Sealing ring and method of forming a metal-to-metal seal

Abstract

A sealing ring (301) for forming a metal-to-metal seal between two opposing metal surfaces (303, 305). The sealing ring comprises an expandable body (311) and a metal jacket (315) fitted around the expandable body. The metal jacket has a discontinuity (317) that extends around an inner or outer circumference of the expandable body. The expandable body is adapted to expand, on inflation, towards or into the discontinuity to force opposing sections of the metal jacket adjacent the discontinuity against the metal surfaces to form the seal.

Description

[0001] SEALING RING AND METHOD OF FORMING A METAL-TO-METAL SEAL

[0002] Technical Field

[0003] The present invention relates to a sealing ring or gasket and a method of forming a metal- to-metal seal. In particular, but not exclusively, the present invention relates to a sealing ring for use in sealing together two sections of a vacuum chamber.

[0004] Background

[0005] Metal sealing rings are often used to provide a gas-tight or liquid-tight seal between two metal surfaces, such as between the flanged ports of two vacuum chambers that are being joined together. In some applications, the metal sealing ring is a flat, circular metal gasket made of a relatively soft metal such as a copper or aluminium, which is crushed between the metal surfaces or flanges such as “GF” flanges, which are generally made of a harder metal, such as stainless steel. CF flanges are each provided with a circular ridge or “knife-edge” which bites into respective faces of the gasket causing the metal of the gasket to be extruded around the knife-edges, thereby forming a seal between the two metal surfaces. Whilst flanges and metal gaskets can be used to form very effective seals, for example in ultrahigh vacuum systems, they suffer from a number of drawbacks, including the need for careful alignment (“mating”) of the flanges with the metal gasket and high clamping forces. The quality of the seal may also be severely reduced if the compression load on the gasket is uneven or too high.

[0006] Metal surfaces typically contain microscopic asperities, i.e. irregularities in the height of the surface. When two hard metal surfaces are in contact, the asperities do not readily deform into each other, such that passages remain between the asperities through which fluids (e.g. gases or liquids) may be transmitted.

[0007] Metal seals work on the principle of plastic deformation of a soft metal layer into the asperities of the hard metal surface, a process which may be termed “keying in”, such that passages between asperities are closed off or greatly reduced in size, thereby forming an effective seal. This process is disrupted if the soft metal surface is moved laterally over the hard metal surface. The sealing element (e.g. sealing ring) may also be damaged by such lateral movement such that it may not be possible to form an effective seal. Sealing surfaces are therefore generally brought into contact and compressed along a normal direction, i.e. a direction that is perpendicular to the surfaces, to allow correct engagement of the sealing surfaces and to prevent damage to the sealing element. In particular, ultrahigh vacuum (UHV) sealing technologies typically require the metal surfaces to engage one another in a direction that is perpendicular to their surfaces.

[0008] Figure 1A shows a schematic cross section view of a metal sealing ring 101 that is deformed against an irregular metal surface 103 through a compressive force that is directed perpendicularly to the surface 103, which results in the sealing ring being “keyed in” to the irregularities of the metal surface 103. Figure 1 B shows how the metal sealing ring fails to conform to the irregularities of the metal surface 103 when the compressive force comprises a component 107 directed transverse to the metal surface, thereby providing a plurality of potential leak paths 109 that may allow a fluid to be transmitted through the seal, i.e. between the sealing ring 101 and the metal surface 103.

[0009] In some applications, it may not be possible for the surfaces to be brought together along a direction that is perpendicular to the surfaces because of geometrical constraints. For example, some vacuum chambers may be manufactured in angular segments (sectors) that need to be joined together, as may be the case for toroidal or spheroidal (e.g. spherical) vacuum chambers, e.g. where the segments are arranged like the segments of an orange. In such cases, it may not be possible to assemble the vacuum chamber without the segments having to move laterally with respect to one another, at least to some extent. Even when surfaces can be brought together along a perpendicular direction, lateral movement of the surfaces with respect to one another may still occur because of unbalanced forces being applied to the surfaces, e.g. unbalanced forces resulting from tightening bolts around the circumference of a flange one at a time.

[0010] Figure 2 shows a segmented toroidal vacuum chamber 201 , which is formed from 6 equiangular segments, of which only 3 segments 203, 205, 207 are shown in the figure. Sealing rings 209 are provided between the sealing faces 211 of the segments. During assembly of the vacuum chamber 201 , the final segment 205 is installed along a radial installation direction, i.e. along a direction towards the central axis of the vacuum chamber 201. The relative motion of the final segment 205 with respect to each of the other two segments 203, 207 therefore comprises both a tangential component (i.e. a component that is perpendicular to the adjacent surfaces 209) and a radial component (i.e. a component that is parallel to the surfaces 209). The tangential component of the motion generates a compressive force that deforms (keys in) the sealing ring 209 to form the seal, whilst the radial component of the motion may reduce the extent to which the sealing ring 209 is able to deform into asperities on the metal surface (e.g. as described above with reference to Figure 1 B), thereby reducing the effectiveness of the seal. The thickness of the metal sealing ring 209 is also limited by the clearance between the segments 203, 205, 207 during assembly of the vacuum chamber.

[0011] WO2020254543 describes an inflatable a metal sealing ring for forming a metal-to-metal seal between two opposing metal surfaces. The metal sealing ring comprises a tubular metal body and an inlet tube extending from the body for introducing an internal pressure into the body. The body is adapted to deform under the internal pressure against each of the opposing metal surfaces to form the seal.

[0012] Summary of the Invention

[0013] The present disclosure seeks to overcome or at least alleviate the issues mentioned above with existing approaches to forming metal-to-metal seals.

[0014] According to a first aspect of the present invention there is provided a sealing ring or gasket for forming a metal-to-metal seal between two opposing metal surfaces, the gasket comprising: an expandable body in the form of a closed loop; and a metal jacket extending around the closed loop and at least partly around an outer surface of the expandable body, the metal jacket having a discontinuity that extends around the closed loop, wherein, on expansion, the expandable body is configured to force apart opposing sections of the metal jacket adjacent the discontinuity to form a seal in use.

