ABSTRACT:

The jaw crusher is often used for the initial size reduction of ores. The consumption energy of the crusher is calculated by the Bond indices. In this work, the PFC3D discrete element method (DEM) software was employed to model the crushing behavior of some rocks with different mechanical properties in a laboratory jaw crusher. FLAC3D software was adopted to analyze the stress distribution in the rocks. The rocks studied were modeled as granular assemblies in the shape of a sphere and located between two jaws, and the consumption energy in the processing zone of the jaw crusher was determined. To verify the eliminated results from the model, nine different types of rocks were studied, and the energies consumed by the crusher were compared to those of the Bond comminution energy eliminated from the Bond crushability index. There is fairly good agreement between the energies acquired by the DEM model and the Bond crushing energies for the spherical specimen. It appears that the DEM is a suitable method for predicting the crushing energy. The eliminated results show that there is a linear relationship between the Bond crushability index and consumption energy; the higher the Bond index, the higher is the consumption energy in the jaw crusher. The fracture behavior of the crushed rocks was examined using high speed camera in a jaw crusher and was compared to the PFC3D results. Because the jaw face is corrugated, the tensile stresses may be developed in the rocks and the tensile mode of fracturing may occur in the rocks. The tensile mode of fracturing is favorably modeled by the PFC3D software.

1. INTRODUCTION

The discrete element method (DEM) was first proposed by Cundall and Strack to model the behavior of soil particles subject to dynamic loading conditions (Cundall and Strack, 1979). Mishra and Rajamani pioneered the application of DEM to grinding mills and demonstrated that despite the fact that the DEM simulations are based on two dimensions (2D), the technique is able to predict the power draw of mills with reasonable accuracy over a wide range of mill diameters (Mishra and Rajamani, 1992, 1994). More than 10 years since then, the DEM technique has been successfully applied to ball mills (Cleary, 1998, 2001; van Nierop et al., 2001; Djordjevic, 2003), SAG mills (Rajamani et al., 2000; Cleary, 2001; Morrison et al., 2001) and centrifugal mills (Inoue and Okaya, 1996; Cleary and Hoyer, 2000). DEM has also been applied to study impactinduced particle breakage. Using DEM simulation of impact breakage of agglomerates (Thornton et al., 1999; Kafui and Thornton, 2000; Mishra and Thornton, 2001) and aggregates that are hardened by cement (Potapov and Campbell, 1994; Tomas et al., 1999; Shubert et al., 2005), different parameters that influence the impact fracture have been analyzed. The finite element method (FEM) is usually adopted to determine stress patterns, and DEM has been used to show crack distributions in rocks under loading (Schubert et al., 2005). Also, using DEM modeling of the compact strength and drop weight test, the relationship between strain rate, impact energy and the degree of fragmentation has been determined (Whittles et al., 2006).

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