Frost protection mat, assembly comprising such a mat and a method for manufacturing such a mat

Abstract

The invention relates to an anti-icing mat (1) for an aircraft part (P), the mat (1) comprising: at least one contact layer (10) for application to a surface (S) of said part (P), an encapsulation layer (15), and a resistive structure (20) interposed between the contact layer (10) and the encapsulation layer (15), the resistive structure (20) having at least one heating layer (22) capable of generating a heat flux through the surface (S), made of a material comprising a nonwoven of carbon nanotubes impregnated with an epoxy resin, the heating layer (22) being in the form of a pattern comprising a plurality of resistive segments (23) electrically insulated from each other by the encapsulation layer (15). Figure for the abstract: Fig. 4

Description

Title of the invention: Frost protection mat, assembly comprising such a mat and a method for manufacturing such a mat Technical field of the invention

[0001] The present invention relates to a frost protection mat, an assembly comprising such a mat and a method for manufacturing such a mat. Technical background

[0002] An aircraft turbomachine generally extends along a longitudinal axis. It comprises a gas generator which typically includes, from upstream to downstream in the direction of gas flow in the turbomachine, a low-pressure compressor, a high-pressure compressor, a gas combustion chamber, a high-pressure turbine and a low-pressure turbine.

[0003] The rotor of the low-pressure compressor is typically connected to the rotor of the low-pressure turbine via a low-pressure shaft. The rotor of the high-pressure compressor, on the other hand, is connected to the rotor of the high-pressure turbine via a high-pressure shaft.

[0004] The turbomachine further comprises a fan located upstream of the gas generator. The fan comprises a rotor driven in rotation about its longitudinal axis by a fan shaft. The fan further comprises blades extending radially from a disk.

[0005] Among blowers, there are enclosed blowers and unenclosed blowers, also known by the English expression "open rotor". Unlike enclosed blowers, the blades of unenclosed blowers are not surrounded by a blower housing.

[0006] Turbomachines, whether with a shrouded fan or an unshrouded fan, are subject to risks of ice or frost formation.

[0007] Ice accretion or frost formation on the rotor blades of fan-driven turbomachines, particularly unshod ones, affects their operability, their ability to absorb vibrations, and has potential mechanical consequences for the turbomachine. The loss of operability typically results from a degradation of the aerodynamic properties of the impacted surface, the potential ingestion of ice or frost by the turbomachine, or the blocking of the blade pitches. The difficulty the turbomachine has in absorbing vibrations generally stems from the added weight generated by the presence of ice imbalances. These not only unbalance the turbomachine but also represent a real risk because they are likely to damage to the internal components of the turbomachine by penetrating it. Besides the rotor blades, other aircraft parts are likely to be impacted by ice accretion or frost formation, such as wing leading edges and engine air intakes.

[0008] To limit the risk of frost or ice formation, it has been proposed to equip aircraft parts with anti-icing or de-icing devices. An anti-icing device prevents the formation of frost or ice, while a de-icing device cyclically detaches the ice or frost from the part. The de-icing device therefore does not prevent the formation of frost or ice but allows the removal of frost or ice after it has formed.

[0009] There are many solutions for limiting the risk of frost or ice formation on aircraft parts, particularly aircraft rotor blades. These solutions are based on the use of: - Heating elements: Heating elements are electrical components capable of generating heat by resisting the flow of an electric current. The most commonly used heating elements are made from metal sheets, for example stainless steel, formed by chemical etching. There are also heating elements based on carbon nanotubes, conductive fibers (for example carbon fibers), coated or uncoated, inductive heating elements, etc. The geometry and arrangement of heating elements vary depending on the geometry of the aircraft part that needs to be protected from frost or ice. - Mechanical or electromechanical means: According to a technique known in the prior art, a shape-memory material deforms under the action of heat generated by a heating element, thus enabling mechanical defrosting. The shape-memory material is protected by a deformable superplastic coating, which allows the aerodynamic profile of the surface of the part to be protected from frost to be maintained. According to another technique known in the prior art, the piezoelectric properties of a material are used to achieve defrosting. The piezoelectric properties of the material allow it to deform, thus enabling mechanical defrosting. - a fluid: some solutions use a flow of hot air from the engine, water flow and / or evaporation, or a de-icing fluid such as ethylene glycol or propylene glycol. These de-icing fluids pose a risk to the environment. Solutions based on drawing hot air from the engine are becoming less common. used because they cause a decrease in engine efficiency, and therefore a reduction in performance. - Pneumatic: Generally, anti-icing devices use flexible pneumatic coatings placed on the surface to be protected from frost. The pneumatic coating deforms periodically thanks to a fluid supply, which allows it to crack any ice or frost that may have accumulated on its surface. - Coatings and materials: Coatings and materials can prevent the formation of frost or limit the adhesion of ice by the nature of the material used in these coatings and materials. - System architecture: for example, by modifying the electrical contacts used between the stator and the rotor. The use of bearing-type electrical contacts prevents mechanical load-bearing capacity and therefore the accumulation of ice or frost. - Acoustic means in combination with inductive heating means: this is a hybrid technology using inductive heating and acoustic pressure.

[0010] Among these technologies, anti-icing protection using heating elements remains the most widespread currently because, in addition to being effective, it has a limited environmental impact compared, for example, to de-icing liquids. Furthermore, it allows for better use of the aircraft's electrical power by utilizing the aircraft's electrical resources more evenly between the different phases of flight, which is not possible, for example, with certain coatings and materials such as copper, which use up to 50% of the available electrical power during landing and / or takeoff.