[0015] According to a second aspect of the present invention there is provided a gasket or sealing ring for forming a metal-to-metal seal between two opposing metal surfaces. The sealing ring comprises an expandable or inflatable ring-shaped body (e.g. a ring-shaped body adapted for inflation) and a metal jacket (e.g. a substantially tubular metal jacket), disposed, wrapped or fitted around the ring-shaped body. The metal jacket has a discontinuity (e.g. a break or opening). In other words, the metal jacket may comprise, for example, a split tube around the ring of the ring-shaped body. The discontinuity extends around an inner or outer circumference of the ring-shaped body (i.e. an inner or outer perimeter of the ring-shaped body). The ring-shaped body is adapted to expand, on inflation, towards or into the discontinuity to force opposing sections of the metal jacket adjacent the discontinuity (e.g. in opposite directions out of a plane of the ringshaped body) against the metal surfaces to form the seal.

[0016] Embodiments of the present invention provide a gasket having a body that can be expanded or inflated under an internal pressure to force a surrounding metal jacket against first and second metal surfaces to create a seal between the surfaces. Because the body is expanded in use, the body and the metal jacket can be contained entirely within a groove in the first surface such that the second surface can be brought into place against the first surface from any direction without contacting and damaging the gasket. Expansion of the body then forces open the metal jacket around the whole of the closed loop to create the seal. In some implementations, the body may be adapted to expand (substantially) elastically, whilst the metal jacket is adapted to deform plastically in response to expansion of the body. For example, the body may be adapted to be more resilient than the metal jacket, which can allow it to exert a greater force on the metal jacket and hence achieve a more effective seal.

[0017] The discontinuity in the metal jacket may allow a greater proportion of a force that is used to inflate the expandable body to go into deforming the metal jacket against the metal surfaces (as compared to a metal jacket that lacks such a discontinuity). Less metal may also be required to make the metal jacket in some cases. Respective contact areas between the metal jacket and the metal surfaces may be increased by expansion of the expandable body towards or into the discontinuity. For example, portions of the cross section of the metal jacket adjacent the discontinuity that initially curve away from the metal surfaces may be flattened or straightened against the metal surfaces as the expandable body expands to increase the contact area between the metal jacket and each of the metal surfaces. Increasing the contact areas may allow more effective (e.g. lower leak rate) and / or robust seals to be formed.

[0018] After the metal-to-metal seal has been formed, the metal jacket provides an impermeable barrier preventing fluid (e.g. gas or liquid) from passing into or out of a central region enclosed by the expandable body. The metal jacket extends continuously around the expandable body. That is, the metal jacket does not have any discontinuities (e.g. breaks or openings) other than the discontinuity that extends around the loop of the expandable body.

[0019] Typically, the discontinuity in the metal jacket extends around an outer circumference (i.e. the radially outermost perimeter) of the expandable body, such that the metal jacket extends between the expandable body and a central region encircled or enclosed by the expandable body. Alternatively, in some implementations, the discontinuity extends around an inner circumference of the expandable body, such that the metal jacket extends between the expandable body and a region radially outside the expandable body.

[0020] The expandable body may be adapted to expand axially on inflation towards the opposing metal surfaces before or during expansion of the expandable body towards or into the discontinuity of the metal jacket. For example, the expandable body may be adapted to expand along an axial direction defined with respect to a central axis of the sealing ring (with the expansion of the sealing ring towards or into the discontinuity being along a radial direction with respect to the central axis). The expandable body may be adapted such that the amount of axial expansion exceeds the amount of radial expansion at least prior to the metal jacket contacting the opposing metal surfaces.

[0021] At least prior to inflation, the outer surface of the expandable body may have a radial cross section (defined with respect to the central axis of the sealing ring) that comprises a concave portion facing the discontinuity of the metal jacket. In some implementations, the radial cross section of the outer surface of the expandable body may be C-shaped.

[0022] Preferably, the metal jacket contacts the expandable body around an outer or inner circumference of the expandable body opposite the discontinuity. For example, the discontinuity may extend around an outer circumference of the expandable body, with the metal jacket contacting an inner circumference of the expandable body. That is, the discontinuity may be located radially outwards with respect to where the metal jacket contacts the expandable body prior to inflation.

[0023] In some implementations, the metal jacket comprises one or more outwardly directed ridges (i.e. protrusions formed on an exterior surface of the metal jacket) for deforming against the opposing metal surfaces upon expansion of the expandable body to form the seal. Each ridge is preferably provided on a respective one of the opposing sections of the metal jacket. Expanding the expandable body may force one or more ridges provided on the exterior of the metal jacket into contact with the second metal surface and / or the sealing groove. The edge(s) may provide increased contact pressure between the metal jacket and the second metal surface and / or the sealing groove. In some implementations, the ridges(s) may be plastically deformable.

[0024] The metal jacket and the expandable body may be formed of different respective materials, the material of the metal jacket being softer (and / or more ductile) than the material of the expandable body. Thus, the expandable body may be able to exert a greater force on the metal jacket to cause the metal jacket to deform against the metal surfaces.

[0025] In some implementations, the expandable body can be bistable (e.g. at least at least when disposed between (e.g. confined by) two opposing metal surfaces for forming the metal-to-metal seal). That is, the expandable body may have alternative equilibrium configurations, i.e. stable configurations that the expandable body can transition between (at least in one direction), e.g. in response to a change in temperature of the expandable body or a change in internal pressure within the expandable body.

[0026] For example, the expandable body can have an alternative equilibrium configuration in which the curvature of an internal or external part or section of the expandable body is inverted or flattened relative to a starting equilibrium configuration. As used herein, the expandable body being bistable encompasses the expandable body being multistable, i.e. having more than two equilibrium configurations, e.g. the expandable body may have multiple sections for which the curvature can be inverted or flattened.

