Structure Design and Laboratory Testings of an Axial & Torsional Coupling Impactor

To improve the penetration depth of cutters on polycrystalline diamond compact (PDC) bits in hard formations and eliminate the harm caused by torsional vibration, a hydraulic pulse-type axial impact assembly was added based on the structure of the self-excited reversing torsional impact assembly. A new type of axial & torsional coupling impactor was designed by using the fork in the torsional impact assembly to drive the dynamic disc-type valve in the axial impact assembly to rotate synchronously, causing periodic changes in the flow area and generating hydraulic pulse-type axial impact load, which forms axial & torsional coupling impact together with the torsional impact load. The impactor had the characteristics of simple structure with the same impact frequency. In addition, a mathematical model of impactor performance parameters was established based on law of conservation of energy. Laboratory experiments on performance parameters of the axial & torsional coupling impactor were conducted. The results showed that the pressure drop and the axial impact load of the impactor were proportional to the square of the flow rate, and the torsional impact load and impact frequency were linearly increased with the flow rate. The maximum relative error was only 7.91%, which verified the accuracy of the mathematical model. This study provides theoretical guidance for the development of similar impact drilling tools.