Method for infusing a fibre preform

Abstract

The invention relates to a method for infusing a fibre preform with a polycondensation resin, the method comprising at least: A) supplying an intermediate container (13) with a resin at a pressure higher than atmospheric pressure, the supplying operation comprising at least: A1) transferring the resin (20) from the initial container (11) to a heater (12); A2) heating the resin using the heater; and A3) transferring the heated resin (22) to the intermediate container (13); B) infusing the fibre preform (14) with the thus-transferred polycondensation resin by means of suction from the intermediate container which is kept at an infusion temperature higher than or equal to the injection temperature; the intermediate container being supplied at a pressure higher than or equal to 1.5 bar absolute and the fibre preform being infused at a pressure lower than or equal to 0.1 bar absolute.

Description

Description Title of the invention: Method for infusing a fibrous preform Technical Field

[0001] This presentation concerns a process for impregnating fibrous architectures with a phenolic resin for the manufacture of composite material parts. Prior art

[0002] Composite materials are experiencing significant industrial growth.

[0003] These materials are characterized by a fibrous texture, also called fibrous preform, whose porosity is filled with a resin, the resin forming a matrix after cooking.

[0004] Their properties depend not only on the nature of the fibers of the fibrous texture but also on the nature of the bonds between the fibers or even the nature of the matrix.

[0005] The various possible choices thus offer a wide range of possibilities, which makes it possible to obtain materials with properties specially defined for particular applications.

[0006] In particular, for an aeronautical or aerospace application, these materials are often considered as advantageous alternatives to metallic components, because they are lighter than the latter while offering at least identical if not better mechanical properties.

[0007] However, impregnation of the porosity of the fibrous texture sometimes presents an industrial difficulty. Indeed, the properties of composite materials depend on the fibrous preform but also on the matrix it comprises and this is why it is essential that the internal porosity of the fibrous preform is filled with matrix and that this filling is homogeneous throughout the entire fibrous preform.

[0008] An area of ​​the preform that is not impregnated with matrix would not have the same mechanical or thermal properties as the rest of the composite part, which is not desirable.

[0009] Many methods of impregnating fiber preforms have been developed, each adapted to particular matrices or preforms.

[0010] However, none of the prior art methods appear to be suitable for obtaining thick infused parts, with a polycondensation resin matrix, with controlled porosity.

[0011] Polycondensation resins have a very high viscosity at room temperature. Although it is known to heat such resins to reduce their viscosity, this process is not used industrially because it causes, on the one hand, the premature start of the polymerization of the resin and, on the other hand, the volatilization of the solvents contained in the resin. This last point is also triggered when the resin is placed under reduced pressure. In addition to the fact that an uncontrolled temperature can lead to exothermic runaway, the risk of which must be controlled, the volatilization of the solvents contained in the resin can lead to significant variations in porosity in the final part, resulting from variations in the chemorheological properties of the infused resin.

[0012] These effects make the use of polyphenolic resins complex and there remains a need for new manufacturing processes which would be adapted to the constraints set out above to allow their use in the manufacture of a composite material part. Statement of the invention

[0013] The present invention aims precisely to respond to the problems set out above.

[0014] For this purpose, it concerns a process for infusing a fibrous preform with a polycondensation resin comprising at least: A) a supply of an intermediate container with said polycondensation resin during which said resin is injected at a pressure higher than atmospheric pressure into the intermediate container from an initial container, the supply comprising at least: Al) a transfer of the resin from the initial container where the resin is stored at a storage temperature to a heater; A2) heating the resin by the heater to an injection temperature, higher than the storage temperature; and A3) a transfer of the resin thus heated from the heater to the intermediate container at a pressure higher than atmospheric pressure; B) an infusion of the fibrous preform by the polycondensation resin thus transferred carried out by suction from the intermediate container which is maintained at a infusion temperature greater than or equal to the injection temperature; the supply A) of the intermediate container being carried out by imposing on the resin a pressure greater than or equal to 1.5 bar absolute and the infusion B) of the fibrous preform being carried out by imposing on the resin a pressure less than or equal to 0.1 bar absolute.

[0015] On the one hand, such a process ensures that the start of resin polymerization cannot take place before the latter is infused into the preform.