[0027] The expandable body can be adapted to force apart the opposing sections of the metal jacket to form the seal during a transition from a starting equilibrium configuration of the expandable body towards or to an alternative equilibrium configuration of the expandable body. In this context, an “equilibrium” configuration refers to a shape, geometry or arrangement of the expandable body that is a local or global potential energy minimum, i.e. stable with respect to (small) perturbations or deformations of the expandable body. In some implementations, the expandable body is adapted to deform elastically during (e.g. throughout) the transition, e.g. such that the expandable body can transition from the starting equilibrium configuration towards or to the alternative equilibrium configuration multiple times without (significant) loss of resiliency. For example, the transition to or towards the alternative equilibrium configuration can be reversible such that the gasket, or at least the expandable body can be re-used, e.g. to reform the seal or to create a new seal. The metal jacket can be configured to deform plastically during the transition, e.g. to form a more effective seal.

[0028] For example, the expandable body can be adapted to force apart the opposing sections of the metal jacket to form the seal during a transition from a starting equilibrium configuration of the expandable body towards or to an alternative equilibrium configuration of the expandable body. In use, the expandable body might not reach the alternative equilibrium configuration, e.g. because of geometric constraints from the opposing metal surfaces, such as the sidewalls of a sealing groove in which the gasket is disposed or provided. The expandable body may then only reach a configuration intermediate the starting equilibrium configuration and the alternative equilibrium configuration. However, the expandable body can be adapted so that, in the intermediate configuration, the expandable body exerts spring forces on the opposing sections of the metal jacket. For example, when in the intermediate configuration, the expandable body can have a greater extent along a direction towards the opposing surfaces (e.g. size in a direction perpendicular to one or more of the opposing surfaces) than when in either of the starting or alternative equilibrium configurations. The intermediate configuration can be resiliently biased towards the alternative equilibrium configuration, e.g. such that the expandable body is prevented from transitioning back to the starting equilibrium configuration. For example, the expandable body may be adapted to have a transition state or configuration from which the expandable body can relax towards the alternative equilibrium configuration in preference to the starting equilibrium configuration.

[0029] The expandable body may comprise an inlet into an internal volume enclosed by walls of the expandable body through which to expand or inflate the expandable body. For example, the inlet may comprise a tube extending from the expandable body for connection to a pressure source. The tube may pass through a sidewall of the metal jacket in some instances. The expandable body may be inflated by introducing a fluid into the internal volume through the inlet. In some examples, the tube can include a valve, which can allow an internal pressure to be maintained within the expandable body after the pressure source has been removed. The valve can also be used to allow the pressure source to be reconnected such that the internal pressure in the expandable body can be increased further or restored to a previous level, or otherwise varied.

[0030] Alternatively, the expandable body may be inflated by a physical or chemical change of a substance contained within the internal volume. In such cases, the internal volume of the expandable body may remain sealed (with no inlet) to prevent loss of pressure, at least during inflation of the expandable body. Manufacture and use of the gasket can be simplified in some cases.

[0031] In such cases, inflation of the expandable body may be initiated in a number of different ways. For example, the expandable body may initially comprise a substance that has been cooled below its boiling point or sublimation point, such that subsequent active or passive heating of the expandable body increases the vapour pressure of the substance and thereby drives expansion of the expandable body. For example, the expandable body may initially comprise liquid nitrogen (or another liquefied gas) or solid carbon dioxide, such that the expansion is driven by boiling of the liquid nitrogen or sublimation of the carbon dioxide. More generally, expansion of the expandable body may be driven by causing a substance or material within the expandable body to undergo a phase transition (e.g. by heating or cooling). As one example, the expandable body can comprise a material (such as germanium, silicon, gallium, bismuth, or antimony), that expands on freezing, such that the phase transition can be caused by cooling the molten material to below its melting point.

[0032] As another example, the expansion may be driven by decomposition of a substance or material within the expandable body. For example, the expandable body may comprise a substance or material that can decompose by deflagration or detonation, such that the decomposition can be initiated through ignition or an acoustic wave, such as a shockwave. For example, the expansion can be drive by decomposition or detonation of a primary or secondary explosive, such as sodium azide. In some implementations, the expansion may be driven by heat generated by decomposition or chemical reaction of one or more substances (e.g. substances within the internal volume of the expandable body). The heat may, for example, cause expansion of a gas within the expandable body.

[0033] Thus the expandable body may be adapted for inflation. For example, the expandable body can comprise an internal volume enclosed by walls of the expandable body, the internal volume comprising (i) an inlet through which to introduce fluid into the internal volume to inflate the body, or (ii) a substance for introducing fluid into the internal volume by a physical or chemical change of the substance to inflate the body, or both. The expandable body can comprise an initiation mechanism that can be used to initiate the chemical or physical change, e.g. a heater, an electrical stimulus or spark generator, an electromagnetic coupling mechanism (e.g. for inducing electrical currents for heating the expandable body or surrounding apparatus), a shockwave generator, such as a percussion cap, and so on.

[0034] In some implementations, the expandable body can comprise a shape memory alloy (which may also be referred to as a heat recoverable alloy or shape memory effect alloy). Shape memory alloys are those which can be deformed at temperatures below a transition temperature (e.g. a phase transition temperature), but which are induced to return to (e.g. become biased towards) a particular configuration at temperatures greater than the transition temperature. That is, the shape memory alloy can be adapted to return to a pre-set configuration when heated. In one example, the expandable body is introduced into the metal jacket at a temperature below the transition temperature (e.g. a cryogenic temperature) and then heated, actively or passively by being allowed to come into thermal equilibrium with the environment (e.g. at room temperature), to cause the expandable body to expand as it attempts to return to a pre-set “expanded” configuration (i.e. a configuration that has a dimension larger than a corresponding dimension of the metal jacket). Thus, the opposing sections of the metal jacket can be forced apart as the expandable body returns or attempts to return to the expanded configuration. The shape memory effect alloy may, for example, comprise an alloy of copper-aluminium-nickel or nickel-titanium (NiTi).

