Aerospace Fluorosilicones

Aerospace Fluorosilicones

Aerospace Fluorosilicones


The “Gold Standard” for Jet Fuel

Because of their good hydrocarbon compatibility and unmatched low temperature performance, fluorosilicone O-ring materials have become the standard seal materials for use in most jet fuel applications and many low temperature hydrocarbon hydraulic applications. To meet the needs of multiple applications, Parker has three different hardnesses of fluorosilicone O-ring materials.

Extreme Low Temperature Performance

Fluorosilicones have long been used for their outstanding low temperature properties. With a functional temperature range of -100°F to +350°F (-73°C to +177°C), fluorosilicone rubber has the thermal stability to accommodate nearly all aerospace applications. This thermal stability comes from the silicone backbone that forms the base polymer chain.

Outstanding Fuel and Oil Resistance

Fluorosilicone rubber also has fluorinated side chains branching off of the silicone backbone that give it chemical compatibility that approaches that of fluorocarbon rubber; resistance to petroleum-based oils, greases, and fuels is excellent. Fluorosilicones have become the seal material of choice for handling jet fuel on commercial, military, and general aviation aircraft of all types. Testing in ASTM Fuel B (also called TT-S-735 Type III) shows good compatibility with aggressive hydrocarbon fuels. In addition, fluorosilicone O-rings have found a niche in sealing fire-resistant synthetic hydrocarbon hydraulic fluids in static applications, expecially those used at low temperatures.

Good Rebound Resilience

Historically, fluorosilicones have not offered good short-term rebound resilience. When stretched to fit into a male O-ring gland, fluorosilicone materials tended to sag rather than snap back tight against the groove. These new fluorosilicone compounds exhibit dramatic improvements in this category. While there are no industry standard test procedures for this type of test, it can be easily observed. This improvement in rebound resilience should make automated assembly more feasible and decrease the incidence of torn O-rings during installation.

Other Properties

Fluorosilicones generally have poor mechanical properties. As a result, they wear quickly in dynamic applications and are easy to tear during installation. Fluorosilicones also have poor gas permeation resistance. In vacuum and pressurized gas applications, fluorosilicone O-rings will allow some gas to permeate through the seal over long periods of time.

Applications

  • Low temperature hydrocarbon-based hydraulic fluids

  • Aviation fuels down to -100°F (-73°C)

Available Hardness

  • LM159-70
    • -100°F to +350°F
      (-73°C to +177°C)
    • Standard fluorosilicone O-ring material

  • LM158-60
    • -100°F to +350°F
      (-73°C to +177°C)
    • Softer fluorosilicone O-ring material

  • LM160-80
    • -90°F to +350°F
      (-68°C to +177°C)
    • Harder fluorosilicone O-ring material
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