[0016] This is because the polymerization of the resin only begins when the temperature is high enough and is not observed at room temperature.

[0017] The pressure applied for feed A) ensures that the composition of the resin remains the same, and in particular that the volatile species including the solvent do not escape during this stage, which could be observed by applying reduced pressure.

[0018] Polymerization can begin at the earliest when the resin arrives in the intermediate container because room temperature is within the reaction temperature range of the resin.

[0019] In one embodiment, step A) can be carried out at a pressure of between 1.5 bars absolute and 5.0 bars absolute or between 1.5 bars absolute and 3.0 bars absolute.

[0020] The "absolute bar" is understood in the sense that it usually has in the field, namely that it defines a pressure relative to the vacuum whose pressure is taken as a reference and arbitrarily set as equal to 0 bar absolute. On the other hand, this process makes it possible to ensure, through the control of the time / temperature couple, that the resin reaches the intermediate container at a temperature compatible with its injection, that is to say a temperature at which it is sufficiently low in viscosity.

[0021] Thus, it is to the credit of the inventors that they have succeeded in proposing a process in which a polycondensation resin is brought to a temperature satisfactory for its injection, without it beginning to polymerize or to evacuate its volatiles.

[0022] In addition, the process allows a large quantity of phenolic resin to be brought to the infusion temperature without the risk of premature chemical evolution, because it is supplied there and then removed at controlled flow rates to be infused into the fiber preform.

[0023] B) Infusion of the resin into the preform maintained at reduced pressure has two further advantages.

[0024] This reduced pressure facilitates the removal of solvents and other volatile species with which the resin may be formulated, which promotes the polymerization of the resin.

[0025] In addition, the reduced pressure promotes the elimination of water, which is a co-product of the polycondensation of the resin, which shifts the thermodynamic equilibrium of the reaction in favor of polycondensation. This therefore ensures excellent progress of polycondensation. Only the water bound to the cross-linked three-dimensional network will remain in the matrix. Free water is thus extracted.

[0026] In one embodiment, the viscosity of the resin at the storage temperature is greater than or equal to 500 mPa.s or even greater than or equal to 800 mPa.s.

[0027] In one embodiment, the viscosity of the resin is greater than or equal to 500 mPa.s or even greater than or equal to 800 mPa.s in the initial container.

[0028] This viscosity value is in fact sufficient to allow the resin to be transported from the initial container to the overpressure heater, while maintaining the lowest possible resin temperature.

[0029] In one embodiment, the temperature of the resin in the initial container is less than or equal to 40°C, or even at room temperature.

[0030] In one embodiment, the initial container may be at room temperature, which allows for an even simpler process because it does not require any particular packaging system.

[0031] The temperature of the initial container is then sufficient to allow sufficient viscosity for the injection of the resin into the heater, but remains insufficient to initiate its polymerization.

[0032] In one embodiment, the amount of resin contained in the initial container may correspond to all of the resin necessary for filling the interstitial porosity of the fibrous architecture.

[0033] For example, the quantity of resin contained in the initial container may be greater than or equal to 50 kg, or even greater than or equal to 60 kg.

[0034] Preferably, the resin present in the initial container is kept under constant agitation. This allows excellent homogeneity of the resin despite the possibly significant quantity of resin contained in the initial container.

[0035] In one embodiment, the viscosity of the resin at the infusion temperature is less than or equal to 200 mPa.s, or even 150 mPa.s.

[0036] In one embodiment, the viscosity of the resin in the intermediate container is less than or equal to 200 mPa.s, or even 150 mPa.s.

[0037] This viscosity reduced by the rise in temperature then allows excellent infusion of the preform.

[0038] Viscosity in the sense of application is understood as dynamic viscosity and is measured in mPa.s. It characterizes the resistance to flow of a fluid and can be defined as the ratio of the shear stress by the velocity gradient perpendicular to the shear plane.

[0039] For example, it can be measured by a Brookfield brand viscometer according to the NE EN ISO 2555 standard.

[0040] In one embodiment, the infusion temperature is greater than or equal to 70°C, for example between 75°C and 90°C, or even between 75°C and 85°C.

[0041] This temperature ensures a sufficient reduction in the viscosity of the resin on the one hand, and good evacuation of the solvent on the other hand, which allows polymerization.

