Seal for an aircraft and aircraft incorporating at least one such seal

Abstract

The invention relates to a seal for an aircraft incorporating a fire-resistant structure, and an aircraft incorporating at least one such a seal between structural elements of the aircraft connected to each other at a zone of the latter which may be a fire zone according to the standard ISO 2685:1998 or AC 20-135.

According to the invention, this seal (10) comprises: a seal body (11) at least partially elastomeric, the seal body defining at least one generally tubular or annular cavity (10A), and a fire-resistant structure (12) distinct from the seal body and disposed inside the cavity, the fire-resistant structure comprising an intumescent mass able to fill the cavity (10A) in an expanded state,
the intumescent mass being made of a rubber composition having an intumescence trigger temperature equal to or higher than 270° C., measured by a plane-plane rotary rheometer with a temperature scan from 23 to 380° C. according to a ramp of 10° C./min.

Claims

1. A seal (10), comprising: a seal body (11) at least partially elastomeric, the seal body (11) defining at least one generally tubular or annular cavity (10A), and a fire-resistant structure (12) which is distinct from the seal body (11) and which is disposed inside said at least one cavity (10A), the fire-resistant structure (12) comprising at least one intumescent mass able to fill said at least one cavity (10A) in an expanded state, wherein said at least one intumescent mass is made of a rubber composition having an intumescence trigger temperature equal to or higher than 270° C., measured by a plane-plane rotary rheometer with a temperature scan from 23 to 380° C. according to a temperature ramp of 10° C./min, with 1% of deformation and with an evolution, starting from 23° C., of the normal force Fn starting from 0.07 N and of the air gap h between the planes starting from 2 mm, and wherein the seal (10) is configured to connect two structural elements (1 and 2) to each other at a zone of an aircraft which is selected from among the main reactor and auxiliary engine zones, whose temperature in the absence of fire can vary from −55° C. to 250° C. and which is referred to as fire zone according to the standard 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.

3. The seal (10) according to claim 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 dm.sup.3 on a test sample with a circular section with a 25 mm diameter made of the rubber composition, the expansion ratio being calculated by the formula ((E.sub.f−E.sub.i)/E.sub.i).Math.100 with E.sub.i referring to the initial thickness of the test sample equal to 2 mm and E.sub.f the final thickness of the test sample.

4. The seal (10) according to claim 1, wherein the rubber composition is based on at least one silicone rubber.

5. The seal (10) according to claim 4, wherein the rubber composition further comprises: an expandable organic or inorganic material able to confer said intumescence trigger temperature on the rubber composition, a flame-retardant system, comprising fireproof agents, optionally a reinforcing charge, and a crosslinking system comprising a peroxide, the rubber composition not being crosslinked or being only partially crosslinked.

6. The seal (10) according to claim 5, wherein the rubber composition comprises for 100 pee of said at least one silicone rubber (pce: parts by weight for 100 parts of elastomer(s)): said expandable organic or inorganic material according to an amount comprised between 10 and 20 pce, said flame-retardant system according to an amount comprised between 10 and 20 pce, optionally as said reinforcing charge, mineral fibres according to an amount comprised between 18 and 28 pee; and said peroxide according to an amount comprised between 0.05 and 0.5 pee.

7. The seal (10) according to claim 1, 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.

8. The seal (10) according to claim 1, 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 claim 1, 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.

10. The seal (10) according to claim 1, 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.

11. The seal (10) according to claim 1, wherein the seal body (11) is entirely or partially made of an elastomeric material based on at least one silicone rubber.

12. The seal (10) according to claim 11, wherein the seal body (11) is made of said elastomeric material, being 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. The seal (10) according to one claim 1, wherein the seal (10) withstands fire according to the standard ISO 2685:1998, being capable of resisting for 15 minutes: the heat generated by a kerosene calibrated flame at 1,100° C.±80° C. with a heat flux density absorbed by the standardised apparatus described in B.4.2 of the standard ISO 2685:1998 which is 116±10 kW/m.sup.2, and to vibrations of 50 Hz and 0.8 mm peak-to-peak as described in the standard ISO 2685:1998.

