Abstract: A method is provided for releasing a thin foil workpiece from adherence with a resilient surface to which it adheres due to compression occurring in a forming operation. The method includes the steps of applying pneumatic pressure greater than ambient pressure between the first forming element and the workpiece while the workpiece remains held by compression. Thereafter, a second surface of a second forming element is separated from contact with the thin foil workpiece, removing compression, and rapid or shock release of the thin foil workpiece from its adherence to the resilient surface ensues. An alternative method is further provided.

Abstract: A self-contained apparatus for forming metal sheet is adapted for operation within a standard double action press having a base and outer and inner vertically reciprocating slides. A basic die is mountable to the press and specific tooling is replaceably mountable to the basic die. The basic die includes a riser, a manifold and hydraulic cylinder assemblies. A sheet metal blank is positioned on the lower die and is clamped between the upper and lower dies whereby the periphery of the blank is gripped between a male and female bead mounted all around a part print cavity. The cylinder assemblies cause hydraulic fluid to be forced into a region between the clamped blank and the lower die and form the blank in the part print cavity. The male bead exerts varying control on the sheet to allow it to stretch across portions of the cavity while flowing into other portions of the cavity.

Abstract: A method for augmenting an apparatus with pumps and a high pressure multiplier in such a manner that the apparatus can be altered to perform as a draw die press, hydroform press, tube bender, and as a hydraulic bulge form press by utilizing appropriate quick change platens.

Abstract: A method for generating an underliquid shock pressure comprises the steps of igniting a combustible mixture gas to form detonation waves, imploding the detonation waves in their advancing direction, propagating a pressure obtained by imploding the detonation waves to a liquid, and converting the pressure to an underliquid pressure which is applied to a workpiece. The pressure obtained by imploding the detonation waves may be applied directly to an elastic rubber body, thus converting the pressure to an underelastomer shock pressure, which is then applied to the workpiece via the elastic body.

Abstract: A device is provided for drawing sheet materials, in particular, sheet blanks. The device includes a cushion of elastic material disposed in an enclosure, a die for forming the sheet blank, the die having a peripheral portion constituting an upper blank holder. The device also includes a lower blank holder for supporting and maintaining at least a portion of the sheet blank which is placed directly on the cushion of elastic material and cooperates with the upper blank holder for clamping the sheet blank in at least localized zones. The lower blank holder bears against a slidable element disposed around lateral faces of the cushion.

Abstract: Elevated temperature envelope forming includes enclosing a part blank and form tool within an envelope sealed against the atmosphere, heat treating the combination while forming pressure holds the envelope and part against the form tool, and allowing part cool down to occur in an inert atmosphere with forming pressure removed. The forming pressure is provided by evacuating the envelope and may be aided by differential force applied between the envelope and the form tool.

Abstract: Device for pressing sheet material blanks, in particular sheet metal blanks (10), comprising a cushion (2) composed of an elastic material disposed in a retaining box (1), an arrangement for performing the sheet blank constituted by an outer slide carrying an upper blank holder (6), and an arrangement for finally forming the sheet blank constituted by a central slide acting on a punch (8), the device further comprising a lower blank blank holder constituted by an element (3) for supporting and maintaining at least a portion of the sheet blank (10), placed directly on the elastic cushion (2) and cooperative with the upper blank holder (6) for gripping the sheet blank in at least localized region of the blank.

Abstract: Method for pressing sheet material, in particular sheet metal, on a press by way of a cushion (12) composed of an elastic material, comprising disposing a sheet blank (20) to be formed on a support whose peripheral part forms a lower blank holder (2) and whose central part constitutes a die (3), applying, under the action of an outer slide, an upper blank holder (9) on the peripheral portion of the sheet blank (20), then applying a punch (11) under the effect of a ram, the method further comprising, in the course of a first step, applying, under the action of the ram, the cushion (12) on the sheet blank (20) for preforming the sheet blank in such manner as to impart thereto a surface area substantially equal to the surface area of the finished part to be obtained, then, in the course of a second step, continuing, under the action of the ram, the descent of the elastic cushion (12) and simultaneously displacing all or a part of the bottom of the die (3) for achieving the final shaping of the part.

