METHOD FOR DRYING AN IMPRECISED BLANK AND ASSOCIATED MANUFACTURING METHOD

Description

FIELD OF INVENTION

[0001] The invention relates to the drying of a blank part based on impregnated carbon / carbon composite material.

[0002] The invention relates to a drying process for a blank part based on impregnated carbon / carbon composite material and a manufacturing process for a part based on associated carbon / carbon composite material. STATE OF THE ART

[0003] We know of parts made from carbon / carbon (C / C) composite material(s)

[0004] Examples include friction components such as aircraft brake discs, but they can also be used in other applications and / or for other carbon / carbon composite parts, particularly those requiring improved mechanical properties. Aircraft brake discs made of carbon / carbon composite are widely used. Manufacturing such discs typically involves creating a carbon fiber preform with a shape similar to that of the disc to be manufactured. This preform serves as the fibrous reinforcement for the composite material. The preform is then densified with a pyrolytic carbon (PyC) matrix to form a blank.A well-known process for producing a carbon fiber preform involves layering carbon precursor fibers, for example, pre-oxidized polyacrylonitrile (PAN), bonding the layers together, for example by needle punching, and then performing a carbonization heat treatment to convert the precursor to carbon. Reference may be made, among other sources, to US patent 5,792,715.

[0005] The densification of a preform with a PyC matrix can be achieved by chemical vapor infiltration (CVI). Preforms are placed in a chamber into which a gaseous phase containing one or more carbon precursors, such as methane and / or propane, is introduced. The temperature and pressure within the chamber are controlled to allow the gaseous phase to diffuse into the preforms and form a solid pyrolytic carbon deposit through the decomposition of the precursor(s). A process for densifying a plurality of annular brake disc preforms arranged in stacks is described, among other places, in US patent 5,904,957.

[0006] Densification by a carbon matrix can also be carried out by liquid means, i.e. by impregnation of the preform with a carbon precursor, typically a resin, and pyrolysis of the precursor, with several cycles of impregnation and pyrolysis usually being carried out.

[0007] Another known densification process, called "heat densification," involves immersing a preform of the disk to be densified in a bath of carbon precursor, such as toluene, and heating it, for example by coupling with an inductor. The precursor, vaporized upon contact with the preform, diffuses within it to form a PyC deposit through decomposition. This process is described, among other places, in US patent 5,389,152.

[0008] Among the various desired properties of carbon / carbon composite brake discs, low wear is highly desirable. To improve wear resistance, the introduction of ceramic grains into the carbon / carbon composite material has been widely proposed. For example, US patent 6,376,431 describes the impregnation of a carbon fiber blank with a sol-gel solution containing a silica (SiO2) precursor. After heat treatment and chemical reaction with the carbon, this leaves silicon carbide (SiC) grains distributed throughout the blank, these grains representing no more than 1% by weight in the final carbon / carbon composite material.

[0009] Document WO 2006 / 067184 recommends impregnating the fibrous texture of the layers used to create the blank with a sol-gel solution or colloidal suspension to obtain a dispersion of oxide grains such as titanium (TiO2), zirconium (ZrO2), hafnium (HfO2), and silicon (SiO2). Subsequent heat treatment transforms these oxide grains into carbide grains. Document EP 1 748 036 describes the impregnation of a carbon fiber substrate with a slurry containing a carbon precursor resin and metal oxide grains, for example, SiO2, TiO2, ZrO2, etc. After heat treatment, a carbon-on-carbon (C / C) composite material is obtained containing carbide grains produced by transforming the oxide particles. The examples indicate the use of oxide grains several microns in size.Document EP 0 507 564 describes the production of a part made of a carbon / ceramic type composite material by mixing carbon fibers, ceramic powder, and carbon powder, molding, and sintering. The ceramic powder can be, for example, an oxide such as SiO2, TiO2, ZrO2, or a nitride. The use of ZrO2 powder consisting of one-micron grains is mentioned in Example 2, with the quantity of ZrO2 in the final composite material being 6.2%. It should be noted that, among the ceramic powders considered, ZrO2 does not provide the best wear resistance. Document EP 0 404 571 describes a process similar to that of EP 0 507 564, but for producing a sliding part with a low coefficient of friction.

[0010] Methods are known for manufacturing parts with improved properties, including the addition of ceramic fillers to a carbon-based carbon / carbon (C / C) composite blank. These fillers are introduced via an impregnation-drying process using a sol containing the ceramic particles. This process is described in French patent application FR 2 945 529. Such a process yields improved mechanical properties, which is of particular interest for C / C composite parts regardless of their intended use.

