Infusion process for a fibrous preform
The process addresses the challenge of impregnating fibrous preforms with polycondensation resins by controlling pressure and temperature, ensuring homogeneous infusion and preventing premature polymerization, resulting in consistent composite material properties.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- ARIANEGRP SAS
- Filing Date
- 2023-06-07
- Publication Date
- 2026-06-12
AI Technical Summary
Existing methods fail to effectively impregnate fibrous preforms with polycondensation resins, particularly for thick parts, due to high viscosity and risk of premature polymerization or solvent volatilization, leading to inconsistent porosity and mechanical properties.
A process involving controlled pressure and temperature management, including resin transfer at elevated pressure, heating to injection temperature, and infusion at reduced pressure, ensures homogeneous impregnation without premature polymerization, using an intermediate container to maintain resin integrity and control viscosity.
Ensures consistent resin infusion with controlled porosity and mechanical properties, preventing exothermic runaway and solvent loss, allowing for high-quality composite material production.
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Abstract
Description
Title of the invention: Process for infusing a fibrous preform technical field
[0001] The present exposition relates to a process of impregnating fibrous architectures with a phenolic resin for the manufacture of parts in composite material. Previous technique
[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 by 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 on the nature of the matrix.
[0005] The various possible choices thus offer a very wide range of possibilities, which makes it possible to obtain materials with properties specifically defined for particular applications.
[0006] In particular, for an aeronautical or aerospace application, these materials are often considered advantageous alternatives to metallic components, because they are lighter than the latter while offering at least the same, if not better, mechanical properties.
[0007] However, impregnating 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 be filled with matrix and that this filling be homogeneous throughout the entire fibrous preform.
[0008] An area of the preform that is not impregnated by matrix would not have the same mechanical or thermal properties as the rest of the part made of composite material, which is not desirable.
[0009] Numerous methods of impregnating fibrous preforms have been developed, each adapted to particular matrices or preforms.
[0010] However, none of the prior art methods seem suitable for obtaining thick infused parts with a polycondensation resin matrix with controlled porosity.
[0011] Polycondensation resins exhibit 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 leads, on the one hand, to the premature onset of resin polymerization and, on the other hand, The volatilization of solvents contained in the resin. This last point is also triggered when the resin is placed under reduced pressure. Besides the fact that an uncontrolled temperature can lead to exothermic runaway, the risk of which must be strictly controlled, the volatilization of 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 that would be adapted to the constraints set out above to allow their use in the manufacture of a part in composite material. Description of the invention
[0013] The present invention aims precisely to address the problems outlined above.
[0014] For this purpose, it relates to a process of infusing a fibrous preform with a resin of polycondensation comprising at least: A) feeding an intermediate container with said polycondensation resin during which said resin is injected at a pressure greater than atmospheric pressure into the intermediate container from an initial container, the feeding comprising at least: A1) 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 greater than atmospheric pressure; B) an infusion of the fibrous preform by the polycondensation resin thus transferred, carried out by aspiration from the intermediate container which is maintained at an infusion temperature greater than or equal to the injection temperature; the feeding 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 the polymerization of the resin cannot take place before the infusion of the latter into the preform.
[0016] Indeed, the polymerization of the resin only begins when the temperature is sufficiently high and is not observed at room temperature.
[0017] The pressure applied for supply A) ensures that the composition of the resin remains identical, and in particular that the volatile species, including the solvent, do not escape from it. not during this step, which could be observed by applying reduced pressure.
[0018] Polymerization can begin as early as the arrival of the resin in the intermediate container because the ambient temperature belongs to the reaction temperature range of the resin.
[0019] In one embodiment, step A) can be carried out at a pressure between 1.5 absolute bars and 5.0 absolute bars or between 1.5 absolute bars and 3.0 absolute bars.
[0020] The term "absolute bar" is understood in its usual sense in the field, namely that it defines a pressure relative to a vacuum, the reference pressure of which is arbitrarily set at 0 absolute bar. Furthermore, this process ensures, through control of the time / temperature relationship, that the resin reaches the intermediate container at a temperature compatible with its injection, that is, 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 makes it possible to bring a large quantity of phenolic resin to the infusion temperature without risk of premature chemical evolution, because it is brought there and then taken away at controlled rates to be infused into the fibrous preform.
