Impact rock-breaking mechanisms and energy transfer laws of conical tooth bits in hot dry rocks

Abstract

Based on the finite-discrete element method, a three-dimensional numerical model for axial impact rock breaking was established and validated. A computational method for energy conversion during impact rock breaking was proposed, and the effects of conical tooth forward rake angle, rock temperature, and impact velocity on rock breaking characteristics and energy transfer laws were analyzed. The results show that during single impact rock breaking with conical tooth bits, merely 7.52% to 12.51% of the energy is utilized for rock breaking, while a significant 57.26% to 78.10% is dissipated as frictional loss. An insufficient forward rake angle increases tooth penetration depth and frictional loss, whereas an excessive forward rake angle reduces penetration capability, causing bit rebound and greater energy absorption by the drill rod. Thus, an optimal forward rake angle exists. Regarding environmental factors, high temperatures significantly enhance impact-induced rock breaking. Thermal damage from high temperatures reduces rock strength and inhibits its energy absorption. Finally, higher impact velocities intensify rock damage, yet excessively high velocities increase frictional loss and reduce the proportion of energy absorbed by the rock, thereby failing to substantially improve rock breaking efficiency. An optimal impact velocity exists.