AIRCRAFT SEAL AND AIRCRAFT WITH AT LEAST ONE SUCH SEAL

Description

technical field

[0001] The invention relates to an aircraft sealing gasket incorporating a fire-resistant structure, and to an aircraft incorporating at least one such gasket between structural elements of the aircraft connected to one another in an area thereof that may be a fire zone as defined by ISO 2685:1998 or FAA (Federal Aviation Administration) standard AC 20-135. The invention applies in particular to overall tubular gaskets for sealing and protecting against fire areas of an aircraft or helicopter selected from those of main engines and auxiliary engines, such as an engine, a nacelle, a pylon, or an auxiliary power unit (APU), it being specified that any air or space vehicle capable of presenting at least one fire zone is covered by the invention. Previous technique

[0002] On an aircraft, many areas designated as "fire zones" under ISO 2685:1998 or AC 20-135 require the use of seals designed to perform two main functions, the first being a sealing function under normal flight conditions and the second being a fire-proof function in the event of the start or spread of a fire in the area or areas concerned of the aircraft.

[0003] As is known, these two functions are antagonistic, since the sealing function is favored by an increased flexibility of the joint which allows it to conform to the profile of the structural elements in contact with which it is mounted in a constrained state (pressure barrier effect) and to simplify the installation and the watertight closure of the connection by the elastic stiffness of the joint, while the fire resistance function is on the contrary favored by an increased rigidity of the joint by limiting its risk of perforation by the flame (fire barrier effect) and by limiting the transmission of heat to the other side opposite to the origin of the fire.

[0004] US2020 / 025135 A1 features a rear turbofan nacelle assembly, comprising: a fixed thrust reverser structure comprising a half-hood mounted on a pivotally articulated beam by means of a hinge, between a working position and a maintenance position, the half-hood comprising a partition that divides a beam area and delimits a joint-support edge, a nacelle suspension pylon on which the fixed structure is movably mounted, the pylon forming a joint-support wall that is delimited by a lower face arranged opposite the joint-support edge of the half-hood, and an opposite upper face, an access hatch to the hinge of the half-hood, which is delimited by a lower joint-support face arranged opposite the hinge, and an upper fairing face, and a fire-sealing device comprising a sealing gasket adapted to ensure sealing between a mid-section of the nacelle that surrounds a turbojet fan and the beam area,The sealing joint is made in two parts comprising: a lower part of the tubular joint type, which extends at least partially over the said joint-supporting edge of the half-hood, and which is adapted to cooperate with the joint-supporting wall of the pylon, and an upper part comprising an elastically deformable sealing sheet extending from the joint-supporting wall of the pylon to the lower face of the hinged access hatch, the sheet ensuring fire tightness between the pylon and the hinged access hatch.

[0005] US 2018 / 298772 A1 specifies an aircraft propulsion system assembly comprising a first component, a second component, and a sealing assembly configured to seal a gap between the first and second components. The sealing assembly includes a metal spring seal and an elastomer seal. The metal spring seal, mounted on the first component and hermetically sealed against the second component, forms a flame barrier. The elastomer seal is mounted on the metal spring seal and hermetically sealed against the second component.

[0006] The fire-resistant and sealing gaskets designed for this purpose are usually made of an elastomer-fabric composite, resulting in a compromise that is often unsatisfactory between these two functions, particularly regarding fire resistance. Furthermore, this has a significant impact on the surrounding parts of the aircraft's sealed structural elements (which are usually made of composite material or titanium). These parts must, on the one hand, withstand the stiffness of the gasket they constrain without deforming and, on the other hand, often incorporate thermal protection to ensure the fire resistance of the entire area concerned, including the gasket and its adjacent components.

[0007] US 3,566,541 A discloses in Figures 23-28 a fire protection barrier, particularly for container doors and lids, comprising a Neoprene® (polychloroprene) seal and an intumescent mass contained within a cavity in the seal. The seal is designed to disintegrate at a flame temperature of approximately 204°C, and the intumescent mass is designed to swell at approximately 65°C.

[0008] A major drawback of this barrier lies in the unsuitability of the polychloroprene seal to the high temperatures in the immediate vicinity of aircraft engines, which in normal operation (i.e., a fire-free environment) usually vary between -55 and 250°C. Indeed, the intumescent mass according to this document would be the site of premature expansion and the seal incorporating it would disintegrate in normal aircraft operation.

[0009] EP 2 412 409 A1 discloses a one-piece fire damper seal consisting of an intumescent material fully covered by a silicone elastomer profile, which is co-extruded in contact with this intumescent material and cross-linked without the addition of heat by UV radiation. This intumescent material is, for example, made of expandable graphite or a silicate, and its expansion can begin at a temperature of 100-110°C.

[0010] A major drawback of this single-piece seal also lies in its unsuitability to the already hot, non-fire environment of aircraft engines, particularly due to premature expansion of the intumescent material, which also contributes in this document to sealing in the absence of fire because it is enclosed by the seal. Description of the invention

[0011] One aim of the present invention is to provide a sealing gasket comprising: a gasket body at least partly elastomeric, the gasket body defining at least one overall tubular or annular cavity, and a fire-resistant structure which is distinct from the gasket body and which is disposed inside said at least one cavity, the fire-resistant structure comprising at least one intumescent mass capable of filling said at least one cavity in an expanded state, which notably addresses the aforementioned drawbacks.

[0012] For this purpose, a sealing gasket according to the invention is such that said at least one intumescent mass is made of a rubber composition having an intumescence triggering temperature equal to or greater than 270°C, measured by a plane-plane rotary rheometer with a temperature sweep from 23 to 380°C following a temperature ramp of 10°C / min. with 1% deformation and with evolution, from 23°C, of ​​the normal force Fn from 0.07 N and of the air gap h between planes from 2 mm. This sealing joint according to the invention is further designed to connect two structural elements to each other in an area of ​​an aircraft which is chosen from the main engine and auxiliary engine areas, the temperature of which in the absence of fire can vary from -55°C to 250°C and which is designated as a fire area according to ISO 2685:1998 or AC 20-135.

