WO1994029620A1

WO1994029620A1 - Sealing gasket device

Info

Publication number: WO1994029620A1
Application number: PCT/GB1994/001170
Authority: WO
Inventors: Klaus Cierocki
Original assignee: Flexitallic Limited
Priority date: 1993-06-04
Filing date: 1994-05-31
Publication date: 1994-12-22
Also published as: GB9311630D0; DE9490171U1

Abstract

A sealing gasket (100), has an annular core (150) with flat parallel major faces (160, 170) on which are formed concentric ridges (180) of equal height defined as minor arcs of national circles having centres below the respective major faces of the core and equally spaced between inner and outer edge (200, 210) of the core, thereby presenting blunt ridge peaks for displacement and localised compression of soft sealing material (220, 230) overlaying the ridges and mitigating damage by cut-through irrespective of clamping force applied to flanges between which it is located. The equi-spaced notional circles have radii increasing away from the edges of the core to reduce groove width towards the centre region and promote seating in this region at lower flange clamping forces.

Description

Sealing Gasket Device

This invention relates to sealing gasket devices of the general type in which a concentrically (or equivalent) multi-ridged hard sealing ring is overlaid by a sealing material which is soft in comparison to the ring so that when the device is placed between flanges drawn together by bolting, the relatively soft sealing material is pressed by the ridges and displaced into the grooves or chambers defined by, and between, the ridges, the chambered material being confined by the ridges against extrusion radially and compressed by the flanges to define a radially extensive region of sealing with the flange and surface in opposition to the clamping force.

In such gasket devices wherein a deformation or displacement of material is required to effect a sealing condition, the onset of sealing that results from applied forces effecting such displacement may be more properly referred to as seating of the gasket, notwithstanding that further increase in applied forces may be desirable or required to act on a seated gasket device to effect operational sealing for large service pressures and temperatures of materials contained by the gasket devices. This specification is mainly concerned with the seating of such gasket devices. Ideally, the sealing material is present in such a volume that when compressed by a suitable clamping force acting by way of the flanges, so that it completely fills the groove chambers and opposes the clamping forces to effect a seating seal with the flange, there is sufficient material to prevent direct contact between the ridges and the flanges but not an excess forming a continuous layer above the top of the grooves and ridges to be extruded by flange clamping forces or blown out by service pressure, or at the very least, represent a wasteful over-use of materials.

However, such ideal situation does not often occur in which a user has complete control over operating conditions and gasket structure to effect such exact filling of the grooves and to facilitate the practicability of such gasket forms the structures in relation to defined operating conditions are determined in accordance with one or more Standards, such as DIN 2697.

In general, the core of the hard sealing ring is parallel-sided except for the superimposed groove-defining ridges of uniform height and relatively sharp triangular form (albeit possibly with minor truncations) to ensure that the softer sealing material is readily displaced into the groove. The characteristic sharp comb¬ like ridges are responsible for such gaskets being known as kamm- profile, or cam-profile, gaskets. For example, in accordance with the above Standard, a groove depth of 0.75mm is defined by triangular ridges of 1.5mm pitch in a radial direction.

Common sealing materials include expanded exfoliated graphite and polytetrafluoroethylene, which materials are compressible plastically between low and higher densities and at high density, when effectively filling the grooves, are compressible elastically to provide seating and, thereafter, sealing under a range of applied compressive loads from the flanges, including recovery where such load decreases in the range.

It is inherent in such a standard gasket structure as outlined that in response to the clamping force applied to the flanges the sealing material is acted upon by all of the ridges simultaneously, to effect its displacement into all of the radially displaced grooves and then effect compression of the material before seating is achieved at all, and that then such seating is achieved across all of the gasket width substantially simultaneously. Also, it is clear that a significant level of clamping force is required to effect such simultaneous displacement and compression as to define seating and that it may require to be increased to effect final sealing for large service pressures and temperatures.

It has been found, however, that gaskets made and used in accordance with such Standard can behave undesirably.

It has been found that when subjected to large forces by way of the flanges, the sealing material is not only displaced by the sharp ridges but sometimes also the sharp ridges break through the material, possibly to contact a flange with damage to the ridge and/or flange face. Although a metal-to-metal seal is formed at the particular flange load resulting in such breakthrough and contact, such a form of sealing is of limited practical value as it results from plastic deformation of the metal parts and provides no recovery to accommodate reduction in operational clamping force, whilst inhibiting the formation of sealing by way of proper compression of the sealing material in opposition to the flange loading.

Even if no contact occurs between the sharp ridges and the flange face, such breakthrough of the sealing material breaks the radially continuous layer into discrete regions which exhibit inferior recovery (in the direction of flange loading forces) in response to reductions in flange loading forces and thus a reduction in operational efficacy.

