FR2876438A1 - Cryogenic insulation for space vehicle or aircraft components is made from a rigid closed-cell polyetherimide foam - Google Patents

Abstract

The insulation is made from a rigid moulded closed-cell foam with a preferable density of 60 kg/cu m, a tensile strength of about 1.7 MPa and a thermal contraction of 0.7 per cent at 20 (degrees) K. It can be made in panels 15 - 20 mm thick, pre-shaped to give it a curved section, and fixed in place with an adhesive primer.

Description

2876438 1

  CRYOGENIC ISOLATION ARTICLE, METHOD FOR IMPLEMENTING AND USING SAID INSULATION ARTICLE, AND LAUNCHER EQUIPPED WITH SUCH ISOLATION ARTICLE

DESCRIPTION TECHNICAL FIELD

  The present invention relates to the technical field of cryogenic insulation.

  The present invention relates to a cryogenic insulation article, as well as to a method of implementing such a cryogenic insulation article.

  It also relates to the use of such a cryogenic insulation article for the cryogenic insulation of equipment or structures of vehicles or space or aeronautical vehicles, such as thin-walled tanks in which there are propellants, such as only hydrogen or oxygen, which must be maintained in the liquid phase while minimizing heat losses.

  It finally aims a launcher equipped with such a cryogenic insulation article.

  STATE OF THE PRIOR ART In the field of vehicles or space or aeronautical vehicles, it is necessary to provide thermal protection for certain structures or certain equipment of the vehicle or the machine.

  For example, when it comes to a launcher, it is subject to external conditions that vary depending on the phase of the mission it performs. Conventionally, the: launcher experiences a phase of waiting on the ground, a phase of flight between the ground and the launch altitude, and a ballistic phase.

  During the waiting phase on the ground, the launcher is subjected to thermal loads which include: - exchanges by radiation: of its external walls with the ground and with the atmosphere, in the form of infrared emission, the solar illumination, in the form of direct radiation, or radiation scattered by the atmosphere, or radiation reflected from the ground, - exchanges by convection with the ambient air.

  In the flight phase, the launcher is subjected to the aerothermal flows during the crossing of the atmosphere.

  In the ballistic phase, the launcher is subjected to spatial radiation fluxes, such as the radiation of the earth, the radiation of the sun, the albedo.

  In order to limit the effect of these different sources of external thermal loads on the launcher, the tanks of a launcher are thermally insulated on their outer walls. These tanks are conventionally thin-walled cryogenic structures.

  There are different types of insulation articles for such tanks. These items typically provide hybrid solutions, which meet the specific needs of each phase of a launcher's mission, without unduly penalizing its total mass.

  For this purpose, cryogenic insulation articles are often encountered using insulating materials having low density and high thermal resistance.

  As previously indicated, the thermal efficiency of cryogenic insulation articles is related to their ability to limit incoming heat fluxes.

  The thermal efficiency of the insulation articles is also related to the penetration of condensable gases. It is therefore necessary that they be able to exclude condensable gases such as moist air. Indeed, during launch, the air and moisture trapped in the insulating material induce a risk of condensation and freezing that can cause damage to the insulation article. More specifically, during the filling of the tanks, the gases located near a cold wall condense, which generates a temperature gradient in the thickness of the insulating material and increases the thermal conductivity of the insulating article. During the atmospheric rise of the launcher, local increases in pressure can then occur in the insulating material. When this pressure becomes greater than the elastic limit of the material, a spallation occurs, that is to say a swelling, then a burst, at the constituent cells of the insulating material.

  This is called oryopompage of the air.

  In order to reduce this cryopumping phenomenon, it is conventional to use cryogenic insulation articles made from closed cell rigid foams. These are, for example, foams made of polyvinyl chloride, polyurethane foams with or without glass, foams made of polyisocyanurate, or phenolic foams. Insulation articles made from polystyrene foams are also encountered, although such foams are more rarely used in the field of cryogenic insulation, because their thermal properties are lower and because they are very permeable to steam. water.

  It has been found that closed-cell polyurethane foams are not sufficiently impervious to gases, which leads to a degradation of their thermal performance over time.

  The thermal efficiency of the insulation articles is also related to the mechanical characteristics of these insulating articles, which must be able to allow movement of the skin of the tank and support the acceleration loads exerted on the launcher. It is therefore necessary to be able to control the application of these insulating articles on the walls of the tanks, in a reliable, predictable, and reproducible manner.

  In the prior art, there are two methods of installing such a cryogenic insulation article on a thin-walled cryogenic tank.

  A first known method consists in projecting the insulating material directly on the outside face of the tank walls.

