Compression process by chemical vapor filtration using monopile plates for a semi-forced 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 from 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 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, generally 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] The reactors used for research and development studies on brake disc infiltration typically have a loading configuration consisting of a stack of trays, each holding a single stack of discs. These are known as "single-stack" furnaces. This configuration differs from industrial loading, carried out in larger reactors, where the trays hold several stacks of discs side by side, and which are referred to as "multi-stack" furnaces.

[0008] In both cases, the discs are separated by intermediate supports called spacers, and the platters include openings aligned with central passages of the discs to circulate a reactive gas phase through each stack, which then passes through the discs to densify them. A top platter sits atop the loading and closes the internal volume of each stack. The platters supporting the stacks of discs are held in place by vertical supports.

[0009] The classic densification process, used industrially and applicable in the furnace used in research and development, is the directed flow.

[0010] A known example of monopile disk loading that can be used in a reaction vessel commonly called a "densification furnace" is illustrated on the figure 1 .

[0011] The chamber 1 has cylindrical symmetry about a Z-axis. The loading comprises a stack of unit modules 2, each unit module 2 comprising a single stack 3 of porous annular substrates 4 supported by a lower support plate 5. The plates 5 have openings 6 aligned with central passages 7 of the substrates 4 to circulate a reactive gaseous phase through each stack 3, which then passes through the substrates 4 to densify them. Each stack 3 is topped by an annular cover disk 8, and each unit module 2 also includes vertical supports 9 extending between the support plate 5 of unit module 2 and the support plate 5 of the unit module 2 above. The vertical supports 9 bear the mass of the upper support plates 5 and thus ensure the stability of the support plates 5.

[0012] There figure 1is a representation of the hot zone of a directed flow loading. This hot zone comprises, from its base to its top: an inlet of the reaction gas mixture 10, then a preheating zone 11 which increases the temperature of the gases up to the densification temperature, and finally the loading zone 12. At the top of the furnace, at the level of the susceptor cover 13, a chimney 14 is installed in the cover 13, through which the effluent gases from the deposition reaction are evacuated.

[0013] On each tray 5 there is a stack of substrates 4 separated by spacers 15, each stack ending at its top with a cover disc 8 which limits leakage.

[0014] The gases exiting the preheating zone 11 enter each of the columns made up of the stacks 3 of substrates 4. The gas passes from the inside to the outside of the columns of substrates 4, through the leaks made up of the porosity of each preform 4, the gap between the substrates 4 created by the spacers 15, and through the passages between the plates 5.

[0015] A densification process using chemical vapor infiltration of porous substrates, employing a semi-forced flux, is described in document FR 2 821 859. To adapt the semi-forced flux as described in this document, leakage between substrates must be controlled, as well as leakage at the transition between trays. In other words, controlling leakage other than that related to the porosity of the preforms 4 improves the densification kinetics: this is the implementation of the so-called "semi-forced flux" process.

[0016] The implementation of semi-forced flow involves providing calibrated leak passages between the inside and outside of the substrate columns, which implies sealing areas left free in the implementation of the current directed flow process: these areas are located in particular at the level of the inter-disk spacers and the junction between the lower stack and the support plate of the upper unit module.

[0017] A pressure gradient will develop and increase as the preforms densify between the inside (where the gas enters) and the outside of the stacks. The calibrated leaks are designed to limit this pressure gradient and prevent soot deposits inside the substrate stack due to excessive pressure. Monitoring this pressure gradient, which reflects the progress of densification, is therefore essential for controlling the cycle.

[0018] Leaks at the transition between trays are the most difficult to control because the stacks of porous annular substrates are not of the same height. Without excellent control of this sealing at the top of each stack, the pressure difference necessary to force the gas into the pores of the substrates cannot be achieved.

[0019] It is also known from patent FR 3 084 892 to replace the candles with gas distributors, which make it possible to simultaneously ensure the functions of load recovery (function previously done by the candles), of guiding (cold) gases, which avoids cooling the discs, and of distributing gases at the level of the preforms.

[0020] A pressure gradient CVI densification process of porous annular substrates with a central passage is also known from US document 7 892 646 B1. Description of the invention

[0021] The invention aims to provide a technical solution for the implementation of a 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.

[0022] 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.

[0023] According to a general feature of the invention, in each unit module, each first porous annular substrate is supported on a second porous annular substrate, or supported on the support plate, by means of a 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.

