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Low leakage and low instability labyrinth seal
Patents
Patents This is a list of recently published patents covering designs and inventions of relevance to Sealing Technology readers. Countries can be identified by the code in front of the number: US United States AT Austria AU Australia BE Belgium BR Brazil CA Canada CH Switzerland D Germany EP European Patent FR France ES Spain HU Hungary FI Finland GB Britain IR Eire IL Israel JP Japan IT Italy LI Liechtenstein KP North Korea NL Netherlands LU Luxembourg RO Romania SU Former Soviet NO Norway Union WO World Patent SE Sweden Full copies of the original patent documents can be obtained from the following: The British Library Patent Express, 25 Southampton Buildings London WC2A lAW, UK Fax: +44 171412 7930 The British Library will also supply a list of libraries included in the Patent Information Network.) US Patent Office Scientific Library 15th and East Streets, NW Washington, DC 20231, USA The Japanese Patent Office 43 Kaksumigaseki 3-chome Chiyoda-ku, Tokyo 100, Japan
Low leakage and low instability labyrinth seal Patent number: WO 9501524 PubIication date: 12 Jan 1995 Inventor: D Rhode AppIicant: Twentieth Technology This patent describes improved designs for high performance labyrinth seals, where the geometry of the sealing surfaces is optimized to enhance flow deflection and produce maximum turbulent action. Optimum seal performance is accomplished by selecting sealing surfaces and seal geometry to establish minimum clearance between selected portions of the seal and maximum flow turbulence between other selected portions of the seal. A labyrinth seal is generally described by a series of cavities or grooves formed along the adjacent surfaces of two relatively rotatable components - such as a rotor on a rotating shaft and a stator on an adjacent, fixed housing. These components create a partial barrier between areas of high and low fluid pressure. At successive stations along the length of the labyrinth seal, adjacent surfaces of the rotatable parts are situated in close proximity to each other to give annular, slit-like orifices. In many labyrinth seal designs, a series of cavities or chambers are formed at these stations in order to retard fluid flow through the seal to a desired level. One of the basic concepts of any labyrinth seal design is to create a
Figure 1. Isometric drawing showing the flexible knives or spring teeth of the invention. velocity fluid jet exiting an orifice and relatively slow moving fluid in a large cavity immediately downstream. As a result of the combination of these and other friction components, pressure energy is substantially reduced. The substantially reduced pressure in a given cavity results in smaller pressure changes across additional downstream orifices. The net result is overall reduced leakage across the labyrinth seal. Previous systems have employed sharp turns in the fluid flow path to
highly frictional fluid flow path. Such a flow path will convert pressure energy into velocity energy. A large portion of the velocity energy will be dissipated as heat energy via turbulent action. One source of turbulence is created as a result of wall shear friction between high velocity fluids and irregularly spaced adjacent surfaces of the seal. A second and often more important source of turbulence results from intense free shear layer friction between a high
Sealing Technology No. 23
Figure 2. Radial section showing the knives or teeth between a stator and a rotor.
9
Patents provide additional friction or resistance to flow. The through-flow liquid is forced to “zig-zag” through the seal increasing the wall shear friction. This has resulted in labyrinth seal systems having intricate and complex sealing surfaces. As a result many contemporary labyrinth seals are expensive to produce due to the intricate machining required. Such complex sealing surfaces and tight tolerances can also be somewhat fragile and prone to failure in rigorous applications or harsh operating environments. This invention provides designs and methods for optimizing the performance of labyrinth seals which substantially eliminate the disadvantages and problems associated with previous systems. The design dissipates fluid energy and restricts fluid flow by a combination of convex surfaces, fluid cavities, annular flow reversal grooves, and rough surface finishes on selected portions of the fluid cavities and flexible knives or spring teeth as appropriate (Figures 1 & 2). The optimum seal is created by employing specific geometric relationships derived from computer modelling and experimental test rigs. Seal surfaces and components result which may be easily machined and are resistant to damage from shaft vibrations causing rubbing between rotating and stationary parts. In one version, a radially stepped labyrinth seal is formed
between a rotor and a stator. The seal itself involves a rotary shaft having a rotor with several axially spaced angularly stepped portions with high pressure sides and low pressure sides and a stationary housing with a stator surrounding the shaft and corresponding second annular stepped portions on the inside. The combination of the rotor and stator creates a restricted fluid flow path between. Generally the height of a projection is dependent on the minimum clearance between edges of the projection and the adjacent portion of the convex surface. Another version of the invention provides semi-elliptical annular grooves in various surfaces associated with the stator and/or the rotor, oriented against the fluid flow. They may be formed in radial projections from the stator or rotor and fluid cavity surfaces. Advantages of the invention include the provision of flexible knives or spring teeth to establish a fluid barrier in selected areas (Figure 3). The spring teeth may include end fittings which further restrict fluid flow. The spring teeth and their end fittings should be designed to wear only slightly during the first few hours of operation, allowing the minimum required clearance between rotating and stationary components. Another advantage is the provision of spoilers or boundary layer breakers on radial projections and other selected surfaces of the fluid cavities to increase turbulent
r
Figure 3. The flexible knives or spring teeth estabIish a fluid barrier in selected areas.
