FI79750B - TAETNING FOER PLANA SKARVYTOR OCH FOERFARANDE FOER FRAMSTAELLNING AV DEN. - Google Patents

Abstract

1. A sealing gasket (1) for an assembly having flat faces and in particular for a flange connection, said gasket being in the form of a ring and comprising an annular core (7) of moulded expanded graphite contained between two inner and outer metal rings (5 and 4 respectively) characterized in that : - the ring formed by the gasket (1) comprises two parallel flat faces (2) which are essentially those of the moulded graphite core (7) between the inner and outer metal rings (5 and 4 respectively), the edges of said two rings being flush with said flat faces ; - the two inner and outer metal rings (5, 4) both have a spring effect in the direction (X) perpendicular to the parallel flat faces (2) and, in cross-section perpendicular to the flat faces of the gasket (1), have a corrugated wall whose main direction is said direction (X) ; and - the annular core (7) of moulded expanded graphite, prior to use of the gasket (1), is of a density of between 1.4 and 1.9 g/m**3.

Description

, 79750

Seal for flat joints and method of manufacture

The present invention relates to sealing devices, i.e. seals for flanges and planar joints.

Expanded, molded graphite gaskets currently used to seal low or high temperature (-245 ° C to + 1000 ° C) and / or heat-shrinkable pipe joints behave like liquids due to compression or expansion stresses and often need to be checked for tightness, which is awkward and sometimes impossible. Seals made using asbestos-based materials have poor elastic recovery due to the loosening of asbestos when compressed and no longer give satisfactory results.

Thus, an attempt has been made to provide a seal for pipelines, more generally for flat surface connections, which, under the above-mentioned conditions of use, can achieve a more reliable and durable seal.

In "Le vide - Les Couches minces" no 197.1979, 6/7/8, B.L. Blanc et al., 240, describe a seal for planar surfaces consisting of concentric rounds of stainless steel and an asbestos medium replaced at the center of the seal by a soft medium such as unheated PTFE, expanded graphite or lead. It has been shown that the use of such seals under high vacuum must be avoided.

In addition, FR-A-2 517 789 discloses a seal with two annular, concentric metal members having V-shaped grooves on opposite side surfaces that are open toward each other, delimiting a cavity in which coiled expanded graphite is pressed. The graphite settles into an ovoid shape, filling the space between said two metal rings, but protrudes as an annular pillar on each of the opposite surfaces of said rings. At tightness 2 79750, the tightness is ensured only by the elastic return of the expanded graphite thus cast.

The seal according to the invention for flat surfaces, and in particular for flange joints, is, as is known from FR-A-2 517 789, an annular shape and comprises an annular shaped core of expanded graphite pressed between two metal rings, between the outer and the inner. The main features of the seal according to the invention are set out in the characterizing part of claim 1. Thus, of the seal according to the invention: a) the ring formed by the seal has two parallel planar surfaces which are substantially the surfaces of the graphite core sandwiched between the inner and outer metal rings and whose ring edges extend flush, or nearly flush, typically less than 0.3 mm from these planar surfaces; b) these inner and outer metal rings each have a transverse elastic effect, i.e. in a direction (X) perpendicular to the plane planes and having a corrugated wall in a cross section perpendicular to the plane surfaces of the seal, the main direction of which is a direction (X) substantially axial in the case of a seal having a flat circular ring shape; c) the core of compressed, expanded graphite has, prior to the use of the seal, i.e. before the first tightening to achieve a tightness, a specific gravity of between 1.4 and 1.9 g / cm 3.

The elastic behavior of the seal according to the invention when tightened is the result of a combination of the elastic behavior of its extruded graphite core and its inner and outer metal ring.

This behavior differs from that of the seal of FR-A-2 517 789, discussed above, in which the resilient action is performed by a core of extruded, expanded graphite 3,79750 alone, while the inner and outer rings are rigid and act as counter-tighteners. It also differs from the behavior of the helical seal mentioned in "Le vide - Les Couches minces" (Vacuum-thin layers) p. 240, the elastic behavior of which is due solely to the corrugated, word-centered metal coils, with the soft intermediate material only spreading in the interstices.

