Elastomerics Blog

The aerospace industry uses elastomeric materials for environmental sealing, thermal and electrical insulation, and – in some cases – shielding against electromagnetic interference (EMI). Standard silicone and fluorosilicone both resist compression set and wide range of temperatures; however, there are important differences between these molecularly similar materials.

These differences become evident when an aerospace gasket encounters aggressive aviation fluids, non-polar solvents, or harsh environmental contaminants. Stockwell Elastomerics converts aerospace grade silicones and fluorosilicones into finished parts and can help design engineers with material selection, including compliance with AMS or other specifications.

Chemical Resistance and Aviation Fluid Compatibility

Exposure to aviation fluids can cause seal failure in both airborne platforms and ground support equipment. When immersed in petroleum-based fluids, for example, standard silicone swells significantly. In addition to physical distortion, the effects include softening and a loss of tensile strength. By contrast, fluorosilicone maintains its dimensional stability and physical integrity.

The table below compares the chemical resistance of standard silicone and fluorosilicone.

Important: Fluorosilicone offers broad fluid resistance, but it does not resist all aviation fluids. For example, exposure to polar solvents like Skydrol® can cause material degradation.

Mechanical and Thermal Trade-Offs

Fluorosilicone generally excels in fluid-exposed environments, but standard silicone retains key advantages in terms of thermal and mechanical performance.

• Temperature Range: Standard silicones resist temperatures from -80°F to 500°F (-62°C to 260°C), with specialized high-temperature grades exceeding 500°F. The temperature resistance of fluorosilicone is narrower, typically -85°F to 400°F (-65°C to 204°C).
• Tear and Tensile Strength: Solid fluorosilicone exhibits moderate tear resistance and tensile strength. Solid silicones can provide greater mechanical toughness in high-flex or dynamic sealing applications.
• Hardness: Solid silicones are available in durometers from 10 to 80 Shore A. By contrast, solid fluorosilicones usually range from 40 to 70 Shore A.

Note: Silicone is also available in ultra-soft closed-cell foams. Closed-cell fluorosilicone sponge comes in low-closure-force formulations for use with lightweight enclosures.

Aerospace Specifications and Applications

Aerospace applications may require silicone or fluorosilicone materials that meet industry or military specifications besides the numbered designations within AMS. For example, sensor systems on craft exterior and access doors need materials that resist continuous fuel spray and vapors. Fluorosilicone materials that comply with AMS-R-25988 or MIL-DTL-25988 avoid swelling under these conditions.

Stockwell Elastomerics fabricates these spec-grade fluorosilicones via cutting and molding to  meet A-A-59588, which is limited to solid silicone materials. Applications include door seals, window seals, canopy gaskets, and exhaust hangers. Stockwell Elastomerics also fabricates EMI gaskets from silicones and fluorosilicones that meet MIL-DTL-83528 requirements.

Compare Fluorosilicone vs. Silicone for Aerospace

Stockwell Elastomerics is an experienced gasket fabricator that can help aerospace engineers compare fluorosilicone vs. silicone materials. Because fluorosilicone is significantly more expensive than standard silicone, it’s a conversation worth having. To talk to our Applications Engineering Team, complete our on-line form, email service@stockwell.com, or call (215) 335-3005.