  It should be noted that, the higher the mass of the foam, and the more the acceleration loads exerted on the launcher can cause adhesion defects, and consequently less insulation. In order to minimize this disadvantage, it is necessary for the adhesion of the cryogenic insulation article to be greater than the rupture limit of the foam used. This is especially true that the foam used is a foam having a low tensile strength.

  A second known method is to stick against the outer face of the walls of the tank panels made of insulating material, these panels being made for example using molds or shapes.

  On the other hand, it is sometimes desirable for the insulating article to be capable of withstanding high temperatures at particular locations, such as, for example, areas of protuberances which are subject to large aerothermal fluxes, e.g. temperatures that are punctually high. Rigid closed-cell foams are generally capable of withstanding temperatures up to about 100 C. It is therefore generally known to protect the insulation article by means of an additional insulation article, called hot insulation, which is able to withstand high temperatures. Phenolic foams are able to withstand temperatures up to about 160 C, but have the disadvantage of being relatively brittle, which does not allow to use them for all desired applications.

  In view of the foregoing, it has therefore been found that the use of a cryogenic insulation article made from rigid closed cell foams known in the prior art has a number of disadvantages. The need exists to have an alternative cryogenic insulation article that overcomes these disadvantages.

  DISCLOSURE OF THE INVENTION The invention will be described in the case of the insulation of a cryogenic tank of a spacecraft. Such a reservoir is a thin-walled structure having a metal surface and a cold surface temperature with respect to ambient temperature.

  According to a first aspect, the invention relates to a cryogenic insulation article, characterized in that it is made from a rigid closed cell polyetherimide (PEI) foam. An example of such a rigid closed cell polyetherimide foam is known under the name R82 available from the AIREX Company.

  Preferably, the rigid closed cell polyetherimide foam has a density of substantially 55 kg / m3 to 65 kg / m3, for example of the order of 60 kg / m3. This relatively low density advantageously makes it possible to use such an insulation article in the spatial field.

  Such a density value gives the polyetherimide rigid closed-cell foam a good temperature resistance. It can withstand a temperature substantially of the order of 180 C, higher than that which can withstand the closed cell rigid foams of the prior art.

  The rigid closed-cell polyetherimide foam therefore degrades less rapidly at elevated temperature than prior closed-cell rigid foam foams. This advantageously eliminates the addition of additional insulating articles, called hot insulations on certain zones of concentration of aerothermal flows, such as areas of protuberances.

  Rigid closed-cell polyetherimide foam exhibits substantially 0.7% thermal shrinkage at 20K, which is lower than prior art closed cell rigid foams: thermal shrinkage of 1% at 20 K for rigid foam closed-cell polyvinyl chloride, and thermal contraction of 1.2% at 20 K for closed-cell rigid polyurethane foam.

  This property of low thermal contraction has the advantage that it is not necessary to increase the mechanical strength properties of the insulation article, as is the case with prior art materials such as polyurethane for example by increasing its thickness or by adding glass fibers.

  Preferably, the rigid closed cell polyetherimide foam has a tensile strength of substantially 1.5 MPa to 2 MPa, for example of the order of 1.7 MPa. In comparison, rigid closed-cell polyurethane foams have a tensile strength of generally 0.5 to 0.8 MPa, and rigid closed-cell polyvinyl chloride foams have a tensile strength generally of 0 , 8 to 1.0 MPa.

  This property of good tensile strength provides the advantage that the cryogenic insulation article can receive equipment that is directly adhered to it. It is thus possible to avoid mechanical fastening systems of these equipment on the cryogenic insulation article. This results in a saving of mass and a less expensive fixing, because it makes it possible to eliminate the tapping of pieces which would be necessary for a mechanical fixation of these equipments. This also results in improved insulation, since the absence of screws passing through the rigid closed-cell polyetherimide foam prevents thermal bridging. As a result, the risks of cryopumping the air are avoided.

  This property of good tensile strength also provides the cryogenic insulation article of the invention the advantage of being bonded to the structure.

  Preferably, the insulation article comprises at least one rigid closed cell polyetherimide foam board made by molding. Such a panel has for example a thickness ranging from 15 mm to 20 mm. In addition, it is possible to preform the panel, so that it has a curved section, with a radius of curvature corresponding to the radius of curvature of the surface that receives it, if any.

  According to a second aspect, the invention relates to a method of implementing a cryogenic insulation article according to the first aspect, characterized in that it comprises the following successive steps: a step of preparing the surface on which the cryogenic insulation article must be applied, a protective step during which a primer is applied to the surface thus prepared, a fixing step during which said cryogenic insulation article is bonded, in the form of at least one or more panels made from rigid closed cell polyetherimide foam, using a glass cloth impregnated with an adhesive material.