[0042] In one embodiment, the storage temperature is between 20°C and 45°C, the injection temperature is between 65°C and 90°C, and the infusion temperature is between 75°C and 90°C.

[0043] These values ​​for the process temperatures are optimal to ensure the injection of the resin into the intermediate container, without starting the polymerization and at the same time ensuring an easy infusion.

[0044] Feed A) allows, as indicated, the feeding of an intermediate container with the polycondensation resin, and makes it possible to have a polycondensation resin at a compatible infusion temperature, but whose polymerization has not started.

[0045] Infusion B) then allows the polycondensation resin to be infused into the preform.

[0046] In one embodiment, during infusion B) the feed rate of the intermediate container with the resin coming from the heater is between 90% and 110% of the resin withdrawal rate for the infusion of the fiber preform.

[0047] By choosing such balanced flow rates between the supply of the intermediate container and the infusion of the preform, it is ensured that the intermediate container is neither too full, which could cause the resin to remain in the intermediate container for too long, nor too empty, which could cause unwanted air bubbles to be infused into the preform.

[0048] In one embodiment, the feed rate of the intermediate container by the resin coming from the heater is equal to the withdrawal rate for the infusion of the fibrous preform.

[0049] For example, the intermediate container may contain a quantity of resin less than or equal to 5 kg, or even less than or equal to 4 kg, or better still less than or equal to 3 kg.

[0050] In one embodiment, the feed rate of the intermediate container may comprise a first transient filling regime, before the start of the infusion B).

[0051] The use of the intermediate container ensures throughout the process that only a small quantity of resin is able to polymerize.

[0052] In fact, as described above, the resin cannot begin to polymerize until it reaches the intermediate container.

[0053] Furthermore, since it is taken from the intermediate container to be infused into the fiber preform, it ultimately only resides for a short time in the intermediate container, and the polymerization of the resin is therefore only very slightly advanced there.

[0054] In other words, the resin does not have time to polymerize in the intermediate container, and is taken from there to be infused into the preform, where it will finish its polymerization.

[0055] In one embodiment, the infusion of resin B) into the preform can be carried out at different points of the fiber preform.

[0056] Such an embodiment makes it possible to ensure excellent homogeneity of the infusion rate of the resin into the preform, unlike a process where the infusion would be carried out at a single point.

[0057] Indeed, the infusion of the preform causes a desired bulkiness of the fiber preform by the resin. If the preform is infused by the resin at a single point, the infusion rate decreases with the filling of the preform.

[0058] Conversely, if the infusion takes place at several points in the preform, the resin only has to travel a shorter distance in the preform from the infusion point, which ensures better homogeneity of the infusion.

[0059] In one embodiment, the resin is infused at several points of the preform but the feeding takes place at a given time only at a single point.

[0060] In other words, the resin is first infused through a first feed point, then that feed is cut off when the feed to a second feed point is opened, and so on until the last feed point.

[0061] This embodiment ensures, in addition to excellent homogeneity of the infusion, excellent control of the progress of the infusion of the fiber preform.

[0062] In one embodiment, the resin is chosen from polyfuran or polyphenolic resins and preferably polyphenolic resins.

[0063] For example, such resins can be the commercial products RS101 or RA 101 from Solvay or Furolite from TFC.

[0064] These resins are in fact those for which it is difficult to ensure infusion, because they have too high a viscosity at low temperature and polymerize when heated. Therefore, the methods of the prior art are not sufficient to allow the impregnation of a preform by known methods, unlike the infusion method described above.

[0065] In one embodiment, the resin is formulated with at least 20% by weight of species distinct from the resin, or even with at least 30% by weight of species distinct from the resin.

[0066] The expression "formulated with" is intended to characterize the fact that the storage container may include, in addition to the resin, so-called volatile compounds, for example a solvent and / or other particular additives distinct from the resin.

[0067] In one embodiment, the resin is formulated with at least 20% volatile compounds, or even with at least 30% volatile compounds.

[0068] Such volatile compounds can, for example, be used to reduce the viscosity of the resin and / or chemically block its polymerization during storage.

[0069] The process is all the more advantageous as it allows these volatile compounds to be preserved until the intermediate container, due to the high pressure prevailing in the initial container and in the heater.