Abstract: A rotor (1) of a screw hydraulic downhole motor, made as a hollow multiple-start screw featuring a substantially constant wall thickness. The ratio of the length of the rotor (1) cross-sectional outside contour to the length of the circumscribed circle of the contour is substantially within 0.9 and 1.05. When making the rotor (1) a forming element is inserted into a tubular blank, and a fluid pressure is applied to the outside blank surface. A device for making the rotor comprises a hollow housing accommodating a forming element installed on centering bushings. The bushings have fitting areas adapted for the ends of the tubular blank to fit thereon.

Abstract: Method of protecting selected parts of a component against overheating while the component is being thermally treated.

Abstract: A method is provided for uniformly fitting a foil to a die in the manufacture of a porcelain-metal dental restoration, the method including the application isostatic pressure to a foil covered die. The inventive method is more economical and not as laborious as prior art methods, and provides a superior fit of the foil to the die, resulting in a better quality restoration.

Abstract: Process for press-forming sheet materials and in particular metal sheets on a double-action press of the type comprising a cushion (5) of an elastically yieldable material, the process comprising disposing the sheet on a support, applying a first outer slide (1) on the peripheral portion of the sheet (4), then applying a second central slide (10) on a central portion of the sheet, the process further comprising disposing the peripheral portion of the sheet on a lower blank holder (3) forming a tank for the cushion (5) and having an upper surface (6) for maintaining the sheet and located at a higher level than the level of the working surface (7) of the cushion (5), applying the first outer slide, which has a body (8) having a cross-section less than the lower blank holder (3) and includes on its periphery an upper blank holder (2) cooperative with the lower blank holder (3) for gripping the sheet (4), continuing the descent of the outer slide (1) against the cushion for turning up an edge portion (20) of the

Abstract: A press for shaping a sheet metal blank in a cavity with a forming tool which determines the shape of the finished product. The sheet is pressed against the tool by a diaphragm which is influenced by a pressure medium on the side facing away from the cavity. The forming tool consists of an inexpensive casting material supported in a cup-shaped container. The space between the bottom and sides of the container and the bottom and sides of the cavity is filled with an elastic material.

Abstract: A process for manufacturing a spherical shell from a blank utilizing dies, comprising the steps of forming and clamping a flange portion of the blank by pressing with the dies and applying fluid pressure to an elastic diaphragm or flat metal sheet to cause the diaphragm or sheet to bulge the blank so as to form a curved shell surface.

Abstract: A method for the manufacture for the tubes or shafts of a composite material and having a low weight, whereby a blank of a material that can be pressformed and which has a substantially even thickness of material is subjected to isostatic pressing on or in a formation tool thereby providing a shell or a liner (15) of an intended shape and profile and having a mainly by substantially thickness of material, and on or in said shell or liner (15) another material is applied and is bound, for instance a highstrength material like glassfiber, carbon fiber or aramide fiber, so that the liner (15) and said other material (17) provide a solid integral composite tube or composite shaft.

Abstract: A press plant with a forming press of the pressure cell type for enhancing the forming space of the press, especially with regard to depth, which is accomplished according to the invention in that the tray has a planar bottom plate with a detachable tray frame resting thereon, the axial loads induced by the working pressure on the short ends of the tray frame in this manner being absorbed by an annular frame or the like, whereby the forming space of the inventive press plate will not be restricted by working pressure dependent dimensioning factors.

Abstract: A forming press of the pressure cell type comprising a press stand with two opposing force absorbing elements defining between them a working space into which a trough with forming tools and workpiece can be inserted; a press plate in communication with a pressure medium source; a diaphragm forming together with the press plate an expansible pressure cell; and side pieces extending along the side surfaces of the working space while keeping the diaphragm in abutment against a sealing ring disposed around the periphery of the diaphragm, said sealing ring in turn abutting against the press plate, providing thereby a quicker and simpler diaphragm exchange as compared to prior art constructions by the side pieces being turnable so that when upwardly swung, their long sides abut against the underside of the diaphragm, and by means for moving the unit formed of upwardly swung side pieces and diaphragm out of the working space; the invention also including a process for changing diaphragms in said forming press.

Abstract: A method of bonding and shaping a plurality of pieces of material disposed in a fluid tight container includes providing a housing having components with different coefficients of thermal expansion. The container is positioned between upper and lower sections of the housing. The housing is then enclosed in an autoclave. The fluid in the autoclave and housing is heated with a resulting increase in the fluid pressure in the autoclave and housing. As the temperature and pressure in the housing is increased, the joint between the container and the housing sections is sealed by pressing the upper and lower sections of the housing against the container under the influence of forces resulting from different amounts of of thermal expansion of components of the housing. Thereafter, the fluid pressure in the autoclave is increased. Since the joint between the housing and the container has been sealed, the further increase in fluid pressure is applied to only the upper side of the container.

