Experimental study of the energy transfer efficiency and rock fragmentation characteristics in percussive drilling

Abstract

This article conducted studies of percussive drilling, and revealed impact stress wave propagation mechanisms and rock fragmentation characteristics under percussion. In this study, the experimental equipment and numerical calculation platform were built based on percussive drilling system. The incident waves, reflected waves and transmitted waves during percussion were used to evaluate impact energy transfer efficiency. Simultaneously, the Scanning Electron Microscope and three-dimensional Laser Profile Scanner were used to depict the crushed craters and cracks of the rock. The key findings of this study are as follows. For percussive drilling with hemispherical teeth, when the impact velocity is increased, the energy transfer efficiency augments. For percussive drilling with stinger teeth, as the impact velocity increases, the energy transfer efficiency decreases. As the rock temperature increases, the energy transfer efficiency roughly decreases. Compared with stinger teeth, more tensile cracks of the rock are formed under percussion by hemispherical teeth. The stinger teeth tend to concentrate impact energy in the areas under teeth, which is more conducive to generating craters in the rock. The hemispherical teeth tend to spread impact energy out of the areas under teeth, which is more conducive to generation of the tensile cracks. Rocks at high temperatures are more prone to tensile cracks under percussion. This study provides a theoretical basis for the optimal design of percussive drilling based on high temperature hard rock.