[0023] Infusion B) of the resin in 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] Furthermore, the reduced pressure promotes the removal of water, which is a co-product of the resin's polycondensation, thereby shifting the thermodynamic equilibrium of the reaction in favor of polycondensation. This ensures excellent progress of the polycondensation. Only the water bound to the three-dimensional cross-linked network will remain in the matrix. The 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 indeed sufficient to allow the resin to be conveyed from the initial container to the heater by overpressure, while maintaining the resin temperature as low as possible.
[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 can be at room temperature, which allows for a further simplified process as it does not require any special conditioning 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 quantity of resin contained in the initial container may correspond to the entirety of the resin required to fill 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 in the initial container is kept under constant agitation. This ensures excellent homogeneity of the resin despite the potentially large 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 rnPa.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 reduced viscosity due to the rise in temperature then allows for excellent infusion of the preform.
[0038] Viscosity in the sense of the 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 to the velocity gradient perpendicular to the shear plane.
[0039] For example, it can be measured by a Brookfield brand viscometer according to the NF 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 decrease 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 polymerization and ensuring at the same time an facilitated infusion.
[0044] The power supply A) allows, as indicated, the supplying of an inter-container intermediate with the polycondensation resin, and allows to have a polycondensation resin at temperature compatible with infusion, 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 by the resin from the heater is between 90% and 110% of the resin withdrawal rate for the infusion of the fibrous preform.
[0047] By choosing such balanced flow rates between feeding the intermediate container and infusing 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 with the resin 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, preferably less than or equal to 3 kg-
[0050] In one embodiment, the feed flow rate of the intermediate container may include 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 amount of resin is in a position to polymerize.
[0052] Indeed, as described above, the resin cannot begin to polymerize until it has reached the intermediate container.
[0053] Furthermore, since it is taken from the intermediate container to be infused into the fibrous preform, it ultimately resides only 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 it to be infused into the preform, where it will complete its polymerization.
[0055] In one embodiment, the infusion of resin B) into the preform can be carried out at different points of the fibrous preform.
[0056] Such an embodiment makes it possible to ensure excellent homogeneity of the rate of infusion of the resin in 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 enlargement of the The preform is fibrous and infused with resin. If the preform is infused with resin at a single point, the infusion rate decreases as the preform is filled.
[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 point of infusion, 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 instant only at a single point.
[0060] In other words, the resin is first infused by a first supply point, then this supply is cut off when the supply of a second supply point is opened, and so on until the last supply point.
[0061] This embodiment ensures, in addition to excellent homogeneity of the infusion, excellent control of the progress of the infusion of the fibrous preform.
[0062] In one embodiment, the resin is chosen from polyfuranic or polyphenolic resins and preferably polyphenolic.
[0063] For example, such resins may be the commercial products RS 101 or RA 101 from the company Solvay or Furolite from the company TFC.
[0064] These resins are indeed those for which it is difficult to ensure infusion, because they exhibit too high a viscosity at low temperatures and polymerize when heated. Therefore, prior art processes are insufficient to allow the impregnation of a preform by known methods, unlike the infusion process described above.
[0065] In one embodiment, the resin is formulated with at least 20% by mass of distinct resin species, or even with at least 30% by mass of distinct resin species.
[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 decrease 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 kept until the intermediate container, due to the high pressure prevailing in the initial container and in the heater.
[0070] This ensures good preservation of volatile compounds in the resin, unlike prior art processes, and it is thus possible to block the progress of polymerization until the resin reaches 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 include an infusion casing and in such a case, the intermediate container, the fibrous preform and its infusion casing 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. Furthermore, it ensures that the resin cannot cool down between the intermediate container and injection into the preform.
[0074] In one embodiment, the preform includes carbon fibers, or is even made of carbon fibers.
[0075] For example, the preform may have the shape of 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 to 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, an exothermic runaway may be observed if the resin is not in conditions which allow it to dissipate the heat produced by its polymerization.