[0011] However, when implementing these methods, it is very difficult to obtain a homogeneous distribution of particles within the blank, resulting in a charge gradient throughout the material thickness. These charges are typically distributed as follows for a part, for example a friction part: a significant amount of charge is present near the faces, for example the rubbing faces, while only a small amount of charge is present within the core of the blank.

[0012] This atypical load distribution generates risks related, among other things, to variability in tribological properties over the part's lifespan, for example, depending on its wear level, as face wear may be observed. For example, in a friction part, wear on the rubbing faces of several millimeters may be observed during the brake's service life. Documents DE 20 2008 013 487 U1 and EP 2 058 613 A2 disclose other processes for drying blanks. FR 2851244A1 describes the gelation of a refractory material precursor and a process for drying a blank made of carbon / carbon composite material impregnated with a sol-gel solution, the solution comprising a solvent and one or more compounds, in an oven-forming system, the system comprising a chamber configured to receive the blank, the process comprising the following steps: gelation of the solution so as to form a gel within the blank placed in the chamber by heating the chamber, and drying of the gel within the blank by heating. DESCRIPTION OF THE INVENTION

[0013] The invention aims in particular to solve the problems of load distribution within a part whose manufacture involves adding ceramic fillers to a carbon-based carbon / carbon (C / C) composite blank. The invention aims to reduce the risk of variability in the tribological properties of such parts over their service life.

[0014] To this end, a drying process is proposed for a blank part made of carbon / carbon composite material impregnated with a sol-gel type solution, the solution comprising a solvent and one or more compounds, in an oven-forming system, the system comprising: a chamber configured to receive the blank, gas circulation means configured to selectively allow the circulation of a gas between a gas outlet of the chamber and a gas inlet of the chamber, gas desaturation means being configured to selectively allow at least partial desaturation of the gas with solvent, the process comprising the following steps: gelation of the solution so as to form a gel within the blank disposed in the chamber by heating the chamber, the circulation means and the desaturation means being deactivated, so as to limit the circulation and desaturation of the gas in solvent, and drying of the gel within the blank by heating, the circulation means and the desaturation means being activated, so as to allow the circulation and desaturation of the gas in solvent.

[0015] The process can be supplemented by the following features, taken alone or in any technically possible combination thereof: Prior to the gelation stage, a temperature ramp-up stage, with the circulation means activated and the desaturation means deactivated, so as to allow the temperature ramp-up while limiting the desaturation of the gas in solvent, the chamber includes dedicated heating means, configured to selectively heat the chamber, for example independently of the state of the gas circulation means, the chamber heating means being activated during the gelation and drying stages, and for example activated during the temperature ramp-up stage, the chamber heating means including for example a double chamber jacket, the gas circulation means including dedicated heating means, configured to selectively heat the gas circulating between the gas outlet and the gas inlet,the heating means of the circulation means being deactivated during the gelation stage and activated during the drying stage, and for example activated during the temperature rise stage, The drying stage includes a heating substage and a subsequent holding substage, the drying stage being, for example, followed by a cooling stage in which the circulation means, and for example the chamber heating means and / or the heating means for the circulation means, are deactivated, the gas circulation means include a gas circulation circuit extending between the gas outlet and the gas inlet, the circulation circuit including a fan configured to selectively allow the circulation of a gas between the chamber gas outlet and the chamber gas inlet, the heating means for the circulation means including, for example, a heater configured to heat the gas circulating within the circulation means, the heater being, for example, disposed between the fan and the gas inlet,The gas desaturation means include a gas desaturation circuit comprising: a valve configured to selectively allow gas circulation within the gas desaturation circuit, and a condenser configured to allow condensation of the solvent present in the gas circulating within the gas desaturation circuit, and the supply of desaturated gas by the gas desaturation circuit. The gas desaturation circuit is fluidly connected to the chamber via the gas circulation circuit. The gas desaturation circuit includes, for example, a dedicated inlet and outlet. The inlet of the gas desaturation circuit is disposed upstream of the outlet of the gas desaturation circuit in the gas circulation circuit so as to form a bypass. The inlet and outlet of the gas desaturation circuit are, for example, disposed upstream of the fan and / or heater.

[0016] The invention also relates to a method for manufacturing a part made from carbon / carbon composite material comprising the steps of: supply or obtaining a blank part based on carbon / carbon composite material impregnated with a sol-gel type solution within an oven-forming system, and drying of the blank including the drying process. DESCRIPTION OF THE FIGURES

[0017] Other features, purposes and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which: there figure 1 schematically represents a system forming an oven, the figure 2 schematically represents a drying process according to an example of an embodiment of the invention, the figure 3 schematically represents a manufacturing process according to an example of an embodiment of the invention, the figure 4schematically represents a manufacturing assembly, the figure 5 The graph represents an example of the reaction time required for a sol-gel solution to reach a given viscosity. figure 6 graphically represents the evolution of temperature as a function of time during a drying process according to an example of an embodiment of the invention. figure 7 represents in the form of a histogram the impact of the drying process according to an example of an embodiment of the invention compared to the prior art.