15. An aircraft, in particular an airplane or a helicopter, comprising: at least one pair of metallic or composite structural elements (1 and 2) configured to be connected to each other at least at one zone of the aircraft selected from among the main reactor and auxiliary engine zones, whose temperature in the absence of fire fan vary from −55° C. to 250° C. and which is referred to as fire zone according to § 2.1 of the standard ISO 2685; 1998 or according to the standard AC 20-135, and at least one seal (10) which tightly connects the structural elements (1 and 2) of said at least one pair to each other, wherein said at least one seal (10) comprises: a seal body (11) at least partially elastomeric, the seal body (11) defining at least one generally tubular or annular cavity (10A), and a fire-resistant structure (12) which is distinct from the seal body (11) and which is disposed inside said at least one cavity (10A), the fire-resistant structure (12) comprising at least one intumescent mass able to fill said at least one cavity (10A) in an expanded state, wherein said at least one intumescent mass is made of s rubber composition having an intumescence trigger temperature equal to or higher than 270° C. measured by a plane-piano rotary rheometer with a temperature scan from 23 to 380° C. according to a temperature ramp of 10° C./min, with 1% of deformation and with an evolution, starting from 23° C. of the normal force Fn starting from 0.07 N and of the air gap h between the planes starting from 2 mm.

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

17. The seal (10) according to claim 4, wherein the rubber composition is based on a terpolymer derived from phenylmethyl-, vinylmethyl- and dimethylsiloxane (PVMQ).

18. The seal (10) according to claim 5, wherein the expandable organic or inorganic material able to confer said intumescence trigger temperature on the rubber composition comprises an expandable graphite.

19. The seal (10) according to claim 6, wherein the rubber composition comprises for 100 pee of said at least one silicone rubber (pee: parts by weight for 100 parts of elastomer(s)): between 13 and 17 pee of an expandable graphite for said expandable organic or inorganic material, said flame-retardant system which comprises: quartz according to a mass fraction from 15 to 40%, a metal oxide according to a mass fraction from 15 to 40%, dimethyl siloxane with a dimethylvinyl terminal group according to a mass fraction from 15 to 40%; rock fibres for said mineral fibres, according to an amount comprised between 18 and 28 pce; and said peroxide according to an amount comprised between 0.1 and 0.3 pce, said peroxide being an aromatic organic peroxide.

20. The seal (10) according to claim 9, wherein the envelope is based on a non-crosslinked silicone rubber.

21. The seal (10) according to claim 10, wherein said generally parallelepiped geometry is 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 equal to that of said at least one cavity (10A).

22. The seal (10) according to claim 11, wherein the seal body (11) is entirely or partially made of said elastomeric material which is based on a terpolymer derived from phenylmethyl-, vinylmethyl- and dimethylsiloxane (PVMQ), the seal body (11) being selected from among tubular seals with an Q-like cross-section, a P-like cross-section, and from among annular bellows for conduits.

23. The aircraft according to claim 15, wherein said at least one zone of the aircraft referred to as fire zone is selected from among the zones of an engine, a nacelle, a pylon and/or an auxiliary power unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Other features, advantages and details of the present invention will appear upon reading the following description of several embodiments of the invention, provided for illustrative and non-limiting purposes with reference to the appended drawings, among which:

[0077] FIG. 1 is a schematic cross-sectional view of an Ω-like seal 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 seal (i.e. with no fire in the aircraft), the fire-resistant structure of the seal not being expanded.

[0078] FIG. 2 is a schematic cross-sectional view of the seal of FIG. 1 forming a fire barrier in the event of a fire in the aircraft, the fire-resistant structure of the seal being expanded.

[0079] FIG. 3 is a schematic cross-sectional view of an Ω-like seal according to the invention similar to the example of FIG. 1 in normal operation of the seal, the fire-resistant structure of the seal not being expanded.

[0080] FIG. 4 is a schematic cross-sectional view of a P-like seal according to a variant of the invention, in normal operation of the seal, the fire-resistant structure of the seal not being expanded.

[0081] FIG. 5 is a schematic cross-sectional view of a seal according to another variant of the invention forming a bellow for conduits, in normal operation of the seal, the fire-resistant structure of the seal not being expanded.