10
intensity within the seal. Machine finishes or rough surfaces will also enhance the turbulent flow effect. An effective seal is provided even in the case of radial displacement between rotor and stator due to vibration, stresses from unbalanced fluid pressures, large temperature differentials or misalignment. The small clearances between rotor and stator surfaces also help to reduce the tendency for shaft vibration.
Intermediate coating layer for high temperature rubbing seals in rotary regenerators Patent number: US5397649 Publication date: March 14, 1995 Inventors: J. Schienle, T. Strangman Applicant: AUied Signal Inc. This invention concerns protective coatings for metal substrates, and in particular to a regenerator seal multi layer coating having a ceramic surface layer, a yttria stabilized zirconia intermediate layer, and metallic bonding layer. Because rotary regenerators for gas turbine engines are now being made of a ceramic material, they require seals formed from material that can provide sufficient coating wear life. To achieve this life, this material must be oxidation resistant at temperatures up to and exceeding 1600”F, and have a low coefficient of friction to minimize torque loads on the regenerator. A previous patent has described a regenerator seal comprised of a surface layer of nickel oxide, calcium fluoride, and calcium oxide on a steel substrate. A problem with this is the reactive nature of its constituents, especially at temperatures greater than 1600°F. Both nickel oxide and calcium fluoride tend to react with underlying metallic elements. These reactions accelerate the oxidation of
Sealing
Technology
No. 23
Patents This is a list of recently published patents covering designs and inventions of relevance to Sealing Technology readers. Countries can be identified by the code in front of the number: US United States AT Austria AU Australia BE Belgium BR Brazil CA Canada CH Switzerland D Germany EP European Patent FR France ES Spain HU Hungary FI Finland GB Britain IR Eire IL Israel JP Japan IT Italy LI Liechtenstein KP North Korea NL Netherlands LU Luxembourg RO Romania SU Former Soviet NO Norway Union WO World Patent SE Sweden Full copies of the original patent documents can be obtained from the following: The British Library Patent Express, 25 Southampton Buildings London WC2A lAW, UK Fax: +44 171412 7930 The British Library will also supply a list of libraries included in the Patent Information Network.) US Patent Office Scientific Library 15th and East Streets, NW Washington, DC 20231, USA The Japanese Patent Office 43 Kaksumigaseki 3-chome Chiyoda-ku, Tokyo 100, Japan
Low leakage and low instability labyrinth seal Patent number: WO 9501524 PubIication date: 12 Jan 1995 Inventor: D Rhode AppIicant: Twentieth Technology This patent describes improved designs for high performance labyrinth seals, where the geometry of the sealing surfaces is optimized to enhance flow deflection and produce maximum turbulent action. Optimum seal performance is accomplished by selecting sealing surfaces and seal geometry to establish minimum clearance between selected portions of the seal and maximum flow turbulence between other selected portions of the seal. A labyrinth seal is generally described by a series of cavities or grooves formed along the adjacent surfaces of two relatively rotatable components - such as a rotor on a rotating shaft and a stator on an adjacent, fixed housing. These components create a partial barrier between areas of high and low fluid pressure. At successive stations along the length of the labyrinth seal, adjacent surfaces of the rotatable parts are situated in close proximity to each other to give annular, slit-like orifices. In many labyrinth seal designs, a series of cavities or chambers are formed at these stations in order to retard fluid flow through the seal to a desired level. One of the basic concepts of any labyrinth seal design is to create a
Figure 1. Isometric drawing showing the flexible knives or spring teeth of the invention. velocity fluid jet exiting an orifice and relatively slow moving fluid in a large cavity immediately downstream. As a result of the combination of these and other friction components, pressure energy is substantially reduced. The substantially reduced pressure in a given cavity results in smaller pressure changes across additional downstream orifices. The net result is overall reduced leakage across the labyrinth seal. Previous systems have employed sharp turns in the fluid flow path to
highly frictional fluid flow path. Such a flow path will convert pressure energy into velocity energy. A large portion of the velocity energy will be dissipated as heat energy via turbulent action. One source of turbulence is created as a result of wall shear friction between high velocity fluids and irregularly spaced adjacent surfaces of the seal. A second and often more important source of turbulence results from intense free shear layer friction between a high
Sealing Technology No. 23
Figure 2. Radial section showing the knives or teeth between a stator and a rotor.