[0011] Heating elements are electrical components capable of generating heat by resistance to the flow of an electric current, i.e., by Joule heating, particularly used in frost protection mats. Frost protection mats are heating mats intended to be placed on the surface of the part to be protected from frost or to be integrated into the part to be protected from frost.

[0012] In this regard, and as illustrated in [Fig. 3], frost protection mats 1' according to the prior art generally comprise at least one heating layer 20' incorporating the heating element. The heating layer 20' is encapsulated between an encapsulation layer 15' and a contact layer 10' intended to be affixed to the surface of the part to be protected from frost. It enables the defrosting and anti-icing of the surface on which the frost protection mat 1 is affixed or integrated. by the Joule effect, thanks to the circulation of electric current through the heating element. Thus, frost protection mats are also called thermoelectric defrosters.

[0013] In the prior art, frost protection mats have been proposed comprising an electrically conductive heating layer with a resistive heating element based on a carbon nanotube nonwoven fabric. The resistance value is adjusted either by the surface mass of the nonwoven fabric or by the geometry of the carbon nanotubes, particularly their diameter and length. It is therefore necessary to modify the thickness of the carbon nanotube nonwoven fabric and / or the number of heating layers to adapt the resistance value and thus the heat generated. Depending on the required resistance, the design of the aerodynamic profile of the surface on which or in which the heating layer is to be integrated must be completely redesigned. Adapting the resistance is therefore particularly demanding.

[0014] Furthermore, in solutions proposed by the prior art, heating elements are manufactured by chemical etching of metal strips. The elements obtained by this technology do not easily conform to shapes with small radii of curvature, i.e., shapes with radii of curvature less than 1 cm. Moreover, these heating elements are not suitable for parts with non-developable three-dimensional shapes. A three-dimensional shape is said to be "non-developable" when its curvature is complex, i.e., when it exhibits curvature in both directions. This is typically the case for the leading edges of blades and the leading edges of laminar flow airfoils.

[0015] The present invention proposes a solution to at least some of the problems mentioned above. Summary of the invention

[0016] The invention provides a protective mat against frost for an aircraft part, the mat comprising:

[0017] - at least one contact layer intended to be affixed to a surface of said piece,

[0018] - at least one encapsulation layer, and

[0019] - a resistive structure interposed between the contact layer and the layer encapsulation,

[0020] the resistive structure comprising at least one heating layer, capable of generating a heat flux through the surface, made of a material comprising a nonwoven of carbon nanotubes impregnated with an epoxy resin, the heating layer presenting in the form of a pattern comprising a plurality of resistive segments electrically isolated from each other by the encapsulation layer.

[0021] The invention thus provides a frost protection mat that conforms to three-dimensional shapes with a small radius of curvature and / or non-developable forms. Indeed, the heating layer is in the form of a pattern comprising a plurality of resistive segments electrically insulated from each other by the encapsulation layer. The segmentation of the heating layer allows the frost protection mat according to the invention to conform more closely to surfaces with shapes having a small radius of curvature and / or non-developable forms compared to frost protection mats of the prior art. In fact, the dimensions and shape of the resistive segments can be easily adapted to allow for precise adjustment of the frost protection mat to the surface S. Furthermore, this allows for precise control of the heating power density required to defrost or prevent frost formation on the surface of the part.The frost protection mat therefore allows for variable heating power densities.

[0022] According to various features of the invention which may be taken together or separately: - the resistive segments are rectangular parallelepiped in shape, - the resistive segments are in the shape of a square parallelepiped, - the resistive segments are hexagonal in shape, - The resistive segments are curved in shape, - the resistive segments are electrically connected in parallel and / or in series, - each segment has a width of at least 5 mm, preferably at least 20 mm, - The encapsulation layer is made of an elastomer, a thermoplastic film, a thermosetting resin, or a composite material; - The encapsulation layer is a polychloroprene-based elastomer. - the encapsulation layer is a thermoplastic film made of a material chosen from polyamideimide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone (PESU), polyphenylene sulfide (PPS), ponyphenylsulfone (PPSU), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyaryletherketone (PAEK), - the encapsulation layer is made of a thermosetting resin, for example epoxy, - the encapsulation layer is made of a composite based on glass and epoxy resin, - the heating layer has a thickness less than or equal to 200 micrometers, - the resistive structure has a thickness less than or equal to 100 micrometers, - The frost protection mat also includes means for electrically connecting the resistive segments to each other, - the electrical connection means consist of interconnection bars with a thickness between 25 µm and 100 µm, - the protective mat includes a layer for fixing the heating layer to the means of electrical connection to an aircraft network, the fixing layer being made of a conductive resin comprising a metallic filler, - the carbon nanotube nonwoven fabric is impregnated with epoxy resin with an impregnation rate of between 40% and 95% by mass, preferably between 55% and 95% by mass, and even more preferably substantially equal to 85% by mass, - The conductive resin of the fixing layer is an epoxy-based, polychloroprene-based, polyurethane-based, phenolic-based, or acrylic-based resin. - the metallic filler is chosen from a silver filler, a carbon nanotube filler, a copper, aluminum, nickel, or platinum filler, - the frost protection mat includes a reinforcement layer comprising two layers of polychloroprene, and optionally a layer of glass fabric interposed between the two layers of polychloroprene, the electrically conductive heating layer being surmounted by the reinforcement layer.

[0023] The invention also relates to an assembly comprising at least one aircraft part having a surface to be defrosted or protected from frost, said surface being covered with a protective mat against frost as previously described.

