Effects of Thrust on Rock-Drill Performance. Computer simulation of percussive drilling (2nd Report).

A drilling model was previously proposed by Okubo and Nishimatsu (1991), and a computer program which had capability to simulate continuous drilling-process was also developed bythem. The model which consists of a drill-body, a piston, a rod and a bit was analyzed based on the one-dimensional stress-wave theory. A force-penetration curve with hysteresis was assumed for bit/rock interface.In this study, comprehensive simulation for a heavy drifter of 150 kg-class was carried out. Special care was taken to clarify the effect of thrust on rock-drilling performance such as penetration rate, piston stroke, piston velocity, elastic wave in rod. Calculation was performed under more than two-thousand conditions changing thrust, bit/rock interface parameters and attenuation rate on drill/rod interface.An appropriate thrust, Fth_apl, was proposed as follows; Fth-apl≅Aback·Pback-Afront·Pfront, Where ‘A’ denotes effective cross-sectional area, and ‘P’ pressure. Subscripts ‘back’ and ‘front’ indicate back and front cylinders, respectively.