FR3144108A1 - Frost protection mat, particularly for an aircraft part - Google Patents

Abstract

The subject of the invention is an ice protection mat (1) of at least one part (BA), in particular an aircraft part (BA), comprising at least one heating layer (3), in particular integrating at least a heating resistor, and at least one reinforcing layer (5) interposed between the heating layer (3) and an external environment, characterized in that the reinforcing layer (5) has a thermal conductivity perpendicular to a general plane of extension of reinforcement (5) greater than 0.6 W/m.K. at room temperature. Figure for abstract: [FIG. 2]

Description

Frost protection mat, especially for an aircraft part FIELD OF THE INVENTION

The present invention relates to frost protection of aircraft parts. More particularly, it provides a frost protection mat used to protect aircraft parts from frost.

STATE OF THE ART

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

Furthermore, if pieces of ice formed or accumulated on any part of the aircraft fuselage or on engine air intakes become detached, such pieces may strike parts of the aircraft and damage it.

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

This is why aircraft are conventionally equipped with anti-icing devices, also called de-icers, installed, for example, on the leading edges of the wings, a rudder, a radome or even on engine air intakes.

Also, on propeller-driven devices, the leading edges of the blades or cones are usually equipped with frost protection devices.

Such frost protection devices function to remove frost or prevent frost from forming.

Combined frost protection devices for removing frost and preventing frost formation are also known.

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

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

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

Such a heating mat comprises a heating resistor encapsulated in a matrix of one or more elastomeric materials.

During take-off, landing or in flight, all parts equipped with such a heating mat in contact with the external environment may be subject to impacts, in particular impacts from hailstones, stones, etc., which may cause damage to such parts and seriously damage the heating mat.

Frost protection mat structures are already known in which the elastomer encapsulating the heating resistor is reinforced by a polyamide fabric providing shock protection. However, polyamides are poor thermal conductors.

We also know of multi-layer carpet structures comprising a heating resistor sandwiched between two Kapton films glued to each other. However, Kapton has poor thermal conductivity.

One aim of the invention is to propose a solution for protecting a frost protection mat of an aircraft part against impacts, without however degrading the dissipation of the heat flow towards a surface to be defrosted.

Yet another aim of the invention is to propose a solution which makes it possible to save space and reduce the thickness of such a frost protection mat used to protect aircraft parts from frost.

The invention relates to a frost protection mat structure, in particular for an aircraft part, having good temperature homogeneity.

For this purpose, a frost protection mat is proposed for at least one part, in particular an aircraft part, comprising at least one heating layer, in particular incorporating at least one heating resistor, and at least one reinforcing layer interposed between the heating layer and an external environment, characterized in that the reinforcing layer has a thermal conductivity perpendicular to a general plane of extension of the reinforcement greater than 0.6 W/m.K. at room temperature.

According to advantageous and non-limiting characteristics, taken alone or in any combination:

- the reinforcing layer comprises a network of woven, non-woven and/or mesh fibres or threads having a longitudinal thermal conductivity greater than 0.6 W/m.K. at room temperature;

- the fibers or threads of the reinforcing layer have a longitudinal thermal conductivity greater than 50 W/m.K at room temperature;

- the fibers or threads of the reinforcing layer have a longitudinal thermal conductivity greater than 120 W/m.K at room temperature;

- the reinforcing layer comprises carbon threads or fibers;

- carbon threads or fibres are pitch threads or fibres, in particular coal or petroleum pitch;

- the reinforcing layer comprises threads or fibers with a polyacrylonitrile (PAN) type precursor;

- the reinforcing layer comprises threads or fibers chosen from glass fibers, basalt fibers, silica fibers or metal threads.

Also provided is 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 presented above.

Preferably, a contact layer of the frost protection mat, interposed between the part and the heating layer, is glued or co-vulcanized on the part.