[0018] Across all figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION System

[0019] With reference to the figure 1 An example of a system 10 is described, for example a system forming an oven, to implement the drying process as described below.

[0020] The system 10 includes a chamber 11 configured to receive a blank 15 of a part made of carbon / carbon composite material impregnated with a sol-gel type solution. The chamber includes a gas outlet 111 and a gas inlet 112.

[0021] The system 10 includes gas circulation means 12. The circulation means 12 are configured to allow, for example selectively, the circulation of a gas between the chamber gas outlet 111 and the chamber gas inlet 112. The circulation means 12 can, for example, be selectively activated or deactivated.

[0022] The system 10 includes gas desaturation means 13. These gas desaturation means 13 are configured to selectively allow at least partial desaturation of the gas with solvent. For example, the desaturation means 13 can be selectively activated or deactivated. Together

[0023] With reference to the figure 4 A manufacturing assembly 1 for a part based on carbon / carbon composite material is described. The assembly includes system 10.

[0024] The assembly 1 may further include means of obtaining 40, for example a unit for obtaining, a rough part based on carbon / carbon composite material impregnated with a sol-gel type solution within the oven-forming system 10. Ordering methods

[0025] The oven system 10 and / or assembly 1 may include control means 14 for the oven system 10 or assembly 1, for example, a control system comprising one or more control units, the control means 14 comprising data processing means configured to implement the drying process and / or the manufacturing process as described below. The data processing means may include one or more data processing units. The data processing means and / or the data processing unit(s) may include one or more processors.

[0026] The control means 14 can for example implement temperature control, for example the temperature measured at a first temperature sensor and / or a second temperature sensor as described below. Drying process

[0027] With reference to the figure 2 , an example of a process for drying at least one blank 15 of a part based on carbon / carbon composite material impregnated with a sol-gel type solution, for example several such impregnated blanks 15, in a system 10 forming an oven.

[0028] The solution comprises a solvent and one or more compounds.

[0029] The drying process includes a gelation step 203 of the solution to form a gel within the blank 15 arranged in the chamber by heating the chamber. During the gelation step 203, the circulation means 12 and the desaturation means are deactivated, so as to limit the circulation and desaturation of the gas with solvent.

[0030] The drying process includes a drying step 205 of the gel within the blank 15, for example arranged in the chamber, by heating. During the drying step 205, the circulation means 12 and the desaturation means 13 are activated, so as to allow the circulation and desaturation of the gas with solvent.

[0031] Such a drying process makes it possible to solve the problems of charge distribution, and in particular the problem of the presence of a large charge gradient.

[0032] In prior art processes, the precursor macromolecules being of nanometric size, they are transported by the solvent during its evaporation, and the particles present at the core migrate partially towards the periphery of the blank, via a transport phenomenon in a porous medium.

[0033] The proposed process reduces the mobility of precursor macromolecules to decrease the charge distribution gradient. This reduction in macromolecule mobility is achieved by increasing their size, i.e., increasing their degree of polymerization. This increase is induced by raising the temperature while simultaneously limiting evaporation by restricting gas circulation and desaturation. This increased degree of polymerization leads to an increase in the soil's viscosity, or gelation of the solution.

[0034] Indeed, the sol-gel type solution forms a solution composed of compounds. As it ages, induced by temperature, these compounds will gradually react with each other to form a three-dimensional network and cause gelation.

[0035] The drying process may also include, prior to the gelation step 203, a temperature ramp-up step 201. Draft part and part

[0036] The rough draft of the part, for example, has a disc shape.

[0037] The part blank is for example a friction part blank, for example brake disc, for example aircraft brake disc, or part for another application and / or another part in C / C composite material, for example a brake disc for land vehicles, for example automobiles, for example a racing car, and friction parts other than discs, including pads.

[0038] Thus, the part is for example a friction part, for example a brake disc, for example an aircraft brake disc, or a part for another application and / or another part made of C / C composite material.

[0039] The part blank can be a fibrous blank, for example made of carbon fibers. The part blank can be configured to provide fibrous reinforcement for a composite material of the part.

[0040] The part blank may comprise a superposition of fibrous layers, the fibrous layers being bonded together, for example by needle punching. The part blank may be obtained by a blank-making step as described below. Soil / gel type solution

[0041] The solution may include a solvent and one or more compounds.

