FR2850368A1 - Thermal insulation laying procedure e.g. for space vehicle heat shield uses fibre strip passed initially between separators before guide and applicator - Google Patents

Abstract

The procedure for laying continuous fibre insulating strip (I)(5) comprises passing (I) between two separators (6,7) then delivering (I) and separator assembly (4) to a guide and presentation post (9), where inner separator (6) is detached from (I). (I) and outer separator are pressed by applicator (11) against preceding layer on rotating support (1) while traction is applied. The procedure for laying a continuous fibre insulating strip (5) in a series of inclined lines consists of first passing the strip between two separators (6, 7) and then delivering the strip and separator assembly (4) to a guide and presentation post (9), where the inner separator (6) is detached from the strip. The strip and outer separator are then pressed by an applicator (11) against the preceding layer on a rotating support (1) while a traction is applied by a brake (F) on the delivery unit (8). The outer separator (7) is then removed from the strip after accompanying it for a fraction of the support's rotation. The strip layer applicator is able to move along three axes of freedom: parallel and orthogonal to the support's axis of rotation, and orthogonal to the first two axes. The applicator consists of a roller made up of a series of separate freely rotating discs that can lay the strip on a shaped surface without slipping relative to the strip and separator assembly.

Description

METHOD OF DEPOSITION ON A FIBROUS LAYER SUPPORT

  The present invention relates to structures subjected to very significant overheating, such as for example spacecraft re-entry 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 30000C, 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 but also for the shields 10 which "brake" the vehicle.

  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 preforms 3D textiles.

  The matrices can 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 oc determined with respect to the grazing aerodynamic flow.

  This type of architecture is well known.

  US 3140968 describes a method for producing a structure, commonly known as a "clino", consisting of a helical winding around a mandrel of a strip, in successive layers all inclined at a certain degree relative to a generatrix of the 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 and more precisely a strip of fabric, the warp and weft threads of which make with the axis of the strip an angle different from 0 and 900 respectively. It is indeed necessary that during the winding of the strip on the mandrel, this strip can be deformed, the edge on the mandrel side of the strip being subjected to contraction and the outer edge to extension.

  A first difficulty with this technique is the production of a strip suitable for such a winding.

  Suppliers of fibers or fabrics intended for such use, generally 2d 0/90 fabrics, deliver their products in the form of rolls. It is therefore necessary to cut obliquely from these rolls pieces of strip according to the orientation of the fibers which one wishes and then put these pieces end to end either by sewing, or by an adhesive, or by using the tackiness of the fiber impregnation resin as in US 3,140,968.

  However, these various methods have the drawback of causing excess thicknesses localized at the junction zones of the strip sections.

  To remedy this problem, other solutions have been devised.

  Thus, in FR 2,569,237 and US 3,960,626, special fringed bands are proposed and in US 3,583,275 the bands are braids.

  However, these solutions are too specific and marginal and prove to be expensive.

  Furthermore, "clino" structures, whether of revolution or not, often have a longitudinal profile, that is to say taken in a plane containing the axis of symmetry of the structure or the axis of rotation of the support on which the structure is wound, variable.

  However, when depositing by winding on a support a fibrous strip generally pre-impregnated, for the production of a "clino", use is made of a pressure roller intended to ensure control of the spaces between the 10 different layers, that is to say the control of the thickness of the folds, so as to obtain the lowest possible porosity of the finished product.

  Such a pressure roller poses problems in the case of depositing on a surface whose generator is not parallel to the axis of rotation of the support.

  Indeed, when one wants to roll a cylindrical roller on a non-planar surface, it generates slippage and possibly tearing of fibers from the strip.

  One solution would consist in constituting the cylindrical roller using washers stacked on an axis, which would make it possible to have differential rotations of the various washers, but such rollers are unusable for the deposition of fibrous strips pre-impregnated because they get dirty very quickly, fragments of fibers and resin slipping between the washers and quickly rendering said roller unusable.

  Finally, it is necessary to emphasize the difficulty of making "clino" parts of revolution of small diameter which can go down to 50 mm, even 30 mm due to the very significant deformation to be subjected to the bands, the problem being the same for parts not of revolution but with a small radius of curvature.

  The products produced by known techniques are of average quality because pleated layers are formed and, ultimately, the thermal, ablative and mechanical properties are poorly controlled and dispersed.