In the seal according to the invention, the rings are on their side and their corrugations, after yielding deformations and / or compression, allow an elastic decrease in height or width during tightening, which causes a decrease in the thickness of the seal.

When the seal according to the invention is tightened and loosened, its graphite ring core and its flexible inner and outer metal rings act elastically together and synchronously, and this combination is associated with close contact between the graphite and the rings, especially at the corrugation of these rings. The flexible metal rings of the seal according to the invention thus have a dual function: as anti-extrusion rings to prevent graphite run-off, and as means for enhancing the flexibility of the graphite compressed expanded core.

The resilient inner and outer ring can be made from either the same metal strip profile, or from two different profiles. This may depend in particular on their possible connection to an internal reinforcing ring for use with corrosive liquids and / or at high pressures, and / or for use with an external centering ring that allows the joint to be placed in an inaccessible location, for example too far apart or due to too high a temperature. The corrugation of the outer edge of the inner reinforcing ring or the corrugation of the inner edge of the outer centering ring can then allow them to be fastened to the seal, which makes it possible to insert and position the seal with the reinforcing ring and / or the centering ring.

The thickness of such rings must be less than or equal to the thickness of the maximum tightening of the seal.

The metal rings according to the invention consist of a profiled, welded closed rim, or several successive rims which are tightened against each other.

At least one of these metal rims preferably consists of a profiled rim metal which is wrapped around itself and the end of which is welded to the helix which it covers, for example by spot welding. The rim thus comprises either one turn and one end covering this single turn, or several turns, the ends of which are welded in the same way. Overlapping resistance spot welding of the head makes it possible to maintain successive turns of the rim, the waves of which overlap due to their helical rotation, in a tensioned state, when the seal is used. The number of rounds is usually between 1-5. The number of turns of the outer and inner rim metal is chosen in such a way that, when tightened, the graphite is suitably compressed: usually a tightening is achieved in which the thickness is reduced by 10-35%, and typically by 15-30%. The choice of the number of rim metal turns flanking the seal according to the invention then makes it possible to adapt the compressive strength of the seal to the tightening force which it must withstand under its operating conditions (temperature, pressure to be sealed). Typically, both of these metal rings, inner and outer, comprise two to four turns of profiled rim metal with 5 79750 three thickness corrugations between 0.15 and 0.25 mm, which provides better elastic behavior than a single turn of profiled rim metal having the same total thickness.

It is these graphite planar surfaces, bounded by the edges of the inner and outer metal ring, that ensure the tightness of the planar planar surfaces. When the seal is tightened, the graphite is deformed by the compression caused by the tightening into the compartments of the flat surfaces of the combination, for example in any grooves or pits, which ensures a particularly reliable tightness. It has been found advantageous to use a seal with a core of graphite molded at a moderate compression pressure so that this graphite has a better ability to form into small irregularities in the surfaces to be sealed.

The apparent properties of the graphite core of the seal are then in the initial state between 1.3 and 1.9 g / cm 2, preferably between 1.4 and 1.8 g / cm 2. During further compression due to tightening of the seal, the specific gravity increases, for example up to 2.2 g / cm, whereby the seal retains its flexibility as it tightens and loosens, as long as its maximum tightening less than or equal to 35% of thickness is not exceeded. .

The graphite-limiting metal rings make it possible to avoid graphite run-off, and at the same time, together with the graphite, make it possible to adjust the crushing tendency and flexibility of the seal. The seal according to the invention has very little tendency to loosen. It has good chemical inertia associated with graphite and its choice of structural metal or alloy for its metal rings, and good temperature resistance from cooling temperatures (up to -245 ° C) to about + 1000 ° C with or without radioactive radiation.

The metals or alloys used for the outer and inner ring are in particular: stainless steels 6 79750 AISI 304, 304L, 316, 316L, up to about 800 ° C and nickel alloys such as INCONEL.