[0082] FIG. 6 is a detail cross-sectional view of a seal body similar to that of FIG. 1, the seal being shown at rest and devoid of a fire-resistant structure with its dimensions expressed in mm.

[0083] FIG. 7 is a schematic cross-sectional view of a “control” seal at rest formed by the seal body of FIG. 6 with no fire-resistant structure, this “control” seal having undergone fire tests according to the standard ISO 2685:1998.

[0084] FIG. 8 is a schematic cross-sectional view of a seal according to the invention at rest formed by the seal body of FIG. 6 and by a fire-resistant structure, this seal having also undergone fire tests according to the standard ISO 2685:1998.

[0085] FIG. 9 is a photograph showing an open end of the seal of FIG. 8 in the deformed state over its lower base, which is topped by the non-expanded fire-resistant structure.

[0086] 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 silicone rubber PVMQ (curve in solid line), in comparison with a second composition according to the invention based on a silicone rubber VMQ (curve in dotted line), each composition forming a fire-resistant structure of the seal of FIGS. 8-9 and of the carbon residue resulting therefrom.

[0087] FIG. 11 is a graph illustrating the evolution as a function of temperature, measured through an analysis using a plane/plane rheometer, of the normal force Fn (lower curve) and of the inter-plate distance h (upper curve) of the first rubber composition according to the invention based on a PVMQ forming the fire-resistant structure of the seal of FIGS. 8-9 and of the carbon residue resulting therefrom.

[0088] FIG. 12 is a schematic view of a fire test bench according to the standard ISO 2685:1998 used for fire tests on the “control” seals and according to the invention of FIGS. 7 and 8-9, showing a seal sample, the burner and the main devices and corresponding steps used in this test bench.

[0089] FIG. 13 is a schematic view of a camera system disposed on both sides of the test device, inside the test bench of FIG. 12.

[0090] FIG. 14 is a detail view of the test bench of FIG. 12 showing two structural elements for compressing each “control” seal sample or according to the invention, and the direction of the impact of flame generated by the burner during each fire test.

[0091] FIG. 15 contains seven photographs showing a seal sample according to FIGS. 8-9 of the invention and the structural elements adjacent to this sample, upon completion of a fire test implemented according to the standard ISO 2685:1998.

[0092] FIG. 16 contains three photographs showing a “control” seal sample according to FIG. 7 and the structural elements adjacent to this sample, upon completion of a fire test implemented according to the standard ISO 2685:1998.

EMBODIMENTS OF THE INVENTION

[0093] The seal 10 according to the invention visible in FIG. 1 is mounted compressed between two opposing structural elements 1 and 2 to be sealed, and it comprises: [0094] a tubular seal body 11 with a closed Ω-like cross-section, defining a cavity 10A between its rounded top 11A and its planar base 11B which tightly bear against the elements 1 and 2, respectively, and [0095] a fire-resistant structure 12 disposed in this example over the inner face of the base 11B of the seal body 11, over the entire transverse width of the base 11B (in contact with the rounded wall of the cavity 10A on top of the base 11B) and which occupies in the non-expanded state and at rest of the seal body 11 a reduced fraction of the transverse height H of the cavity 10A.

[0096] Only for indication, the fire-resistant structure 12 has, for example, a rectangular section (i.e. a generally parallelepiped geometry over the length of the cavity 10A), and this fraction occupied by the fire-resistant structure 12 is, for example, comprised between only 5 and 20% of said height H (which is defined from the inner face of the base 11B to that of the top 11A of the cavity 10A).

[0097] As explained hereinabove, the seal body 11 is, for example, entirely or partially made of an elastomeric material based on a silicone rubber, in which material is optionally embedded at least one reinforcing fabric ply. As regards the fire-resistant structure 12, it is, for example, made of an intumescent mass formed by a rubber composition based on a silicone rubber and further comprising: [0098] an expandable organic or inorganic material able to confer an intumescence trigger temperature of at least 270° C. on the composition, preferably consisting of an expandable graphite, [0099] a flame-retardant system comprising fireproof agents, [0100] optionally a reinforcing charge, and [0101] a hot-crosslinking system comprising a peroxide.

