Rock Breaking Mechanism And Dynamic Response Analysis Of The Large Diameter Percussive Bit

The Large diameter percussive reverse circulation drilling rig is widely used in percussive drilling of large diameter pile foundation and wellhead.It has the advantages of fast slag discharge,high impact efficiency and good sidewall formation.However,in the long-term continuous work of the percussive drill bit matched with it,there are often defects such as circle fracture,rib shedding and weld cracking,which affect the further popularization of the drilling rig.The process of rock breaking by bit percussion drilling is very complicated and there are many influencing factors.Through the analysis of the theory of rock breaking by bit,the process of rock breaking and its influencing factors are studied,which can provide the basis for setting drilling parameters and optimizing bit structure.Firstly,the development of rock breaking theory and the application of simulation technology in the field of rock breaking are introduced.Because it is difficult to consider the coupling effect of many factors in theoretical calculation,with the development of computer technology,numerical simulation technology provides a possibility for solving complex non-linear problems.Using Ansys and Ls-dyna to conduct joint simulation,the rock-breaking mechanism of 1.6-3m diameter bit is analyzed.The results show that the rock-breaking depth of single impact is limestone > sandstone > granite in turn,and the difficulty of rock-breaking is positively correlated with rock compressive strength.The influence of impact height on rock-breaking depth is analyzed,and the optimum lifting height of bit is determined to be 0.8m-1.3m.After tracing and analyzing the stress of the same step and peripheral unit points,it is found that the trend of stress change of the same step unit is approximately the same,the stress change of peripheral unit is lagging behind,and the stress wave generated by drill bit impact will not cause failure and destruction of the wellbore unit.The variation of residual velocity during the process of drill bit impact on granite is analyzed,and the sparks in the process of impact are obtained.Stress variation of rock mass and forming process of broken pit.The cutter body is the key part where the bit contacts rock directly.The rationality of its structure has a great influence on rock breaking efficiency.Through simulation analysis,it is found that the cutter body with smaller edge dip angle can be used for hard stratum which is difficult to break rock.For soft stratum,the cutter body with larger edge dip angle has higher rock breaking efficiency.The structure of the cutter body is changed from cone to axe.Through comparative simulation experiments,the optimal inclination radius of the axe-shaped cutter body is obtained.Compared with the original cutter body,the volume of the improved cutter body is increased by 21%,and the rock-breaking efficiency is improved.The dynamic response of the bit is analyzed,and the stress distribution of the bit with different levels of cutter body participating in rock breaking is compared.The stress peak of the key parts of the optimized bit is reduced by 3.42%,which provides a basis for the further optimization design of the bit.