DESCRIPTION OF FIGURES

• La représente schématiquement un ensemble comportant une pièce et un tapis de protection au givre conforme à un mode de réalisation de l’invention ;
• La représente schématiquement une structure multicouche du tapis de protection au givre conforme à un mode de réalisation de l’invention ;
• La représente schématiquement un matériau composite d’une couche isolante électrique et conductrice thermique ;
• La illustre un dispositif de mesure pour déterminer une résistance électrique du tapis de protection au givre selon l’invention ; et
• La illustre un dispositif de mesure pour déterminer une résistance électrique et des courants de fuite du tapis de protection au givre selon l’invention.

Other features and advantages of the present invention will become apparent upon reading the following description of a preferred embodiment. This description will be given with reference to the appended figures, including:

• There schematically represents an assembly comprising a part and a frost protection mat in accordance with one embodiment of the invention;
• There schematically represents a multilayer structure of the frost protection mat according to one embodiment of the invention;
• There schematically represents a composite material of an electrically insulating and thermally conductive layer;
• There illustrates a measuring device for determining an electrical resistance of the frost protection mat according to the invention; and
• There illustrates a measuring device for determining an electrical resistance and leakage currents of the frost protection mat according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

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.

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 on the .

Furthermore, the longitudinal direction corresponds to a direction of extension of a fiber and/or a thread of a constituent element of a layer. The fibers and/or 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 on the .

There schematically represents an assembly comprising a BA part, in particular an aircraft BA part, 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.

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

The frost protection mat 1 comprises a multi-layer structure as shown schematically in the .

• une couche de contact 2, destinée à être en contact avec la pièce BA à protéger, en particulier le bord d’attaque, et ayant pour fonction est de constituer une barrière électrique et une barrière thermique ;
• une couche chauffante 3, destinée à être une source de chaleur apte à assurer une fonction de dégivrage et/ou d’antigivrage, notamment par effet Joule, pour la pièce BA à protéger ;
• une couche intermédiaire 4, destinée à assurer une fonction d’isolant électrique et de conducteur thermique ;
• une couche de renfort 5, destinée à assurer une fonction de protection du tapis de protection au givre 1, notamment la couche chauffante 3, des chocs ;
• une couche extérieure 6, destinée à assurer une fonction de résistance à l’environnement extérieur, notamment aux intempéries et aux conditions de température susceptibles d’être rencontrées par l’aéronef.

The multilayer structure includes in particular a stack of layers, in particular, according to the example presented in the , from the BA room, to be protected from frost, to an external environment:

• 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;
• 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;
• an intermediate layer 4, intended to provide an electrical insulating and thermal conductor function;
• a reinforcing layer 5, intended to provide a protection function for the frost protection mat 1, in particular the heating layer 3, from impacts;
• 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.

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.

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

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

According to the example of realization presented in , 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.

Contact layer 2 is designed to be in contact with the BA part to be protected, in particular the leading edge, and its function is to constitute an electrical barrier and a thermal barrier.

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

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

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.

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

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

Thus configured, the contact layer 2 protects the BA part 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 BA part to be protected against frost.

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

In particular, the contact layer 2 may have a volume resistivity of at least 1E9 Ω.m, preferably greater than 1E10 Ω.m.

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/m.K at room temperature. By room temperature, is meant, throughout the present description, a temperature of the order of 20°C.

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 example of realization presented in , 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.

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 BA part to be protected.

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

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

For example, the heating layer 3 can integrate a mesh of metal tracks intended to be traversed by a current to generate the heat flow by Joule effect.

The metal tracks can 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 spacing of the metal tracks greater than that currently possible according to the state of the art.

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.

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

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

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.

According to the example of realization presented in , 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.

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

In particular, the intermediate layer 4 can be made of a composite material chosen to have good electrical insulation and good thermal conduction properties.

The intermediate layer 4 helps to direct the heat flow generated by the heating layer 3 towards the external surface of the frost protection mat 1, i.e. opposite the contact layer 2 and therefore the BA part to be protected against frost.

In particular, the intermediate layer 4 may have a volume resistivity of at least 1E9 Ω.m, preferably greater than 1E10 Ω.m.

