Conveying State And Mechanical Behavior Of Bulk Coal In The Middle Pan Of Scraper Conveyor

The middle pan works as one of the key parts and components of scraper conveyor in comprehensive mechanized coal mining face, so the rationality and reliability of the middle pan directly affects coal mine’s safety and production.In recent years, the development of the comprehensive mechanized technology puts forward higher requirements on performance and structure of the middle pan of scraper conveyor. The researchers also need to analyze the malfunction in conveying process. These all reflect that it is necessary and urgent to study deeply on the process of scraper conveyor conveying coal.However, either current domestic or international researches rarely involve conveying state and mechanical behavior of bulk coal, and the continuum mechanics method adopted usually regards bulk coal in the middle pan as a continuous whole, which is different from the intrinsic characteristics of the discrete system. Based on the discrete element method mainly, combined with the finite element method, this paper studies the conveying state and mechanical behavior of bulk coal in the middle pan. In this case, the research of this paper can make full use of respective advantages of the discrete element method and the finite element method, and it can also get the information of motion and mechanical behavior inside the bulk and between the bulk and the boundary, and thus more reliable research results will be obtained.This paper takes the scraper conveyor and bulk coal as the research objects.Based on the discrete characteristics and mechanical properties of bulk coal, the discrete element model of scraper conveyor conveying bulk coal is established by applying EDEM and UG, and then complex behavior information and particle size information are acquired through simulation. According to the simulation results, this paper analyzes the distribution of coal particles, and it points out that the distribution characteristics of bulk coal can lead to abrasive wear in the chain way of middle pan under severe circumstances. Then all those,which include the flow state of bulk coal, coal particles’ velocity changing over time and position coordinates, and coal particles’ velocity distribution, are analyzed in detail. As a result, the motion characteristics of bulk coal in the middle pan are summarized.This paper studies the influence of many factors on the conveying efficiency of scraper conveyor. And the results show that, within the scope of this study, the conveying efficiency of the middle pan and the speed of scraper chain are positively correlated, while the conveying efficiency is negatively correlated with μ- the coefficient of static friction between coal particles and the middle pan, coal particle size and the laying angle of middle pan. Besides,two factors that are the speed of scraper chain and μ, have significant effects on conveying efficiency, while the other two factors have far less influence.The discrete element wear analysis model of scraper conveyor conveying bulk coal is established and the wear effect of bulk coal on the middle pan is studied, the following conclusions are obtained:①The wear of bulk coal on the middle pan is mainly distributed around the scraper chain. In the acceleration area of coal particles, the wear area is larger than that of stability area, and this is because that the collision of coal particles in the acceleration area is more intense, and that the impact on the middle pan is greater. ②Within the scope ofthis study, the average wear depth of the middle pan is positively correlated with the speed of scraper chain and coal particle size, and the effect is significant.The force properties of bulk coal to the middle pan are also studied, and the coupling analysis model is established by utilizing EDEM and ANSYS Workbench. On this basis, this paper utilizes the coupling model to analyze stress and deformation of the middle pan at the maximum force moment and other moments, then stress and deformation properties of the middle pan caused by bulk coal’s friction and impact effect during the conveying process are summarized: ①The larger stress is mainly distributed in the upper corner of the E shaped ledge, the middle place of the middle plate and the connecting place between the ledge and the middle plate. In addition, the maximum stress ranges from 0 to 100 MPa and it is far less than the yield strength of the material. These positions are contact places between the middle pan and bulk coal, impact places and those places where shape changes largely. Therefore, enough abrasion resistance and strength of middle pan should be ensured in the structure design.Besides, safety round corner design is needed where shape changes largely to reduce the stress concentration. ②Meanwhile, the larger deformation is mainly distributed in the top edge of the E shaped ledge and the middle parts of the middle plate, and the maximum deformation ranges from 0.001 mm to 0.05 mm.This shows that the stiffness of the top edge of the E shaped ledge and the middle parts of the middle pan is smaller than other parts of the middle pan, but it is also within the allowable range.On the basis of the research content, this paper has completed the preliminary design of scraper conveyor conveying and test system as well as specific validation test plan.The research results can provide references for optimum structural design,proper usage and improving conveying efficiency of the middle pan and otherkey parts of scraper conveyor. Besides, they can help to analyze the causes of operation trouble and structural damage of some key parts and components,especially the middle pan.