A LAYERED COMPOSITE MATERIAL AND A PROCESS FOR REALISATION THEREOF

Technical Field

The invention relates to a high-resistance layered material, typically for applications in the aeronautics field, and a process for realising the material.

Background Art

As is known, aeronautics constructions comprise components which are usually subjected, during normal use, to high mechanical and heat stress.

Some components must further be able to resist the heat of flames which can break out in cases of fire in the aircraft, such as to remain substantially whole throughout emergency procedures.

The components therefore must be made using high-resistance materials, together with excellent heat-resistance properties.

At the same time, the materials must be very light in order not to make the components too heavy.

An example of this is constituted by an aircraft nacelle, which is generally realised using a laminate material formed by two aluminium sheets, which provide mechanical support, between which a layer of a special foam providing heat insulation and being heat-resistant is laid.

A drawback of this type of material consists in the fact that in order to perform its function correctly, it must normally have a rather high average overall thickness, comprised between about 10cm and 20cm. Therefore, this material is obviously unsuitable for realising small-size structural components, such as for example an air filter box destined to be associated to internal combustion engines in propeller aircraft.

The filter box of the air filter must in fact be small in order to be housed in the engine compartment, and has also to be very heat-resistant, in order not to break in case of fire, which would cause the detachment of fragments that during aspiration can enter the engine body and place it out of operation.

To realise small components, layered composite materials are known which generally comprise a solid matrix based on polymer resin, internally of which one or more reinforcement layers are sunk, for example made of carbon fibre. These composite materials are very light and have high mechanical resistance, but are not sufficiently resistant to heat to be used in the construction of all the critical components of the aircraft. The aim of the present invention is to make available a material having high mechanical and heat resistance, which can be profitably used in the field of aeronautic constructions, with the aim of realising structural components which are very resistant to both mechanical and heat stress, and which at the same time are small and light.

The aim is attained by a layered composite material comprising a bonding matrix based on a polymer resin to which at least two distinct layers, reciprocally superposed, are added, of which one is a reinforcement layer for giving the matrix a high mechanical resistance, and a further one is a protection layer having high heat resistance.

In this way, a material is obtained which is generally rather light thanks to the polymer resin matrix, which also possesses high mechanical resistance and a high heat resistance, thanks respectively to the reinforcement layer and the protection layer.

In particular, with the material of the invention the performance of the materials at present used in the construction of critical components for aircraft is maintained, while the thickness of the material is comprised between 3mm and 5mm.

The material can thus be effectively used for making both large-dimension components, such as aircraft nacelles, and small-dimension components, such as the air filter box. The reinforcement layer is preferably constituted by one or more sheets of carbon fibre, laid one on another.

Each carbon fibre sheet is generally made of a carbon fibre textile, such as the one supplied by TORAYCA with the commercial name of CARBON T700.

The reinforcement layer is preferably constituted by fibres of a substantially refractory material, such as for example silicon fibres or basalt fibres. A silicon fibre textile which is suitable for the present objective is supplied by KLEVERS ITALIA S.p.A. under the commercial name of BLANKET. Other fibre materials which are suitable for realising an efficient protection layer are, for example, pre-ox polyacryl nitrile (PREOX PAN), such as that supplied by TEX-TECH INDUSTRIES Co. under the commercial name of PREOX-PAN; or methyl aramidic fibres such as those manufactured by 3M Aerospace under the commercial name of NEXTEL and NOMEX; or TEFLON fibres such as those marketed by TESTORI S.p.A. under the series name PTFE PRF 750pt.

Obviously each of the above-listed materials possesses slightly different heat-resistance characteristics, but all are equally suitable, either alone or in combination. Disclosure of Invention

In a preferred embodiment of the invention, to the polymer-based bonding matrix is added a third layer having high reflective properties, which is arranged on the surface of the layered material, such as to define a reflective surface which is exposed to the outside. In this way, the reflective surface reflects the heat emitted by radiation from the flames or other luminous heat sources, such as to prevent propagation through the layered material and protect the underlying layers. The reflective layer is preferably constituted by an aluminium-based material. For example, it can be constituted by a slim aluminium sheet, of a type such as the one supplied by 3M under the commercial name of 3M 427; or by a layer of aluminium powder.