Due to its good elastic behavior and the good adaptation of its graphite core to the surfaces to be sealed, the seal according to the invention makes it possible to maintain good tightness at varying temperatures and especially in the event of thermal shocks.

The invention also relates to a method of manufacturing a gasket according to the invention, which schematically comprises the following steps: a) making an inner metal ring by forming a round profiled rim metal or a plurality of concentric, tensioned turns made of the same profiled rim with a profiled rim wall substantially in the center , and which ring is closed by welding; (b) the outer metal ring is made in the same way, either from the same profiled rim or from a different profiled rim; (c) the rings are filled with expanded graphite and used in such an amount that, after being compressed into a seal, a graphite core having a specific gravity of between 1.3 and 1.9 g / cm3, preferably between 1.4 and 1, is formed, 8 g / cm. Typically, expanded graphite having a nominal specific gravity of "0.7 g / cm" is used to obtain a compressed core with a specific gravity of 3 1.3 to 1.5 g / cm and expanded graphite having a nominal specific gravity of "0.7 g / cm 3". 1.1 g / cm 3 to give a compressed core with a specific gravity of 1.6 to 1.9 g / cm 3, giving good flexibility to the core of the seal; d) performing one or more pre-compressions on the expanded graphite having a specific gravity in this range to increase the overall compression ratio of the graphite and to fit it in place between the rings to facilitate it (step f); 7 79750 (e) the outer and inner rings are placed on the work platform in a seal made according to their final position so that the outer and inner rings rest side by side on the same plane of the work platform and rest outwards and inwards respectively; (f) the pre-compressed "expanded graphite" is placed in the space between and immediately above the outer and inner rings, and then the compression of this graphite into an annular mold formed by the two rings and the plane supporting the rings of the work platform and a plane parallel thereto which forms a working surface of the press mandrel; g) the seal thus obtained is removed from the mold.

Preferably, at least one of these metal rings, external or internal, is made by wrapping a portion of the profiled rim metal on the cylinder along a thread, overlapping, or along a plurality of threads forming a dense helix, and spot welding the end of the profiled rim to the thread it covers. In order to give these rings good flexibility in the transverse direction, it has been found advantageous to use a V-profile, i. A 3-wave V-profile, typically 0.15 to 0.25 mm thick, twisted on itself by 2 to 4 turns, overlapping.

When compressing graphite between the outer and inner rings forming the seal according to the invention, the waves of the metal rings play an important role, not only in adjusting the elastic behavior of the seal, but also in adhering the compressed graphite core to these rings.

The dimensions of the seal according to the invention are typically: an inner diameter ranging from 10 mm to more than 1 meter, a thickness between 2 and 10 mm, and a ring width between 5 and 50 mm. The thickness of the metal rims from which the outer and inner rings are made is typically 79750 between 0.5 and 1.2 mm.

The seal according to the invention is used, for example, for flanges or joints which are planar and non-interlocking, or planar and provided with single or double interleaving, or for flanges or joints with a circumferential, planar bottom groove. Helium tightness tests have compared the gasket of the invention to a metal / graphite threaded gasket, and it has been found that to achieve equal leakage, the gasket of the invention requires half the clamping force and provides twice as much elastic recovery as the helical gasket.

examples

The following examples illustrate and explain the invention in more detail.

Figure 1 shows an example of a seal according to the invention, in a half-section parallel to the center line.

Figures 2a and 2b schematically show two sealing ring profiles, in a parallel section. Figure 3 schematically shows a seal with an inner reinforcing ring and an outer centering ring in a half-section parallel to the center line.

Figures 4a and 4b schematically show a seal for a flange with a circumferential groove, untensioned and tightened, respectively, in half-sections parallel to the center line of the invention.

The seal 1 shown by way of example in Fig. 1 is a circular ring, the main dimensions of which are: outer diameter 86 mm, inner diameter 73, thickness, i.e. the distance between the planar surfaces 2 and 3: 3 mm. Its outer ring 4 and inner ring 5 are made from a flexible, profiled strip of stainless steel AISI 316L with a thickness of 0.2 mm and a width of 3 mm, with a corrugation 6 in the middle of the strip, a width of 1 mm and an excess thickness s, i.e. depth is 0.4 mm, which is shown in cross-section in Figure 1. Each ring 4 and 5 consists of a section 9 79750 strips which are endlessly wound in three turns and the ends of which are welded by spot welding to a strip below with a total "wrap" thickness of 0.8 mm .

