Research On Cutting Performance Of Fully Mechanized Coal Face In Fractured Coal Seam

In the comprehensive mining of Jurassic thick and hard coal seam in Northern Shaanxi,there are many problems such as high cutting power consumption,serious wear of pick teeth and low lump coal rate.Through the softening transformation of thick and hard coal seam,the fractured coal seam is formed.This paper takes fractured and thick coal seam as the background,takes fractured coal seam as the research object,and uses theoretical analysis,numerical simulation and field test method to study the performance of cutting energy consumption and cutting resistance of fractured coal seam.The main research results are as follows:(1)The physical properties and mechanical properties of the coal seam with different fracturing degree are studied by experiments.The relationship between the PRI coefficient of the coal seam with different fractured degree and the coal cutting impedance and the load fluctuation is determined and the fitting relation is given.The movement rule and running track of single pick of shearer drum are studied,and the method of cutting and improving cutting area is analyzed.(2)Stress analysis of the cutting process of the picks picks,and the mechanical model of the pick cutting is established.The process of cutting the teeth to load the coal body during the process of cutting coal is analyzed,and the conditions for the fracture and failure of the coal body are determined.The study shows that when the tensile stress and shear stress of the cutting tooth surface exceed the strength of the coal body itself,the coal body breaks down to produce micro cracks,and the micro cracks expand under the compound action of the tensile shear and produce the tensile shear composite cracks.(3)Based on the minimum strain energy density theory,the conditions for cutting crack propagation are studied.Through the ABAQUS numerical simulation analysis of the critical pressure of the cutting fracture of the fractured coal seam and the fractured coal seam,the study shows that the fractured coal seam is affected by the cutting effect of the cutting teeth,the fracture expansion pressure is small and the cutting fissure extends long distance,which is beneficial to the output of the lump coal.By establishing the interaction model of the cutting force and fracture fracture,it is clear that the cutting force can promote the fracture expansion,in which the fracture fracture angle is 45 degrees,and the expansion pressure is minimum.(4)Based on the I.EVANS tensional stress theory,the optimum intercepting distance between the fractured coal seam is calculated,and the volume of the cut coal is the largest when the spacing of the double teeth cutting is at 0.34M,and the chessboard type cutting is used for the larger area of the plastic zone compared with the sequential cutting,that is,the lump of the cut coal body is high.By studying the fluctuation curve of cutting resistance,it is found that the resistance of sequential cutting is generally greater than that of chessboard type cutting,and chessboard cutting efficiency is high.The ANSYS-LS/DYNA calculation shows that the best cutting speed of the shearer cutting the fractured coal seam is 0.111m/s and the roller speed is 0.45r/s,at this time the cutting performance of the shearer is the best and the lump coal rate is greatly improved.