Engineering Controls Database
Straight-and-Cut Machines – Noise Case Study
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Overview: The case history presented here is one of sixty-one case histories that were published by the National Institute for Occupational Safety and Health (NIOSH) in 1978 as part of an industrial noise control manual [NIOSH 1979]. The case histories are examples of engineering tasks that have been completed not only by professional noise control engineers but also by non-acoustical specialists who used common sense to solve their noise problems. The case histories were chosen primarily because the amount of noise reduction actually achieved was measured. Such engineering results, even if not directly applicable to a specific situation, illustrate general principles that may point the way to a successful result. They are intended to be useful to production and safety engineers, health personnel, and other factory personnel who are not specialists in noise control. Case study: The straight-and-cut machine straightens heavy-gauge wire in an in-feed to a cutoff unit set to cut repeat lengths, resulting in sound levels of 92 dBA at the operator position, with the cutting cycle sound level at 92 dBA (idling cycle at only 83 dBA), indicating that the dominant noise source of the clutch cutter mechanism is the same form as in the close-in diagnostic measurements. Comparison of the measured sound pressure levels with the 90-dBA criterion indicates the required attenuation is between 5 and 11 dB in the 1000- to 8000-Hz octave bands. |
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| Hearing loss is one of the most common occupational diseases in America today and the second most self-reported occupational illness or injury. Approximately 30 million workers are exposed to hazardous noise on the job and there are approximately 16 million Americans with noise-induced hearing loss. | |
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On the basis of discussions with management, it was determined that noise control should take the form of a barrier wall that would block the sound path from the cutting assembly to the operator, rather than machine redesign. The client in this case sought to reduce the sound level to a maximum of 85 dBA at the operator position. Barrier materials for obtaining the required attenuation were 1/4-in. plywood, with 1/8- to 1/4-in. Plexiglas for viewing ports where necessary. The barrier wall was extended 26 in. past the extremities of the area encompassed by the cutter and was close to the cutter, about 6 to 8 in. away. The barrier was hung in place, supported by chains from overhead. In addition, an absorbent layer was hooked to the barrier on both sides. To prevent clogging of absorbent, the 1-in. polyurethane foam absorbent was supplied with Mylar facing. See Figure 1.  |
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| NIOSH [1979]. Industrial noise control manual – revised edition. Cincinnati, OH: U.S. Department of Health Education and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. 79-117. | |
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noise control noise control straight-and-cut machine straight-and-cut machine wire manufacturing wire manufacturing |
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The cutting cycle sound levels at the operator location were reduced from 92 dBA to 85 dBA, a 7-dB reduction in sound level. Idle cycle sound level was reduced from 83 dBA to 76 dBA. Comments: Barriers are easy to remove by the operator for many reasons, real and imaginary, and use must be maintained by supervision. Location of an effective portable barrier must be standardized so that the barrier is not bypassed. Barriers can be bypassed by noise reflections from a low ceiling. If this problem had existed in this case, a section of the ceiling above and about 4 ft on-each side of the barrier could have been treated with absorbing material. |