Compression process for chemical vapor filtration using a multi-plate tool for semi-reinforced flow

Description

Technical Field

[0001] The invention relates to the production of composite material parts comprising a porous annular substrate densified by chemical gas infiltration (CVI), and more particularly to the production of parts with a central passage. The invention is applicable, in particular, but not exclusively, to the production of annular brake discs or rocket engine nozzle divergents made of thermostructural composite material. Previous technique

[0002] Thermostructural composite materials are notable for their high mechanical properties and their ability to retain these properties at high temperatures. Typical examples of thermostructural composite materials are carbon-carbon (CC) composites, comprising a porous carbon fiber reinforcement substrate densified by a carbon matrix, and ceramic matrix composites (CMC), comprising a porous refractory fiber reinforcement substrate (e.g., carbon or ceramic) densified by a ceramic matrix (e.g., silicon carbide).

[0003] CC composite materials are commonly used for the manufacture of aircraft brake discs, due to their high-energy tribological characteristics, their non-brittleness, their thermal characteristics (conductivity and heat capacity) and their density.

[0004] The densification of porous substrates by chemical vapor infiltration (CVI) involves placing annular preforms in a reaction chamber of an infiltration plant and introducing a gaseous phase into the chamber. One or more components of this gaseous phase form a precursor of the matrix material to be deposited within the substrates, thereby ensuring their densification. The infiltration conditions, including the composition and flow rate of the gaseous phase, as well as the temperature and pressure within the chamber, are selected to allow diffusion of the gaseous phase into the accessible internal porosity of the substrates. This ensures that the desired material is deposited through the decomposition of a component of the gaseous phase or through reactions between several components of the gaseous phase. Document FR 2 834 713 describes such a process and a plant for its implementation.

[0005] The conditions for chemical vapor-phase infiltration of pyrolytic carbon, or pyrocarbon, have long been known to those skilled in the art. The carbon precursor is an alkane, an alkyl, or an alkene, usually propane, methane, or a mixture of the two. Infiltration is carried out at a temperature of approximately 1000 °C under a pressure of, for example, about 1 kPa.

[0006] The gaseous phase containing the precursor(s) of material to be deposited within the preforms is admitted at one longitudinal end of the reaction chamber, while the residual gases are discharged at the opposite end from where they are extracted by pumping means.

[0007] When a large number of substrate stacks need to be densified, a large-scale installation is generally used. A well-known example of disk loading that can be used in a reaction vessel commonly called a "densification furnace" is illustrated in the figure 1 .

[0008] The chamber 1 is cylindrical around an axis X. The loading comprises a plurality of stacks of porous ring substrates 2 supported by a single lower support tray 3. Each stack extends in the form of a column and is formed of several sections 4 of stacks superimposed and separated by intermediate support trays 5 common to all stacks. Trays 3 and 5 include openings aligned with central passages of the substrates 2 to circulate a reactive gas phase within each stack, which then passes through the substrates 2 to densify them. A susceptor lid forms an upper tray 6 that surmounts the loading and closes the internal volume of each stack (R1). The intermediate support trays 5 are held in place by means of vertical supports 7.

[0009] The organization of a high-temperature processing workshop, combining industrial CVI (carbon-in-glass) equipment with carbonization or heat treatment of annular preforms and heat treatment of partially or fully densified blanks, is based around trays composed of one to several stacks, typically 8 to 19 stacks, depending on the size of the parts and the size of the furnaces. These trays are moved by overhead cranes with slings. They are also stored in racks or stacker cranes, which are brought to the various workstations (furnace loading, density control, etc.).

[0010] There figure 1 is a representation of the hot zone of a directed-flow loading. As detailed on the figure 2 which represents a cross-sectional view of the densification furnace of the figure 1 , this hot zone includes, from its base to its top: an inlet of the reaction gas mixture 8, then a preheating zone 9 which allows the temperature of the gases to be increased up to the densification temperature, and finally the loading zone 10. At the top of the furnace, at the level of the susceptor cover 11, chimneys 12 are installed in the cover 11, through which the effluent gases from the deposition reaction are evacuated.

