低压磨料空气射流破硬岩规律及特征实验研究

Experimental study on hard rock breaking laws and characteristics by low-pressure abrasive air jet

针对坚硬围岩巷道和隧道的掘进效率低、钻具损耗快等问题,提出低压磨料空气射流辅助破硬岩技术思路。采用Fluent-EDEM数值分析不同压力条件空气射流流场结构和磨料加速机制,确定影响磨料加速的关键因素。基于自行研制的磨料空气射流破煤岩系统,研究射流压力、磨料质量流量和冲蚀时间对冲蚀破碎花岗岩效果的影响规律,明确提高破岩效率的关键因素。采用扫描电镜对花岗岩冲蚀坑进行了形貌分析,揭示低压磨料空气射流破硬岩机制。形成了以下主要结论:在压力2 MPa时,射流可达543 m/s,能够将磨料加速至130 m/s,具备冲蚀破坏硬岩的能力。增大气固两相速度差,提高颗粒所受曳力和虚拟质量力是提高磨料速度的关键。相比于提高压力,提高磨料质量流量和冲蚀时间更能提升破岩效率。入射磨料主要以冲击应力波和反复塑性变形使岩石表面产生裂纹和唇状边缘冲蚀坑,反射磨料以剪应力的形式使冲蚀坑壁面产生微裂纹,形成片状断裂裂纹。低压磨料空气射流破岩机制与高压条件下相同,从理论上验证了低压磨料空气射流破硬岩的可行性。

In response to the problems of low excavation efficiency and rapid wear and tear of drilling tools in hard rock roadways and tunnels,this paper proposes the idea of low pressure abrasive air jet assisted hard rock breaking technology.Fluent-EDEM was used to numerically analyse the structure of the air jet flow field and the abrasive acceleration mechanism under different pressure conditions and to determine the key factors affecting the acceleration of the abrasive.Based on the self-developed abrasive air jet rock breaking system,the influence law of the jet pressure,the abrasive mass flow rate and the erosion time on the effect of erosion crushing granite was studied,and the key factors for improving rock breaking efficiency were clarified.Scanning Electron Microscopy was used to analyse the morphology of granite erosion pits and the hard rock breaking mechanism of low-pressure abrasive air jet was revealed.It is concluded that at a pressure of 2 MPa,the jet can reach 543 m/s and is capable of accelerating the abrasive material to 130 m/s,providing the ability to erode and destroy hard rock.Increasing the difference between air and abrasive velocities as well as the drag force and the virtual mass force on the abrasive is the key to increase the abrasive velocity.Increasing the abrasive mass flow rate and the erosion time will improve rock breaking efficiency more than increasing the pressure.The incident abrasive mainly produces cracks and lip-like edge erosion pits on the rock surface in the forms of impact stress wave and repeated plastic deformation,while the rebound abrasive produces micro-cracks in the form of shear stress,forming flake fracture cracks.The low-pressure abrasive air jet breaking mechanism is the same as that under high-pressure conditions,which theoretically verifies the feasibility of breaking hard rock by low-pressure abrasive air jet.