How to understand the "high concentration, large return sand and even ore feeding" in the operation

The grinding mass fraction is an important factor affecting the productivity of the grinding machine.   It determines the friction between the grinding medium and the ground material, the fluidity of the pulp and the effective density of the medium (the density difference between the medium and the pulp).   In the operation of the grinding machine, a higher grinding mass fraction is generally used, so that a layer of pulp can be attached to the surface of the medium, so as to enhance the grinding effect beneficial to grinding.   At the same time, there is a large amount of ore per unit volume in the ore discharge, so the ore discharge is large.   However, if the pulp mass fraction is too high, due to the increase of pulp density, the effective density, activity ability and striking effect of grinding medium will be weakened.   At the same time, if the pulp mass fraction is high, the viscosity will be large, the fluidity will be poor, and the total ore discharge will be reduced.   On the contrary, the productivity of the grinding machine will be reduced, and even "belly swelling" will occur.   Therefore, "high concentration" refers to appropriately increasing the grinding mass fraction within a certain range, which is conducive to improving the grinding effect.

Sand return refers to the coarse particle size returned by the classifier to the grinder for regrinding during closed-circuit grinding. The amount of ore return is often several times that of the original ore feed. The ratio of return sand volume to raw ore feeding volume is called return sand ratio. Practice has proved that the size of the return sand ratio will directly affect the productivity of the mill. The larger return sand ratio increases the total ore feeding amount of the mill, thus increasing the discharge speed of the mill, shortening the retention time of materials in the mill and speeding up the circulation. In addition, although the return sand is coarse-grained ore, it is finer than the raw ore after all, so the particle size composition of the full feed of the mill becomes finer, and the comprehensive result is conducive to improving the productivity of the mill.

There are two main implications here: first, the ore feeding speed (the amount of ore fed into the mill per unit time) is constant; Second, the ore feeding particle size composition is uniform. In order to improve the grinding efficiency, the feeding amount should be continuous, uniform and stable at a high level. More or less time will make the mass fraction in the grinder fluctuate frequently, which is not conducive to the grinding process. The grinding feed often appears particle size segregation in the silo - the middle is fine, and the surrounding is coarse, which is easy to cause uneven feed composition. If the operation cannot be adjusted in time according to the particle size, there will be "swelling". Therefore, the silo should adopt multi-point discharging and feeding as far as possible.