[0035] According to a third aspect of the present invention there is provided a method of forming a metal-to-metal seal between opposing first and second metal surfaces. The method comprises: providing a gasket or sealing ring as described above between the first and second metal surfaces; and inflating or expanding the expandable body towards or into the discontinuity in the metal jacket to force opposing sections of the metal jacket adjacent the discontinuity against the metal surfaces to form the seal. Preferably, at least during an initial stage of inflation, the curvature of the concave portion of the radial cross section of the outer surface of the expandable body reduces, thereby forcing the opposing sections of the metal jacket adjacent the discontinuity against the metal surfaces. In some implementations of the method, the first metal surface comprises a sealing grove and providing the sealing ring between the first and second metal surfaces comprises locating the sealing ring within the sealing groove. Inversion or flattening of the curvature of the concave portion of the radial cross section of the outer surface of the expandable body may be limited by contact of the metal jacket with a sidewall of the sealing groove. Thus, the concave portion of the radial cross section of the expandable body may be straightened against the sidewall of the sealing groove following inflation of the expandable body. In some implementations, the concave portion becomes convex (at least to some extent) before contacting the sidewall. Thus, the expandable body can be bistable as it can transition from an initial equilibrium configuration having the concave portion to another equilibrium configuration in which the concave portion has become convex or flattened. In some examples, the transition is reversible such that the gasket, or at least the expandable body, can be re-used. The inversion or flattening of the concave portion (i.e. the transition between the equilibrium configurations) can generate a force for forcing apart the opposing sections of the metal jacket to form the seal. The internal pressure in the expandable body may then be reduced to cause relaxation (i.e. partial contraction) of the expandable body to provide an additional spring force to support the seal.

[0036] In general, the sealing groove may have any cross section that can accommodate the metal sealing ring, e.g. a square or rectangular cross section or a curved cross section such as a semi-circle.

[0037] The sealing ring may be accommodated within the sealing groove without protruding therefrom in a direction perpendicular to the first metal surface. As the sealing ring does not protrude from the sealing groove (at least along the direction perpendicular to the first metal surface), the first and second metal surfaces are not required to approach one another along the direction perpendicular to the first metal surface. For example, the first and second metal surfaces may approach one another closely or even contact one another as they are brought into position, e.g. the second metal surface may be able to slide over the first metal surface (or vice versa). The method therefore allows the coming together of the first and second metal surfaces to be decoupled from the deformation of the metal jacket. Scraping or scratching of the surface of the metal jacket is also avoided, which is particularly important for Ultra High Vacuum (UHV) seals, which are known for their sensitivity to such types of damage.

[0038] Accordingly, more effective seals may be created, particularly in cases where there are geometric constraints on how the first and second metal surfaces can be brought together (i.e. mated) that mean that at least some lateral motion of the surfaces is needed as the sealing ring is engaged. The method may further comprise positioning the second metal surface over the first metal surface to cover the sealing groove, e.g. by moving the first and / or the second metal surface into position. The first and / or second metal surface(s) may be positioned by sliding, such the metal surfaces are (substantially) parallel to and in contact with one another during the positioning. The sealing ring may deform against a bottom surface of the sealing groove, such that the sealing ring is provided between the second metal surface and the bottom surface of the sealing groove.

[0039] Metal jackets of varying respective thicknesses (i.e. jackets having walls of different thicknesses) may be used together with a common (e.g. the same) design of expandable body to produce sealing rings of different heights. Thus, selection of a suitable metal jacket may allow the metal sealing ring to be adapted for sealing grooves of different depths. For example, a metal jacket may be selected to provide a pre-determined separation or clearance between the metal jacket and the second metal surface prior to the expandable body being inflated. Thus, the thickness of the metal sealing ring can be accurately matched to the depth of the sealing groove whilst still allowing the first and second metal surfaces to slide over one another. Some separation or clearance between the metal jacket and the second metal face prior to expanding the expandable body may be preferable to account for manufacturing tolerances (for example). Thus, in some implementations, the thickness of the metal sealing ring may be selected to provide a predetermined separation that is the same as or exceeds expected manufacturing tolerances for the metal sealing ring, the first and second metal surfaces, and / or the sealing groove.

[0040] The method may additionally comprise coupling components (e.g. vacuum chamber parts) on which the first and second metal surfaces are provided to prevent relative movement between the first and second surfaces during the inflation of the expandable body. The components may be bolted together, for example.

[0041] The first and second metal surfaces may be provided on respective angular segments of a vacuum chamber. For example, the vacuum chamber may be a toroidal vacuum chamber comprising a plurality of angular segments that require sealing together end- to-end to provide a toroidal inner volume in which a vacuum can be maintained. The angular segments are aligned prior to forming a seal between them, which may comprise moving the second metal surface and / or the first metal surface to bring the surfaces into contact, with at least a component of that motion (or all of it) being parallel to the first and / or second metal surface.

[0042] The first and second metal surfaces may be provided on respective angular segments of a vacuum chamber, e.g. a toroidal or spheroidal vacuum chamber. The vacuum chamber may be assembled, including the angular segments, before the sealing ring is expanded.

[0043] According to a fourth aspect of the present invention, there is provided a metal-to-metal seal formed between two opposing metal surfaces using the method described above.

[0044] According to a fifth aspect of the present invention, there is provided a vacuum chamber comprising one or more metal seals or sealing rings as described above. The first and second metal surfaces are provided on different respective segments or parts of the vacuum chamber. Each sealing ring may be located in a corresponding sealing groove provided in the metal surface of one of the vacuum chamber parts (the metal surface of the other vacuum chamber part may also comprise a complementary sealing groove in some cases). In some implementations, the vacuum chamber may comprise a plurality of angular segments arranged to enclose an inner volume (e.g. a toroidal inner volume), the one or more metal sealing rings forming respective seals between pairs of the angular segments. In some examples, the vacuum chamber may be a plasma chamber, e.g., a tokamak plasma chamber or a stellarator plasma chamber.