[0024] The invention further relates to a method for manufacturing a carpet as previously described, the manufacturing method comprising the following steps:

[0025] (110) provide a tool having the shape of a surface of the part to be defrosted or to protect from frost,

[0026] (120) apply a contact layer to the tooling,

[0027] (130) to produce a resistive structure comprising at least one heating layer electrically conductive, the heating layer is capable of generating a heat flow through the surface, made of a material containing a nonwoven of nanotubes carbons impregnated with an epoxy resin, the heating layer being in the form of a pattern comprising a plurality of segments,

[0028] (140) to place at least one encapsulation layer on the resistive structure so as to to isolate the segments coelectrically from each other,

[0029] (150) perform a co-firing of the contact layer, the resistive structure and the encapsulation layer. Brief description of the figures

[0030] Other objects, features and advantages of the invention will become more apparent in the following description, made with reference to the accompanying figures, in which:

[0031] - Fig. 1 illustrates a turbomachine and an anti-icing mat according to the prior art, the carpet being installed on the propellers of the turbomachine,

[0032] - [Fig. 2a] is a schematic half-view in axial cross-section of a turbomachine for an aircraft,

[0033] - [Fig. 2b] is a schematic axial cross-sectional view of the turbomachine of the [Fig. 2a] and its suspension pylon to an aircraft, and illustrates a configuration of the suspension components,

[0034] - Figure 3 illustrates a thermal protection mat according to the prior art,

[0035] - [Fig.4] is an exploded schematic view of a frost protection mat according to one embodiment of the present invention,

[0036] - [Fig. 5] is a schematic view of a heating layer and the means of electrical connection of the different segments of the heating layer,

[0037] - Figure 6 schematically illustrates the different stages of a process of manufacturing a protective mat against frost according to an embodiment of the invention,

[0038] - [Fig. 7] illustrates a prototype of a protective mat against frost according to the invention, the protective mat being equipped with temperature probes,

[0039] - [Fig. 8] is an X-ray of a prototype thermal protection mat according to one embodiment of the invention,

[0040] - Figure [Fig. 9a] illustrates a heating layer according to one variant,

[0041] - [Fig.9b] illustrates a heating layer according to another variant. Detailed description of the invention

[0042] Figures 1 and 2 illustrate an example of an aircraft turbomachine 200. The turbomachine 200 is, for example, a turbofan engine.

[0043] As is more precisely illustrated in Figures 2a and 2b, the turbomachine 200 extends along a longitudinal axis X. A gas flow F flows into the turbomachine 200.

[0044] For the purposes of the present invention, the terms "upstream" and "downstream" are understood relative to the direction of flow of the gas flow F in the turbomachine 200 along the longitudinal axis X.

[0045] The terms "radial", "radially", "longitudinally", "axial", "axially", are understood with respect to the longitudinal axis X of the turbomachine 200.

[0046] The terms "internal", "internally", "externally", "externally", are understood in relation to the distance of the longitudinal axis X along a radial axis to the longitudinal axis X.

[0047] As shown in [Fig. 2a], the turbomachine 200 then comprises a secondary propeller 230 driven in rotation by a shaft of the gas generator 212. This propeller 230 is located in the flow channel VI of the primary flow Fl and upstream of a second annular nozzle 232 separating an annular flow channel Vil of an internal flow FIL

[0048] The internal flow Fl 1 feeds a compressor 214.

[0049] Fig. 2a shows that the gas generator 212 comprises two annular compartments Cl, C2 which extend around the X axis.

[0050] The first annular compartment Cl is called the hot compartment because it is relatively close to the flow line VI1 and therefore more exposed to the heat generated by compression, by the combustion chamber 216, and by the combustion gases. This hot compartment Cl extends axially between the second nozzle 232 and a first nozzle 234 for ejecting the flow Fl1 from the turbine(s). This hot compartment Cl is further delimited radially by first and second annular walls 236 and 238, respectively internal and external, which extend coaxially around each other. The first wall 236 externally defines the flow line VI1 of the internal flow FIL

[0051] The second annular compartment C2 is called the cold compartment because it is less exposed to heat. This cold compartment C2 extends axially between the first nozzle 222 and a second nozzle 240 for ejecting the second external flow F12. This cold compartment C2 is further delimited radially by third and fourth annular walls 242, 244, respectively internal and external, which extend coaxially around each other. The fourth wall 244 internally defines the flow channel V2 of the secondary flow F2.

[0052] Many components of the turbomachine 200 are installed in the large hot compartment Cl. The cold compartment C2 is relatively small and reserved for equipment that cannot withstand the temperatures of the hot compartment Cl, particularly electronic equipment.

[0053] Figure 2b shows a possible configuration for the suspension of the turbomachine 200 of Figure 2a. The upstream 248 and downstream 250 suspension members are located at the cold compartment C2. The downstream 250 suspension members are connected to the intermediate casing 254, and the thrust connecting rods 256 extend from the gas generator 212 to a mounting point on the pylon 228, which is located well downstream of the suspension members 248 and 250.

[0054] Certain parts P of the turbomachine 200, such as the disc 5 or the blades 6, 7, are particularly susceptible to the risk of frost or ice formation due to the flow of cold air sweeping over them. This risk of frost or ice formation also exists for wing leading edges, engine air intake leading edges, and aircraft tail assemblies.