[0024] In other words, each unit module comprises a plurality of sealing rings, each sealing ring being positioned to support between two successive porous annular substrates or between a porous annular substrate and the support plate.

[0025] By "radial sealing", we mean sealing that prevents the circulation of the gas phase in a radial direction between the internal volume of the stacks and the outside of the stacks.

[0026] The invention thus makes it possible to better control the circulation of the gas around the porous annular substrates and therefore to improve the distribution of the gas in the furnace chamber.

[0027] In addition, in each unit module, each sealing ring is coupled to an annular shim having an internal diameter equal to an internal diameter of the porous annular substrates.

[0028] The annular shims allow the sealing rings to be centered and thus facilitate their positioning.

[0029] Each annular spacer has a thickness less than that of the sealing ring to which it is coupled. This thickness ratio ensures that the porous annular substrate bears down on the sealing ring, thus guaranteeing radial sealing. Furthermore, this thickness ratio allows for free circulation of the gas phase around the porous annular substrates.

[0030] In one embodiment, each stack includes at least one cover disc supported on the porous annular substrate at the top of the stack by means of a sealing ring ensuring radial sealing between said cover disc and said porous annular substrate at the top of the stack.

[0031] Each stack may also include a deformable annular seal arranged to be compressed between the cover disc and the support tray of the upper unit module.

[0032] The deformable annular seal is, for example, made of carbon fiber felt.

[0033] In addition, each stack can also include an expanded graphite disc positioned between the deformable ring seal and the support plate of the upper unit module. The expanded graphite disc prevents the deformable ring seal from sticking to the support plate above.

[0034] According to a first embodiment, in each unit module, the sealing rings are arranged at the radially external periphery of the porous annular substrates.

[0035] According to a second embodiment, in each unit module, the sealing rings are alternately arranged, according to the direction in which the porous annular substrates are stacked, at the radially external periphery of the porous annular substrates and at the radially internal periphery of the porous annular substrates.

[0036] These two embodiments maximize the contact surfaces of the porous annular substrates with the gaseous phase.

[0037] The sealing rings are for example made of Inconel ®< .

[0038] The annular shims can also be made of Inconel ®< .

[0039] Each sealing ring, for example, is welded to the annular spacer to which it is coupled. This welding facilitates the formation of the stacks.

[0040] In one particular embodiment, the process further includes placing a solid cover on top of the stack of unit modules. This solid cover compresses the deformable elements, including the sealing rings and deformable annular seals.

[0041] According to a particular embodiment, the method further comprises a step of sealing the unit modules of the stack comprising, for each first unit module stacked on a second unit module, an insertion of the second end of the injection tube of the second unit module into the gas inlet opening of the first unit module stacked on said second unit module, an annular seal being disposed between the second end of the injection tube of the second unit module and the gas inlet opening of the first unit module stacked on said second unit module.

[0042] In one example embodiment, for each unit module, the support platform may include a first face on which the stack of the unit module is arranged and a second face opposite to the first face, the 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 platform, and the second end of the injection tube may include a complementary frustoconical shape cooperating with the frustoconical shape of the gas inlet opening.

[0043] The injection tube thus forms a male centering tool and the gas inlet opening a female centering tool cooperating together to ensure proper centering of the unit modules with each other.

[0044] Preferably, each support plate may include, on its first face, a centering ring centered around a gas opening and shaped to accommodate an injection tube.

[0045] The centering ring thus makes it easier and more efficient to place the injection tubes on the support plates.

[0046] In one example of implementation of the process, the process may further include a step of arranging the stack of unit modules on a load-carrying shell arranged on a preheating zone of the densification furnace.

[0047] In one example embodiment, each unit module may include an annular foot disposed between the support plate of the unit module and the stack of porous annular substrates of the unit module, the annular foot having radial grooves forming passages, in a direction orthogonal to the direction in which the porous annular substrates are stacked between a central cavity of the annular foot and the outside of the annular foot.

[0048] According to a particular embodiment, the step of injecting a gaseous phase into the internal volume of each stack includes maintaining a pressure difference between the internal volume of the stacks and the outside of the stacks of between 0 and 100 millibars.

[0049] In one embodiment example, each porous ring substrate may include carbon.

[0050] In one embodiment example, each porous annular substrate can constitute a fibrous preform of a brake disc. Brief description of the drawings

[0051] [ 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 schematically illustrates a cross-sectional view of an example of a stack of porous annular substrates according to the invention. Fig. 3 ] There figure 3 schematically presents a cross-sectional view of a densification furnace according to the invention. Fig. 4 ] There figure 4 schematically presents a top view of a ring foot. Fig. 5 ] There figure 5 schematically presents a cross-sectional view of a ring foot. Description of the implementation methods

[0052] 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.

