Tube coupling

Abstract: A tube or pipe coupling joint structure comprises a pair of spaced flanged members (12,14) adapted for relative movement towards each other along a longitudinal axis (18). Each of the flange members (12,14) has a face surface (26,26') which is a surface of revolution about the longitudinal axis (28) with the face surfaces on the respective flange members being located in opposed relationship to each other. A relatively smooth thin metal gasket (30) is positioned between the opposed face surfaces (26,26') of the flange members and each of the face surfaces comprises a sealing protrusion (50,50') and a stop surface (54,54') for limiting penetration of the sealing protrusion into the gasket (30). Each stop surface (54,54') lies radially outwards of the associated sealing band (52,52') and is inclined at an angle in the range of 3 to 15 degrees relative to a plane normal to the longitudinal axis (28).

Description: The invention relates to tube or pipe joints and couplings and, more particularly , to a metal gasket or seal coupling arrangement. The invention is especially suited for use in high vacuum systems and will be described with reference thereto; however, the invention could be used in a variety of types of pressure and vacuum systems. The typical coupling used in vacuum systems comprises opposed flanges with axially extending circumferential beads or protuberances arranged to engage with the opposite faces of a thin metallic gasket (US-A-3 521 910). During joint make-up, the flanges are driven axially together causing the beads to penetrate the gasket and form seals therewith. The degree of bead penetration must be relatively closely controlled to produce a good seal. For example, if penetration is inadequate, an effective seal is not produced. Similarly, if penetration is too deep, it is possible to cut through the gasket and totally lose the seal. The forces required to produce the proper penetration tend to vary widely depending upon the specific size and cross-sectional configuration of the protuberance, as well as upon the gasket material. As the forces increase, the components of the coupling body must be made increasingly heavier to handle the increased forces. Attempts at reducing the forces required to produce the necessary penetration have often resulted in a fitting wherein there is no distinct point at which the fitting has a "feel" of final make-up. The problem with this lack of a distinct "feel" is that the person making-up the joint will sometimes continue tightening the coupling components until cutting through the gasket results. In addition to the above noted difficulties, the prior sealing face designs sometimes result in producing a seal in which the seal components produce entrapment areas or pockets wherein particles can accumulate. In many processing systems, such entrapment areas are totally unacceptable. An object of the invention is to overcome the above-discussed problems and to provide an improved coupling or joint structure assembly especially suited for use in vacuum systems. WO-A-89/03495 discloses in Fig. 4 a joint structure especially suited for vacuum systems and of the kind comprising; a pair of flange components adapted for relative movement towards each other along a longitudinal axis, each of the flange components having an end face normal to the longitudinal axis; and a metal gasket positioned normal to the longitudinal axis between the end faces of the flange components, each of the end faces having a circumferentially continuous sealing protrusion for engaging the gasket with the protrusions being positioned in aligned opposed relationship at opposite sides of the gasket, and each of the end faces also having a flange face surface to constitute a stop surface for limiting penetration of said sealing protrusions into said gasket, each of said sealing protrusions being located at a distance (d) axially proud of the portion of the respective stop surface which is radially closest to the sealing protrusion. In this joint structure, the sealing protrusions are in the form of sealing beads and the metal gasket has on each side a surface of revolution whose profile is substantially a quarter circle conforming to the profile of the sealing protrusions. The stop surfaces are located radially inwardly of the sealing protrusions and are normal to the longitudinal axis. EP-A-0439328, claiming a priority date of 23 January 1990 and published on 31 July 1991, discloses a joint structure having a smooth flat metal gasket positioned between flat sealing bands provided on the sealing protrusions of the flange components. According to the present invention, a joint structure of the above-mentioned kind is characterised in that the metal gasket (30) is smooth and flat before compression and each said protrusion (50,50') comprises a flat sealing band (52,52') having a radial width (W) substantially normal to said axis (28), and in that each stop surface (54,54') is located radially outwardly of its respective sealing band (52,52') and is inclined axially away from the gasket by an angle in the range of approximately 3 to 15 degrees. Preferably, and in accordance with a somewhat more limited aspect of the invention, the sealing band is located at a distance d in the range of 0.05 to 0.30mm (0.002 to 0.012 inch) axially outwards of the stop surface portion which is radially closest to the sealing band. Preferably, and in accordance with a further aspect of the invention, the sealing bands connect to their associated stop surface by an arcuate transition surface. Preferably, and in accordance with yet another aspect of the invention, the radially innermost portion of each sealing band extends axially outwardly by a distance at least as great as the remaining portions of the associated sealing band such that the sealing band is normal or inclined relative to the longitudinal axis at an angle no greater than 3° relative to the normal. The invention