways to increase the output of the vertical roller mill.

It is normal to get different outputs from the mill with materials from different sources. This will depend on the hardness of individual materials. There are ways to increase the output from a vertical mill. These involved justments to the separator and the airflow through the mill. A number of case studies have been reported by Siam Cement where major increases in output were achieved by these means.

I would like to know how to estimate the quantity of grinding media of each size required for a ball mill using the data; mill size, number of chambers and type of material to be ground. Kindly explain me what formula is to be used.

The total quantity of media required for each chamber is determined by calculating the internal volume of the chambers. A rule of thumb is to change the first chamber to 30 per cent of this volume and the second chamber to 27 per cent. You can use 4.6t/m³ as the density of grinding media. As for the individual ball size gradings this has to be determined by conducting a series of axial tests in the mill while you are building up the media charge.