[0042] The solvent may include or be an alcohol-based solvent. The solvent may include or be butanol and / or ethanol, for example, a mixture of butanol and ethanol.

[0043] The compound(s) may be or include one or more precursors, for example ceramic precursor(s), for example one or more precursors of silica (SiO2), and / or titanium dioxide (TiO2), and / or zirconium dioxide (ZrO2), and / or hafnium dioxide (HfO2). It will thus be possible to form grains of silicon carbide (SiC) and / or titanium carbide and / or zirconium carbide and / or hafnium carbide, distributed throughout the blank.

[0044] The solution may also include a chelating agent, allowing, for example, control of gelation kinetics.

[0045] The solution may include a hydrolysis agent, for example water. Bedroom

[0046] The chamber 11 may include dedicated heating means 113. The heating means 113 of the chamber are, for example, referred to as primary heating means 113. The heating means 113 of the chamber may be configured to selectively heat the chamber 11, for example, independently of the state of the gas circulation means 12, for example, independently of whether the circulation means are activated or deactivated and / or independently of whether heating means of the circulation means, described below, are activated or deactivated.

[0047] The heating means 113 of the chamber can be activated during the gelation step 203. The heating means 113 of the chamber can also be activated during the drying steps 205, and / or the temperature rise 201, so as to accelerate the respective steps and to accelerate the process.

[0048] The heating means 113 of the room may include a double envelope 1131 of the room.

[0049] The impregnated part blanks 15 are, for example, positioned in a stack in chamber 11.

[0050] Chamber 11, for example, forms an enclosure. System 10 comprises a tank containing chamber 11.

[0051] The chamber inlet 112 can be adapted to allow gas injection from the circulation means 12. The chamber inlet 112 can be positioned at a lower part of the chamber 11, for example at the bottom of the enclosure. The chamber outlet 111 can be positioned at an upper part of the chamber 11, for example at the top of the enclosure, for example at the top of the enclosure. Means of transportation

[0052] The gas circulation means 12 may include dedicated heating means 123. The heating means 123 of the circulation means are, for example, called secondary heating means. The heating means 123 of the circulation means may be configured to selectively heat the gas circulating between the gas outlet 111 and the gas inlet 112, for example, before the gas is injected into the chamber 11.

[0053] The activation of the heating means 123 of the circulation means may depend on the state of the circulation means 12. For example, the heating means 123 of the circulation means are deactivated when the circulation means 12 are deactivated and / or can only be activated if the circulation means 12 are activated.

[0054] The heating means 123 of the circulation means can be deactivated during the gelation step 203 and / or activated during the drying step 205, and / or activated during the temperature rise step 201.

[0055] The heating means 123 of the circulation means can be deactivated during the gelation step 203 and activated during the drying step 205, and for example activated during the temperature rise step 201.

[0056] The gas circulation means 12 may include a gas circulation circuit 121 extending between the gas outlet 111 and the gas inlet 112.

[0057] The circulation circuit 121 may include a fan 122 configured to selectively allow the circulation of a gas between the chamber gas outlet 111 and the chamber gas inlet 112. Activation, or deactivation, of the fan 122 may correspond to the activation, or deactivation, of the circulation means 12. The fan 122 may include a propeller with blades.

[0058] The heating means 123 for the circulation means may include a heater configured to heat the gas circulating within the circulation means 12, the heater being, for example, located between the fan and the gas inlet. The heater may be or include a coil heater, for example, a heater comprising a coil through which steam, for example, water vapor, circulates when the heater or the heating means 123 are activated. It is thus possible to reuse steam produced elsewhere, or to use energy produced elsewhere, for example, by hydrocarbon combustion, the energy being used to produce steam. Alternatively or in addition, the heater may be or include, for example, an electric heater.

[0059] The circulation means 12, for example the circulation circuit 12, may include one or more temperature sensor(s), for example a first temperature sensor 124 and / or a second temperature sensor 125. The first temperature sensor 124 may be upstream of the second temperature sensor 125.

[0060] The first temperature sensor 124 can be adapted to measure a temperature of the gas flowing at the outlet 111 of the chamber and / or upstream of the heating means 123 and / or between the outlet 111 of the chamber and the heating means 123, and / or between the outlet 111 of the chamber and the desaturation means 13, for example an inlet 134 of a desaturation circuit as described below.

[0061] The second temperature sensor 125 can be adapted to measure the temperature of the gas at the outlet of the heating means 123, for example circulating at the inlet 112 of the chamber and / or downstream of the heating means 123 and / or between the inlet 112 of the chamber and the heating means 123. The second temperature sensor 125 can be connected to the control means 14, for example so as to allow temperature control, for example so as to allow temperature control during the heating stage 201 and / or the determination of the transition to the gelation stage 203.

