EMI aerospace gaskets that are made of electrically conductive silicones provide shielding against electromagnetic interference (EMI), environmental sealing, and temperature insulation. Silicones, a family of synthetic elastomers, are normally electrically insulating. When they are filled with metal or metal-coated particles, however, they become electrically conductive and provide protection against EMI, electronic “noise” or crosstalk that can disrupt or disable circuits.
The causes of EMI are numerous and can range from cellphones and power supplies to auroras and solar flares. In the aerospace industry, EMI can affect avionics, displays, fuel dispensing systems, and air-to-ground communications – just to name a few examples. Conductive silicone gaskets are only one part of the solution, but they’re an important part because they fill gaps between mating surfaces in electronic enclosures. In addition to keeping out EMI, they provide needed sealing and insulation.
EMI Silicones: The Best of All Worlds
EMI silicones are elastomeric compounds that combine the advantages of silicone rubber with the electrical properties of metals. Silicones resist the high temperatures that are common to electronics, but these elastomers also provide thermal stability over a wide temperature range. In addition, silicones resist water, ozone, and sunlight. When filled with tiny metal or metal-coated particles, silicone compounds also provide electrical conductivity and EMI shielding.
The table below lists common filler types and shows the relationship between each filler type, electrical conductivity, and typical volume resistivity (VR) – a measure of EMI shielding. Direct methods for measuring shielding effectiveness can be expensive and complex, so VR is a commonly-used method instead. Typically, EMI aerospace gaskets use particle-filled silicones that contain pure silver, or a silver-plated or nickel-coated material.
Filler Type | Electrical | Typical VR (ohms/cm) |
Silver | Extremely Conductive | .0009 |
Silver-Aluminum | Super Conductive | .003 |
Silver-Copper | Super Conductive | .003 |
Silver-Glass | Very Conductive | .006 |
Nickel-Graphite | Conductive | .01 |
Carbon Black | Semi-Conductive | 8.0 |
Nickel-Graphite Silicones for EMI Aerospace Gaskets
Nickel-graphite silicones are cost-effective compounds that provide comparable shielding levels to silver-aluminum filled products. Silver has long been used a filler material but is subject to price fluctuations that can increase the costs of EMI aerospace gaskets. MIL-DTL-83528, a U.S. military standard for elastomeric shielding gaskets, specifies a minimum shielding effectiveness of 100 decibels (dB); however, Elasto Proxy can source less expensive nickel-graphite silicones with a shielding effectiveness of 125 dB.
Nickel-graphite silicones also provide attractive material properties. For example, they are available in durometers from 30 to 80 on the Shore A scale. Durometer, a measure of hardness, is related to compression set, a measure of a material’s ability to return to its original thickness after prolonged compressive stresses have been removed. An example of these compressive stresses is that of a hatch seal on an aircraft enclosure that is opened infrequently.
The nickel-graphite EMI silicones that Elasto Proxy can source are suitable replacements for the more expensive silver-aluminum materials that are found on many part drawings of aircraft seals and gaskets. As the table below shows, nickel-graphite silicones for EMI aerospace gaskets have a shielding effectiveness (dB) that exceeds the MIL-DTL-83528 standard across a range of MHz frequencies.