[0045] Brief description of the drawings Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawing in which corresponding reference symbols indicate corresponding parts, and in which:

[0046] Figure 1A is a schematic cross section view of a metal seal in which a compressive force is applied to a sealing ring along a direction that is normal to a surface;

[0047] Figure 1 B is a schematic cross section view of a metal seal in which a compressive force is applied to a sealing ring along a direction that has a component parallel to a surface;

[0048] Figure 2 is a schematic top view of half of a segmented toroidal vacuum chamber;

[0049] Figure 3A is a schematic vertical cross section view of a metal sealing ring according to an embodiment of the present invention;

[0050] Figure 3B is an enlarged portion of Figure 3A;

[0051] Figure 4 is a schematic vertical cross section view of the metal sealing ring of Figures 3A and 3B at various stages of expansion;

[0052] Figure 5 is a schematic vertical cross section view of the metal sealing ring of Figures 3A and 3B showing an inlet tube;

[0053] Figure 6 is a schematic vertical cross section view of another metal sealing ring in which the inlet tube is used as an access inlet; and

[0054] Figure 7 is a schematic vertical cross section view of an alternative configuration of the metal sealing ring of Figure 5.

[0055] Detailed

[0056] Figure 3A shows a cross section through a metal gasket or sealing ring 301 for forming a metal-to-metal seal between two opposing metal surfaces 303, 305. The metal sealing ring 301 is provided in a sealing groove (or channel) 307 formed in a first of the metal surfaces 303. The cross section shown in Figure 3A is a radial cross section taken with respect to an axis, Z, perpendicular to a plane of the sealing ring 301. The metal surfaces 303, 305 are provided on different respective parts of a vacuum chamber, with a radially- inner region (on the left-hand side of Figure 3A, in which the Z-axis is provided) corresponding to an interior volume of the vacuum chamber. In use, the sealing ring 301 provides a seal that prevents gas (e.g. air) from being transmitted between the metal surfaces 303, 305 from a high pressure, radially-outer region (the right-hand side of Figure 3A) to the low pressure, radially-inner region (the left-hand side of Figure 3A). The metal sealing ring 301 should be understood as having a generally toroidal structure, e.g. a structure formed by rotating the cross section of the metal sealing ring 301 around the Z-axis. In general, the metal sealing ring 301 is not a circle around the Z-axis and may have different shapes depending on the application, e.g. the metal sealing ring 301 may be ellipsoidal or follow any shape of closed path that encloses the Z-axis. The metal sealing ring 301 is preferably substantially planar, i.e. has a uniform extent along the Z- axis, but can be non-planar in some cases. The sealing ring 301 can be used in any orientation such that the Z-axis may be vertical, as shown in Figure 3A, or aligned along any other direction, e.g. horizontal, depending on the orientations of the surfaces 303, 305 being sealed.

[0057] The metal sealing ring 301 comprises an expandable or inflatable ring-shaped body 311 and a metal jacket 315 around the expandable body 311.

[0058] The expandable body 311 comprises a ring-shaped conduit or tube describing a closed path. The expandable body 311 is hollow and has an internal volume 313. The internal volume 313 preferably has no walls such that the path of the conduit around the expandable body 311 is uninterrupted. The expandable body 311 is configured to expand or inflate when a pressure is generated inside the internal volume 313. For example, the expandable body 311 may have one or more inlets for introducing a fluid into the internal volume 313, and / or compressing a fluid contained in the internal volume 313, to generate an internal pressure. The fluid may be a liquid, such as a hydraulic fluid, or a gas. The (or each) inlet may be a tube connecting to the internal volume 313 and connectable to an external pressure source such as a pump or compressor. In some implementations, an internal pressure may instead be generated by heating a substance (solid, liquid or gas) trapped within the internal volume, or through a pressure-generating chemical reaction such as vaporising or decomposing a solid or liquid substance into a gas. The substance may be introduced into the internal volume 313 via an inlet before closing the inlet to seal the internal volume 313.

[0059] The metal jacket 315 is wrapped or fitted at least partly around an outer surface of the expandable body 311 . Expansion of the expandable body 311 deforms the metal jacket 315 and, in use, deforms the metal jacket 315 against the opposing metal surfaces 303, 305 to form a seal between them. The expandable body 311 may deform plastically such that the internal pressure can be relieved without the expandable body 311 returning to its initial form in order to maintain the seal. Alternatively, the internal pressure may be continuously maintained by an external pressure source, or the expandable body 311 may be sealed by, for example, closing the inlet to maintain the internal pressure. Alternatively, as described in more detail below with respect to Figures 4A-F, the expandable body 311 may be configured to provide a spring force that maintains the seal when the internal pressure is relieved.

[0060] The expandable body 311 is preferably made of a high strength and relatively high ductility material, e.g. a metal, such as an austenitic nickel-chromium based alloy, such as Iconel 718. Other (non-metal) materials may be used additionally or alternatively depending on the application. The metal jacket 315 is preferably made of a soft or ductile material so that it deforms easily (e.g. more easily than the expandable body 311) to form an effective seal. For example, a non-ferrous metal (preferably a substantially pure non-ferrous material), such as aluminium or copper, may be used.

[0061] The metal jacket 315 comprises a split tube and extends around the entire length of the expandable body 311 in a closed loop. The metal jacket 315 has a discontinuity, preferably only a single discontinuity, that extends around its length such that, in radial cross section, the jacket 315 does not form a continuous, closed loop around the expandable body 311 . In the example shown in Figure 3A, the discontinuity is an opening 317 formed between edges 318A,318B of the metal jacket 315 that are spaced apart from one another, e.g. such that the metal jacket 315 has a C-shaped or U-shaped cross section. Alternatively, the edges 318A,318B may touch each other or overlap and extend past one another such that, in radial cross section, the jacket 315 fully surrounds or wraps around the expandable body 311. The edges 318A,318B are nevertheless able to move relative to one another when the metal jacket 315 is deformed by inflation of the expandable body 311.

