FR2958576A1 - Tool such as open mold for forming composite materials in an organic matrix, comprises a refractory concrete comprising mineral aggregates associated with a hydraulic binder having cement and reinforced with fibers - Google Patents

Abstract

The tool comprises a refractory concrete comprising mineral aggregates (60-99 wt.%) associated with a hydraulic binder having cement (2 wt.%) and reinforced with fibers (0.1-10 vol.%), where 50% of the aggregates are made of silicon carbide (85 wt.%). The cement comprises greater than 50% of alumina. The aggregates have a maximum size of 1-10 mm. The fibers are metal fibers, mineral fibers, polymer fibers and natural fibers, and have a length of 5-100 mm and a diameter of less than 2 mm. The refractory concrete is resistant to temperature of up to 500[deg] C.

Description

The present invention relates to a tool used for the implementation of organic matrix composites by liquid and prepreg processes. The field considered here is the shaping of composite materials which generally have long fibers and an organic matrix. The main processes used for such shaping fall into two categories: liquid processes and dry processes. They are used for the production of large parts generally in the field of aeronautical construction (nacelle, trim part, ...), shipbuilding (composite parts for ships), etc. In a process in a liquid way, the matrix (polymer) is in the liquid state before forming the material. Several processes are concerned here, such as, for example, the VARTM (English Vacuum Assisted Resin Transfer Molding) process or a LRI (Liquid Infusion Resin) process. in French by resin infusion process). In a dry process, the polymer matrix and the fibers are bonded before forming the workpiece and during the implementation of the process, the resin becomes viscous before polymerization or is melted (depending on the type of resin used). These methods include, for example: draping of prepregs, discontinuous or continuous filament removal, stamping and stamping. In these processes, temperatures up to about 450 ° C, rarely up to 500 ° C, are used. The tools, also called molds, implemented are ideally made in a metal called Invar (registered trademark). It is a metal alloy containing a high proportion of nickel (> 36%) and having the particularity of having a very low coefficient of expansion (of the order of 0.5 10-6) below 200 ° C. Since such a metal is on the one hand very expensive and, on the other hand, dense, it is also known to produce tools made of composite materials (with fibers and polymers). Such tools have the disadvantage of being too expensive and have problems of durability. The resin deteriorates during cycles of temperature variation and is also sensitive to external aggressions leading to scratches. In addition, there are problems of recycling such tools. When the temperatures to be reached are limited, it is also known to use steel or aluminum alloy tooling. As indicated, these tools have a limited temperature range of use if it is desired to limit the deformation by expansion and the materials used require, as for the Invar, a manufacturing time, including machining, relatively long. The present invention relates more particularly to processes using open molds. This is for example a VARTM process or most of the dry processes. The object of the present invention is therefore to provide a material for the production of tools used for the shaping of organic matrix composite parts which has a cost price lower than the known materials used while ensuring good thermal conductivity, a low coefficient of expansion to obtain a high stability for the considered temperatures (below 500 ° C). For this purpose, it proposes a tool for shaping organic matrix composite materials, characterized in that it is made of a refractory concrete comprising bound mineral aggregates using a hydraulic binder, at a low cement content and fiber-reinforced, in that the aggregates constitute between 60% and 99% by weight of the concrete composition, in that at least 50% by weight of the aggregates are formed of silicon carbide, and in that that the cement is an aluminous cement mainly containing alumina (> 50%). The fact of making such a tool in a refractory concrete is quite new compared to the prior art of the present invention and it allows in particular to improve the performance of the tool while limiting its cost. Such a tool, thanks in particular to the selected aggregates, also limits the coefficient of thermal expansion. In a preferred embodiment, which makes it possible in particular to obtain good performance for the tool (good thermal conductivity and low coefficient of expansion), the aggregates are preferably composed of 85% by weight of silicon carbide. In a tool according to the present invention, the aggregates used, in addition to silicon carbide, are for example chosen from the group consisting of graphite, bauxite, mullite, andalusite, chamotte, tabular alumina and / or the corundum. Still in order to have good performance of the final tool, it is preferable that the aggregates have a maximum size of between 1 and 10 mm.

The weight content of the cement in a tool according to the present invention, relative to the total weight of the tool, is for example less than 10%, preferably less than 2%. The fibers used for the manufacture of a tool according to the present invention are advantageously chosen from the assembly containing the metal fibers, the mineral fibers, the polymer fibers and the natural fibers. For mechanical reasons, the fibers advantageously have a length of between 5 and 100 mm and a diameter of less than 2 mm. In this way, the fibers make it possible to ensure good cohesion of the refractory concrete without damaging the structure of the latter.