Independently of the presence (or not) of the above-mentioned reflective layer, a support layer can be further added to the bonding matrix, which support layer lends greater elasticity. The support layer is preferably obtained with a glass fibre textile, for example a type E fibre with a density of about 300gr/m ² , such as the one marketed by HEXCEL Co., under the commercial name of E-GLASS.

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In a preferred embodiment of the invention, a pile of superposed layers comprising at least a layer of each of the above-described types is joined to the matrix.

In particular, excellent results have been obtained with a layered material comprising: two reinforcement layers separated by a protection layer, a reflective surface layer, and an elastic support layer interposed between the reflective layer and the group of reinforcement layers. One or more further protection layers might be interposed between the reflective surface layer and the reinforcement layers, which further protection layers might be made, for example, using fibres of refractory material (silicon or basalt), pre-ox poly acryl nitrile (PREOX PAN) fibres, methyl aramidic fibres or TEFLON fibres.

It is stressed that all the above-described layers singly have an average thickness comprised between about 0.1 mm and 0.5mm. It is therefore possible to superpose numerous different layers in order to realise a material which is very mechanically and heat resistant, while maintaining the overall thickness of the material comprised between 3mm and 5mm. In a preferred aspect of the invention, the bonding matrix can be realised by a phenolic or epoxy polymer resin, to which catalysing additives can be added, typically with a hardening action.

Generally the quantity in weight of the catalysing additives, if added to the polymer resin, is about one tenth of the weight of the resin itself. The bonding matrix can further comprise a filler substance having self- extinguishing properties, mixed with the polymer resin. The self-extinguishing substance is a substance that when invested by fire has the property of extinguishing the combustion and thus the fire itself. The filler substance can thus be, for example, alumina hydrate, such as the one supplied by MICHELS S.p.A. under the commercial name of CARICA F70. Alumina hydrate is a powder, the particles of which explode on contact with fire, stifling combustion.

The invention also makes available a process for realising the layered composite material.

The process comprises operating stages of: predisposing a pile comprising at least a protection layer having high heat resistance, and at least a fibre reinforcement layer having high mechanical resistance and being impregnated with a fluid polymer resin; compressing the pile; and heating the pile such as to cause polymerisation of the polymer resin.

In this way, the compression action exerted by the press enables diffusion of the fluid polymer resin into the protection layer, such that thanks to the subsequent polymerisation a bonding matrix in obtained which unites all the layers, while keeping the thickness of the finished layered material usefully small.

The fluid polymer resin can also be previously mixed with catalysing additives having a hardening action and/or with a filler substance, of the type mentioned herein above.

In a preferred embodiment of the invention, the process of the invention includes predisposing a pile also comprising a reflective surface layer and/or an elastically-supporting fibre layer, of the type described herein above. According to the invention, the elastic support fibre layer can be previously impregnated with the fluid polymer resin.

In general, in the process of the invention a pile is formed, made of layers of reinforcement, protection, reflection and elastic support, the number, arrangement and material of which are selected such as to obtain any predetermined final structure of the layered material, selected for example from among those described herein above.

In this context, it is always preferable to impregnate only the fibre reinforcement layers and the elastic support layers, if present, with the fluid polymer resin. On compression, the fluid polymer resin spreads into all the other layers, keeping the final thickness of the final layered material small.

In a preferred aspect of the invention, the impregnation of the reinforcement layers, and if present also the elastic support layers, is done by manually spreading the fluid polymer resin using a brush or a spatula.

In this way, it is possible to cover all the fibres constituting the material of the layer substantially uniformly with the fluid resin.

Brief description of the Drawings

Further characteristics and advantages of the invention will better emerge from a reading of the following description, provided by way of non-limiting example, with the help of the figures of the accompanying drawings, in which: figure 1 schematically illustrates, in section, the structure of a layered material of a first embodiment of the invention; figure 2 schematically illustrates, in section, the structure of a layered material according to a second embodiment of the invention; figure 3 schematically illustrates, in section, the structure of a layered material according to a third embodiment of the invention; figures 4 and 5 illustrate two successive stages of the realisation process of a material according to the invention.

