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Microscopic pores in thin-walled aluminum castings are sealed by impregnation pretreatment. Technique was developed for investment castings used in hermetically sealed chassic for electronic circuitry. Excessively high leakage rates were previously measured in some chassis.
The feasibility of silicon carbide composite structures was evaluated for 1644 K gas turbine seal applications. The silicon carbide composites evaluated consisted of Si/SiC Silcomp (Trademark) - and sintered silicon carbide as substrates, both with attached surface layers containing BN as an additive. A total of twenty-eight candidates with variations in substrate type and density, and layer chemistry, density, microstructure, and thickness were evaluated for abradability, cold particle erosion resistance, static oxidation resistance, ballistic impact resistance, and fabricability. The BN-free layers with variations in density and pore size were later added for evaluation. The most promising candidates were evaluated for Mach 1.0 gas oxidation/erosion resistance from 1477 K to 1644 K. The as-fabricated rub layers did not perform satisfactorily in the gas oxidation/erosion tests. However, preoxidation was found to be beneficial in improving the hot gas erosion resistance. Overall, the laboratory and rig test evaluations show that material properties are suitable for 1477 K gas turbine seal applications.
Flow induced aerodynamic spring coefficients of labyrinth seals are discussed and the restoring force in the deflection plane of the rotor and the lateral force acting perpendicularly to it are also considered. The effects of operational conditions on the spring characteristics of these components are examined, such as differential pressure, speed, inlet flow conditions, and the geometry of the labyrinth seals. Estimation formulas for the lateral forces due to shaft rotation and inlet swirl, which are developed through experiments, are presented. The utilization of the investigations is explained and results of stability calculations, especially for high pressure centrifugal compressors, are added. Suggestions are made concerning the avoidance of exciting forces in labyrinths.
The leak rates through shaft seals with large pressure drops were simulated using gaseous hydrogen, or nitrogen flowing through an annulus with a nonrotating centerbody. The flows were choked. For concentric or eccentric position of the rotor and parallel or convergent tapered flow passages, data and analysis revealed that mass flux or leak rate can be determined from a relation whose normalizing parameters depend on the thermodynamic critical constants of the working fluid and an average flow area expressed in terms of the inlet and exit cross-sectional areas. Using these normalized relations, the flow data for parallel and three convergent, tapered, shaft-seal configurations are in good agreement. Generalization to any simple gas or gas mixtures is implied and demonstrated in part.
Analytical studies of phase change effects in parallel and tapered liquid face seals are presented. An isothermal and adiabatic model of low Reynolds number flow are considered by numerical integration of the descriptive equations for a real fluid, and its thermodynamic properties are calculated for each step, using a computer program for the steam tables or fluid thermodynamic properties. It was shown that for low leakage rate the isothermal model is more accurate and for high leakage rates the adiabatic model is more accurate; that both models yield the same conclusions regarding stability; and that the transient of collapse is described by the adiabatic model which predicts a catastrophic collapse and then either failure or explosive return to a larger film thickness value. Finally, it is shown that converging seals may become unstable and the mass leakage rate is reduced significantly below the all liquid value when boiling occurs.
The effect of coning on radial forces in face seals having angular misalignment is analyzed. Both the hydrostatic and hydrodynamic components of the resultant radial force are presented. It is shown that the displacement of the primary seal ring due to the action of radial forces is always in a direction which may cause inward pumping. However, in most cases the radial force is very small.
Sliding-gate valve originally developed for rocket exhaust-gas ducts is sealed by a Belleville spring. It is simple, compact, and operates over a wider range of temperatures than conventional O-ring sealed valves.
Spring clips seal housings for electronic circuitry, preventing electromagnetic interference from entering or leaving housings. Clips also keep dust out of housing. Since no bolts are used, housing can be opened quickly; unlike bolts, clips can be used on thin-walled housing. Seal was developed for an X-band array amplifier.
A pendulum-type test device has been built for use in studying rubs between a turbine or compressor blade tip or labyrinth seal knife edge and specimens of abradable gas path seal materials. The device allows measurement of the rub energy dissipated in a single wear event, along with friction and normal forces and wear. Subsequent rubs over the same surface can also be monitored, with microscopic observation of the rub surface being possible after any of the passes. The device was used in tests of several potential abradable materials, ranging from porous to fully dense. It was shown that the rub energy dissipated in initial and subsequent passes is a fundamental parameter in the evaluation of material abradability. Rub energy was found to be influenced by such factors as: density and tensile (or yield) strength of the abradable material, prior densification or work hardening of the rub surface, and the sharpness of the leading edge of the blade tip.
