Ice protection mat, in particular for an aircraft part and method for installing same

Abstract

The invention relates to an ice protection mat (1) for a part (BA), in particular an aircraft part (BA), which mat comprises a multilayer structure with at least one heating layer (3) capable of generating a heat flux, a contact layer (2) forming at least one thermal barrier between the heating layer (3) and the part (BA), and at least one intermediate layer (4) and / or reinforcing layer (5) and / or outer layer (6) which is / are thermally conductive and arranged between the heating layer (3) and an external environment.

Description

[0001] Frost protection mat, in particular for an aircraft part and method for its installation

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the protection of aircraft parts from frost. More particularly, it provides an frost protection mat used to protect aircraft parts from frost.

[0004] STATE OF THE ART

[0005] An accumulation of ice on an aircraft, particularly in flight, can modify the aerodynamic properties of the aircraft and impair its performance.

[0006] Furthermore, if pieces of ice formed or accumulated on any part of the aircraft fuselage or on engine air intakes break off, these pieces can strike parts of the aircraft and damage it.

[0007] A build-up of frost can cause at least partial obstruction of the air intakes, which could also cause power losses or even engine shutdown.

[0008] This is why aircraft are traditionally equipped with ice protection devices, also called de-icers, installed, for example, on the leading edges of the wings, a rudder, a radome or even engine air intakes.

[0009] Also, on propeller-driven aircraft, the leading edges of the blades or cones are usually equipped with ice protection devices.

[0010] Such frost protection devices having the function of either removing frost or preventing frost formation are also known.

[0011] Different technologies of frost protection devices exist such as pneumatic devices with mechanical effect, hot air circulation defrosters, etc.

[0012] The invention relates more particularly to frost protection devices with frost protection mats, in particular thermoelectric mats.

[0013] Such a frost protection mat is a heating mat applied to a surface of a part that is to be protected against frost. It provides defrosting or anti-frosting by the Joule effect, by circulating a current in a layer incorporating at least one heating resistor. It can be operated cyclically or be controlled according to an operating mode ensuring permanent heating.

[0014] In particular, structures are known in which the layer incorporating at least one heating resistor is generally covered with an electrically insulating layer which remains flexible at low temperature, i.e. the temperature at which ice is likely to form on the surfaces to be defrosted, and which has good resistance to the maximum temperature of the heating resistors. For example, an elastomer or a thermoplastic, such as polyimide or a rubber mixture, is chosen.

[0015] The materials used until now for this electrical insulation are not thermal conductors.

[0016] STATEMENT OF THE INVENTION

[0017] One aim of the invention is to propose a solution allowing better dissipation of the heat flow towards a surface to be defrosted while ensuring good electrical insulation. Another aim of the invention is to propose a solution allowing to save space and reduce the thickness of a frost protection mat used to protect aircraft parts from frost.

[0018] To this end, the invention proposes a frost protection mat for a part, in particular an aircraft part, comprising a multi-layer structure with at least one heating layer, capable of generating a heat flow, characterized in that it comprises at least

[0019] - a contact layer forming at least one thermal barrier between the heating layer and the part, and at least one intermediate layer and / or one reinforcing layer and / or one thermally conductive outer layer(s) arranged between the heating layer and an external environment.

[0020] Furthermore, according to advantageous and non-limiting characteristics, taken alone or in any combination:

[0021] - an intermediate layer has electrical insulating and thermal conducting properties;

[0022] - the reinforcing layer is interposed between the intermediate layer and the outer layer;

[0023] - the reinforcing layer comprises a network of woven, non-woven and / or mesh fibers or threads;

[0024] - the reinforcing layer is electrically conductive and is connected to a ground;

[0025] - an outer layer is interposed between the reinforcement layer and the external environment;

[0026] - the outer layer is coated with a layer of paint;

[0027] - the heating layer, respectively the contact layer, the intermediate layer (4), the reinforcing layer or the outer layer, has a thickness of less than 1.5 mm, in particular less than 1 mm, in particular less than 0.7 mm; - the heating layer, respectively the contact layer, the intermediate layer, the reinforcing layer or the outer layer, has a thickness of greater than 0.2 mm, in particular greater than 0.3 mm, in particular of the order of 0.4 mm.

[0028] The invention further relates to an assembly comprising at least one part, in particular an aircraft part, having an external surface, characterized in that the external surface is covered by a frost protection mat of the type proposed.

[0029] The invention also provides a method for placing a frost protection mat as proposed on an external surface of a part, in particular an aircraft part, in which the contact layer is bonded or co-vulcanized to the part.

[0030] DESCRIPTION OF FIGURES

[0031] Other characteristics and advantages of the present invention will appear on reading the following description of a preferred embodiment. This description will be given with reference to the appended figures including:

[0032] - Figure 1 schematically represents an assembly comprising a part and a frost protection mat in accordance with one embodiment of the invention;

[0033] - Figure 2 schematically represents a multi-layer structure of the frost protection mat according to one embodiment of the invention;

[0034] - Figure 3 schematically represents a composite material of an electrically insulating and thermally conductive layer;

[0035] - Figure 4 illustrates a measuring device for determining an electrical resistance of the frost protection mat according to the invention; and

[0036] - Figure 5 illustrates a measuring device for determining electrical resistance and leakage currents of the frost protection mat according to the invention.

