WO2004067943A1

WO2004067943A1 - Method of producing a thermal barrier coating comprising inclined layers and structures thus obtained

Info

Publication number: WO2004067943A1
Application number: PCT/FR2004/000142
Authority: WO
Inventors: Christophe Arnould; Lucien Fantino; François Monget
Original assignee: Eads Space Transportation Sa.
Priority date: 2003-01-23
Filing date: 2004-01-22
Publication date: 2004-08-12
Also published as: FR2850369A1; EP1590565A1; FR2850369B1

Abstract

The invention relates to a method of producing a thermal barrier coating comprising inclined layers, by winding a band of pre-impregnated fibres onto a revolving surface. The invention is characterised in that it consists in: depositing the aforementioned layers (3, 3', 5a, 5b) at an angle (α, β) in relation to the deposit surface which is adjusted locally such as to promote ablation and/or thermal conductivity in the area of interest; and subsequently, after polymerisation of the coating, machining the surface which is exposed to the aerodynamic flow, in order locally to adjust the thickness of the coating.

Description

METHOD FOR PRODUCING A THERMAL PROTECTION COATING WITH INCLINED LAYERS AND STRUCTURES OBTAINED

The present invention relates to structures subjected to very significant overheating, such as for example spacecraft return shields or elements of a propulsion system such as a nozzle divergent. These structures are particularly stressed because, in addition to their resistance to temperatures which can reach or exceed 3000 ° C., they must retain good mechanical properties, this being particularly the case for the diverging nozzles which also have a structural recovery function. the thrust. In addition, these structures are asked to have an aerodynamic function, that is to say to ensure good gas flow and therefore to keep an unchanged shape despite the effects of ablation due to the high temperatures.

The materials used for these types of structures are often thermostructural composite materials composed for example of fibers of Si02, “Nextel”, SiC or carbon (for the highest temperatures) arranged in the form of wires, 2D fabrics or even preforms 3D textiles. The matrices may be ceramic based on SiO2, SiC or C, or else based on resins with a high coke content such as phenolic or furan resins, or certain silicone resins which, during pyrolysis, give, depending on the case, carbon or silica. The present invention relates more particularly to structures made up or covered with a succession of inclined layers formed of fibers embedded in an appropriate matrix, the layers forming an angle with respect to the surface on which they are deposited. This type of architecture is well known.

US 31 40968 describes a process for producing a structure, commonly known as a "clino", consisting of a helical winding around a cylindrical mandrel of a strip, in successive layers all inclined at the same angle relative to a generator of the mandrel, the first winding turn being carried out on a starting block giving the angle of inclination of the successive layers.

The material wound on the mandrel is a strip of prepreg fibers, for example a strip of fabric.

The object of the invention is to optimize the mass of parts of the shield, divergent nozzle or similar type, integrating a "clino" structure so as to provide launchers, propellants, or space vehicles provided with such parts with a payload as high as possible, while giving the parts in question an optimized mechanical-aero-thermal resistance, that is to say adjusted locally. To this end, the subject of the invention is a process for producing a thermal protective coating with inclined layers by winding on a surface of revolution from a strip of prepreg fibers, characterized in that it consists depositing said layers at an angle relative to the deposit area adjusted locally so as to favor ablation and / or thermal conductivity in the zone or zones considered, then, after polymerization of the coating, to machine the surface exposed to the flow aerodynamic, so as to locally adjust the thickness of said coating.

The invention applies to the production of a coating on surfaces of revolution with constant profile, for example cylindrical or conical surfaces, but also on surfaces of revolution with evolving profile such as that of reentry shields or diverging nozzle. The subject of the invention is also the coatings obtained in accordance with the process as well as the structures incorporating such coatings such as shields, divergent or others.

We will now describe two applications of the invention for producing a nozzle divergence and a reentry shield with reference to the appended drawings in which:

Figure 1 is a half view in axial section of a diverging nozzle whose wall consists of a coating according to the invention; - Figure 2 is a half view in axial section of a space vehicle re-entry shield;

Figure 3 is a diagram illustrating a device capable of producing structures according to claim 1 or 2, and Figure 4 is a strip made up of sections of fabric of prepreg fibers usable with the device of Figure 3.

In Figure 1, there is shown in axial half-section a diverging nozzle 1 whose wall 2, of evolving profile, consists of a structure according to the invention, namely of a succession of layers 3 of equal thickness inclined by the same angle α relative to the internal surface of said wall 2 which is the surface exposed to the aerodynamic flow (arrow a).

However, locally, the layers 3 may have a slightly different inclination from the value α, either more or less. We know, in fact, that in a “clino” structure, the ablation is directly linked to the inclination of the layers. The more the layers are at a slight inclination relative to the surface to be protected, the greater the ablation.