[0055] At this stage, it can undoubtedly be specified that ice is distinguished from frost in that it is formed by accretion, i.e., by accumulation, on a surface S of the part P concerned, whereas frost is ice formed by the freezing of fine supercooled droplets. As seen in the introduction to this description, the accretion of ice or the formation of frost on the rotor blades of fan-driven turbomachines leads to a loss of operability, which typically results from a degradation of the aerodynamic properties of the impacted surface, the potential ingestion of ice or frost by the turbomachine, or the blocking of the blade pitches. In addition, the formation of frost or ice can create an imbalance and destabilize the turbomachine 200. Also, the frost or ice formed on these parts P can enter the gas generator and cause serious damage.

[0056] In order to prevent the formation of ice or frost and / or to defrost, i.e., to remove the ice or frost that has formed, a frost protection mat 1, 1' is affixed to or integrated into certain parts P, such as the disc 5 or the blades 6, 7. The frost protection mat 1 may be affixed to an external or internal surface S of the part P to be protected from frost or integrated into a body of the part P. In the latter case, if the part P is made of a composite structure, the frost protection mat 1 is arranged in a sandwich between two layers of fibers of the composite structure. Even more preferably, the frost protection mat 1, 1' is located between a first layer of fibers adjacent to the surface S swept by the cold airflow and a second layer of fibers adjacent to the first layer of fibers.For example, the 1.1" frost protection mat can be affixed to an external rear face of a flow separator on an unshrouded blower.

[0057] With reference to [Fig. 4], the invention relates to an anti-icing mat for a part P of an aircraft, for example the disc 5 or the blades 6, 7 as described above. In this description, "anti-icing protection" refers to preventing frost or ice from forming (anti-icing). and / or to defrost a surface S on which frost or ice has already formed (defrosting).

[0058] The frost protection mat 1 typically comprises at least one contact layer 10 intended to be applied to the surface S of the part to be protected from frost, an encapsulation layer 15, and a resistive structure 20 interposed between the contact layer 10 and the encapsulation layer.

[0059] The contact layer 10 supports the resistive structure 20 and provides electrical insulation. Furthermore, the frost protection mat 1 is affixed to the internal or external surface of part P via the contact layer 10, i.e., in configurations where the frost protection mat 1 is not integrated into the body of part P. The contact layer 10 thus protects part P from direct contact with the resistive structure 20, which, as will be seen later, is likely to generate heat.

[0060] The contact layer 10 can be an elastomeric layer made of polychloroprene (CR). Polychloroprene, also called neoprene, has excellent mechanical strength. The contact layer 10 can be made of any other material having good or even excellent mechanical strength. Other elastomers also have satisfactory mechanical properties. This is the case, for example, with natural rubber, ethylene acrylic rubber (EA), styrene-butadiene rubber (SBR), elastomeric polyurethane (PU), etc.

[0061] The contact layer 10 can also be made of a material other than an elastomer. The contact layer 10 can be a thermoplastic film made of a material selected from polyamideimide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone (PESU), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyaryletherketone (PAEK), and polyimide (PI). These materials also provide protection of the structure from the external environment as well as electrical insulation.

[0062] The frost protection mat 1 may comprise one or more contact layers 10. Preferably, the number of contact layers 10 is no more than three in order to limit the thickness of the frost protection mat 1 and avoid altering the aerodynamic profile of the surface S. In the embodiment illustrated in [Fig. 4], the frost protection mat 1 comprises two contact layers 10. This provides a good compromise between good mechanical strength and a limited size of the frost protection mat 1.

[0063] The encapsulation layer 15 protects the resistive structure 20 from the external environment, thus protecting it from weathering. Furthermore, layer 15 The encapsulation also serves to provide electrical insulation. We will return to this point later.

[0064] When the frost protection mat 1 is intended to be affixed to the internal or external surface S of the part P, the encapsulation layer 15 is located on the opposite side of the frost protection mat 1 from the side bearing against the surface S of the part P that is to be protected from frost. Indeed, it is the contact layer 10 that bears against this surface S. The encapsulation layer 15 is located on the side of the cold airflow that is likely to generate frost or ice. When the frost protection mat 1 is intended to be integrated into the body of the part P, the encapsulation layer 15 is located on the side of the surface S to be protected from frost, while the contact layer 10 is oriented towards the internal structure of the part P. This embodiment is illustrated in [Fig. 4], the boxed "S" representing the surface to be protected from frost.

[0065] The encapsulation layer 15 can be made of an elastomer-based material, a thermoplastic film, a thermosetting resin, or a composite. In a preferred embodiment, the encapsulation layer is made of a polychloroprene-based elastomer, which enables it to protect the resistive structure from the external environment, in particular protection against erosion (sandblasting, rain) and electrical insulation. The encapsulation layer 15 can advantageously be thermally conductive.

[0066] The encapsulation layer 15 can also be made of a material other than an elastomer. The encapsulation layer 15 can be a thermoplastic film made of a material selected from polyamideimide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone (PESU), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyaryletherketone (PAEK), and polyimide (PI). These materials also provide protection of the resistive structure from the external environment as well as electrical insulation.

[0067] Alternatively, the encapsulation layer 15 can be made of a thermosetting resin, for example an epoxy resin, or of a composite based on glass and epoxy resin. These materials make it possible to reduce the weight of the encapsulation layer 15 while maintaining adequate protection against the external environment and ensuring electrical insulation.

[0068] It is advantageous for the encapsulation layer 15 and the contact layer 10 to be made of the same material. Indeed, this promotes good adhesion between the contact layer 10 and the encapsulation layer 15 during the co-baking process carried out during the manufacture of the frost protection mat 1.