[0102] After intumescence of the fire-resistant structure 12 in the event of a fire on-board the aircraft, one could see in FIG. 2 that the structure 12 occupies in the expanded state substantially the entirety of the height H and of the inner volume of the cavity 10A, also with the application of a multi-directional force (generally radial in this example) on the wall of the cavity 10A by the expanded structure 12, which is reduced to a carbonized state by the combustion reaction, which results in conferring an additional stiffness on the seal body 11 in the event of a fire.

[0103] The Ω-like seal 10 according to the invention visible in FIG. 3 differs from that of FIG. 1 essentially in that its fire-resistant structure 12 is wedged between two vertical spurs 11a and 11b connecting the inner face 11c of the base 11B to the rounded portion of the cavity 10A.

[0104] The seal 10 according to the invention visible in FIG. 4 comprises a P-like seal body 11, and a fire-resistant structure 12 for example with a rectangular section disposed inside the tubular cavity 10A of the “P”, over the inner face 11c of a base 11B of this cavity 10A (i.e. in the continuation of the leg of the “P”). As shown in FIG. 4, the fire-resistant structure 12 may be mounted, possibly with some clearance, in contact with the rounded wall of the cavity 10A of the “P”.

[0105] The seal 10 according to the invention visible in FIG. 5 is of the bellow type for two radially inner and outer conduits, respectively. The seal 10 comprises a two-walled seal body 11, and a fire-resistant structure 12 formed by a coating disposed inside the annular cavity 10A, over an inner face of the outer wall 11B′ of the seal body 11. Thus, the fire-resistant structure 12 can extend over the entire circumference of the outer wall 11B′ of the seal 10.

[0106] The Ω-like seal body illustrated in FIG. 6 is similar to the seal body 11 of FIG. 1, with: [0107] its generally planar base 11B provided over its outer face with a pair of external mount feet (lower feet in FIG. 6, defining an outer transverse width of 40.3 mm for the base) for mounting the seal body 11 bearing on a structural element 2 such as that of FIG. 1, and [0108] its rounded wall defining the cavity 10A from this base 11B, this wall (with a 1.5 mm thickness) being in this example generally in the form of an ellipse with a major axis (i.e. transverse width) equal to 40 mm and with a minor axis (i.e. transverse height) equal to about 29 mm, and laterally having a circular orifice.

[0109] As illustrated in FIG. 7, samples of a seal body 11 have been made according to the geometry and the dimensions of FIG. 6 by embedding, in an elastomeric material based on a silicone rubber PVMQ, a ply 11d of a glass fabric, so that the ply 11d extends in the mass of the rounded wall of the cavity 10A over its elliptical circumference and over the length of the cavity 10A. Thus, samples of the “control” seal of FIG. 7 have been obtained, consisting of only this rubber body 11 (with no fire-resistant structure therein).

[0110] As illustrated in FIG. 8, a fire-resistant structure 12 according to the invention, i.e. as described hereinabove with reference to FIG. 1, has been added to the seal body 11 of FIG. 7 (made of an elastomeric material based on said silicone rubber, in which a glass fabric ply 11d is embedded for reinforcement thereof). The fire-resistant structure 12 consisted of an intumescent mass with a generally rectangular section (i.e. with a generally parallelepiped geometry over the length of the cavity 10A), with a width and a height of 20 mm and 6 mm, respectively. Thus, samples of the seal 10 according to the invention of FIG. 8 have been obtained, formed by the same seal body 11 as in FIG. 7 and by the fire-resistant structure 12 therein, this seal 10 being visible in the photograph of FIG. 9.

[0111] The intumescent mass of the fire-resistant structure 12 of this seal 10 according to the invention has been prepared as described hereinafter.

[0112] The formulation of this intumescent mass is indicated in Table 1 hereinafter, representative of an example of said first composition according to the invention.