[0011] The loading consists of N1 trays, labeled P1 to PN, each capable of supporting N2 stacks of porous annular substrates, labeled S1 to SN. The number of trays and the number of stacks are related to the dimensions of the furnace and those of the discs, i.e., the porous annular substrates.

[0012] Each platter contains stacks of discs 2 separated by spacers 13, each stack ending at its top with a cover disc 14 that limits leakage. At the base of each stack is a ferrule 15 resting on the cover disc 14 of the stack below. This ferrule 15 allows, by sliding, compensation for height differences between stacks. Finally, supports 7 are installed between stacks S1 to SN which serve to bear the mass of the upper platters P2 to PN.

[0013] The gases exiting the preheating zone 9 enter each of the columns made up of the stacks S1 to SN of discs 2. The gas passes from the inside to the outside of the disc columns, through the leaks made up of the porosity of each preform 2, the gap between the discs 2 created by the spacers 13, and through the passages between the plates 3 and 5 (P1 to PN), at the point of the sliding clearances of the ferrule, the ferrule 15 letting the gases escape by its sliding.

[0014] A densification process using chemical vapor infiltration of porous substrates, employing a semi-forced flow, is described in document FR 2 821 859. To adapt the semi-forced flow as described in this document, leakage between the discs must be controlled, as well as leakage at the transition between platens. This latter point is the most difficult because the disc stacks are not of uniform height. Without excellent control of this sealing at the top of each stack, the pressure differential necessary to force the gas into the pores of the discs cannot be achieved.It is also known from patent FR 3 084 892 to replace the jack stands with gas distributors, which allow to simultaneously ensure the functions of load recovery (function previously ensured by the jack stands), of guiding the (cold) gases, which avoids the cooling of the discs, and of distributing the gases at the level of the.

[0015] A pressure gradient CVI densification process of porous annular substrates with a central passage is also known from US document 2005 / 178327 A1. Description of the invention

[0016] The invention aims to provide a technical solution for the implementation of a pressure gradient densification process which improves the distribution of reactive gas within a loading zone of a densification furnace and, in general, reduces densification gradients between substrates located in different locations of the loading zone, without affecting the loading capacity of the furnace, or even increasing it.

[0017] One object of the invention proposes a densification process by chemical infiltration in gas phase with pressure gradient of porous annular substrates having a central passage, as defined in claims 1-13.

[0018] According to a general feature of the invention, for each second unit module surmounted by a first unit module, each stack comprises at least one cover ring supported on the top of the stack of porous annular substrates via an annular wedge and a sealing ring disposed around the annular wedge in a plane perpendicular to the direction in which the porous annular substrates are stacked, and a deformable annular seal disposed between the at least one cover ring and the support plate of said first unit module.

[0019] At least one cover ring forms a lid resting on the top of the stack via an annular wedge. The stack lid and its associated annular seal function to create a tight seal around the stack, thereby reducing gas leakage. The lid and its deformable annular seal thus enhance the seal between the support plate of the upper unit module and the lid.

[0020] In addition, in the event that a stack is shorter than one or more other stacks of the same unit module, the stack in question may include several superimposed lids to compensate for the height deficit.

[0021] The spacers maintain a gap between the porous annular substrates, thus increasing the surface area in direct contact with the gas. Furthermore, the sealing rings positioned between the annular substrates prevent radial leakage, thereby maximizing the amount of gas flowing through them. These sealing rings are preferably located at the radially outer edge of the porous annular substrates. For example, the sealing rings are made of Inconel.

[0022] In one embodiment, each deformable annular joint can be arranged to undergo deformation along the direction in which the porous annular substrates are stacked, greater than or equal to the thickness of the cover ring, for example, 3 mm. Furthermore, each deformable annular joint exhibits, for example, thermal resistance at a temperature of 1100 °C.

[0023] The deformable annular seal can be made of expanded graphite or of braids or cords of carbon fibers or ceramic fibers.

[0024] In one embodiment, each stack may include at least three legs extending, depending on the direction in which the porous annular substrates are stacked, from the cover disc to the support tray on which the stack is placed.