[0037] DETAILED DESCRIPTION OF THE INVENTION

[0038] In the description which will be given of the invention, the terms "transverse", "longitudinal" and "radial" qualify a direction of extension of a layer, a fiber and / or a wire.

[0039] Thus, the transverse direction corresponds to a direction perpendicular to an extension surface of a layer. It corresponds to a thickness of the layer. In addition, the transverse direction is assimilated to a radial direction of a fiber or a wire of a constituent element of a layer. The transverse direction is represented by the T axis in Figure 2. Furthermore, the longitudinal direction corresponds to an extension direction of a fiber and / or a wire of a constituent element of a layer. The fibers and / or the threads extending along the surface of the constituent element of the layer, the longitudinal direction can be according to two components represented by the X axis and the Y axis in figure 2. Figure 1 schematically represents an assembly comprising a part BÀ, in particular an aircraft part BÀ, in particular a leading edge of a wing or a propeller of an aircraft, protected from frost by a frost protection mat 1, in particular a thermoelectric mat 1.

[0040] The frost protection mat 1 is attached to an external surface 11 of the part BÀ to which it conforms, for example by gluing using an adhesive layer not shown.

[0041] The frost protection mat 1 comprises a multi-layer structure as shown schematically in Figure 2.

[0042] The multi-layer structure includes in particular a stack of layers, in particular, according to the example presented in figure 2, from the BA part, to be protected from frost, towards an external environment:

[0043] - a contact layer 2, intended to be in contact with the BA part to be protected, in particular the leading edge, and having the function of constituting an electrical barrier and a thermal barrier;

[0044] - a heating layer 3, intended to be a heat source capable of providing a defrosting and / or anti-frosting function, in particular by Joule effect, for the BA part to be protected;

[0045] - an intermediate layer 4, intended to provide an electrical insulating and thermal conductor function;

[0046] - a reinforcing layer 5, intended to provide a function of protecting the frost protection mat 1, in particular the heating layer 3, from impacts;

[0047] - an outer layer 6, intended to provide a resistance function to the external environment, in particular to bad weather and temperature conditions likely to be encountered by the aircraft.

[0048] The stacking of the different layers is of a low thickness, typically less than 2 mm, in particular less than 1.5 mm, advantageously less than 1 mm.

[0049] If necessary, the multi-layer structure may be covered with a layer of paint 7.

[0050] In particular, the frost protection mat 1 comprising the multilayer structure may have an electrical insulation resistance of at least 10 MO, in particular at least 100 MO.

[0051] According to the exemplary embodiment presented in figure 2, the contact layer 2 is arranged in the multilayer structure so as to be interposed between an external surface 11 of the part BA to be protected from frost and the heating layer 3. The contact layer 2 is designed so as to be in contact with the part BA to be protected, in particular the leading edge, and having the function of constituting an electrical barrier and a thermal barrier.

[0052] In particular, the contact layer 2 can be made of a material having electrical and thermal insulation properties.

[0053] Contact layer 2 thus makes it possible to avoid excessively high contact temperatures with the part BÀ to be protected against frost.

[0054] The material of the contact layer 2 may be an elastomer, a polymer, in particular a thermoplastic polymer or a thermosetting polymer, in particular an epoxy resin.

[0055] Alternatively, the contact layer 2 may be made of an insulating foam.

[0056] According to a particular embodiment, the contact layer 2 may also be made of an insulating honeycomb structure. Alternatively or additionally, the contact layer 2 may also be made of a mixture of elastomer or polymer filled with glass beads, in particular hollow glass beads.

[0057] Thus configured, the contact layer 2 protects the part BA on which the frost protection mat 1 is mounted from possible overheating. Indeed, due to the thermal insulation properties of the contact layer 2, the heat released by the heating layer 3 is directed towards an outer surface of the frost protection mat 1 on which frost is likely to form, arranged, according to the multilayer structure, opposite the contact layer 2 and therefore the part BA to be protected against frost.

[0058] Furthermore, it is desirable to avoid any circulation of an electric current between the heating layer 3 and the part BA.

[0059] In particular, the contact layer 2 may have a volume resistivity of at least 1 E9 Qm, preferably greater than 1 E10 Qm.

[0060] A thermal conductivity of the contact layer 2, considered perpendicular to a general plane of extension of the contact layer 2, also called transverse thermal conductivity, is less than 0.4 W / mK at room temperature. By room temperature, is meant, throughout the present description, a temperature of the order of 20°C.

[0061] The contact layer 2 may have a thickness of less than 1.5 mm, in particular less than 1 mm, advantageously less than 0.7 mm. Furthermore, the contact layer 2 may have a thickness greater than 0.2 mm, in particular greater than 0.3 mm, advantageously greater than 0.6 mm. According to the exemplary embodiment presented in FIG. 2, the heating layer 3 is arranged in the multilayer structure so as to be interposed between the contact layer 2 and the intermediate layer 4.

[0062] The heating layer 3 is designed to provide a heat source capable of ensuring a defrosting and / or anti-frosting function by Joule effect for the part BÀ to be protected.