[0069] The frost protection mat 1, like the contact layer 10, may comprise one or more encapsulation layers 15. The number of encapsulation layers 15 is preferably no more than three in order to limit the thickness of the frost protection mat 1 and avoid altering the aerodynamic profile of the surface S, when the encapsulation layer(s) 15 are made of elastomer. In the embodiment illustrated in [Fig. 4], the frost protection mat 1 comprises two contact layers 10. This provides a good compromise between good mechanical strength and a limited size of the frost protection mat 1.

[0070] As previously stated, the resistive structure 20 is interposed between the contact layer 10 and the encapsulation layer 15. The resistive structure 20 is the core of the frost protection mat 1 according to the invention and represents its active part.

[0071] The resistive structure 20 comprises at least one heating layer 22 capable of generating a heat flux through the surface S to be protected from frost. In this respect, the heating layer 22 is advantageously a resistive layer configured to perform heating by Joule effect. In other words, the heating layer 22 is capable of generating heat by resisting the flow of an electric current. Put another way, the heating layer 22 functions like a heating resistor.

[0072] In the context of the invention, the heating layer 22 is made of a material comprising a nonwoven fabric of carbon nanotubes (CNTs) impregnated with an epoxy resin. The carbon nanotube fabric generates heat through the Joule effect. It is itself a very good thermal conductor. The nanotubes have an elongated tubular shape. They are advantageously randomly oriented. The impregnation with the epoxy resin is intended to allow the heating layer 22 to adhere to the contact layer 10 without the addition of adhesives. This reduces the number of industrial operations required. Furthermore, it protects manufacturing operators from the chemical risks associated with adhesives. Indeed, these adhesives are often solvent-based and generate volatile organic compounds (VOCs).

[0073] In this regard, it is preferable that the non-woven NTCs be impregnated with epoxy resin with an impregnation rate of between 40% and 95% by mass.

[0074] An impregnation rate of the non-woven fabric of NTCs of at least 40% by mass of epoxy resin makes it possible to fill in sufficient quantity the volumes left free between the NTCs of the non-woven fabric so that chemical bonds can be created at the interface between the heating layer 22 and, respectively, the contact layer 10 and / or the encapsulation layer 15 during the curing under temperature and pressure of the frost protection mat 1.

[0075] The impregnation rate of the non-woven fabric with NTCs is preferably no more than 95% by mass of epoxy resin in order to avoid the creation of an electrically thick layer An insulating layer of epoxy resin is provided at the interface between the heating layer 22 and the electrical connection means 30, which will be described later. A "thick layer" is defined as an electrically insulating layer of epoxy resin that extends sufficiently beyond the heating layer 22 to prevent electrical conduction between the heating layer 22 and the electrical connection means 30. Indeed, the formation of such an electrically insulating layer would generate significant contact resistance, leading to unwanted local overheating. Therefore, when the impregnation rate of the nonwoven fabric with epoxy resin is at most 95% by mass, the electrically insulating layer of epoxy resin is either very thin or nonexistent.

[0076] Advantageously, the impregnation rate of the non-woven NTCs with epoxy resin is between 55% and 95% by mass. An impregnation rate of at least 55% by mass of epoxy resin in the non-woven NTCs further improves the adhesion of the heating layer 22 to, respectively, the contact layer 10 and / or the encapsulation layer 15. Particularly advantageously, the impregnation rate of the non-woven NTCs with epoxy resin is 85% by mass of epoxy resin, which makes it possible to obtain a compromise between low contact resistance at the interface between the heating layer 22 and the electrical connection means 30, and satisfactory adhesion of the heating layer 22 to, respectively, the contact layer 10 and / or the encapsulation layer 15. For such a rate of impregnation, the measured adhesion is equal to 1.9 daN / cm.

[0077] According to the invention, the heating layer 22 is in the form of a pattern comprising a plurality of resistive segments 23 electrically insulated from each other by the encapsulation layer 15. The word "segment" is understood in the conventional sense of the term and designates a well-defined part of the heating layer, distinct from the other parts, i.e., the other segments. The heating layer 22 is therefore in the form of a plurality of resistive segments 23 arranged to form a pattern. Incidentally, each resistive segment thus forms an independent heating element. In practice, the pattern extends in a plane orthogonal to the stacking axis Z of the frost protection mat 1. More precisely, the pattern extends along a longitudinal axis X and / or a transverse axis Y of the frost protection mat 1.

[0078] The frost protection mat 1 according to the invention is thus configured to conform to three-dimensional shapes with a small radius of curvature and / or non-developable shapes. A "small radius of curvature" is defined as a radius of curvature less than 1 cm. A three-dimensional shape is said to be "non-developable" when its curvature is complex, that is, when it exhibits curvature in both directions.

[0079] The segmentation of the heating layer 22, i.e., the fact that the heating layer 22 is segmented into several segments 23, allows the frost protection mat 1 according to the invention to better conform to surfaces having small radii of curvature and / or non-developable shapes compared to frost protection mats of the prior art. Indeed, the dimensions and shape of the resistive segments 23 can be easily adapted to allow for precise adjustment of the frost protection mat 1 to the surface S. Thus, the invention makes it possible to cover more than 70% of the surface S of a part by possibly juxtaposing several frost protection mats 1, which allows for a homogeneously heated surface S.

[0080] Furthermore, since the surface power can be adjusted by varying the dimensions of the segments, it is possible to precisely adjust the dimensions of the segments according to the desired heating power density to defrost or prevent the formation of frost on the surface S of the part P. The heating power densities of the frost protection mat 1 can therefore be modified.

[0081] Furthermore, electrically insulating the resistive segments 23 prevents a loss of heating power and thus prevents subsequent defrosting or anti-icing. The frost protection mat 1 according to the invention therefore provides optimal heating power to the surface S.