[0025] Ideally, the joints are made of a material more deformable than the porous annular substrates of the stacks. The three legs suspended from the lid prevent the opposite scenario: the deformation of the porous annular substrates is thus limited by the three legs suspended from the lid, which form a load-bearing system.

[0026] Advantageously, each unit module may include, for each stack, an injection tube mounted on the gas inlet opening and extending into the internal volume of the stack between a first tube end connected to the support tray and a second tube end which is free, the injection tube further including gas injection ports opening into the internal volume, each gas inlet opening of the support tray of a first unit module mounted on a second unit module communicating with a second end of one of the injection tubes of the second unit module so as to permit the circulation of a gas between the unit modules.

[0027] In one example embodiment, each support plate may include a first face on which the stacks are arranged and a second face opposite the first face, each gas inlet opening may include a frustoconical shape with a first diameter formed in the second face of the support and a second diameter smaller than the first diameter and formed in the first face or between the first and second face of the support plate, and the second end of each injection tube may include a complementary frustoconical shape cooperating with the frustoconical shape of a gas inlet opening.

[0028] The injection tubes thus form male centering tools and the gas inlet openings female centering tools which cooperate together to ensure proper centering of the unit modules with each other.

[0029] Advantageously, the process can further include a step of hermetically sealing the unit modules of the stack, the second end of each injection tube being inserted into a gas inlet opening of the first unit module, and the first unit module further comprising, for each injection tube, an annular tube seal disposed between the second end of the injection tube of the second unit module and the gas inlet opening of the first unit module with which it cooperates.

[0030] The invention thus improves gas distribution within the furnace chamber and facilitates the installation of the densification furnace. The seal between two modules, ensured by the annular tube seal, is achieved solely by the force of weight during furnace loading.

[0031] The tube annular seal can be made of expanded graphite or of braids or cords of carbon fibers or ceramic fibers.

[0032] In one embodiment, each injection tube may include a main tubular portion forming a shoulder with the truncated conical shape of the second end, the shoulder allowing the annular tube joint to deform in a plane perpendicular to the direction in which the porous annular substrates are stacked.

[0033] In one embodiment, the tube annular seal is preferably frustoconical in shape to fit the shapes of the second end of the injection tubes and the gas inlet opening.

[0034] In one embodiment, each support plate may include, for each injection tube, a centering ring centered around a gas inlet opening and shaped to accommodate an injection tube.

[0035] The centering ring thus makes it easier and more efficient to place the injection tubes on the support plates.

[0036] In one embodiment, each porous ring substrate may include carbon.

[0037] In one embodiment example, each porous annular substrate can constitute a fibrous preform of a brake disc.

[0038] In one embodiment, each first porous annular substrate is supported on a second porous annular substrate, or supported on the support plate, by means of an annular wedge and a sealing ring surrounding the annular wedge, the sealing ring ensuring radial sealing between the first porous annular substrate and the second porous annular substrate or between the first porous annular substrate and said support plate.

[0039] Advantageously, each unit module surmounted by another unit module may include a plurality of supports extending between the support plate of said unit module and the support plate of said unit module which surmounts it to take up the mass of said at least one higher unit module.

[0040] Preferably, each candle has a height less than the height of the stacks of porous annular substrates.

[0041] In particular, each column may have a height less than the sum, in each stack, of the thickness of the deformable annular joint, the thickness of the cover ring, the thickness of the sealing ring(s), and the thicknesses of the porous annular substrates of said stack. The thicknesses of the deformable annular joint and the sealing rings are to be considered without compression. When a stack includes several cover rings, the thickness to be considered is that of all the cover rings combined.

[0042] Furthermore, each candle preferably has a height greater than the sum, in each stack, of the thickness of the cover ring and the thicknesses of the porous annular substrates of said stack. When a stack comprises several cover rings, the thickness to be taken into account is then that of all the cover rings.