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/m.K at room temperature, in particular greater than 0.6 W/m.K at room temperature, in particular greater than 0.8 W/m.K at room temperature, specifically greater than 1.5 W/m.K at room temperature, determined according to the methods described in the ISO 8302 or ASTM 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 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 on the , the intermediate layer 4 can be made of a composite material 40 comprising a matrix 42 and inclusions 41.

According to the example of realization presented in , 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.

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

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 BA part to be protected against frost.

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

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/m.K at room temperature, in particular greater than 0.6 W/m.K at room temperature, in particular greater than 0.8 W/m.K at room temperature, specifically greater than 1.5 W/m.K at room temperature, determined according to the methods described in the ISO 8302 or ASTM C177 standards.

More specifically, the reinforcing layer 5 may comprise fibers and/or threads. In such a configuration, the fibers and/or threads of the reinforcing layer may further have a longitudinal thermal conductivity greater than 0.6 W/m.K at room temperature.

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.

The longitudinal thermal conductivity at room temperature greater than 10 W/m.K allows a longitudinal homogenization of the temperature of the reinforcement layer 5, i.e. in the general plane of extension of the reinforcement layer 5.

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

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.

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 flow emitted by the metal tracks of the heating layer 3 is longitudinally heterogeneous.

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

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 spaced further apart from each other compared to what is currently possible in the known solutions of the state of the art.

Consequently, the invention thus offers the possibility of using manufacturing technologies for 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/m.K.

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/m.K.

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.

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.

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/m.k, in particular greater than 10 W/m.K, and/or a longitudinal thermal conductivity greater than 50 W/mK, in particular greater than 120 W/m.K.

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

It will further be noted that the reinforcing layer 5 can also participate in the protection function participate in the protection function against electrostatic discharges, also called by the acronym “ESD” for “ElectroStatic discharge” in English.

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.

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

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 example of realization presented in , 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.

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

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

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.

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

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

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

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

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.

According to the example of realization presented in , the paint layer 7 can be applied to the multilayer structure so as to cover the multilayer structure.

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.

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

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 of 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.

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

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.

The maximum operating temperature of the frost protection mat 1 is a temperature likely to be reached by the heating layer 3 during generation of the heat flow necessary for a defrosting cycle.

Since 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.

Since the heating layer 3 is covered by the intermediate layer 4, there is further an accumulation effect 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.

Preferably, the matrix 42 is made of a thermosetting polymer, in particular an elastomer material or an epoxy resin.

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

To obtain good resistance and guarantee suitable mechanical properties in the range of operating temperatures 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.

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.

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.

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 fixing of the position of the inclusions 41.

Another advantage of such vulcanization shaping is the possibility of co-vulcanization with another material of an adjacent layer, for example the heating layer 3 with which close contact is necessary.

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.

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

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 1E9 Ω.m, preferably greater than 1E10 Ω.m.

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.

Furthermore, inclusions 41 have a thermal conductivity greater than 1.5 W/m.K at room temperature, in particular greater than 20 W/m.K.

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 towards the surface to be defrosted.

By increasing the heat flow transmission, it is possible to achieve savings in the energy required to ensure the defrosting and/or anti-frosting function for the BA part to be protected.

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.

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 BA part to be protected remains within a reasonable range.

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

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

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

According to a particular embodiment, the inclusions 41 have a volume rate 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.

Such a volumetric rate 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.

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

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.

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.

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

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

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.

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 can be between 0.2 mm and 0.7 mm, typically a thickness of the order of 0.4 mm.

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…

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.

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.

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

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.

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

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.

Alternatively, 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 immersed in the quantity of water 402.

Subsequently, 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.

An electrical voltage, in particular an electrical voltage of 500 V continuous, 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 the operating voltage of the defrosting and/or anti-frosting device for the BA part to be protected from frost, which can 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 can be supplied at 110 V.

