FR2759387A1 - REALIZATION OF ANNULAR FIBROUS PREFORM BY TAPE WINDING - Google Patents

Abstract

The ring-shaped textile structure (30) is produced by unwinding a textile ribbon (24) in a can (26) forming several tiered up ring-shaped textile layers each consisting of a plurality of flat spires. The ribbon for instance comes directly from carding. The unwinding can be carried out by repetitively forming spires around the axis of a can. The tiered up layers of spires are interwoven, for instance by needle bonding. The method is applicable to the production of preforms for composite brake discs, in particular carbon-carbon composite.

Description

 The present invention relates to the production of annular fibrous structures, or preforms, intended in particular for the manufacture of annular parts made of composite material.

 A particular but non-exclusive field of application of the invention is the production of annular fibrous preforms for the manufacture of brake discs in composite material, in particular in carbon-carbon composite (C-C).

 C-C composite brake discs are manufactured by making an annular carbon fiber preform and densifying the preform with a carbon matrix.

 The brake disc preforms in composite C-C are generally produced by superimposing layers of a basic fibrous texture of carbon fibers or carbon precursor and possible bonding of the layers together, for example by needling.

 The basic fibrous texture can be a felt, a fabric, a unidirectional ply of cables, wires or strands, or even a complex formed by several plies superimposed with different directions and linked together by needling.

 Processes for manufacturing fibrous preforms by stacking and needling layers are described for example in documents US-A4 790 052, FR-A-2 626 294, and FR-A-2 726013.

 The different strata can be solid strata, in which case the annular preform is cut after stacking the strata, or precut annular strata. This results in significant material falls which burden manufacturing costs significantly due to the price of the basic fibrous textures, in particular when they are made of carbon or of carbon precursor.

 The object of the present invention is to remedy this drawback by proposing a method for making annular fibrous preforms without loss of fibrous material.

 The present invention also aims to provide a method for making annular fibrous preforms capable of being suitable for the manufacture of brake discs made of composite material, that is to say preforms capable of giving the discs the ability to resist to friction forces and to transmit these to the members to which they are connected, without causing destruction of the composite material.

 These aims are achieved by a method according to which the preform is produced by winding a fibrous ribbon in a jar, forming several superimposed annular layers each consisting of a plurality of flat turns.

 By flat turn here is meant a turn or loop described by the ribbon substantially in a plane parallel to the bottom of the pot.

 Advantageously, the winding is carried out by forming turns repeatedly around a vertical axis of the pot. Different winding modes can be used, depending in particular on the desired distribution of the fiber content in the radial direction, but preferably preserving the axial symmetry of the winding.

 The ribbon can be formed of staple fibers, for example staple fibers which are substantially parallel to each other and slightly twisted. The ribbon is for example a ribbon coming from a carding machine, or a cable coming from a cracking device, capable of being deposited in flattening in the pot.

 The use of a ribbon coming from a card is particularly advantageous because the winding can be carried out in the jar directly at the exit of card, as it is customary to do for the storage of a ribbon coming from card while waiting for its use for a subsequent textile operation. A similar benefit arises from the use of a ribbon from a cracked cable.

 In this case, not only is an annular preform produced without loss of material, but, moreover, the preform is obtained directly, without additional operation, and with a conventional installation.

 In addition, the use of a ribbon formed from staple fibers weakly bonded together, as is the case with a ribbon made from carding or a cracked cable, even with slight twisting, allows a certain amount of expansion. fibers. In this way, not only can one achieve a less irregular porosity favorable for the densification of the preform, but moreover a certain intermingling of fibers between superposed layers which is favorable for the bond between layers and the resistance to delamination.

 This does not exclude the possibility of making a connection between layers by needling. This can be done on the rolled preform, possibly compressed in the axial direction, or as the layers are formed, during the winding of the ribbon.

 The invention also relates to a method of manufacturing annular parts of composite material by densification of preforms obtained as described above, and possibly compressed.

 Densification is carried out by chemical infiltration in the vapor phase or by the liquid route or by a combination of both.

The invention will be better understood on reading the description given below, by way of indication but not limitation. Reference is made to the appended drawings in which:
- Figure 1 is a very schematic view of an installation allowing the implementation of a method according to the invention for the development of annular fiber preforms;
- Figures 2A, 2B, 2C and 2D illustrate different stages of winding a turn flat in a pot, for the implementation of a method according to the invention by means of the installation of Figure 1;
- Figure 3 shows schematically an embodiment of the pot winding device of Figure 1, to allow winding as illustrated in Figures 2A to 2D;
- Figure 4 shows very schematically the kinematic chain of the winding device of Figure 3;
- Figures SA and 5B schematically show other modes of winding a turn flat in a pot, for the implementation of a method according to the invention.