[0013] It should be noted that this seal of the invention thus integrates the sealing function during normal aircraft operation (i.e., at a temperature below 270°C, which could, for example, vary from -55°C to 250°C), and the two functions of sealing and fire barrier in the event of a fire in an area of ​​the aircraft in the immediate vicinity of the seal, thanks to the expansion of said at least one intumescent mass at temperatures above 270°C. Indeed, the intumescent mass or masses cooperate synergistically in their expanded state with the seal body, which they completely fill, thus providing additional stiffness to the wall of the seal cavity against which the mass or masses press and also effectively protecting this wall during the fire.

[0014] In other words, the joint of the invention with separate joint body and intumescent mass(s) makes it possible to significantly improve the sealing and fire barrier performance by decoupling these two functions in normal aircraft operation, due to the non-participation of said at least one intumescent mass in the sealing function in normal operation which is favored by being fulfilled only by the flexibility and elasticity of the joint body, whereas in the event of a fire the expansion of the intumescent mass or masses provides the dual function of sealing and fire barrier by giving increased rigidity to the joint body during the duration of the fire, while limiting the heating of the joint body wall against which it presses.

[0015] It should also be noted that, in addition to jointly and independently integrating these two opposing functions without compromising either of them during normal operation or in the event of a fire, the joint of the invention simplifies the technical constraints on surrounding parts. Indeed, metallic or composite structural elements connected to one another in a fire zone of the aircraft (as defined by § 2.1 of ISO 2685:1998 or by AC 20-135) can advantageously be designed, thanks to the joint of the invention, with reduced dimensions compared to prior art fire-resistant structural elements, because this joint remains more flexible during normal aircraft operation.And as in the case of fire, the expansion of the intumescent mass helps to limit the heating of the wall in contact with the joint body and also to improve the joint's resistance to the passage of the flame to the other side (as will be developed below), it follows that this joint of the invention makes it possible to eliminate in whole or in part the need for thermal protection devices on the surrounding structural elements on each side of the joint.

[0016] Advantageously, said intumescence triggering temperature can be between 280 and 400°C, preferably between 320 and 360°C and for example between 330 and 350°C.

[0017] It should be noted that these temperatures are significantly higher than the maximum temperature of approximately 250°C which usually characterizes aircraft engines such as airplanes, in particular, which further improves the decorrelation of the two aforementioned functions and therefore the sealing performance in normal operation, since it is thus certain to avoid any premature and therefore undesirable start of expansion of said at least one intumescent mass.

[0018] According to another feature of the invention, the rubber composition can exhibit, in its expanded state, a volumetric expansion rate equal to or greater than 800%, preferably between 820 and 950%, and for example between 850 and 900%, measured for 15 minutes at 600°C ± 10°C in a Nabertherm® N17 / HR muffle furnace with a usable volume of 17 dm³ on a circular specimen with a diameter of 25 mm made of the rubber composition. This expansion rate (%) is calculated using the formula ((Ef - Ei) / Ei) × 100, where Ei represents the initial thickness of the specimen, equal to 2 mm, and Ef represents the final thickness of the specimen.

[0019] It should be noted that this very high expansion rate advantageously allows the corresponding cavity of the joint body to be filled while generating the exercise by the or each expanded mass of a multidirectional force on the whole wall of this cavity, which makes it possible to give this wall the aforementioned additional stiffness contributing to the fire barrier function.

[0020] It should also be noted that the mass or masses thus expanded by intumescence (commonly called "char" in the state of the art to designate the alveolar residue of thermal degradation) advantageously exhibit a sufficiently high volumetric expansion rate (at least 800%) to achieve the aforementioned wall filling and stiffness, but not an excessive one (preferably less than 950%) so that this expansion does not negatively impact the mechanical properties of the char. Thus, the fire-resistant structure forming this intumescent char contributes to making the seal sufficiently resistant in case of fire, preventing its destruction by combustion and the generated vibrations, as will be explained below.

[0021] According to another feature of the invention, the rubber composition can be based (i.e. made up of more than 50% by weight, preferably more than 75% by weight and more preferably made up exclusively of) at least one silicone rubber, preferably a phenyl-vinyl-methyl silicone (phenylmethyl-, vinylmethyl- and dimethylsiloxane terpolymer, PVMQ for short).

[0022] Indeed, the Applicant has highlighted that the use of at least one silicone rubber specifically of the PVMQ type to constitute the majority or exclusively by weight of the elastomer matrix of the composition of the or each intumescent mass, unexpectedly makes it possible to significantly increase the thermal stability of the or each mass (by reducing its mass loss when the temperature increases beyond 600° C, for example), compared to other silicone rubbers such as vinyl-methyl silicones (VMQ).

[0023] It should be noted that the silicone rubber preferentially used in the rubber composition makes it possible to significantly improve the fire resistance of the intumescent mass(es) at very high temperatures, typically up to 1100°C, while meeting the operating temperature range of the joint and the structural elements it connects in the relevant fire zone of the aircraft.

[0024] It should be noted, however, that vinyl-methyl silicone (VMQ) and fluorosilicone (FVMQ) rubbers can also be used in the composition of said at least one intumescent mass, even if PVMQs are preferred.

[0025] According to a preferred embodiment of the invention, the rubber composition further comprises: an expandable organic or inorganic material capable of giving the composition said intumescence triggering temperature (of at least 270°C, preferably between 280 and 400°C, for example between 320 and 360°C), preferably comprising an expandable graphite, a flame retardant system comprising flame retardants, optionally a reinforcing filler, and a crosslinking system comprising a peroxide.