In these rings 4 and 5, the main direction X of the wall of the profiled strip is at all points the direction of the center line, and the small clearance between the threads facilitates the deformation of the rings when the seal is tightened and loosened.

The expanded, compressed graphite forming the core 7 of the seal is perfectly adhered to the opposing surfaces 8 and 9 belonging to the outer ring 4 and the inner ring 5, respectively.

The thickness of this core 7 is equal to the width of the rings 4 and 5, so that the compressibility and elastic reactions of the seal 1 when tightened / loosened depend simultaneously on the three components 4, 5, 7. Tightening the seal 1 in use causes planar surfaces 2 and 3 or close to the close adhesion of the graphite on these planar surfaces to the surfaces to be sealed, and the penetration into possible small cavities, and at the same time a slight transverse back pressure corresponding to the bending to and from the wave 6 and a largely reversible density variation.

In this way, the specific mass of the graphite cast in the seal 1 is about 1.6. The seal 1 is typically intended to provide a seal between the parallel surfaces of the flange joints up to about 800 ° C, under corrosive conditions and pressures of up to 250 bar, with or without irradiation. To ensure tightness, the minimum tightening position corresponds to a thickness of 2.65 mm, while the maximum tightening thickness is 2.2 mm. In the meantime, the chances of the seal recovering flexibly remain in the order of 10% by volume or thickness.

10 79750

Figures 2a and 2b show diagrammatically, in center line sections, variants of the profile of the outer or inner metal rings, which rings here comprise four turns wrapped on top of each other.

The ring 10 according to Figure 2a consists of a self-wrapped strip having a single wave in the cross-section in the direction of the center line, the concavity of which extends outwards. In the case of the ring 11 of Fig. 2b, in the section parallel to the center line of the turns of the self-wound strip, two waves occur, the concavity of which is directed outwards from the ring.

In the case of relatively thick seals, several corrugations are often preferred, at least in the case where the intention is not to flatten the outer and inner ring by means of an external deformation guide; this is the case for a flange with a circumferential, flat bottom, groove of suitable profile (Figures 4a and 4b).

Figure 3 shows a seal 100 according to the invention comprising an expanded graphite core 107 sandwiched between an inner helical five-turn ring 105 and an outer helical ring 104, which further comprises five turns between the flanges, wherein are parallel planes. An external centering ring 112 is connected to the seal 100 by a latch connection, which has a dual function: it allows centering at a distance from the bolt 113, shown in broken lines, and its thickness determines the maximum tightening of the seal 100. This outer centering ring 112, which is exposed to a reasonable temperature, usually below 150 ° C, is typically of ordinary coated steel. The seal 100 is likewise provided with a sheath and, on the corrosive and hot fluid side of the piping 113, an internal reinforcing ring 115 made of, for example, 11 79750 stainless steel 316L, which limits temperature, corrosion problems and stress problems in the plane of the seal 100.

Figure 4a shows another seal 200 according to the invention comprising a graphite core 207 / sandwiched between an outer ring 204 and an inner ring 205, each of which comprises one circular, overlapped welded end. These rings 200 and 205 each have a height-limited corrugation 206 and 206 'at each medium height, which is visible on the side surfaces of the outer Mana seal. The seal 200 is located between the circumferential, circular grooves of the flanges to be joined. The grooves 216 each have a flat, circular annular base 217 having a width equal to the width of the planar surfaces 202 of the seal 200, and the conical sides 218 allow the seal 200 to deform in a bulging manner.

Figure 4b shows the combination tightened. The corrugations 206, 206 'have acted as initiators of the deformation of the flattened seal 200, and the continuation of this deformation is guided and controlled by the sides 218 of the grooves 216. The position shown in the figure corresponds to the maximum tightening of the seal 200 and represents an excellent reliable sealing solution.

