Research On Rock Breaking Performance Of Pick Assisted With Abrasive Water Jet

The roadheader is the key equipment to the tunnel and laneway mechanization excavation.In the process of hard rock breaking,the concial pick bear great force and wear,and is difficult to break hard rock.The above problems,lead to low tunneling efficiency and high footage cost,have become important factor affecting efficient,safe,green mining of China's coal resources.Therefore,in order to solve the problems of hard rock breaking,low drivage efficiency and high abnormal failure probability of pick,it is urgent to study a new type of hard rock breaking technology.Based on this,this paper puts forward the method of rock breaking by pick assisted with abrasive water jet,and the rock breaking performance of the method is studied by combining theoretical analysis,simulation and experiment.Based on the theory of rock breaking by pick and water jet,the mechanism of rock breaking by pick assisted with abrasive water jet is analyzed by AUTODYN.Under the action of pick,the main crack and radial crack of rock propagate fast,the layered crack mainly distributes around the compacting rock core of the pick tip.Under the action of abrasive water jet,the crack propagates slowly along the axial and radial direction of the abrasive water jet column,the propagation distance of layered crack and the main crack is short,and there are few radial cracks around the main crack.The shear failure zone of rock is covered with layered cracks and the intersecting of layered cracks accelerates the process of rock breaking under the action of abrasive water jet.Based on the two-phase flow theory,the abrasive water jet nozzle is designed by FLUENT.The angle of nozzle contraction is based on the loss of kinetic energy of abrasive particle,and the length of nozzle cylinder section is based on the velocity of abrasive particle at the nozzle outlet.Finally,it is determined that the nozzle shrinkage angle is 7° and the cylinder section length is 16 mm.The internal and external flow field and abrasive particle velocity field of the designed nozzle show that the diameter of the abrasive water jet column at the nozzle outlet is 1.55 mm,all abrasive particles are uniformly distributed in the cylinder at the center of the abrasive water jet column,and the diameter of the cylinder is 1.55 mm.The speed of abrasive particle is about 94% of the speed of water.Using the designed nozzle,the rock breaking performance by pick assisted with abrasive water jet under different abrasive water jet pressure and different cutting depth was studied.The results show that the greater pressure of the abrasive water jet,the higher mean cutting resistance reduction rate of pick.Compared with rock breaking by pick,when the depth is 3 mm and 5 mm,the reduction rate of mean cutting resistance is between 21% and 47%.When the depth is 8mm and 10 mm,the reduction rate of mean cutting resistance is between 21% and 47%.The mean cutting resistance reduction rate of pick is above 32% during the second cut,and the maximum cutting resistance reduction rate of pick is above 72%.The greater pressure of the abrasive water jet,the less the cutting resistance fluctuates,and the better the stability of pick is.Therefore,the technology of rock breaking by pick assisted with abrasive water jet has good rock breaking performance,strong damage to rock,and can weaken the strength of rock.According to the theory of elasticity and the Mohr-Coulomb criterion,the rock breaking by pick assisted with abrasive water jet model under different confining pressures is established.The validity of the simulation model is verified by comparing the rock breaking state and the cutting resistance in the process of numerical simulation and test.The results show that,as the confining pressure increases,the radiation surface of the stress concentration area on the rock increases,and the stress concentration area mainly occurs around the wall surface of the rock crushing pit.The larger the confining pressure,the more obvious the suppression effect on the tensile stress propagation is.When the confining pressure increases from 0MPa to 20 MPa,the cutting resistance of rock breaking by pick increases by 46.69%.At a cutting depth of 5 mm,and a water pressure of 30 MPa,when the confining pressure increases from 0MPa to 20 MPa,the cutting resistance of rock breaking by pick increases by 21.9%.At a cutting depth of 5 mm,and a confining pressure of 20 MPa,when the water pressure increases from 0MPa to 46 MPa,the cutting resistance decreases by 38.14%.From the above analysis,the technology of rock breaking by pick assisted with abrasive water jet can reduce the increase range of cutting resistance caused by confining pressure,reduce the difficulty of crushing rock under high confining pressure and improve the efficiency of tunneling.