Freudenberg-NOK Sealing Technologies is currently developing two new materials that reportedly will help aircraft manufacturers save weight and production costs while exceeding fire resistance and fireproof requirements for engine nacelles.

Seals in engine nacelles must withstand fire of more than 1832°F (1000°C) for 15 min per ISO 2685 and AC 20-135. Special, fabric-reinforced materials traditionally have been used in these applications. Freudenberg-NOK is developing a new silicone material that will meet fireproof requirements in traditional fabric-reinforced constructions but offers a 15-20% weight savings over other existing elastomers. The company has also developed a lower-cost alternative material and construction for fire seals.

To conserve fuel, modern engines have been employing increasingly high combustion chamber temperatures that expose seals to higher thermal stresses. For example, the inner side of the engine casing is exposed to temperatures of up to nearly 600°F (315°C) while the air flowing on the outside can be as low as -85°F (-65°C).

“Freudenberg-NOK is continuously engaged in research on materials that offer the required temperature/fire resistance on one hand, and are as light as possible to maximize the payload on the other hand,” said Todd Blair, Business and Development Manager at the Tillsonburg, Ontario, facility where the components are developed and manufactured.

Engineers at the sealing specialist are testing the new silicone material that it expects to replace traditional fire-resistant/proof aviation elastomers.

“A similar material technology was previously developed by Freudenberg-NOK for non-fire applications and is currently in use on commercial aircraft providing customers tremendous weight savings,” Blair said. “We are now taking this technology into fire applications by developing a lower density elastomer that can meet fireproof requirements when properly constructed with fabric reinforcement.”

Adapting the existing material for fire applications is not without its challenges, according to Dr. Paul Hochgesang, Fellow, Technology, Freudenberg-NOK. “Challenges are still being verified. We do not anticipate that adjusting usage from current materials to the new materials will pose significant challenges; however, the materials are still in validation. Each individual application needs to be evaluated as to whether or not the new material is appropriate and applicable for use,” he shared with Aerospace Engineering.

The other material under development is an elastomer that can meet fire resistance and fireproof standards with reduced fabric layers and in some cases no fabric at all.

“The material ‘ceramitizes’ upon exposure to heat and fire,” Hochgesang explained. “Although ‘ceramitizing’ materials have existed in industry for years, we believe applying this material to engine nacelle seals is a new innovation.”

When the surface of the silicone is exposed to direct flame contact, the surface takes on characteristics similar to ceramic material and becomes a fireproof barrier. According to Freudenberg-NOK, this surface barrier slows the progress of elastomer degradation underneath. This material change enables the elastomer to withstand direct contact with fire much longer than traditional elastomers. Since the seal construction can be simplified and the amount of expensive ceramic and aramid fabric layers can be reduced and potentially eliminated, the manufacturing process is simplified and costs reduced, the company claims.

Specialists at Freudenberg-NOK in Tillsonburg work closely with engine manufacturers on material selection and design, since the seal’s geometry affects the airflow within the engine and plays a key part in its ability to meet fire requirements. This is even more critical today, according to the company, as industry authorities convert from propane to Jet A burners for testing fireproof capabilities, which can be “much more challenging.”

Asked if the two new materials could find use in other transportation sectors such as automotive and commercial vehicle, Hochgesang replied: “All transportation industries are concerned with fuel economy, lower fuel consumption, and lightweighting challenges. We see these developments potentially having applications across many industries and areas.”

Freudenberg-NOK anticipates the materials will be available later this year.