[0063] In particular, the heating layer 3 may be a resistive layer for Joule heating.

[0064] However, the heating layer 3 can be produced from any heating means capable of generating a heat flow, such as, but not limited to, metal tracks, heating wires, conductive inks, fabrics or non-wovens using fibers, etc.

[0065] For example, the heating layer 3 may incorporate a mesh of metal tracks intended to be traversed by a current to generate the heat flow by Joule effect. The metal tracks may be very close to each other to cover the surface as homogeneously as possible. As will nevertheless be understood more particularly through the description which follows, the longitudinal thermal conduction ensured by fibers and / or wires of the reinforcement allows a greater spacing of the metal tracks than that currently possible according to the state of the art.

[0066] In particular, the metal tracks cover at least 50% of the surface of the heating layer 3, in particular at least 70% of the surface of the heating layer 3.

[0067] Power supply electrical connections allow connection to a power source to energize the metal tracks.

[0068] Typically, the heating layer 3 releases a heating power of between 1 and 5 W / cm 2 , especially between 2 and 5 W / cm 2 , depending on whether it operates in cyclic mode or in continuous mode.

[0069] The heating layer 3 may have a thickness of less than 0.3 mm, in particular less than 0.25 mm, advantageously less than 0.15 mm. Furthermore, the heating layer 3 may have a thickness greater than 0.015 mm, in particular greater than 0.05 mm. Typically, the heating layer 3 may have a thickness of the order of 0.15 mm.

[0070] According to the embodiment shown in Figure 2, the intermediate layer 4 is arranged in the multilayer structure so as to be interposed between the heating layer 3 and the reinforcing layer 5.

[0071] The intermediate layer 4 is designed to provide an electrical insulating and thermal conductor function.

[0072] In particular, the intermediate layer 4 may be made of a composite material chosen to have good electrical insulation and good thermal conduction properties. The intermediate layer 4 contributes to directing the heat flow generated by the heating layer 3 towards the external surface of the frost protection mat 1, that is to say opposite the contact layer 2 and therefore the part BÀ to be protected against frost.

[0073] In particular, the intermediate layer 4 may have a volume resistivity of at least 1 E9 Qm, preferably greater than 1 E10 Qm.

[0074] A thermal conductivity of the intermediate layer 4, considered perpendicular to a general plane of extension of the intermediate layer 4, also called transverse thermal conductivity, is greater than 0.4 W / mK at room temperature, in particular greater than 0.6 W / mK at room temperature, in particular greater than 0.8 W / mK at room temperature, specifically greater than 1.5 W / mK at room temperature, determined according to the methods described in the ISO 8302 or ÀSTM C177 standards. The intermediate layer 4 may have a thickness of less than 1.5 mm, in particular less than 1 mm, advantageously less than 0.7 mm. Furthermore, the intermediate layer 4 may have a thickness of greater than 0.2 mm, in particular greater than 0.3 mm. Typically, the intermediate layer 4 may have a thickness of the order of 0.4 mm.As more particularly illustrated in FIG. 3, the intermediate layer 4 can be made from a composite material 40 comprising a matrix 42 and inclusions 41.

[0075] According to the exemplary embodiment presented in figure 2, the reinforcing layer 5 is arranged in the multilayer structure so as to be interposed between the heating layer 3 and the outer layer 6.

[0076] The reinforcing layer 5 is designed to provide a function of protecting the frost protection mat 1, in particular the heating layer 3, from impacts, such as gravel, hailstones, blows related to maintenance, etc.

[0077] In particular, the reinforcing layer 5 can be made of a material allowing circulation of the heat flow generated by the heating layer 3, towards the external surface of the frost protection mat 1, that is to say opposite the contact layer 2 and therefore the part BÀ to be protected against frost.

[0078] In particular, the reinforcing layer 5 may be in the form, for example, of a woven, non-woven, such as felt, or mesh reinforcement extending along a general plane of extension of the reinforcing layer 5.

[0079] A thermal conductivity of the reinforcing layer 5, considered perpendicular to the general plane of extension of the reinforcing layer 5, also called transverse thermal conductivity, greater than 0.4 W / mK at room temperature, in particular greater than 0.6 W / mK at room temperature, in particular greater than 0.8 W / mK at room temperature, specifically greater than 1.5 W / mK at room temperature, determined according to the methods described in the ISO 8302 or ÀSTM C177 standards. More specifically, the reinforcing layer 5 may comprise fibers and / or yarns. In such a configuration, the fibers and / or yarns of the reinforcing layer may further have a longitudinal thermal conductivity greater than 0.6 W / mK at room temperature.

[0080] Longitudinal thermal conductivity is a thermal conductivity considered in a direction parallel to a direction of extension of the fibers and / or yarns. Consequently, the longitudinal thermal conductivity of the fibers and / or yarns corresponds to the thermal conductivity along the general plane of extension of the reinforcing layer 5.

[0081] The longitudinal thermal conductivity at room temperature greater than 10 W / mK allows longitudinal homogenization of the temperature of the reinforcement layer 5, i.e. in the general plane of extension of the reinforcement layer 5.

