3 Ways Polymers Have Revolutionized Aerospace Seals

Aviation continues to push the boundaries of innovation. From zero-emission aircraft and advanced materials to digital software changes, industry pioneers are always seeking ways to reduce fuel costs, lower emissions, and reduce weight.

Polymers and thermoplastics such as polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE) play a significant role in solving critical engineering problems. Their advantages make them ideal for many aerospace parts and compounds, including seals that must operate in extreme temperatures and pressures while enduring constant degradation from fuels and other chemicals.

High-Performance Seals and the Aerospace Industry

When lives are on the line, every component on an aircraft must be carefully considered. Seals are among the most important components. Not only do they prevent fluid leakage, but they keep air, dirt, and debris out of systems. Any contamination can lead to internal leakage and lowered efficiency.

If seals fail, the entire plane’s performance can be jeopardized. That’s why quality and reliability can’t be compromised. Seals are heavily used across the aerospace industry in countless applications and system-critical areas, including:

• Braking systems
• Flaperons
• Landing gear system
• Fuel systems
• Hydraulic systems
• Pneumatic systems
• Cargo bay doors and lifts
• Actuators (e.g., electro-hydraulic, electro-mechanical, ball screw)
• Thrust reversers
• Ailerons
• Rudders
• Elevators

Seals help thwart the spread of fire or flames in the aircraft engine, avoid water or dust intrusion, and prevent corrosion or any fluid leakage. For a seal to perform optimally, its material must possess physical and chemical properties that are compatible for the given application conditions.

Some commonly used aerospace polymer seals include:

• Slipper seal, which is a separate circumferential band typically made of polytetrafluoroethylene (PTFE) filled to the inside (ID), outside (OD) the face of an elastomer O-ring or other shape of a molded elastomeric sealing element which also acts as an energizer.

• Spring-energized seals are normally comprised of a machined polymer material body (or jacket), containing a spring energizer.
• T-seal, which consist of a T-shaped elastomer sealing component supported by thermoplastic backup rings on both side of the elastomer. T-seals were originally developed to preserve the advantages of O-rings in dynamic fluid power applications while ending two of their most serious reliability problems. (1) extrusion through the gap between static and dynamic surfaces and (2) instability in their grooves which led to spiral or twisting failure. The T-seal eliminates both these problems while retaining the space saving attributes of the compact O-ring groove.
• Plate seals, which bond elastomer to metal to separate and isolate sections of fluid assemblies.

3 Benefits of Polymer-Based Aerospace Seals

1. Low Friction

One of PTFE's most outstanding characteristics is extremely low friction. It is self-lubricating and can be used in dry-running applications without a problem. PTFE also does not exhibit problematic stick-slip behavior. These features also reduce power and torque requirements while increasing overall efficiency.

2. Harsh Environment

Aerospace applications often involve extreme temperatures, and PTFE is made for extreme temperatures. It can handle a wide range of temperatures, with a maximum continuous operating temperature of 550°F down to cryogenic temperatures like -450°F. In addition, it remains extremely stable even at high temperatures while retaining flexibility at low temperatures.

Aerospace seals typically operate under extreme pressures, ranging from 20,000 PSI to vacuum pressures. PTFE is also known for its excellent compressive strength. And fillers can be added to PTFE specifically for high-pressure applications.

3. Chemical Inertness 

PTFE is one of the most chemically compatible polymers on the market today. It will not contaminate any sensitive media it comes into contact with and is non-soluble. This makes it ideal for the aggressive chemicals encountered in aerospace applications, including jet fuels, de-icers, cleaning agents, and hydraulic fluids. Its primary weakness is alkali metals.

Polymers Play an Important Role in Aerospace Sealing

Any sealing device used in aviation must handle critical demands. Polymers provide long-lasting seals that enable creating different geometries and sealing profiles for extended life. Expertise in materials science is key to ensuring strong sealing across the broad pressures, temperatures, and media found in the aerospace industry.