will be further described, by way of example, with reference to the accompanying drawings, wherein: Fig. 1 is a longitudinal sectional view through a tube coupling which incorporates features of the invention; Fig. 2 is an enlarged longitudinal sectional view showing the sealing rib configuration; Fig. 3 is an enlarged view of the circled area of Fig 1; and Fig. 4 is a view like Fig. 2 but showing a modified form of sealing rib construction. Fig.1 shows the overall arrangement of a coupling assembly 10 particularly suited for joining tubing in either vacuum or pressure systems. The coupling assembly 10 could take a variety of specific configurations and structural arrangements but, in the illustrated embodiment, it comprises a pair of substantially identical tube coupling components 12 and 14 which are joined in the aligned mated relationship shown by a cooperating pair of threaded nut members 16 and 18. The first coupling component 12 includes first and second cylindrical sections 20 and 22 which have a centrally extending through passage 24. The first coupling component 12 terminates in first and second end faces 25 and 26, respectively. In the embodiment under consideration, each of the first and second end faces 25, 26 is substantially perpendicular to the axis 28 of the passageway 24. The end face 25 illustrated is intended to be butt welded to an associated fluid line. Other types of end fittings or connectors could be used to join the associated lines to the coupling component 12. The second coupling component 14 is identical to the first coupling component 12. Accordingly, it has been identified with the same reference numerals used with respect to the coupling component 12 but differentially therefrom through the addition of prime suffixes. The tube coupling components 12 and 14 are retained in their aligned relationship and driven axially towards one another to sealingly engage on opposite sides of a thin annular metal gasket 30. The means for maintaining the coupling members 12 and 14 in the relationship shown and producing the required axially directed sealing forces comprise the previously-mentioned conventional threaded nut members 16 and 18. The first nut member 16 has a somewhat cylindrical body 32 with a central, axially extending passage 34 formed therethrough. Passage 34 is only slightly larger in diameter than the exterior of the cylindrical section 20 so that the coupling component 12 can be closely and freely received therein. The left-hand end of the member 16 has a hexagonal configuration so that it can be gripped with a suitable wrench for threadingly driving it into engagement with nut member 18. The right-hand end of the nut member 16 has an end face 36 having a counter-bored section to receive a radially extending flange 23 formed on the coupling component 12 between the cylindrical sections 20, 22. The exterior of the cylindrical section 32 of nut member 16 is provided with suitable threads 38 which cooperate with the nut member 18. In this embodiment, member 18 comprises a female nut having a hexagonal exterior 40 and an inwardly open chamber section 42 which is provided with threads 44 adjacent its left-hand or inlet end. The right-hand end of the member 18 has an opening 46 sized to receive the cylindrical section 20' of coupling component 14. This allows the bottom of the chamber 42 to act against the flange 23' such that, during tightening of the nut members 16 and 18, the end faces 26 and 26' of the coupling components 12 and 14, respectively, are driven into sealing engagement with the opposite faces of the annular metal gasket 30. The general coupling components thus far described are relatively conventional and well-known. Additional structure is sometimes included in these particular types of coupling. For example, as shown in the co-pending European Patent Application No. 91300475.0 (EP-A-0 439 328), various drive members or anti-torque members can be incorporated to prevent transmission of torque from the coupling nuts to the sealing end faces of the coupling components. Likewise, it is well-known to provide various forms of gasket-retaining devices to locate and retain the gasket 30 in proper position relative to the sealing end faces during assembly and disassembly of the coupling. Such additional features and structures can be included with the coupling of the invention. A feature of particular importance to the present invention is, however, the particular shape and arrangement of a sealing rib and sealing end face provided on the end faces 26, 26' of the coupling components 12 and 14. In the past, a typical sealing rib or protrusion has comprised a semi-circular bead formation. Alternatively, many such couplings have used a somewhat sharp-edged, V-shaped rib. With both of these two prior standard designs, there has been difficulty in assuring proper make-up of the coupling and/or in providing a proper feel so that the assembler recognises when make-up is complete or has been sufficiently carried out. In fact, under certain environments, it has been possible to inadvertently drive the sealing bead completely through the gasket. The sealing rib of the invention is arranged so that it provides a design wherein the forces required for make-up are not unduly high and, further, a distinct feel is provided to assure that the assembler knows when make-up or proper sealing has been achieved. Because the forces are generally less, the sizes of the coupling nuts and associated structure can be somewhat reduced. Referring in particular to Figs. 2 and 3, the preferred form for the annular sealing rib is shown in detail. The sealing face 26' has a circumferentially extending sealing rib 50' positioned closely adjacent the central passage 24'. As shown in Fig. 3, this assures that sealing takes place close to the bore line of passage 24'. This is desirable since it reduces fluid entrapment areas and provides a smooth flow area through the coupling. In the preferred