[0082] According to a preferred embodiment illustrated in [Fig. 5], the resistive segments 23 are rectangular in shape. In other words, the resistive segments 23 are in the form of strips whose width-to-length ratio can be precisely adjusted at a constant thickness to adapt the heating power. Indeed, the heating power developed by a resistive segment 23 is given by:

[0083] p= with R = ps X (1)

[0084] Where U is the voltage applied across the terminals of segment 23 (in Volts), R is the electrical resistance of segment 23 (in Ohm), ps is the surface resistivity of the NTCs woven fabric (1 Ohm / square), Lo is the length of the resistive segment 23 (in mm), La is the width of the resistive segment 23 (in mm).

[0085] The surface power Ps developed by the resistive segment 23 (W / cm2) is therefore:

[0086] „ _ P _ U2 _ U2 _ U2 , Lo x La ~ LoxLaxR ~ LoxLax psx^ ~ psxLo2

[0087] Thus, when the resistive segments 23 are rectangular parallelepiped in shape, the surface power Ps developed can therefore be adjusted by varying the width of the resistive segments 23. This allows the surface power to be varied as needed. Developed simply by modulating the width of the 23 resistive segments on the surface S to be protected from frost. In this respect, the nonwoven NTCs advantageously offer a surface resistivity of 1 Ohm / square. Huntsman supplies such nonwovens under the Miralon brand. Preferably, a range of several thicknesses of nonwoven NTCs with different resistivities ps should be available to cover all the aircraft's needs, for example, nonwovens with resistivities ps of 0.10 - 1 and 1.5 or 2.5 Ohm / square.

[0088] Still within the framework of this embodiment and preferably, each resistive segment 23 has a width of at least 5 mm, preferably at least 20 mm. The smaller the width of the resistive segments 23, the easier it will be for the frost protection mat 1 to conform to complex shapes. Resistive segments 23 with a width greater than or equal to 20 mm advantageously reduce the relative dispersions of the resistance values. These dispersions are typically explained by the tolerance due to the cutting of the rectangular parallelepiped resistive segments 23, as well as the width of the segments. For example, to obtain a tolerance of 5% on 5 mm, a tolerance of ± 0.25 mm on the cut width would be required. It is therefore advantageous to perform a precise cutting of the resistive segments 23 so that the resistance value is also precise.

[0089] In general, it is useful to control the geometry, arrangement and properties of the resistive segments 23 in order to obtain a stable resistance in the temperature range of use of the frost protection mat 1. In other words, this makes it possible to obtain a linear variation over a temperature range between -40°C and +100°C, the resistance deviation being less than 20% between the maximum value and the minimum value of the temperature range.

[0090] It is also possible to adjust the surface heating power by using the arrangement of the rectangular parallelepiped resistive segments 23. Advantageously, in this respect, the resistive segments 23 are electrically connected in parallel and / or in series. In the embodiment illustrated in [Fig. 5], the resistive segments are arranged in series. It is then preferable for the frost protection mat 1 to have only one inlet and one outlet per part P. The resistive segments 23 are then connected to each other by electrical connection means 30, which are themselves connected to the inlet and outlet. Other shapes of resistive segments 23 are possible.

[0091] According to a first variant not illustrated, the resistive segments 23 can be of square parallelepiped shape.

[0092] According to a second embodiment illustrated in [Fig. 9a], the resistive segments 23 are hexagonal in shape. In this embodiment, there is a risk that the surface temperature will be less homogeneous because the cross-section varies at the 23 resistive segments. That being said, the nonwoven of NTCs or another element can be used to compensate for this loss of homogeneity.

[0093] According to a third variant illustrated in [Fig.9b], the resistive segments 23 are curved in shape, which allows, for example, to cover an air intake or to follow the leading edge of a propeller.

[0094] According to a preferred embodiment, the heating layer 22 has a thickness of 200 micrometers or less, and preferably less than 100 micrometers. It is advantageous to maintain a thin anti-icing mat 1 so as not to degrade the aerodynamics of the propeller blades.

[0095] According to a particular embodiment, the frost protection mat 1 may further comprise means 30 for electrically connecting the resistive segments 23 together (visible in [Fig. 4]). Such means 30 were introduced in the preceding sections. This advantageously allows the formation of a network of resistive segments 23 in series or in parallel.

[0096] Preferably, the electrical connection means 30 consist of metallic interconnecting bars. They may, for example, be made of copper, silver, gold, aluminum, nickel, platinum, stainless steel, or any other metal known to those skilled in the art for making this type of electrical connection.

[0097] It should be noted that an aircraft generally has two terminals, a + terminal and a - terminal, to power the entire network of electrical resistors connected together in parallel or in series. Typically, each part P to be protected from icing is associated with a single power supply having a + terminal and a - terminal. For example, each blade has its own power supply. The electrical connections are generally made by welding.

[0098] The interconnection means 30 link the resistive segments 23 together and are connected to the aircraft connector at two points, 31a and 31b ([Fig. 5]), with only one power supply generally provided per room for the sake of simplicity. This makes it possible to create variable power zones within the rooms even with a single aircraft power supply.

[0099] Preferably, the metallic interconnecting bars 30 also have a thickness between 25 µm and 100 µm, preferably between 60 µm and 80 µm, and more preferably equal to 70 µm. This depends on the metal from which the interconnecting bars 30 are made. If the interconnecting bars 30 are made of stainless steel, since stainless steel is less conductive, the interconnecting bars 30 must be thicker. A thickness of at least 25 µm allows the metallic interconnecting bars 30 to withstand a manual grinding operation. Grinding is a light sanding operation by which a surface is smoothed by means of a rotating cylinder lined with emery. The range of values ​​previously The specified temperature range, i.e., between 25 pm and 100 pm, allows for the production of 30 mm metallic busbars with negligible electrical resistance that do not overheat. It is preferable to position the 30 mm metallic busbars outside the area S to be protected from frost.