It has also been found that if high clamping forces are applied to the flanges to the extent that bending of the flanges occurs, different pressures are created within the sealing material at adjacent ridge peaks and the pressure concentrations caused by, and acting on, the relatively thin peak portions of the ridges may result in plastic deformation of at least those portions of the ridges.

As indicated, notwithstanding the ridged nature of the core, it is essentially a rectangular-sectioned gasket element to which seating is effected across the whole surface only when the applied flange clamping force is sufficiently high and with a risk, at high clamping forces, that the flanges do not maintain optimal alignment with the core. It is well known in respect of gaskets per se for sealing between flanges that a generally rounded, raised or convex cross section to a gasket element permits seating to initiate over a smaller area of contact with the flanges, at lower flange clamping forces and with less dependency on precise alignment between flanges and gasket element, with the seated area thereafter spreading radially as flange clamping force increases.

It has been proposed in patent specification GB-A-2010417 (DE 2750351) to combine such a progressively-seating element structure with the sealing material chambering function of a kamm-profile gasket by constructing a kamm-profile gasket core with at least one convex face on which the ridges are superimposed in order to effect commencement of seating at lower flange closing forces than parallel sided cores.

Whilst the property (of seating being initiated at the middle of the flange at lower flange closing forces and spread radially as flange closing forces increase) is attractive in mitigating the need to provide a large closing force initially applied across the whole flange to effect seating, such a core geometry does nothing to prevent the sharp ridges from breaking through the sealing material to damage the ridges and/or flanges. Thus it will be seen that the main source of difficulties with the use of kamm-profile gaskets is not eliminated.

The potentially damaging effects of such a sharp-ridged kamm profile core structure have been addressed by the same inventor in patent specification No US-A-4784411 (DE-A-3623310) wherein it is proposed that instead of a series of ridges and grooves only inner and outer boundary ridges are required in combination with the basic convex (or possibly concave) core body, if those bulges or ridges are not sharp and saw-like and thus incapable of damaging sealing material or flanges. Such a structure coexists with a proposed method of manufacture which avoids machining by rolling a slightly deformable core to displace material from regions that are to become recesses near each boundary to form what become rounded bulges, or ridges, at the boundaries and the curved central section.

Such core design and its implementation is therefore based upon having only two chambers for the displacement of sealing material in seating adjacent each boundary and concentrating the compressive flange clamping force that is normally applied to a plurality of sharp ridges to a few blunter ones.

However, for many circumstances of use it is considered inappropriate to rely upon sealing at just two boundary ridges and/or a core that is deformable.

It is an object of the present invention to provide a sealing gasket device of the aforementioned general type having a multi- ridged core structure which provides progressive seating of the associated compressible sealing material whilst both mitigating the disadvantages of sharp kam ridges and avoiding the complexity of simultaneously machining both the ridges and variations in underlying core thickness.

According to the present invention a sealing gasket device comprises (1) a core of uniform thickness between major faces thereof, at least one major face being flat and supporting a plurality of ridges running substantially orthogonally to a direction between inner and outer edges of the supporting core face, and (2) a layer of sealing material soft in comparison with the core and deformable overlying said ridges, said supported ridges having blunt generally arcuate elevational cross sections, and being of uniform height with respect to said supporting major face and, in said direction, being disposed in such numbers and with such dimensions at said major face as to provide a series of inter-ridge grooves of equal depth which individually vary in volume as a function of groove distance from said inner and outer edges.

Preferably such ridges associated with a major face conform in elevational cross-section to a minor arc of a notional closed conic section generated by a focal point below the surface of the major face, conveniently a circle.

In this specification the term minor arc is used to define an arc length of no more than half of the periphery of the notional closed conic section.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which

Figure 1 is a sectional elevation through a known form of kamm- profile gasket,

Figure 2(a) is a sectional elevation through part of a sealing gasket device according to the present invention, and

Figure 2(b) is a plan view of a portion of the core of the gasket device of Figure 2(a).

Referring to Figure 1, a known form of kamm-profile gasket 10 comprises a rigid core 11, of steel, in the form of a flattened annulus. The core 11 has a radially outer portion 12 formed as a guide ring, by way of which the core is operationally centred within a circle of bolts 13 (shown ghosted) between a pair of flanges 14 (also shown ghosted), and a main portion 15. The main portion 15 has essentially parallel major faces 16, 17 defining its thickness on which are superimposed a plurality of ridges 18, 19 respectively, each ridge running orthogonally to a direction between inner edge 20 and outer edge 21 of the gasket, that is, concentrically with respect to each other. The ridges 18, 19 are of uniform height and define in cross sectional elevation, triangles with respect to the faces 16, 17 of the core. The peaks of the ridges defined by the converging walls of the triangles may have peaks sharp or slightly truncated to less than 10% of the length (in the radial direction) of the base of the triangle. The main portion 15 of the core is thus of uniform thickness and the ridges of uniform height. In practice the ridges are defined and formed by machining the grooves in the core material and defining said major faces at the bases of the grooves.

