Appliance Design - August 2007 - (Page 25)

NOISE & VIBRATION Various coatings available (e.g. phosphate, pre-paint, e-coat, etc.) Damping When isolation is not possible, another strategy is to employ materials that will damp the vibrational energy at or near the source. Demonstrations of the effectiveness of damping materials can be dramatic: drum cymbals that “tink” instead of crash and splash when damped; a metal plate dropped onto a desk and producing only a meek thud because it has been quieted with a damping material. The materials come in a variety of different formats, including homogenous free-layer materials that are applied by trowel or sprayed on; a peel-and-stick version; and constrainedlayer damping materials that are bonded to the application with adhesives. The common thread is that it turns the vibrational energy into thermal energy and dissipates it. Material Sciences Corp., Elk Grove Village, Ill., manufactures a laminated product called Quiet Steel® that features two layers of metal that encapsulate a highly engineered viscoelastic core. With this material, the vibrational energy is converted into heat that is then dissipated through the core. Clifford Nastas, CEO, MSC, says to think of the concept as two hands rubbing together quickly, generating heat from the friction. For example, noise from a clothes dryer can occur when the dryer is tumbling clothes and buttons are hitting the drum. When the buttons hit the drum, the drum acts like a vibrating speaker. With this type of material, the vibration energy is dissipated through the constraint layer as the two layers of metal move back and forth turning the noise into heat. Because each application is different, the Engineered Viscoplastic Layer (0.001 in.) Cold-rolled steel, EG, GA, hot-dip, stainless, aluminum, etc. With MSC’s Quiet Steel, the viscoelastic material is laminated with two sheets of metal encapsulating a viscous core. And, as always, cost looms as an important issue, too. That’s why designers often take a strategic approach where possible, specifically targeting the problem areas. In some applications, like a dishwasher, where the entire tub radiates noise, there is no choice but to wrap it in a big blanket. But in other cases, the source can be more narrowly addressed, such as using isolation mounts on a motor or using a sounddamping shell over a compressor. Structure-borne noises One way to reduce the transmission of vibrational energy is by isolating the source. Eliminating or reducing noise and vibration through isolation requires upfront planning and it should be one of the first things considered when designing a new product, says Carl Wolaver, of Polymer Technologies, Newark, Del. After the product has been designed, adding an isolation mount can be challenging. Isolation mounts are often made from rubber, metal springs or other material. Isolators provide a means of connecting two structures so as to provide relative motion between them under dynamic loads. According to application information from Indianapolis-based E-A-R Specialty Composites, the amount of motion required depends on variables such as the range of frequencies over which the isolator must be effective. For instance, noise in the A-weight frequency range above 250 Hz can be accomplished with a low-deflection mount. Vibration not only causes sound, but it can cause damage to the product due to excessive motion. Sorbothane, Kent, Ohio, designs custom mounts made from its Sorbothane viscoelastic material. At the 2007 Medical Design & Manufacturing West Show in February, the company exhibited mounts to reduce shock damage to portable medical equipment, gasket isolators to protect LCD screens and a variety of components to isolate damaging shock waves. www.applianceDESIGN.com A manufacture of infusion pumps, for instance, used a Sorbothane, gasket-type isolator that was engineered to protect the LCD from shock damage. To test the unit, it was thrown from a car traveling at 45 MPH, and it survived and was fully operational. The company said that it has achieved shock absorption levels up to 94.7 percent while maintaining stability and damping over a broad temperature range. In addition to isolation mounts, a number of companies offer molded products that blocks noise from entering or exiting, absorbs sound and reduces vibration shock load. Polymer Technologies, for example, offers the PolyForm molded products that encapsulate and isolate components. Whichever product is chosen, Wolaver says that a good isolation system will take out 95 percent of the energy. “If it is only taking out 80 to 85 percent of the energy, then that remaining energy will continue to travel along the structure,” he says. “That could cause the skin to vibrate at its natural frequency, and then that frequency is just radiated out.” Conformable acoustic insulation from 3M can be configured for a variety of applications. applianceDESIGN August 2007 25 http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - August 2007

Contents Editorial Shipments/Forecasts News Watch A Reed Switch is Simople, yet Versatile, and Designers are Finding New Uses for this Time-Tested Technology A Novel Actuation and Sensing Technology can Register a Light Touch, but Resist Blows from a Hammer Tracing the Source of Noise is Made Easier with Noise Source Identification Methods Appliance Noise can be Annoying, but Designers have Many Material Choices to Help Rein in the Racket Nanocomposites are No Longer a Technology for the Future. These Plastic Materials are Already on the Job A New High-Strength, Low-Density Glass-Microsphere Additive can Improve Plastic Part and Molding Performance A New Electromagnetic Weld/Bonding Process Helps Ensure Long-Term Integrity of Joints in Plastic Parts Snap-Based Technology Eases Installation and Makes Products More Serviceable Two-Part Silicone Adhesives Provide a Rapid-Cure Alternative to Traditional One-Part Silicones Classified DesignMart Advertiser’s Index Association Report: GAMA

Appliance Design - August 2007

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