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

• L’empilement comportant la couche chauffante 3 est intact, à savoir qu’aucun dommage dû à un arc électrique n’est visible entre la couche chauffante 3 et la surface de la couche de contact 2 et/ou entre la couche chauffante 3 et la surface de la couche extérieure 6 ; et
• Une résistance d’isolation mesurée par le dispositif de mesure de résistance 410 est supérieure à 10 MΩ, notamment supérieure à 100 MΩ.

A result of the first test step is considered validated if the following conditions are met:

• 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
• An insulation resistance measured by the resistance measuring device 410 is greater than 10 MΩ, in particular greater than 100 MΩ.

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

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

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

The test device 400 for the second test step is illustrated by the . The common elements of the test device of the are indicated by the same references and will not be described again.

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.

In addition, the test device 400 comprises a voltage source 430 in electrical connection with the leakage current measuring device 420 and the tank 401. As an 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.

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 defrosting and/or anti-icing device increased by 1000 V for 20 seconds. The electrical voltage obtained is then maintained for one minute.

• L’empilement comportant la couche chauffante 3 et la couche intermédiaire 4 est intact, à savoir qu’aucun dommage dû à un arc électrique entre les composants du dispositif de test 400 et/ou entre la couche chauffante 3 et la couche intermédiaire 4 n’est visible ;
• L’empilement comportant la couche chauffante 3 est intact, à savoir qu’aucun dommage dû à un arc électrique n’est visible entre la couche chauffante 3 et la surface de la couche de contact 2 et/ou entre la couche chauffante 3 et la surface de la couche extérieure 6 ; et
• Un courant de fuite mesuré par le dispositif de mesure de courant de fuite 420 est inférieur à 200 mA, en particulier inférieur à 50 mA, notamment inférieur à 30 mA.

A result of the second test step is considered validated if the following conditions are met:

• 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;
• 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
• 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.

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

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

In the case of the thermoelectric frost protection mat 1 of the , 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.

The reduction in 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.

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.

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.

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).

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

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.

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 insulator 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.

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

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

In another possible implementation mode, the various layers of the multilayer structure are superimposed on each other, manually or by automatic draping, then assembled together by various assembly processes.

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

• La couche de contact 2, la couche intermédiaire 4 et/ou la couche extérieure 6 sont calandrés à partir de mélanges élastomères, avantageusement utilisés sous une forme crue durant toutes les étapes du procédé de fabrication ;

• La couche chauffante 3 est préférentiellement une résistance chauffante obtenue par découpe chimique d’un feuillard métallique, une valeur de la résistance chauffante du tapis de protection au givre 1 étant contrôlée lors de cette étape ;
• La couche chauffante 3 est recouverte d’au moins un primaire pour permettre une liaison avec les élastomères lors de l’étape de vulcanisation, la couche chauffante 3 pouvant être constituée de plusieurs morceaux ;
• un outillage de confection, dont une géométrie correspond à la forme a pièce BA à protéger contre le givre, est utilisée, l’outillage de confection pouvant être éventuellement recouvert d’un anti-adhérent ;
• La couche de renfort 5 est un renfort textile adhérisé par un apport de produits chimiques, de types primaires en solution aqueuse ou comprenant un solvant, par voie sèche, par un dépôt de poudre, par plasma etc. ;
• La couche extérieure 6 est déposée sur l’outillage de confection, notamment manuellement ou de façon automatisée ;
• La couche de renfort 5, en particulier éventuellement préalablement festonné pour pouvoir épouser l’outillage de confection, est déposée sur la couche extérieure 6 ;
• La couche intermédiaire 4 est déposée sur la couche de renfort 5 ;
• La couche chauffante 3 est déposée sur la couche intermédiaire 4 ;
• Les connexions électriques d’alimentation sont réalisées, par exemple par soudure ;
• La couche de contact 2 est déposée sur la couche chauffante 3 ;
• Une poche à vide est ensuite réalisée sur la structure multicouche ainsi constituée ;
• L’ensemble est ensuite vulcanisé sous vide dans un four autoclave ;
• A l’issue de la vulcanisation, une étape de démoulage est opérée et différentes opérations de finition, telles que notamment une opération de détourage, sont réalisées ;
• Une couche de peinture 7 peut être ajoutée sur la couche extérieure 6 ;
• Le tapis de protection au givre 1 ainsi constitué pourra être par la suite assemblé à l la pièce BA à protéger, par exemple par un procédé de collage à froid.