  The present invention aims to improve the manufacture of structures made of "clino" materials, in particular the quality and control of the deposition and deformation of the fibrous strip on the winding support constituted either by the surface of the object to be coated, either by a mandrel with the shapes and dimensions of the part to be produced, even for small radii of curvature. The invention also aims to allow the angle ac of inclination of the layers relative to the deposition surface to be varied at will or, on the contrary, to keep the angle ac of inclination relative to a deposition surface constant. evolutionary profile.

  The invention also aims to automate the deposition of the fibrous strip.

  To this end, the subject of the invention is a method of depositing on a support successive inclined fibrous layers, from a continuous strip 10 wound on said support, characterized in that it consists in: continuous fibrous strip between two separators, to be conveyed by an appropriate delivery system all the separator strips to a guiding station1 5 presentation o the so-called internal separator covering the face of the strip intended to be pressed on the layer which has just been deposited is detached from the strip, then depositing the strip and its so-called external separator on said layer using an applicator device pressing the strip against said previous layer, the strip being driven by the rotation of the strip. support, while the traction exerted on said strip and its external separator is controlled both by the engine torque applied to said support and by the braking of said support delivery system for all 25 strip-separators, - the external separator being detached from the strip deposited after accompanying the latter over a fraction of a turn. Such a method makes it possible to deposit a fibrous strip under tension on the wound support without generating deformation linked to this deposit in tension because the tensile force on the strip exerted by the motor torque applied to the rotary support is transmitted to the separator. external which remains pressed against the strip at the time of its contact with the support via the applicator-presser device, said separator continuing to press the strip during depositing at least over a fraction of a turn and thus contributing to good control of the spaces between the different layers, that is to say a constant fold thickness, without wrinkling and with the lowest porosity of the stacking of the layers.

  The regulation of the tension exerted on the strip can be controlled automatically by a control taking into account the nature of the strip to be deposited, the diameter of the support to be wound, the tension of the strip being all the more important as said diameter decreases.

  This regulation can be carried out by taking into account as a parameter, the motor torque applied to the rotary support, the braking exerted on the strip at the delivery system of the strip-separator assembly, as well as the rewinding tension of the external separator.

  According to another characteristic of the process of the invention, the fiber strip is removed using a presser applicator device consisting of a cylindrical roller mounted movable along three axes of freedom, namely a first axis parallel to the axis of rotation of the support, a second axis orthogonal to the axis of rotation of the support and an axis of rotation of said roller orthogonal to said first and second axes, said cylindrical roller being moreover formed of a stack of free individual rollers in rotation thus making it possible to wind on a support with an evolving profile or not without sliding between the roller and the band-separator assembly, each individual roller automatically adjusting its speed of rotation as a function of the radius of the support. Such a roller, moreover, does not clog since it is not in direct contact with the prepreg fabric.

  In order to further facilitate the deformation of the strip when it is removed, the roller with multiple rollers has an axis which can be slightly inclined, of the order of a few degrees, relative to a plane containing the axis of rotation of the support and passing through the center of said roller.

  According to another characteristic of the process of the invention applied to the deposition of a continuous strip made up of a fabric of prepreg fibers with warp and weft threads having an orientation relative to the longitudinal axis of the strip different from 0 5 and 90, a continuous strip formed of butted sections without extra thickness is produced by proceeding to manufacture the strip separator assembly, for example in the following manner.

  From a commercial strip of standard width of a fabric of prepreg fibers coated on each side with a suitable separating film 10, the strips of a determined width are cut at an angle which are then butted together, as well as the associated separator sections, and at the right of each junction between separator sections is attached to each face of the assembly an adhesive element overlapping the facing separators. Then, the strip-separator assembly thus formed is cut again along narrow strips parallel to the axis of said assembly.

  The strips thus obtained are then abutted in the same manner as above to reach the desired length of strip to be deposited, this length possibly reaching several thousand 20 meters, for a width of a few tens of millimeters, depending on the thickness of the "clino "to be wound and the angle of inclination of the layers thereof.

  The continuous strip thus obtained, with its separators, is wound on a reel provided with a reel system with controlled braking.