Best Mode for Carrying Out the Invention

Figure 1 schematically illustrates the structure of a layered material 1 according to a first embodiment of the invention.

The layered material 1 comprises a synthetic resin bonding matrix 2, which permeates and keeps together a plurality of substantially flat distinct layers, which are reciprocally superposed to form a pile 3.

In particular, the pile 3 comprises two distinct reinforcement layers 30 which give the matrix 2 a high mechanical resistance.

A protection layer 31 having high heat-resistance properties is interposed between the reinforcement layers 30.

The pile 3 further comprises a reflective layer 32 located at an end of the pile

3 itself, such as to define a reflective surface which remains exposed to the outside with the material finished.

A support layer 33 is interposed between the reflective layer 32 and the reinforcement layers 30, which support layer 33 lends the matrix 2 greater elasticity.

In a preferred embodiment of the structure of figure 1 , each of the reinforcement layers 30 is constituted by two slim sheets of carbon fibre.

In more detail, the carbon sheets are of a type marketed by TORAYCA under the name CARBON T700.

The intermediate protection layer 31 is a methyl amidic textile, of a type marketed by 3M Aerospace under the name NEXTEL. The reflective layer 32 and the elastic support layer 33 are realised respectively in aluminium and glass fibre.

In particular, the layers are realised in a single commercial composite material, which is formed by an aluminium layer and a glass fibre layer.

The composite material is selected from among those marketed by Insul.tecno S.r.l. under the commercial name of ALFOIL and ALPES.

The difference between the two materials is that with ALFOIL the layer of aluminium is constituted by a sheet of aluminium, while in the ALPES the sheet is formed by aluminium powders deposited and fixed on the layer of glass fibre. The bonding matrix 2 comprises an epoxy resin, of the type marketed by

AXSON under the name EPOLAM 2500, to which a hardening catalyser is added, of the type marketed by AXON under the name INDURENTE

EPOLAM 2500, the quantity in weight of which is about a tenth of the weight of the resin. With the listed materials a sample plate of about one square metre with a thickness of about 3mm can be obtained, using 2kg of epoxy resin and 20Og of hardening catalyser.

Figure 2 schematically illustrates the structure of a layered material 1 ' in a second embodiment of the invention. The layered material 1 ' is the same as the one illustrated in figure 1 , with the difference that two further layers of heat-resistant protection 34 and 35 are

interposed between the reflective surface layer 32 and the reinforcement layers 30.

In this case too, each further layer is joined to the adjacent layers by the bonding matrix 2. In a preferred embodiment of the structure of figure 2, each of the reinforcement layers 30 is constituted by two slim sheets of carbon in a net- form, of a type marketed by TORAYCA under the name CARBON T700. The intermediate protection layer 31 is a silicon fibre textile, of the type distributed by KLEVER ITALIA S.p.A., under the name of BLANKET. The reflective surface layer 32 and the elastic support layer 33 are realised in a single commercially-available composite material formed by an aluminium layer and a glass fibre layer, of the type marketed by MOMEC SaS, which contains aluminium with a density of 60g/m ² and glass with a density of 300g/m ² . Alternatively the layers 32 and 33 can be made using two distinct commercially-available materials.

In particular, the reflective layer 32 can be realised using an aluminium sheet, of the type marketed by Insul.tecno SrI, under the commercial name of ALUMINIUM FOIL TAPE or of the type marketed by 3M under the name of 3M 427; while the elastic support layer 33 can be realised with a glass fibre textile of type E and with a density of 300g/m ² , of the type marketed by HEXCEL Co. with the name of E-GLASS.