[0081] The inventors have found that, in an embodiment where the volume occupied by the resin in the intermediate container comprises two dimensions much larger than the third, limiting the space occupied by the resin in said third dimension is sufficient to prevent exothermic runaway of the polymerization. More specifically, the inventors have found that it is the smallest dimension of the volume occupied by the resin that controls, to a first approximation, the capacity of a given volume of resin to exchange heat with the container.
[0082] A dimension will be said to be "much greater" than another if it is 3 times, or even 5 times greater.
[0083] This embodiment ensures that it is possible for the resin present in the intermediate container to exchange a controlled amount of heat with the outside of the intermediate container.
[0084] This heat exchange advantageously prevents an exo- runaway thermal reaction.
[0085] Indeed, the heat generated by polymerization is either dissipated through heat exchange with the surroundings or it contributes to raising the temperature of the resin. However, when the resin temperature increases, the resin polymerizes, which again releases energy, thus contributing to exothermic runaway.
[0086] In the worst case, thermodynamic runaway can lead to the degradation of the equipment used for the process or to a degradation of the preform, which would render the entire part unfit for its intended use.
[0087] Thus, it is advantageous, in order not to risk thermodynamic runaway, to have an intermediate container allowing a sufficient amount of heat exchange when the resin is brought to the infusion temperature.
[0088] It is to the credit of the inventors that they have succeeded in understanding and modeling the evolution of the temperature in a given volume of resin in order to be able to define a maximum permissible 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, heat capacity, and enthalpy of polymerization are determined by differential calorimetry tests. The kinetic behavior of the resin is then modeled by an autocatalytic kinetic model, and the polymerization behavior of the resin is simulated and then experimentally validated by comparing the Fournier law established in 1D / 2D with an experimental heating / polymerization test instrumented by thermocouples in a thermal chamber. The thermo-chemorheological properties of the resin are then represented by a dimensionless material model.
[0090] They have thus succeeded in establishing a law defining the maximum permissible dimension for the smallest dimension of the space occupied by the resin in the intermediate container allowing 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 fibrous 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 that determines whether the resin risks an exothermic runaway or not.
[0094] In one embodiment, the thickness of the fibrous 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 fibrous preform is greater than or equal to 10 mm, or greater than or equal to 65 mm, or greater than or equal to 80 mm.
[0096] The thickness of the preform is understood in the usual sense of this 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 quantity of resin is introduced and the infusion of resin into such preforms by prior art processes is not possible because there is a risk that the resin will thermally run 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 any given time in the process.
[0100] Indeed, the use of the intermediate container ensures, in addition to the advantages already described, that only a small amount of resin is in a position to polymerize at any given moment of the process.
[0101] In addition, 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 amount of resin brought to the infusion temperature, makes it possible to limit the risk of exothermic runaway while having a rheostable resin over the duration of the infusion.
[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 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 include a variable infusion rate between infusion phases and rest phases during which no infusion takes place.
[0106] In such an embodiment, the feeding A) of the intermediate container may include an infusion rate 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 It fills during resting phases and empties during infusion phases. Furthermore, 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 cm². Brief description of the drawings
[0108] [Fig.1] Fig.1 is a schematic representation of a device for carrying out a process according to an embodiment of the invention. Description of the implementation methods
[0109] The invention is now described by means of a figure, presented for descriptive purposes to illustrate certain embodiments of the invention and which shall not be construed as limiting the invention.
[0110] Fig. 1 schematically illustrates a device which enables the implementation of a process as described above.
[0111] The [Fig.1] includes an initial container 11 comprising a significant 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 conceivable and allow for improved energy efficiency of heat transfer.
[0117] In one embodiment, the heater 12 can be a counter-current 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 arranged 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 area are chosen so that the resin exiting 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 are kept under pressure.
[0122] The resin exiting the heater 12 through the channel 22 reaches the inter- container median 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] Indeed, the resin 23 contained in the intermediate container is infused into the preform 14 via the feed channels 24.
[0126] As shown, in one embodiment, the injection can take place at different locations in the preform.
[0127] During the infusion of the resin 23 into the preform 14, the porosity of the preform is maintained at reduced pressure by means of a vacuum device 15.