  The fibrous strip thus obtained has no excess thickness since the sections are simply butted and the joining between sections is obtained by the separators flanking the fibrous strip which, although being themselves in the form of butted sections, are linked together the others by the adhesive elements which overlap them.

  Such a strip can be installed without problem thanks to the removal process of the invention since the traction exerted on the strip is in fact supported by the external separator which "accompanies" the strip at the time of its removal thus saving it from be subjected to traction while allowing it to move freely and optimally up to the applicator device pressing the strip on the previous layer.

  It is thus possible to deposit a constant bandwidth while maintaining a constant layer thickness and without any wrinkling.

  Other characteristics and advantages of the process of the invention will emerge from the description which follows, given by way of example 10 only and with reference to the appended drawings in which: - Figure 1 is a schematic axial section view of a mandrel bearing a "clino" coating; - Figure 2 is a schematic view of a device for producing a "clino" according to the method of the invention; 15 - Figure 3 shows a segmented dispensing roller according to the invention; - Figure 4 shows a segmented roll having a slight inclination of its axis relative to the plane containing the axis of the winding support and passing through the center of said roll, and - Figure 5a to 5c illustrate three stages of making a strip continuous fibrous without excess thickness according to the invention. In FIG. 1 is shown schematically at 1 a winding mandrel of a "clino" structure, having two cylindrical sections l a, i b of different diameter separated by a frustoconical section 1 c.

  A "clino" structure is a well-known structure formed by a helical winding of a continuous strip, for example a strip of fabric of prepreg fibers, on a deposition surface which is that of the part to be coated or that of a mandrel with the shapes and dimensions of the part to be produced.

  The <clino "structure consists of successive layers such as layers 2 of FIG. 1, deposited with the same degree of inclination relative to a generatrix of the surface (cylindrical la) on which they are deposited.

  The deposition on the mandrel 1 of the fibrous strip to form the inclined layers 2 is difficult because it is necessary to be able to deform this strip in a controlled manner. A suitable system is also required for the presentation and deformation of this strip in order to obtain layers 2 of constant thickness, without localized wrinkling and with the lowest possible porosity of the stack of layers.

  Removal is even more difficult if it is necessary, on the same cylindrical surface such as la, to vary the angle (x, or if the longitudinal profile of the mandrel 1 varies as is the case in the figure 1. Thus, if in the frustoconical area lc, we want to deposit layers such as 2 'having the same angle of inclination (x relative to the generatrix of the truncated cone lc. The problem is even more difficult if the surface to 15 cover has a continuously evolving profile, the depositing surface being for example a parabolode.

  To overcome these difficulties, the invention proposes a removal method, an implementation device of which is schematically illustrated in FIG. 2.

  In this FIG. 2, there is shown diagrammatically, seen in axial section, a mandrel 1 for example similar to that of FIG. 1, driven in rotation about its axis 3 by a motor M, the mandrel being metallic or made of a foam of material suitable plastic.

  The material for depositing on the mandrel 1 is in accordance with the invention 25 an assembly 4 formed by a continuous fibrous strip 5, 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 6 and 7 of the same length and width.

  The assembly 4 is stored on a supply reel 8 provided with a reeling system symbolized at F making it possible to brake in a controlled manner the routing of the assembly 4 to a set 9 of guide rollers and presentation of the 'assembly 4 at a station 1 0 for removing the fibrous strip 5.

  The fibrous strip 5 can be of any known type, including the fringed or braided type.

  The depositing station 10 disposed above the mandrel 1 comprises an applicator device responsible for pressing the strip 5 against the preceding inclined layer which has just been deposited on the mandrel and consisting of a cylindrical roller 11 carried by a device shown schematically in Figure 1, ensuring three degrees of freedom to said roller 1 1.

  The roller 1 1 is, for example, mounted journalling on an axis 12 (Figure 1) fixed to the end of a lever 1 3 rotatably mounted around an axis 1 4 orthogonal or vertical plane containing the axis 3 of the mandrel 1. The axis 1 4 is carried by a winding carriage 1 5 itself carried by a beam 1 6 parallel to the axis 3 of the mandrel, the carriage 1 5 being capable of moving 1 5 both vertically ( double arrow W) relative to the beam 1 6 and horizontally along the beam (double arrow Y).

  The rollers 9 are provided with a non-stick coating, for example in "Teflon", and have guide shoulders. They are mounted in parallel on a rotary axis in order to optimally present the assembly 4 to the laying roller 11.

