Fast test method for the determination of the grindability of fine materials

This paper presents briefly the standard grindability testing methods such as Bond- and Hardgrove process. Then the study shows two relatively fast alternative way for the determination of specific grinding work and Bond work index of brittle materials.The standard laboratory grindability tests can be applied to the grinding of materials in a relatively coarse particle size interval (Bond method: x < 3.36 mm, Hardgrove: x = 0.59–1.19 mm, Zeisel process: x = 0.75–1.00 mm). However, there has been huge industrial demand for the production of different kind of fine materials for few decades. The feed material particle size is generally below 50–100 μm. That is way the reliable mill dimensioning demands the investigation of the grindability of fine materials. One of the main aims of grindability research carried out by the University of Miskolc, Institute of Raw Material Processing and Environment Process Engineering – coordinated by Csőke – is to develop a grindability determination method, mainly for fine materials, by means of the improvement of Hardgrove and Bond measuring methods and devices. Therefore, the Hardgrove- and Bond mills were equipped with torque and power input measuring instruments (torque-meter, electric energy meter).Standard and modified Bond- and Hardgrove tests were carried out systematically with different kind of brittle materials in the standard particle size range. Furthermore, locked-cycle grinding experiments were completed with Universal Hardgrove mill in order to compare the results with the values obtained previously by the “one-step” Hardgrove grindability test. The results proved the reliability of the new modified tests. Thereafter experiment series were performed with fine materials such as alumina and power station coal fly ash. In case of alumina sample the laboratory specific grinding work results were compared with those values of industrial ball mill.