Frequency (MHz) | Reference Level (dB) | Dynamic Range (Analyzer Reading) | Test Sample (Analyzer Reading) | Dynamic Range (dB) | Nickel Graphite Gasket (Shielding Effectiveness) (dB) |
20 | 95 | -26.9 | -25.1 | 121.9 | 120.1 |
30 | 100 | -27.9 | -24.5 | 129.9 | 124.5 |
40 | 100 | -28 | -24.3 | 128 | 124.3 |
60 | 100 | -28.2 | -25.1 | 128.2 | 125.1 |
80 | 100 | -27.7 | -25.5 | 127.7 | 125.5 |
100 | 100 | -27.9 | -25.2 | 127.9 | 125.2 |
200 | 100 | -28.9 | -27.7 | 128.9 | 127.2 |
400 | 100 | -28.3 | -26.3 | 128.3 | 126.3 |
601 | 100 | -28.7 | -26.1 | 128.7 | 126.1 |
800 | 100 | -29.2 | -27.1 | 129.2 | 127.1 |
1000 | 100 | -17.8 | -15.7 | 117.8 | 115.7 |
2000 | 100 | -18.2 | -15.5 | 118.2 | 115.5 |
4100 | 100 | -17.9 | -13.7 | 117.9 | 113.7 |
6000 | 100 | -17.1 | -13.1 | 117.1 | 113.1 |
8000 | 100 | -17.2 | -14.1 | 117.2 | 114.1 |
10000 | 100 | -17.5 | -15.7 | 117.5 | 115.7 |
Nickel-graphite silicones for EMI aerospace gaskets also have good tensile strength, elongation, and tear resistance. They can be reinforced with an inner layer of conductive fabric to provide increased strength and electrical conductivity and are available in formulations that resist salt spray and corrosion or that provide UL-94 flame resistance. The table below provides a few examples of the nickel-graphite silicones that Elasto Proxy can fabricate.
Durometer | Tensile Strength (psi) | Elongation (%) | Tear B (ppi) | Maximum VR (ohm/cm) |
30 | 100 | 400 | N/A | 0.300 |
45 | 150 | 200 | 25 | 0.030 |
55 | 150 | 200 | 25 | 0.040 |
65 | 200 | 200 | 35 | 0.040 |
75 | 270 | 250 | 35 | 0.040 |
Silver and Silver-Filled Conductive Silicones
If your application requires them, Elasto Proxy can fabricate EMI aerospace gaskets from conductive silicones that are filled with pure silver or silver-plated particles. These materials are available in a range of durometers and can meet MIL-DTL-83528 requirements. Gasket designers can also specify fluorosilicone as the base material. These elastomers have physical and mechanical properties that are similar to standard silicones, but with improved resistance to fuels, oils, chemicals and solvents.
Fill Material | Base Elastomer | Durometer | Maximum VR (ohm/cm) |
Silver-Copper | Silicone | 65 | 0.004 |
Silver-Aluminum | Silicone | 65 | 0.008 |
Silver-Aluminum | Fluorosilicone | 70 | 0.012 |
Silver-Aluminum | Fluorosilicone | 45 | 0.004 |
Silver-Aluminum | Fluorosilicone | 70 | .012 |
Silver | Silicone | 65 | 0.002 |
Silver-Nickel | Silicone | 75 | 0.005 |
Silver-Copper | Silicone | 80 | 0.005 |
Silver-Glass | Silicone | 65 | 0.006 |
EMI Aerospace Gasket Fabrication
Elasto Proxy specializes in low-to-medium volumes of industrial rubber products and can source EMI aerospace silicones in sheets, rolls, and extrusions for fabrication with our water jet equipment. Unlike die cutting, water cut jutting doesn’t require metal tooling. Yet, water jet cutting is also capable of making fine, fast cuts such as chamfers, angles, and holes. The EMI silicones that we fabricate come in 15” wide (381 mm) rolls to support cost-effective fabrication and are available in standard sheet sizes as thin as .010” (0.254 mm).
With water jet cutting, EMI elastomers won’t stretch or become deformed. Connector holes align properly, and the conductive silicone’s structural properties support greater tear resistance – an important consideration for thinner wall gaskets. Designers of EMI aerospace gaskets can also specify the use of adhesive backing for ease-of-installation. For shielding applications where Z-axis conductivity is required, the EMI elastomers we fabricate can support the use of electrically-conductive adhesives.
Elasto Proxy is AS9100 D certified and ready to fabricate your EMI aerospace gaskets at our headquarters near Montreal, Canada, one of the world’s leading aerospace and aviation centers. We can also supply you with EMI bonded O-rings and molded EMI aerospace gaskets. With our supply chain strength, we’ve formed partnerships that allow us to provide you with “one stop shopping” – including metal fabrication. At our Montreal facility, we also have several types of abrasive water jet cutting equipment.
Contact Elasto Proxy to discuss your application requirements and let our solutions providers know what you need.