The added protection layer 34 is made of silicon fibre textile, of the type marketed by KLEVER ITALIA S.p.A. under the name of BLANKET. The added protection layer 35 is made of methyl amidic fibre textile, of the type marketed by 3M Aerospace under the name of NEXTEL. The bonding matrix comprises an epoxy resin, of the type distributed by AXSON under the name EPOLAM 2500, to which a hardening catalyser is added, of the type distributed by AXON under the name of INDURENTE EPOLAM 2500, with a quantity in weight of about a tenth of the weight of the resin.

With the materials listed, a sample plate of about one square metre of surface and thickness of about 3mm can be obtained, using 2kg of epoxy resin and 20Og of catalyser.

Figure 3 schematically illustrates the structure of a layered material 1 " in a third embodiment of the invention, which differs from the embodiment of figure 2 only inasmuch as the elastic support layer 33 is interposed between the auxiliary protection layers 34 and 35.

In a first realisation of the structure of figure 3, each of the reinforcement layers 30 is constituted by two slim sheets of net carbon, of the type marketed by TORAYCA under the name CARBONIO T700.

The layer of intermediate protection 31 is a silicon fibre textile sheet, of the type marketed by KLEVER ITALIA SpA under the name BLANKET.

The reflective surface layer 32 is realised using an aluminium sheet, of the type marketed by 3M under the commercial name of 3M 427. The added protection layer 34 is a further sheet of silicon fibre textile, of the type marketed by KLEVER ITALIA SpA under the name BLANKET.

The layer of elastic support 33 is a sheet of glass fibre textile of type E and with a density of 300g/m ² , of the type marketed by HEXCEL Co. with the name of E-GLASS. The added layer of protection 35 is a textile of pre-ox poly acryl nitrile

(PREOX PAN), of the type marketed by TEX TECG INDUSTRIES, under the name of PREOX-PAN.

The bonding matrix comprises a phenolic resin, of the type distributed by

DYNO CHEMICAL under the name of AERODUX 185, to which a hardening catalyser is added, of the type marketed by DYNO CHEMICAL under the name of INDURENTE HRP 150, of which the quantity in weight is about a tenth of the weight of the resin.

The bonding matrix further comprises a self-extinguishing filler substance, which in the present case is ALUMINA HYDRATE, of the type marketed by MICHELS SpA, under the name of CARICA F70, of which the quantity in weight is about half the weight of the synthetic resin used.

With the above-listed materials a sample plate of about 0.65m ² of surface and about 5mm thickness can be obtained, using 30Og of phenolic resin, 3Og of catalyser and 15Og of ALUMINA HYDRATE.

The overall weight of the sample plate is about 241 g, with high resistance properties.

In a second embodiment of the structure of figure 3, each of the reinforcement layers 30 is constituted by two slim sheets of carbon in net form, of the type marketed by TORAYCA under the name of CARBONIO T700. The layer of intermediate protection 31 is a silicon fibre textile sheet, of the type marketed by KLEVER ITALIA SpA under the name BLANKET. The reflective surface layer 32 is realised using an aluminium sheet, of the type marketed by 3M under the commercial name of 3M 427. The added protection layer 34 is a further sheet of silicon fibre textile, of the type marketed by KLEVER ITALIA SpA under the name BLANKET.

The layer of elastic support 33 is a sheet of glass fibre textile of type E and with a density of 300g/m ² , of the type marketed by HEXCEL Co. with the name of E-GLASS. The added layer of protection 35 is a sheet of TEFLON, of the type marketed by TESTORI SpA, under the name of PTFE PRF 750pt.

The bonding matrix comprises an epoxy resin, of the type distributed by BAKELITE AG under the name of BAKELITE EPR 320, to which a hardening catalyser is added, of the type marketed by BAKELITE AG under the name of BAKELITE EPH 960, of which the quantity in weight is about a tenth of the weight of the resin.

The bonding matrix further comprises a self-extinguishing filler substance, which in the present case is ALUMINA HYDRATE, of the type marketed by MICHELS SpA, under the name of CARICA F70, of which the quantity in weight is about half the weight of the synthetic resin used. With the above-listed materials a sample plate of about 0.63m ² of surface and about 3.1 mm thickness can be obtained, using 30Og of epoxy resin, 3Og of catalyser and 15Og of ALUMINA HYDRATE.

