Research On The Rock Breaking Performance Of High-pressure Pulsed Jet Assisted Mechanical Impact

In order to realize safe and efficient mining of hard coal in deep and complex formations,improve the efficiency and capacity of rock breaking by mechanical impact,reduce the wear of mechanical spherical bit and the amount of dust.With the characteristics of low temperature impact of high-pressure water jet,integrating the high-pressure pulsed jet technology into rock breaking with mechanical impact,the rock breaking method by the high-pressure pulsed jet assisted mechanical impact is proposed.The combination of theoretical analysis,experiments and numerical simulation are used to investigate the rock breaking performance of high-pressure pulsed jet assisted mechanical impact.Based on the Boussinesq problem,the stress of rock under the impact load is analyzed,and the mathematical model of element stress under concentrated force is established.According to elastic mechanics and the theory of strength,the rock breaking by impact of conical bit and spherical bit is analyzed.According to the impact dynamics,the rock breaking process under water jet impact is analyzed,and the dynamic stress caused by water jet inside the rock is analyzed based on the wave dynamics.Based on the stress structure theory,the stress superposition formed inside the rock under the condition of water jet assisted mechanical impact is investigated.The computational fluid dynamics method is used to study the effect of the internal flow channel structure of different nozzles on the velocity field and pressure field,which indicates that the suitable nozzle type is a cone-straight nozzle.The fluid-structure coupling method was used to set up a numerical model of high-pressure jet formation,and the effect of impact energy,nozzle diameter,liquid level height and chamber diameter on pressure and velocity of high-pressure pulsed jet were studied.Based on the hard rock constitutive model,the rock breaking model of high-pressure water jet is established,and the factors(jet fluidity,jet diameter and pulsed frequency)affecting the rock breaking performance of high pressure pulsed jet,are studied,and the influence rules of each factor on the rock breaking performance of high pressure pulsed jet are investigated.The simulation and experimental results are consistent,which confirms the correctness and reliability of rock breaking model by the water jet.The parameters such as bit shape,impact energy and bit margin affecting the rock breaking performance were studied through experiments.The influence of relevant parameters on rock breaking performance indexes such as volume,depth and specific energy consumption are investigated.The rock breaking performance under double-bit condition is analyzed,and the preferred double-bit center distance is provided.The explicit finite element method is used to establish the rock breaking model of mechanical impact,and the micro fracture of rock under mechanical impact load was investigated.The numerical simulation and the experimental results are consistent,which proves that the rock breaking model with mechanical impact is feasible and correct.The impact force in rock breaking process with high-pressure pulsed jet and the mechanical impact is analyzed,and the influence law of the hammer initial velocity on the mechanical impact force is obtained,as well as the relationship between impact force of water jet and initial velocity of impact hammer,jet flow rate,change angle of jet flow.Fluid-structure coupling method is also used to establish the numerical model of rock breaking with high pressure jet assisted spherical bit impact,and the rock breaking performance by the high pressure pulsed jet assisted mechanical impact is investigated.The effect of the center distance between the water jet and spherical bit,the water jet number and angle on the rock breaking performance with the high-pressure pulsed jet assisted mechanical impact were studied.The preferred pulsed jet parameters assisted mechanical spherical bit impact are provided,which confirms that the pulsed jet assistance can significantly reduce the stress of the mechanical spherical bit,increase the rock damage depth,and greatly improve the rock breaking conditions by mechanical impact.