The pneumatic rock drill, a percussion tool basic to the mining industry, causes one of the worst noise hazards to which mine workers are exposed. Sound pressure levels range from 115 to 130 db at the operator's position with unmodified drills. Modifications have been developed that reduce the sound pressure level of a portable commercial drill to about 100 db. A close-fitting case, consisting of a metallic skeleton filled with viscoelastic material and a hard, metallic cover, provides a high degree of suppression of mechanical noise and the necessary rigidity and durability. Expansion chambers incorporated in the case provide the essential exhaust muffling. Damping alloys have been substituted at strategic points in the drill. The drill steel resonance noise is reduced by a special damping treatment on the outside of the drill rod. The performance of this equipment, its evaluation according to the criteria set forth, and additional prospects for better noise suppression receive comment in this report.
Proc. Inter-noise 72, 1972 Int'l. Noise Control Eng. Conf. & Equip. Expo, 10/4/72, PP. 282-287