[0062] Upstream and downstream respectively, we mean upstream and downstream, respectively, according to the direction of gas flow. Desaturation methods

[0063] The means for desaturation of gas 13 may include a desaturation of gas circuit 131.

[0064] The gas desaturation circuit 131 can be fluidically connected to chamber 11 via the gas circulation circuit 121. The gas desaturation circuit 131 may include a dedicated inlet 134 and outlet 135. The inlet 134 of the gas desaturation circuit may be located upstream of the outlet of the gas desaturation circuit 131 in the gas circulation circuit 121 to form a bypass. The inlet 134 and outlet 135 of the gas desaturation circuit may, for example, be located upstream of the fan 122 and / or the heater 123.

[0065] The gas desaturation circuit 131 can form a bypass circuit, or selective bypass, of a part of the circulation circuit 121 located upstream of the heating means 123.

[0066] The desaturation circuit 131 may include a valve 133 configured to selectively allow gas circulation within the gas desaturation circuit.

[0067] Valve 133, for example, can allow different degrees of opening. The degree of opening of the valve is controlled, for example, by the control means 14, for example, according to a target level of desaturated or clean nitrogen.

[0068] The desaturation circuit 131 may include a condenser 136 configured to allow the condensation of the solvent present in the gas circulating within the gas desaturation circuit, and the supply of desaturated gas by the gas desaturation circuit. The condenser 136 allows for the partial or total desaturation of the solvent. The condenser 136 is, for example, configured to condense the solvent present in the gas circulating between the valve 133 and the outlet 135. The condenser 136 may include a discharge outlet Y for the condensed solvent from the system 10. The activation or opening, or deactivation or closing, of the valve 133 may correspond to the activation, or deactivation, of the desaturation means 13. The activation, or deactivation, of the condenser 136 may correspond to the activation, or deactivation, of the desaturation means 13.The activation or opening, respectively the deactivation or closing, of the valve 133 and the activation, respectively the deactivation, of the condenser 136 can correspond to the activation, respectively the deactivation, of the desaturation means 13.

[0069] The system 10, for example the desaturation means 13, may include a flow sensor 137, for example a flow transmitter, for example configured to measure the flow within the desaturation circuit 131, for example between the valve 133 and the outlet 135, for example between the condenser 136 and the outlet 135, for example downstream of the valve 133, for example downstream of the condenser 136, for example upstream of the outlet 135. Temperature rise stage

[0070] The drying process may include, prior to the gelation step 203, the temperature ramp-up step 201, for example up to a first temperature threshold.

[0071] During the temperature rise step 201, the circulation means 12 are activated and the desaturation means 13 are deactivated, so as to allow the temperature rise while limiting the desaturation of the gas with solvent, and therefore the evaporation of the solvent. It is thus possible to limit the transport of precursor macromolecules within the porosity of the blanks.

[0072] During the temperature rise stage 201, the heating means 113 of the chamber can be activated to allow the temperature rise.

[0073] During the temperature rise stage 201, the heating means 123 of the circulation means can be activated to allow the temperature rise.

[0074] During the temperature rise stage 201, the temperature can be controlled, for example from the temperature measured by the second temperature sensor 125, for example by the control means 14, until a first temperature threshold is reached, for example of about 75°C.

[0075] Valve 133 can be closed, so that system 10 operates in a closed system.

[0076] The rate of temperature rise, or ramp-up to the first temperature threshold, is determined, for example, based on the capacity of chamber 11 and the amount of impregnated part blanks 15 loaded into chamber 11. The ramp is, for example, between 5 and 30°C / h, or between 10 and 25°C / h. Gelation stage

[0077] During the gelation step 203, the heating means 113 of the chamber can be activated, for example to maintain the temperature above the first temperature threshold and allow gelation.

[0078] During the gelation step 203, the heating means 123 of the circulation means can be deactivated, the circulation means 12 being deactivated so as to maintain the static gas and to reduce the phenomenon of solvent evaporation, responsible for the appearance of charge distribution gradient, and because it is no longer necessary to increase the temperature as in the temperature rise step 201.

[0079] The gelation step 203 is, for example, carried out at a given temperature and / or for a given duration(s) to reach a predetermined gelation threshold of the sol-gel type solution. The gelation threshold is, for example, between 500 and 1200 mPa.s, for example between 700 and 1000 mPa.s, for example between 800 and 900 mPa.s, for example approximately 850 mPa.s.

[0080] The temperature is, for example, lower than the boiling point of the sol-gel solution, so as to prevent boiling within the blank during the gelation step. The temperature of the gelation step is, for example, between the first temperature threshold and a second temperature threshold higher than the first.