[0100] Furthermore, the frost protection mat 1 advantageously comprises a fixing layer 25 for the heating layer 22 to the electrical connection means 30, the fixing layer 25 being made of a conductive resin comprising a metallic filler. Such a fixing layer 25 is particularly advantageous because it allows the heating layer 22 to be fixed, and thus mechanically connected, to the electrical connection means 30, while ensuring sufficient electrical conductivity between these two layers.

[0101] In this regard, the conductive resin may advantageously comprise a conductive resin having at least one metallic filler. The conductive resin of the fixing layer 25 is advantageously an epoxy, polychloroprene, polyurethane, phenolic, or acrylic-based resin. The metallic filler is selected from a silver filler, a carbon nanotube filler, or a copper, aluminum, nickel, platinum, or graphene filler. Fixing layers 25 made from such conductive resins and metallic fillers exhibit high electrical conductivity, such that the electrical connection between the heating layer 22 and the electrical connection means 30 is of good quality. Indeed, this electrical connection is achieved without adding any cumulative additional electrical resistance (i.e., the sum of the connection resistances) exceeding 1% of the total resistance.

[0102] Alternatively, the fixing layer 25 may also be in the form of a film, a paste, or a sprayable solution. The aforementioned metallic fillers are not limiting in any way. Furthermore, it is preferable that the thickness of the fixing layer 25 not exceed 200 µm, preferably 100 µm.

[0103] The frost protection mat 1 may further include a reinforcing layer 21 comprising two polychloroprene layers 21a, 21c, and a glass fabric layer 21b interposed between the two polychloroprene layers 21a, 21c, the electrically conductive heating layer 22 being surmounted by the reinforcing layer 21. The glass fabric layer 21b is optional. The reinforcing layer 21 facilitates the manufacture of the non-woven NTCs in the form of a pattern comprising a plurality of segments. Indeed, during the manufacture of the frost protection mat 1, the reinforcing layer 21 is bonded, without glue, to the non-woven NTCs in order to cut the non-woven NTCs more precisely. The reinforcing layer 21 thus stabilizes the non-woven NTCs during cutting. Alternatively, it is possible to replace the reinforcing layer 21 The aforementioned structure comprises two layers 21a, 21c of polychloroprene, and a layer of glass fabric 21b interposed between the two polychloroprene layers 21a, 21c by an unreinforced elastomeric sheet. Other solutions for supporting the heating layer 22 during implementation may be considered. The proposals described here are not exhaustive.

[0104] The invention also relates to an assembly comprising at least one aircraft part having a surface S to be protected from frost, in which the surface S is covered with a frost protection mat 1 as previously described.

[0105] With reference to [Fig. 6], the invention further relates to a method 100 for manufacturing a frost protection mat as previously described. The manufacturing method 100 comprises the steps described below.

[0106] In step 110, a tool in the shape of a surface S of the part P to be defrosted or protected from frost is provided. Optionally, a peel ply is applied to the surface S to be protected from frost, onto which the frost protection mat 1 is to be affixed or integrated. A granular surface finish advantageously improves the adhesion performance of the defroster to its substrate.

[0107] The tooling can be metallic or made of any other material resistant to autoclave curing when this curing method is used. The tooling can be made of composite material or high-temperature thermoplastic reinforced with carbon fibers. What is important in the context of the present invention is to have tooling that has the shape of the surface S of the part to be produced. When the shape to be manufactured is developable, the process 100 according to the invention can also be used to manufacture frost protection mats for flat surfaces.

[0108] During a step 120, at least one contact layer 10 is applied to the metal tooling. The contact layer 10 can, for example, be an elastomeric layer based on polychloroprene.

[0109] According to a particular embodiment, before carrying out step 130, which will be described below, the electrical connection means 30, preferably metallic interconnecting bars 30, are prepared. In this regard, the interconnecting bars are lightly sanded, i.e., ground, and then adhesion primers 28b are applied. Typically, there are two adhesion primers 28b, a primary coat and a secondary coat. Next, one or two coats 28a of adhesive, for example, a polychloroprene-based adhesive, are applied.

[0110] According to a particular embodiment, once the metallic interconnecting bars 30 are prepared, they are deposited on the contact layer 10 so that the polychloroprene-based adhesive layer(s) 28a face the contact layer 10. The metallic interconnecting bars 30 are deposited in a stacking Z-axis direction. This facilitates the adhesion of the interconnecting bars 30 to the contact layer 10.

[0111] Preferably, a fixing layer 25 is applied to the metallic interconnecting bars 30 in a stacking Z-axis direction. The fixing layer 25 advantageously comprises a conductive resin, preferably epoxy, containing a silver metallic filler.

[0112] In a step 130, a resistive structure 20 is produced comprising at least one heating layer 22, the heating layer 22 being capable of generating a heat flux through the surface S, made of a material comprising a nonwoven of carbon nanotubes impregnated with an epoxy resin, the heating layer 22 being in the form of a pattern comprising a plurality of resistive segments 23. The heating layer 22 may be pre-doubled and cut so as to form the resistive segments 23, and then placed on the fixing layer 25 in a stacking direction along the Z-axis.