[0070] This ensures good preservation of the volatile compounds in the resin, unlike the methods of the prior art, and it is thus possible to block the progress of the polymerization until the arrival of the resin in the intermediate container.

[0071] In one embodiment, the intermediate container and the fibrous preform are placed in the same oven.

[0072] In one embodiment, the fibrous preform may further comprise an infusion jacket and in such a case, the intermediate container, the fibrous preform and its infusion jacket may be placed in the same oven.

[0073] This embodiment ensures that the resin is maintained at the infusion temperature after passing through the heater and arriving in the intermediate container. In addition, it ensures that the resin cannot cool between the intermediate container and injection into the preform.

[0074] In one embodiment, the preform comprises carbon fibers, or is made of carbon fibers.

[0075] For example, the preform may be shaped like an atmospheric reentry element for an aerospace machine.

[0076] Such an atmospheric reentry element may have a first spherical surface and a second spherical surface opposite the first spherical surface.

[0077] For example, the element is conical with rounded ends and apex.

[0078] In one embodiment, in the intermediate container, the resin is heated to a temperature between 75°C and 90°C, or even between 75°C and 85°C. At such a temperature, the resin can begin its polymerization.

[0079] In one embodiment, the smallest dimension of the space occupied by the resin in the intermediate container is less than or equal to 10 cm, or even less than or equal to 5 cm.

[0080] Since the polymerization of the resin is exothermic, exothermic runaway may be observed if the resin is not in conditions that allow it to evacuate the heat produced by its polymerization.

[0081] The inventors found that, in an embodiment where the volume occupied by the resin in the intermediate container comprises two dimensions much greater than the third, limiting the space occupied by the resin in said third dimension was sufficient to prevent exothermic runaway of the polymerization. More specifically, the inventors found that it is the smallest dimension of the volume occupied by the resin which controls to the first order the capacity of a given volume of resin to exchange heat with the container.

[0082] A dimension will be said to be “much superior” to another if it is 3 times, or even 5 times superior.

[0083] This embodiment ensures that it is possible for the resin present in the intermediate container to exchange a controlled quantity of heat with the exterior of the intermediate container.

[0084] This heat exchange advantageously prevents exothermic runaway reaction.

[0085] Indeed, the heat generated by polymerization is either dissipated via thermal exchanges with the outside or it contributes to raising the temperature of the resin. However, when the temperature of the resin increases, the resin polymerizes which releases energy again, thus contributing to exothermic runaway.

[0086] Thermodynamic runaway can lead in the worst case to the degradation of the devices used for the process or to degradation of the preform which would make the entire part unfit for the desired use.

[0087] Thus, it is advantageous, in order to avoid the risk of thermodynamic runaway, to have an intermediate container allowing a sufficient quantity of thermal exchanges when the resin is brought to the infusion temperature.

[0088] It is to the credit of the inventors that they were able to understand and model the evolution of temperature in a given volume of resin in order to be able to define a maximum admissible dimension for the smallest dimension of the volume occupied by the resin, allowing the infusion temperature to control the exothermic runaway of the resin.

[0089] The reaction kinetics, the thermal heat capacity, as well as the polymerization enthalpy are determined by differential scanning calorimetry tests. The kinetic behavior of the resin is then modeled by an autocatalytic kinetic model, then the behavior of the resin in polymerization is simulated and then experimentally validated by comparing the Fournier law established in 1D / 2D and an experimental heating / polymerization test instrumented by themocouple in a thermal enclosure. The thermo-chemo-rheological properties of the resin are translated by a non-dimensional material model.

[0090] They thus succeeded in establishing a law defining the maximum admissible dimension for the smallest dimension of the space occupied by the resin in the intermediate container, making it possible to minimize the risk of exothermic runaway for a given volume of resin at a given temperature and knowing the residence time of the resin in said volume.

[0091] It is the result of this understanding by the inventors of the thermal and kinetic behavior of the polymerization reaction which is translated by "the smallest dimension of the space occupied by the resin in the intermediate container".

[0092] This embodiment makes it possible to limit the risk of exothermic runaway of the resin once it has been infused into the fiber preform, and ensures that the polymerization of the resin can take place without risk of runaway.