A preferred embodiment of the invention provides that the volume fraction of the fibers in the refractory concrete is between 0.1 and 10%. The present invention is more particularly adapted to the case where the concrete tool according to the invention is an open mold. The present invention also relates to the use of a refractory concrete resistant to temperatures of at least up to 500 ° C., comprising mineral aggregates predominantly comprising silicon carbide, linked by means of a hydraulic binder, to Low content of aluminous and fiber-reinforced cement for the realization of a tool for the shaping of organic matrix composite materials.

The present invention will be better understood from the following description, describing a preferred embodiment and variants. The description below relates to the production of tools for using organic matrix composites by liquid and prepreg methods. In an original way, this tooling is made of refractory concrete with a hydraulic binder reinforced with fibers. The tools discussed here are also commonly called molds. The present invention relates more particularly to open molds, that is to say molds in which the molding material is brought into the mold and comes into contact with the mold on one side.

Several types of refractory concretes can be used here and are described hereinafter. The refractory concretes considered are conventionally made up of aggregates, fines, ultrafine, additives, a cement matrix and porosities.

The aggregates chosen here are oxides, carbides or nitrides in crystallized or amorphous form. They constitute between 60 and 99% of the composition of the refractory concrete used to form the tool. The aggregates may be in particular bauxite, mullite, andalusite, chamotte, tabular alumina, silicon carbide or corundum. The maximum size of the aggregates can vary from 1 to 10 mm. Among these aggregates, the majority is formed of silicon carbide. The refractory concrete used to form the tooling therefore contains at least 30 to 50% silicon carbide (SiC). Preferably, 85% by weight of the aggregates used in the refractory concrete to produce a tool according to the present invention is formed of silicon carbide.

The connection of the constituents in the concrete is of the hydraulic type and is ensured by the hydration of an aluminous cement added to the concrete, this cement belonging to the CaO-Al2O3-SiO2 ternary system. It is called refractory because it has a high alumina content (Al2O3). The alumina content is preferably greater than 65%. A type of cement that can be used here is sold under the trade name Secar 71. The concretes considered for the present invention have either a low cement content (from 2 to 10%) or an ultra low cement content (less than 2% ). The additives, or additives, present in the refractory concrete may be solvents, binders, plasticisers, accelerators or retarders of setting, air entrainers, water reducers, .... These chemical additives are used for controlling and modifying the properties of the cement, in particular for improving the rheological behavior of refractory concrete during the mixing and casting steps that are used to produce the tooling. As an illustrative and non-limiting example, an additive marketed under the trademark Darvan 7 can be used here. Polymeric fibers can also be added to the concrete to facilitate the evacuation of the various forms of water contained in the material during drying and baking steps of the tooling. Refractory concretes with a low cement content, possibly reinforced with fibers, used for producing a tool according to the present invention may be prestressed or reinforced by continuous elements. A refractory concrete used for producing a tool according to the present invention withstands temperatures up to about 800 ° C without breaking up and remaining stable. Generally, in the processes used for the shaping of organic matrix composite materials, the temperatures reached are less than 450 ° C. If the heat is provided by the mold (tooling), it should be expected that it can withstand temperatures a little higher than those at the heart of the shaped material.

The shaping tool according to the invention is reinforced with fibers to be introduced into the refractory concrete with hydraulic binder. These fibers are preferably metal fibers but other types of fibers can be used here. When metal fibers are used, these are, for example, fibers made of steel, titanium, aluminum, superalloy or nickel alloy, or a mixture of such fibers. These fibers can be shaped by plastic deformation (hot or cold drawing, folding, ...) or by solidification (molding, liquid extraction). Their shape can be straight, straight with hook, flat or in the form of a gutter. Any other form may also be suitable. The more complex their shape, the greater the contribution of fibers to the performance of reinforced refractory concrete. The length of the fibers can range from 5 mm to 100 mm. Their diameter preferably does not exceed 2 mm so as to prevent the fibers from damaging the refractory concrete too much at the time of the cooking thereof. In some particular cases, microfibers less than 5 mm in length may also be envisaged. It can also be envisaged to use, in addition to or in replacement of metal fibers, mineral fibers which are, for example, glass fibers R and / or AR glass fibers and / or carbon fibers and or high alumina fibers and / or silicon carbide fibers and / or basalt fibers, etc. Similarly, polymeric fibers which may be, for example, polyethylene fibers, polypropylene fibers, Acrylic or polyamides, aramid fibers, polyester, polyvinyl alcohol (PVA) can enter the composition of refractory concrete in addition to or instead of fibers mentioned above. It is also possible to use, instead of or in addition to the aforementioned fibers, natural fibers such as for example wood fibers and / or coconut and / or jute and / or linen. The volume fraction of fibers to be added is between 0.1% and 10%. Hybrid reinforcements, combining different types of fibers, can also be used. Preferably, the volume fraction of fibers to be added is between 0.2% and 3%. The refractory concrete used to produce a tool according to the present invention can be castable and vibrable, self-placing or projectable. A refractory concrete shaped by vibration is preferable for obtaining surface states compatible with the methods of using organic matrix composites. To reduce the porosity rate of the refractory concrete, centrifugation or pressing processes may be used. The steps of implementing a reinforced refractory concrete to manufacture a tool according to the present invention are for example the following. A dry mixture with the constituents of the refractory concrete is premixed. If the concrete is reinforced with mineral or polymeric fibers these latter are incorporated in the dry mix and are kneaded with it. Then, a quantity of water corresponding to the grade of refractory concrete used is added to the dry mixture. Once the mixture is homogeneous, the metal fibers are added. Everything is still mixed a few moments. Finally, the mixture is poured into a formwork in which is the imprint of the counterform of the tool to be obtained. Depending on the type of concrete, the whole can be vibrated, centrifuged or pressed.