[0082] Alternatively, to ensure homogeneity, the longitudinal thermal conductivity can be greater than 50 W / m K, particularly in the fiber axis.

[0083] Advantageously, a radial conductivity of the fibers corresponds to the transverse conductivity of the frost protection mat 1. It must therefore logically be equivalent to that of the intermediate layer 4 and of an outer layer 6, described below.

[0084] Such thermal conductivity is particularly important when the heating layer 3 is constituted by a network of metal tracks not having a homogeneous heating surface. Indeed, in such a case, the heat flux emitted by the metal tracks of the heating layer 3 is longitudinally heterogeneous.

[0085] The homogenization of the heat flow in the general plane of extension of the reinforcement layer 5 allows greater defrosting or anti-frosting efficiency, since the diffusion of the heat flow generated by the heating layer 3 in order to ensure the defrosting and / or anti-frosting function is diffused over the entire surface of the frost protection mat 1 without heterogeneity.

[0086] It will also be noted that the homogenization function that the reinforcing layer 5 provides, in particular in the form of a fabric, a non-woven fabric, a knit, a mesh and / or a unidirectional reinforcement, a combination and / or a stack of these, makes it possible to relax constraints on the spacing of the tracks of the heating layer 3. It is thus possible to use heating metal tracks that are further apart from each other compared to what is currently possible in the known solutions of the state of the art.

[0087] Consequently, the invention thus offers the possibility of using technologies for manufacturing the heating layer 3, in particular the heating resistors, in particular by additive manufacturing. Preferably, the reinforcing layer 5 incorporates a network of woven, non-woven, knitted, meshed fibers and / or threads, and / or a unidirectional reinforcement, in particular carbon fibers manufactured from a pitch fiber precursor, in particular coal or petroleum pitch, and / or threads having a longitudinal thermal conductivity at room temperature greater than 50 W / mK

[0088] More preferably, the woven or mesh reinforcement of the reinforcement layer 5 incorporates fibers having a longitudinal thermal conductivity at room temperature greater than 120 W / mK.

[0089] The fibers and / or threads of the reinforcing layer 5 may be of different types such as, for example, glass fibers, basalt fibers, silica fibers, metal threads, etc.

[0090] Preferably, the reinforcing layer 5, in particular in the form of a woven, non-woven or mesh reinforcement, is made of carbon fibers, which have the advantage of having good thermal conductivity properties.

[0091] More preferably, the carbon fibers of the reinforcing layer 5 are made from coal or petroleum pitch. Such a production of the carbon fibers allows a radial thermal conductivity greater than 0.6 W / mK, in particular greater than 10 W / mK, and / or a longitudinal thermal conductivity greater than 50 W / mK, in particular greater than 120 W / mK.

[0092] According to another embodiment, the fibers of the reinforcing layer 5 comprise carbon fibers with a polyacrylonitrile (PAN) type precursor. Such an embodiment has a radial thermal conductivity greater than 1 W / mK and a longitudinal thermal conductivity greater than 10 W / mK.

[0093] It will also be noted that the reinforcing layer 5 can also participate in the protection function against electrostatic discharges, also referred to by the acronym “ESD” for “Electrostatic discharge” in English.

[0094] For example, in the case where the reinforcing layer 5 is made of carbon fabric and / or contains metal, the reinforcing layer 5 can be used for grounding intended to ensure the evacuation of electrostatic charges.

[0095] In such a hypothesis, the reinforcing layer 5 can contribute, at least in part, to protection against lightning.

[0096] The reinforcing layer 5 may have a thickness of less than 1.5 mm, in particular less than 1 mm, in particular less than 0.7 mm, advantageously less than 0.3 mm. Furthermore, the reinforcing layer 5 may have a thickness greater than 0.02 mm, in particular greater than 0.05 mm. Typically, the reinforcing layer 5 may have a thickness of the order of 0.1 mm. According to the exemplary embodiment presented in FIG. 2, the outer layer 6 is arranged in the multilayer structure so as to be interposed between the reinforcing layer 5 and the paint layer 7.

[0097] Alternatively, the outer layer 6 is arranged in the multi-layer structure so as to be disposed on the reinforcing layer 5 and in direct contact with the external environment.

[0098] The outer layer 6 is designed to provide a function of resistance to the external environment, in particular to bad weather, temperature conditions, and fluid projections likely to be encountered by the aircraft.

[0099] In particular, the outer layer 6 may be made of an elastomer or polymer resistant to the external environment, in particular to bad weather and temperature conditions likely to be encountered by the aircraft.

[0100] In particular, the outer layer 6 resists erosion under the conditions defined by the Sand & Dust standard RTCA-DO-160.

[0101] In addition, the outer layer 6 contributes to shock protection.

[0102] In addition, the outer layer 6 may also be of a composition comprising fillers enabling it to dissipate electrostatic charges.

[0103] In addition, the outer layer 6 is thermally conductive and does not necessarily have electrically insulating properties.

[0104] The outer layer 6 may have a thickness of less than 1.5 mm, in particular less than 1 mm, advantageously less than 0.5 mm. Furthermore, the outer layer 6 may have a thickness greater than 0.1 mm, in particular greater than 0.2 mm. Typically, the outer layer 6 may have a thickness of the order of 0.2 mm.

