The effects of process parameters on the rock-breaking efficiency of multi-nozzle jet

Abstract This paper examines the effect of multi-nozzle bit on sandstone specimens by means of numerical simulation and experiment, and the rationality is verified. Numerically, the effects of jets with different diameters and angles on rock were simulated by using LS-DYNA, and the rock-breaking shapes of jets with different angles are analyzed. Experimentally, the effects of jet pressure, impact standoff distance, erosion time and rotation speed on the crushing effect of sandstone are studied by building an experimental platform of high-pressure water jet impacting sandstone. The research shows that the rock-breaking depth decreases with the increase of the inclination angle, and the rock-breaking width increases with the increase of the inclination angle. Through comparing the rock-breaking depth and width, the reasonable structure of nozzle with diameter of 1.0 mm and inclination angle of 20°, 30° and 60° are determined. The volume of broken rock gradually increases with the increase of jet pressure, and the numerical simulation results are consistent with the experimental results. Meanwhile, the rock-breaking efficiency gradually decreases with the increase of the standoff distance, and gradually increases with the increase of the erosion time, and finally stabilizes. Through experiments, it is found that the rock-breaking depth, width and volume decrease with the increase of the rotation speed. The optimal standoff distance for the rock-breaking efficiency is 3 mm, the erosion time is no less than 60 s, and the critical rotation speed is 300 rpm.