  The purpose of the preparation step is to give the surface sufficient surface tension to ensure optimum adhesion of a bonding primer. This preparation can take various forms well known to those skilled in the art.

  For example, it comprises an alkaline degreasing operation and a sulfochromic etching operation when the surface is an aluminum alloy surface. Then it comprises a rinsing operation with demineralized water or an emerization operation using a fine-grade sandpaper, or a sanding operation corundum small particle size.

  It is desirable that the time between the preparation step and the protection step be as short as possible. Preferably, this duration is substantially less than 8 hours.

  The protection step consists of applying a primer to the pre-prepared surface by spraying. The purpose of this protection step is to improve the adhesion of the adhesive material subsequently used to secure the insulation article, and to protect the surface to which the cryogenic insulation article is to be applied.

  Preferably, the primer is an epoxy resin. Such a material has the advantage of maintaining its physical properties up to a temperature of approximately -253.15 C (20 K). For example, such an epoxy resin may be a material referenced PZ 820 / HZ820 available from the company SODIEMA.

  It is desirable to prevent the surface that has just been protected from being polluted. For this purpose, the time between the protection step and the fixing step is preferably substantially 36 hours after the end of the projection of the primer to 30 days after the polymerization of the primer.

  Advantageously, the primer forms a film having a thickness ranging substantially from 10 microns to 50 microns. Even more advantageously, its thickness is substantially equal to 20 microns.

  During the fixing step, the insulating article made from polyetherimide closed-cell rigid foam is deposited on the surface, which has been previously prepared and coated with a primer. in the form of one or more panels (x). Bonding is done by means of an adhesive material.

  The adhesive material must be able to withstand the cryogenic temperatures without losing its integrity, and must, in addition, be chemically compatible with the materials which it ensures the bonding. Preferably, the adhesive material is an adhesive of the family of epoxies, such as glue available under the reference AY103 / HY953F from the company VANTICO, and better known under the name ARALDITE (registered trademark).

  Preferably, the adhesive material is applied by means of a glass fabric which is impregnated therewith and which is applied directly to the surface. When it comes to the surface of a spacecraft or aeronautical tank, the glass fabric impregnated with adhesive material is wound around this tank, in one or more layers.

  Preferably, the glass fabric has a density per unit area of substantially 30 g / m 2 to 40 g / m 2.

  Preferably, the layer of deposited adhesive material has a density per unit area of substantially from 150 g / m2 to 200 g / m2. More preferably, this density of basis weight is substantially from 150 to 170 g / m2.

  Preferably, the adhesive material has a shear strength in the range of 3 MPa to -253.15 C (20 K). By way of illustration, this means that a panel of the cryogenic insulation article according to the invention, which would be bonded to a surface of a cryogenic structure on a 10 cm 2 bonding surface, could withstand a stress on the surface. The fixing step preferably comprises a holding operation during which said panel is held by means of a vacuum bag, at a given holding pressure and during a holding period. given.

  The cryogenic insulation article generally comprises a plurality of panels. The panels are applied to the surface of the structure, preferably leaving a clearance of about 1 millimeter between two adjacent panels. Then they are maintained by means of a vacuum bag, with a holding pressure and for a holding time necessary for the polymerization of the adhesive material, for example 0.7 bar and about 36 hours for ARALDITE.

  The vacuum bag is then deposited, which makes it possible to verify that the panels have been bonded correctly, and in particular to check the presence of adhesive material at the joints separating two adjacent panels. Indeed, if a joint separating two adjacent panels has no or insufficient adhesive, it may occur a phenomenon of cryopompage air at the time of cold setting of the structure, which could lead to damage to the cryogenic insulation article.

  The cryogenic insulation article according to the invention may advantageously be used for the insulation of a thin-walled structure of a spacecraft or aeronautical vehicle.

  The cryogenic insulation article just described, made from rigid polyetherimide rigid cell foam, has a number of advantages over those of the prior art, which are made from other rigid foams with closed cells.

  When applied to a thin-walled structure such as a cryogenic launcher tank, the insulation article according to the invention allows movements of the skin of this structure which are due to hyperstatic forces, such as contractions. and the pressurization of the tank, during the filling phase of the tanks on the ground, or which are due to the general forces supported by the launcher in flight. The polyetherimide closed cell rigid foam has excellent impact resistance, and also high peel strength, which is required if the panels of the cryogenic insulation article are applied to a dynamically loaded structure.