[0105] According to the embodiment shown in Figure 2, the paint layer 7 can be applied to the multi-layer structure so as to cover the multi-layer structure.

[0106] In particular, the paint layer 7 is designed to have properties of resistance to the external environment and / or resistance to erosion, in particular under the conditions of the Sand & Dust RTCA-DO-160 standard.

[0107] In addition, the paint layer 7 may also be of a composition comprising charges enabling it to dissipate electrostatic charges.

[0108] In addition, an application of the paint layer 7 on the multilayer structure may require a prior application of an adhesion primer on the multilayer structure, in particular on the reinforcement layer 5, or a dry adhesion treatment, for example by plasma. Thus arranged and according to the invention, the frost protection mat 1 has a total thickness of less than 1.9 mm, in particular less than 1.5 mm, in particular less than 1 mm.

[0109] As previously specified, the intermediate layer 4 can be made from a composite material 40 comprising a matrix 42 and inclusions 41.

[0110] The matrix 42 is made of an electrically insulating elastomer. Such an elastomer is chosen to exhibit good resistance in a range of temperatures typical of use of the frost protection mat 1.

[0111] The maximum operating temperature of the frost protection mat 1 is a temperature that can be reached by the heating layer 3 during generation of the heat flow necessary for a defrosting cycle.

[0112] Because the intermediate layer 4 is in direct contact with the heating layer 3, one face of the intermediate layer 4 in contact with the heating layer 3 must withstand the maximum operating temperature.

[0113] Because the heating layer 3 is covered by the intermediate layer 4, there is further an effect of accumulation of the heat flow at an interface between the heating layer 3 and the intermediate layer 4. The maximum temperature can typically be between 100°C and 110°C.

[0114] Preferably, the matrix 42 is made of a thermosetting polymer, in particular an elastomeric material or an epoxy resin.

[0115] It is nevertheless possible that the matrix 42 is made of another type of polymer, such as, for example, a thermoplastic polymer.

[0116] To obtain good resistance and guarantee suitable mechanical properties in the operating temperature range between the minimum temperature and the maximum temperature, it is particularly advantageous for the matrix 42 to be made of a polymer chosen from polyurethanes, nitriles, neoprenes, silicones, fluorinated silicones and / or epoxies.

[0117] In particular, the matrix 42 may be made of a thermoplastic polymer, such as a polyetheretherketone, also designated by the acronym PEEK, a polyetherketoneketone, also designated by the acronym PEKK, a polyetherimide, also designated by the acronym PEI, a polysulfone, also designated by the acronym PSU, a polyethersulfone, also designated by the acronym PESU, a polyphenylsulfone, also designated by the acronym PPSU, a polyamide-imide, also designated by the acronym PAI, or a polyphthalamide, also designated by the acronym PPA.

[0118] Such materials have the advantage in particular of withstanding a contact temperature with the heating layer 3, capable of generating the heat flow, of the order of 100°C continuously, particularly favorable for ensuring the defrosting and / or anti-frosting function.

[0119] Advantageously, the material of the matrix 42 is adapted to be shaped by a vulcanization process after incorporation of the inclusions 41. Such a process allows the position of the inclusions 41 to be fixed.

[0120] Another advantage of such vulcanization shaping is the possibility of carrying out co-vulcanization with another material of an adjacent layer, for example the heating layer 3 with which close contact is required.

[0121] In the embodiment in which the heating layer 3 is made from metal tracks or heating wires, the latter are advantageously coated with a primer capable of ensuring a connection with the matrix 42.

[0122] Furthermore, it is entirely possible to have different methods of connection between the different layers of the multi-layer structure of the frost protection mat 1, such as, for example, bonding, co-vulcanization or, more generally, co-firing.

[0123] The matrix 42 comprises inclusions 41. In particular, the inclusions 41 are made of a material having a high electrical volume resistivity, in particular greater than 1 E9 Qm, preferably greater than 1 E10 Qm.

[0124] Such electrical resistivity of the inclusions 41 makes it possible to obtain a material whose overall electrical resistivity corresponds to the electrical insulation requirements of the intermediate layer 4 arranged in direct contact with the heating layer 3.

[0125] Furthermore, inclusions 41 have a thermal conductivity greater than 1.5 W / mK at room temperature, in particular greater than 20 W / mK.

[0126] Such thermal conductivity of the inclusions 41 makes it possible to increase the thermal conductivity of the intermediate layer 4. Such a configuration thus allows better transmission of the heat flow generated by the heating layer 3 to the surface to be defrosted. By increasing the transmission of the heat flow, it is possible to achieve savings in the energy necessary to ensure the defrosting and / or anti-icing function for the BA part to be protected.

[0127] Furthermore, good thermal conductivity of the intermediate layer 4 makes it possible to reduce an accumulation effect of the heat flow at the level of the heating layer 3. It is thus possible to lower the temperature to which the intermediate layer 4 is exposed near the contact zone with the heating layer 3. Such a reduction in temperature in such a contact zone prevents, to a certain degree, the degradation of the material of the matrix 42.

