Seal with Integrated Shroud to Protect from Exposure to Extreme Environments

For extremely high-temperature sealing applications, Glenn researchers have devised novel methods for fabricating single-crystal preloaders. NASA's high-temperature preloaders consist of investment cast or machined parts that are fabricated in various configurations from single crystal superalloys. Machined preloaders include a variety of spring configurations, compressed axially or radially, fabricated from single crystal slabs. Before machining, the slabs are carefully oriented in a special goniometer using x-diffraction techniques. This helps to maintain proper crystal orientation relative to the machined part and the applied loads. For more complex geometry components which cannot be easily and economically machined, an investment casting approach would be used. Complex preloader geometries include wire coil springs of various configurations. These single crystal preloaders would be designed with the appropriate stiffness for the intended thermal barrier/seal application and placed underneath, or integrated within, the seal/barrier. At extrememly high temperature, the preload device keeps the seal/barrier mated against the opposing surface as the gap between the two surfaces changes, maintaining contact between surfaces and preventing convective heat transfer.

NASA designed an inflatable habitat intended for space whose exterior incorporates an expandable layer known as the bladder – the main pressure shell of a module to which astronauts may reside while off-world. The bladder is made from a polymer material and is surrounded by protective layers to ensure it is not damaged and does not leak. On every module, there are two areas where the bladder and other flexible layers interface with the ends of a cylindrical core, at the bulkheads. Seals between the non-metallic bladder and the metallic bulkhead are critical in maintaining a safe pressurized environment for astronauts to live and work. With both bulkhead plates assembled, RTV silicone is deposited in specially designed channels which are sandwiched between the plates. After the channels are filled, a cure-in-place seal is formed between the bladder and the bulkhead. The RTV sealing method worked successfully during prototype testing as confirmed by a helium leak test and post-test visual inspection of the seals. In prototype testing, this method created a consistent and reliable seal between the bladder and bulkhead assembly replicated from the inflatable module design. The RTV sealing method may benefit terrestrial applications that may demand cure-in-place internal seals. The method could also innovate manufacturing processes for components by enhancing the speed of assembly while increasing seal integrity.

This NASA innovation applies the concepts of electrodynamic dust shielding (EDS) to develop seals (e.g., O-rings) with active self-cleaning capabilities. NASA’s self-cleaning seals are manufactured in the following manner: A seal with a conductive surface (or otherwise fabricated to be conductive) is generated and an electrical connection, lead or electrode is attached. Next, a dielectric material is coated or placed over the conductive surface of the seal. (NOTE: Using conductive elastomer materials eliminates the need for a conductive cover layer) A high voltage (nominally >1kV) power supply is connected to the conductive layer on the seal and grounded to the metallic groove or gland that houses the seal. Given the design, dust accumulates on the outer dielectric layer (a high-voltage insulator) of the seal. To clean the seal, a time varying alternating voltage is applied from the power supply, through the high voltage lead and onto the conductive layer of the seal. When this voltage is applied, the resulting electric field produces Coulomb and dielectrophoretic forces that cause the dust to be repelled from the sealing surface. In practice, NASA’s self-cleaning seals could be operated in continuous cleaning mode (actively repelling dust at all times, preventing it from ever contacting the seal surface) or in a periodic cleaning cycle mode (removing dust from the seal surface at regular intervals). NASA’s self-cleaning seals have been prototyped and demonstrated to be highly effective at dust removal. The invention could serve as the basis of an active, self-cleaning seal product line marketed for in-space and/or terrestrial applications. Additionally, companies developing space assets destined for operation on dusty planetary surfaces (e.g., the Moon) may be interested in leveraging the technology to protect seals from dust/regolith accumulation, ensuring continuous low leakage operations.

There are multiple space-related systems that can benefit from high performance, thin film, self-healing/sealing systems. Space vehicles and related ground support equipment can contain miles of wire, much of which is buried inside structures making it very difficult to access for inspection and repair. Space-based inflatable structures, solar panels, and astronauts performing extra-vehicular activities are subject to being struck by micrometeoroids and orbital debris. Self-healing or sealing layers on inflatables, solar panels and spacesuits would increase the safety and survivability of astronauts as well as the survivability and functionality of inflatables and solar panels. Self-healing insulation on wiring would greatly improve the reliability and safety of systems containing such wiring and reduce inspection and repair time over the lifetime of those systems. This technology combines the use of a self-sealing low melt, high performance polyimide film that exhibits the ability, when cut, for separated edges to slowly flow back together and seal itself, with the options of a laminate system and the inclusion of healant microcapsules that, when broken, release healant which can then additionally assist in the healing process. Combinations of the healing approaches can be enabling to the healing process proceeding at a much greater rate and dual mode healing approach can also allow for healing of a larger area.

Prior approaches to bonding a SiC sensor and a SiC cover member relied on either electrostatic bonding or direct bonding using glass frits. The problem with the former is that its relatively weak bond strength may lead to debonding during thermal cycling, while the latter requires the creation of apertures that can allow sealant to leak. Glenn's innovation uses NASA's microelectromechanical system direct chip attach (MEMS-DCA) technology that can be bulk-manufactured to reduce sensor costs. The MEMS-DCA process allows a direct connection to be made between chip and pins, thereby eliminating wire bonding. Sensors and electronics are attached in a single-stage process to a multifunctional package, which, unlike previous systems, can be directly inserted into the housing. Additional thick pins within the electrical outlet allow the package to be connected to external circuitry. Furthermore, because the top and bottom substrates' thermomechanical properties are similar to that of the sensors, the problem of mismatch in the coefficient of thermal expansion is significantly reduced, minimizing thermal cycling and component fatigue. By protecting sensors and electronics in temperatures up to 600°C, approximately twice what has previously been achievable, Glenn's innovation enables SiC components to realize one of their most exciting possibilities - direct placement within high-temperature environments.