Abstract: A press of pressure cell type comprises a press stand with two opposing force-absorbing elements between which a space is formed. In this space there is located a plate with a recess in which an elastic diaphragm is arranged. The diaphragm forms, together with the plate, a pressure cell. Elongated side supports for the diaphragm are provided at the sides of the said space. A tray insertable into the space forms, together with the plate and the diaphragm, a closed press space. The pressure cell is connected to a pressure medium source. Each side support is formed with an elongated recess, in which there is arranged an expansible membr of elastic material. Each expansible member forms a side support for a press tool located in the tray.

Abstract: An apparatus and method for radially expanding a tubular member and comprising first and second spaced apart end caps rigidly connected to each other by a post. An expandable bladder fixed to each end cap and extending around the post to define an annular space. A propellant disposed in the annular space and ignition apparatus associated with the propellant. The propellant being of the type which burns rapidly to generate large amounts of gas for expanding the bladder. The tubular member being disposed around the bladder for radial expansion.

Abstract: A press comprising a press stand, a pressure cell arranged in the press stand with an elastic diaphragm and a tray-shaped tool-carrying member, insertable into the press, in which a forming tool and a workpiece are located. In the inserted position of the tool-carrying member in the press, a closed working space is formed between the pressure cell and the tool-carrying member. The diaphragm is placed in a recess in a press plate. The seal between the diaphragm and the press plate consists of a U-shaped sealing ring having flanges directed inwards towards the center of the pressure cell.

Abstract: Metal articles are shaped by contacting a metal blank with a diaphragm of plastically deformable metal which may be superplastic aluminium and urging the diaphragm against the blank and against a mould so that the diaphragm and body are deformed. The mould may be male or female. Thin metal articles of complex shape may be made easily and cheaply.

Abstract: A hydraulic press with a pressure cell comprises a tray-shaped press plate with a bag-like diaphragm and a forming rubber pad and a press tray for a forming tool and a workpiece. The end wall portions projecting from the mid portions of each of the press plate and from the base of the press tray, provide thickness transitions which define a cavity in the operating position of the press tray. Between the press plate and/or the base of the press tray and the confronting force-absorbing surfaces of the yokes of the press frame of the press, play is provided in a portion above and below, respectively, the thickness transitions. This play allows the high stress levels which would otherwise arise at the thickness transitions to be reduced.

Abstract: Method for the manufacture of a conical tubular member, and a conical tubular member manufactured according to the method, wherein as a first step a tubular member is formed having inwardly directed profilings (2, 2', 3, 3'), and said member thereafter is placed over a core with grooves arranged to receive said profilings (2, 2', 3, 3') and having a conical shape substantially corresponding to the internal shape of the member to be manufactured. By means of hydraulically and/or pneumatically applied force, divided over the surface of the tubular member by means of at least one flexible pressure applying member arranged surrounding the tubular member, said member is thereafter formed into a conical shape corresponding to the shape of the core, the reduction in diameter of the member being compensated for by means of a change in the shape of the profilings (2, 2', 3, 3'). The member is advantageously manufactured from a material having through perforations, or a wire mesh material.

Abstract: Method for producing structures from metal workpieces which may or may not be capable of superplastic forming, such as titanium alloy and steel, using a forming die having a predetermined contour or shape and a cooperating pressure diaphragm formed of a metal capable of superplastic forming. Fluid pressure is applied to one side of the pressure diaphragm to cause stretching or expansion thereof by superplastic forming, and forcing the diaphragm against the workpiece, which in turn is caused to move or expand into contact with the forming die, to produce a structural component of predetermined shape. With the proper application of pressure, temperature and time, metal parts, e.g. 8 to 12 inches thick, can be formed in addition to parts formed from comparatively thin sheet metal.

Abstract: A rotating die system for cold forming of sheet metal wherein a male die rotates relative to both an hydraulically supported resilient diaphragm backing the sheet metal blank and the driving force on the male die. The male die is pivotly connected to both a draw ring and the transmitted driving force. A sheet of metal to be formed is held in place on the upper surface of a draw ring die over a forming aperture. The male die is caused to rotate within the aperture against the sheet metal to accomplish the desired forming.