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

• 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;

• 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 checked during this step;
• 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;
• a manufacturing tool, the geometry of which corresponds to the shape of the BA part to be protected against frost, is used, the manufacturing tool possibly being covered with a non-stick coating;
• 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.;
• The outer layer 6 is deposited on the manufacturing tool, in particular manually or automatically;
• The reinforcing layer 5, in particular possibly previously scalloped to be able to fit the manufacturing tooling, is deposited on the outer layer 6;
• The intermediate layer 4 is deposited on the reinforcement layer 5;
• The heating layer 3 is deposited on the intermediate layer 4;
• The electrical power connections are made, for example by soldering;
• Contact layer 2 is deposited on heating layer 3;
• A vacuum pocket is then made on the multi-layer structure thus formed;
• The whole is then vulcanized under vacuum in an autoclave oven;
• At the end of vulcanization, a demolding step is carried out and various finishing operations, such as a trimming operation, are carried out;
• A layer of paint 7 can be added on the outer layer 6;
• The frost protection mat 1 thus formed can subsequently be assembled to the BA part to be protected, for example by a cold bonding process.

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

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

An adhesion primer may be added before depositing the glue 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, deposition of primer or any other dry or plasma adhesion treatment.

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

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.

It should be noted that the multi-layer structure proposed for the frost protection mat 1 is particularly flexible and conformable. It is able to adapt to the different three-dimensional shapes that can be envisaged for BA parts.

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 may have formed on the outer surface of the frost protection mat 1.

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/cm ² and 3 W/cm ² , in particular between 2 and 3 W/cm ² .

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 BA part to be protected from frost.

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/cm ² .

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 a person skilled in the art by applying his general knowledge to the implementation of the teaching just disclosed to him.

Claims (10)

Frost protection mat (1) for at least one part (BA), in particular an aircraft part (BA), comprising at least one heating layer (3), in particular incorporating at least one heating resistor, and at least one reinforcing layer (5) interposed between the heating layer (3) and an external environment,
characterized in that the reinforcing layer (5) has a thermal conductivity perpendicular to a general plane of extension of the reinforcement (5) greater than 0.6 W/mK at room temperature. Frost protection mat (1) according to claim 1, wherein the reinforcing layer (5) comprises a network of woven, non-woven and/or mesh fibres or threads having a longitudinal thermal conductivity greater than 0.6 W/m.K. at room temperature. Frost protection mat (1) according to claim 2, wherein the fibers or threads of the reinforcing layer (5) have a longitudinal thermal conductivity greater than 50 W/m.K at room temperature. Frost protection mat (1) according to claim 3, wherein the fibers or threads of the reinforcing layer (5) have a longitudinal thermal conductivity greater than 120 W/m.K at room temperature. Frost protection mat (1) according to one of claims 2 to 4, in which the reinforcing layer (5) comprises carbon threads or fibers. Frost protection mat (1) according to claim 5, wherein the carbon threads or fibres are pitch threads or fibres, in particular coal or petroleum pitch. Frost protection mat (1) according to one of claims 2 to 5, in which the reinforcing layer (5) comprises threads or fibers with a precursor of polyacrylonitrile (PAN) type. Frost protection mat (1) according to one of claims 2 to 5, in which the reinforcing layer (5) comprises threads or fibers chosen from glass fibers, basalt fibers, silica fibers or metal threads. Assembly comprising at least one part (BA), in particular an aircraft part (BA), 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. Assembly according to claim 9, in which a contact layer (2) of the frost protection mat (1), interposed between the part (BA) and the heating layer (3), is glued or co-vulcanized on the part (BA).