 In the example illustrated in FIG. 1, a preform is produced by winding a ribbon directly in a jar at the card outlet. In this example, the card used is a hat card. In Figure 1, different parts of the installation are shown on an enlarged scale, in circles.

 Conventionally, such a card comprises a rotary breaker roller 10 furnished with fine inclined metal points 10a and receiving a textile to be carded 20. The textile 20 is for example a sheet of fibers or a felt and is formed from fibers of the material of the preform or a precursor of this material. It is possible to use a felt or a sheet formed from fibers of the same kind or from a mixture of different fibers. For example, it is possible to mix carbon fibers coming from different precursors, such as fibers with polyacrylonitrile precursor (PAN) in the preoxidized state, or isotropic pitch, or anisotropic pitch, or cellulosic, or phenolic, or mix fibers of these different precursors.

 The breaker roller 10 cooperates with a rotary drum 12, or large drum, rotating faster than the breaker roller and also provided with metal spikes 12a. The carding fabric is dispersed fiber by fiber on the large drum with the help of hats carried by an endless chain 14 and provided with inclined points 14a. The chain 14 substantially follows the shape of the outline of the large drum 12, on a sector thereof.

 The fibers are taken up from the large drum 12 by a combing drum 16 provided with needles 16a. The combing drum 16 rotates more slowly than the large drum, which promotes the regrouping of the fibers. These are detached on a combing drum in the form of a veil of fibers 22 using a detaching comb 18 driven by a rapid oscillatory movement of short stroke.

 The veil of fibers 22 is condensed into a ribbon or wick 24 which is wound flat in a fixed or rotating pot 26, by means of a winding or tamping device 40.

 FIGS. 2A to 2D show a particular mode of winding the ribbon 24 in the cylindrical pot 26 with a vertical axis 25, having an external cylindrical wall 26a and a horizontal bottom 26k.

 A first turn S (FIG. 2A) of substantially circular shape is formed flat on the bottom 26k. This turn surrounds a cylindrical surface 30 while being tangent to the latter at a single point Ti and is tangent at a point Tj on the internal side of a cylindrical surface 30k, the points Ti and Tj being located on the same diameter. The surfaces 30 and 30h have the same vertical axis as the pot and materialize the internal and external faces of the annular preform to be produced. It will be noted that the surface 30k can be substantially coincident with the external wall 26 of the pot 26.

 The winding device is made so that, possibly in combination with the rotation of the pot 26 around its axis, each new turn is formed by being offset by an angle a with respect to the previous turn, around the axis of the pot. Figures 2B and 2C show the winding produced after, respectively, 15 and 30 turns. After a full turn, corresponding here to 44 turns, a complete layer is formed on the bottom of the pot (Figure 2D).

The winding is continued thus by forming superimposed layers parallel to the bottom of the pot until reaching a desired height. This can reach several tens of centimeters. A particular embodiment of the winding device 40 will be described later with reference to FIG. 3.

 The annular preform 30 thus formed can be used to make parts of composite material of annular shapes. To this end, the preform is preferably compacted, so as to obtain a desired volume ratio of fibers, that is to say the desired percentage of the apparent volume of the preform actually occupied by the fibers.

 The preform maintained in the compacted state is densified by the liquid route and / or by chemical vapor infiltration. Liquid densification consists in impregnating the preform with a liquid precursor of the material constituting the desired matrix of the composite material, for example a resin. The transformation of the precursor of the matrix is carried out by heat treatment.

Chemical vapor infiltration consists in placing the preform in an enclosure and in admitting, in the enclosure, a gaseous phase precursor of the matrix which, under predetermined conditions of temperature and pressure, diffuses within the porosity of the preform and forms, on contact with the fibers, a matrix deposit produced by decomposition of one or more constituents of the gas phase or chemical reaction between several constituents.

 The densification processes by liquid and by chemical vapor infiltration, to form matrices for example of carbon or ceramic, are well known. It will be noted that densification may first be carried out partially by liquid means in order to consolidate the preform, so that further densification can be carried out by chemical vapor infiltration without requiring holding tools.