[0128] The improved thermal conductivity thus makes it possible to increase the service life of the heating layer 3 and / or to use other materials for producing the matrix 42 which have less resistance to high temperatures, provided that the surface temperature of the part BÀ to be protected remains within a reasonable range.

[0129] Advantageously, the material of the inclusions 41 is a ceramic having good thermal conductivity and electrical insulation properties.

[0130] Preferably, the inclusions 41 are made of boron nitride, aluminum nitride, alumina or a coupling of such fillers.

[0131] Other ceramics with electrical resistivity and thermal conductivity parameters can be used.

[0132] According to a particular embodiment, the inclusions 41 have a volume ratio in the matrix 42 typically between 10% and 70% by volume, in particular between 20 and 50% by volume, in particular between 30% and 50% by volume.

[0133] Such a volume ratio makes it possible to maintain the mechanical properties of the matrix 42 for shaping and use of the intermediate layer 4 while making it possible to use the thermal properties of the inclusions 41 to improve the thermal conductivity of the material as a whole.

[0134] We will now describe an example of the manufacture of a composite material capable of constituting the intermediate layer 4.

[0135] A first step consists of providing a base material for a formulation of the matrix polymer 42. Such a base material is typically provided in the form of plates, petals or granules and does not include any solvent. For example, the starting material may be rubber.

[0136] In a second step, the base material is mixed, for example in a closed mixer with several propellers or a cylinder mixer, also called an open mixer.

[0137] The elements of the base material are heated by a shear effect occurring during mixing.

[0138] During the second stage, the base material transforms into a homogeneous viscous material.

[0139] In a third step, particles intended to form inclusions 41 are added. Such particles are provided in the form of powders and can be agglomerated during their production or storage.

[0140] The particles are added during the third step consisting of a mixing step. The third step makes it possible to separate any agglomerates and to distribute the particles homogeneously in the viscous material intended to form the matrix 42, in particular made of polymer. When the inclusions 41 are distributed in the matrix 42, during a fourth step, the intermediate layer 4 is formed, the thickness of which may be between 0.2 mm and 0.7 mm, typically a thickness of the order of 0.4 mm.

[0141] The formation of the intermediate layer 4 can be carried out by calendering, by extrusion, in particular by extrusion of film in a flat die...

[0142] Subsequently, during a fifth step, the matrix 42 is shaped using dedicated tooling and then vulcanization is carried out in order to hold the inclusions 41 in place and to fix a geometry of the intermediate layer 4.

[0143] In some embodiments, it is possible to form the intermediate layer 4 directly in contact with the heating layer 3. In such cases, co-vulcanization is carried out between the polymer matrix 42 and the heating layer 3. Such co-vulcanization makes it possible to ensure good mechanical and thermal contact between the intermediate layer 4 and the heating layer 3.

[0144] To test the intermediate layer 4 and more generally the structure of the frost protection mat 1, a test device 400 as illustrated in FIG. 4 is used.

[0145] Advantageously, the frost protection mat 1, comprising the contact layer 2, the heating layer 3, the intermediate layer 4, the reinforcing layer 5, and the outer layer 6, is tested.

[0146] The test device 400 comprises an electrically conductive reservoir 401, typically a metal reservoir, filled with a quantity of water 402.

[0147] A stack comprising at least the contact layer 2, the intermediate layer 4, in particular electrically insulating in composite material 40, and the heating layer 3 is immersed in the quantity of water 402.

[0148] Alternatively, the frost protection mat 1, comprising the contact layer 2, the heating layer 3, the intermediate layer 4, the reinforcement layer 5, and the outer layer 6, is immersed in the quantity of water 402.

[0149] As a result, two electrodes 411, 412 are connected to the heating layer 3 via the power supply wires and establish an electrical connection 413 with a resistance measuring device 410, such as an ohmmeter. The resistance measuring device 410 is electrically connected to the tank 401.

[0150] An electrical voltage, in particular an electrical voltage of 500 V continuously, is then applied between the reservoir 401 and the electrodes 411, 412 connected to the heating layer 3. Preferably, the voltage applied during the test is twice as high as an operating voltage of the defrosting and / or anti-frosting device for the BA part to be protected from frost, which may be 220 V to 230 V. Alternatively, the operating voltage of the defrosting and / or anti-frosting device for the BA part to be protected from frost may be supplied with 110 V.

[0151] Subsequently, a first test step consists of a measurement of an insulation resistance measured by the resistance measuring device 410.

[0152] A result of the first test stage is considered validated if the following conditions are met:

[0153] - The stack comprising the heating layer 3 is intact, namely that no damage due to an electric arc is visible between the heating layer 3 and the surface of the contact layer 2 and / or between the heating layer 3 and the surface of the outer layer 6; and

[0154] - An insulation resistance measured by the resistance measuring device 410 is greater than 10 MO, in particular greater than 100 MO.

[0155] The value of the measured insulation resistance can be adjusted according to the specifications of the intended application.

[0156] Additionally, in order to confirm the reliability of the material, several repetitions of the test can be carried out successively.

[0157] Subsequently, a second test step consists of a verification of dielectric resistivity and leakage currents.

