Study On Cutting And Conveying Performance Of Novel Auger Miner Drilling Tool

In order to overcome defects of the auger miner such as low mining efficiency, long drilling pipe connection time and serious drilling deflection and promote its use in thin seam mining, the project named “Key Technology and Equipment of Almost Thin Seam Auger Miner” has been approved by “National High Technology Research and Development Program of China(863 Program)” to develop a novel high-performance auger miner with high efficiency, high reliability and good economy. The drilling tool is the working mechanism of the auger miner, as the key part, whose cutting and conveying performance directly affects the reliability, running stability, production efficiency and mining economy of the machine. So it’s one of the most important works to develop a drilling tool with good cutting and conveying performance in developing the novel auger miner. With regard to this, the drilling tool of the novel auger miner was chosen as the research object and its cutting and conveying performance was studied by combining theoretical analysis, experiment and numerical simulation to guide the design of the drilling tool and drilling technology.The research on coal-cutting theory was carried out for current aiguilles, mainly the pick kinematics characteristics, aiguille cutting mechanism, pick cutting condition and pick coal-cutting volume were analyzed and mastered. Combined with cutting conditions of the pick on the aiguille, the discrete element simulation model of pick cutting coal is established to simulate the process of pick drilling and cutting coal. On this basis, the influence on pick cutting performance of the cutting groove space, pick working angle and pick motion parameter were studied to provide the basis for further analysis on the cutting performance of the aiguille.The cutting performance evaluation system of the aiguille was established firstly combined with the drilling condition, then a series of coal-rock cutting experiments were conducted on the coal-rock cutting test-bed with test aiguilles to study the influence of the aiguille shape, pick working angle, motion parameter, cutting line space and pick arrangement pattern on the cutting performance of the aiguille. The research shows that the “plane and paraboloid” aiguille is better than the “plane and taper” one in cutting performance. There is an optimal value for pick cutting angle, pick inclination angle and feed pitch to optimize cutting performance of the aiguille. Under constant feed pitch, all cutting performance indexes of the aiguille will deteriorate linearly with increasing rotational speed. The influence of cutting line space on cutting performance of the aiguille depends on the feed pitch, so the cutting line space should be chosen by the feed pitch when designing the aiguille. The distortion aiguille has the smallest loads and energy consumption but the worst load stability. By contrast, it appears on the opposite situation for the sequence aiguille. The pick arrangement pattern of the aiguille should be chosen by its use occasion.Based on the theory of elasticity and fracture mechanics, the influence of the confining pressure on the strength and crack propagation of the coal was analyzed. On this basis, the cutting performance of both the aiguille and the drilling tool was studied under different confining pressure conditions by simulating the process of aiguilles cutting coal by nonlinear finite element method. The research shows that with the increase of value and dimensions of the confining pressure, loads and cutting specific energy consumption of the aiguille will increase but average coal-cutting rate will decrease. The influence of confining pressure on the cutting performance of the aiguille can’t be ignored. When several aiguilles cut the coal in parallel, the cutting performance of the aiguille is mainly affected by the coal-cutting process of adjacent aiguilles. The interaction between adjacent aiguilles can improve their cutting performance to a certain extent. The cutting performance of the aiguille on the drilling tool depends on its drilling conditions. Strength weakening of the coal between adjacent coal-holes is the root cause of the cutting performance difference among aiguilles with different drilling conditions, while the confining pressure is only the immediate cause to enlarge the difference. There is only slight difference in cutting performance between the drilling tool with slave aiguille leading arrangement and the one with slave aiguille lag arrangement. The parallel arrangement pattern should not be used to arrange aiguilles when designing the drilling tool.Numerical simulation model of drilling tool conveying coal was built by software PFC3 D based on the discrete element theory, meanwhile the conveying performance evaluation system of the drilling tool was established systematically. On this basis, the conveying behavior of the drilling tool was studied by simulation. The research shows that stable material accumulation around vent pipes provides the precondition for the central drilling pipe to convey material effectively. The coal plough should be eliminated on the novel auger miner to avoid circulatory material flow between the middle drilling pipe and vent pipes. Because of unidirectional and uneven material flow between aiguilles, the material distribution along the traverse direction of the drilling tool is unbalanced. In other words, there is remarkable difference in material fill level, power and material conveying rate among similar components. The lateral conveying zone of the gearbox should be enlarged as far as possible. The material vortex motion around aiguilles is very intense because of large material fill level and material flow resistance. When designing the drilling tool, the feed power of components can be ignored, but their feed force must be considered. In the back drilling process, the recovery ratio of residual material around vent pipes is relatively low. The height-regulating cylinder play a leading role and aiguilles play a secondary role in the material recovery process.The material conveying process of the drilling tool was simulated using the numerical simulation model of drilling tool conveying coal under different missing blade length of the first drilling pipe, aiguille arrangement schemes, coal seam azimuth angles and rotational speeds and the influence of above factors was studied on conveying performance indexes of the drilling tool such as the material fill level, power and material conveying rate. The research shows that with increasing missing blade length of the first drilling pipe, the material blockage risk around aiguilles and gearboxes will increase and the drilling recovery ratio of the drilling tool will decrease, so it’s necessary to decrease missing blade length of the first drilling pipe as far as possible. Among four aiguille arrangement schemes, scheme 1 and scheme 3 are better than scheme 2 and scheme 4, especially scheme 1 can make the drilling tool achieve the most optimum conveying performance at higher feed speed. The material fill level, power and material conveying rate of components on the drilling tool will decrease with increasing positive dip angle and increase with increasing negative dip angle of the coal seam, so the roadway should, as far as possible, be designed to ensure the drilling tool work in up-dip mining state. The conveying performance of the drilling tool will deteriorate with increasing positive strike angle and get better with increasing negative strike angle of the coal seam. The rotational direction and blade spiral direction of the middle drilling pipe and the middle aiguille can be changed to indirectly ensure the drilling tool work in negative strike angle of the coal seam. Both the drilling pipe and the aiguille have an optimal rotational speed, and the optimal rotational speed of the drilling pipe can be selected as the one of the drilling tool to ensure good conveying performance of the drilling tool.