The Breakage Process in an Impact Crusher, Experiments and 3D-DEM-Simulations

The breakage process in an impact crusher has been simulated three-dimensionally using the Discrete Element Method (DEM). The ordinary building material "concrete" was chosen as the particle compound material examined since concrete recycling became more and more important in the last years.   Experiments on a large scale crusher were done to investigate the best process conditions for concrete recycling, especially for the liberation of the aggregate component. Central process parameters have been varied, such as the feed rate of the concrete pieces, the gap width and the circumferential rotor speed between 4.5 and 13.3 t/h, 20 and 35 mm, 25 and 38 m/s respectively. The tested specimens were concrete balls and cylinders as well as sand and mustard granules. The particle trajectories were recorded by a high-speed video camera and the energy consumption was measured by a torque meter and a speed gauge.   The obtained experimental results are the basis for the evaluation of the DEM-model, wherein the particle compound is modelled out of small spherical particles sticking together and forming a complex mechanic network. So, the concrete is modelled by larger particles representing the aggregates and smaller ones representing the hardened cement paste. Solid and moveable walls form the grinding chamber, in which the breakage phenomena have been simulated.  
The fracture patterns, particle size distributions and liberation degrees from both experiments and simulations were recorded and the comparison shows both results in close correspondence. One can say that this method has great potential to assist engineers in adjusting crushers and optimising the comminution process in the near future.