[0158] The test device 400 for the second test step is illustrated in Figure 5. Elements common to the test device of Figure 4 are indicated by the same references and will not be described again.

[0159] The test device 400 comprises a leakage current measuring device 420, for example in the form of an ammeter, in electrical connection with the electrodes 411 and 412 connected to the intermediate layer 4.

[0160] In addition, the test device 400 comprises a voltage source 430 in electrical connection with the leakage current measuring device 420 and the reservoir 401. For example, the voltage source 430 provides an electrical voltage of at least 1500 V in alternating current with a frequency between 50 Hz and 60 Hz.

[0161] In the second test step, the electrical voltage is applied. For this purpose, the electrical voltage is gradually increased between 0 V and twice the operating voltage of the de-icing and / or anti-icing device increased by 1000 V for 20 seconds. The resulting electrical voltage is then maintained for one minute.

[0162] A result of the second test stage is considered validated if the following conditions are met:

[0163] - The stack comprising the heating layer 3 and the intermediate layer 4 is intact, namely that no damage due to an electric arc between the components of the test device 400 and / or between the heating layer 3 and the intermediate layer 4 is visible;

[0164] - The stack comprising the heating layer 3 is intact, namely that no damage due to an electric arc is visible between the heating layer 3 and the surface of the contact layer 2 and / or between the heating layer 3 and the surface of the outer layer 6; and

[0165] - A leakage current measured by the leakage current measuring device 420 is less than 200 mA, in particular less than 50 mA, in particular less than 30 mA.

[0166] The leakage current value measured by the leakage current measuring device 420 can be adjusted according to the specifications of the intended application.

[0167] The intermediate layer 4 can be integrated into any stack of functional layers, requiring both electrical insulation and thermal conduction.

[0168] In the case of the thermoelectric frost protection mat 1 of Figure 1, the intermediate layer 4 arranged on the heating layer 3 improves the defrosting performance and makes it possible to reduce the heating temperature of the heating layer 3.

[0169] Reducing the temperature of the heating layer 3 presents an advantage for the integration of the frost protection mat 1 on temperature-sensitive parts, and in particular composite parts.

[0170] Furthermore, the matrix 41 is advantageously made of an elastomer, thus making it possible to adapt the intermediate layer 4 and the frost protection mat 1 to complex part shapes, in particular to three-dimensional parts, in particular non-developable three-dimensional parts.

[0171] The shaping is done with the unvulcanized elastomer, the intermediate layer 4 then being fixed by vulcanization. After vulcanization, however, it is possible to maintain elasticity for the intermediate layer 4.

[0172] Other applications than those of thermoelectric frost protection mats 1 are of course possible for the material just described, such as, for example, heat sinks).

[0173] Different techniques can be envisaged for assembling the different layers of the frost protection mat 1, according to the invention.

[0174] In one possible embodiment, the contact layer 2, which constitutes a thermal and electrical barrier, can be directly formed on the heating layer 3, in particular by projection.

[0175] Alternatively or in addition, the contact layer 2 comprises elastomer sheets which are superimposed manually or with automatic draping. The material of the contact layer 2 may be an elastomer, a polymer, in particular a thermoplastic polymer or a thermosetting polymer, in particular an epoxy resin. Similarly, the intermediate layer 4, which provides an electrical insulating and thermal conductor function and has a greater thermal conductivity than the contact layer 2 to direct the dissipation of the heat flow towards the external environment.

[0176] The reinforcing layer 5 can then be assembled to the intermediate layer 4 and the outer layer 6, for example by gluing.

[0177] The outer layer 6 can be formed directly on the reinforcing layer 5, in particular by projection.

[0178] In another possible embodiment, the various layers of the multi-layer structure are superimposed on each other, manually or by automatic draping, then assembled together by various assembly processes.

[0179] For the various bonding operations, the surfaces to be bonded can be prepared by any adhesion treatment, in particular dry or plasma.

[0180] A method of manufacturing the frost protection mat 1 may comprise at least the following steps taken separately or in combination:

[0181] - The contact layer 2, the intermediate layer 4 and / or the outer layer 6 are calendered from elastomer mixtures, advantageously used in a raw form during all stages of the manufacturing process;

[0182] - The heating layer 3 is preferably a heating resistor obtained by chemical cutting of a metal strip, a value of the heating resistance of the frost protection mat 1 being controlled during this step;

[0183] - The heating layer 3 is covered with at least one primer to allow a bond with the elastomers during the vulcanization step, the heating layer 3 being able to be made up of several pieces;

[0184] - a manufacturing tool, the geometry of which corresponds to the shape of the part BÀ to be protected against frost, is used, the manufacturing tool possibly being covered with a non-stick coating;

[0185] - The reinforcing layer 5 is a textile reinforcement adhered by the addition of chemical products, of primary types in aqueous solution or comprising a solvent, by dry method, by powder deposition, by plasma, etc.;

[0186] - The outer layer 6 is deposited on the manufacturing tool, in particular manually or automatically;

[0187] - The reinforcing layer 5, in particular possibly pre-scalloped to be able to fit the manufacturing tooling, is deposited on the outer layer 6; - The intermediate layer 4 is deposited on the reinforcing layer 5;

[0188] - The heating layer 3 is deposited on the intermediate layer 4;

[0189] - The electrical power connections are made, for example by soldering;

[0190] - Contact layer 2 is deposited on heating layer 3;

[0191] - A vacuum pocket is then created on the multi-layer structure thus formed;

[0192] - The whole is then vulcanized under vacuum in an autoclave oven;

[0193] - At the end of vulcanization, a demolding step is carried out and various finishing operations, such as a trimming operation, are carried out;

[0194] - A layer of paint 7 can be added on the outer layer 6;

[0195] - The frost protection mat 1 thus formed can subsequently be assembled to the part BÀ to be protected, for example by a cold bonding process.