TABLE-US-00001 TABLE 1 Formulation Nature of the products Characteristics (pce) Flame-retardant system cf. Table 2 15.40 Silicon rubber PVMQ 100.00 Expandable graphite GHL 95 HT 270 15.40 Mineral fibres “LAPINUS” CF-50 23.10 Crosslinking agent Dicumyl peroxide 0.2 Total (pce) 154.1

[0113] More specifically, amongst these ingredients: [0114] the PVMQ silicone (as defined in ASTM D-1418, also called PMVQ) was a phenyl polydimethylsiloxane (phenylmethyl-, vinylmethyl- and dimethylsiloxane terpolymer which, in the non-crosslinked state, was translucent, had a density of 1.22±0.03, and a Williams plasticity measured according to ASTM 926 equal to 400), [0115] the GHL 95 HT 270 was a graphite grade expandable at a trigger temperature of 270° C., [0116] the “Lapinus” CF 50 reinforcing mineral fibres of the composition consisted of rock fibres with an average length of 500+/−150 μm and a diameter D90 of 7 μm, and [0117] the used flame-retardant system was a mixture of several compounds and fireproof agents pre-dispersed in a silicone oil, to facilitate dispersal thereof upon mixing of the rubber composition.

[0118] The composition of the flame-retardant system is indicated in Table 2 hereinafter.

TABLE-US-00002 TABLE 2 Mass Flame-retardant system fractions (%) Quartz - titanium dioxide - carbon black 40.0-70.0 Dimethyl siloxane, with a dimethylvinyl end 15.0-40.0 Cerium hydroxide 3.0-7.0 Polydimethyl siloxane with a hydroxy end 3.0-7.0 Dimethyl, methylvinyl siloxane, with a 3.0-7.0 dimethylvinyl end Platinum 115 ppm

[0119] The following properties of the rubber composition obtained by thermomechanical mixing of the aforementioned ingredients have been measured, whose values are reported in Table 3 hereinafter. For this mixing, a Haake® tangential mixer with a useful volume of 250 cm3 with a fill coefficient equal to 1 has been used, this mixing having been implemented at a temperature of 30° C. for a mixing duration of 2 min. 30 s.

TABLE-US-00003 TABLE 3 Properties of the obtained rubber composition ML(1 + 4) Mooney viscosity at 20 points 40° C. Volumetric expansion ratio after 875% intumescence in the oven (15 min. at 600° C.) Mechanical properties of the carbon Limited - brittle residue obtained by intumescence carbon residue (qualitative) Creeping in the oven, without load:  0% 1 h at 250° C. Vertical flame test according to the No residual flame - standard FAR25.853 Appendix F part the mixture is extinguished 1 (a) (1) (i): flammability time of directly after removal of 60 seconds the methane flame

[0120] These properties of the obtained rubber composition in the non-crosslinked (Mooney viscosity and creeping) and partially crosslinked (expansion ratio, mechanical properties and flammability) were well suited for the obtainment of a fire barrier of the seal 10 according to the invention incorporating a fire-resistant structure 12 made of this composition.

[0121] FIG. 10 illustrates the result of a TGA analysis (performed under N.sub.2 with a temperature ramp of 20° C./min.) showing the weight loss with the 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 non-crosslinked state, was a colourless solid with a volumetric mass of 1.10 g/cm3 (measured according to the standard DIN 53 479 A) and with a ML(4) viscosity at 25° C. equal to 26, and this second composition had, except for VMQ, the same formulation in terms of ingredients and amounts as that of the first compositions of Tables 1-2 based on PVMQ.

[0122] This TGA analysis of FIG. 10 shows that the first composition based on PVMQ has a heavier residue after thermal degradation than that of the second composition based on VMQ. More specifically, one can see in this graph that starting from about 600° C. the weight of the PVMQ-based residue decreases less rapidly with temperature than is the case for the VMQ-based residue, with a weight loss of about 25% for the PVMQ-based residue compared to about 40% for the VMQ-based residue at 900° C. Thus, the Applicant has demonstrated that the addition of the phenyl group in the polymeric chain of the silicone rubber increases the thermal stability of the intumescent mass.

[0123] As illustrated in FIG. 11, the analysis using a plane/plane rheometer of the first rubber composition according to the invention based on PVMQ according to Tables 1-3, with a temperature scan from 23 to 380° C. according to a temperature ramp of 10° C./min, with 1% of deformation and by control of the normal force (Fn of 0.07 N, namely a pressure of 200 Pa), has shown the following two transitions: [0124] between 160 and 220° C., a first transition corresponding to a partial crosslinking of the rubber composition, and [0125] starting from about 340° C., a second transition corresponding to the expansion of the rubber composition.