[0093] Indeed, as described for the intermediate container, it is the smallest dimension of the space occupied by the preform which determines whether the resin risks exothermic runaway or not.

[0094] In one embodiment, the thickness of the fiber preform is less than or equal to 100 mm, or even less than or equal to 60 mm.

[0095] In one embodiment, the thickness of the fiber preform is greater than or equal to 10 mm, or even greater than or equal to 65 mm, or even greater than or equal to 80 mm.

[0096] The thickness of the preform is understood in the usual sense of the term as the smallest dimension of the preform and the thickness proposed above ensures that the polymerization reaction does not run away.

[0097] The infusion process described above is even more advantageous for preforms of such thickness, because the latter require a greater quantity of resin for impregnation for an identical shape.

[0098] In preforms of such thickness, a larger amount of resin is introduced and infusion of resin into such preforms by prior art methods is not possible because there are risks of the resin thermally running away as described above.

[0099] On the contrary, the process described above allows the infusion of such preforms because the infusion of the preform is much better controlled and only a part of the resin is in a position to be able to polymerize at a given moment of the process.

[0100] In fact, the use of the intermediate container ensures, in addition to the advantages already described, that only a small quantity of resin is able to polymerize at any given moment in the process.

[0101] Furthermore and as described above, in one embodiment, the infusion temperature is greater than or equal to 70°C, for example between 75°C and 85°C.

[0102] This temperature, together with limiting the quantity of resin brought to the infusion temperature, limits the risk of exothermic runaway while having a rheostable resin over the infusion period.

[0103] In addition, the feed rate of the intermediate container on the one hand and the infusion rate of the preform on the other hand can be easily modulated so as to infuse small volumes of resin without the risk of exothermic runaway.

[0104] In one embodiment, the fibrous preform comprises carbon fibers and has a thickness greater than or equal to 10 mm.

[0105] In one embodiment, the infusion B) may comprise a variable infusion rate between infusion phases and rest phases during which no infusion takes place.

[0106] In such an embodiment, the supply A) of the intermediate container may comprise an infusion flow rate of between 90% and 110% of that of the infusion B).

[0107] Alternatively, the feed A) may comprise a constant flow rate, but lower than the flow rate of the infusion phases so that the intermediate container fills during the rest phases and empties during the infusion phases. In addition, the flow rates are adjusted to ensure that the smallest dimension of the space occupied by the resin in the intermediate container is constantly less than 10 cm in the intermediate container. Brief description of the drawings

[0108] [Fig. 1] Figure 1 is a schematic representation of a device for carrying out a method according to one embodiment of the invention. Description of the embodiments

[0109] The invention is now described by means of a figure, presented for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the invention.

[0110] Figure 1 schematically illustrates a device which allows the implementation of a method as described above.

[0111] Figure 1 includes an initial container 11 comprising a large volume of resin 20.

[0112] The resin 20 is then injected into a heater 12 via the channel 21.

[0113] The resin is then injected into the intermediate container 13, via the channel 22.

[0114] It will be noted that the volume of resin 23 in the intermediate container 13 is much less than that 20 in the initial container 11.

[0115] The heater 12 shown here is a water bath heater, in which the resin passes through coils soaking in a thermostatically controlled bath, at the injection temperature.

[0116] Other heater geometries are possible and can improve the energy efficiency of heat transfer.

[0117] In one embodiment, the heater 12 may be a counter-flow heater.

[0118] In such a heater, the resin enters through a conduit 21 at the storage temperature, i.e. the temperature of the initial container 11.

[0119] In the heater, the resin is brought into contact with a heat transfer fluid at a higher temperature than the resin, for example placed around the conduit in which the resin is conveyed.

[0120] Upon contact with the heat transfer fluid, the resin heats up and the heat transfer fluid cools down. The temperature of the heat transfer fluid and the exchange surface are chosen so that the resin leaving the heater is at the injection temperature.

[0121] As described, the resin 20 in the initial container 11, the resin passing through the heater and that exiting the heater 12 is maintained under pressure.

[0122] The resin leaving the heater 12 via the channel 22 reaches the intermediate container 13.

[0123] The resin 23 in the intermediate container 13 is at atmospheric pressure and then begins to polymerize.