If we want to improve the ablation, that is to say, reduce it, we must increase the angle of inclination of the layers. With regard to thermal conductivity, the larger the angle of inclination of the layers, the better the conductivity. With an equal coating thickness, the thermal conductivity is less good with a lower angle of inclination of the layers. Indeed, the preferred path of propagation of heat in a composite material being the fibers, the heat will take longer to pass through the coating via inclined layers having a greater width than that of the less inclined layers.

The method of the invention will thus allow for example in the zone 2a of the wall of the divergent 1 close to the nozzle neck, to give the layers 3 'an inclination α' relative to the internal surface of the divergent greater than the inclination α in the zone 2b near the exit of the divergent, so as to reduce the effects of ablation, which is desirable in this zone 2a which is particularly stressed at the exit of the nozzle neck. Furthermore, this increase in the inclination concomitantly causing a slight increase in the thermal conductivity, to both compensate for this loss of thermal insulation and reinforce the latter, we will, in accordance with the invention, give the wall of the divergent in this zone 2a, a thickness greater than that of the wall in zone 2b less thermally stressed. This adjustment of the thickness of the wall of the divergent is effected after polymerization of the coating in an autoclave, by machining the internal face of the divergent during which more material will be removed in zone 2b than in zone 2a. Thus, from one end to the other of the profile of the divergent, we can optimize the mass of the divergent, that is to say reduce it as much as possible, while giving at each point of the wall the most physical properties suitable for the aerodynamic flow prevailing at this location, this being obtained by varying the inclination of the layers combined with an adaptation of the thickness of the wall. In the zone 2b of the divergent the conditions of the aerodynamic flow are less severe, it is therefore possible to further reduce the thickness of the wall 2 and reduce the angle of inclination α of the layers 3 a little more. Ablation will certainly be favored, but this has no consequences because the flow is in this reduced area. As for the thermal conductivity, its reduction caused by the reduction in thickness will be compensated by a greater inclination of the layers 3. The variations in thickness of the wall 2 and of the inclination (α, α ') of the layers (3 , 3 ') can be in stages or, better, continuous along the profile of the divergent from the nozzle neck (2a) to the end (2b) of the divergent. In Figure 2, there is shown in axial half-section a shield 4 for the return of a space vehicle whose wall 5, also of evolutive profile, consists of a structure according to the invention, namely of a succession of layers (5a, 5b) of equal thickness inclined at the same angle β with respect to the internal surface of said wall 5. In b is represented the direction of flow of the aerodynamic flow on the external face of the shield and in C is represented a reported cap.

Just as for the divergent 1 of FIG. 1, the shield 4 can comprise a zone 4a close to the cap C with layers 5a whose inclination β is slightly greater than that of the layers 5b of the zone 4b close to the outer edge of the shield and local thickness adjustments of the wall 5 of the shield can be made during the machining of the external face.

The goals of the adjusted control of both the angle β and the thickness are the same as for divergent 1, namely reduction of mass and improvement of the properties of mechanical strength and resistance to heating, with the difference that the local value of the depositing angle β in the case of the shield 4 is determined so that after machining the face opposite to that facing the layer depositing surface, that is to say the external face of the shield, the inclination of said layers relative to this external face corresponds to that calculated. The angles α, α ′, β are advantageously around 20 ° from one end to the other of the profile of the part.

FIG. 3 illustrates a winding device suitable for producing structures according to FIGS. 1 and 2 and FIG. 4 represents a fibrous strip suitable for producing, using the device in FIG. 3, such structures.

In Figure 3, there is shown schematically, seen in axial section, a mandrel 6 rotated about its axis 7 by a motor M, the mandrel being metallic or made of a suitable plastic foam. The material for depositing on the mandrel 6 is an assembly 8 formed (FIG.

4) of a continuous fibrous strip 9, for example of a length of several hundreds, even thousands of meters and a width of a few tens of millimeters, sandwiched between two separating films 1 0 and 1 1 of the same length and width. More specifically, the fibrous strip 9 consists of butted sections 9a of a fabric of warp and weft threads making with the axis of the strip 9 an angle different from 0 ° and 90 ° respectively. Each section 9a is flanked by two sections of separator 1 0a and 1 1a respectively, abutted and joined by adhesive elements 1 2 straddling said sections 1 0a, 1 1 a.

The assembly 8 is stored on a supply reel 1 3 provided with a reeling system symbolized at F making it possible to brake in a controlled manner the routing of the assembly 8 to a set 14 of guide rollers and presentation of the 8 together at a station 1 5 for removing the fibrous strip 9.