[0026] Advantageously, the rubber composition constituting said at least one intumescent mass is not fully crosslinked, but may be non-crosslinked or only partially crosslinked. Preferably, the rubber composition incorporating this crosslinking system with a reduced amount of peroxide is only weakly crosslinked (by heating to a temperature e.g., between 160 and 220°C). Indeed, the Applicant observed a significant improvement in the mechanical properties of the tank resulting from the expansion of a composition according to the invention that was not fully crosslinked within the seal cavity, whereas a fully crosslinked composition was unable to expand sufficiently there.

[0027] It should be noted that this non-totally cross-linked rubber composition is designed to be sufficiently flexible so that the intumescent mass or masses can be inserted inside the cavity of the seal while resisting any deformation of the seal during the different phases of its life, including in particular its storage and assembly on the aircraft.

[0028] According to an example of an embodiment of this preferred mode of the invention, the rubber composition comprises, for every 100 parts of said rubber, at least one silicone rubber (parts: parts by weight per 100 parts of elastomer(s)): said expandable organic or inorganic material in an amount of between 10 and 20 parts per annum, preferably between 13 and 17 parts per annum of said expandable graphite, said flame retardant system in an amount of between 10 and 20 parts per annum, said flame retardant system comprising, for example: quartz in a mass fraction of 15 to 40%, a metal oxide in a mass fraction of 15 to 40%, such as titanium dioxide, dimethyl siloxane with a dimethyl vinyl terminal group in a mass fraction of 15 to 40%, and platinum in a mass fraction of less than 0.02% and preferably between 50 and 200 ppm; as said optional reinforcing filler, mineral fibers such as rock fibers, in an amount of between 18 and 28 parts per annum;and said peroxide in an amount between 0.05 and 0.5 parts per liter, for example between 0.1 and 0.3 parts per liter, said peroxide preferably being an aromatic organic peroxide and for example a dicumyl peroxide.

[0029] It should be noted that the quartz, metal oxide, dimethyl siloxane with a terminal dimethylvinyl group and platinum mentioned above are cited by way of no limitation whatsoever, it being specified that other flame retardants chosen from cerium hydroxide, dimethyl siloxane with a terminal hydroxy group, dimethyl, methylvinyl siloxane with a terminal dimethylvinyl group, carbon black and mixtures of at least two of these other agents, are also usable in said flame retardant system by being previously dispersed in a silicone oil.

[0030] Alternatively, a solution of ammonium polyphosphate could be used in the said flame retardant system, for example mixed with pentaerythritol and melamine, among other things.

[0031] It should also be noted that the aforementioned quantity of expandable graphite of 10-20 pc (preferably 13-17 pc) unexpectedly makes it possible to achieve a compromise between the volumetric expansion rate of the rubber composition in the expanded state and the mechanical properties obtained for the char generated by this expanded composition, it being specified that an increase in the quantity used of expandable graphite not only has the effect of raising this expansion rate, but also of decreasing the mechanical properties of the char.

[0032] It should also be noted that the rubber composition according to the invention can be devoid of any reinforcing filler, and that the possible use in the composition of the aforementioned mineral fibers can allow to mechanically reinforce the char formed during the expansion of this composition, which contains the peroxide (e.g. dicumyl) in the reduced quantity of 0.05-0.5 pc, preferably of 0.1-0.3 pc, to limit the subsequent hot creep of the rubber composition without impacting its expansion by intumescence.

[0033] Advantageously, the rubber composition may exhibit, in the uncrosslinked state, a Mooney viscosity ML(1+4) at 40°C, measured according to ASTM D-1646, which is between 15 and 25 and for example between 18 and 22.

[0034] It should be noted that these Mooney viscosity ranges for the non-crosslinked rubber composition demonstrate its suitability for processing (i.e. shaping into a determined form) following its mixing, possibly before its partial hot crosslinking.

[0035] According to another aspect of the invention, the rubber composition of the intumescent mass or each mass, in the expanded state, is advantageously tested by the vertical flammability test as described in FAR25.853, Annex F Part I (a) (1) (i), the rubber composition then exhibiting no residual flame after the removal of an 843°C methane flame for an ignition time of 60 seconds.

[0036] It should be noted that this absence of residual flame at the end of this vertical flammability test (in which the samples tested are supported vertically, as precisely described in this standard FAR25.853, Annex F part I (b) (1) to (4)), which can be translated by the fact that the expanded and ignited rubber composition is extinguished directly after the removal of the methane flame generated by a burner, testifies to the reduced flammability of the or each intumescent mass according to the invention.

[0037] According to a particular embodiment of the invention, the fireproof structure may further comprise an envelope which is separate from the joint body and which encapsulates said at least one intumescent mass in particular to protect it from surrounding fluids, the envelope being for example based on a non-crosslinked silicone rubber and being able to form a "skin" in contact with the or each mass.

[0038] It should be noted that this protective encapsulation of the intumescent mass or each mass by such an envelope can also limit the movement of this mass inside the corresponding cavity of the sealing joint, in normal operation of the aircraft.

[0039] According to another feature of the invention, the fireproof structure can be disposed on an internal area of ​​the joint body independent of the sealing provided by the joint, without the fireproof structure being fixed to the joint body.

[0040] It should be noted that this lack of fixing of the fireproof structure to the joint body can result in a lack of physical or chemical adhesion between the fireproof structure and the joint body, until the intumescence of the or each mass.

[0041] According to another feature of the invention, the fireproof structure can have, in a non-expanded state before intumescence of the or each mass, any geometry, for example globally parallelepiped (i.e. prismatic type), preferably defined in this case by a width along a transverse dimension of said at least one cavity, by a height perpendicular and less than said width and by a length, for example, equal to that of said at least one cavity.

