Molded Polyurethane Foam Inserts for Protection and Insulation

DN Staff

August 30, 2010

5 Min Read
Molded Polyurethane Foam Inserts for Protection and Insulation

Molded polyurethane foam has long been used to packagecomponents. Many design engineers, however, are not aware that properlyformulated foam and carefully designed foamed parts can also be used for thermalmanagement, acoustical insulation, vibration isolation and shock mitigation. Inaddition, these inserts can be used to reduce the number of parts in anassembly, thereby reducing assembly time.

Energy Management

Electro-mechanical assemblies require designs that take energymanagement into account, whether the energy is thermal, acoustical or kinetic. Therefore,the longevity of electro-mechanical components is closely tied to theenvironment in which the equipment they are housed in operates.

An effective approach to efficiently removing heat from anelectronic assembly is by integrating ducted cooling in the assembly enclosure.Typically colder is better, but the economics of the assembly dictates what isconsidered cold enough. Forced convection heat transfer calculations canquickly become rather complex, but it is intuitive that the cooler the airflowacross a hot surface, the greater the potential for cooling that surface.

Consider the possibility of dissipating the heat generatedin an assembly by directing the cooling airflow specifically across the heatsource. There will always be a need for general airflow in any enclosurehousing electronic components, but instead of over sizing the cooling fan sothat enough cool air will reach the hot components, a properly sized fan cancool those components by concentrating streams of cooling air specifically onthose components. Problematic in enclosures is the mixing, or recirculation, ofwarm air across hot components. A similar problem is the bypass of cooling airinto the exhaust stream. Ducting the cold air across the hot surfaces, theninto the exhaust stream can maximize efficient cooling. Designing channels,ducts, into engineered molded foam inserts, can make this possible.

Acoustic Insulation

Noise caused by a cooling fan, the airflow and theelectro-mechanical components can also be effectively managed with anengineered molded foam insert set. The default method used by engineers to attenuatesound 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, electrical wiring, etc. Openings in enclosures presentchallenges acoustically since the omni-directional sound waves can easilyescape without being attenuated. Because of this it is crucial to eliminateline-of-sight access to the noise source. One way to do this is to build abaffle system that forces the sound waves to travel along a long, tortuous,acoustically treated path.

A sound spectrum analysis of the components in an assembly,as well as of the assembly as a whole, can reveal the problematic frequenciesthat are propagating to the environment. From this analysis, the wavelengths ofthe sound waves can be calculated and an acoustical attenuation package can bedesigned by estimating the amount of mass needed to provide a measure oftransmission loss, the amount of absorption material needed to soak up some ofthe acoustical energy, and the length of the air path needed to attenuate someof the noise before it escapes. By designing air path channels in properlyformulated molded foam insert sets, these acoustical principles can be employedto attenuate the generated sound.

Molded polyurethane foam is open cell foam with a skin ofvariable thickness and density at the tool surface, and can be formulated toprovide a measure of transmission loss and acoustical absorption. There arecoatings that can be integrated on the foam surface that enhance the surfacecharacteristics of the foam as well. Typically, die-cut pieces of open-cellpolyurethane foam insulation, with specific acoustical properties, areinstalled in enclosures as patchwork. A considerable reduction of the number ofparts involved can be realized, resulting in cost savings by making thecomponents easier to assemble and reducing inventory maintenance.

Vibration Isolation& Shock Dissipation

Engineered, molded open cell polyurethane foam providesvibration isolation much the same way as it provides acoustical attenuation.The structure borne energy is dissipated in the foam due to the cellularinteraction of the open cell foam. An engineered, molded foam insert set can beutilized to isolate sensitive components from the vibrating assembly, orisolate the vibrating components from the assembly.

Controlling the density of the foam is integral to providingmolded foam inserts that provide the desired damping. Another importantparameter to consider is the durability of the material providing the vibrationisolation. The skinning feature of molded polyurethane foam and theavailability of surface coatings can provide the wear surface required toencapsulate the equipment while providing durability. Designing the insertsproperly can also eliminate the need for separate vibration mounts, reducingthe number of parts required and making assembly easier.

As with vibration isolation, the cellular structure ofmolded open cell polyurethane foam helps dissipate the energy induced bydropping or bumping an assembly. The longevity of electronic equipment canoften be enhanced by protecting the components from excessive movement and engineered,molded foam inserts can be used to capture the components in an assembly inshock absorbing material. Like the materials used for vibration isolation, thedensity of the molded foam is crucial to providing the shock absorptiondesired.

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