| Coal resources occupy a dominant position in energy consumption and will remain at a peak during the 14 th Five-Year Plan period.With the completion of medium thick and high quality coal seam mining,in order to meet the demand of coal resources,it is imperative to study the efficient mining of thin coal seam.Due to the complex geological conditions of thin coal seam,there are a lot of gangue and hard concretions which are hard to break.As a result,the load of shearer drum fluctuates greatly in the cutting process,the stress of the cutting part changes obviously,and the friction and wear of the picks are serious,thus affecting the service life of the drum and the economic benefits of mining.The hard concretion coal in Yangcun Mine of Yanzhou mining area is sampled and tested for physical and mechanical properties.Then,the coal breaking process of pick type cutting pick is analyzed,the drum cutting force model is established and the program for calculating cutting force is designed.Then,the hard concretion collapse mode is discussed,and the feasibility of simulating coal breaking process by finite element method is proposed.Based on the established theoretical model,the target coal seam and MG2×70/325-BWD shearer drum are taken as the research object.The 3D model was built by UG and then imported into Hypermesh.Solid Edit function was used to cut the non-mapping bodies in the model,such as cutters,hard concretion and coal seams.The ellipsoidal grid common nodes of hard concretion in contact with coal seams are ensured,and the hexahedral division of the whole model is realized.After reasonable simplification of the model,the solving time is greatly reduced,which lays a foundation for accurate and efficient calculation of K files.LS-DYNA was used to analyze the stress variation of the alloy head,pick body and seat.The results showed that the larger stress area appeared at the connection of the alloy head and pick body when the pick acted on the hard concretion,and the stress value was about 1340 MPa,followed by the connection of the pick body and pick base,and the stress value was about 1070 MPa.By analyzing the stress variation of coal seam and hard concretion,it can be concluded that the coal seam will produce stress concentration phenomenon and constantly break under the action of the cutters,and the maximum stress value of the coal seam will increase with the increase of the number of cutters.When the cutters cut hard concretion in the coal seam,the surface of hard concretion will appear local depression under the impact of the cutters,and the whole will produce a certain Angle deviation.The coal seam below the hard concretion is subjected to great stress and the phenomenon of "Compacted concretion" appears and gradually loses its support to the hard concretion with the expansion of cracks.Through the analysis of the three-way force curve of the drum,it can be concluded that the cutting resistance increases most obviously when the hard concretion are cut,followed by the traction resistance,and the lateral force changes little.In order to verify the accuracy of the results,the three-way force curve of the drum is generated by using the previously established cutting force calculation program.The relative error values of the three forces on the surface are2.2%,7.9% and 15.7% respectively,which are all within a reasonable range,indicating that the simulation results are reliable.In order to study the influence law of drum kinematic parameters on cutting force and stress,orthogonal experiment was used to simulate the drum traction speed of 2,3,4,5 6m/min,corresponding to the speed of 50,60,70,80,90r/min,a total of 25 groups of working conditions cutting process.By analyzing the simulation results and fitting the corresponding formula,it is concluded that the peak value of the cutting force of the drum increases with the increase of the drum traction speed and decreases with the increase of the rotating speed.When the shearer drum cuts the coal,the kinematic parameters are as follows:when the drum speed is 50r/min and the traction speed is 6m/s,the peak cutting force reaches 25 simulated maximum values of 766 kN;When the kinematic parameters are 90r/min of drum speed and 2m/s of traction speed,the peak value of cutting force is 264 kN,the minimum value of 25 simulation groups.The higher traction speed and the lower drum speed will make the hard concretion easier to be peeled off.The stress peaks of the alloy head,pick body and seat increase with the increase of traction speed when the hard concretion are broken.In order to ensure that the cutting pick work within the allowable stress,it is recommended to avoid the drum cutting hard concretion coal with a traction speed greater than 5m/min and a rotation speed less than60r/min.The above research results make contributions to reveal the stress variation law of coal seam and pick in the process of collapse,reasonable matching of drum kinematic parameters,and green and efficient mining of hard concretion coal.At the same time,it also contributes to the improvement of hard concretions collapse mechanism and the design of thin seam drum shearer,which has certain reference significance. |