[0081] The second temperature threshold of the gelation step 203 is for example between 65 and 95 °C, for example less than or equal to 90°C and / or greater than or equal to 70°C, for example about 85°C, and / or the duration of the gelation step is for example between 22h and 1h, for example between 6h and 1h30, for example about 2h.

[0082] The temperature of the first means of heating 113 is for example fixed between 100 and 110°C, for example at 105°C.

[0083] The process is implemented for example in such a way that the temperature rise step 201 ends and / or the gelation step 203 begins when the first temperature threshold is reached, for example measured by the second temperature sensor 125.

[0084] The control means 14 can, for example, control the temperature during the gelation stage.

[0085] During the gelation step 203, the temperature can be controlled, for example from the temperature measured by the first temperature sensor 124, for example by the control means 14, in order to be maintained between the first temperature threshold and the second temperature threshold and / or according to a setpoint temperature between the first temperature threshold and the second temperature threshold, for the duration of the gelation step. Drying stage

[0086] The drying step 205 may include a heating substep 2051. The drying step 205 may include, for example after the heating substep 2051, a subsequent holding substep 2053.

[0087] During drying step 205, the heating means 113 of the chamber can be activated, and the heating means 123 of the circulation means can be activated to allow the complete drying of the part blanks 15, without the risk of a temperature gradient due to gelation. Indeed, such drying has no impact on the charge distribution, because the ground was gelled during segment 2, and consequently, the mobility of the macromolecules is zero: the resulting material no longer exhibits a charge distribution gradient.

[0088] During the drying step 205, the part blank(s) 15 may be swept by partially desaturated gas and / or a mixture of saturated and desaturated gas, called clean gas, from the desaturation means 13.

[0089] The drying step 205 may include opening the valve 133, the degree of opening of the valve 133 being, for example, a function of the target clean nitrogen rate.

[0090] During the drying step 205, the temperature can be controlled, for example from the temperature measured by the first temperature sensor 124, for example by the control means 14, for example according to a temperature setpoint.

[0091] The temperature ramp-up substep 2051 may include a temperature ramp, for example, until a third temperature threshold is reached that is higher than the second temperature threshold. The third temperature threshold may be 10 to 40°C higher, for example, 15 to 30°C higher, for example, approximately 20°C higher than the second temperature threshold. The third temperature threshold may be between 95 and 115°C, for example, between 100 and 110°C, for example, approximately 105°C higher.

[0092] The rate of temperature rise, or ramp-up to the third temperature threshold, is determined, for example, based on the capacity of chamber 11 and the number of blanks 15 loaded into chamber 11. The ramp is, for example, between 2 and 25°C / h, or between 5 and 20°C / h. The limited duration of the temperature rise reduces the overall drying cycle time.

[0093] The subsequent temperature holding substep 2053 may include holding the temperature at the third temperature threshold, for example between 1 a.m. and 8 p.m., or for example between 5 a.m. and 3 p.m. The holding time depends on the amount of solvent remaining in the part blanks 15. Cooling stage

[0094] Subsequent to the drying step 205, the drying process may include a cooling step 207.

[0095] During the cooling stage 207, the circulation means 12 can be activated, which increases the cooling efficiency, and for example the heating means 113 of the chamber and / or the heating means 123 of the circulation means, are deactivated, which prevents the insertion of heat. During the cooling stage 207, the desaturation means 13 can be activated, for example with the valve 133 open, condensation reducing the gas temperature. Manufacturing process

[0096] With reference to the figure 3 , a manufacturing process for a part, for example the part, based on carbon / carbon composite material is described.

[0097] The manufacturing process may include a step of supplying and / or obtaining 301 a blank 15 of a part based on carbon / carbon composite material, for example blank 15, impregnated with a sol-gel type solution within a system 1 forming an oven, for example system 1. The step of supplying or obtaining 301 may include positioning the impregnated blanks 15 of a part in a stack in the chamber 11.

[0098] Subsequent to the supply or obtaining step 301, the process may include a drying step 303 of the blank 15, the drying step including the drying process.

[0099] The blank production step 301 may include a preform production substep 3011. The preform production substep 3011 may include the layering of fibrous layers, for example, of carbon precursor fibers, such as pre-oxidized polyacrylonitrile (PAN). The preform production substep 3011 may include bonding the fibrous layers together, for example, by needle punching. The preform production substep 3011 may include, for example, after the bonding of the fibrous layers, a carbonization heat treatment to convert the carbon precursor into carbon.

[0100] The roughing step 301 may include, for example after the realization substep, a densification substep 3012 of the made preform, for example by a matrix, for example by a pyrolytic carbon (PyC) matrix, so as to transform the preform into the rough.