Metal inserts may be deposited in the formwork if the tooling needs to have vents, handling points or mooring points to a structure. These inserts can be removed during setting or as an integral part of the final tooling. The tooling may also contain a thermal regulation system.

Thus a coolant circulation circuit and / or heating resistors can be integrated into the tooling. This equipment can be placed in the formwork before, during or after pouring the reinforced concrete. After drying, the reinforced refractory concrete is baked at a temperature at least equal, and preferably greater than, the temperature of use of the tooling. The geometry of the tooling must take into account the shrinkage associated with the firing of the reinforced refractory concrete as well as the dimensional variations of the part used.

As can be seen from the foregoing description, an application contemplated by the present invention is the production of tools for the manufacture or repair of parts made of organic matrix composite materials. These materials consist of a polymer matrix and are reinforced with fibers. The pieces can be monolithic. It may also be parts having a sandwich structure, that is to say contain a honeycomb core or foam between two walls. These materials may for example be used in structural or engine elements, propeller blades, equipment and interior fittings in aeronautical and / or space construction. Such elements are then for example used for the manufacture of any type of aircraft: transport of passengers or cargo, combat, training, business, tourism, aerobatics, etc. and also for the manufacture of gliders, aerostats, helicopters, Ultra Light Motorized, launchers and satellites. They can also be used in land and sea transport, defense and sports equipment. The materials used for producing these elements can be varied and different polymer matrices can be used, for example: thermosetting polymers: phenolics, epoxides, unsaturated polyester, thermosetting polymers, polybismaleimide (BMI), ester-cyanate, silicones, etc., thermoplastic polymers: polypropylene, saturated polyester, polyarylenesulfones (PSU, PES, PAS), phenylene polysulfides (PPS), polyaryletherketones (PAEK, PEEK, PEKK), polyetherimide, polyamideimides, thermoplastic polyimides, etc. The matrices these various materials may contain additives and fillers to improve their properties of use or implementation. They can also combine different polymers in the form of mixtures, alloys or copolymers.

These dies are most often reinforced with long or short fibers. Different families of fibers can be used, for example glass, aramid, carbon, basalt, boron, silicon carbide, natural fibers (for example hemp, flax or jute) or metal fibers. (eg copper or steel). These fibers can be randomly distributed, oriented, woven or knitted, .... Reinforcements other than fibers can also (but not necessarily) be integrated into the part implemented such as metal sheets. The part used can also contain inserts directly deposited in the mold before or during the implementation of the latter. The refractory concrete tools with low fiber-reinforced cement content according to the present invention can be used for various methods of using organic matrix composites. These processes can be classified into two categories: - liquid processes: the polymer matrix is in the liquid state before forming the workpiece. Among these methods there are for example: the VARTM (English Vacuum Assisted Resin Transfer Molding process being translated into French by vacuum resin transfer molding) or the LRI (English Liquid Infusion Resin) process resulting in French by resin infusion process), the SCRIMP (Seeman Composite Resin Infusion Molding Process and also known as the vacuum infusion molding method), the RRIM reaction injection molding (of the English Reinforced-Reaction Injection Molding and resulting for example by injection-injection molding), contact molding, projection molding. - Dry processes: the polymer matrix and the fibers are bonded before forming the workpiece and during the process the resin becomes viscous before polymerization (thermosetting polymers) or is melted (thermoplastic polymers). Among these methods there is for example: draping prepregs (autoclave or under canvas), discontinuous or continuous filamentary depositing, stamping, stamping. Tools made of refractory concrete with a low content of fiber-reinforced cement are a good alternative to the metal and composite tools usually used for the implementation of organic matrix composite materials. The refractory concretes considered have a low coefficient of thermal expansion thanks to the high content of silicon carbide. Moreover, this coefficient is isotropic and it does not change with temperature.

