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Special Report: Noise

Listen up

By Nick Wright

Metal fabricating will never be silent, but solutions abound for reducing noise

November 2013 - Spending four days at Fabtech wears you out. After walking miles on the show floor, talking shop for hours and getting into nightlife, sitting down for the ride home is a welcome relief. But it’s not just your legs, it’s also your ears. Manufacturers crank up their machines for the show, creating a cycling cacophony of bangs, thuds and hums that certainly draws attention despite the decibels.

You might not give much thought to the noise at Fabtech, but back at the fabrication plants and job shops where operators spend hours, days, weeks or years, sometimes there’s no escape from the spectrum of noise accompanying metalwork. Technology has hushed products like computers, dishwashers and cars, however, machines that punch, press or blast metal in some form are inherently noisy—hearing protection is usually the remedy rather than a machine makeover. 

When buying a new machine, how much noise it produces falls far below productivity and efficiency on the list of selling points. If it turns out to be hazardously loud, it’s usually too late: downtime and shipping are costly. In that case, earplugs it is. Of course, not all processes make a racket, just as some employers encourage hearing protection more than others. Still, the issue of noise isn’t new but it’s not being ignored. Some companies take noise management further than others, and the extent to which OEMs, fabricators and noise solution companies control the clamor might redefine what it means to get more bang for your buck.

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Drowning sound

Plasma cutters are among be the loudest cutting operations, producing noise levels in the 95 dB to 115 dB range. One way to squelch that noise is by submerging it.

One company that opted for that solution is C.G. Bretting Manufacturing Co., Ashland, Wis. The firm fabricates paper conversion machinery—that is, equipment that folds napkins, tissues and other paper products. Its fabricating operations are contained in a separate hearing conservation area, about 9,400 sq. ft., where anyone who enters must wear hearing protection. But even with earplugs, the plasma cutter was a nuisance. C.G. Bretting’s customers require their machines to run at a certain decibel level, so when the company was checking customer machines, it decided to check its own.

“You had to make sure to talk louder over it,” says Mark Smith, manufacturing engineer at C.G. Bretting. “All while paying attention to what you’re doing. We knew we had to quiet it down.”

Most of the noise comes from the plasma arc itself, with additional noise coming from large fans in the plasma power source and water coolers, according to Steve Zlotnicki, product manager, cutting, at ESAB Cutting Systems, the supplier of C.G. Bretting’s plasma machine. “Plasma cutting under water is the cheapest and easiest way to reduce plasma noise. The more expensive and more sophisticated method is a total machine enclosure.”

C.G. Bretting selected the former option. The company wanted to move the plasma cutter outside of the fabrication area for logistical reasons, which meant it would sit outside an office. Smith says installing a water table, which submerged the cutting head, eliminated smoke and reduced noise. “The supervisors were concerned about the machine going there and now it doesn’t faze them a bit.”

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Constant versus intermittent

A big distinction to note is between constant noise and intermittent noise. The Occupational Safety and Health Administration mandates 85 dB for 8 hours as the maximum average exposure level for employees. For higher decibel levels, 5 dB increments are considered twice as loud. For example, 90 dB is twice as loud as 85 dB; the permissible exposure time for 90 dB is 4 hours. However, when average noise measurements are taken, referred to as dBA, they don’t account for the noise spikes in environments where an extremely loud process occurs infrequently. In job shops, no two days are the same.

William Daniell, an epidemiologist and associate professor of environmental and occupation health sciences at the University of Washington, says when noise is intermittent, people get casual about it and don’t wear protection all the time. “When the noise starts again, workers aren’t controlling it and thus are not anticipating it,” which could lead to complacency and eventually hearing loss over time.

In 2005, Daniell co-authored “Occupational Noise Exposure and Hearing Loss Prevention,” a technical guidebook for sheet metal manufacturing companies. The guide explains that in a study of 10 metal manufacturers, most employees were not well informed about noise exposures. Only 17 percent recalled being told specific noise levels for their job or for other jobs at their worksite. Overall, 40 percent didn’t recall being told they might be overexposed to noise because of their job. Many of these workers were monitored for this study and had full-day noise exposures of 85 dB or higher. 

