1、1 英文翻译原文NOISE CONTROLS FOR VIBRATING SCREEN MECHANISMS M. J. Lowe, NIOSH, Pittsburgh, PA D. S. Yantek, NIOSH, Pittsburgh, PA H. E. Camargo, NIOSH, Pittsburgh, PA L. A. Alcorn, NIOSH, Pittsburgh, PA M. Shields, Conn-Weld Industries, Inc., Princeton, WVABSTRACT: National Institute for Occupational Saf
2、ety and Health (NIOSH) studies show that 43.5% of surveyed coal preparation plant workers had noise exposures exceeding the Mine Safety and Health Administration Permissible Exposure Level. Sound levels around vibrating screens in these plants often exceed 90 dB(A). NIOSH is currently developing noi
3、se controls for horizontal vibrating screens. To characterize noise sources, NIOSH researchers performed sound pressure level (SPL) measurements on a vibrating screen at their Pittsburgh Research Laboratory. The results show that the entire screen contributes to noise below 1 kHz and the vibration m
4、echanism housings are most significant above 1 kHz. Constrained layer damping (CLD) treatments and an enclosure were used to reduce mechanism housing noise. These were evaluated using sound power level measurements according to ISO 3744. The CLD treatments reduced the A-weighted sound power level by
5、 3.1 dB in the 1 to 10 kHz one-third-octave bands. A panel-on-frame vibration mechanism enclosure using various types of panels further reduced the A-weighted sound power level from the CLD configuration in the 1 to 10 kHz one-third-octave bands by 3.7, 4.0, and 3.9 dB for aluminum, steel, and Dynal
6、am panels, respectively. The combination yielded a 7 dB reduction from baseline in A-weighted sound power for the same frequency range. INTRODUCTION: Hearing loss is one of the most common occupational illnesses in the United States (Franks et al. 1996). However, in the mining industry, hearing loss
7、 is 2.5-3 times greater than what is expected for the average of the population that is not exposed to occupational noise. Additionally, the same National Institute for Occupational Safety and Health (NIOSH) studies have shown that by the age of 50, 90% of coal miners have a hearing impairment versu
8、s only 10% of the population not exposed to occupational noise (Franks 1996). Noise-induced hearing loss is not just a problem in underground mining. In fact, a Mine Safety and Health Administration (MSHA) study of 60,000 full shift noise surveys showed that based upon federal noise regulations, 26.
9、5% of workers from surface mining operations were overexposed to noise, compared to 21.6% of workers in underground mines (Seiler et al. 1994).Above ground at coal preparation plants, a NIOSH study shows that 43.5% of employees are overexposed to noise. Furthermore, the study found that not only wer
10、e vibrating screens one of the loudest pieces of equipment at the preparation plants, they were also the most numerous, thus making vibrating screens a key noise source to address (Vipperman et al. 2007). In that light, a team of NIOSH researchers in partnership with Conn-Weld Industries, Inc., have
11、 used acoustic beamforming techniques to locate noise sources on a Conn-Weld G-Master 1000 de-watering vibrating screen. From the noise sources identified, they developed noise controls to mitigate the sound radiated by the mechanism housings. Additional noise controls for the screen body will be th
12、e subject of future investigations. A horizontal vibrating screen (Figure 1) is a large machine used to process coal. The screen body has four sides made of steel plates with a bottom screening surface also known as a screen deck made of steel wire welded to a frame with small gaps between the wires
13、. The body of the screen is supported on a steel coil spring suspension. For the Conn-Weld screen tested at NIOSH, two vibration mechanisms are mounted to a steel beam that spans the width of the screen. These vibration mechanisms, which use rotating eccentric shafts to generate vibration, are belt-
14、driven using an electric motor.（A）（B）Figure 1. A horizontal vibrating screen used to process coal viewed from (a) feed end and (b) discharge end.The screen is designed in such a way that it vibrates on roughly a 45 degree angle. In operation, coal flows into the feed end of the screen from a deliver
15、y chute. As the screen vibrates, the material moves along the deck and under a water spray that rinses the coal. The liquid and fine coal particles pass through the gaps in the screening deck as the material flows toward the discharge end of the screen. Finally, the rinsed coal falls off the dischar
16、ge end of the screen to continue with further processing.Noise Source IdentificationNoise source identification was performed using the beamforming technique (Christensen and Hald 2004). The screen was positioned in the NIOSH Pittsburgh Research Laboratory (PRL) hemi-anechoic chamber with the screen directly on the chamber floor with wooden wedges driven under the frame rails to prevent rocking. The chamber dimensions are approximately 16.7 meters