[0113] In a step 140, at least one encapsulation layer 15 is placed on the resistive structure 20 so as to electrically insulate the resistive segments 23 from each other. This step 140 can be carried out in two substeps: a first substep consisting of placing a first encapsulation layer 15 in the form of profiles intended to fill the spaces left empty between the resistive segments 23, and a second substep consisting of placing a second encapsulation layer 15 in the form of one or more sheets. The encapsulation layer(s) are preferably made of a polychloroprene-based elastomer. When the contact layer 10 is also made of polychloroprene, this promotes chemical bonding of the layers to each other after co-baking.

[0114] In a step 150, the contact layer(s) 10, the resistive structure 20, and the encapsulation layer(s) 15 are co-baked. At the end of this step, the frost protection mat 1 forms a solid assembly.

[0115] Co-curing eliminates the need for adhesives. It can be implemented for the contact layer 10 and the epoxy resin of the heating layer 22. It can also be implemented when a glass / epoxy prepreg is used for the contact layer 10 and the encapsulation layer 15. In this respect, the curing kinetics are advantageously chosen to be compatible with the selected materials.

[0116] Co-cooking can be carried out under a vacuum bag in an autoclave. Alternatively, co-cooking can also be carried out outside an autoclave, for example, under a heated press or on a heated mold. Description of an example of implementation

[0117] Figure 7 illustrates a prototype frost protection mat 1 according to an embodiment of the invention, the protection mat 1 being equipped with temperature probes.

[0118] The contact layer 10 is a polychloroprene-based elastomeric bilayer. It comprises a first polychloroprene layer and a second polychloroprene layer. Preferably, the first polychloroprene layer has a different color from the second polychloroprene layer, making them distinguishable.

[0119] The encapsulation layer is made of polychloroprene.

[0120] The heating layer 22 is made of a nonwoven fabric of NTCs from the Miralon brand supplied by Huntsman. The heating layer 22 is in the form of a pattern comprising a plurality of rectangular resistive parallelepiped segments 23 electrically insulated from each other by the encapsulation layer. The resistive segments 23 have a width of 50 mm, a length of 190 mm, and are separated by a distance of 5 mm.

[0121] The electrical connection means 30 are copper interconnecting bars having a thickness of 70 µm. The copper interconnecting bars can be easily distinguished on the radiograph of [Fig. 8].

[0122] The fixing layer 25 is a silver-filled epoxy resin 100 µm thick. Henkel's LOCTITE ABLESTICK CF 3350-004 adhesive can be used as the fixing layer 25.

[0123] The configurations shown in the cited figures are only possible examples, in no way limiting, of the invention which on the contrary encompasses design variants within the reach of a person skilled in the art.

Claims

Demands

1. Frost protection mat (1) for an aircraft part (P), the mat (1) comprising: - at least one contact layer (10) intended to be affixed to a surface (S) of said part (P), - at least one encapsulation layer (15), and - a resistive structure (20) interposed between the contact layer (10) and the encapsulation layer (15), the structure (20) comprising at least one heating layer (22), capable of generating a heat flow through the surface (S), made of a material comprising a carbon nanotube nonwoven impregnated with an epoxy resin, the heating layer (22) being in the form of a pattern comprising a plurality of resistive segments (23) electrically insulated from each other by the encapsulation layer (15).

2. Frost protection mat (1) according to claim 1, wherein the resistive segments (23) are of rectangular parallelepiped shape.

3. Frost protection mat (1) according to any one of claims 1 or 2, wherein the resistive segments (23) are electrically connected in parallel and / or in series.

4. Frost protection mat (1) according to any one of claims 1 to 3, wherein the encapsulation layer (15) is made of an elastomeric material, a thermoplastic film, a thermosetting resin or a composite.

5. Frost protection mat (1) according to any one of claims 1 to 4, wherein the heating layer (22) has a thickness less than or equal to 200 micrometers, preferably less than 100 micrometers.

6. Frost protection mat (1) according to any one of claims 1 to 5, further comprising means (30) for electrically connecting the resistive segments (23) together, and a fixing layer (25) for the heating layer (22) to the electrically connecting means (30), the fixing layer (25) being made of a conductive resin comprising a metallic filler.

7. Frost protection mat (1) according to any one of claims 1 to 6, comprising a reinforcing layer (21) comprising two layers (21a, 21c) of polychloroprene, and optionally a layer of glass fabric (21b) interposed between the two layers (21a, 21c) of polychloroprene, the electrically conductive heating layer (22) being surmounted by the reinforcing layer (21).

8. Frost protection mat (1) according to any one of claims 1 to 7, wherein the contact layer (10) is made of an elastomeric material, a thermoplastic film, a thermosetting resin or a composite.

9. Assembly comprising at least one aircraft part (P) having a surface (S) to be de-iced or protected from frost, said surface (S) being covered with a frost protection mat (1) according to any one of claims 1 to 8.

10. A method (100) for manufacturing a carpet according to any one of claims 1 to 8, the manufacturing method (100) comprising the following steps: (110) provide a tool having the shape of a surface (S) of the part (P) to be defrosted or protected from frost, (120) place at least one contact layer (10) on the tooling, (130) produce a resistive structure (20) comprising at least one heating layer (22), the heating layer (22) being capable of generating a heat flux through the surface (S), made of a material comprising a nonwoven of carbon nanotubes impregnated with an epoxy resin, the heating layer (22) being in the form of a pattern comprising a plurality of resistive segments (23), (140) place at least one encapsulation layer (15) on the structure (20) so as to electrically insulate the resistive segments (23) from each other, (150) perform a co-baking of the contact layer (10), the resistive structure (20) and the encapsulation layer (15).

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