[0101] The densification substep 3012 can be carried out by chemical vapor infiltration (CVI). During the chemical vapor infiltration densification substep 3012, the preform(s) can be placed in a chamber into which a gaseous phase containing one or more carbon precursors, such as methane and / or propane, is introduced. The temperature and pressure within the chamber can be controlled to allow the gaseous phase to diffuse into the preforms and form a solid pyrolytic carbon deposit through the decomposition of the precursor(s). During the densification substep 3012, the preforms can be stacked.

[0102] Alternatively, the densification substep 3012 can be carried out using a liquid process. This substep may include impregnation of the blank with a carbon precursor, for example, a resin. Following impregnation, the densification substep 3012 may include pyrolysis of the precursor. Impregnation and pyrolysis may be repeated successively, one or more times, for example, to form several successive cycles of impregnation and pyrolysis.

[0103] Alternatively, the densification substep 3012 can be carried out by heat treatment. This substep may involve immersing the blank in a carbon precursor bath, for example, toluene. The substep may also include a heating step of the immersed blank, for example, by coupling with an inductor, so that the precursor in contact with the blank diffuses within it to form a PyC deposit by decomposition.

[0104] The roughing step 301 may include a roughing impregnation substep 3011 with a sol-gel type solution, for example implemented within chamber 11. Example

[0105] With reference to the figure 5 An example of the reaction time for a sol-gel solution to reach a given viscosity, for example 850 mPa·s, is described in graphical form. The graph of the figure 5represents the time t required for the soil to gel to reach a viscosity of 850 mPa.s in hours as a function of the reaction temperature T in °C.

[0106] This graph is the result of laboratory tests aimed at defining the heating time, without solvent evaporation, necessary to reach the defined gelation threshold.

[0107] It is therefore possible to define a pair of parameters, time, temperature to be applied in particular during the gelation stage.

[0108] Since the boiling point of the sol-gel type solution presented as an example, comprising a mixture of butanol and ethanol and a zirconium precursor, is greater than 90°C, the temperature of the chosen gas, nitrogen, at the outlet of the heater is fixed at 90°C, in order to avoid boiling within the carbon blank during the implementation of the drying process.

[0109] The time required for the soil in the carbonaceous blank to gel is estimated at 4 hours at a temperature of 80°C. In other words, to obtain a material without a charge distribution gradient, all parts in the industrial equipment must be exposed, for example, to 80°C for 4 hours, with minimal solvent evaporation. Other operating points can be observed on the graph of the figure 5 : (85°C, 2h), (75°C, 6h), (70°C, 11h), (65°C, 22h), always with the lowest possible evaporation rates.

[0110] With reference to the figure 6The evolution of the temperature in °C over time during the drying process is shown. Segment 601 corresponds to the temperature ramp-up stage 201, during which heat is supplied by the first and second heating elements, saturating the nitrogen until a first temperature threshold is reached, for example 75°C, for example at the second temperature sensor 125. Segment 602 corresponds to the gelation stage 203. Segment 603 corresponds to the drying stage 205.

[0111] With reference to figure 7, the impact of the sequenced drying process according to the invention compared to the continuous drying of the prior art is represented in the form of a histogram.

[0112] A ratio R is calculated, R being the ratio between the quantity of charges present on the surface of a blank, over a thickness of 5mm, and the quantity of charges present in the core, also over a thickness of 5 mm.

[0113] Rectangle 701 represents the R-value for the prior art, within the framework of a continuous drying cycle, with a temperature following the first temperature sensor at 75°C, the control valve partially open, and the fan and heater activated. The material then exhibits a gradient in charge distribution. The average R-value of 6 demonstrates that there is a quantity of charge 6 times greater on the friction face than in the core.

[0114] Rectangle 702 represents the R-value for the drying process presented here, within the framework of a sequenced drying cycle. The material does not exhibit a charge distribution gradient: indeed, the average R-value of 0.96 demonstrates that there is the same amount of ceramic precursor charge in the core as on the surface.

[0115] The broken line 703 denotes the target R ratio of 1 with no load gradient.

[0116] The method for obtaining these R-values ​​involves sampling. Samples are taken from composite cylinders measuring 36 mm in diameter and 5 mm in thickness. Nitro gas is used. The impregnation process uses a mixture of ethanol and butanol as a solvent and a zirconium oxide precursor. Three samples are taken from different thicknesses within each zone of the material. a first one 3 mm from the upper rough rubbing face, a second one 3 mm from the lower rough rubbing face, and a third one at the core of the material.

