Research On Impact Compaction Mechanism And Discrete Element Numerical Simulation Of Viscous Carbon Paste

In the aluminum reduction cell construction process, the impact compaction method is widely used to compact the carbon paste. The quality of the compacted paste has the mainly effect on the lifetime of the cell. The research of the paste compaction is important to advance the lifetime of the cell. The current study and application of paste compacting process under the impact load are based on the macroscopic hypothesis and experiments. The mechanism of impact compaction and the relations of the compaction and the physical mechanics characteristic of the paste are not fully understood, and the numerical simulation technology is also lacked. The status quo makes the automation production level of aluminum electrolysis improve slowly. In order to enhance the lifetime and economic benefits of the cell, it is necessary to improve production level and efficiency of the cell construction by using modern technology and optimal methods. It is indispensable to research the viscous carbon paste and it's impaction by new theory and technology.The paste is a thermoplastic granular material that made up of particle and porosity, and the character is very complicated. The bulk properties are related to the microscopic parameters such as particle size, shape and their distribution. The physical mechanical bulk properties of the paste are varied with the variety of these parameters. The evolution rule of the paste packing under the external loading is studied by using micromechanics. The mechanical simulation model is established by relating the microstructure characteristic to macroscopic mechanical variable. The study of paste characteristics is consummated by connecting the microscopic with macroscopic. On the basis of mechanical model, the mechanical character simulation model of paste is established by using discrete element method. The microstructure parameters of paste are fitted by mechanical experimental results and the paste impact compaction is simulated by using the model. The main work as follow:The physical and mechanical characteristic of carbon paste is premise base of paste compaction. The influence of the component,the physical and mechanical characteristics of the paste on the mechanical properties are researched by the synthetically compare, analysis, study and summarization of research achievements. The different scale of the paste is defined, and the deformation mechanism of the paste compaction is analyzed from the view of microcosmic and macroscopic.On the basis of granular material interparticle studies, the mainly interparticle forces and its influence on the paste interaction are analyzed from the view of microcosmic. Through studying the contact force model of the paste particles, the adaptive contact force-displacement relation of viscous paste particle microcosmic contact is obtained. The dynamic stress-strain properties of the paste are obtained through the mechanical experiments.Based on the paste mechanical experiments, the particle discrete element method is introduced to establish the microscopic mechanical characteristic simulation model. The theory and mechanism of the system construction is discussed. The algorithm which calculated the contact force through relative displacement of this model is realized by using the second development interface of the PFC program. Through analyzing the particle movement, deformation, the interparticle contact force and its distribution, the relation of the interparticle microscopic contact and its macroscopic stress-strain is established. The influence of microscopic structure parameters such as frictional coefficient, elastic modulus and particle diameter ratio on the constitutive relation is studied by changing these parameters.Through the impact compaction experiment, the effect of different parameters on the paste dynamic variation is tested and the adaptive range is figured out from the view of the paste macroscopic deformation. The key parameters such as compacting work, depth of paste are optimized in the adaptive range by using the orthogonal experiment method. According the experiment data, the equation that relates the compaction density to the compacting work and depth of paste is gained by fitting. The investigation of the paste microscopic characteristic shows that the microscopic characteristic parameters are corresponding to the macroscopic deformation in the different compaction phase.The impact compaction simulation system of paste is established by using particle discrete element method. The theory and algorithm of sample generation are analyzed, and the detail approach is given. Through simulating the evolution of particle position, velocity, displacement, and contact forces in the paste impact compaction process, the particle arrangement and displacement change is analyzed, and the variation law of macroscopic configuration and microscopic structure is discussed. The paste mechanical response characteristic in the simulation is corresponded with in the experiments. The particle discrete element method can explain the macroscopic configuration evolution of the paste through simulating the microscopic movement of the paste particle, and the law of dynamic trend of the paste is gained in essence. The simulation system can be used to judge the rationality of the paste compacting techniques and optimize the technical parameters of compaction.