The depositing station 1 5 disposed above the mandrel 6 comprises an applicator device responsible for pressing the strip 9 against the preceding inclined layer which has just been deposited on the mandrel and consisting of a cylindrical roller 1 6 carried by a device (not shown) ensuring three degrees of freedom to said roller 1 6.

In line with the output roller 14a of the assembly 14, one of the separators 10, 11 is detached, in this case the separator said internal 10 which is on the face of the strip 9 intended to be pressed against the last layer deposited on the mandrel 6. For this purpose, the assembly 8 is clamped between said last roller 14a and a separating roller 17 on which s rolls up the internal separator 10 and is then automatically rewound on a reel 18.

The strip 9 and the remaining separator 11, called the external separator, are directed onto the roller 16, the external separator being interposed between the roller 16 and the strip 9. On a fraction of a turn of the mandrel 6, the separator 11 is pressed against the strip 9 then detached to be rewound on the same reel 18 as the internal separator 10.

The coil 18 is driven for example by a pneumatic motor MP with torque and variable speed of rotation. Thus, the strip 9 is regularly and optimally pressed against the previous layer by the separator 11 which acts as a transmission belt driven by the rotation of the mandrel 6.

The fibrous strip 9 is not subjected to the tensile force which is the result of the motor force generated by the mandrel and the resistant force provided by the unwinding system (13, F). It is easy to control this effort and to automate the removal by a pilot system P with programmed numerical control controlling the speed of rotation of the mandrel 6, the braking of the device F, the rewinding of the separators on the reel 18 and controlling the movements and the positioning of the roller 16. The fibrous strip 9 undergoes as deformation only that which develops when the strip is placed on the preceding layer, the strip then passing from a rectilinear shape to a curved shape. Thanks to the possible inclination of the axis of the roller 1 6 and by using a mandrel 6 with the shapes and dimensions of the divergent 1 or of the shield 4 it is possible to deposit on the mandrel layers such as layers 3, 3 ′, 5a, 5b according to a constant inclination (α, β) relative to the depositing surface and capable of localized adjustments and thus to produce the said diverging 1 and shield 4. Furthermore, in order to reduce the friction between the roller 16 and the inevitable separator 11 since the roller is a cylindrical body rolling on a non-planar surface, the roller 16 advantageously consists of a stack of thin rollers and likewise free diameter in rotation on the axis of the roller.

Thus, each of the rollers adapts its speed of rotation according to its location along the axis of the roller and whatever the radius of the mandrel 6. For more details on the operation of the device of FIG. refer to the patent application filed on the same day in the name of the applicant and entitled "process for depositing on a support successive fibrous layers inclined from a continuous strip". It should be noted that all types of fibrous bands, conventional or not, with fringes, in the form of a braid, can be used in the process of the invention.

Of course, the structures of FIGS. 1 and 2 or any other structure of revolution with an evolving profile made up or covered with a thermal protective coating with successive inclined layers in accordance with the invention, can be produced by other winding means than those described above by way of example only. Furthermore, the materials used for the production of parts according to the invention can be of all types as indicated above in the preamble, both with regard to the fibers and with regard to the dies.

Claims

1. Method for producing a thermal protective coating with inclined layers by winding on a surface of revolution from a strip of prepreg fibers, characterized in that it consists in depositing said layers (3, 3 ', 5a , 5b) at an angle (α, β) relative to the deposit area adjusted locally so as to favor in the area considered ablation and / or thermal conductivity, then, after polymerization of the coating, to machine the exposed surface to the aerodynamic flow, so as to locally adjust the thickness of said coating.

2. Method according to claim 1, characterized in that the deposition of the layers (3, 3 '; 5a, 5b) is carried out on a surface of changing profile.

3. Method according to claim 1 or 2, characterized in that the evolution of the inclination (α, α ', β) of the layers (3, 3'; 5a, 5b) and of the thickness of the coating is continuous or in stages from one end to the other of the coating.

4. Thermal protective coating with inclined layers obtained in accordance with the method according to one of claims 1 to 3.

5. Covering according to claim 4, characterized in that the strip of fibers is a fabric whose warp and weft threads make with the axis of the strip an angle different from 0 ° to 90 ° respectively.

6. Coating according to claim 5, characterized in that the inclined layers (3, 3 '; 5a, 5b) are formed of a continuous helical strip (9) consisting of butted sections (9a) without any excess thickness at the junctions .

7. Coating according to one of claims 4 to 6, characterized in that the inclination (α, α ', β) of the layers (3, 3'; 5a, 5b) is around

20 °.

8. Piece of revolution constituted by or integrating a coating according to one of claims 4 to 7.

9. Piece of revolution according to claim 8, constituted by a diverging nozzle (1).

1 0. Part of revolution according to claim 8, consisting of a reentry shield (4) for a space vehicle.