Abstract: A moulding tool unit for semi-isostatic compaction of a powder has a mould cavity (14) defined by an elastomeric jacket (121). The jacket (121) is surrounded with clearance by an elastomeric sleeve (122) which is sealingly joined to the jacket (121). The space (123) between the sleeve (122) and jacket (121 ) is filled with an isostatic pressure translating medium such as a hydraulic liquid (127). The jacket (121) may be supported in a direction towards the sleeve (122) by a stiff jacket (125) having perforations (126) through which the hydraulic liquid (127) can flow. The unit is adapted such that for a pressing operation it can be inserted with a small clearance and pressurized in the dry pressing chamber of a hydraulic press.

Abstract: A pipe and sleeve telescoped joint with the pipe and sleeve in sealing engagement and keys embedded in both pipe and sleeve at their interface. The size and number of the keys are calculated from the size and strength of the pipe. The sleeve is sized and its strength selected from the strength of the pipe, and the sleeve ends are shaped to hold the joint circular when it is made. The apparatus includes means for holding the midportion of the sleeve circular when creating the joint, and for cooperating with the sleeve ends to keep them circular. The sealing engagement is created by firing a propellant into a substantially incompressible medium, like water, held by the apparatus in a cavity about the sleeve, and a piston separates the explosive propellant from the pressure medium.

Abstract: A machine for use in forming ductile metal sheets into shaped bodies having first and second open-ended, annular chambers which are relatively movable, while maintaining their open ends in register with one another, between a position in which the open ends meet and a position in which the open ends are spaced apart, a plate in at least one of the chambers which is movable independently of both chambers in directions parallel with the directions of relative movement between the chambers between a first position in which it constitutes a gas tight sealed base for said one chamber and a second position in which it is adjacent the open end of that chamber.

Abstract: A press operating with hydraulic pressure comprises a pair of relatively movable components (8, 11) which during a pressing operation carry out a relative movement which is sensed. By use of the sensed relative movement a control signal is generated which is used for regulating the hydraulic pressure so that this is caused to vary with the relative movement according to a certain functional relationship. For generating the control signal a manually programmable electrical function generator (23) is provided, preferably a panel (29) comprising plug contacts (34), on which a plurality of pairwise associated pressure and movement values, constituting electrically and visually readable points in the desired functional relationship, can be set up.

Abstract: A die construction for forming or reforming a fan blade to press dies in which opposed dies have cooperating cavities to form a recess to receive the blade, at least a part of one of the cavities having a diaphragm welded thereto to form a chamber beneath the diaphragm so that by pressing the chamber the adjacent part of the blade will be shaped against the surface of the opposing recess.

Abstract: An apparatus for calibration of tubular articles, especially cylinder linings for internal combustion engines, manufactured through isostatic compression of pulverulent metallic materials, comprises piston means for effecting an axial displacement between the tubular article and a mandrel which it surrounds during the calibration. Preferably, the tubular article is first subjected to a rather modest radial inwardly directed pressure which is increased after an axial relative movement between the mandrel and the tubular article has taken place.

Abstract: A hydraulic press elastic stamping tool having a tool body with a recess wherein is situated a flat elastic diaphragm whose flange makes contact with the tool body, forming a closed chamber. That chamber communicates with a source of working fluid under pressure through ducts in the tool body. The end portions of the diaphragm flange form, in conjunction with the main body of the diaphragm, an aperture closed at one end and dimensioned several times smaller than the thickness of the diaphragm. The aperture, in cross section thereof, is smoothly curved with respect to the plane of the diaphragm toward the bottom of the recess and the closed end of the aperture is situated in the zone which is not subjected to tension strain when working fluid is delivered under pressure into the chamber.

Abstract: A metal sheet is deformed to produce a blank which has one side which is smooth and another side which is ornamented with a pattern of raised and/or depressed areas. The blank is deformed to produce a cooking vessel which has the ornamented side located on its exterior surface.