[0043] In this document, height is understood as the dimension along which the porous annular substrates are stacked, and generally corresponds to the vertical direction. Brief description of the drawings

[0044] [ Fig. 1 ] There figure 1 The diagram already described shows, in a very schematic way, an example of loading porous annular substrates according to the prior art. Fig. 2 ] There figure 2 , already described, presents a cross-sectional view of the densification furnace of the figure 1 . [ Fig. 3 ] There figure 3 schematically illustrates a cross-sectional view of an example of a stack of porous annular substrates according to the invention. Fig. 4 ] There figure 4 schematically presents a cross-sectional view of an example of a unit module according to the invention. Fig. 5 ] There figure 5 presents a cross-sectional view of an initial example of a tube annular seal. Fig. 6 ] There figure 6 schematically presents a cross-sectional view of a second example of an annular tube seal. Fig. 7 ] There figure 7 schematically presents a cross-sectional view of an alternative embodiment of an injection tube according to the invention. Fig. 8 ] There figure 8 schematically presents a cross-sectional view of an example of a unit module according to another embodiment of the invention. Description of the implementation methods

[0045] A gas-phase chemical infiltration densification process according to the invention first comprises a step during which a plurality of stacks of porous annular substrates are provided for treatment by gas-phase chemical infiltration.

[0046] On the figure 3 A cross-sectional view of an example of a stack 20 of porous annular substrates 21 is illustrated. The porous annular substrates 21 have cylindrical symmetry and are stacked along a first direction DZ. Each porous annular substrate 21 extends mainly in a plane perpendicular to the first direction DZ. The cross-sectional plane of the illustration of the figure 3 includes the first direction DZ and a second direction DR perpendicular to the first direction DZ. The first direction DZ coincides with the axis of revolution symmetry of the porous annular substrates 21, and the second direction DR corresponds to a radial direction.

[0047] Each porous annular substrate 21 of the stack 20 thus has a ring shape with a central passage 21a. Each porous annular substrate 21 is arranged on an annular wedge 22 whose outer radial diameter is smaller than the outer radial diameter of the porous annular substrates 21, the diameters of the orifices of the wedges 22 and the porous annular substrates 21 being equal.

[0048] Each wedge 22 is surrounded by a sealing ring 23 in the plane perpendicular to the first direction DZ. Each porous annular substrate 21 thus rests on an annular wedge 22 and on a sealing ring 23.

[0049] The alternative stacking of the porous annular substrates 21 and the wedges 22 forms, at the center of the stack 20, an internal volume 24 of the stack 20.

[0050] Furthermore, the stack 20 is closed at its top by an annular cover 25. The cover 25 is placed on the stack via an annular wedge 22 and a sealing ring 23.

[0051] The gas-phase chemical infiltration densification process according to the invention then comprises a step during which a plurality of unit modules 30 are supplied.

[0052] On the figure 4 is schematically represented a cross-sectional view of a unit module 30 according to the invention.

[0053] Each unit module 30 comprises a support tray 31 and several stacks 20 of porous annular substrates 21 arranged on the support tray 30. For each stack 20, the support tray 31 has a gas inlet opening 32 and an injection tube 33 mounted on the gas inlet opening 32 and extending into the internal volume 24 of a stack 20 between a first tube end 33a connected to the support tray 31 and a second tube end 33b which is free.

[0054] The injection tube 33 further includes gas injection ports 34 opening into the internal volume 24.

[0055] The gas-phase chemical infiltration densification process according to the invention then includes a step during which a stack of unit modules 30 superimposed on each other along the first direction DZ is formed in the enclosure of a densification furnace.

[0056] On the figure 4 is shown the support plate 31 of a first unit module 30a about to be superimposed on a second unit module 30b.

[0057] The stacking step of the 30 unit modules further includes a step of watertight alignment of the 30 unit modules in the stack. As illustrated in the figure 4 , to achieve alignment, the second end 33b of each injection tube 33 of the second unit module 30b is inserted into a gas inlet opening 32 of the first unit module 30a.

[0058] To seal the junction between the injection tubes 33 of the second unit module 30b and the gas inlet openings 32 of the first unit module 30a, the second unit module 30a further comprises, for each injection tube 33, an annular seal 35 disposed between the second end 33b of the injection tube 33 of the second unit module 30b and the gas inlet opening 32 of the first unit module 30a with which it cooperates.