[0128] Such a vacuum device 15 can, for example, be a pump.
[0129] As described, the resin is infused into the preform at the infusion temperature, which is greater than or equal to the injection temperature of the resin into the intermediate container 13.
[0130] For this purpose, and as is the case in [Fig.1], the fibrous 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, we do not depart from 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 process of the invention as represented 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 remain there long enough or for long enough, nor is it present in sufficient quantity.
[0136] Thermal runaway increases with residence time, resin temperature, and the volume of resin stored.
[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 have thus succeeded in writing a general law of temperature evolution.
[0141] Such a law makes it possible to predict the evolution of the temperature, and therefore the appearance of a 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.l] dï ... ttsï v dt ' ' '
[0145] In formula [Math 1]: p is the density of the resin / composite (kg.m 4, Cp is the specific heat capacity of the resin / composite (J.kg *.K '), X is the conductivity of the resin / composite (Wm *.K ') AHtot is the total enthalpy of polymerization (J.kg '), Vm is the mass fraction of the material, da / dt is the reaction kinetics of the resin (s1).
[0146] The reaction rate of the resin da / dt can be written according to the formula [Math 2].
[0147] [Math.2] bed ' ' Ju '
[0148] In formula [Math 2]: A, E, n and m are constants specific to the resin studied.
[0149] Table 1 groups together typical orders of magnitude for the applications envisaged.
[0150] [Tables 1] Material P (kg. c» p.kgôKh âHA (Ug'9 A (s'3 E n I m | Resin lû 10- 10® 104 1 J 1 । Composite W5 w5 ..............1.............. I
[0151] In the example illustrated by [Fig.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 begun to polymerize, is continuously drawn 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 present for illustrative 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 applicable the diameter thereof, is much greater than the height of resin present in the intermediate container 13.
[0155] It is to the credit of the inventors that they succeeded in characterizing the thermal behavior of the resin and then in identifying a maximum quantity of resin in the intermediate container 13 to ensure that the resin does not present, in the intermediate container, any risk of thermal runaway.
[0156] The same reasoning is applicable to the resin entering the internal porosity of the preform 14.
[0157] Indeed, 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 evacuated by the fibrous preform 14 in order to avoid thermal runaway.
[0159] However, it should be noted that since the resin infusion is carried out successively, and the infused resin polymerizes as soon as it enters 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. risation.
[0160] Thus, 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] Fig. 1 also includes 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] Temperature T and pressure P are presented schematically, respectively with respect to ambient temperature Tamb and atmospheric pressure Patm.
[0163] As can be seen from the graph and as has just been described, the initial container 11 is at room temperature Tamb, at a pressure greater than atmospheric pressure.
[0164] The resin, still at a pressure greater than atmospheric pressure Patm, is transferred to the intermediate container 13.
[0165] In the heater 12, the resin's temperature increases, up 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 fibrous preform 14.
Claims
Demands
1. A process for infusing a fibrous preform with a polycondensation resin comprising at least: A) feeding an intermediate container (13) with said polycondensation resin during which said resin (22) is injected at a pressure greater than atmospheric pressure into the intermediate container from an initial container (11), the feeding comprising at least: A1) a transfer of 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, greater 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 aspiration 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. Infusion process according to claim 1, wherein the viscosity of the resin (20) at the storage temperature is greater than or equal to 800 mPa.s.
3. Infusion process 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. Infusion process 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. An infusion method according to any one of claims 1 to 4, wherein, during infusion, the feed rate of the intermediate container (13) with resin from the heater (12) is between 90% and 110% of the resin withdrawal rate (24) for the infusion of the fibrous preform.
6. Infusion method according to any one of claims 1 to 5, wherein the intermediate container (13) and the fibrous preform (14) are placed in the same oven (16) maintained at the infusion temperature.
7. Infusion process according to any one of claims 1 to 6, wherein the resin (20, 23) is selected from polyphenolic or polyfuranic resins.
8. Infusion process according to any one of claims 1 to 7, wherein the resin (20, 23) is formulated with at least 20% volatile compounds.
9. 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. Infusion process 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.