[0196] The frost protection mat 1 thus produced can be added by gluing the contact layer 2 to the external surface 11 of the part BÀ to be protected.

[0197] Other assembly techniques other than gluing are also possible, such as, for example, co-curing or co-vulcanization, particularly when the BÀ part to be protected is made of a composite material.

[0198] An adhesion primer may be added before the adhesive is deposited on the BA part to be protected from frost and / or on the contact layer 2, at least one of the surfaces of the BA part or of the contact layer 2 intended to be attached to each other being able to be subject to a surface preparation treatment, such as abrasion, primer deposition or any other dry or plasma adhesion treatment.

[0199] In the foregoing description, the BA part to be protected was, for the purposes of the example, a leading edge of an aircraft wing.

[0200] The frost protection mat 1 according to the invention can be attached to any other aircraft part requiring protection against frost, such as engine air intakes, turbomachine rectifiers, airplane or helicopter propeller blades, propeller engine cones, protective radomes, etc.

[0201] It should be noted that the multi-layer structure proposed for the frost protection mat 1 is particularly flexible and conformable. It is capable of adapting to the different three-dimensional shapes that can be envisaged for BA parts.

[0202] In the case of a defrosting type operating mode, the heating layer 3 is advantageously supplied in cycles so as to allow detachment of frost which would have formed on the outer surface of the frost protection mat 1.

[0203] For example, in the case of a defrosting type operating mode, the heating layer 3 is supplied with electricity for a determined duration at regular intervals. Typically, in the case of a defrosting type operating mode, an electrical power applied to the heating layer 3 is between 1 W / cm2 and 3 W / cm2, in particular between 2 and 3 W / cm2.

[0204] In the case of an anti-icing type operating mode, the heating layer 3 is supplied continuously, so as to permanently prevent any formation of frost on the part BÀ to be protected from frost.

[0205] Typically, in the case of an anti-icing type operating mode, an electrical power applied to the heating layer 3 can reach up to 5 W / cm2.

[0206] In the detailed presentation of the invention given above, the terms used should not be considered as limiting the invention to the embodiments set forth in the description just given, but should be interpreted to include all equivalents the prediction of which is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching just disclosed to them.

Claims

CLAIMS 1. Frost protection mat (1) for a part (BA), in particular an aircraft part (BA), comprising a multi-layer structure with at least one heating layer (3), capable of generating a heat flow, characterized in that it comprises at least - a contact layer (2) forming at least one thermal barrier between the heating layer (3) and the part (BA), and at least one intermediate layer (4) and / or one reinforcing layer (5) and / or one thermally conductive outer layer (6) arranged between the heating layer (3) and an external environment.

2. Frost protection mat (1) according to claim 1, wherein an intermediate layer (4) has electrical insulating and thermally conductive properties.

3. Frost protection mat (1) according to any one of the preceding claims, wherein the reinforcing layer (5) is interposed between the intermediate layer (4) and the outer layer (6).

4. Frost protection mat (1) according to any one of the preceding claims, wherein the reinforcing layer (5) comprises a network of woven, non-woven and / or mesh fibers or threads.

5. Frost protection mat (1) according to any one of the preceding claims, wherein the reinforcing layer (5) is electrically conductive and is connected to a ground.

6. Frost protection mat (1) according to any one of the preceding claims, wherein an outer layer (6) is interposed between the reinforcing layer (5) and the external environment.

7. Frost protection mat (1) according to any one of the preceding claims, wherein the outer layer (6) is coated with a layer of paint (7).

8. Frost protection mat (1) according to any one of the preceding claims, wherein the heating layer (3), respectively the contact layer (2), the intermediate layer (4), the reinforcing layer (5) or the outer layer (6), has a thickness of less than 1.5 mm, in particular less than 1 mm, in particular less than 0.7 mm.

9. Frost protection mat (1) according to any one of the preceding claims, wherein the heating layer (3), respectively the contact layer (2), the intermediate layer (4), the reinforcing layer (5) or the outer layer (6), has a thickness greater than 0.2 mm, in particular greater than 0.3 mm, in particular of the order of 0.4 mm.

10. Assembly comprising at least one part (BÀ), in particular an aircraft part (BÀ), having an external surface (11), characterized in that the external surface (11) is covered by a frost protection mat (1) according to one of the preceding claims.

11. Method for placing a frost protection mat (1) according to one of claims 1 to 9 on an external surface (11) of a part (BA), in particular an aircraft part (BA), in which the contact layer (2) is bonded or co-vulcanized on the part (BA).

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