Evaluation of stiffeners for reducing noise from horizontal vibrating screens.

Abstract

Sound levels around vibrating screens in coal preparation plants often exceed 90 dB(A). The National Institute for Occupational Safety and Health (NIOSH) is developing noise controls to reduce noise generated by horizontal vibrating screens. NIOSH determined the vibration mechanism housings and the screen body to be the dominant noise sources on a horizontal vibrating screen. Researchers used beamforming, experimental modal analysis, and operating deflection shape analysis to examine noise radiated by the screen body. Based on these results, finite element analysis and a NIOSH-written program were used to estimate the sound power level reduction resulting from adding rib stiffeners to key locations on the screen sides. Rib stiffeners made from two sizes of steel channel and two different cross-sections, C and T, were evaluated. In addition, the effects of orienting the stiffeners horizontally and vertically were examined. Finally, the stiffeners were evaluated with the ends welded to the existing ribs on the screen sides and with the ends free. The results indicate that for a broadband input, the smaller T cross-section oriented vertically with the ends welded to the existing ribs was the best option. This configuration reduced the predicted A-weighted sound power level by 7 dB.