The overall weight of the sample plate is about 169g, with high resistance properties.

In a third embodiment of the structure of figure 3, each of the reinforcement layers 30 is constituted by two slim carbon sheets in net form, of the type marketed by TORAYCA under the name of CARBONIO T700.

The layer of intermediate protection 31 is a silicon fibre textile sheet, of the type marketed by KLEVER ITALIA SpA under the name BLANKET. The reflective surface layer 32 is realised using an aluminium sheet, of the type marketed by 3M under the commercial name of 3M 427. The added protection layer 34 is a further sheet of silicon fibre textile, of the type marketed by KLEVER ITALIA SpA under the name BLANKET. The layer of elastic support 33 is a sheet of glass fibre textile of type E and with a density of 300g/m ² , of the type marketed by HEXCEL Co. with the name of E-GLASS. The added protection layer 35 is made of methyl amidic fibre textile, of the type marketed by TESTORI under the name of NOMEX 402 SA. The bonding matrix comprises an epoxy resin, of the type distributed by BAKELITE AG under the name of BAKELITE EPR 320, to which a hardening catalyser is added, of the type marketed by BAKELITE AG under the name of BAKELITE EPH 960, of which the quantity in weight is about a tenth of the weight of the resin.

The bonding matrix further comprises a self-extinguishing filler substance, which in the present case is ALUMINA HYDRATE, of the type marketed by MICHELS SpA, under the name of CARICA F70, of which the quantity in weight is about half the weight of the synthetic resin used.

With the above-listed materials a sample plate of about 0.62m ² of surface and about 3.4mm thickness can be obtained, using 30Og of epoxy resin, 3Og of catalyser and 15Og of ALUMINA HYDRATE. The overall weight of the sample plate is about 142g, with high resistance properties.

In a fourth embodiment of the structure of figure 3, each of the reinforcement layers 30 is constituted by two slim carbon sheets in net form, of the type marketed by TORAYCA under the name of CARBONIO T700. The layer of intermediate protection 31 is a silicon fibre textile sheet, of the type marketed by KLEVER ITALIA SpA under the name BLANKET.

The reflective surface layer 32 is realised using an aluminium sheet, of the type marketed by 3M under the commercial name of 3M 427. The added protection layer 34 is a further sheet of silicon fibre textile, of the type marketed by KLEVER ITALIA SpA under the name BLANKET. The layer of elastic support 33 is a sheet of glass fibre textile of type E and with a density of 300g/m ² , of the type marketed by HEXCEL Co. with the name of E-GLASS.

The added layer of protection 35 is a textile of pre-ox poly acryl nitrile , of the type marketed by TEX TECG INDUSTRIES Co., under the name of PREOX- PAN.

The bonding matrix comprises a phenolic resin, of the type distributed by AXSON under the name of EPOLAM 2500, to which a hardening catalyser is added, of the type marketed by AXON under the name of INDURENTE EPOLAM 2500, of which the quantity in weight is about a tenth of the weight of the resin.

The bonding matrix further comprises a self-extinguishing filler substance, which in the present case is ALUMINA HYDRATE, of the type marketed by MICHELS SpA, under the name of CARICA F70, of which the quantity in weight is about half the weight of the synthetic resin used. With the above-listed materials a sample plate of about 0.9m ² of surface and about 4mm thickness can be obtained, using 30Og of phenolic resin, 3Og of catalyser and 15Og of ALUMINA HYDRATE.

In a fifth embodiment of the structure of figure 3, each of the reinforcement layers 30 is constituted by two slim carbon sheets in net form, of the type marketed by TORAYCA under the name of CARBONIO T700.

The layer of intermediate protection 31 is a silicon fibre textile sheet, of the type marketed by KLEVER ITALIA SpA under the name BLANKET.

The reflective surface layer 32 is realised using an aluminium sheet, of the type marketed by 3M under the commercial name of 3M 427.

