Microcomputer simulation of percussive drilling

Abstract

Churn drilling, down-the-hole drilling, hammer drilling, and related drilling and breaking processes are simulated by means of a microcomputer. The simulation programs are written in Apple Pascal for the Apple II family of computers. Accounts are given of the simulation programs and their theoretical basis, and results are presented from two different simulation studies. The first study concerns the efficiency of a simple percussive system which consists of a cylindrical hammer and a cylindrical bit, both with the same characteristic impedance. Sharp maxima are obtained when the bit-to-hammer length ratio is equal to unity or zero. Also it is shown that the efficiency is generally an oscillating function of the initial gap between bit and rock. If the bit is longer than the hammer, this function is periodic. The second simulation study concerns a commercial percussive drill, namely, Atlas Copco's COP 1038 HD. Stresses in the drill, efficiency, coefficient of restitution of the hammer, and force acting on the rock are determined. For both simulation studies, comparisons are made with exact theoretical results.