Chicago, IL —When it comes to credit card interest rates and cholesterol levels, lower is always better. The same is true for conveyor noise, as evidenced by the number of quiet-running systems on display at the ProMat materials handling show, held in mid-February at McCormick Place.
"The operations people running today's distribution centers are trying to create a better environment for workers," says David Cotter, manager of mechanical engineering for Rapistan Systems (Grand Rapids, MI), a supplier of materials handling equipment. "One way to do that is by reducing overall sound levels," he adds.
Although maximum permissible exposure limit for noise set by OSHA is 90 dBA, a range of 50 to 60 dBA is actually considered comfortable. Noise levels generated by a typical lineshaft conveyor system—whose sources of noise include shaft clatter, bearing rattle, and roller tube ringing—can exceed 70 dBA. By applying various noise reduction strategies in this newest generation of conveyor systems, engineers have been able to achieve decibel levels in the low 60's—all the more impressive when you consider that decibels are logarithms of noise levels.
Rapistan engineers improved upon the noise output of the 1265 ESAC roller conveyor by replacing the chain drive with a patented polyurethane belt, reinforced with aramid fibers to achieve the requisite strength and tensile characteristics. Other design tricks included the use of optical, rather than mechanical sensors for accumulation, and development of a new module housing that snap fits rather than bolts to the conveyor structure. "We've eliminated all the clatter associated with mechanical fasteners," says Cotter.
A quieter drive technology was also key to reducing sound levels of HK System's (Milwaukee, WI) new WhisperFlex accumulation conveyor. Instead of using a belt, however, engineers opted for a cable geometry that has the added benefit of allowing the rollers to accumulate (momentarily stop a load) around a curve. "Bottom line, we've eliminated the need for additional drives, which can produce point source noise," says Mechanical Engineer Jerry Vaughn. Loads are also sensed optically, rather than mechanically.
Engineers at FKI Logistex (Danville, KY) tackled the noise issue by locating the motors inside the conveyor rollers of the company's Accu-Zone conveyor. Part of a growing trend in accumulation conveyor technology, the hollow rollers help muffle the sound of noisy motors. "We have no external gear boxes or motors, which are a major source of noise," says Kevin Kozuszek, manager, marketing communications. "An added benefit is that only rollers in active zones are powered, which contributes substantially to the noise reduction."
VanderLande Industries (Atlanta, GA) engineers took a different tack by eliminating the rollers altogether on the company's Distrisorter conveyor technology. Rather than relying on rollers—which make an excellent sounding board—engineers devised a series of small belts to transport loads. To stop or accumulate a load, the section of belt beneath the load drops down against the bottom structure of the conveyor. "In addition to the noise reduction, this gives us very rapid fire accumulation since we do not have to overcome any inertia," says VanderLande's Frans van Duren.
All of the conveyors described above operate at less than 65 dBA depending on speed, which can reach 300 ft/minute. So can the technology get any quieter? "I think engineers are beginning to reach the point of diminishing returns in terms of further noise reductions in the conveyor structure," says Rapistan's Ken Ruehrdanz, "The next frontier is probably load noise, which can be significant."
Ironically, as conveyor technology gets quieter, ways must be found to notify workers that a conveyor system is about to start up or is running—including the use of loud warning bells and flashing lights.