[0042] Alternatively, the fireproof structure could have any other elongated geometry extending along the length of the joint body, e.g. globally cylindrical with a circular or non-circular cross-section.

[0043] According to another feature of the invention, the seal body may be made entirely or partially of an elastomeric material based on at least one silicone rubber, preferably a terpolymer derived from phenylmethyl-, vinylmethyl-, and dimethylsiloxane (PVMQ). This elastomeric material of the seal body may consist of more than 50% by weight, preferably more than 75% by weight, and more preferably exclusively of said at least one silicone rubber.

[0044] It should be noted that the silicone rubber used in the elastomer material of the seal body significantly improves its resistance to fire at very high temperatures, up to 1100°C, typically in the relevant fire zone of the aircraft.

[0045] It should also be noted that fluorosilicone rubbers (FVMQ) are not usable in the elastomer material of the seal body.

[0046] According to preferred embodiments of the invention, the joint body is for example chosen from tubular joints with a cross-section of Ω, with a cross-section of P, and from annular bellows for conduits.

[0047] It should be noted that other geometries can be used for the joint body, particularly among those commonly used for sealing gaskets in the aeronautical industry.

[0048] According to a particular embodiment of the invention, the joint body can be made of said elastomeric material, being devoid of a reinforcing layer embedded in said elastomeric material.

[0049] It should be noted that this exclusively elastomer structure of the joint body has the advantage of a simplified manufacturing process which can be implemented by a single extrusion step, for example.

[0050] According to another embodiment of the invention, the joint body can be made of a composite comprising said elastomeric material and at least one layer of a fabric, said at least one layer being embedded in said elastomeric material and being selected from glass fabrics, aromatic polyamide fabrics (e.g. aramid) and their combinations.

[0051] It should be noted that this composite structure of the joint body, obtained by a usual manufacturing process, thus requires one or more layers (respectively made up of identical or different fabrics), the fabric or each fabric having to present sufficient resistance to temperatures of about 1100° C during a fire.

[0052] For example, a single layer of glass fabric can be used to reinforce the joint body, it being specified that this reduced reinforcement of the joint body is advantageously compensated by the intumescence aptitude of the fireproof structure and by the mechanical properties of the tank obtained after intumescence, when exposed to fire.

[0053] According to another general aspect of the invention which can be combined with any of the aforementioned features and examples of the seal (including the seal body and / or fire-resistant structure), the sealing gasket is fireproof according to ISO 2685:1998, being capable of withstanding fire for 15 minutes: to the heat generated by a calibrated kerosene flame at 1100°C ± 80°C with a heat flux density absorbed by the standard equipment described in B.4.2 of ISO 2685:1998, which is 116 ± 10 kW / m², and to vibrations of 50 Hz and 0.8 mm peak-to-peak as described in ISO 2685:1998.

[0054] A sealing gasket according to the invention is also fireproof according to standard AC 20-135, being capable of withstanding fire for 15 minutes: to the heat generated by a calibrated kerosene flame at 1093° C ± 83° C with a heat flux density of 105.62 ± 10 kW / m 2< minimum, and to vibrations of 50 Hz and 0.8 mm peak to peak.

[0055] It should be noted that this satisfactory resistance to heat and vibration during the 15 minutes of the fire test, as precisely described in the ISO 2685:1998 or AC 20-135 standard, demonstrates that the combination according to the invention of the joint body and the fireproof structure forming the aforementioned tank by intumescence makes it possible to make the joint sufficiently resistant in case of fire, preventing its destruction or disintegration by combustion and vibrations generated by the fire.

[0056] An aircraft according to the invention, in particular an airplane or a helicopter, comprises: at least one pair of metallic or composite structural elements designed to be connected to each other in at least one area of ​​the aircraft designated as a fire zone, for example according to § 2.1 of ISO 2685:1998 or AC 20-135, said at least one area preferably being chosen from the main engine and auxiliary engine areas of the aircraft, such as, for example, the areas of an engine, a nacelle, a pylon and / or an auxiliary power unit (APU), and at least one sealing joint that hermetically seals the structural elements of said at least one pair to each other, and according to the invention, at least one sealing joint is as defined above.

[0057] It should be noted that the said at least one fire zone of the aircraft, such as an aerial or space vehicle, could be defined in a different way than according to ISO 2685:1998 or AC 20-135, and that it could therefore refer to other zones than those identified above. Brief description of the drawings