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Are those results indicative of a larger problem with noise in metalworking? They do suggest that the problem facing the workers is also a problem for the management. People at management levels often think that hearing protection is the domain of the employees, says Daniell. “The one thing people don’t understand is that there are many options for noise control along the whole process. People assume these machines are noisy and always will be, and that the ultimate solution is hearing protection. But that’s inherently flawed because it counts on human behavior being perfect.” That’s like a dentist guaranteeing perfect teeth as long as everyone flosses daily.

The best noise control strategy is to stem it at the source. In metal fabricating, it’d be a long shot to silence every process, and it’s generally not an OEM’s priority. With CNC punching or heavy tonnage presses, which will always make noise, sound enclosures, tooling and programming cycles take the noisy edge off. For example, Trumpf makes a beveled punch tooling line called WhisperTools that, depending on sheet thickness and material, can cut noise by half. When used with the SoftPunch function on its punch presses, 80 percent less noise is emitted, according to the company.

FFJ-1113-special-image4LVD Strippit similarly has a quiet punch cycle on its CNC turret punch presses. This is achieved by programming the tool to rapidly approach the material then slowing it to contact and shear through. After the punch, the ram completes its cycle rapidly. This reduces noise and shock while remaining productive.

Bad vibrations

In other cases, it’s not the noise that bothers fabricators, it’s machine vibration. High shock generating machines send vibration into floors and shop structures, which can cause audible rattling. Walls and windows effectively become sounding boards. Vibration energy moves outward from machinery like ripples on water.  Heavier presses, such as mechanical and pneumatic stamping presses, or forging hammers and shredders, are examples of high shock sources.

In between OEM machine improvements and workers with earplugs are companies that specialize in dampening vibration and sound. Vibro/Dynamics Corp., Broadview, Ill., finds that vibration is usually more of a concern than audible noise because it can fatigue workers, bother office staff, affect part quality, and disrupt nearby high precision areas like metrology labs and CNC operations.

“For the workers near the machinery, OSHA noise exposure requirements, safety and communication are big factors that make audible noise very important, too,” says Steve Veroeven, vice president of engineering at Vibro/Dynamics. The company manufactures vibration and shock control mounts for metalforming machines, as well as other industries. Vibro/Dynamics will install elastomer vibration isolation mounts for precision machinery, essentially cushioning them. The company’s coil spring mounts for stamping presses or heavy blanking also double as seismic isolating solutions under foundations or concrete slabs.

The most common effect excessive vibration has on equipment is shortened component life, says Veroeven. “Awareness and education of vibration levels along with modern building construction and the use of vibration isolators have made structural building problems due to vibration very rare.”

Airam, based in Covington, Ohio, manufactures standard and custom pneumatic presses for metalforming, high speed roll forming and other processes. John Bornhorst, Airam’s vice president of engineering, says his customers worry more about vibrations than noise levels, even though some of its pneumatic presses and stamping presses can be unavoidably loud.

To cut down on noise, he recommends keeping excess tonnage low and slowing ram speed—easy and obvious for most fabricators doing any sort of punching. “We will furnish vibration pads between the press bed and base to reduce vibration transmitted to the floor, and this will reduce noise,” he says. “The main purpose is to reduce vibration, but a byproduct of that is reduced noise.”

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Fitting mufflers on air exhaust valves and supplying mounts between the floor and press base are other ways to quiet processes. “We supply enclosures around the complete press when requested,” he says. However, the material being processed still needs to enter and exit the enclosure, so noise is reduced, not eliminated. The highest percentage of noise comes from die punching the metal, a process that can generate an intermittent 90 dB to 100 dB. Because punching and stamping—metal on metal impacting—are naturally loud, the most realistic remedy is to enclose the sound, separate the machine from the operator and make sure machines are maintained.

In reality, all fabricators know very few metalworking processes are quiet enough that they don’t warrant hearing protection. Whether a machine is stamping or forming parts, a grinder eating away an edge or a hammer striking a saw blade, metalwork is loud, sometimes deafening—which is good news for noise control companies. In the short term, the easiest thing for fabricators to do is encourage hearing protection as a culture as well as ensuring equipment is running properly and well maintained, says Daniell. Hearing protection with adequate noise reduction ratings goes a long way. In the long term, consider retooling and capital investments as opportunities to get quieter machines. In the meantime, common sense is the best practice. “Don’t assume noise is something that ends with the annual training session and setting out a box of earplugs,” he says. Years later, your ears will thank you. FFJ

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