[0117] The method for obtaining these R ratios then involves determining the ratios. The three samples are oxidized at 1000°C for 15 hours to remove the carbonaceous portion composed of the fibrous reinforcement and the pyrocarbon matrix. Following this oxidation phase, the solid residue (commonly called "ash") recovered consists of zirconium fillers completely oxidized in the form of ZrO₂, or zirconia. This quantity of zirconia recovered (a few tens of mg) is then directly related to the quantity of fillers present in the sample.

[0118] The ash content after oxidation is calculated for each test specimen by relating the mass of ash recovered to the initial mass of the test specimen according to the following formula: σ = m cendres / m éprouvette where σ is the center rate, m ash is the mass of ash obtained at the end of the oxidation, and m test specimen is the mass of the test specimen before oxidation.

[0119] The R ratio can then be calculated as the ratio between the ash content of the specimen taken from the core and the ash content of one of the 2 specimens taken from the rubbing face: in fact 2 R ratios can be calculated per triplet of specimen.

Claims

1. A method for drying a blank (15) of a part made of a carbon / carbon composite material impregnated with a sol-gel solution, the solution comprising a solvent and one or more compounds, in a system (10) forming an oven, the system comprising: - a chamber (11) configured to receive the blank, - gas circulation means (12) configured to selectively enable a gas to be circulated between a gas outlet (111) of the chamber and a gas inlet (112) of the chamber, - gas desaturation means (13) being configured to selectively enable at least partial desaturation of the gas in a solvent, the method comprising steps of : - gelling (203) the solution so as to form a gel within the blank disposed in the chamber by heating the chamber, the circulation means and the desaturation means being deactivated, so as to restrict circulation and desaturation of the gas in a solvent, and - drying (205) the gel within the blank by heating, the circulation means and the desaturation means being activated, so as to enable circulation and desaturation of the gas in a solvent.

2. The drying method according to claim 1, comprising, prior to the gelation step, a temperature rise step (201), the circulation means (12) being activated and the desaturation means (13) being deactivated, so as to allow the temperature rise by restricting the desaturation of the gas in a solvent.

3. The drying method according to claim 1 or 2, the chamber (11) comprising dedicated heating means (113), configured to selectively heat the chamber (11), for example independently of the state of the gas circulation means (12), the means (113) for heating the chamber being activated during the gelation (203) and drying (205) steps, and for example activated during the temperature rise step (201), the means (113) for heating the chamber comprising for example a double envelope (1131) of the chamber.

4. The drying method according to any one of the preceding claims, the gas circulation means (12) comprising dedicated heating means (123), configured to selectively heat the gas circulating between the gas outlet (111) and the gas inlet (112), the means (123) for heating the circulation means being deactivated during the gelation step (203) and activated during the drying step (205), and for example activated during the temperature rise step (201).

5. The drying method according to any one of the preceding claims, wherein the drying step (205) comprises a temperature rise sub-step (2051) and a subsequent temperature maintenance sub-step (2053), the drying step being for example followed by a cooling step (207) in which the circulation means (12) are activated, and for example the means (113) for heating the chamber and / or the means (123) for heating the circulation means, are deactivated, and for example the desaturation means (13) are activated.

6. The drying method according to any one of the preceding claims, wherein the gas circulation means (12) comprise a gas circulation circuit (121) extending between the gas outlet (111) and the gas inlet (112), the circulation circuit (121) comprising a fan (122) configured to selectively enable a gas to be circulated between the gas outlet (111) of the chamber and the gas inlet (112) of the chamber, the means (123) for heating the circulation means comprising for example a heater configured to heat the gas circulating within the circulation means, the heater being for example disposed between the fan and the gas inlet.

7. The drying method according to any one of the preceding claims, wherein the gas desaturation means (13) comprise a gas desaturation circuit (134) comprising: - a valve (133) configured to selectively enable the gas to be circulated within the gas desaturation circuit, and - a condenser (136) configured to allow the condensation of the solvent present within the gas circulating within the gas desaturation circuit, and the supply of desaturated gas by the gas desaturation circuit.

8. The drying method according to claims 6 and 7, wherein the gas desaturation circuit (131) is fluidly connected to the chamber (11) via the gas circulation circuit (121), the gas desaturation circuit comprising for example a dedicated inlet (134) and outlet (135), the inlet of the gas desaturation circuit being disposed upstream of the outlet of the gas desaturation circuit at the gas circulation circuit so as to form a bypass, the inlet and the outlet of the gas desaturation circuit being for example disposed upstream of the fan (122) and / or of the heater (123).

9. A method for manufacturing a part made of a carbon / carbon composite material comprising steps of: - supplying or obtaining (301) a blank (15) of a part made of a carbon / carbon composite material impregnated with a sol-gel solution within a system (1) forming an oven, and - drying (303) the blank comprising the drying method according to any one of the preceding claims.