Efficiency of a percussive rock drilling process with consideration of wave energy radiation into the rock

The efficiency of churn drilling was studied with consideration of wave energy radiation into the rock. In this percussive drilling process, a hammer with cutters on its front subjects the rock to direct impact. A 3D elastic finite element model was used for the hammer and the rock, with a nonlinear force versus penetration relationship representing the rock crushing process. Two rock models with the same crushing properties were employed: (i) one perfectly rigid and (ii) one linearly elastic, representing Westerly Granite. Under favourable drilling conditions, with efficiencies higher than 60%, the elastic response of the rock significantly influences the efficiency of the drilling process. However, the radiation of wave energy into the rock, less than 3% of the impact energy, does not play an important role. Under unfavourable drilling conditions, with efficiencies lower than 40%, the elastic response of the rock does not significantly influence the efficiency of the drilling process even though the energy radiated into the rock is greater than 5% of the impact energy.