[0058] Other features, advantages and details of the present invention will become apparent from the following description of several illustrative and non-limiting examples of embodiments of the invention, in conjunction with the accompanying drawings, among which: Fig. 1 [ Fig. 1 ] is a schematic cross-sectional view of an Ω sealing joint according to an example of the invention mounted between and against two structural elements to be sealed in an aircraft, in normal operation of the joint (i.e. without fire in the aircraft), the fire-resistant structure of the joint being non-expanded. Fig. 2 [ Fig. 2] is a schematic cross-sectional view of the sealing joint of the figure 1 forming a fire barrier in the event of a fire in the aircraft, the fireproof structure of the seal being expanded. Fig. 3 [ Fig. 3 [ ] is a schematic cross-sectional view of an Ω sealing joint according to the invention, similar to the example of the figure 1 in normal operation of the seal, the fireproof structure of the seal is not expanded. Fig. 4 [ Fig. 4 ] is a schematic cross-sectional view of a P-type sealing joint according to a variant of the invention, in normal operation of the joint, the fire-resistant structure of the joint being non-expanded. Fig. 5 [ Fig. 5 ] is a schematic cross-sectional view of a sealing joint according to another variant of the invention forming a bellows for conduits, in normal operation of the joint, the fire-resistant structure of the joint being non-expanded. Fig. 6 [ Fig. 6] is a detailed cross-sectional view of a sealing gasket body similar to that of the figure 1 the joint being shown at rest and without fireproof structure with its dimensions expressed in mm. Fig. 7 [ Fig. 7 ] is a schematic cross-sectional view of a "test" seal at rest, consisting of the seal body of the figure 6 without a fireproof structure, this "test" seal has been subjected to fire tests according to ISO 2685:1998. Fig. 8 [ Fig. 8 [ ] is a schematic cross-sectional view of a sealing gasket according to the invention at rest, consisting of the gasket body of the figure 6 and a fire-resistant structure, this joint has also been subjected to fire tests according to ISO 2685:1998. Fig. 9 [ Fig. 9 ] is a photograph showing an open end of the sealing gasket of the figure 8in a deformed state on its lower base, which is surmounted by the non-expanded fire-resistant structure. Fig. 10 [ Fig. 10 [ ] is a graph illustrating the evolution, as a function of temperature measured by thermogravimetric analysis (TGA), of the weight of a first composition according to the invention based on a PVMQ silicone rubber (solid line curve), compared to a second composition according to the invention based on a VMQ silicone rubber (dashed line curve), each composition constituting a fire-resistant structure of the joint of the figures 8-9 and the resulting chariot. Fig. 11 [ Fig. 11 ] is a graph illustrating the evolution as a function of temperature, measured via a plane-on-plane rheometer analysis, of the normal force Fn (lower curve) and the inter-plate distance h (upper curve) of the first rubber composition according to the invention based on a PVMQ constituting the fire-resistant structure of the joint of the figures 8-9and the resulting chariot. Fig. 12 [ Fig. 12 [ ] is a schematic view of a fire test bench according to ISO 2685:1998 used for fire testing on "test" joints and according to the invention of figures 7 And 8-9 showing a sample of the seal, the burner and the corresponding main devices and stages used in this test bench. Fig. 13 [ Fig. 13 [ ] is a schematic view of a camera system arranged on both sides of the test device, inside the test bench of the figure 12 . Fig. 14 [ Fig. 14 ] is a detailed view of the test bench of the figure 12 showing two structural compression elements of each "control" joint sample or according to the invention, and the direction of the flame impact generated by the burner during each fire test. Fig. 15 [ Fig. 15 ] contains seven photographs showing a sample of the joint according to the figures 8-9of the invention and the structural elements adjacent to this sample, following a fire test carried out according to ISO 2685:1998. Fig. 16 [ Fig. 16 ] contains three photographs showing a sample of "control" joint according to the figure 7 and the structural elements adjacent to this sample, following a fire test implemented according to ISO 2685:1998. Examples of implementation of the invention

[0059] The sealing gasket 10 according to the invention visible at the figure 1 is mounted in compression between two opposing structural elements 1 and 2 to be sealed, and it comprises: a tubular joint body 11 with a closed Ω cross-section, defining a cavity 10A between its rounded top 11A and its flat base 11B which press tightly against the elements 1 and 2, respectively, and a fire-resistant structure 12 disposed in this example on the inner face of the base 11B of the joint body 11, over the entire transverse width of the base 11B (in contact with the rounded wall of the cavity 10A surmounting the base 11B) and which occupies in the unexpanded state and at rest of the joint body 11 a reduced fraction of the transverse height H of the cavity 10A.

[0060] For example, the fireproof structure 12 is rectangular in section (i.e., overall parallelepiped geometry along the length of the cavity 10A), and the fraction occupied by the fireproof structure 12 is, for example, between 5 and 20% of the said height H (which is defined from the inner face of the base 11B to that of the top 11A of the cavity 10A).

[0061] As explained above, the seal body 11 is, for example, made entirely or partly of a silicone rubber-based elastomer material, in which at least one layer of reinforcing fabric is optionally embedded. As for the fire-resistant structure 12, it is, for example, made of an intumescent mass formed from a silicone rubber-based composition and further comprising: an expandable organic or inorganic material capable of giving the composition an intumescence triggering temperature of at least 270°C, preferably consisting of an expandable graphite, a flame retardant system including flame retardants, optionally a reinforcing filler, and a hot crosslinking system including a peroxide.

[0062] After intumescence of the fire-resistant structure 12 during a fire on board the aircraft, we see at the figure 2that the structure 12 in the expanded state occupies substantially the entire height H and internal volume of the cavity 10A, with in addition the exercise of a multidirectional force (globally radial in this example) on the wall of the cavity 10A by the expanded structure 12, which is reduced to the state of a tank by the combustion reaction, which has the effect of giving additional stiffness to the joint body 11 during the fire.

[0063] The 10-ohm sealing gasket according to the invention, visible at the figure 3 differs essentially from that of the figure 1 , in that its fireproof structure 12 is wedged between two vertical lugs 11a and 11b connecting the inner face 11c of the base 11B to the rounded portion of the cavity 10A.

[0064] The sealing gasket 10 according to the invention visible at the figure 4includes a P-shaped joint body 11, and a fire-resistant structure 12, for example, of rectangular cross-section, disposed inside the tubular cavity 10A of the "P", on the inner face 11c of a base 11B of this cavity 10A (i.e., in line with the leg of the "P"). As shown in the figure 4 , the fireproof structure 12 can be mounted with minimal clearance in contact with the rounded wall of cavity 10A of the “P”.

[0065] The sealing gasket 10 according to the invention visible at the figure 5 is of the bellows type for two radially internal and external conduits, respectively. The seal 10 comprises a double-walled seal body 11, and a fire-resistant structure 12 formed of a lining disposed inside the annular cavity 10A, on an inner face of the outer wall 11B' of the seal body 11. The fire-resistant structure 12 can thus extend over the entire circumference of the outer wall 11B' of the seal 10.

