Bottomhole Model and Rock-Breaking Features Study of New Drill Bit with Swirling-Cutting Motion

For improving the center rock-breaking efficiency, a new drill bit called ＂swirling-cutting bit＂, which has swirling-cutting motion and tornado-like bottomhole model during the rock-breaking process, is presented. Cylindrical coordinates are used for the analysis of swirling-cutting bit motion, in which the rotation and longitudinal motion of bit body are considered as transport motion while the rotation of the cone around its axis is taken as relative motion. According to the equations of its radius vector, polar angle and vertical height, the bottomhole models are analyzed, together with the influences of the wheel angle β, the cone offset distance s and the wheel body ratio. On the basis of the shock and shear equations of swirling-cutting bit on different gear rings, the impact force, shear force and rock-breaking volume on cutters were obtained and compared with each other. The results show that the elements of the largest ring of the tornado-like bottomhole model cross the borehole center during the rock-breaking process, which can improve the rate of penetration and provide an effective solution to the low efficiency of center rock-breaking. Meanwhile, the analysis results of key parameters of bottomhole model are useful for structural optimization of swirling-cutting bit.