Research On Rock Breaking Mechanism Of Pick Based On Particle Mechanics

The interaction between the pick and the coal rock will produce complex changes during the rock breaking process of the pick.It is very important to understand the cutting performance of the pick and the crushing process of the coal rock.On the drums of mining machinery and coal mining machinery,the quality of the cutting performance of the pick directly affects the production cost of the enterprise.Under the action of the pick,the high-strength stress concentration between particles can increase the yield of coal and rock on the one hand,and there are also potential safety hazards on the other hand.Therefore,based on the particle mechanics method,the variation laws of coal and rock particle cracks,force chain and stress were further analyzed.This paper takes the mesoscopic force chain as the link to establish the connection between the microscopic-mesoscopic-macroscopic coal and rock,and further study the mechanical properties of the coal and rock material,which is of great significance to the efficient and safe production of coal and rock.In this paper,the general law of the influence of particle mesoscopic parameters on the macroscopic properties of rock materials is firstly analyzed.The particle flow PFC2 D software was used to conduct direct tensile and uniaxial compression tests on rock materials,and the mesoscopic parameters that could reflect the macroscopic deformation of the rock were obtained.Based on CAD software,the two-dimensional model of the pick was established,and it was imported into PFC2 D software to establish the rock-breaking model of the pick.Dynamic simulations were performed at cutting angles of 44°,48°,52° and cutting depths of 2 mm,3mm,and 4 mm.Secondly,the influence of cutting parameters on the microscopic force chain of rock particles in the process of rock crushing is analyzed,including the length,number and direction of the force chain.Using the method of measuring circle to analyze the change of rock internal stress.Thirdly,the mechanism of rock crushing is analyzed,and the changing law of rock cracks under different cutting parameters is explored.Finally,the change of cutting load and the changing law of cutting performance under different cutting parameters are analyzed.The main conclusions of this study are as follows:(1)The length of the force chain preferentially reaches the maximum value at a smaller cutting angle and a larger cutting depth.As the cutting angle decreases,a small contact force will be generated between the rock particles,which is conducive to the formation of the force chain.As the cutting angle decreases and the cutting depth increases,the number of force chains increases logarithmically.During the cutting process,the direction of the average contact force of the force chain lags behind the direction of the cutting angle,the direction of the normal average contact force of the force chain is distributed in a peanut shape,and the direction of the tangential average contact force is distributed in a petal shape.Comprehensive consideration,choosing a smaller cutting angle and a relatively high cutting depth in the cutting process is conducive to the formation and expansion of the force chain,which can ensure the safe production of coal and rock.(2)Large tensile stress and shear stress will destroy the contact state between particles and form cracks.The greater the tensile and shear stress,the greater the number of cracks produced.By recording the number of cracks,it is found that the number of tensile cracks is about 7 times the number of shear cracks.With the increase of cutting angle and cutting depth,the number of cracks will gradually increase,and the stronger the damage of the pick to the rock,the proportion of shear damage will gradually increase.Therefore,increasing the cutting angle and cutting depth is beneficial to the generation of cracks.(3)By analyzing the change of cutting load under different cutting parameters,it is found that the cutting tangential force and cutting normal force change in a step-like manner.The average tangential and normal forces increase nonlinearly with decreasing cutting angle and increasing cutting depth.By analyzing the variation law of productivity(PR),pulse number(PN),specific energy consumption(SE),and fluctuation index(FI)under different cutting parameters,and normalizing them.The research found that when the cutting angle was 52° and the cutting depth was 3 mm,the comprehensive cutting performance of the pick was the best.