Today’s Tech Tip is on selecting high-temperature materials to meet the unique sealing needs of the aerospace industry. This topic seems especially appropriate given the recent celebration of Earth Day; an event that is synonymous with environmental protection. Sealing is itself a way to protect the environment; especially when you are sealing chemicals or oils as in the case of a turbofan jet engine where the high temperature makes this task more challenging. Turbofans are the most-common type of jet engine since they are used in commercial aircraft, transports and military aircraft; therefore, selecting the right high-temperature material is essentially an automatic concern for aerospace designers, along with reducing total weight for better fuel efficiency.
How does sealing make a difference? Let’s first quickly review aeronautical engine design.
In simple terms, the temperature of the engine and the need for higher-temperature sealing materials increases with each successive section of the engine. At the front is the air intake fan, which runs at about room temperature or up to approximately 122° F (50° C). After the fan comes the compressor, which grows increasingly hotter as the air is compressed and moves closer to the combustion chamber. The next level is the combustion chamber where the temperature is very high; going up to and even beyond 1,832°F (1,000°C). This is followed by the turbine, and the exhaust system where the temperature slowly goes down to 752°F (400°C) and lower at the gases’ emission.
Sealing solutions such as spring-energized seals have the temperature capabilities to handle applications in engine sections within the 392-662°F (200-350°C) range, including the compressor and turbine sections. This range is higher compared to most sealing products in the market.
Can elastomer or metal seals be used?
Elastomer and metal seals are also sealing material options for engine design, yet each of these materials pose challenges. There are specific elastomer compositions for high temperatures however, they:
- are mostly limited to 617°F (325°C)
- have chemical compatibility constraints with HTS (High Thermal Stability according to MIL-PRF-23699F)
- have chemical compatibility constraints with HPC (High Performance Capability according to SAE AS5780) jet engine oils
- suffer thermal aging
Additionally, elastomers are affected by oil coking (carbonization of the oil at high temperatures). Swelling or softening of the material can also occur at high temperatures due to oil or fluid penetration, which can eventually cause leakage.
Metal seals, though they can tolerate very high temperatures, also require more bolts and nuts for proper installation. These fasteners are more difficult to use, are expensive, and also add weight to the system. Aerospace manufacturers continually focus on weight reduction in order to optimize fuel consumption as well as reduce carbon emissions. This principle applies to other systems in the jet engine such as electric harnesses where engineered materials like Meldin® 7001 polyimides contribute to savings due to thinner walls and lighter weight.
Consider another sealing option
OmniSeal® polymer seals provide reliable technology that is tested, validated, and continues to evolve in line with the markets and the specific equipment where it is installed. Linked with reduction of emissions and fuel consumption, a recent trend in turbofan jet engine is to increase the compression ratio in the compressor’s section to make it more efficient. The side effect is that temperatures inside a jet engine increase. The same sealing application on today’s engine may easily need 122°F (50°C) more as compared to 20 years ago. As sealing manufacturers, it is very important to work closely with the engine manufacturers and their engineers to help them solve these new challenges. An example of this collaboration is our Fluoroloy® A90 polymer material which withstands static hot air sealing in temperature up to 662°F (350°C) while retaining the mechanical properties with same or less leakage, surface indentation and material degradation.
OmniSeal® spring-energized seals are also widely used in the space industry where challenges are not only linked with high temperatures but with very low, cryogenic temperatures. Most of the fluids used in space launch vehicles as propellants are stored at cryogenic temperature such as liquid oxygen (-320°F/-196°C) or liquid hydrogen (-425°F/-254°C). The OmniSeal RACO® seal design in particular is 60 years old and has been used from the start of NASA’s space program. Due to the design of the spring that compensates for the physical shrinkage of the fluoropolymer-based jacket, the seal provides exceptional sealing capability at low and cryogenic temperatures while maintaining sealing functionality at the high temperature (392°F/ 200°C) that similar seals see in many applications close to the engine area, after the rocket is ignited. Explore more about cryogenic space seals.
Today’s Tech Tip? Consider your options closely when sourcing high-temperatures seals. We can help you find the right fit!