The thermal properties of the refractory concretes considered can be adapted by modifying their compositions. Thus, different aggregates, fines and fibers can be used to modify the thermal conductivity, heat capacity and thermal diffusivity of refractory concrete. The concrete used, and therefore the tooling, can be adapted to the shaping process to which the tooling is intended. The refractory concretes described above can have a temperature of use much higher than the temperatures usually used for shaping organic matrix composite materials and are resistant to cyclic temperature variations. Thus, the durability of the refractory concrete tools according to the present invention is better than that of tools made of existing organic matrix composite materials. The addition of fibers improves the resistance of concrete to thermomechanical stresses. It limits the priming and especially the catastrophic propagation of cracks in the core of the tooling. It also improves the mechanical properties of refractory concrete. Indeed, the fibers make it possible to bridge a crack or cracks and to delay their propagation. Thus, the lifetime of the refractory concrete is increased because the tool can continue to work despite the presence of cracks. This is essential in an industrial environment. The tooling can not undergo a break that could be dangerous. It is particularly original and innovative here to use a refractory concrete with low fiber-reinforced cement content to produce tools for using organic matrix composites. Indeed, the use of such a material for this particular application has many advantages over the materials used in the prior art. Compared with the use of steels and aluminum-based alloys for producing tools for shaping composite materials with an organic matrix, a concrete tool has the particular advantage of having a lower coefficient of expansion. thermal, which allows it to be used over a larger temperature range. Tooling according to the present invention is also less time consuming to manufacture. Finally, the cost of the raw material used and the means to implement the tooling is less with the invention.

Compared to tools made in alloys with a high nickel content of the type marketed under the Invar brand, a tool according to the present invention has a higher thermal diffusivity. In addition, as for aluminum alloys or steel, the present invention makes it possible to shorten the manufacturing time of the tool and to limit, even more than for steel and aluminum, the price of the materials. first used and means to implement for the manufacture of tools. It is also known to use tools themselves made in organic matrix composite materials. Compared with these tools, the present invention makes it possible to obtain tooling having a higher thermal diffusivity, greater durability, better dimensional stability, lower raw material costs and better recyclability. Concrete tooling according to the present invention also has a higher surface hardness than composite tooling. As a result, a tool according to the invention has a better scratch resistance. This is compared with each type of tool known from the prior art of very important advantages because they allow on the one hand to have a better quality tool and on the other hand, without sacrificing quality, to limit the cost of tooling in a very sensitive way.

The use of hydraulically bonded refractory concrete for the production of the tool according to the invention also makes it possible to reduce the density of the tooling relative to the use of metal alloys. Of course, the present invention is not limited to the embodiments described above by way of non-limiting examples. It also relates to all the variants within the scope of those skilled in the art within the scope of the claims below.

Claims (10)

REVENDICATIONS1. Tool for shaping organic matrix composite materials, characterized in that it is made of a refractory concrete comprising bound mineral aggregates using a hydraulic binder, low in cement and reinforced with fibers, in that the aggregates comprise between 60% and 99% by weight of the concrete composition, in that at least 50% by weight of the aggregates are formed of silicon carbide, and in that the cement is an aluminous cement containing mostly alumina (> 50%). 2. Tool according to claim 1, characterized in that the aggregates are composed of 85% by weight of silicon carbide. 3. Tool according to one of claims 1 or 2, characterized in that in addition to the silicon carbide, the aggregates used are selected from the group consisting of graphite, bauxite, mullite, andalusite, chamotte, tabular alumina and / or corundum. 4. Tool according to one of claims 1 to 3, characterized in that the aggregates have a maximum size of between 1 and 10 mm. 5. Tool according to one of claims 1 to 4, characterized in that the weight content of the cement, relative to the total weight of the tool, is less than 10%, preferably less than 2%. 6. Tool according to one of claims 1 to 5, characterized in that the fibers are selected from the assembly containing the metal fibers, mineral fibers, polymeric fibers and natural fibers. 7. Tool according to one of claims 1 to 6, characterized in that the fibers have a length of between 5 and 100 mm and a diameter of less than 2 mm. 8. Tool according to one of claims 1 to 7, characterized in that the volume fraction of the fibers in the refractory concrete is between 0.1 and 10%. 30 9. Tool according to one of claims 1 to 8, characterized in that it is an open mold. 10. Use of a refractory concrete resistant to temperatures up to 500 ° C, comprising mineral aggregates mainly comprising silicon carbide, linked by means of a hydraulic binder, low in gravity and reinforced with fibers for producing a tool for shaping organic matrix composite materials.