[0053] On the figure 2 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 Z direction. Each porous annular substrate 21 extends mainly in a plane perpendicular to the first Z direction. The cross-sectional plane of the illustration of the figure 2 includes the first direction Z and a second direction X perpendicular to the first direction Z. The first direction Z coincides with the axis of revolution symmetry of the porous annular substrates 21, and the second direction X corresponds to a radial direction.

[0054] 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 assembly comprising an annular wedge 22 and a sealing ring 23. The outer radial diameter of the annular wedge 22 is smaller than the outer radial diameter of the porous annular substrates 21, the diameters of the orifices of the annular wedges 22 and the porous annular substrates 21 being equal.

[0055] Each annular spacer 22 is surrounded by a sealing ring 23 in the plane perpendicular to the first Z direction. The thickness of the sealing ring 23 measured along the first Z direction is greater than that of the annular spacer 22, so that each porous annular substrate 21 rests on a sealing ring 23. The annular spacers 23 allow the sealing rings 23 to be centered on the first Z direction.

[0056] The alternative stacking of the porous annular substrates 21 and the sealing rings 23 forms, at the center of the stack 20, an internal volume 24 of the stack 20.

[0057] Furthermore, the stack 20 is closed at its top by an annular cover disc 25. The cover disc 25 is placed on the stack via an annular spacer 22 and a sealing ring 23. The stack also includes a deformable annular seal 26 made of compressed carbon fiber felt disposed on the cover disc 25, and a disc 27 made of expanded graphite disposed on the deformable annular seal 26 to prevent this deformable annular seal 26 from sticking to the support plate above.

[0058] The stack 20 also includes a secondary annular sealing ring 28 also made of compressed carbon fiber felt directly on the annular wedge 22 supporting the cover disc 25. The secondary sealing ring 28 covers the part of the annular wedge 22 not covered by the cover disc 25.

[0059] 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.

[0060] On the figure 3 A schematic cross-sectional view of a densification oven according to the invention is shown.

[0061] The densification furnace 40 according to the invention comprises a stack of a plurality of unit modules 30. Each unit module 30 comprises a support tray 31 on which is arranged a stack 20 of porous annular substrates via an annular foot 29, the annular foot 29 being arranged between the support tray 31 and the stack 20 of the same unit module 30.

[0062] As depicted on the Figures 4 and 5 which present a top view and a cross-sectional view of an annular foot 29, the annular foot 29 has radial grooves 295 forming passages, in a radial direction, between a central cavity 290 of the annular foot 29 and the outside of the annular foot 29.

[0063] As illustrated on the figure 3, the support plate 31 of a unit module 30 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 the stack 20 between a first tube end 33a connected to the support plate 31 and a second tube end 33b which is free.

[0064] The injection tube 33 further includes gas injection ports 34 opening into the internal volume 24.

[0065] The gas-phase chemical infiltration densification process according to the invention then includes a step during which a stack of unit modules 30 is formed in the enclosure of a densification furnace 40.

[0066] On the figure 3 is shown the support plate 31 of a first unit module 30a about to be superimposed on a second unit module 30b.

[0067] 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 3 , to achieve alignment, the second end 33b of the injection tube 33 of the second unit module 30b is inserted into the gas inlet opening 32 of the first unit module 30a.

[0068] To seal the junction between the injection tube 33 of the second unit module 30b and the gas inlet opening 32 of the first unit module 30a, the second unit module 30a further comprises 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.

[0069] More specifically, each support plate 31 comprises a first face 31a on which the stack 20 is arranged and a second face 31b opposite the first face 31a. The 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 d2 and formed between the first face 31a and the second face 31b of the support plate 31.

[0070] 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 third diameter larger than a fourth diameter, the fourth diameter being measured on a free distal end while the first diameter is measured on a proximal end coupled to the rest of the injection tube 33, and in particular to a main portion 33c.

[0071] As illustrated on the figure 3 , to improve the sealing of the stack of unit modules 30, the deformable annular seal 26 is dimensioned to fill the space, along the first direction Z, between the cover disc 25 of the stack 20 of the second unit module 30b and the support tray 31 of the first unit module 30a.