[0126] The analysis illustrated by FIG. 11 demonstrates that triggering of the intumescence of the first rubber composition has occurred beyond 270° C., at least at 340° C. This graph further demonstrates that the normal force exerted on the upper plate during the expansion of the first rubber composition was linear and progressive, and that the mechanical integrity of the expanded first composition according to the invention has been preserved until the end of the analysis.

[0127] For the fire tests concerning the seal 10 according to the invention of FIGS. 8-9 and 10-11 with the fire-resistant structure 12 described hereinabove with reference to Tables 1-3, on the one hand, and concerning the “control” seal 11 of FIG. 7 devoid of a fire-resistant structure, on the other hand, a test bench according to the standard ISO 2685:1998 which is schematized in FIG. 12 and which shows in particular, related to each tested “control seal ample and according to the invention:

a) a fuel (i.e. kerosene) burner,
b) a K-type thermocouple for measuring temperature during step 1 of calibrating the flame generated by the burner, these K thermocouples being remote by 100 mm from the burner,
c) a calorimetric device, comprising a copper tube and PT 100 type thermocouple forming a calorimeter used for calculating the heat flux in order to calibrate the flame during step 2 of calibrating the heat flux of the flame, and a flowmeter 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 at the rear of the test device), which cameras are visible in FIG. 13,
e) a test device (visible in FIG. 14) comprising an assembly and setting wedges supporting each seal sample to be tested during the test step 3 compressed, at a distance of 100 mm from the burner, and
f) a vibrating table for imparting to each tested sample the vibrations required by the standard ISO 2685:1998.

[0128] The monitored conditions for these fire tests being those prescribed in the standard ISO 2685:1998, they will not be detailed hereinafter, while pointing out that each fire test, implemented for 15 minutes, has subjected the tested seal sample to:

(i) the heat generated by a kerosene calibrated flame at 1,100° C.±80° C. with a heat flux density absorbed by the standardised apparatus described in B.4.2 of the standard ISO 2685:1998 which is 116±10 kW/m.sup.2, and to
(ii) vibrations of 50 Hz and 0.8 mm peak-to-peak as described in this same standard.

[0129] A thermal camera has been disposed at the rear of each assembly to measure the temperatures at the rear of each tested “control” sample and according to the invention (i.e. on the side opposite to the flame, cf. the left side of FIG. 13 with respect to the test device equipped with the two video cameras), and the temperatures reported in Table 4 hereinafter have thus been obtained for the rear face of each sample as a function of the elapsed fire time (from 1 to 16 minutes).

TABLE-US-00004 TABLE 4 Temperature at the rear of the Temperature at Elapsed fire seal according to the rear of the time the invention “control” seal (min.) (° C.) (° 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

[0130] These measurements of temperature at the rear of each seal sample have revealed: [0131] for the “control” seal sample, the destruction (i.e. disintegration by combustion of its rear face opposite to the flame) of the seal after 12 minutes and 19 seconds of the fire test, and [0132] for the seal sample according to the invention, the successful conclusion of the fire test given that this sample has preserved 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 with the temperature of about 400° C. of the rear face of the “control” seal after 12 minutes).

[0133] To conclude, and as this is confirmed by the photographs of FIGS. 15-16, the seal 10 according to the invention with a fire-resistant structure 12 has a fire resistance (barrier effect and protection of the seal body 11 by limiting the heat-up of its wall) that is very significantly improved in comparison with the “control” seal without the fire-resistant structure.

[0134] Indeed, one could see in FIG. 15 that after the 15 min. of testing, the rear face of the body 11 of the seal 10 according to the invention has not been disintegrated (cf. in FIG. 15 the third photograph to the left starting from the top), the same applies to the carbon residue forming the residue of the fire-resistant structure 12 which has served as a fire-barrier in contact with the seal body 11 (this carbon residue according to the invention is visible in the photograph at the bottom to the left and in the three photographs to the right of FIG. 15). Unlike the seal 10 according to the invention, the “control” seal 11 has its rear face largely destroyed after the 12 min. of the fire test, as visible in the third photograph of FIG. 16 starting from the top.