Calculation of energy required for grinding in a ball mill

Abstract

The Bond work index, W i, as an indicator of the grindability of raw materials is not a material constant but rather it changes with change of size of the grinding product. Therefore, in practice we can expect some difficulties and errors when the energy consumption is determined according to this formula in the case when, for a given size of grinding product, the value of the work index W i, which is determined by experiments, is not known. This problem is considered in this paper and some solutions are put forward. Experiments were made on copper ore, andesite and limestone, and it was found that the change of the mass passing a test screen G could be related to the aperture size P k of the screen by the formula: G=K 1 P k . The grinding-product size, P, in a Bond ball mill, which is given by the aperture size which passes 80% of the grinding product as a function of the aperture size of the test screen P k, can be expressed by the formula P= P k K 2 . These functions for G and P enable us to calculate the value of W i for any other size of grinding product if we know the work index W i and aperture size of the screen P k.