by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Finding the right sealing solution for aerospace applications involves a host of considerations, especially when it comes to the jacket material. However, there is one high-performance solution that rises to the top over and over: PTFE aerospace seals. 

Aerospace Seal Challenges

Aerospace sealing solutions can face a wide range of harsh environments that can include exposure to extreme temperatures, high pressures, and corrosive chemicals such as de-icing liquids and aviation fuels. There is also the ever-present demand for energy-efficient solutions,  critical requirements related to safety, and compliance with industry standards. 

In addition, aerospace seals must often perform in potentially explosive or flammable environments. There are other constraints in aerospace applications as well, such as the need to minimize weight and promote energy efficiency. And looking to the future, there will also be demand for more environmentally friendly, sustainable solutions.

Why PTFE Works Well for Aerospace Applications

Here are some of the reasons why PTFE is a common choice for aerospace sealing applications:

  • Reliable extreme-temperature performance
  • Inherently non-flammable
  • Extremely low friction
  • Self-lubricating
  • Excellent chemical resistance
  • Wide variety of fillers available

Reliable Extreme Temperature Performance

One of PTFE’s most outstanding qualities for aerospace applications is its performance even when exposed to temperatures ranging from cryogenic at -328 F to 500 F. PTFE is able to retain the material properties that effective seals depend on even when exposed to these temperatures as well as extreme temperature changes and differentials.

Inherently Non-Flammable

Because PTFE has a very high oxygen index, it is inherently non-flammable. PTFE also exhibits limited flame spread (NFPA 262-1990) and low smoke generation (UL-910).

Extremely Low Friction

PTFE’s extremely low friction (the lowest of any material currently on the market) also leads to very low breakout friction, very low torque generation, and no stick-slip behavior. Low friction also means very little heat is generated by the seal in dynamic applications which in turn leads to reduced energy losses and contributes to overall system efficiency.

Self-Lubricating

In addition, PTFE is naturally self-lubricating, which eliminates the need for lubrication. This can be especially important for certain cryogenic applications where there is a danger of lubricants freezing and seizing or at high temperatures where lubricants might not be able to perform well.

Excellent Chemical Resistance

PTFE is the most chemically inert polymer and can perform in the presence of an extremely wide range of corrosive media, even at high temperatures. PTFE is weak to certain chemicals, however. The list includes fluorine gas, extremely potent oxidizers, and liquid or dissolved alkali metals.

Wide Variety of Fillers Available

Among the additives and fillers available for PTFE are …

  • Glass to enhance dimensional stability
  • Carbon to increase stiffness and compressive strength
  • Graphite to increase compressive strength and enhance dimensional stability
  • Bronze to enhance compressive strength, stiffness, and dimensional stability 
  • Molybdenum disulfide combined with other fillers to improve tribological properties
  • Polyimide to enhance abrasion resistance

Types of PTFE Seals Used in Aerospace

PTFE seals are used in numerous aerospace applications including turbo engines, auxiliary power units (APU), engine bearing damper rings, valves gearboxes, environmental control units (ECU), flight actuators, and bearing compartments. 

PTFE Rotary Shaft Seals

When combined with a PTFE seal jacket, rotary shaft seals maintain excellent performance at high PV (pressure and velocities) than their non-PTFE counterparts. PTFE rotary shaft seals are able to successfully bridge the gap between elastomeric sealing solutions and mechanical face seals. These rotary shaft seals are available in hydrodynamic, plain, and multi-lip configurations and  

PTFE Spring-Energized Seals

Spring-energized seals include a spring energizer to ensure reliable contact between the seal lip and the sealing surface. The energizer enables the seal to maintain contact despite temperatures and pressure fluctuation and is also able to compensate for eccentricity, out of roundness, hardware misalignment, and seal jacket wear. PTFE spring-energized seals are an excellent option for aerospace applications and are already used extensively with rockets.

PTFE Labyrinth Seals

Labyrinth seals are non-contact mechanical seals designed with a cross-section resembling a maze that effectively creates areas of turbulence to prevent leaks and ingression of contaminants while reducing the clearance that is available for particles to enter. PTFE labyrinth seals contribute to overall system efficiency, exhibit excellent gall resistance, and are easy to install. These seals are often found in aircraft engines where their job is to reduce air leakage.

Conclusion

If you are looking for a highly effective sealing solution that can handle the often extreme operating environments of aerospace, Advanced EMC experts can help you find the ideal type of seal and optimum material to meet your design requirements.

To take advantage of our extensive knowledge of seals and experience in dealing with the various national and international aerospace standards, contact us today.

 

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