A layer 22, 23 of sealing material that is relatively soft in comparison with the core and deformable, such as expanded exfoliated graphite, polytetrafluoroethylene or other material well known in the art, is disposed adjacent and overlying each set of ridges.

In use, the gasket 10 is disposed as shown between flanges 14 and then bolts 13 are tightened to draw or clamp the flanges together. The flanges apply clamping pressure across the full radial width of each layer of sealing material which is deformed locally by the ridge peaks, being displaced into the grooves between them and then compressed to increase its density and provide, at maximum density, a sealing layer between each flange and the core.

Clearly, because the displacement of the sealing material is effected by all peaks simultaneously a considerable force has to be exerted in the flanges by the bolts before all the grooves are filled and the material therein and remaining above the ridges compressed by the flanges to the extent that sealing is initiated, that is, seating occurs. Furthermore, it has been found that when a clamping force is employed that is computed in advance from the anticipated resistance to sealing material deformation by the ridges, it frequently occurs that non- uniformity within the sealing material or ridge peak sharpness permits the ridge peaks to penetrate the sealing material completely disrupt the radial continuity of the layer, effecting at least loss of sealing efficiency and at worst damage to ridges and/or flanges as discussed hereinbefore. Such breakthrough effect may occur also if sealing forces are concentrated at, or act principally through, a small region of the device to promote seating at lower flange clamping forces and the forces are then increased to seat all regions.

Referring now to Figures 2(a) and 2(b) which illustrate part of a sealing gasket device 100 in accordance with the invention, the gasket comprises a rigid core 110 of steel in the form of a flattened annulus, somewhat similar to the core of the kamm- profile gasket 10 in that it has a radially outer portion 120 formed as a guide ring and a main portion 150 having essentially parallel faces 160, 170 on which are formed a plurality of ridges

180, 190 respectively. The ridges run orthogonally to the direction between inner edge 200 and outer edge 210 of the core and like those of gasket 10 are of uniform height.

The gasket core differs however from that of a kamm-profile gasket in that the ridges 180, 190 superimposed upon the core major faces are in cross-sectional elevation not generally triangular but each has a generally arcuate profile conforming to a minor arc of a notional circle centred below the level of the surface of the particular major face, in this instance within the core 150, manufactured by cutting the intervening grooves 280, 290 in the surface of the core material. The circle centres, and therefore the ridges, are equally spaced in the direction between the inner and outer edges 200 and 210. The ridges therefore do not have sharp peaks and are thus blunt and flattened. A layer of compressible sealing material 220, 230 overlies each of the faces 160, 170 respectively.

In addition to the ridges having a blunt arcuate profile based upon notional circles, such as ridge 181 and circle 181,, ridge 182, circle 182, etc., the equi-spaced notional circles are of smaller diameter towards the edges 200, 210 of the gasket than towards the centre of the gasket. As illustrated, circles at

181, and 187, are smaller in diameter than 182, and 186, which in turn are smaller than circles 183, and 185,. It will be appreciated that because the ridges are all of the same height with respect to the core, this height represents a common tangent to the notional circles. It will be seen that because the ridges are spaced at a uniform pitch, the central ones, conforming to the larger circles, are wider and thus reduce the spacing between neighbouring ridges compared with those near the edges, that is, the inter-ridge grooves of equal depths vary individually with volume as a function of groove distance from said inner and outer edges.

In operation, when the sealing material is pressed towards the ridges by flange pressure, the material is displaced by the locally higher pressure at the rounded ridges into the inter- ridge grooves. However, because the walls of the grooves towards the centre of the gasket are closer to each other, and thus have less capacity in relation to their length to accept displaced sealing material, they become filled before those towards the inner and outer edges 200, 210 of the gasket, the effect being the density of the sealing material is maximised firstly in the vicinity of said central region and seating is established there firstly, and at lower clamping pressures, than for those grooves and ridges progressively outwardly and inwardly. At increased flange clamping forces seating is effected in respect of the ridges associated with, and each groove filled in turn by sealing material under pressure with only small danger of the ridges at any point cutting through the material overlying them or of the increased pressure at the ridges between the earlier-filled grooves causing deformation of the ridges.

