Engineering Controls Database
Folding Carton Packing Stations, Air Hammer Noise – 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: In the manufacture of folding cartons, the individual cartons are cut, and the cut sheets are stacked by the cutting press on a pallet. To deliver the multiple sheets from the press, the cartons are held together with a nick or uncut portion. When stacked, the individual cartons are separated by stripping with an air-driven chisel which breaks the nicks and frees an entire stack. When no additional operations are needed, these stacks are packed in cases for shipment. Air hammers/chisels produce noise that has not yet been eliminated by equipment manufacturers. Currently available air hammer mufflers do not reduce the noise to an acceptable level. The air hammer operator therefore must wear ear protection. The problem in this case was to protect other workers (packers) from the air hammer noise. A typical production air hammer stripping and packing set-up is shown in Figure 1. The production sequence for this operation is for the stripper to air hammer a stack of cartons (precounted by the cutting press) and place them on the conveyor at Point C. The packer, at the end of conveyor E, prepares the case, packs the stacks of cartons, seals, labels, and stacks the finished pack on a delivery skid. Two packers are required to handle the output from one stripper. The stripper is actually using the air hammer about 50% of his time, with the balance of the time used in stacking or preparing the load. Thus, s/he can get some relief from continuous use of ear muffs by hanging them around his/her neck while not actually using the hammer. |
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The noise level at the ear of the operator was measured to be around 92-97 dBA. According to NIOSH exposure guidelines, this only allows for 30 minutes of safe exposure time. To allow a worker to fully complete a workday safely, the noise level had to be dropped down to 85 dBA. 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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It was decided to protect the packers from the air hammer stripping noise by using a barrier wall. A convenient rule-of-thumb is that useful protection is afforded by the barrier wall beyond 30 degrees into the acoustical shadow (see Figure 1).  The barrier will need be no better acoustically than the attenuation afforded around the sides and top of the wall. Therefore, the wall was fabricated with a 2 x 4 in. frame faced on both sides by l/4 in. plywood for a simple sturdy barrier wall.   |
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Beranek LL [1971]. Noise and Vibration Control. McGraw-Hill, New York, N.Y. 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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air hammers air hammers chisels chisels folding cartons folding cartons noise noise noise barriers noise barriers noise control noise control |
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If there had been any reason to reduce noise reflections from the noise source side, this side could have been faced with sound-absorbing acoustic materials. The rule-of-thumb of aiming for the packer to be well within the 30-degree line from the acoustic shadow line was used in this case. The attenuation calculated for this barrier wall ranges from 10 to 15 dB, depending on the wavelength. This agreed with the measured attenuation of 7 to 12 dB and the noise reduction from the 92-97-dBA range to about the 85-dBA average measured at the packer's ear level. Comments In this installation, there were, fortunately, no low ceilings which would have established a serious sound reflection problem and defeated the barrier wall. Barrier walls will not give good results in a highly reverberant, low-ceilinged room. If there had been a low ceiling, useful noise reduction would still have been possible by adding sound-absorbing material at the reflecting portion on the ceiling (about 12 ft over the barrier wall and the noise source), The amount of attenuation gained is easily estimated by using the ratio of absorption of new material to that of the existing ceiling. Ceiling reflection is a major pitfall of the use of barrier walls indoors. The design of the wall alone is based on free-field conditions. |