FR2850369A1 - Application of heat-resistant coating to rocket nozzle or space vehicle re-entry shield consists of applying layers at constant angle and adjusting thickness - Google Patents

Abstract

The procedure, using pre-impregnated fibre strip, consists of applying layers (3,3') at constant angle to surface, making local adjustments according to degree of ablation or thermal conductivity. After polymerisation of layers, the surface exposed to aerodynamic flow is machined to produce localised adjustment of its thickness. The procedure, using pre-impregnated fibre strip, consists of applying layers (3,3') at constant angle to surface, making local adjustments according to degree of ablation or thermal conductivity. After polymerisation of layers, the surface exposed to aerodynamic flow is machined to produce localised adjustment of its thickness. The fibre strip is in the form of a weave with warp and weft fibres lying at angles other than 0degrees and 90degrees respectively to its lengthwise axis. It can be wound, for example, in a constant spiral at an angle of around 20degrees, with no increase in thickness along adjoining edges.

Description

PROCESS FOR PRODUCING A PROTECTIVE COATING

  THERMAL 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 30001C, they must retain good mechanical properties, this being particularly the case for the diverging nozzles which also have a structural function of resumption of 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 SiO2, "Nextel", SiC or carbon fibers (for the highest temperatures) arranged in the form of wires, 2D fabrics or even of 3D textile preforms.

  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 furanic 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 3140968 describes a method for producing a structure, commonly called "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 10 mandrel, the first winding turn being carried out by pressing 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 ensure launchers, propellants, or space vehicles equipped with such parts 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 a constant angle relative to the deposition surface by locally adjusting said inclination so as to favor ablation and / or thermal conductivity in the zone or zones considered, then, after polymerization of the coating, to be machined the surface exposed to the aerodynamic flow, so as to locally adjust the thickness of said coating.

  The invention applies to the production of a coating on surfaces of revolution with a constant profile, for example cylindrical or conical surfaces, but also on surfaces of revolution with an evolving profile such as that of reentry shields or diverging nozzles.

  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 to the embodiment 5 of a diverging nozzle and a reentry shield with reference to the accompanying drawings in which: - Figure 1 is a half-view in axial section of a divergent 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 a relative to the internal surface 20 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 aE, either more or less.

  It is known, 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. In fact, the preferred path for the propagation of heat in a composite material being 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 make it possible 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 c ′ with respect to the internal surface of the divergent 10 greater than the cc inclination in 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 resulting in a concomitant slight increase in thermal conductivity, in order both to compensate for this loss of thermal insulation and to reinforce it, we will, in accordance with the invention, give the wall 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, the mass of the divergent can be optimized, that is to say to reduce it as much as possible, while giving at each point of the wall the physical properties the more appropriate to 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 area 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 tilt 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 the inclination (aE, cL ') 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 of 10 space vehicle re-entry whose wall 5, also of evolving profile, consists of a structure according to the invention, namely a succession of layers (5a, 5b) of equal thickness inclined at the same angle f3 with respect to the internal surface of said wall 5.

  In b is shown the direction of flow of the aerodynamic flow on the external face of the shield and in C is represented an attached nose 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 D 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 aims of the adjusted control of both the angle f3 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.

  The angles (x, ac ', f are advantageously around 200 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. 5 4) of a continuous fibrous strip 9, for example with 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 is made up of butted sections 10 a 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 Oa and 1a respectively, abutted and joined by adhesive elements 1 2 straddling said sections 1 Oa, 1 1a.

  1 5 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 and presentation rollers of the assembly 8 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 1 0, 11 is detached, in this case the so-called internal separator 10 which is located on the face of the strip 9 intended to be pressed against the last layer deposited on the mandrel 6.

  To this end, the assembly 8 is pinched between said last roller 14a and a separator roller 30 on which the internal separator 10 is wound up to then be 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 preceding 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 deposit 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 the layers 3, 3 ' , 5a, 5b according to a constant inclination (a, y) relative to the depositing surface and capable of localized adjustments and thus to achieve said divergence 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 same free diameter in rotation on the axis of the roller.

  Thus, each of the rollers adapts its speed of rotation as a function of 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. 3, it will be useful to refer to the patent application filed on the same day in the name of the applicant and entitled "method of depositing on a support of successive fibrous layers inclined from 'a continuous band ".

  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 (10)

R E V E N D I C A T I 0 N S   1. Method for producing a thermal protection 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 (a, to) constant with respect to the depositing surface by locally adjusting said inclination so as to favor in the area considered ablation and / or thermal conductivity, then, after polymerization of the coating to machine the surface exposed 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 10 layers (3, 3 '; 5a, 5b) is carried out on a surface of evolving profile.   3. Method according to claim 1 or 2, characterized in that the evolution of the inclination (a, ax ', P3) 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. Coating 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 900 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 (a, a ', 13) 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).   10. Piece of revolution according to claim 8, consisting of a shield (4) reentry for space vehicle.