Study On Cutting Characteristics Of Shearer Mining Coal Seam With Coal-rock Interface

Shearer is an important part of the comprehensive mechanized coal mining.The shearer drum undertakes coal cutting, transporting and other key tasks as the coal cutting mechanism. Picks are the main strength of the coal cutting process,its cutting performance directly affects the production efficiency and reliability of the shearer.In recent years, the drum cutting performance has become the research focus of scholars at home and abroad. How to improve the performance of shearer in mining thin coal seam with coal-rock interface is becoming a more urgent problem.Therefore, the theoretical and experimental researches on the dynamics characteristics and cutting performance of picks and drum cutting coal seam with coal-rock interface, are carried out in this dissertation.In this dissertation, based on the Evans rock breaking theory and the experimental results of the unidirection loading tests, the mechanical models of picks and drum rotary cutting homogeneous coal and rock are established. Combining with layered rock mass stress and strain state analysis, and Griffith strength theory, the mechanical models of picks and drum rotary cutting coal seam with coal-rock interface are established.Based on the similarity theory, the similarity criterion of coal and rock properties, the drum, the pick and the cutting load are established.The coal cutting test-bed, picks and drum are developed.And the embedded wireless data transmission test system which can obtain three directions force of the shearer cutting coal and rock is developed.The compressive strength as the main basis for allocation of simulation coal and rock seam and considering the joint, bedding and other characteristics of coal and rock, the simulation coal seam used in test are developed. The relationship between the compressive strength and the matching ratio of pulverized coal(sand) and cement is obtained through uniaxial compressive test, which provides basis for subsequent allocation simulation coal and rock materials.The cutting performance test research of single pick cutting homogeneous coal seam, rock seam and coal seam with coal-rock interface are carried out on the coal and rock cutting test-bed. Firstly, cutting load time domain characteristics of cutting various objects are studied under different cutting conditions. The research concludes some basic properties of the cutting load change over times. Secondly, finding out the coal seam with coal-rock interface appears larger impact load and other time domain characteristics. From the above, analyzing the cutting load statistics in the time domain, cutting load variation with cutting material parameters is obtained. Meanwhile, the correctness of theoretical mechanics model is validated and corrected. Comparing with cutting load of coal seam with coal-rock interface and homogeneous coal seam, the results show that coal-rock interface has an important impact on cutting load. The cutting load increases largely between the coal and rock, which leads to the violent change of cutting load, and this change had a bad effect on the cutting performance.Indexes like cutting energy consumption, lump rate, pick wearing capacity are conducted to research the effect of different cutting material parameters on pick cutting performance. The results show that cutting load, cutting energy consumption are increasing with the cutting material compressive strength,so cutting load is the main factor affecting single pick cutting energy consumption. In addition, the results also show that the location of the interfacial layer interface seam of coal-bearing rock has a significant effect on cutting load and pick wearing capacity.Under the cutting condition of coal seam with coal-rock interface and homogeneous coal seam, combining the theoretical mathematical models of pick and drum rotary cutting,the single pick cutting torque and the drum cutting torque are compared, and its internal relations are analyzed. The study concluded that drum cutting torque load consists of the load generated by pick cutting and drum coal loading as well as pick base cutting. Obviously, it indicates that cutting load studies have a significant meaning on measuring the performance of pick cutting.The signal denoising schemes are compared, and the suitable EMD signal denoising scheme for test load is selected. Then through the analysis of cutting load power spectrum and 3-D time frequency, the relationship of pick cutting load main frequency band with the coal and rock material property and breaking are obtained,and the rule of the main frequency band change with the time and the coal and rock material property is obtained. According to the cutting load and mutation theory, coal and rock breaking mechanism by pick is analyzed.Furthermore, the mutation characteristics of coal and rock breaking process for pick pressing into the coal and rock until spallation are revealed, and the mutation mechanical model taking the load as disturbance factor is established.Comparing the load of single pick cutting homogeneous coal seam with the load in cutting coal seam with coal-rock interface, the load characteristics of cutting system are effectively identified and the intrinsic properties of the cutting loads are studied by using Lyapunov exponent, correlation dimension, complexity and other parameters based on the chaos and fractal theory. The studies provide technical support to ensure the safety and reliability of shearer cutting coal seam with complex structure, and play a guiding role for the coal-rock interface recognition in shear cutting process.The cutting performance test research of picks cutting coal seam with coal-rock interface is carried out on the coal and rock cutting test bed. The cutting load is taken as the measure indexes of cutting performance.The influences of pick structure parameters, installation parameters and kinematics parameters of coal seam with coal-rock interface on the cutting efficiency are studied, and the relational expressions among the relevant parameters are obtained. In the scope of this test study, the results show that the cutting load increase with the increase of pick tip cone angle, pick body cone angle, cutting line space, cutting depth, the decrease of drum rotating speed.With the increase of impact angle, the cutting load firstly decreases and then increases, and the minimum load is around 48°.With the increase of inclination angle, the cutting load firstly decreases and then increases, which is consistent with the theoretical research that increasing the inclination angle can improve the cutting efficiency. To reduce the pick wearing capacity, welding a wearable ribs in the body of cutting pick is proposed in this dissertation. Studies have shown that although the pick with rib can increase the pick cutting load at a certain extent, pick wearing capacity can be reduced. Thus, the service life of the cutting pick is improved and the guidance for the design and manufacture is provided.