[0072] The gas-phase chemical infiltration densification process according to the invention then includes a step of arranging the stack of unit modules 30 on a load-carrying shell 42 arranged on a preheating zone 44 of the densification furnace 40.

[0073] The gas-phase chemical infiltration densification process according to the invention then includes placing a massive lid 46 on top of the stack of unit modules 30.

[0074] 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 3indicated by arrows G. The step of injecting a gaseous phase into the internal volume 24 of the stacks 20 preferably includes regulating the pressure difference between the internal volume 24 of the stacks 20 and the outside of the stacks. The pressure difference is preferably maintained between 0 and 100 millibars. Such a range ensures a flow of the gaseous phase around the porous annular substrates 21 while preventing soot deposition.

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 a single stack (20) of porous annular substrates (21) disposed on the support plate (31), the support plate (31) comprising 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 the stack (20) disposed on the support plate (31) 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 orifices (34) opening into the internal volume (24), - forming, in the chamber of a densification furnace (40), a stack of individual modules (30), each first individual module (30a) stacked on a second individual module (30b) having its gas inlet opening (32) of the support plate (31) communicating with the second end (33b) of the injection tube (33) of the second individual module (30b) on which it is stacked so as to permit circulation of a gas 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, in each individual module (30), each first porous annular substrate (21) is supported on a second porous annular substrate (21), or supported on the support plate (31), by means of a sealing ring (23) providing radial sealing between the first porous annular substrate (21) and the second porous annular substrate (21) or between the first porous annular substrate (21) and said support plate (31), and each sealing ring (23) is coupled to an annular spacer (22) having an inner diameter equal to an inner diameter of the porous annular substrates (21), each annular space (22) being surrounded by the sealing ring (23) with which it is associated in a plane perpendicular to the direction in which the porous annular substrates (21) are stacked, and having a thickness less than the thickness of the sealing ring (23) with which it is coupled.

2. The method according to claim 1, wherein each stack (20) comprises at least one cover disk (25) supported on the porous annular substrate (21) at the top of the stack (20) by means of a sealing ring (23) providing radial sealing between said cover disk (25) and said porous annular substrate (21) at the top of the stack (20).

3. The method according to claim 2, wherein each stack (20) further comprises a deformable annular seal (26) arranged to be compressed between the cover disk (25) and the support plate (31) of the upper individual module (30).

4. The method according to any one of claims 1 to 3, wherein, in each individual module (30), the sealing rings (23) are disposed at the radially outer periphery of the porous annular substrates (21).

5. The method according to any one of claims 1 to 3, wherein, in each individual module (30), the sealing rings (23) are alternately disposed, along the direction in which the porous annular substrates are stacked, at the radially outer periphery of the porous annular substrates (21) and at the radially inner periphery of the porous annular substrates (21).

6. The method according to any one of claims 1 to 5, wherein the sealing rings (23) are made of Inconel®.

7. The method according to any one of claims 1 to 6, wherein each sealing ring (23) is welded to the annular spacer (22) to which it is coupled.

8. The method according to any one of claims 1 to 7, further comprising a seal alignment step of the individual modules (30) of the stack comprising, for each first individual module (30a) stacked on a second individual module (30b), insertion of the second end (33b) of the injection tube (33) of the second individual module (30b) into the gas inlet opening (32) of the first individual module (30a) stacked on said second individual module (30b), an annular seal (35) being 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) stacked on said second individual module (30b).

9. The method according to claim 8, wherein, for each individual module (30), the support plate (31) comprises a first face (31a) supporting the stack (20) of the individual module (30) and a second face (31b) opposite the first face (31a), the 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 the injection tube (33) comprises a complementary frustoconical shape cooperating with the frustoconical shape of the gas inlet opening (32).

10. The method according to any one of claims 1 to 9, further comprising a step of disposing the stack of individual modules (30) on a load-carrying shell (42) disposed on a preheating zone (44) of the densification furnace (40).

11. The method according to any one of claims 1 to 10, wherein each individual module (30) comprises an annular foot (29) disposed between the support plate (31) of the individual module (30) and the stack (20) of porous annular substrates (21) of the individual module (30), the annular foot having radial grooves forming passages, along a direction (X) orthogonal to the direction in which the porous annular substrates are stacked between a central cavity of the annular foot and the outside of the annular foot.

12. The method according to any one of claims 1 to 11, wherein each porous annular substrate (21) comprises carbon.

13. The method according to any one of claims 1 to 12, wherein each porous annular substrate (21) constitutes a fibrous brake disc preform.