[0062] The opening 317 or other discontinuity preferably extends around the metal jacket 315 at the substantially the same relative position relative to the expandable body 311 to ensure even deformation of the metal jacket 315. More preferably, the discontinuity is located at either of substantially the inner or outer circumference of the expandable body 311 such that the metal jacket 315 deforms substantially evenly in both directions along the Z-axis. More preferably, the discontinuity extends around substantially the outer circumference of the metal jacket 315, i.e., is directed away from the Z-axis and away from a space enclosed by the metal sealing ring 301 , as shown in Figure 3A. The opening 317 is therefore directed away from a high vacuum (i.e. low pressure) side of the seal such that the metal jacket 315 forms a barrier between the high vacuum side and the expandable body 311 .

[0063] The metal jacket 315 comprises ridges 319 on its outer surface, i.e. externally directed protrusions for deforming, preferably plastically, against the second metal surface 303 and the sealing groove 307. Each ridge may extend all the way around the metal jacket (i.e. enclose the Z-axis). In the present example, opposing ridges 319 are formed on either side of the opening 317. However, ridges may be formed in other locations, e.g. closer to the Z-axis, or on an opposite side of the metal jacket 315 to the opening 317. Ridges 319 are generally optional however, and the metal jacket 315 may, for example, comprise none, 1 , or 2 or more ridges. In some implementations, the ridges may be “knife edges” that are able to cut into the metal surfaces 303, 305, e.g. the ridges 319 may be coated with aluminium (or another relatively hard metal) to create the knife-edge.

[0064] The expandable body 311 has a radial cross section that comprises a concave portion 321 facing the opening 317 or other discontinuity in the metal jacket 315. Thus, the expandable body 311 comprises an indentation or channel that extends circumferentially around the expandable body (i.e. around the Z-axis), and which is directed towards the opening 317 of the metal jacket 315. In the present example, the radial cross section of the expandable body 311 is otherwise convex, i.e. there is a single concave region 321 . As described, below in connection with Figures 4A-F, the concave region 321 causes the expandable body 311 to expand preferentially towards the opposing metal surfaces 303, 305 as the concave region straightens, which increases performance of the seal by increasing the pressure exerted on the metal jacket 315 as the seal is being formed.

[0065] Prior to inflation, the metal sealing ring 301 is configured to fit into the sealing groove 307 formed in the first metal surface 303. In the present example, the sealing groove 307 has a square cross section, but other shapes of cross section can be used, e.g. rectangular, ellipsoidal, semi-circular, etc.

[0066] Before the seal is formed, the metal sealing ring 301 does not protrude from the sealing groove 307, i.e. does not extend past the first metal surface 303 in a direction perpendicular to the first metal surface 303 (which, in the figures, corresponds to the direction of the Z-axis). Thus, the second metal surface 305 may be moved over the first metal surface 303 to cover the sealing groove 307 without contacting the metal sealing ring 301 , i.e. the second metal surface 305 may approach the first metal surface 303 from any direction (limited only by the surfaces 303, 305 coming into contact), or slid into position over the first metal surface 301 , with the two surfaces in contact. As can be appreciated from the enlarged view provided by Figure 3B, a small amount of clearance 309 (measured in a direction perpendicular to the first metal surface 303) may be provided between the metal sealing ring 301 and the second metal surface 305. The clearance 309 may be selected to account for manufacturing tolerances, e.g. to ensure that there is a high likelihood that the metal sealing ring 301 does not protrude from the sealing groove 307. In some cases, the clearance 309 may be from 0.1 mm to 0.5 mm. The sealing ring may have a thickness of around 5 mm in some cases (the thickness being the extent of the sealing ring in a direction parallel to the Z-axis).

[0067] Figure 4 shows the metal sealing ring 301 (without ridges 319) at different stages A-F during formation of the seal. In this example, the seal is formed by progressively increasing the pressure within the internal volume of the expandable body 311.

[0068] In step A, the metal sealing ring 301 is accommodated within the sealing groove 307 in the first metal surface 303, with clearances 309 between the metal sealing ring 301 and the second metal surface 305 and the bottom of the sealing groove 307.

[0069] In step B, the vacuum chamber parts on which the first and second metal surfaces 303, 305 are provided are coupled to one another using fixings 401 (e.g. bolts) to prevent relative movement between the metal surfaces 303, 305 as the expandable body 311 is expanded.

[0070] In step C, the metal jacket 315 expands until there is zero clearance 309 between the metal jacket 315 and the second metal surface 305 and the bottom of the sealing groove 307. The metal jacket 315 therefore begins to deform against the second metal surface 305 and the bottom of the sealing groove 307. The configuration of the expandable body 311 (i.e. the inclusion of the concave region 321) means that the initial expansion of the expandable body 311 acts to straighten the concave region 321 and thereby force the metal jacket 315 towards the second metal surface 305 and the bottom of the sealing groove 307. Following contact of the metal jacket 315 with the opposing metal surface 303, 305, the expandable body 311 begins or continues to expand radially (i.e. parallel to the first metal surface 303, and away from the Z-axis in the embodiment illustrated in the Figures).

[0071] In step D, contact areas 403, 405 between the metal jacket 315 and the second metal surface 305 and the bottom of the sealing groove 307 increases as the expandable body 311 expands radially. The radial expansion of the expandable body 311 reduces the curvature of the edges 318A,B of the metal jacket 315 adjacent the opening 317 in the metal jacket 315, causing these sections to unroll against the second metal surface 305 and the bottom of the sealing groove 307. The curvature of the concave region 321 also reduces, i.e. the concave region 321 straightens to generate an increased force to deform the metal jacket 315 against the second metal surface 305 and the bottom of the sealing groove 307.

[0072] In step E, the radial expansion of the expandable body 311 continues until the body contacts a sidewall 405 of the sealing groove 307, and the concave region 321 has become substantially straightened. The sidewall 405 acts as a stop to prevent the expandable body 311 from over-expanding, which may lead to reduction of contact pressure between the seal and the sealing faces, thereby weakening the seal, which may ultimately cause the metal jacket 315 to lose contact with the second metal surface 305 and the bottom of the sealing groove 307.