[0124] However, the resin 23 in the intermediate container 13 does not remain there long enough to polymerize completely.

[0125] In fact, the resin 23 contained in the intermediate container is infused into the preform 14 via the supply channels 24.

[0126] As shown, in one embodiment, injection may occur at different locations of the preform.

[0127] When infusing the resin 23 into the preform 14, the porosity of the preform is maintained at reduced pressure using a vacuum device 15.

[0128] Such a vacuum device 15 may for example be a pump.

[0129] As described, the resin is infused into the preform at the infusion temperature, greater than or equal to the injection temperature of the resin into the intermediate container 13.

[0130] For this, and as is the case in Figure 1, the fiber preform 14 can be placed in an oven 16.

[0131] In the embodiment shown, the intermediate container 13 is present in the same oven 16 as the preform 14. However, it does not go beyond the scope of the invention if this is not the case, provided that the intermediate container 13 is maintained at the injection temperature.

[0132] The method of the invention as shown also makes it possible to avoid any exothermic runaway of the resin.

[0133] Indeed, thermal runaway cannot take place in the initial container 11, because the storage temperature is low enough to prevent the resin 20 from polymerizing.

[0134] The pressure applied to the resin 20 in the initial container also helps to prevent polymerization, since it prevents the elimination of volatile species formulated with the resin.

[0135] Thermal runaway cannot take place in the intermediate container 23 either, because the resin does not stay there long enough, nor is it present in sufficient quantity.

[0136] Thermal runaway increases with residence time, resin temperature, and stored resin volume.

[0137] Thermal runaway is characterized by a rapid rise in the temperature of the resin, due to its polymerization which is favored by temperature and exothermic.

[0138] Due to the short residence time of the resin 23 in the intermediate container 13, the latter cannot polymerize there.

[0139] However, to further reduce the probability of a thermal runaway event, the inventors studied in detail the thermal behavior of the resin, as a function of its volume and residence time.

[0140] They thus managed to write a general law of temperature evolution.

[0141] Such a law makes it possible to predict the evolution of temperature, and therefore the appearance of thermal runaway, as a function of the given parameters.

[0142] Knowing the operating conditions of the process and in particular, the flow rates of resins entering and leaving the intermediate container 13, the injection and infusion temperatures, they were able to define an upper limit of the minimum dimension of the space occupied by the resin to ensure, among other advantages of the process, that a given volume of resin cannot exhibit exothermic runaway.

[0143] Such a law of thermal evolution of the resin can be written according to the formula [Math 1] proposed below.

[0144] [Math 1]

[0145] In the formula [Math 1]: p is the density of the resin / composite (kg.m -3 ), Cp is the specific heat capacity of the resin / composite (J. kg -1 . K -1 ), À is the conductivity of the resin / composite (Wm^.K' 1 ) AH tot is the total enthalpy of polymerization (J. kg -1 ), V m is the mass fraction of the material, da / dt is the reaction kinetics of the resin (s' 1 ).

[0146] The reaction rate of the resin da / dt can be written according to the formula [Math 2].

[0147] [Math 2]

[0148] In the formula [Math 2]: A, E, n and m are constants specific to the resin studied.

[0149] Table 1 groups together classic orders of magnitude for the applications envisaged.

[0150] [Table 1]

[0151] In the example illustrated by figure 1, the external surface of the container, in intermediate contact 13 is located in the oven 16. This external surface is therefore maintained at the temperature of the oven 16, i.e. the infusion temperature.

[0152] Thus, the temperature of the resin 23 remains stable because the resin having started to polymerize is continuously sucked towards the preform. This container is therefore maintained at the temperature of the oven 16, which will prevent thermal runaway of the resin 23, provided that the smallest dimension of the volume occupied by the resin, in practice the height of the resin in the intermediate container 13, is less than 10 cm, in which case the resin is able to dissipate the excess energy.

[0153] The figure shown is not to scale and is for illustration purposes only.

[0154] In one embodiment, the height of resin in the intermediate container 13 is the smallest dimension of the volume occupied by the resin in the intermediate container 13. In other words, the width and length of the intermediate container, or where appropriate the diameter of the latter, is much greater than the height of resin present in the intermediate container 13.