9
Patents provide additional friction or resistance to flow. The through-flow liquid is forced to “zig-zag” through the seal increasing the wall shear friction. This has resulted in labyrinth seal systems having intricate and complex sealing surfaces. As a result many contemporary labyrinth seals are expensive to produce due to the intricate machining required. Such complex sealing surfaces and tight tolerances can also be somewhat fragile and prone to failure in rigorous applications or harsh operating environments. This invention provides designs and methods for optimizing the performance of labyrinth seals which substantially eliminate the disadvantages and problems associated with previous systems. The design dissipates fluid energy and restricts fluid flow by a combination of convex surfaces, fluid cavities, annular flow reversal grooves, and rough surface finishes on selected portions of the fluid cavities and flexible knives or spring teeth as appropriate (Figures 1 & 2). The optimum seal is created by employing specific geometric relationships derived from computer modelling and experimental test rigs. Seal surfaces and components result which may be easily machined and are resistant to damage from shaft vibrations causing rubbing between rotating and stationary parts. In one version, a radially stepped labyrinth seal is formed
between a rotor and a stator. The seal itself involves a rotary shaft having a rotor with several axially spaced angularly stepped portions with high pressure sides and low pressure sides and a stationary housing with a stator surrounding the shaft and corresponding second annular stepped portions on the inside. The combination of the rotor and stator creates a restricted fluid flow path between. Generally the height of a projection is dependent on the minimum clearance between edges of the projection and the adjacent portion of the convex surface. Another version of the invention provides semi-elliptical annular grooves in various surfaces associated with the stator and/or the rotor, oriented against the fluid flow. They may be formed in radial projections from the stator or rotor and fluid cavity surfaces. Advantages of the invention include the provision of flexible knives or spring teeth to establish a fluid barrier in selected areas (Figure 3). The spring teeth may include end fittings which further restrict fluid flow. The spring teeth and their end fittings should be designed to wear only slightly during the first few hours of operation, allowing the minimum required clearance between rotating and stationary components. Another advantage is the provision of spoilers or boundary layer breakers on radial projections and other selected surfaces of the fluid cavities to increase turbulent
r
Figure 3. The flexible knives or spring teeth estabIish a fluid barrier in selected areas.
10
intensity within the seal. Machine finishes or rough surfaces will also enhance the turbulent flow effect. An effective seal is provided even in the case of radial displacement between rotor and stator due to vibration, stresses from unbalanced fluid pressures, large temperature differentials or misalignment. The small clearances between rotor and stator surfaces also help to reduce the tendency for shaft vibration.
Intermediate coating layer for high temperature rubbing seals in rotary regenerators Patent number: US5397649 Publication date: March 14, 1995 Inventors: J. Schienle, T. Strangman Applicant: AUied Signal Inc. This invention concerns protective coatings for metal substrates, and in particular to a regenerator seal multi layer coating having a ceramic surface layer, a yttria stabilized zirconia intermediate layer, and metallic bonding layer. Because rotary regenerators for gas turbine engines are now being made of a ceramic material, they require seals formed from material that can provide sufficient coating wear life. To achieve this life, this material must be oxidation resistant at temperatures up to and exceeding 1600”F, and have a low coefficient of friction to minimize torque loads on the regenerator. A previous patent has described a regenerator seal comprised of a surface layer of nickel oxide, calcium fluoride, and calcium oxide on a steel substrate. A problem with this is the reactive nature of its constituents, especially at temperatures greater than 1600°F. Both nickel oxide and calcium fluoride tend to react with underlying metallic elements. These reactions accelerate the oxidation of
Sealing
Technology
No. 23