Engineering Controls Database
Braiding Machine – 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: Braiding machines are used in the textile industry to combine several filaments of material into a single braided strand. The braiding process is accomplished mechanically by having many individual material "carriers" move simultaneously around the periphery of a table in such a fashion that the carriers crisscross each other as they move. The material strands, fed from the carriers, are thus formed into a braid. Considerable noise is generated by the gearing and the impacts associated with the carriers as they constantly change direction. Typically, many braiding machines are assembled in multiple rows and operate simultaneously, tended by operators who make sure the machines are functioning properly. |
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The sound level was 101 dBA with the bank of 26 braiders running and 57 dBA maximum with the machines turned off, indicating that the problem noise originated at the braiding machines. 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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An enclosure was the selected control. The enclosure design had to provide a minimum of 16 dB of noise reduction on a dBA scale, to achieve 85 dBA guaranteed. In addition to the acoustical requirements, the client specified that the control would have to be robust and sanitary (a medical product was involved) and could not cause any significant worker inconvenience. For the project involved in this case history, the company’s Noise Control Division was called in to help the manufacturer of medical sutures bring worker noise exposures of his braider operators down to an equivalent of 85 dBA or less when a bank of machines was operated. Because of funding limitations, the company was asked to work on a prototype installation that would be evaluated after normal working hours, when the treated equipment could be run independently of other untreated machines in the area. The custom-designed enclosure constructed for this problem is shown in Figure 1. From the photograph, it is easy to see that the operators retain good visibility of their machines. Several aspects are not revealed by the pictures: The windows slide on roller bearing, making worker accessibility relatively easy and fast. Panels on the bottom of the enclosure also slide. All windows and the bottom panels are removable for maintenance. Sufficient ventilation for these machines is furnished via the silenced supply air vent openings below the bottom panels, and warm air rising through the open top of the enclosure. The outer skin of the enclosure panels is made of corrosion-resistant steel. The inner skin of the panels is of perforated sheet metal that covers an acoustical fill material, thereby making the inner surface acoustically absorbent and thereby minimizing any build-up of sound inside the enclosure. A layer of woven glass fiber fabric protects the inner fill from working out of the perforated sheet metal.   |
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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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braiding machine braiding machine manufacturing manufacturing noise noise noise control noise control textile textile |
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Sound levels at the aisle positions have been reduced by 18 dB to 83 dBA when only the treated bank of machines is running. It should be noted that the achieved noise reduction is not a characteristic reduction of acoustic panels but rather an overall reduction of the entire system; consisting of approximately 50% glazed area of the total enclosure surface. The vents at the bottom of the enclosure are acoustically treated and compatible with the enclosure attenuation. Operators are exposed to higher sound level only for short periods of time, when opening one of the windows to work on a particular machine. Under these circumstances, the machine being worked on is typically shut off, and the worker is exposed to noise coming from more distant machines. Measurements taken at the enclosure at a position occupied by an operator tending a machine, while the other 25 machines are running, confirmed that such an exposure would contribute only a small fraction to his overall noise exposure. Since the enclosure, when installed in an existing plant, reduces aisle clearance between adjacent rows of equipment, some braiding equipment users may find it necessary to move their equipment in order to accommodate the 10- to 20-cm loss of clearance caused by the treatment. New plant layouts, of course, can accommodate required walkway clearances. |