Abstract: A hydropunch comprises a cylinder, with one end thereof facing the working surface of a die intended for positioning thereon a workpiece to be treated. Accommodated inside the cylinder and forming an above-the-ram chamber and a below-the-ram chamber is a ram which is actuated by means of a suitable actuator mounted on that end of the cylinder which is opposite to the aforementioned end thereof, the ram being connected with a system for returning the ram to its original position. In addition, the hydropunch includes a compressed gas receiver communicating with the above-the-ram chamber of the cylinder, and a cover adapted for closing both the cylinder and receiver. In accordance with the invention, the system for returning the ram to its original position comprises a closed chamber communicating with the below-the-ram chamber of the cylinder, and a value intended for communicating the above-the-ram chamber with the atmosphere.

Abstract: An apparatus for calibration of tubular articles, especially cylinder linings for internal combustion engines, manufactured through isostatic compression of pulverulent metallic materials, comprises piston means for effecting an axial displacement between the tubular article and a mandrel which it surrounds during the calibration. Preferably, the tubular article is first subjected to a rather modest radial inwardly directed pressure which is increased after an axial relative movement between the mandrel and the tubular article has taken place.

Abstract: Disclosed is an improved method of fabricating boron fiber and aluminum matrix composite structures, especially gas turbine compressor blades having titanium metal skins. Titanium skins and boron aluminum composite cores are preformed by gas pressure and hard dies prior to hot pressing. The composite sheets of the core are preformed with the use of expendable carrier sheets, which hold the stacked sheets firmly as both the carrier sheets and composites are shaped through moderate temperature and gas pressure against a hard die. The preforming permanently shapes and lightly bonds the composite sheets. The skins are preformed in an analogous process using gas pressurization of a metal envelope into die cavities. The skins and composite core are then hot pressed in hard dies to form the finished part.

Abstract: Methods for shaping metallic workpieces which utilize a single faced die and the use of heat and pressure to conform the article to the shape of the die surface by creep forming.

Abstract: In a hydraulic press for forming sheet material, a vertically extending forming cavity is formed in a horizontally extending press stand between a pair of spaced forming pads extending between the inner surfaces of the press stand, and an elastically deformable member extends between the respective end of each of the forming pads for supporting the same. A tool carrier, with an upstanding tool support member having a tool forming depression on each side thereof on which sheet material is formed, is movable into and out of the forming cavity on respective support and guide rails which are engaged by respective support and guide rollers on the tool carrier. The tool carrier divides the forming cavity into a pressure seal on each side of the upstanding tool support member. A pressure medium is injected into each of the pressure cells to form the sheet metal.

Abstract: A method for fabrication of honeycomb metallic structures combining superplastic forming and metallurgical bonding wherein a face sheet is formed and bonded to another face sheet and a core to form the desired structure. A metal honeycomb core is positioned between the first and second metal face sheets. The first face sheet, which has superplastic characteristics, is brought to within a temperature range suitable for superplastic forming. A pressure loading is applied to the first face sheet causing it to deform against the core and second metal face sheet. The face sheets and core are maintained under coordinated temperature-pressure-time duration conditions to produce metallurgical bonding to one another to form the desired honeycomb structure.

Abstract: Each of the ends of an elongated plate-formed attachment member, to which is attached a diaphragm and a press pad, is connected to a transportation unit which allow for the plate-formed attachment member to be moved into and out of a press stand along suitably provided tracks. The transportation units include bogies and connection units mounted on the bogies which support the plate-formed attachment member. The connection units include bearings so that the plate-formed attachment member can be rotated when positioned outside of the press stand, and at least one of the connection units include lifting cylinders to raise and lower the plate-formed attachment member as appropriate.

Abstract: A press for molding large sheets around a forming surface which includes an elastic press pad, a first frame member on the side of the press pad away from the working surface thereof, the first frame member having a top wall and side walls forming a pressure cell area therebetween, an elastic diaphragm in the pressure cell area in contact with the press pad, a second frame member formed in a generally L-shaped configuration to encompass and hold an annular bead of the elastic diaphragm, a trough-shaped supporting member positioned adjacent the end walls of the first frame member and the press pad such that a gap is formed between the end walls and the supporting member, a movable seal strip positioned in the gap to prevent the press pad from being pressed out of the pressure cell area when the elastic diaphragm is expanded, and a supporting strip attached to the end walls of the first frame member at a point within the pressure cell area to secure the press pad within the pressure cell area.