  In line with the output roller 9a of the assembly 9, one of the separators 6, 7 is made to detach, in this case the so-called internal separator 6 which is located on the face of the strip 5 intended to be plated against the last layer deposited on the mandrel 1.

  To this end, the assembly 4 is clamped between said last roller 9a and a separating roller 17 with non-stick coating on which the internal separator 6 is wound up to then be automatically rewound on a reel 18.

  The strip 5 and the remaining separator 7, called the external separator, are directed onto the roller 11, the external separator being interposed between the roller 11 and the strip 5.

  On a fraction of a turn of the mandrel 1, the separator 7 is pressed against the strip 5 then detached to be rewound on the same reel 18 as the internal separator 6.

  The coil 18 is driven for example by a pneumatic motor MP with torque and variable speed of rotation.

  Thus, the strip 5 is regularly and optimally pressed against the previous layer by the separator 7 which acts as a transmission belt driven by the rotation of the mandrel 1.

  The fibrous strip 5 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 (8, F). It is easy to control this effort and to automate the deposit by a pilot system P with numerical control 10 programmed controlling the speed of rotation of the mandrel 1, the braking of the device F, the rewinding of the separators on the reel 18 and controlling the movements of the carriage 15 and the positioning of the roller 1 1.

  The fibrous strip 5 only undergoes deformation as that which develops when the strip is placed on the preceding layer, the strip then passing from a rectilinear shape to a curved shape.

  The possible inclination of the axis of the roller 11 resulting from the possibility of pivoting the latter around the axis 14 (double arrow C) allows the deposition of layers (2, 2 ') according to a constant or variable inclination by 20 relative to a cylindrical depositing surface, or a deposit according to a constant inclination relative to a surface of evolving profile, either in stages as illustrated in FIG. 1, or continuously.

  Furthermore, in order to reduce the friction between the roller 11 and the inevitable separator 7 since the roller is a cylindrical body rolling on a frustoconical surface, the roller 11 advantageously consists of a stack of rollers 11 'of small thickness and of same diameter illustrated in FIG. 3. The individual rollers 11 are free to rotate on the common axis 12 and are provided with a non-stick coating.

  Thus, each of the rollers 11 adapts its speed of rotation as a function of its location along the axis 12 and whatever the radius of the mandrel, evolving as in FIG. 3, or not.

  FIG. 4 highlights yet another characteristic of the roller 11 according to which it is possible to give the axis 12 of the roller a slight inclination i of the order of 3 to 50 for example relative to the plane containing the axis of rotation of the mandrel 1 and passing through the center of the roller i1.

  To this end, the roller 11 is provided with an axis of rotation relative to the normal of the profile of said mandrel 1. This facilitates the deformation of the strip 5 during winding.

  According to another characteristic of the depositing device of the invention, a heating device 19 can be provided immediately upstream of the depositing station 10 making it possible to increase the tackiness of the resin for impregnating the fibers of the strip 5, as well as the deformation of the latter when depositing on the mandrel.

  Similarly, a cooling device R can be provided facing the sector of the mandrel 1 o the separator 7 is pressed against the latter, upstream of the detachment zone of said separator in order to consolidate the fibrous layer which has just been deposited.

  1 5 After completion of the "lino" coating on the mandrel 1, the latter is placed in an autoclave for the purpose of polymerizing the resin of the composite material.

  According to yet another characteristic of the process of the invention, the fibrous strip 5 is a continuous strip formed of butted sections without excess thickness, said sections being made of a fabric of fibers preimpregnated with a suitable resin, with warp threads and of weft having an orientation relative to the longitudinal axis of the strip 5 different from 0 and 900 respectively.

  FIGS. 5a and 5c illustrate a method for producing such a continuous strip 5.

  From (FIG. 5a) a commercial strip 20 of standard width (for example 1200 mm) of a fabric of prepreg fibers coated on each side with a separating film of suitable material, cut at an angle (at 450 for example) strips 21 of a determined width, for example 30 500 mm, which are then abutted (FIG. 5b).