 When the preform is produced by winding a ribbon of fibers consisting of a precursor of the material constituting the fibrous reinforcement of the composite material, the transformation of the precursor is carried out after the preform has been produced and before densification thereof, for example at during a temperature rise process before densification.

 After densification, different annular parts, for example brake discs of composite material, can be obtained by cutting along radial planes, and finishing machining.

 Preferably, the different layers of preforms are bonded to each other in order to improve the cohesion of the preform and, consequently, to increase the resistance of the pieces of composite material to delamination, that is to say damage by separation between preform layers.

 The bond of the layers between. they can be produced by needling or by sewing the preform, after winding. Preferably, the needling or sewing are then carried out with compression of the preform in the axial direction.

 The needling of the preform layers can also be carried out during the process of forming the annular preform in the jar. The layers are needled as they are produced, so as to have a substantially constant needling density throughout the volume of the preform.

 For this purpose, a needle board 32 (FIG. 1) is used which extends radially over a distance substantially equal to the radial dimension of the preform and can penetrate into the pot 26.

 The needle board 32 is provided with needles 34 which are distributed regularly over a sector-shaped area, so as to have a constant needling area density between the internal and external faces of the preform.

 The needle board 32 is driven in a vertical back-and-forth movement (arrows F1) to allow the needles to penetrate the preform to a depth equal to several times the thickness of a needled layer. In order to be able to carry out the needling of the first layers, the bottom of the pot 26 is provided with a coating 27 forming base felt into which the needles can penetrate without being damaged. The base felt is for example made of polypropylene. It can be coated with a sheet, for example of elastomer, which prevents the anchoring in the base felt of fibers displaced by the needles and thus then makes it possible to easily separate the needled preform from the base felt.

 After each complete needling of a layer, the pot 26 can be lowered by a distance substantially equal to the thickness of a needled layer, so that the needling depth is kept substantially constant. To this end, the pot 26 is placed on a table 28 which can move vertically (arrow F2).

When the pot 26 is rotary (Figure 1), the needle board is non-rotary. Note that an annular preform needling device with substantially constant needling density is already described in the document.
FR-A-2 626 294 by the applicant.

 When the pot is fixed, the needle board is thus animated in a rotary movement around the axis of the pot, so as to sweep the entire surface of a layer. The rotation of the needle board is synchronized with the angular displacement of the position of the center of the turns around the axis of the pot.

The needling, with progressive lowering of the pot, being carried out in the same way.

 In all cases, in order to avoid interference between the process of forming turns and the needling process, the location of the needle board is chosen so as to be diametrically opposite that of the center of the current turn training.

 It will be noted that the preform, the layers of which are linked together by needling or stitching after winding, or by needling during winding, may then be compressed again before densification.

 It will also be noted that, in the case where the preform layers are bonded after winding, the pot can be simply mounted on an elastic support, for example a spring, allowing the bottom of the pot to descend gradually under the weight of the preform during training, as is well known for pots for receiving ribbons at the outlet of the card.

 An embodiment of the winding device 40 will now be described with reference mainly to FIGS. 3 and 4.

 In this example, the pot 26 is fixed. A complete layer of turns is formed, as shown in FIGS. 2A to 2D, by imposing on the current point B of a turn S a movement composed of two rotations: one centered on the axis A of the turn S and l other centered on the axis O of the pot and driving the axis A.

The ribbon 24 is called by passing between two cylinders 42 and is directed towards the pot 26 while being guided through an orifice 44 of a distribution plate 46 forming a winding head. The plate 46 is in the form of a horizontal axis disc
Has provided with the orifice 44 in the vicinity of its periphery. The plate 46 has a rim 48 forming on the outside a toothed crown which is engaged with the internal toothed crown 50 of a ring 52 to drive the disc 46 around the axis A. The ring 52 meshes with its crown external toothed 54 with a pinion 56 itself engaged with a pinion 58 driven in rotation about a vertical axis M by a motor device 60.

 The assembly comprising the cylinders 42, the distribution plate 46 and the needle board 32 is carried by a rotary plate 66 of axis O. The plate 66 is engaged for this purpose by its outer ring 64 with a toothed wheel 62 driven by motor 60.

 The distribution plate 46 is housed in an annular opening 68 formed in the plate 66, so as to be able to rotate about the axis A freely relative to the plate 66. It will be noted that the rotary plate 66, the rotary annular part 52 and the rotary dispensing head 46 are supported by a frame (not shown).