[0073] In step F, once the pressure in the expandable body 311 reaches a maximum, it may be reduced, e.g. down to atmospheric pressure, which may in some cases cause the expandable body 311 to stop contacting the sidewall 405 as a result of elastic strain in the expandable body 311 being relieved. Such contraction may increase the contact pressure between the metal jacket 315 and the second metal surface 305 and the bottom of the sealing groove 307. Elastic strain stored in the expandable body 311 may therefore act as an energising force to help prevent loss of sealing capability, e.g. during small relative motion of the first and second metal surfaces 303, 305 (fretting, shock loading, etc.). In some examples, the expandable body 311 is configured and positioned with the sealing groove 307 such that the concave region 321 becomes convex during inflation of the expandable body 311 and then becomes substantially straight when the internal pressure in the expandable body 311 is relieved. Alternatively, in some implementations, the pressure may be maintained e.g. so that there may be no contraction of expandable body 311 .

[0074] Once the seal has been formed, the parts may be heated (e.g. to 300°C), which may reduce the contact pressure to some extent, but it has been found that the seal remains effective nonetheless. Thus seal integrity may be maintained even at “bake out” temperatures used in high vacuum application.

[0075] One or more seals formed using metal sealing rings 301 as described above in connection with Figures 3A, 3B and 4 may be used in the toroidal vacuum chamber 201 described above in connection with Figure 2, for example.

[0076] The metal sealing ring 301 may be formed entirely of metal, which makes it particularly suited to harsh chemical and physical environments that may cause sealing rings made of other materials to degrade.

[0077] Figure 5 is a schematic vertical cross section view of the sealing ring 301 taken at a different location from the cross sections of Figures 3A, 3B and 4. The expandable body 311 comprises an inlet 502 on a side opposite the discontinuity in the metal jacket 315. The inlet 502 is connected to an inlet tube 504 that extends through the metal jacket 315 and a sidewall of the sealing groove 307. A fluid or pressure source (not shown) can be connected to the inlet tube 504 to introduce fluid into the internal volume 313 of the expandable body 311 through the inlet 502.

[0078] Figure 6 is a schematic vertical cross section view of another sealing ring 601 , which is similar to the sealing ring 301 of Figure 5, except that there is no inlet into the expandable body 611 and the inlet tube 604 terminates after the metal jacket 315, i.e. at or before the expandable body 611. The inlet tube 604 comprises one or more wires 606 that are used to initiate expansion of the expandable body 611. For example, the one or more wires 606 can be used to supply electrical current to a heater 608 (which in this case, extends around an outer circumference of the expandable body 611) or another initiation mechanism that initiates a chemical or physical reaction (e.g. phase change) of a substance or material (not shown) within the internal volume 313 of the expandable body 611. In another implementation, the expandable body may comprise (e.g. be formed from) a shape memory effect alloy (such as NiTi) and the heater 608 used to raise the temperature of the shape memory effect alloy above a transition temperature and thereby drive expansion of the expandable body 611. The expandable body 611 may or may not have an internal volume in such cases. As another example, the one or more wires 606 can be used to ignite or detonate a combustible or explosive substance (e.g. sodium azide) within the inner volume 313 of the expandable body 611.

[0079] In another implementation of the sealing ring 601 shown in Figure 6, the inlet tube 606 is omitted, but there is nonetheless a through hole extending through the metal jacket 315 and a sidewall of the sealing groove 307 that allows the one or more wires 606 to reach the heater 608 or other initiation mechanism.

[0080] Figure 6 is a schematic vertical cross section view of yet another sealing ring 701 , which is similar to the sealing ring 301 of Figure 5, except that the a concave portion 721 of the expandable body 715 faces away from the opening 317 in the metal jacket 315. Thus, the expandable body 715 can expand radially within the metal jacket 315. The inlet tube 704 in this case does not extend through the metal jacket 315, which may simplify construction.

[0081] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

CLAIMS:

1. A gasket for forming a metal-to-metal seal between two opposing metal surfaces, the gasket comprising: an expandable body in the form of a closed loop; and a metal jacket extending around the closed loop and at least partly around an outer surface of the expandable body, and having a discontinuity that extends around the closed loop, wherein, in use, the expandable body is configured to expand to force apart opposing sections of the metal jacket adjacent the discontinuity to form a seal.

2. A gasket according to claim 1 , wherein the expandable body is bistable, at least when disposed between two opposing metal surfaces for forming a metal-to-metal seal.

3. A gasket according to claim 1 or 2, wherein the expandable body is adapted to force apart the opposing sections of the metal jacket to form the seal during a transition from a starting equilibrium configuration of the expandable body towards or to an alternative equilibrium configuration of the expandable body.

4. A gasket according to claim 3, wherein the expandable body is adapted to exert spring forces on the opposing sections of the metal jacket when the expandable body is in a configuration intermediate the starting equilibrium configuration and the alternative equilibrium configuration.

5. A gasket according to claim 4, wherein the configuration of the expandable body intermediate the starting equilibrium configuration and the alternative equilibrium configuration is resiliently biased towards the alternative equilibrium configuration.

6. A gasket according to any one of claims 3 to 5, wherein the expandable body is adapted to deform elastically during or throughout the transition.

7. A gasket according to any one of claims 3 to 6, wherein the metal jacket is adapted to deform plastically during the transition.

8. A gasket according to any one of claims 3 to 7, wherein the expandable body is adapted to transition from the starting equilibrium configuration of the expandable body towards or to the alternative equilibrium configuration of the expandable body in response to a change in temperature of the expandable body or a change in internal pressure within the expandable body.

9. A gasket according to any one of the preceding claims, wherein the expandable body comprises a shape memory alloy.

10. A gasket according to claim 9, wherein the shape memory alloy is adapted to transition to an expanded state on heating above a transition temperature of the shape memory alloy.

