Abstract
Understanding fragmentation behaviour of rock under crushing process is fundamental to improved productivity and efficiency in mining operations. During crushing, rock is subjected to dynamic loading and the particle shape influent the fragmentation of crushed rock. Thus, a highly controlled single particle test, the dynamic spherical crushing test, should be performed to establish the relation between the energy and size reduction for better understanding the crushing mechanism. In this work, a split Hopkinson pressure bar system in combination with high speed cameras was utilized to carry out a single particle crushing test. Spherical rocks samples were adopted to avoid the shape effect for fragmentation process. The energy absorbed by samples was accurately determined from the one-dimensional wave analysis and the kinetic energy of the sample fragments estimated from the high speed camera snapshots. The crushed samples were recycled after the test. Further by counting the newly generated surface from sample fragments, the surface energy was determined for each sample. The indirect tensile strength is consistent with that of reported Brazilian disc test. The determined surface energy increases with the loading rate. Above results indicate a trade-off should be established between the fragment size and energy consumption .
1. INTRODUCTION
Crushers are widely used in the mining industry all over the world, which break rocks to extract specific minerals or specific size fractionation of fragmented rocks for construction. Suggested by many researches, highly controllable single particle test should be performed to understand the fundamental crushing mechanism of rock particle [1-3]. From single particle breakage data, we can acquire several important factors for crusher design and selection: particle strength [1-3] and the energy-size reduction relationships [1]. A wide range of laboratory techniques have been developed, which were broadly classified into three types based on loading methods [4]: slow compression breakage; single impact; double impact. The slow compression breakage method is known as utilizing two rigid plates break rock particle with slow speed (e.g. strain rate 10-3 s-1). The single impact utilized compressed air to accelerate rock particles to a designed speed and hit a solid surface, and investigate the breakage probability of particles; while the double impact test, such as drop weight test or pendulum test, is named in that particle is crushed by two hard surfaces. The disadvantage of the static compression test is that the loading speed is too slow as compared with those encountered in real crushers. The energy absorbed by particles during fragmentation cannot be acquired for single impact tests, which is also impossible for double impact test, except of some attempts made on the pendulum tester [2].