Claims (10)

A seal (1) for flat joints, and especially for flange joints, which seal is annular and comprises an annular core (7) of expanded, pressed graphite, located between two metal rings, an inner (5) and an outer ( 4) ring, characterized in that - the sealing ring (1) has two parallel planar surfaces (2) which substantially coincide with the surfaces of the graphite core (7), the graphite being pressed between the inner metal ring (5) and the outer metal ring (4), - that the two metal rings, the inner (5) and the outer (4), are each resilient in a direction (X) which is perpendicular to the flat surfaces of the seal, and that in the direction (X) which is perpendicular to the seal (1) ) flat surfaces, have a road-shaped wall, the main direction of which is said direction (X), and that the specific mass of the pressed, expanded graphite core (7) before the use of the seal (1) is between 1.4 and 1.9 g / cm 3. Sealing according to claim 1, characterized in that at least one of its two metal rings (4, 5) is rotated around itself and welded. Sealing according to claim 2, characterized in that its two metal rings (4, 5) are rotated about themselves and welded, and that they have a similarly selected amount of rotated turns, that the seal (1), which is loaded in conditions of use, is pressed. in hops 10-35 mm. Sealing according to claim 3, characterized in that each metal ring, the inner (5) and the outer (4), comprises 2-4 turns of a three-way profiled metal strip, the thickness of which is between 0.15 and 0. 25 mm. 5. A method for producing a seal (1) for flat joint joints, in particular flange joints, said seal (1) having the shape of a flat ring bounded by two parallel surfaces (2) and characterized by graphite and metal1. The process comprises the following steps: a) an inner metal ring is formed by forming one turn of a profiled metal band or several cloncentric, pressed against each other of such profiled bands, the wall of the profiled band in the ring (5) having a substantially axial main direction (X), and that the ring is closed by welding; b) an outer metal ring is produced in the same manner either by the same or by another profiled metal band; c) reserving against the rings such an amount of expanded graphite that its specific mass or molding for sealing form will be between 1.3 and 1.9 g / cm 3; d) one or more pre-compressions are carried out with expanded graphite, whose specific mass is average; e) an outer ring (4) and an inner ring (5) are placed on the work base in such a position that they will eventually occupy the seal (1), so that the outer ring (4) and the inner ring (5) rest on the side On the work surface the same plane surface and lean out and in, respectively; f) the pre-compressed graphite is placed between the outer ring (4) and the inner ring (5) and immediately thereon, and the compression of this graphite is carried out in a form which is formed by the two rings (4, 5), and by the working surface of the surface of the working surface. supporting the rings and of one with this parallel tab, which constitutes the pressing surface of the pressing tool; g) the sA obtained is removed from the mold. 6. A method according to claim 5, characterized in that at least one of the metal rings (4 or 5 is produced by winding part of the profiled metal band on a cylinder in helical shape sA, that the windings overlap each other, or sA, several windings being wound into a tensioned coil, and by spot welding each end of the profiled metal strip into the winding covered by the strip. 7. A method according to claim 6, characterized in that each metal strip, the outer (4) and the inner (5) is produced by winding a part of the metal strip with a W profile, i.e.. three walls, and with a thickness of 0.15-0.25 mm, on itself in 2-4 overlapping turns. 8. A method according to claim 5, characterized in that in the case that the specific mass of the sealing graphite core should be between 1.3 and 1.5 g / cm 3, strips of expanded graphite whose specific weight is "1.1 g / cm 3. " Use of the seal as claimed in claims 1-4 together with an inner reinforcing ring (115), which is secured with a locking connection to the inner metal ring (105) of the seal (100), and together with an outer centering ring (112) , which is secured with an interlocking connection around an outer metal ring (104). Use of the seal as claimed in claims 1-4 together with an inner reinforcing ring (115), which is secured with a locking connection to the inner metal ring (105) of the seal (100), and together with an outer centering ring (112) , which is secured with an interlocking connection around an outer metal ring (104).