Sandwich panels incorporating a heating function

Abstract

The invention relates to a sandwich panel comprising a thermally conductive upper skin and a lower skin; a core disposed between the upper and lower skins; and a heating resistive cable. The panel is characterized in that the heating resistive cable is single-conductor, the core comprises one or more cavities, the single-conductor heating resistive cable being housed in one or more cavities of the core, and the coverage rate is greater than 70%. The invention also relates to its manufacturing process, its use in a railway or aeronautical vehicle, and a floor or partition incorporating it. Abstract: Figure 1

Description

Title of the invention: SANDWICH PANELS INCORPORATING A HEATING FUNCTION Technical field

[0001] The present disclosure relates to the field of panels incorporating a heating function, a method of manufacturing them and their uses. Prior art

[0002] It is known to manufacture composite panels having a sandwich architecture used for the production of floors or partitions in the interior of means of transport, such as train cabins, airplanes, cable cars, elevators or used in the building sector for heating homes or common areas. In order to control the temperature inside the enclosures and ensure thermal comfort, the sandwich panels can integrate a heating function.

[0003] Current composite panels include heating devices that are generally electrical. For example, heating elements configured in the form of heating films are glued to conventional floor panels installed in passenger compartments of railway vehicles and covered with floor covering. These heating films, especially those with an IP rating of at least 66 (minimum IP66 rating), are not hermetically sealed, so that penetrating moisture can damage them. The IP rating indicates the degree of protection of the device against the penetration of solid bodies (1st digit) and against the penetration of water (2nd digit). The classification is carried out in increasing efficiency. It is assigned to the material following a series of tests defined by the NF EN 60.529 standard, the IP standard is published by the IEC (in English International Electrotechnical Commission - the International Electrotechnical Commission).

[0004] Sandwich panels generally have a configuration where a core is placed between two skins. This does not exclude the presence of additional layers that can be integrated into the panel to provide additional functions, such as heating, acoustic or mechanical functions. Heating elements can be encapsulated in a film (Cu, Al, stainless steel), the latter being able to be integrated in the form of a layer in a sandwich panel or backed onto one of the skins of the panel. A floor according to the prior art is illustrated schematically in [Fig.l]. The floor 1 can be composed of an aluminum sandwich panel with a honeycomb 14 between two aluminum skins (13, 15). The sandwich panel is composed of an upper skin 15, a honeycomb core 14 and a lower skin 13. Above this sandwich panel is a re floor covering 16, such as carpet. The sandwich panel comprises a heating film 12 encapsulating the heating elements. The heating film 12 is backed against the lower skin of the panel 13, located between the latter and an insulating wool 11. The heating film 12 is self-adhesive, it is glued to the skin of the panel 13 using a transfer adhesive.

[0005] According to the experiments of the present Applicant, the data from the thermal behavior tests of heating panels incorporating heating films encapsulating the heating function show that the panels are sometimes subject to problems of temperature inhomogeneity. Indeed, this is due to several factors including edge effects: heat losses on the edges of the panel due to the aluminum profiles thereof but also to numerous external factors such as mechanical constraints and variations in environmental conditions in the case of vehicles. In addition, the problems of temperature inhomogeneity can also be due to the concentration of heat around the heating films. Indeed, the heating films have a homogeneous construction thus leading to greater heating in the center of the film than at its ends, therefore less homogeneity.As a result, temperature peaks occur at the heating elements and reduce the heating power or lead to unnecessarily high energy consumption to achieve the desired temperature in the passenger compartment.

[0006] Furthermore, the shape of the films adapts poorly to the shapes of the panels, or not at all in the case of panels with more complex or irregular geometry. Consequently, parts of the panels risk being heated little or not at all, because they are not covered by these films. These panels have an insufficient coverage rate.

[0007] There is therefore a need to provide panels allowing a more homogeneous diffusion of the same quantity of heat over the entire surface thereof, or at least more controlled, presenting a high coverage rate and this without particular constraint imposed by the geometry of the panel.

[0008] Although efficient, heating films nevertheless have many limitations. On the one hand, their cost remains high. On the other hand, as explained above, heating films have a standard architecture that is not very adaptable. Indeed, each change in panel geometry requires a change in the architecture of the film. In turn, any change in the internal architecture of the heating films (for example, arrangement of the heating elements inside the film) requires a change in tooling, which involves additional costs and delays during the manufacturing process. Its production process is therefore not flexible, and therefore not very attractive.

