Circular EMI gaskets and washers are precision-engineered shielding components that maintain electrical continuity and environmental integrity across bolted interfaces and waveguide flanges. They are essential for electromagnetic interference (EMI) and radio frequency interference (RFI) control in high-performance electronics, particularly where MIL-DTL-83528 compliance is required.
MIL-DTL-83528/012 & /013 — Understanding the Callouts
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MIL-DTL-83528/012 — covers circular EMI washers with controlled inner and outer diameters, used primarily under fasteners, standoffs, and bulkhead penetrations to maintain low impedance ground paths and block EMI leakage.
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MIL-DTL-83528/013 — defines waveguide interface gaskets and separates them into:
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Configuration A — flat profile waveguide flange gaskets.
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Configuration B — circular profile waveguide gaskets, often used when a round flange or rotational symmetry is present.
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By referencing these slash sheets, engineers can guarantee dimensional interchangeability, mechanical performance, and shielding levels across suppliers.
Material Systems — Conductive Elastomers for Harsh Environments
NEDC works with MIL-qualified conductive elastomers specifically formulated for EMI performance and long-term environmental durability:
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Silver-Aluminum Filled Silicone
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Extremely low volume resistivity (typically <0.010 Ω·cm).
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Excellent galvanic compatibility with aluminum housings.
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Commonly supplied in Cho-Seal® series such as Cho-Seal 1285 — a widely used silver-aluminum silicone for aerospace and defense electronics.
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Fluorosilicone Conductive Elastomers (for aggressive chemical and fuel exposure)
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Maintain shielding and sealing integrity where hydrocarbon or hydraulic fluids are present.
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Representative compounds: Cho-Seal 1298, Cho-Seal 1287, Cho-Seal 1299.
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Offer similar conductivity with enhanced solvent resistance vs. standard silicone.
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These materials regularly deliver shielding effectiveness >100 dB from 20 MHz up through several GHz, depending on flange finish and compression.
Critical Design Considerations
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Compression Deflection:
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For circular washers and Configuration B gaskets, target 10–30% compression to achieve intimate metal-to-elastomer contact without over-stressing the polymer.
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Flange Preparation:
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Smooth, flat, clean mating surfaces reduce contact resistance and improve repeatability across assemblies.
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Galvanic Compatibility:
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Match filler type to the mating metal to minimize corrosion potential — e.g., silver-aluminum for aluminum housings, nickel-graphite for stainless steel.
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Manufacturing — Precision Conversion at NEDC
Our process ensures dimensional stability and repeatable performance:
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Die Cutting — fast, cost-efficient for production volumes of MIL-standard OD/ID washers.
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Waterjet Cutting — ideal for thick sections or non-standard diameters and for rapid prototypes.
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CNC Knife Cutting — useful for short runs or iterative design builds.
We can also integrate PSA backings for assembly aid or inventory simplification.
Applications
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Waveguide Assemblies: MIL-DTL-83528/013 gaskets maintain high shielding and gas-tight performance at radar, satcom, and microwave interfaces.
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Fastener Bonding: /012 washers ensure every screw and standoff stays conductive while sealing environmental ingress.
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High Reliability Electronics: avionics boxes, telecom RF modules, and ruggedized defense systems where leakage or corrosion cannot be tolerated.
NEDC’s Custom Capabilities
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Stocking a broad range of MIL-qualified Cho-Seal materials for immediate turnaround.
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Support for Configuration A & B profiles, including odd diameters, special flange patterns, and hybrid environmental/EMI sealing requirements.
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Small to medium lot manufacturing with no punitive minimums.
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Tight dimensional tolerances on ID/OD and thickness to maintain compliance and shield performance.