Theoretical And Experimental Study On Rock Cutting In Deep Mining

The main component of shearer cutting institution is the drum which interates with coal and rock directly.The cutting performance and characteristics of loads on the drum have crutial effect on the cutting efficiency of mining equipments.Meanwhile,with the increase of mining depth in China,the problem caused by high in-situ stress in deep mining is growing.In order to study the pick cutting mechanism,design method of efficient drum and the effect of high in-situ stress on cutting process,this dissertation focuses on two aspects,i.e.the shearer cutting institution load prediction and the effect mechanism of confining pressure on rock cutting process.The problems in the current study in terms of shearer cutting mechanism were analyzed.The characteristics of cutting loads on conical pick and shearer drum were studied.The main conclusions are as follows:(1)The full-scale pick cutting tester under confining pressure is built.The maximum confining pressure capacity of this cutting tester is approximately 32 MPa and the corresponding mining depth is about 1280 m.(2)The influence of confining pressure,arrangement parameters(cutting space and attack angle)and feed motion parameters(cutting depth and cutting speed)on pick cutting force is studied by full-scale cutting tests.The experimental results show that the mean cutting force and specific energy increase linearly with the increase of confining pressure while the chip coarseness index decrease linearly.The optimum cutting space is determined by cutting depth and rock crack angle,i.e.S=2dtan?.There is a well linear relationship between cutting force and cutting space to cutting depth ratio,i.e.y=0.067x+0.399,which is the theory basis for superposition of forces during multi-pick cutting process.The mean cutting force and specific energy increase and the chip coarsemess index decreases with the increase of attack angle.With the increase of cutting depth,the pick cutting force increases nonlinearly while the specific energy decreases and the coarseness index increases.Meanwhile the rock crack angle increases with the increase of cutting depth.Besides,the cutting speed has little effect on pick cutting force,specific energy and coarseness index under the condition of the same cutting depth.(3)The peak cutting force theoretical model of conical pick based on fracture mechanics is established.The computational algorithm for instantaneous cutting depth of a pick during drum rotation is established.The calculation method of random shearer drum torque is proposed and validated by full-scale shearer cutting tests.(4)The effect mechanism of confining pressure and rock brittleness on cutting process is studied from a microscopic perspective with the discrete element method software(i.e.PFC2D).According to the simulative results,the vertical crack propagation is restrained during cutting under confining pressure.The rock failure mode translates from tensile failure to shear failure with the increase of confining pressure,which results in the increase of cutting force and specific energy.Besides,the failure mode of rocks with different brittleness indexes translates from ductile to brittle with the increase of cutting depth,and brittle failure characteristic is more notable for more brittle rocks.In addition,under confined cutting conditions,rocks with small brittleness are damaged thoroughly when the confining pressure/UCS ratio is 0.6 while rock with large brittleness can be cut stably.Consequently,more brittle rocks are more difficult to be destroyed under the synergistic effect of confining pressures and cutting disturbance.(5)The software for shearer drum torque estimation is designed.The structure of MG500/1130-WD shearer drum is optimized,and the cutting processes of the drums before and after optimization are simulated using PFC3 D.Although the pick number of the optimized drum is reduced,it performs as well as the drum before optimization even the mean and variance of drum torque,fluctuation index and specific energy slightly decrease.Consequently,the optimization method of shearer drum is valid.