 One of the cylinders 42 is driven in rotation about its axis N, and drives the other cylinder 42 in rotation by friction. The shaft of the driving cylinder 42 is carried by an angled arm 70 projecting from the upper surface of the plate 66, while the needle board 30 is suspended under the plate 66 by means of a support 72.

 The driving cylinder 42 is driven in rotation from the distribution plate 46 by means of a toothed wheel 74, in engagement with the crown 48, and of a bevel gear formed by two bevel gears 76 , 78 (Figure 4).

 The ratios between the wheel 62 and the crown 64, on the one hand, and the pinions and crowns 58, 56, 50 and 48, on the other hand, are determined so that the distribution plate completes N turns, for each turn of the plateau 66, N being the number of turns forming a complete layer on the bottom of the pot 26 (in the example mentioned above, N = 44).

 As for the ribbon call cylinder 42, it is driven at a speed such that the linear speed of the called ribbon is preferably substantially equal to the linear speed of the current point B of a turn S.

 The winding device which has just been described makes it possible to produce a winding as illustrated in FIGS. 2A to 2D, with a fixed pot.

 It will immediately appear to those skilled in the art that the same winding mode with fixed pot or that other winding modes, with fixed pots or rotating pots, can be adopted, by correspondingly adapting the kinematics of the winding device.

 By way of examples, two variants of winding modes are illustrated diagrammatically by FIGS. SA and 5B.

 In the case of FIG. SA, each substantially circular turn fits in the interval between internal surface 30a and external surface 30b while being tangent thereto at two respective points located on the same radius. This winding mode can be implemented with a fixed or mobile pot. It is more particularly advantageous in the case of needling of the preform during winding. Indeed, the needling can then be carried out with a needle board in a location diametrically opposite to that where the winding is located, therefore without interference with the winding. The needle board is rotated around the axis of the pot in synchronism with the winding head around this axis, when the pot is fixed, or occupies a fixed angular position relative to the axis of the pot when the pot is movable in rotation around its axis.

 Finally, in the case of FIG. 5B, each turn has a substantially elliptical shape and envelops the internal surface 30a, to which it is tangent at two opposite points, and extends between two opposite points on the external surface 3012.

In the foregoing, the case of a ribbon from hat card has been considered. Of course, we can also wind a ribbon from other types of cards, for example chain gills. In addition, as already indicated, the method according to the invention can also be implemented with a ribbon coming from a cable cracking device. Such cracking devices, including for carbon fiber cables, are well known. We could refer for example to the document
FR-A-2 608641. The winding of the ribbon in a jar is carried out in the same way as for a ribbon from carding. A ribbon formed from a mixture of fibers can also be obtained by supplying the cracking device with carbon cables from different precursors, or by cables with different carbon precursors.

 Different embodiments of annular preforms using a method according to the invention will now be described.

EXAMPLE 1
We start with a carding fabric made of pre-oxidized PAN fibers, crimped and cut, with a density of 1.37 g / cm3. By means of a card as illustrated in FIG. 1, a ribbon of title equal to approximately 5,000 tex is produced. The ribbon is wound as shown in Figures 2A to 2D, but forming each layer with 20 turns. The internal and external diameters of the preform are respectively 150 and 600 mm. Each turn has a length of 1.25 m and each layer has a thickness, in the uncompressed state, equal to about 25 mm.

 After having formed 25 layers, without needling, the preform obtained is removed from the pot and charred while being kept in its shape.

 Then, the preform is compressed in order to obtain the desired volume ratio of fibers and is densified by chemical vapor infiltration to form a pyrolytic carbon matrix. At the start of densification and at least until consolidation, the preform is kept in a tool. After densification, the annular part obtained is cut to obtain the desired thickness discs.

EXAMPLE 2
As in Example 1, we start with a carding textile made up of crimped pre-oxidized PAN fibers. Several ribbons are formed by carding with a titer of approximately 5,000 tex. After carding, 10 ribbons are joined and stretched so as to lengthen them by 10 times, in order to obtain a ribbon always having a title of 5,000 tex, but of higher density allowing, in comparison with Example 1, to multiply the volume ratio of fibers in the winding by 1.5.

 The ribbon is wound as illustrated in FIGS. 2A to 2D, but forming each layer with 20 turns. The internal and external diameters of the preform are equal to 120 and 400 mm respectively, and the length of a turn is equal to 80 cm.

 The rest of the process is the same as in Example 1.

EXEMPT E 3
The procedure is exactly as in Example 2, but using 5 card tapes made of phenolic carbon precursor fibers and 5 card tapes made of preoxidized PAN fibers.

