We operate one open circuit two chambers ball mill of size 4m dia X 13.5m long for Cement grinding. Capacity:100tpd drive motor: 2x1500 kW (twin drive) Power drawn: 2500 kW (more data on grinding media). >We are maintaining a blaines of 2700 to 2800. The cement is coarser having a residue of 10 per cent over 90 micron sieve and 30 per cent over 45 micron sieve. Increasing the blaines reduces output and increases the power consumption. How to achieve lesser residue keeping the same blaines.

There is no easy way to adjust the particle size distribution of an open circuit mill while maintaining the same Blaine. To do that you need a separator in closed circuit with the mill to send the oversize material for regrinding. You may have some success with grinding aids. Alternatively you could try for a more coarse media grading in the second chamber. However the results of doing that cannot be precisely predicted.

After 18 years operation of 65tph ball mill, feed end cone has developed a crack. It was welded as per procedure taking all precautionary measures, but this crack has further propagated after 24 hrs operation and now a series of welding it is being operated with a close watch. This mill is 2 compartment mill with simple mechanical dynamic separator and is discharge end drive. Will you please help me to sort out the reason for cracks.

The reason for the cracks is that the mill end castings and flanges are among the most stressed parts of a cement works. The data that I have suggests that the mean time between failures for such parts is about 19 years. Your mill has operated for 18 years therefore is has exhibited typical behaviour. Now that you have cracks you need to have a rigorous inspection and repair regime. What means are you using for inspection? Magnetic particles? Dye penetration or ultra-sonic? Presumably the mill supplier has told you the material the cone is manufactured from and the correct materials for the welding repair. The depth of penetration of the cracks is also a critical factor. If the cracks are right through the casting then any repair will only extend the life of the part by a short time. I would suggest ordering and preparing for a replacement.