Noise Control for the Pneumatic Rock Drill.
Ann Mtg SME AIME Chicago Illinois SME Preprint 73-Au-62 Feb 25 - 1973 Mar; :17 pages
Unmodified pneumatic rock drills may have noise levels of 115 to 130 db at the operator's position. Experimental modifications have been made to a standard drill to suppress the noise from the three main sources: the air exhaust noise, the noise radiated from the drill, and the resonance noise of the steel drill rods. A prototype model developed at the Bureau of Mines, Rolla Metallurgy Research Center, operates at a noise level below 100 db. A close-fitting case and muffler unit, consisting of a metallic skeleton filled with viscoelastic absorber and having a durable cover, provided both muffling and noise absorption. Damping alloys were used at strategic points in the drill. Drill steel resonance noise was reduced by a constrained-layer treatment on the outside of the drill rod. The singular and combined effects of the treatments are presented in detail.
Ann. Mtg., SME, AIME, Chicago, Illinois, SME Preprint 73-Au-62, Feb. 25 - Mar. 1, 1973