In the aerospace and defense industries, enclosure sealing and insulation needs to meet challenging and complex requirements. For example, the EMI gaskets that are used in military touchscreens must shield sensitive electronics from electromagnetic interference (EMI) while providing electrical conductivity and ensuring environmental sealing. These enclosure gaskets must also cushion the unit from mechanical shock and avoid interfering with the display's touch function.

Custom enclosure gaskets can meet these and other requirements, but designers need to specify the right materials and manufacturing methods. Unlike commodity rubber, specialty elastomers come with higher prices and minimum order quantities (MOQs). If part features such as holes, notches, or chamfers are required, manual gasket cutting may not be able to achieve the required degree of precision. Poor-quality cuts don't just suggest poor workmanship; they can result in sealing or insulation failure.

Designers also need to comply with the aerospace standards or military specifications listed on part drawings. Manufacturing at an AS9100D certified facility may be required, too. Meeting all of these demands can add considerable costs, which is why outsourced fabrication is now used with many projects. Examples of these engineered solutions include finished gaskets for EMI shielding or high flex-fatigue resistance, and custom insulation for heat and noise control.

EMI Shielding and Flex-Fatigue Resistance

With the proliferation of sensors and electronics, many enclosure gaskets need to provide a combination of sealing, shielding, and shock absorption. Thanks to innovations in material compounding, gasket materials can combine the advantages of elastomers with the electrical properties of metals. Silicones, a family of synthetic elastomers, offer thermal stability over a wide temperature range and resistance to ozone, water, and sunlight. When packed with metal or metal-coated particles, silicone sheets and rolls can provide EMI shielding and electrical conductivity.

Water jet cutting can create precise holes, notches, and chamfers to accommodate fastener heads and enclosure features.

Older particle-filled elastomers could be too hard or too brittle, but newer EMI silicones come in durometers as soft as 30 Shore A. During gasket cutting, these materials won't stretch or become deformed. Connector holes align properly, and the material's structural properties support greater tear resistance – a key consideration for gaskets with thinner walls. For shielding applications where Z-axis conductivity is required, EMI enclosure gaskets support the use of electrically conductive adhesives. Designers who choose an engineered solution can also specify an adhesive backing for ease-of-installation.

EMI enclosure gaskets support the use of electrically conductive adhesives. Enclosure designers have a choice of bonding methods.

Importantly, enclosure designers now have a choice of fill materials. Historically, many EMI gaskets were filled with silver or silver-aluminum particles. Today, nickel-graphite particles can provide silver-like connectivity. These gasket materials cost less than silver-filled compounds and can meet the lettered requirements of MIL-DTL-83528, a U.S. military specification.

Acoustic and thermal insulation can absorb sounds, dampens vibrations, reflects radiant heat, or resist the spread of fire.

For cost-effective fabrication, water jet cutting can be used. Unlike manual cutting, water jet equipment limits mis-cuts and material waste. Fluorosilicones have physical and mechanical properties that are similar to silicones, but provide improved resistance to fuels, oils, and solvents. In some aerospace and defense applications, fluorosilicone enclosure gaskets are required because of the splash of jet fuel, deicing fluids, or cleaning agents. During compound selection, designers can choose compounds that meet SAE AMS standards, or that meet the EMI shielding requirements of the MIL-DTL-83528 specification.

Silicone compounds have many desirable properties, but some have inadequate flex-fatigue resistance – a measure of a material's ability to withstand repeated flexing or bending without cracking. That's a problem in aerospace and defense, where materials with high flex-fatigue resistance are needed for door seals, window seals, and the vibration-isolating mounts for alternators, compressors and assembly bolts. Aerospace and military enclosures need gaskets with high flex-fatigue resistance, too.

During material selection, designers can specify materials that meet the full requirements of the A-A-59588 3B specification – with no exceptions for flexural testing. This standard from the U.S. General Services Administration (GSA) references the DeMattia Flex Resistance Test, which measures crack growth in inches over thousands of flexural cycles. Some A-A-59588 3B materials aren't fully compliant, however, so it's important to partner with a fabricator that can source certified 3B materials.

Gasket fabricators differ in terms of manufacturing capabilities, too. In addition to the cutting method, designers need to consider the best way to bond rubber gaskets. Hot splicing requires clean, straight cuts but support higher production volumes. By contrast, vulcanization is more forgiving since the cuts don't have to be smooth and precise. Cold bonding is a manual process that's performed with a brush or an adhesive or glue. It's ideal for low-volume quantities, but cold bonded gaskets won't last as long as hot spliced ones. Molding is the only bonding technique that can create rounded corners.