[0066] The Ω joint body illustrated in detail at the figure 6 is similar to the joint body 11 of the figure 1 , with : its generally flat base 11B is provided on its external face with a pair of external mounting lugs (lower lugs to the figure 6 defining an external transverse width of 40.3 mm for the base) for mounting the joint body 11 against a structural element 2 such as that of the figure 1 , and its rounded wall defining the cavity 10A from this base 11B, this wall (1.5 mm thick) being in this example generally in the shape of an ellipse with a major axis (i.e. transverse width) equal to 40 mm and a minor axis (i.e. transverse height) equal to approximately 29 mm, and presenting laterally a circular orifice.

[0067] As illustrated in the figure 7 Samples of a joint body 11 were made according to the geometry and dimensions of the figure 6by embedding, in a PVMQ silicone rubber-based elastomer material, a layer 11d of a glass fabric, so that the layer 11d extends into the mass of the rounded wall of cavity 10A along its elliptical circumference and along the length of cavity 10A. Samples of the "control" seal of the figure 7 , consisting solely of this joint body 11 (without fireproof structure inside).

[0068] As illustrated in the figure 8 , we added to the joint body 11 of the figure 7 (in elastomeric material based on said silicone rubber, in which a layer 11d of glass fabric is embedded for its reinforcement) a fire-resistant structure 12 according to the invention, i.e. as described above with reference to the figure 1The fire-resistant structure 12 consisted of an intumescent mass with a generally rectangular cross-section (i.e., a generally parallelepiped geometry along the length of cavity 10A), with a width and height of 20 mm and 6 mm, respectively. Samples of the seal 10 according to the invention were thus obtained. figure 8 , consisting of the same joint body 11 as the figure 7 and the fire-resistant structure 12 inside, this seal 10 being visible in the photograph of the figure 9 .

[0069] The intumescent mass of the fireproof structure 12 of this joint 10 was prepared according to the invention as described below.

[0070] The formulation of this intumescent mass is shown in Table 1 below, which is representative of an example of said first composition according to the invention. [Table 1] Nature of the products Features Formulation (pc) Flame retardant system See table 2 15,40 Silicone rubber PVMQ 100,00 Expandable graphite GHL 95 HT 270 15,40 Mineral fibers "LAPINUS" CF-50 23,10 Crosslinking agent Dicumyl peroxide 0,2 Total (pieces) 154,1

[0071] More specifically, among these ingredients: The PVMQ silicone (as defined in ASTM D-1418, also called PMVQ) was a phenyl polydimethylsiloxane (phenylmethyl-, vinylmethyl-, and dimethylsiloxane terpolymer which, in its uncrosslinked state, was translucent, had a density of 1.22 ± 0.03, and a Williams plasticity measured according to ASTM 926 equal to 400), the GHL 95 HT 270 was a grade of graphite expandable to a trigger temperature of 270°C, the "Lapinus" CF 50 mineral fibers reinforcing the composition consisted of rock fibers with an average length of 500 + / - 150 µm and a D90 diameter of 7 µm, and the flame retardant system used was a mixture of several compounds and flame retardants pre-dispersed in a silicone oil, to facilitate their dispersion during the mixing of the composition. rubber.

[0072] The composition of the flame retardant system is shown in Table 2 below. [Table 2] Flame retardant system Mass fractions (%) Quartz - titanium dioxide - carbon black 40,0 - 70,0 Dimethyl siloxane, with a dimethyl vinyl end 15,0 - 40,0 Cerium hydroxide 3,0 - 7,0 Hydroxy-end polydimethyl siloxane 3,0 - 7,0 Dimethyl, methyl vinyl siloxane, with a dimethyl vinyl end 3,0 - 7,0 Platinum 115 ppm

[0073] The following properties of the rubber composition obtained by thermomechanical mixing of the aforementioned ingredients were measured, and their values ​​are listed in Table 3 below. A Haake® tangential mixer with a working volume of 250 cm³ and a filling factor of 1 was used for this mixing, and the mixing was carried out at a temperature of 30°C for a duration of 2 minutes and 30 seconds. [Table 3] Properties of the resulting rubber composition Mooney viscosity ML(1+4) at 40°C 20 points Volumetric expansion rate following intumescence in an oven (15 min. at 600°C) 875 % Mechanical properties of the tank obtained by intumescence (qualitative) Limited - brittle char Oven creep, without load: 1 hour at 250°C 0% Vertical flammability test according to FAR25.853 Annex F Part 1 (a) (1) (i): ignition time of 60 seconds No residual flame - the mixture extinguishes itself immediately after the methane flame is removed

[0074] These properties of the rubber composition obtained in the non-crosslinked state (Mooney viscosity and creep) and partially crosslinked state (expansion rate, mechanical properties and flammability) were well suited for obtaining a fire barrier for the joint 10 according to the invention incorporating a fire-resistant structure 12 made up of this composition.

[0075] There Figure 10illustrates the result of a TGA analysis (carried out under N2 with a temperature ramp of 20°C / min.) showing the weight loss with temperature of two intumescent rubber compositions according to the invention, the first composition being based on the aforementioned PVMQ and the second composition based on a VMQ. The VMQ used for the second composition, in the uncrosslinked state, was a colorless solid with a density of 1.10 g / cm³ (measured according to DIN 53479A) and a viscosity ML(4) at 25°C of 26, and this second composition, with the exception of the VMQ, had the same formulation in terms of ingredients and quantities as the first composition in Tables 1-2 based on PVMQ.

[0076] This analysis by ATG of the Figure 10This shows that the first PVMQ-based composition exhibited a heavier residue after thermal degradation than the second VMQ-based composition. More specifically, this graph shows that from approximately 600°C, the weight of the PVMQ-based residue decreases less rapidly with temperature than that of the VMQ-based residue, with a weight loss of approximately 25% for the PVMQ-based residue at 900°C compared to nearly 40% for the VMQ-based residue. The Applicant has thus demonstrated that the addition of the phenyl group to the polymer chain of silicone rubber increases the thermal stability of the intumescent mass.