The added protection layer 34 is a further sheet of silicon fibre textile, of the type marketed by KLEVER ITALIA SpA under the name BLANKET. The layer of elastic support 33 is a sheet of glass fibre textile of type E and with a density of 300g/m ² , of the type marketed by HEXCEL Co. with the name of E-GLASS.

The added layer of protection 35 is a textile of pre-ox poly acryl nitrile , of the type marketed by TEX INDUSTRIES Co., under the name of PREOX-PAN. The bonding matrix comprises an epoxy resin, of the type distributed by

BAKELITE AG under the name of BAKELITE EPR 320, to which a hardening catalyser is added, of the type marketed by BAKELITE AG under the name of

BAKELITE EPH 960, of which the quantity in weight is about a tenth of the weight of the resin. The bonding matrix further comprises a self-extinguishing filler substance, which in the present case is ALUMINA HYDRATE, of the type marketed by

MICHELS SpA, under the name of CARICA F70, of which the quantity in weight is about half the weight of the synthetic resin used.

With the above-listed materials a sample plate of about 0.64m ² of surface and about 3.2mm thickness can be obtained, using 30Og of phenolic resin,

3Og of catalyser and 15Og of ALUMINA HYDRATE.

The overall weight of the sample plate is about 152g, with high resistance properties.

With reference to the last embodiment, the following is a description of a process for manufacturing the layered composite material of the invention.

The process includes separately preparing the reinforcement layers 30, the protection layers 31 , 34 and 35, the reflective layer 32 and the elastic support layer 33.

Since each layer is constituted by materials which are commercially sourced, the process includes cutting the materials to obtain sheets of predetermined sizes and shapes, selected time-by-time according to requirements.

At this point the carbon fibre sheets which make up the reinforcement sheets

30 are impregnated with a fluid polymer resin destined to realise the bonding matrix 2.

The fluid polymer resin is prepared separately, possibly by mixing with a hardening catalyser and/or a self-extinguishing filler substance.

The impregnation stage is done manually, by spreading the fluid polymer resin on the carbon fibre textiles using a brush or a spatula, such as to coat the fibres evenly.

In a preferred aspect of the invention, the glass fibre sheet constituting the elastic support layer is also impregnated with the fluid polymer resin, using the same technique.

It is stressed that the polymer resin is applied only to the reinforcement layers

30 and possibly to the support layer 33, since the carbon and glass fibres they are made of exhibit better qualities in terms of holding the resin, with respect to the fibres that make up the protection layers 31 , 34, 35 and the material that makes up the reflective layer 32.

Further, in this way a saving can be made in the quantity of polymer resin used, as will be clear from the following.

Once the preliminary stages are completed, the layers are piled on one another in the correct order for structure being realised, with the single condition that the reflective layer 32 is positioned at an end of the pile 3, in order that it can be a surface exposed to the outside.

In this particular example, the layers are superposed in the order required for the structure illustrated in figure 3. With reference to figures 4 and 5, the pile 3 obtained is located internally of the cavity of a matrix 4, which matrix 4 collaborates with an overlying and vertically alternating punch 5 of a press (not shown).

The body of the matrix 4 is crossed by electrical resistances 40 for heating.

Obviously the pile 3 can be prepared externally of the matrix 4 and subsequently located internally thereof, or it can be directly formed internally of the matrix 4.

When the pile 3 is in the matrix 4 cavity, the punch 5 is lowered to compress the layers.

Thanks to this compression, the fluid polymer resin present only in the reinforcement layers 30, and possibly in the support layer 33, are diffused between the fibres of the protection layers 31 , 34, 35 up until they reach the reflective layer 32.

In this way, the polymer resin permeates more or less uniformly through the whole pile 3.

At the same time as the compression is performed, the resistances 40 in the matrix 4 are activated to heat the pile 3 such as to initiate the polymerisation of the polymer resin.

Once the polymerisation is complete, a solidified polymer resin bonding matrix 2 is obtained, to which the layers of the pile 3 are solidly gripped and in which the layers are substantially sunk, realising the finished layered composite material.

Obviously the same process can be applied to any layered structure of a material according to the invention.