Assessment of noise and effect of thrust on penetration rate in percussive drilling

Abstract

Rock drills are a major source of noise in the mining industry, with levels reaching as high as 115 dbA at the operator's ear. Noise of this amplitude has long been recognized as a serious health hazard. The two major noise sources in pneumatic rock drills are exhaust air and impact of the piston against the drill rod shank. The exhausted compressed air produces noise because it is released at a relatively high pressure and in bursts or pulses. While the impact of the piston against the shank causes vibrations in the drill rod and in different parts of the drill body which then radiate noise. Mufflers can reduce the noise to the order of 105 dbA, at which level the drill rod vibrations become the dominant noise source. The rock types selected for the present study are basalt, gabro granite, pink granite and lime stone. The range of applied thrust varies between 10 kg to 100 kg. All the holes were drilled for a fixed time of one minute and penetration rates were obtained. It was observed that very low thrust results in low penetration rates but on the other hand, even very high thrusts do not produce high penetration rates at high operating air pressures. Optimum thrusts were obtained for each rock type experimentally. This paper deals in detail effect of applied thrust on the penetration rate and sound level of a conventional percussive drill.