[0077] As illustrated in the figure 11The analysis by a plane-on-plane rheometer of the first rubber composition according to the invention based on PVMQ according to Tables 1-3, with a temperature sweep from 23 to 380°C following a temperature ramp of 10°C / min, with 1% strain and by controlling the normal force (Fn of 0.07 N, i.e., a pressure of 200 Pa), showed the following two transitions: Between 160 and 220°C, a first transition corresponding to a partial crosslinking of the rubber composition, and from about 340°C, a second transition corresponding to the expansion of the rubber composition.

[0078] The analysis illustrated by the figure 11establishes that the onset of intumescence of the first rubber composition took place above 270°C, at at least 340°C. This graph further establishes that the normal force exerted on the upper plate during the expansion of the first rubber composition was linear and not jerky, and that the mechanical integrity of the first composition expanded according to the invention was maintained until the end of the analysis.

[0079] Fire tests were performed on the sealing gasket 10 according to the invention of figures 8-9 And 10-11 with the fire-resistant structure 12 described above in relation to Tables 1-3, on the one hand, and on the "test" sealing joint 11 of the figure 7 devoid of a fireproof structure, on the other hand, a test bench according to the ISO 2685:1998 standard which is schematically represented in the figure 12 and which shows in particular, in relation to each sample of seal according to the invention and "control" tested: a) a fuel burner (i.e., kerosene), b) type K thermocouples for measuring the temperature during step 1 of flame calibration by the burner, these type K thermocouples being 100 mm from the burner, c) a calorimetry device, comprising a copper tube and type PT 100 thermocouples forming a calorimeter used to calculate the heat flux in order to calibrate the flame during step 2 of flame heat flux calibration, and a flow meter for measuring the water flow rate in this tube during step 2, d) a digital camera and three video cameras (arranged at the front and rear of the test device), which cameras are visible at the figure 13 , e) a test device (visible at the figure 14) comprising an assembly and adjustment shims supporting in compression each sample of seal to be tested during test step 3, at a distance of 100 mm from the burner, and f) a vibrating table to impart to each sample tested the vibrations required by ISO 2685:1998.

[0080] The conditions followed for these fire tests being those prescribed in ISO 2685:1998, they will not be detailed below, it being only specified that each fire test, carried out for 15 minutes, subjected the tested joint sample to: (i) the heat generated by a calibrated kerosene flame at 1100°C ± 80°C with a heat flux density absorbed by the standardized equipment described in B.4.2 of ISO 2685:1998 which is 116 ± 10 kW / m2, and (ii) vibrations of 50 Hz and 0.8 mm peak-to-peak as described in the same standard.

[0081] A thermal camera was placed at the rear of each assembly to measure the temperatures at the rear of each "control" sample and according to the invention being tested (i.e., on the side opposite the flame, see left side of the figure 13 compared to the test device equipped with the two video cameras), and the temperatures recorded in Table 4 below were obtained for the rear face of each sample as a function of the elapsed burning time (from 1 to 16 minutes). [Table 4] Elapsed firing time (min.) Temperature at the rear of the seal according to the invention (°C) Temperature at the rear of the "indicator" seal (°C) 1 - 125,3 2 166,2 161,8 3 180,4 172,4 4 189,1 215,9 5 202,3 244,4 6 225,1 265,9 7 244,8 288,6 8 263,1 320,7 9 276,2 343,6 10 290,0 340,3 11 304,0 351,5 12 314,7 397,1 13 324,3 - 14 331,0 - 15 333,4 - 16 326,7

[0082] These temperature measurements taken on the back of each gasket sample revealed: for the "control" seal sample, the destruction (i.e., disintegration by combustion of its rear face opposite the flame) of the seal after 12 minutes and 19 seconds of the fire test, and for the seal sample according to the invention, the successful passing of the fire test since this sample retained its rear face after 15 minutes of the fire test (this rear face, not destroyed, was at a moderate temperature of about 330°C after 15 minutes, in comparison to the temperature of nearly 400°C of the rear face of the "control" seal after 12 minutes).

[0083] In conclusion, and as confirmed by the photographs of figures 15-16 , the joint 10 according to the invention with fireproof structure 12 presents a fire resistance (barrier effect and protection of the joint body 11 by limiting the heating of its wall) very significantly improved compared to the "control" joint without fireproof structure.

[0084] Indeed, we see at the figure 15 that after the 15-minute test, the rear face of the body 11 of the seal 10 according to the invention was not disintegrated (see the figure 15 the third photograph from the left from the top), as well as the tank forming the residue of the fireproof structure 12 which played its role as a fire barrier in contact with the joint body 11 (this tank according to the invention is visible in the bottom left photograph and the three photographs on the right of the figure 15 ). Unlike the seal 10 according to the invention, the "test" seal 11 had its rear face largely destroyed after the 12 min. fire test, as can be seen in the third photograph of the figure 16 from the top.

Claims

1. Seal (10), comprising: - a seal body (11) at least in part elastomeric, the seal body (11) defining at least one roughly tubular or annular cavity (10A), and a fire-resistant structure (12) that is separate from the seal body (11) and is located within said at least one cavity (10A), the fire-resistant structure (12) comprising at least one intumescent mass capable of filling said at least one cavity (10A) in an expanded state, wherein said at least one intumescent mass is composed of a rubber composition that has an intumescence-triggering temperature equal to or greater than 270°C, as measured by a surface-surface rotational rheometer with a temperature scan ranging from 23 to 380°C, in a temperature ramp of 10°C / min, with 1% deformation, and with the change, starting from 23° C, of the normal force Fn from 0.07 N and of the air gap h between the planes from 2 mm, and wherein the seal (10) is designed to connect two structural elements (1 and 2) to one another in a zone of an aircraft selected from the zones of main engines and auxiliary engines, where the temperature in the absence of fire may range from -55°C to 250°C and which is designated as a fire zone in accordance with ISO 2685:1998 or AC 20-135.