Abstract: The invention covers a method of and tools for producing structures from suitable materials which are sequentially formed superplastically and then diffusion bonded using forming dies that are flexible to conform to desired contours imparted to the mating dies, which can accommodate compound curvatures, and which utilize fluid pressures internal to the tool to force the dies to conform as well as to achieve forming and bonding. The tools consist of a forming die providing contoured cavities or recesses for shaping a superplastically formable component, a flexible die having a shape of the finished structure and cooperating with the forming die, a fluid container for pressure fluid to operate the flexible die, and a retaining structure that cooperates with the forming die to contain and direct the forming pressure in the desired manner.

Abstract: In a hydraulic press which has an expansible pressure cell arranged in a cavity and a pad of elastic material for forming workpieces, with a trough-shaped supporting member for forming tools and workpieces, displaceable into and out of the press, the press includes a second pressure cell arranged below the trough-shaped supporting member, positioned in a cavity formed between two discs which form supporting members for the trough-shaped supporting member.

Abstract: A press for molding large sheets around a forming surface which includes an elastic press pad, a first frame member on the side of the press pad away from the working surface thereof, a pressure cell formed between the press pad and the first frame member, the pressure cell containing an elastic diaphragm in contact with the press pad, a second frame member formed in a generally L-shaped configuration to encompass and hold an annular bead of the elastic diaphragm, mounting bolts for adjusting the positioning of the second frame member with respect to the first frame member, and channels in the first frame member for supplying a pressure medium to a pressure zone between the first and second frame members and the elastic diaphragm.

Abstract: The disclosed hammer comprises a power frame, having a working chamber for the deforming medium, a die block adapted to accommodate therein a blank and an impact head with a housing having fastened therein a hollow separating bush coaxial with the housing. Received concentrically within this bush is a sleeve enclosing a plunger mounted in this sleeve for vertical reciprocation, to define a working cylinder between the top end face of the plunger and the bottom of the sleeve. An annular space is defined by the housing of the impact head and the body of the separating bush, surrounding the working cylinder and communicating with the hydraulic hammer control system. The essence of the invention consists in that the working chamber for the deforming medium, has a built-in container having a bottom made of an elastic material. The container is mounted for cooperation of its bottom with the blank accommodated in the die block.

Abstract: Nuclear fuel rod cladding tubes are sized internally to diameters precisely fitting nuclear fuel pellets with which the tubes are charged, by externally applying hydraulic pressure to short lengths of each tube, the pressure being applied while the tube is stationary and the tube then moved to bring a new length within the hydraulic pressure zone. The volume of the hydraulic liquid used and the pressure applied to this liquid is such that the liquid is compressed slightly so that the length being sized yields, the expansion of the liquid then completing the sizing. The lengths being sized step-by-step are internally supported by either the fuel pellets or a mandrel having the same diameter as the pellets.

Abstract: A pair of mating die halves are employed to die form an elongate strip or ribbon composed of material capable of undergoing plastic deformation. The first die half is an elongate, substantially rigid member having a die face of predetermined configuration. The second die half is an elongate, flexible die member having a die face of configuration complementary to the die face of the rigid die half. The die face of the rigid die half is fed into registering relationship along a substantially straight path with the die face of the flexible die half. The flexible die half is fed toward the rigid die half along an arcuate path until it registers with the rigid die half, after which it is fed along a straight path parallel to that of the rigid die half. The elongate ribbon to be formed is fed between the die halves as the latter are fed into registration.

Abstract: Fluid forming apparatus having a constant-volume pressure cavity has oppositely movable rigid forming tool parts, each connected with a piston comprising a double acting cylinder mechanism. Forming pressure is developed by hydraulically forcing one tool part in the direction that tends to reduce cavity volume, thus, by reaction, forcing the other tool part in the opposite direction against restraint. A cam mechanism moving with said one tool part defines a pressure program. Sensor means, cooperating with the cam and with pressure regulating valve mechanism, controls pressure of the fluid driving said one tool part in accordance with the program and the position of that tool part.

Abstract: A hydraulic press includes a pressure cell which includes a diaphragm of flexible material with an opening therein surrounded by an annular bead. There are two disc-shaped attachment members for the diaphragm which form between them a first annular groove which fits the bead. The bead and one of the annular members have opposed annular recesses therein, which face a surface of the other annular member. These thus form an annular channel, in which are arranged two sealing rings, one fitting between the bead and one of the attachment members and the other fitting between the two attachment members.