[0155] It is to the credit of the inventors to have succeeded in characterizing the thermal behavior of the resin and then to identify a maximum quantity of resin in the intermediate container 13 to ensure that the resin does not present, in the intermediate container, a risk of thermal runaway.

[0156] The same reasoning is applicable to the resin entering the internal porosity of the preform 14.

[0157] In fact, the resin introduced into the internal porosity of the preform must polymerize to form the desired part in composite material.

[0158] In doing so, it releases heat, which must be removed by the fiber preform 14 so as to avoid thermal runaway.

[0159] However, it should be noted that since the infusion of the resin is done successively, and the infused resin polymerizes upon arrival in the preform, the resin introduced at the beginning of the infusion can be polymerized before the entire infusion is finished, which already limits the risk of thermal runaway of the polymerization reaction.

[0160] Thus, and although the quantity of resin introduced into the preform 14 may be equal to the initial quantity of resin 20 stored in the initial container 11, the resin introduced into the preform does not cause thermal runaway.

[0161] Figure 1 also shows a graph showing the temperature T, curve 101 to be read on axis 100, and the pressure P, curve 201 to be read on axis 200, which prevail in the different elements of the resin path in one embodiment.

[0162] The temperature T and pressure P are presented schematically, respectively relative to the ambient temperature Tamb and the atmospheric pressure Patm.

[0163] As can be read on the graph and as has just been described, the initial container 11 is at room temperature Tamb, at a pressure higher than atmospheric pressure.

[0164] The resin, still at a pressure higher than atmospheric pressure Patm, is transferred to the intermediate container 13.

[0165] In heater 12, the resin temperature increases to the injection temperature.

[0166] The resin then reaches the intermediate container where it remains at atmospheric pressure before being infused under a pressure lower than atmospheric pressure Patm, into the fiber preform 14.

Claims

Claims

1. Method of infusing a fibrous preform with a polycondensation resin comprising at least: A) a supply of an intermediate container (13) with said polycondensation resin during which said resin (22) is injected at a pressure higher than atmospheric pressure into the intermediate container from an initial container (11), the supply comprising at least: Al) transferring the resin (20) from the initial container (11) where the resin is stored at a storage temperature to a heater (12); A2) heating the resin by the heater to an injection temperature, higher than the storage temperature; and A3) a transfer of the resin thus heated (22) from the heater (12) to the intermediate container (13); B) an infusion of the fibrous preform (14) by the polycondensation resin thus transferred carried out by suction from the intermediate container which is maintained at an infusion temperature greater than or equal to the injection temperature; the supply of the intermediate container being carried out by imposing on the resin a pressure greater than or equal to 1.5 bar absolute and the infusion of the fibrous preform being carried out by imposing on the resin a pressure less than or equal to 0.1 bar absolute.

2. The infusion method of claim 1, wherein the viscosity of the resin (20) at the storage temperature is greater than or equal to 800 mPa.s.

3. The infusion method according to claim 1 or 2, wherein the viscosity of the resin (23) at the infusion temperature is less than or equal to 200 mPa.s.

4. The infusion method according to any one of claims 1 to 3, wherein the storage temperature is between 20°C and 45°C, the injection temperature is between 65°C and 90°C, and the infusion temperature is between 75°C and 90°C.

5. Infusion method according to any one of claims 1 to 4, wherein, during the infusion, the feed rate of the intermediate container (13) by the resin coming from the heater (12) is between 90% and 110% of the withdrawal rate of the resin (24) for the infusion of the fibrous preform.

6. Infusion method according to any one of claims 1 to 5, in which the intermediate container (13) and the fibrous preform (14) are placed in the same oven (16) maintained at the infusion temperature.

7. Infusion method according to any one of claims 1 to 6, in which the resin (20, 23) is chosen from polyphenolic or polyfuranic resins.

8. An infusion method according to any one of claims 1 to 7, wherein the resin (20, 23) is formulated with at least 20% volatile compounds.

9. An infusion method according to any one of claims 1 to 8, wherein the smallest dimension of the space occupied by the resin in the intermediate container (13) is less than or equal to 10 cm.

10. An infusion method according to any one of claims 1 to 9, wherein the fibrous preform (14) comprises carbon fibers and has a thickness greater than or equal to 10 mm.

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