[0059] More specifically, each support plate 31 comprises a first face 31a on which the stacks 20 are arranged and a second face 31b opposite the first face 31a. Each gas inlet opening 32 comprises a frustoconical shape with a first diameter d1 formed in the second face 31b of the support plate 31 and a second diameter d2 smaller than the first diameter d1 and formed between the first face 31a and the second face 31b of the support plate 31.

[0060] The second end 33b of each injection tube 33 comprises a frustoconical shape complementary to the frustoconical shape of a gas inlet opening 32, so that the two frustoconical shapes cooperate. The complementary frustoconical shape of the second end 33b of the injection tube 33 comprises a first diameter D1 larger than a second diameter D2, the second diameter D2 being measured on a free distal end while the first diameter D1 is measured on a proximal end coupled to the rest of the injection tube 33 and in particular to a main portion 33c.

[0061] On the figures 5 et 6 are illustrated two examples of annular seal 35 mounted at the interface between the second end 33b of the injection tube 33 of the second unit module 30b and the gas inlet opening 32 of the first unit module 30a.

[0062] There figure 5 presents a cross-sectional view of an annular joint with a tapered end, and the figure 6 presents a cross-sectional view of an annular joint having a parallelogram cross-section.

[0063] As illustrated on the figure 4 , to improve the sealing of the stack of unit modules 30, more particularly to prevent leakage from the annular spaces between the injection tube 33 and the porous annular substrates 21 to the outside of the stacks 20, when two unit modules 30 are stacked one on top of the other, the lower unit module, here the second unit module 30b, includes, for each stack 20, a deformable annular seal 36 disposed between the cover 25 of the stack 20 and the support tray 31 of the upper unit module, here the first unit module 30a.

[0064] Furthermore, as illustrated on the figures 3 et 4 The stack of 20 also includes three legs (only one per stack is visible on these figures 3 et 4 ). Each leg 26 extends, along the Z direction in which the porous annular substrates 21 are stacked, from the annular cover 25 to the support tray 31 on which the stack 20 is arranged.

[0065] As illustrated on the figure 7 which represents an example of an alternative embodiment of an injection tube according to the invention, each injection tube 33 may comprise a main tubular portion 33c forming a shoulder 37 with the frustoconical shape of the second end 33b. The shoulder 37 allows the annular joint 35 to deform in a plane perpendicular to the first direction DZ along which the porous annular substrates 21 are stacked.

[0066] The gas-phase chemical infiltration densification process according to the invention further comprises a step in which a gaseous phase comprising a gaseous precursor of a matrix material to be deposited within the porosity of the substrates 21 is injected into the internal volume 24 of each stack 20 of porous annular substrates 21. The gas injection is shown in the figure 4 by the arrows G.

[0067] In the embodiment illustrated on the figure 8 , each unit module 30 surmounted by another unit module 30 further comprises a plurality of candles 70 extending between the support plate 31 of the unit module 30 and the support plate 31 of the unit module 30 which surmounts it to take up the mass of the upper unit module(s) 30(s).

[0068] Each candle 70 has a height less than the height of the stacks 20 of porous annular substrates 21. More precisely, each candle 70 has a height less than the sum, in each stack 20, of the thickness of the deformable annular joint 36, the thickness of the cover ring 25, the thicknesses of the sealing rings 23, and the thicknesses of the porous annular substrates 21 of said stack.

Claims

1. A method for densification by pressure gradient chemical vapor infiltration of porous annular substrates (21) having a central passage (21a), the method comprising at least the following steps: - providing a plurality of stacks (20) of porous annular substrates (21), each stack (20) comprising an internal volume (24) formed by the central passages (21a) of the stacked substrates (21), - providing a plurality of individual modules (30), each individual module (30) comprising a support plate (31) and stacks (20) of porous annular substrates (21) disposed on the support plate (31), the support plate (31) comprising, for each stack (20), a gas inlet opening (32) emerging into the internal volume (24), - forming, in the chamber of a densification furnace, a stack of individual modules (30), each gas inlet opening (32) of the support plate (31) of a first individual module (30a) mounted on a second individual module (30b) communicating with the internal volume (24) of one of the stacks (20) of the second individual module (30b) so as to allow a gas to flow between the individual modules (30), and - injecting into the internal volume (24) of each stack (20) of porous annular substrates (21) a gas phase comprising a gaseous precursor of a matrix material to be deposited within the porosities of the substrates (21), characterized in that, for each second individual module (30b) surmounted by a first individual module (30a), each stack (20) comprises at least one cover ring (25) supported on the top of the stack of porous annular substrates (21) via an annular spacer (22) and a sealing ring (23) disposed around the annular spacer (22) in a plane perpendicular to the direction (DZ) in which the porous annular substrates (21) are stacked, and a deformable annular seal (36) is disposed between the at least one cover ring (25) and the support plate (31) of said first individual module (30a).

