Electronics Protection - January/February 2012 - (Page 10)

Feature Energy Management Using Molded Polyurethane Foam Inserts Robert Marsh, Technical Director Polymer Technologies, Inc. Molded polyurethane foam has long been used to package components, but properly formulated foam and carefully designed parts can also allow for heat dissipation, acoustical insulation, vibration isolation and shock mitigation, all while reducing the number of parts in an assembly and reducing the assembly time. Electronic assemblies require designs that take thermal management, typically heat dissipation, into account. From portable electronic gadgets to components in rack-mount cabinets, the longevity of the device is closely tied to the environment in which the equipment operates. A manufacturer’s goal of providing high performance, low maintenance, long life and low cost assemblies have to be met while managing the thermal loading of the equipment. An effective approach to efficiently managing heat in an electronic assembly is to utilize three-dimensional molded polyurethane foam inserts to direct the airflow to the right components. In addition to thermal management, these inserts can also address sound attenuation, shock and vibration isolation, and packaging. Forced convection heat transfer calculations can quickly become rather complex, but it is intuitive that the cooler the airflow across a hot surface the greater the potential for cooling that surface. Consider the possibility of dissipating the heat generated in an assembly by directing the cooling airflow specifically across the heat source. There will always be a need for general airflow in any enclosure housing electronic components, but instead of over sizing the cooling fan so that enough cool air will reach the hot components, a properly sized fan can cool those components by concentrating streams of cooling air specifically on those components. Problematic in some enclosures is the mixing, or recirculation, of warm air across hot components. A similar problem is the bypass of cooling air right into the exhaust stream. Ducting the cold air across the hot surfaces, then into the exhaust stream can maximize efficient cooling. Designing channels, or ducts, into molded foam inserts can make this possible. Noise caused by the cooling fan, the airflow, and other electrical components can be effectively managed with the same molded foam insert set. Sound radiates in all directions from a sound source. One excellent way to attenuate sound is to build an enclosure around the source to block it. Unfortunately, most noise sources require openings in an enclosure to allow for airflow, mechanical linkages and electrical wiring. Figure 1. Openings in enclosures present challenges acoustically since the omni-directional sound waves can easily escape without being attenuated. It is crucial to eliminate line-of-sight access to the noise source. An effective way to do this is to build a baffle system that forces the sound waves to travel along a long, tortuous, acoustically treated path. A frequency spectrum analysis (Figure 1) of the noise generated by the components in an assembly, as well as of the assembly as a whole, can reveal the problematic frequencies that are propagating to the environment. From this analysis, the wavelengths of the sound waves can be calculated and an acoustical attenuation package can be designed by estimating the amount of mass needed to provide a measure of transmission loss, the amount of absorption material needed to soak up some of the acoustical energy, and the length of the air path needed to attenuate some of the noise before it escapes. By designing air path channels (Figure 2) in properly formulated molded foam insert sets these acoustical principles can be employed to attenuate the generated sound. Molded polyurethane foam is open cell foam with a skin of variable thickness and density at the tool surface, and can be formulated to provide a measure of transmission loss and acoustical absorption. There are coatings that can be integrated on the foam surface that will enhance the surface characteristics of the foam as well. Molded open cell polyurethane foam provides vibration isolation much the same way as it provides acoustical attenuation. The structure borne energy is dissipated in the foam due to the cellular interaction of the open cell foam. A molded foam insert set 10 January/February 2012 www.ElectronicsProtectionMagazine.com http://www.infowebcom.com/newsletters_form.php http://www.ElectronicsProtectionMagazine.com

Table of Contents for the Digital Edition of Electronics Protection - January/February 2012

Pentair Technical Products Expands Hoffman Line of Floor-Mount Type 4 Enclosures
A Look Ahead to 2012: The New UL 50 12th Edition Standard for Electrical Enclosures
Extending the Life of Electronics
Energy Management Using Molded Polyurethane Foam Inserts
Tools for Custom Connector and Cable Solutions
PowerSkin Unveils Battery-Boosting Skin for HTC Amaze 4G
Emerson Network Power Introduces the DCF Optimized Rack System
Littelfuse Introduces the SP3012 Series TVS Diode Arrays for Protection of USB 3.0 Ports
Schneider Electric’s Cooling Solution Portfolio Brings Efficiency, Flexibility and Reliability to Data Center Cooling
Eaton’s 9E UPS Delivers Simple Power Management for Complex IT Environments
PEM C.A.P.S. Captive Panel Screws Offered in Three Mounting Styles26
Industry News
Calendar of Events

Electronics Protection - January/February 2012