Although it may be expected that such a plurality of blunt arcuate ridge profiles would require a significantly greater flange clamping force for the multiple ridges to achieve a simultaneous seating or sealing, albeit at different rates, this has been found untrue in practice with no significant increase required when polytetrafluoroethylene or exfoliated graphite is employed as the sealing material. The profiles of the ridges furthermore enable large final clamping pressure to be applied to the sealing material with reduced risk of the ridges penetrating or breaking through the material. However, even if material malfunction does result in such penetration any ridge contacts a flange surface extending tangentially thereto with little damage to the flange and particularly without significant deformation of the ridge because of the absence of thin (in a radial direction) peak regions.

Furthermore, it is found that in the absence of such thin peak regions, exceedingly large clamping forces can be applied with no plastic deformation of the ridges caused by pressure concentrations in the sealing material between them and the flanges.

Also the provision of a plurality of individual seating positions at different distances from the edges of the main core portion ensures that even if the sealing material is disrupted at the inner or outer ridge, perhaps due to a local defect in the sealing material, flange surface or even ridge surface, the neighbouring, and failing that the next-neighbouring, ridge provides its own seating point.

It will be seen that the structure of Figure 2(a) enables a differential seating effect to be achieved with a parallel-sided core and ridges of uniform height; that is, the ridges all lie in one plane and may be formed by a relatively simple machining operation between fixed limits of travel.

It will be appreciated that although the ridges (or their notional circles) have been described above as having uniform radial spacing, such spacing may be non-uniform and/or the variations on circle diameter may vary differently, such as decreasing towards the centre or increasing and decreasing cyclically between the inner and outer core edges 200 and 210.

Furthermore, the radii of the notional circles maybe sufficiently large that the notional circles (but not the ridges) overlap and the centre of any notional circle may not necessarily lie within the core but may be at such depth below the surface of the relevant major face that it is in fact above the surface of the other major face.

In this specification, in relation to the effects concerned with sealing gasket devices of this type, reference to a plurality of concentric ridges or grooves defined thereby is to be understood as extending to a ridge of a spiral or gramaphonic form wherein a single ridge is employed but which, in any radial direction appears, and has effect as, a plurality of discrete ridges and intervening grooves.

Whereas it is convenient from the point of view of manufacture to form the blunt ridges with a profile that conforms to a minor arc of a notional circle it will be appreciated that the elevation profile of any ridge may depart from such a shape providing it is machinable by a suitable programmed machining tool. It may comprise an alternative mathematically simple shape, such as an ellipse, or may comprise a completely heuristically derived shape having a blunt generally arcuate profile, as long as it has an absence of any sharp or tapered edge or edges which could by stress concentration damage the sealing material or deform under high clamping forces.

It will be understood that many other variations may be made to the above described embodiments such as the ridges being formed on one face only of the core, the radially outer portion 120 that forms a guide ring being omitted (if a guide ring is not required) or provided by a separate annular body located with respect to the main portion 150. Similarly, the materials may be any usually employed with kamm-profile gaskets.

It will be appreciated also that the form of the sealing gasket device need not be that of a circular ring that is employed with flanged pipe joints but may take any closed figure configuration in plan view that corresponds to an interface between parts that requires sealing by drawing the parts together.

Claims

1. A sealing gasket device (100) comprising

(1) a core (110) of uniform thickness between major faces thereof (160,170), at least one major face being flat and supporting a plurality of ridges (180, 190) running substantially orthogonally to a direction between inner and outer edges of the supporting core face, and

(2) a layer (220, 230) of sealing material soft in comparison with the core and deformable overlying said ridges, characterised by said supported ridges having blunt generally arcuate elevational cross sections being of uniform height with respect to said supporting major faces and, in said direction, being disposed in such numbers and with such dimensions at said major face as to provide a series of inter-ridge grooves (280, 290) of equal depth which individually vary in volume as a function of groove distance from said inner and outer edges.

2. A gasket device as claimed in claim 1 characterised in that the peaks of the arcuate ridges (180, 190) are uniformly spaced with respect to each other between the inner and outer edges (200, 210) of the gasket core (110) and the bases of the ridges at said major face vary in width in said direction with distance from said edges.

3. A gasket as claimed in claim 1 or claim 2 characterised in that the ridges (181) each conform to a minor arc of a notional closed conic section (181,) generated by a focal point below the surface (160) of the particular major face of the core and have radii of curvature which vary with ridge position between said inner and outer edges (200, 210) of the gasket.

4. A gasket device as claimed in claim 3 characterised in that the ridges have radii of curvature which are smaller towards the inner and outer edges of the gasket core than towards the centre of the gasket core.

5. A gasket device as claimed in claim 3 or claim 4 characterised in that the focal points of the closed conic sections are all within the core.