2. The method according to claim 1, wherein each deformable annular seal (36) is arranged to be capable of undergoing deformation, along the direction (DZ) in which the porous annular substrates (21) are stacked, greater than or equal to a thickness of a cover ring (25).

3. The method according to one of claims 1 and 2, wherein each stack (20) comprises at least three legs (26) extending in the direction (DZ) in which the porous annular substrates (21) are stacked, from the cover ring (25) to the support plate (31) on which the stack (20) is disposed.

4. The method according to any one of claims 1 to 3, wherein the support plate (31) of each individual module (30) comprises, for each stack (20), an injection tube (33) mounted on the gas inlet opening (32) and extending into the internal volume (24) of the stack (20) between a first tube end (33a) connected to the support plate (31) and a second tube end (33b) which is free, the injection tube (33) further comprising gas injection openings (34) emerging into the internal volume (24), each gas inlet opening (32) of the support plate (31) of a first individual module (30a) mounted on a second individual module (30b) communicating with a second end (33b) of one of the injection tubes (33) of the second individual module (30b) so as to allow a gas to flow between the individual modules (30).

5. The method according to claim 4, wherein each support plate (31) comprises a first face (31a) on which are disposed stacks (20) and a second face (31b) opposite the first face (31a), each gas inlet opening (32) comprises a frustoconical shape with a first diameter (d1) formed in the second face (31b) of the support (31) and a second diameter (d2) smaller than the first diameter (d1) and formed in the first face (31a) or between the first face (31a) and second face (31b) of the support plate (31), and the second end (33b) of each injection tube (33) comprises a complementary frustoconical shape cooperating with the frustoconical shape of the gas inlet opening (32).

6. The method according to claim 4 or 5, further comprising a sealed alignment step of the individual modules (30) of the stack, the second end (33b) of each injection tube (33) of the second individual module (30b) being inserted into a gas inlet opening (32) of the first individual module (30a), and the second individual module (30b) further comprising, for each injection tube (33), an annular tube seal (35) disposed between the second end (33b) of the injection tube (33) of the second individual module (30b) and the gas inlet opening (32) of the first individual module (30a) with which it cooperates.

7. The method according to claim 6, wherein each injection tube (33) comprises a main tubular portion (33c) forming a shoulder (37) with the frustoconical shape of the second end (33b), the shoulder (37) allowing the annular seal (35) to deform in a plane perpendicular to the direction (DZ) along which the porous annular substrates (21) are stacked.

8. The method according to one of claims 6 to 7, wherein each annular seal (35) is frustoconical in shape.

9. The method according to any one of claims 1 to 8, wherein each support plate (31) comprises, for each injection tube (33), a centering ring centered around a gas opening (32) and shaped to receive an injection tube (33).

10. The method according to any one of claims 1 to 9, wherein each porous annular substrate (21) comprises carbon.

11. The method according to any one of claims 1 to 10, wherein each porous annular substrate (21) constitutes a fibrous brake disc preform.

12. The method according to any one of claims 1 to 11, wherein each individual module (30) surmounted by another individual module (30) comprises a plurality of rods (70) extending between the support plate (31) of said individual module (30) and the support plate (31) of said individual module (30) which surmounts it to take up the mass of said at least one upper individual module (30).

13. The method of claim 12, wherein each rod (70) has a height less than the height of the stacks (20) of porous annular substrates (21).