The Heat is On

fire seals are used in the fuselage, pylons, thrust reversers and engines. They act as a barrier to prevent airflow from one area of a plane to another during normal operating conditions. This is an important function, but even more crucially, they serve as a precaution in an incident that leads to fire. Then they act to contain the fire to one section of an aircraft and allow the airplane to land safely within a 15 minute period.

The hotter the engines run, the more thrust is obtained from the same amount of fuel, so the more efficient the engine and the lower the fuel consumption. This has led aircraft designers to aim at running engines at continuously higher temperatures with the latest options operating at up to +600 °F, significantly higher than their predecessors.

“Up until now there has been no high temperature fire seal that can operate up to +600 °F and also meet all the customer requirements for a fire seal. There has always been a compromise,” says Quinn Collett, Airframe General Manager.

“Competitive products, such as metal mesh seals, do not meet all the requirements of a fire seal. Claims have been made by other suppliers that they have achieved a silicone fire seal that can operate at high temperatures. However, when put to the test in typical dynamic requirements at elevated temperature, we have found them to fail.”

Seal Characteristics

•  Prevents airflow and flame penetration from one area of the aircraft to another
• Fully operational with minimum compression set over a seal compression range of 15% to 40%
• Proven to operate at a temperature range from -40 °C/ -40°F up to +315 °C/ +600 °F
• Meets all customers’ fire seal requirements
• Engineered to have a life time of 60,000 flight cycles (take off, flight and landing) dependent on application
• Eliminates need for thermal protection of sealing elements
• Customizable to geometry and specification requirements
• Drop-in replacement of existing seals

Seal Benefits

• Due to its compression set performance, the Ultra High Temp seals retain positive contact with the surrounding hardware over a seal compression range of 15% to 40%
• Performs to all customer requirements without compromise
• Overall weight savings and part count reduction due to elimination of additional thermal protection
• Lower total cost of ownership due to extended life and reduced part count

As a leading supplier of seals to the global aerospace industry, Trelleborg Sealing Solutions has been supplying fire seals for decades. Our fire seal range is well-established in the market and the Ultra High Temp seal is the next generation. The Ultra High Temp seal demonstrates all of the sealing capabilities of traditional fire seals and performs at the higher temperatures experienced in the latest aircraft designs.

“The seal is completely unique. It’s patent-pending design overcomes the inherent silicone characteristic of relaxation and compression set at elevated temperatures; a major cause of failure in a fire seal’s ability to perform against all requirements,” Quinn continues.

“To manufacture the product we developed a proprietary methodology to integrate all components and make complex geometries. To increase its usability, the Ultra High Temp seal can be a drop in replacement for seals that currently fail at elevated temperatures or for customers seeking extended life.”

The Ultra High Temp seal meets the requirements of US Federal Aviation standard AC20-135 Powerplant Installation and Propulsion System Component Fire Protection Test Methods and Standards and Criteria, as well as ISO 2685:1998 Aircraft – Environmental Test Procedure for Airborne Equipment – Resistance to Fire in Designated Fire Zones.

“Meeting these standards is a necessity for this type of fire seal, but they can be extremely difficult to achieve,” says Quinn. “In addition, a full test program was undertaken to prove the product’s capabilities at different compressions. In heat soak tests, the Ultra High Temp seal performed better than other fire seals and in all cases it was below a 15% permanent set target. 

“And we are not stopping there. As temperatures potentially increase even further and designs change, there are options to modify materials and layup for even better performance,” concludes Quinn.