2. The seal (10) according to claim 1, wherein said intumescence trigger temperature is comprised between 280 and 400°C, preferably between 320 and 360°C.

3. Seal (10) according to claim 1 or 2, wherein the rubber composition has, in the expanded state, a volumetric expansion ratio equal to or higher than 800%, measured for 15 min, at 600°C + / - 10°C in a Nabertherm® N17 / HR muffle furnace with a useful volume equal to 17 dm3 on a test sample with a circular cross-section with a 25 mm diameter made of the rubber composition, the expansion ratio being calculated by the formula ((Ef-Ei) / Ei). 100 with Ei denoting the initial thickness of the test piece equal to 2 mm and Ef the final thickness of the test piece.

4. The seal (10) according to one of the preceding claims, wherein the rubber composition is based on at least one silicone rubber, preferably a terpolymer derived from phenylmethyl-, vinylmethyl- and dimethylsiloxane (PVMQ).

5. Seal (10) according to claim 4, wherein the rubber composition further comprises: - an expandable organic or inorganic material capable of imparting the intumescence-triggering temperature to the rubber composition, preferably comprising an expandable graphite, - a flame retardant system, comprising fire retardants, - optionally a reinforcing filler, and a crosslinking system comprising a peroxide, the rubber composition being either not crosslinked or being only partially crosslinked.

6. Seal (10) according to claim 5, wherein the rubber composition comprises, for 100 pce of said at least one silicone rubber (pce: parts by weight for 100 parts of elastomer): - said organic or inorganic material expandable in an amount between 10 and 20 pce, preferably between 13 and 17 pce of said expandable graphite, the flame retardant system in question in a quantity ranging from 10 to 20 pce, the flame retardant system comprising, for example: quartz in a mass fraction of 15 to 40%, a metal oxide in a mass fraction of 15 to 40%, preferably titanium dioxide, dimethyl siloxane with a dimethylvinyl end group in a mass fraction of 15 to 40%; - optionally as said reinforcing filler, mineral fibres such as rock fibres, in an amount ranging from 18 to 28 pce; and - said peroxide in an amount ranging from 0.05 to 0.5 pce, for instance between 0.1 and 0.3 pce the aforementioned peroxide being preferably an aromatic organic peroxide, for example a dicumyl peroxide.

7. The seal (10) according to one of the preceding claims, wherein the rubber composition has, in the non-crosslinked state, a Mooney viscosity ML(1+4) at 40°C, measured according to the standard ASTM D-1646, which is comprised between 15 and 25 and for example between 18 and 22.

8. Seal (10) according to one of the preceding claims, wherein the rubber composition, in the expanded state, withstands the vertical flame test according to the standard FAR25.853, Appendix F part I (a) (1) (i), the rubber composition having no residual flame after removal of a methane flame for a flammability time of 60 seconds.

9. The seal (10) according to one of the preceding claims, wherein the fire-resistant structure (12) further comprises an envelope which is separated from the seal body and which encapsulates said at least one intumescent mass in particular to protect it from surrounding fluids, the envelope being for example based on a non-crosslinked silicone rubber.

10. The seal (10) according to one of the preceding claims, wherein the fire-resistant structure (12) is disposed over an inner zone of the seal body (11) independent of the tightness ensured by the seal (10) without the fire-resistant structure (12) being fastened to the seal body (11), the fire-resistant structure (12) having, in a non-expanded state before intumescence of said at least one intumescent mass, a generally parallelepiped geometry preferably defined by a width along a transverse dimension of said at least one cavity (10A), by a height perpendicular to and smaller than said width and by a length for example equal to that of said at least one cavity (10A).

11. Seal (10) according to one of the preceding claims, wherein the seal body (11) is entirely or partially made of an elastomeric material based on at least one silicone rubber, preferably a terpolymer derived from phenylmethyl-, vinylmethyl- and dimethylsiloxane (PVMQ), the seal body (11) being for example selected from among tubular seals with a Ω cross-section, a P cross-section, and from among annular bellows for conduits.

12. The seal (10) according to claim 11, wherein the seal body (11) is made of said elastomeric material, devoid of a reinforcing layer embedded in said elastomeric material.

13. The seal (10) according to claim 11, wherein the seal body (11) is made of a composite comprising said elastomeric material and at least one ply (11d) of a fabric, said at least one ply (11d) being embedded in said elastomeric material and being selected from among glass fabrics, aromatic polyamide fabrics and combinations thereof.

14. Seal (10) according to one of the preceding claims, wherein the seal (10) withstands fire according to the standard ISO 2685:1998, being capable of withstanding for 15 minutes: - heat generated by a kerosene calibrated flame at 1100° C ± 80° C with a heat flux density absorbed by the standardised apparatus described in B.4.2 of ISO 2685:1998 which is 116 ± 10 kW / m2, and - vibrations of 50 Hz and 0.8 mm peak to peak as described in ISO 2685:1998.

15. Aircraft, in particular an aeroplane or a helicopter, comprising: at least one pair of metallic or composite structural elements (1 and 2) designed to be connected to each other in at least one zone of the aircraft designated as a fire zone, for example in accordance with § 2.1 of ISO 2685:1998, said at least one zone preferably being selected from the zones of the main jet engines and auxiliary engines of the aircraft, such as the zones of an engine, of a nacelle, of a strut, and / or of an auxiliary power unit, and - at least one seal (10) that sealingly connects the structural elements (1 and 2) of said at least one pair to each other, wherein said at least one seal (10) is as defined in one of the preceding claims.