  The fact that the polyetherimide rigid closed-cell foam has good temperature stability relative to closed-cell rigid foams of the prior art has the advantage that when subjected to an aerothermal flow peak, the surface of the closed-cell polyetherimide foam chars less quickly, and to a lesser thickness. As a result, changes in the physical characteristics of rigid closed cell polyetherimide foam are not critical and allow the launcher to continue its mission, which may not be the case with rigid closed-cell foams of the art. earlier.

  Finally, the cryogenic insulation article made from rigid closed-cell polyetherimide foam is unaffected or unaffected by the absorption of water and moisture. It thus reduces the risk of its resistance and compression stiffness diminishing over time.

  According to a third aspect, the invention also relates to a launcher equipped with at least one cryogenic insulation article according to the first aspect.

  According to a fourth aspect, the invention also relates to a use of a cryogenic insulation article according to the first aspect, for the isolation of a thin-walled structure of a spacecraft or aeronautical vehicle.

Claims (24)

  1. Cryogenic insulation article, characterized in that it is made from a closed-cell polyetherimide rigid foam.   2. Cryogenic insulation article according to claim 1, characterized in that said rigid closed-cell polyetherimide foam has a density of substantially 55 kg / m3 to 65 kg / m3.   3. The cryogenic insulation article according to claim 2, characterized in that said rigid closed cell polyetherimide foam has a density of the order of 60 kg / m3.   4. Cryogenic insulation article according to any one of claims 1 to 3, characterized in that said rigid closed cell polyetherimide foam has a tensile strength of substantially 1.5 MPa to 2 MPa.   5. The cryogenic insulation article according to claim 4, characterized in that said rigid closed cell polyetherimide foam has a tensile strength of the order of 1.7 MPa.   6. The cryogenic insulation article according to any one of claims 1 to 5, characterized in that said rigid closed-cell SP 24683 VD 2876438 polyetherimide foam has substantially a thermal contraction of 0.7% to 20K.   7. Cryogenic insulation article according to any one of claims 1 to 6, characterized in that it comprises at least one closed rigid foam polyetherimide closed foam board made by molding.   8. The cryogenic insulation article according to claim 7, characterized in that said panel has a thickness ranging from 15 mm to 20 mm.   9. The cryogenic insulation article according to claim 7 or 8, characterized in that said panel is preformed so as to have a curved section.   10. A method of implementing a cryogenic insulation article according to any one of claims 1 to 9, characterized in that it comprises the following successive steps.   a step of preparing the surface on which the cryogenic insulation article is to be applied; a protective step during which a primer is applied to the surface thus prepared; from which said cryogenic insulation article, in the form of at least one panel made from a rigid polyetherimide closed cell foam, is glued with a glass fabric impregnated with a adhesive material.   11. Implementation method according to claim 10, characterized in that the time between the preparation step and the protection step is substantially less than 8 hours.   12. Method of implementation according to any one of claims 10 to 11, characterized in that the duration between the protection step and the fixing step is substantially between 36 hours after the end of the projection of the primary and 30 days after the polymerization of the primer.   13. Method of implementation according to any one of claims 10 to 12, characterized in that the primer is an epoxy resin.   14. Method of implementation according to any one of claims 10 to 13, characterized in that the bonding primer forms a film having a thickness of substantially from 10 microns to 50 microns.   15. Method of implementation according to any one of claims 10 to 14, characterized in that the bonding primer forms a film having a thickness substantially equal to 20 microns.   SP 4683 VD 16. The method of implementation according to any one of claims 10 to 15, characterized in that the adhesive material is a glue of the family of epoxies.   17. The method of implementation according to any one of claims 10 to 16, characterized in that the adhesive material is deposited in a layer which has a density of mass per unit area ranging substantially from 150 g / m2 to 200 g / m2.   18. A method of implementation according to any one of claims 10 to 17, characterized in that the adhesive material is deposited in a layer which has a density of surface density substantially from 150 g / m2 to 170 g / m2.   19. Method of implementation according to any one of claims 10 to 18, characterized in that the adhesive material has a shear strength of the order of 3 MPa to -253,15 C (20 K).   20. A method of implementation according to any one of claims 10 to 19, characterized in that the glass fabric has a density of the density of substantially 30 to 40 g / m2.   21. Method of implementation according to any one of claims 10 to 20, characterized in that during the fixing step, glue panels leaving between two adjacent panels a game substantially of the order of 1 mm.   22. A method of implementation according to any one of claims 10 to 21, characterized in that the fixing step comprises a holding operation during which said panel is maintained by means of a vacuum bag, to a given holding pressure and for a given holding time.   23. Use of a cryogenic insulation article according to any one of claims 1 to 9, for the insulation of a thin-walled structure of a spacecraft or aeronautical vehicle.   24. Launcher, characterized in that it is equipped with at least one cryogenic insulation article according to any one of claims 1 to 9.