  In Figure 5b there are shown two strips 21 abutted with their respective separators 22 and 23 also abutted, in line with the junction between the two bands 21 being disposed astride the external face of the separators 22, 23 an adhesive element 24. 1 2

  The strip-separator assembly thus formed is cut again (FIG. 5c) along narrow strips parallel to the longitudinal edges of said assembly.

  The strips 25 thus obtained, of a width for example of between 5 and 50 mm, are then abutted like the sections 21 of FIG. 5b to finally form a continuous strip 5 (21) of several hundreds or even thousands of meters long and a few tens of millimeters wide. Such a strip consists of end-to-end sections and without any excess thickness of fabric of prepreg fibers, flanked by 10 end-to-end sections and of the same length of separators 6, 7 (22, 23) connected together by adhesive elements. (24) thus making it possible to exert traction on the fibrous strip via the separators without dissociating the sections of strip end to end.

  The fibers of the strip can be of any type used for making a "clino", as can the impregnation resin. 1 3

Claims (9)

R E V E N D I C A T IO N S   1. A method of depositing on a support successive inclined fibrous layers (2), from a continuous wound strip (5) on said support, characterized in that it consists: - to have beforehand the continuous fibrous strip ( 5) between two separators (6, 7), - to be conveyed by an appropriate delivery system (8) the strip-separator assembly (4) to a presentation guide station (9) o the so-called internal separator (6) covering the face of the strip (5) intended to be pressed onto the layer which has just been deposited is detached from the strip, - then to deposit the strip (5) and its so-called external separator (7) on said layer at the using an applicator device (1 1) pressing the strip against said preceding layer, the strip being driven by the rotation of the support (1), while the traction exerted on said strip (5) and its separator external (7) is controlled both by the motor torque applied to said support and by braking (F) of said delivery system (8) of the band-separator assembly (4), - the external separator (7) being detached from the band (5) deposited after accompanying the latter over a fraction of a turn.   2. Method according to claim 1, characterized in that the removal of the fibrous strip is carried out using a presser applicator device 25 consisting of a cylindrical roller (1 1) mounted movable along three axes of freedom, namely a first axis parallel to the axis of rotation of the support (1), a second axis orthogonal to the axis of rotation of the support (1) and an axis of rotation of said roller (1 1) orthogonal to said first and second axes, said cylindrical roller (11) being by 1 4 elsewhere formed of a stack of individual rollers (11 ') free in rotation thus making it possible to wind on a support with evolving profile or not without sliding between the roller (1 1) and the assembly separator tape (5, 7).   3. Method according to claim 2, characterized in that a slight inclination, of the order of a few degrees, is given to the axis of said roller (1 1) relative to a plane containing the axis (3) of rotation of the support (1) and passing through the center of said roller (1 1).   4. Method according to one of claims 1 to 3, characterized in that the continuous fibrous strip (5) is produced in the form of sections of fabric of fibers pre-impregnated with resin with warp and weft yarns having a orientation relative to the longitudinal axis of the strip different from 0 and 90 respectively, said sections being abutted without additional thickness.   5. Method according to claim 4, characterized in that the manufacturing of said continuous fibrous strip (5) is carried out by implementing the following steps: i. oblique cutting of a strip (20) of commercial prepreg fiber fabric coated on both sides with a separating film, ii. abutting the cut strips (21) and their separators (22, 23) and joining together with adhesive elements (24) arranged astride the sections of separators (22, 23) iii. re-cutting the butted strips parallel to their longitudinal edges to form narrow strips (25), and iv. butting of said narrow strips with fixing of the separating elements (22, 23) by adhesive elements (24) added in accordance with step ii., so as to form said continuous strip (5).   6. Method according to claim 4 or 5, characterized in that the fibrous strip (5) is subjected to heating immediately upstream of the deposition station (10). 1 5   7. Method according to claim 6, characterized in that the fibrous strip deposited (5) is, before removal of said external separator (7), subjected to cooling (R).   8. Method according to one of claims 1 to 7, characterized in that the internal (6) and external (7) separators are rewound simultaneously on the same reel driven at a determined, adjustable speed.   9. Method according to one of claims 1 to 8, characterized in that the removal of the fibrous strip (5) is automated by a pilot system (P) with programmed numerical control controlling the speed of rotation of the support (1) , braking the device (8, F) for delivering the strip (5), rewinding said separators (6, 7) and controlling the movements and positioning of the applicator roller (Il 1). 1 5