Final Acoustics Project Names_____________________ MECH 440 rjs F20 MECH 440 Acoustics / Noise Control Final Project Introduction You and your partners are all brand-new employees of RJS Forging, Inc., and your first assignment is an acoustic-related design problem. You need to provide a quick initial layout for the redesign of an existing room with inspection stations and a supervisor area, while providing space for: 1) forklift maneuverability (large forklifts have a 10 ft turning radius), 2) general industrial cleaning/maintenance needs, and 3) an acceptable acoustic environment that meets OSHA noise regulations. Problem Definition When ore rock, forgings, metal parts, castings, etc. are handled in metal chutes, shaker tables, tumbling machines, and metal bins, substantial noise levels can be generated by the impacting of parts and by the abrasive sliding action which occurs during these processes. Consider the proposed inspection room in your forging plant. Each inspection bench has six parts inspection stations with large metal supply hoppers situated above and in front of each inspector, as shown in Figure 1. Small forgings are loaded (dumped) into each metal hopper by means of a forklift truck prior to the inspection process. A worker must stand in front of the hopper being loaded and hold a retaining board over the bin slot to prevent forgings from spilling out onto the inspection table as the forklift dumps the parts into the bin. Noise Measurements Noise levels measured at the inspectors’ ear position during the loading operation show peak levels of 120-123 dBA, which may be sustained for 8-10 seconds. Although the frequency with which the hoppers are loaded during the day is such that the workers’ total noise exposure is within acceptable limits as specified in the OSHA Noise Regulations, the workers complain about excessive noise which occurs during the loading operation. Of particular concern are the frequency ranges around 250 Hz (due to parts impact) and 4 kHz (parts impacting metal chutes and hoppers). Final Acoustics Project Names_____________________ MECH 440 rjs F20 The octave-band sound levels measured at a typical inspector’s ear position during the dumping operation are: Freq (Hz) 31.5 63 125 250 500 1k 2k 4k 8k dB 45 51 87 98 93 98 112 118 115 Inspection Benches Each inspection bench has six inspection stations. The benches (metal surface) are 24 feet in length and 8 feet deep. The sheet metal hoppers that sit on the rear portion of the benches are 4 ft x 4 ft x 4 ft. The openings in the bench surface lead to sheet metal chutes for inspected parts which slide into metal tote boxes under the rear of the benches for later removal to other locations. The noise due to the parts sliding down the metal chutes and impacting with each other in the tote boxes is also objectionable to the workers (but again, the frequency of this action is not sufficient to exceed OSHA requirements, but it is very much a worker complaint). Figure 1. Typical six-station parts inspection bench Final Acoustics Project Names_____________________ MECH 440 rjs F20 Room The room you are laying out is 100 ft x 80 ft x 20 ft high. The floor is poured concrete, the walls are unpainted cement block, and the ceiling is corrugated metal panels. There is a standard metal roll-up access door for the forklift trucks on one of the 80 ft walls, and each 100 ft wall has a normal entry door located on the opposite end of the room from the metal roll-up door. You also need to plan for enough cooling fans (each fan is rated for a room volume of 20000 ft3, has a noise level of 85 dBA when operating at rated speed, and runs continuously) to keep inspectors comfortable. Typical installation of one of these fans is shown in Figure 2. Figure 2. Typical cooling fan installation Your Assignment Your team is to arrange the layout of the inspection room to accommodate two of the six-station inspection benches, one supervisor desk area, sufficient number of cooling fans, and space for forklift maneuverability. Your proposed design should address efficiency of the inspection operation, with a strong emphasis on establishing an acceptable acoustic environment to eliminate worker complaints. The inspectors at the benches and the supervisor must be able to communicate effectively at all times. Ideally, the room acoustic quality should be comparable to that of a hall used for opera. Written Submittal In the write-up of your layout proposal, include a dimensioned floor plan of the room, complete descriptions of all surfaces, and any other drawings, data, calculations, and assumptions that were used to justify your team’s proposed layout. Describe specifically the benefits of any acoustic enhancements your team makes to the room.
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