embodiment, the annular sealing rib 50' has a substantially flat outer sealing surface 52' which is circumferentially and radially continuous and has a radial extent in the range of 0.38 to 0.89 mm (0.015 to 0.035 inch) in width. With this width, the force required to produce sealing penetration of the face into the associated gasket 30 is reduced by about 15% to 50% compared with most prior designs. For further example, with such a fitting suitable for 6.35mm (one-quarter inch) tubing, the inner edge of the sealing surface 52' is preferably located on a diameter of 4.62mm (0.182 inch) and the outer periphery of the sealing surface 52' is located on a diameter of 5.77mm (0.227 inch) so that the band has a width of 0.58mm (0.023 inch). As previously discussed, the sealing surface 52' is preferably in a plane which is perpendicular to the axis of the flow passage 24'. Alternatively, however, and as shown in Fig. 4, it is possible for this surface to be inclined from one degree up to as much as three degrees from the perpendicular. That is, the innermost edge can extend axially outwardly beyond the remaining sealing surface and the sealing surface has the shape of a very shallow truncated cone. The surface finish R A of the sealing surfaces 52, 52' is preferably 25 to 125 micrometers (1 to 5 microinches). By making the sealing surface with the one to three degree incline, the opposed surfaces 52, 52' can be brought into direct engagement and no permanent deformation of the surfaces occurs up to the point that they have compressed into full engagement. Thus, with proper use, these components can withstand many make-ups without damage to the seal surfaces. Associated with the sealing surface 52' and lying radially outwardly therefrom is a second circumferentially continuous surface 54' which functions as a stop surface to limit penetration of the sealing surface into the associated gasket and to provide a rapid buildup in force to produce a distinct feel when proper sealing make-up has been achieved. This stop surface 54' is preferably inclined in the manner shown at an angle of 10 degrees but angles in the range of approximately 3 to 15 degrees from a plane perpendicular to the axis of passage 24' can be used. Thus, when surface 52 has penetrated the gasket 30 to a predetermined depth, the surface 54' comes into engagement with the gasket surface and the forces required to produce penetration increase drastically. If the angle significantly exceeds 15°, penetration to the surface 54' does not result in a distinct feel with respect to proper tightening and overtightening is possible. Preferably, the distance d from the surface 52' to the start of surface 54' is in the range of 0.10 to 0.15 mm (0.004 to 0.006 inch) but a range 0.05 to 0.30mm (0.002 inch to 0.012 inch) appears to be satisfactory for most situations. This assures sufficient penetration to provide a proper seal. The invention has been described with reference to preferred and alternative embodiments.

Claims: A joint structure especially suited for vacuum systems comprising; a pair of flange components (12,14) adapted for relative movement towards each other along a longitudinal axis (28), each of the flange components having an end face (26,26') normal to the longitudinal axis (28); and a metal gasket (30) positioned normal to the longitudinal axis (28) between the end faces (26,26') of the flange components (12,14), each of the end faces (26,26') having a circumferentially continuous sealing protrusion (50,50') for engaging the gasket (30) with the protrusions (50, 50') being positioned in aligned opposed relationship at opposite sides of the gasket (30), and each of the end faces (26,26') also having a flange face surface (54, 54') to constitute a stop surface for limiting penetration of said sealing protrusions (50,50') into said gasket (30), each of said sealing protrusions (50,50') being located at a distance (d) axially proud of the portion of the respective stop surface (54, 54') which is radially closest to the sealing protrusion (50,50'), characterised in that the metal gasket (30) is smooth and flat before compression and each said protrusion (50,50') comprises a flat sealing band (52,52') having a radial width (W) substantially normal to said axis (28), and in that each stop surface (54,54') is located radially outwardly of its respective sealing band (52,52') and is inclined axially away from the gasket by an angle in the range of approximately 3 to 15 degrees. A joint structure according to claim 1, wherein said continuous sealing bands (52,52') are inclined from normal to said axis (28) by no more than three degrees. A joint structure according to claim 1 or 2, wherein each sealing band (52,52') is joined to its associated stop surface (54,54') by an arcuate transition surface. A joint structure according any preceding claim, wherein said axial distance ("d") is at least about 0.05mm (0.002 inch). A joint structure according to any preceding claim, wherein said axial distance ("d") is not significantly greater than about 0.030mm (0.012 inch). A joint structure as claimed in claim 5 including a threaded coupling nut for moving the flange members toward each other. A joint structure according to any preceding claim, wherein a flow passage (24,24') of circular cross-section extends through each end face (26,26') and wherein each sealing band (52,52') closely encircles the respective flow passage (26,26') in the associated end face. A joint structure according to claim 7, wherein the sealing band on each flange face surface extends axially outward to a maximum distance adjacent the flow passage. A joint structure according to any preceding claim, wherein said sealing bands (52,52') have a surface finish (R A ) in the range of 25 to 125 micrometres (1 to 5 Microinches).

Inventors: BABUDER GERALD ALAN, BABUDER, GERALD ALAN
Applicants: CAJON CO, CAJON COMPANY
Application year: 1991
Main classification: F16L19
IPC codes: F16L19