 This example shows the possibility of mixing different types of carbon precursor giving carbon fibers of higher or lower modulus, depending on the expected properties of the preform.

EXAMPLE 4
A starting textile product is used consisting of a 50K carbon fiber cable (that is to say formed from 50,000 filaments). The cable is subjected to a stretch-cracking operation giving a ribbon having a titer of 4,500 tex.

 The ribbon is wound as in Example 1, the preform obtained having a fiber content of 25%.

 The preform is compacted to increase the volume ratio of fibers to the desired value and maintained in the compacted state by needling, which allows it to be densified without the need for tools.

EXAMPLES
The procedure is as in Example 4, but by needling the layers formed by the turns of ribbon as and when winding. Needling produces compaction, so that the volume content of fibers in the preform obtained is 50%.

 The needled preform can be densified without necessarily undergoing additional compaction.

Claims (26)

1 Method for producing an annular fibrous structure by winding a fibrous texture, characterized in that the annular fibrous structure is produced by winding a fibrous ribbon in a jar by forming several superimposed annular fibrous layers each consisting of a plurality of flat turns. 2. Method according to claim 1, characterized in that the winding is carried out by forming turns repeatedly around an axis of the pot. 3. Method according to any one of claims 1 and 2, characterized in that the winding is carried out by forming turns along paths parallel to a bottom of the pot. 4. Method according to claim 3, characterized in that each turn is formed between the internal cylindrical surface and the external cylindrical surface of the preform. 5. Method according to claim 3, characterized in that each turn envelops the internal cylindrical surface of the preform and is tangent to the latter at a single point. 6. Method according to claim 3, characterized in that each turn extends between two points of the external cylindrical surface of the preform along a path tangent to the internal cylindrical surface of the preform. 7. Method according to any one of claims 1 to 6, characterized in that the layers of superposed turns are linked together. 8. Method according to claim 7, characterized in that the bonding of the layers together is carried out after winding the ribbon. 9. Method according to claim 8, characterized in that the connection is effected by needling. 10. Method according to claim 8, characterized cn that the connection is made by sewing. 11. Method according to claim 7, characterized in that the connection of the layers together is carried out by needling during the winding of the ribbon. 12 Method according to claim 11, characterized in that the needling is carried out with a substantially constant needling depth. 13. Method according to any one of claims 11 and 12, characterized in that the needling head is rotated about an axis of the pot. 14. Method according to claim 13, characterized in that the ribbon is brought into the pot by means of a distribution device having an axis, the distribution device is rotated about its axis to form a turn, and the dispensing device is rotated about the axis of the pot to form a plurality of successive turns, the pot being fixed, and in that the needling is carried out by means of a needling head which extends substantially radially in the pot and which is rotated about the axis of the pot in synchronism with the dispensing device. 15. Method according to any one of claims 11 and 12, characterized in that the pot is cylindrical with a vertical axis and is driven in rotation about its axis and the needling head is fixed relative to the axis of the pot. 16. Method according to any one of claims 1 to 15, characterized in that a fibrous texture is used in the form of a ribbon of staple fibers. 17. The method of claim 16, characterized in that one uses a ribbon from carding. 18. The method of claim 17, characterized in that the fibrous structure is produced by winding the ribbon directly at the card outlet. 19. The method of claim 16, characterized in that one uses a fibrous texture in the form of a ribbon obtained by joining and stretching several ribbons. 20. The method of claim 19, characterized in that several ribbons formed of fibers of different natures are used. 21. The method of claim 16, characterized in that a ribbon is used in the form of a cracked cable. 22. Method according to claim 21, characterized in that the fibrous structure is produced by winding the ribbon directly at the outlet of the cable cracking device. 23. Method for manufacturing an annular piece of composite material comprising a fibrous reinforcement and a matrix connecting the fibers of the reinforcement together, the method comprising producing an annular fibrous preform and densifying the preform by the matrix, characterized in that the preform is produced by a method according to any one of claims 1 to 22. 24. The method of claim 23, characterized in that the preform is produced by winding a ribbon of fibers made of a precursor of the material constituting the fibrous reinforcement of the composite material, and the transformation of the precursor is carried out after completion of the preform and before densification thereof. 25. Method according to any one of claims 23 and 24, characterized in that the fibrous preform is compressed before densification. 26. Method according to any one of claims 23 to 25, characterized in that the preform is produced by winding a ribbon formed of fibers of several different natures.