A High Energy Crushing Test (HECT) system was used to simulate the operational settings of a jaw crusher so that comparison of fracture toughness and specific comminution energy (the energy required to reduce a rock particle to a given size) could be performed. Since power consumption is a function of the crusher settings, as well as the material being crushed, the closed side set of the HECT system was varied, resulting in single particle breakage tests run at two reduction ratios, 1.5 and 3. The results of the fracture toughness and HECT system tests indicate a strong and linearly proportional relationship between fracture toughness and specific comminution energy. Additionally, fracture toughness was shown to be related to specific comminution energy more strongly than any other material property tested, including tensile strength. A model for the prediction of power consumption has been developed based on the results. At the experimental level the model has been able to predict the specific comminution energy to within 3%. At the operational level the model allows for the determination of jaw crusher power consumption based on the nature of the rock being broken and the average amount of size reduction being done on the feed material.
1. INTRODUCTION
The size reduction of brittle materials is the most essential mechanical operation within the raw material processing, i.e. mining, industry. It is also an inefficient, energy intensive process that consumes billions of kilowatt-hours of electricity per year (approximately 3-5% of all electricity consumed on the national level [1, 2]. In fact only 1% of the total energy input into size reduction processes is used in fragmentation and the creation of smaller particles, with most of the energy manifesting in the form of heat and noise. How has a process so fundamental, and costly, to the mining industry remained so inefficient? In a large part because the scientific research required to lay down he theoretical foundations of particle size reduction has lagged behind the actual achievements of technology, resulting in the design and operation of crushing equipment based on standards that fail to adequately describe the entire particle breakage process [3]. Since the technology is already in place, improvements in comminution are dependent upon optimizing the application and operation of that technology. In fact, the United States National Materials Advisory Board estimated that improving the energy efficiency of comminution processes, using practical approaches, could result in energy savings of over 20 billion kilowatt-hours per year [4].
The importance of classical comminution work (Von Rittinger, Kick, and Bond) is that it indicates some relationship between the energy required to decrease the size of a particle and the resultant size of the broken particle. Bond's work in particular highlights the importance of selecting and evaluating crushing equipment, and determining power requirements, based on product size and some measure of a materials resistance to fracture. Over the last three decades more research has focused on the physics of particle fracture during the crushing process and the material characteristics related to fragmentation.