A thermal analysis was made of a blade-seal configuration to determine the effects of thermal contact resistance, blade speed, and thermal properties upon the interfacial temperature. The analysis disclosed that while the thermal properties of the blade or the seal specimen strongly affect the temperatures in their respective parts, the factors which control the overall temperature field are the contact resistance and the heat generated at the interface.
New technique rapidly evacuates and seals fused-quartz ampoule with precise clearance over contents without appreciably thinning ampoule walls. Quartz plug is lowered into working section of ampoule after ampoule has been evacuated. Plug is then fused to ampoule walls, forming vacuum seal. New technique maintains wall strength and pumping speed.
Proposed tubular gasket for doors performs dual function: seals in pressure, and seals out heat. Composed of quartz fabric filled with alumina matting, gasket is bonded with room-temperature-vulcanizing material to periphery of door. When door is closed, gasket is compressed like O-ring: fills gap between door and frame; and prevents leakage of air and heat.
Proposed valve employs ferrofluid to make tight seal. Seal requires no precisely machined parts, and hand lapping of valve seats are unnecessary. Magnetic fluid fills gap between shaft and annular pole piece in chamber wall. Precise shaft fit is not necessary.
Proposed design for hybrid high-voltage power-circuit package uses molded plastic for hermetic sealing instead of glass-to-metal seal. New package used to house high-voltage regulators and solid-state switches for applications in aircraft, electric automobiles, industrial equipment, satellites, solarcell arrays, and other equipment in extreme environments.
The abradability and durability characteristics of the plasma sprayed system were improved by refinement and optimization of the plasma spray process and the metal substrate design. The acceptability of the final seal system for engine testing was demonstrated by an extensive rig test program which included thermal shock tolerance, thermal gradient, thermal cycle, erosion, and abradability tests. An interim seal system design was also subjected to 2500 endurance test cycles in a JT9D-7 engine.
An hermetic seal for a linear rod having a portion thereof projected axially through a port defined in a wall for a pressure chamber and supported thereby for omni-directional motion is described. The seal is characterized by a resilient, impervious, cylindrical body having a first section concentrically related to the shaft and integrally affixed thereto comprising a linear ordered array of annular flutes. A second section integrally is affixed to the wall of the chamber and concentrically related to the port comprising a second linear ordered array of annular flutes. A third section is interposed between the first and second sections and integrally affixed in coaxial alignment therewith comprising an annular ordered array of linear flutes concentrically related to the shaft, whereby axial, angular, and pivotal motion of the rod is accommodated.
A seal with a high temperature abradable lining material which encircles the tips of turbine blades in turbomachinery was designed. The seal is directed to maintaining the minimum operating clearances between the blade tips and the lining of a high pressure turbine. A low temperature easily decomposable material in powder form is blended with a high temperature oxidation resistant metal powder. The two materials are simultaneously deposited on a substrate formed by the turbine casing. Alternately, the polymer powder may be added to the metal powder during plasma spraying. A ceramic layer is then deposited directly onto the metal-polymer composite. The polymer additive mixed with the metal is then completely volatilized to provide a porous layer between the ceramic layer and the substrate. Thermal stresses are reduced by the porous structure which gives a cushion effect. No brazing is required by using only plasma spraying for depositing both the powders of the metal and polymer material as well as the ceramic powder.
Some experimental and analytical studies of plasma sprayed ZrO2-Y2O3 thick seal thermoprotective materials over NiCrAlY bond coats with testing to 1040 deg C in a Mach 0.3 burner flame are reviewed. These results indicate the need for material to have both compliance and sufficient strength to function successfully as a thick thermoprotective seal material. Fibrous materials may satisfy many of these requirements. A preliminary analysis simulating the simplified behavior of a 25 mm cylindrical SiO2-fiber material indicated significant radial temperature gradients, a relatively cool interface and generally acceptable stresses over the initial portion of the thermal cycle. Subsequent testing of these fiberlike materials in a Mach 0.3 Jet A/air burner flame confirmed these results.