11. A gasket according to any one of the preceding claims, wherein the expandable body comprises a tube configured to expand under an internal pressure.

12. A gasket according to any one of the preceding claims, wherein the expandable body is adapted for inflation and wherein, on inflation, the expandable body is configured to force apart the opposing sections of the metal jacket adjacent the discontinuity to form the seal in use.

13. A gasket according to any one of the preceding claims, wherein the discontinuity extends around one of an inner circumference or an outer circumference of the closed loop.

14. A gasket according to any one of the preceding claims, wherein the expandable body is configured to expand towards or into the discontinuity.

15. A gasket according to claim 13 or 14, wherein the expandable body is configured to expand along an axis that is substantially perpendicular to a plane of the expandable body.

16. A gasket according to any one of the preceding claims, wherein, on expansion, the expandable body is configured to force the metal jacket against adjacent metal surfaces to form a seal in use.

17. A gasket according to any one of the preceding claims, wherein the expandable body is configured to force apart opposing sections of the metal jacket adjacent the discontinuity in opposite directions along an axis substantially perpendicular to a plane of the closed loop.

18. A gasket according to any one of the preceding claims, wherein, at least prior to inflation the outer surface of the expandable body has a radial cross section that comprises a concave portion facing the discontinuity in the metal jacket.

19. A gasket according to claim 18, wherein the radial cross section of the outer surface of the expandable body is a hollow C-shape.

20. A gasket according to any one of the preceding claims, wherein the metal jacket contacts the expandable body around an outer or inner circumference of the expandable body opposite the discontinuity.21 . A gasket according to any one of the preceding claims, wherein the metal jacket comprises one or more outwardly directed ridges.

22. A gasket according to any one of the preceding claims, wherein the metal jacket and the expandable body are formed of different respective materials, the material of the metal jacket being softer than the material of the expandable body.

23. A gasket according to any one of the preceding claims, wherein the expandable body comprises an inlet into an internal volume enclosed by walls of the expandable body.

24. A gasket according to claim 23, wherein the inlet comprises a tube extending from the expandable body for connection to a pressure source.

25. A gasket according to any one of the preceding claims wherein the expandable body is configured to expand under an internal pressure and, following expansion of the expandable body and relief of the internal pressure, the expandable body is configured to maintain a spring force against the opposing sections of the metal jacket.

26. A gasket for forming a metal-to-metal seal between two opposing metal surfaces, the gasket comprising: a ring-shaped body adapted for inflation; and a metal jacket disposed around the ring-shaped body and having a discontinuity that extends around an inner or outer circumference of the ring-shaped body, and wherein the ring-shaped body is adapted to expand, on inflation, towards or into the discontinuity to force opposing sections of the metal jacket adjacent the discontinuity against the metal surfaces to form the seal.

27. A method of forming a metal-to-metal seal between opposing first and second metal surfaces, the method comprising: providing, between the first and second metal surfaces, a gasket according to any one of the preceding claims; and expanding the expandable body towards or into the discontinuity in the metal jacket to force opposing sections of the metal jacket adjacent the discontinuity against the metal surfaces to form the seal.

28. A method according to claim 27, wherein the expandable body forces apart the opposing sections of the metal jacket to form the seal during a transition from a starting equilibrium configuration of the expandable body towards or to an alternative equilibrium configuration of the expandable body.

29. A method according to claim 28, wherein the expandable body is prevented from reaching the alternative equilibrium configuration by one or both of the opposing first and second surfaces, or a sealing groove therein, whereby the expandable body reaches a configuration intermediate the starting equilibrium configuration and the alternative equilibrium configuration in which the expandable body exerts spring forces on the opposing sections of the metal jacket.

30. The method according to claim 29, wherein the configuration of the expandable body intermediate the starting equilibrium configuration and the alternative equilibrium configuration is resiliently biased towards the alternative equilibrium configuration.

31. A method according to any one of claims 27 to 30, wherein, at least prior to expansion, the outer surface of the ring-shaped body has a radial cross section that comprises a concave portion facing the discontinuity in the metal jacket, and at least during an initial stage of expansion, the curvature of the concave portion of the radial cross section of the outer surface of the expandable body reduces, thereby forcing the opposing sections of the metal jacket adjacent the discontinuity against the metal surfaces.

32. A method according to any one of claims 27-31 , wherein the first metal surface comprises a sealing grove and providing the gasket between the first and second metal surfaces comprises locating the gasket within the sealing groove.

33. A method according to claim 32, wherein inversion or flattening of the curvature of the concave portion of the radial cross section of the outer surface of the expandable body is limited by contact of the expandable body with a sidewall of the sealing groove.

34. A method according to claim 33, wherein the in the concave portion of the radial cross section of the expandable body is straightened against the sidewall of the sealing groove during expansion of the expandable body.

35. A method according to any one of claims 32 to 34, wherein the sealing ring is accommodated within the sealing groove without protruding therefrom in a direction perpendicular to the first metal surface, the method further comprising positioning the second metal surface over the first metal surface to cover the sealing groove.

36. A method according to any one of claims 27 to 35, further comprising coupling components on which the first and second metal surfaces are provided to prevent relative movement between the first and second metal surfaces during the expansion of the expandable body.

37. A method according to any one of claims 27 to 36, wherein the first and second metal surfaces are provided on respective angular segments of a vacuum chamber.

38. A method according to any one of claims 27 to 37, wherein the expandable body is bistable, the method further comprising causing the expandable body to transitionbetween alternative stable configurations, whereby during the transition, the expandable body forces apart the opposing sections of the metal jacket to form the seal.

39. A metal-to-metal seal formed between two opposing metal surfaces using the method of any one of claims 27 to 38.

40. A vacuum chamber comprising one or more metal-to-metal seals according to claim 39.

41. A vacuum chamber according to claim 40 and comprising a plurality of angular segments arranged to enclose an inner volume, the one or more metal-to-metal seals being formed between pairs of the angular segments.

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