Experimental Study On Mechanical Behavior Of Pick-Rock Cutting Process

Pick-rock cutting fragmentation process is a complex interaction pick and coal and rock mass. It is closely connected to rock breaking parameters, cutting pattern and physical properties of coal and rock, etc. The mechanism of pick-rock cutting fragmentation serves as an vital theoretical basis for mining equipment cutting machine design, cutting parameter plan and selection of mining equipment. In this paper, the coal rock cutting mechanics behavior and fracture mechanism are researched based on the mechanism of cutting tooth breaking rock and its process is explained with application of test method and PFC2 D discrete element simulation method from both macro and micro views. In addition, the rock breaking performance of different cutting patterns and energy consumption of the cutter breaking rock is discussed. The main conclusions gained are as follows:(1).The process of cutting tooth breaking rocks includes initial extrusion stage which is characterized by a linear increase in load and temperature, almost no fragments on rock surface; steady extrusion stage which features that load increases in the shape of zigzag, a small amount of debris appears on the surface and there is an inflection point in temperature curve; Large pieces of rock-falling stage, load falls sharply, the temperature decreases, and large granularity is produced on the surface. The process of Cutting tooth breaking coal includes, cut tooth initial squeezing phase---linear load and temperature increase, the coal surface produces a small amount of debris; Stable extrusion stage---there is a turning point in load and temperature with a linear increase, the coal surface produces a large amount of debris; Large pieces of rock stripping stage---gentle and reduce load show that the creep damage characteristics, the temperature decreases, and there are large pieces of debris.(2).The influence Cutting parameters have on cutting process---index of cutting load and the particle size distribution increases with the increase of cutting thickness; Cutting energy consumption and cutting temperature decrease with the increase of cutting depth; Cutting load has a linear relation with the cutting depth; there is a power function relationship among particle size distribution index, cutting energy consumption and cutting depth and high correlation; when cutting tooth installation angle is 55 °, cutting load, energy consumption and the cutting temperature are the maximum, instead particle size distribution index value is the minimum; when 45 °, cutting load, the energy consumption and the cutting temperature are the minimum, and particle size distribution index value of the maximum. The bigger the particle size distribution index is, the greater the proportion of large debris is, the smaller the value of energy consumption is, the lower cutting temperature is, the smaller the particle size distribution index is.(3).When cutting teeth breaking rock is stimulated by PFC2 D discrete element, micro failure of cutting teeth breaking rock is mainly about tensile failure. Cutting thickness has an important effect on rock damage form, when cutting thickness d = 2 mm, d = 3 mm, pick rock damage process of rock is mainly about granular destruction, and the crack is mainly about the micro crack. The breaking form of coal and rock is a ductile fracture; When d = 4 mm, d = 5 mm, the cutter tooth and rock produce stress concentration in the tooth top and the macroscopic crack. The rock caves in block form. The greater the cutting thickness is, the more macroscopic crack is produced, the breaking form of the block of coal transforms from ductile into brittle breaking.(4).Semi-enclosed cutting pattern is a power-wasting cutting pattern, which is not beneficial to the form of large debris in the cutting process. Free cutting pattern is an efficient cutting mode, and it is good for the large debris form with little damage. The study of repeat plane cutting mode shows that the best ratio between cutting space and cut depth is about 5.(5).Through study of the correlation between coal and rock mechanics performance and energy consumption, it can be concluded that there is good relativity between energy consumption and uniaxial compressive strength, elastic modulus, tensile strength and the correlation of point load while bad relativity with poisson’s ratio. Through correlation analysis, it shows that the key factors influencing energy SE are uniaxial compressive strength and elastic modulus, then the equation SE = exp(aσc+bE+c) about energy consumption, uniaxial compressive strength and the multiple regression elastic modulus is established, including: a value between 0.158 to 0.247; b value is 0.01; c as a constant related to cutting parameters. By studying the correlation between specific energy SE and particle size distribution index CI, it is concluded that there is a power function relationship between both two. The SE decreases with the increase of particle size distribution index CI, and particle size distribution index CI can be an evaluation index of coal and rock cutting potential.