[0009] We therefore remain in search of a sandwich panel easily integrating a heating function, said panel allowing a homogeneous distribution of heat. and a good coverage rate, while minimizing heat loss, particularly at the side edges. This disclosure improves the situation. Summary

[0010] According to a first aspect, the invention relates to a sandwich panel comprising: - a thermally conductive upper skin and a lower skin; - a core arranged between the upper skin and the lower skin and - a resistive heating cable; said panel being remarkable in that the resistive cable is single-conductor, the core comprises one or more cavities, the single-conductor heating resistive cable being housed in one or more cavities of the core and in that the coverage rate is greater than 70%.

[0011] By adapting the structure of the core, it is possible to place the heating means there, possibly by pressure, before adding the skins to manufacture the panel. This new heating system will allow the heat to be selectively distributed through the skins of the panel. Indeed, the core protects the heating means from the ambient environment, in particular from external temperature variations and mechanical shocks. Thus, heat losses at the edges of the panel are limited. The core also provides electrical insulation to prevent current leaks outside the panel, for example into the floor or partition of which the panel is part.

[0012] Such a panel therefore allows for uniform and efficient heating while having a rigid structure, resistant to mechanical shocks and sufficiently thin.

[0013] Furthermore, the manufacturing process of these panels is flexible because the shape of the circuit of the single-conductor resistive cable can be easily adapted by adapting the arrangement of the cavity(ies) according to the needs and application of the person skilled in the art.

[0014] A panel according to the invention has a coverage rate greater than 70%, preferably greater than 75%, more preferably greater than 80%, whereas a panel incorporating heating films rarely achieves a coverage rate greater than 66% (ratio between the surface covered by a heating film and the total surface of a panel).

[0015] In order to ensure uniform heating, it is estimated, according to the invention, that the coverage rate is greater than 70%.

[0016] According to the invention, by "coverage rate" is meant the ratio between the surface area covered by the single-conductor resistive heating cable and the total surface area of ​​a panel.

[0017] According to another aspect, there is provided a method of manufacturing a panel according to the first aspect comprising the following steps: - Provide two skins and a core with one or more cavities provided; - Place a single-conductor resistive heating cable inside the cavities; - Apply an adhesive layer to each of the two faces of the core; - Cover the faces of the core with the skins so as to form a together ; - Press the whole thing for more than 20 minutes.

[0018] According to another aspect, there is proposed a use of a panel according to the first aspect or obtained according to the second aspect in a railway vehicle as a heating panel by circulation of an electric current in the single-conductor resistive heating cable.

[0019] According to another aspect, there is proposed a use of a panel according to the first aspect or obtained according to the second aspect in an aeronautical vehicle as a heating panel by circulation of an electric current in the single-conductor resistive heating cable.

[0020] According to another aspect, there is provided a floor or a partition comprising a panel according to the first aspect or obtained according to the second aspect.

[0021] The features set out in the following paragraphs may, optionally, be implemented, independently of one another or in combination with one another:

[0022] - the core has a total thickness EA and one or more cavities has a depth PC, the depth PC being less than the total thickness EA of the core;

[0023] - two adhesive layers can be located on either side of the core so as to to connect the upper face of the core to the upper skin and the lower face of the core to the lower skin;

[0024] - the upper and lower skins can be made of aluminum;

[0025] - the core can be a polymeric foam;

[0026] - the diameter of the cavity can be between 0.5 mm and 5.5 mm;

[0027] - the panel may be devoid of a thermally conductive layer arranged between the heating means and the thermally insulating layer;

[0028] - the cable can extend along the length of the cavity or each of the cavities, the or the cavities being grooves having a section of depth PC between 2 mm and 8 mm and width between 1 mm and 5.5 mm;

[0029] - the single-conductor resistive heating cable may comprise a resistive conductor and an electrically insulating envelope;

[0030] - the diameter of the single-conductor resistive heating cable can be between 1 mm and 5mm, preferably between 1.2mm and 3mm;

[0031] - the cavity(ies) have a groove entrance width greater than the diameter of the cable, said cavity can be sized to allow the insertion of the cable in elastically deforming the throat inlet(s) of said cavity(ies);

[0032] - the core has an upper face adjacent to the thermally conductive upper skin mically and a lower face adjacent to the lower skin and in that the core comprises one or more cavities provided opening onto at least one of the faces of the core;

[0033] - the panel having an intermediate portion located between two edge zones, said panel being characterized in that the coverage density of the resistive cable is greater at two edge zones of the panel compared to an intermediate portion. Brief description of the drawings

[0034] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which: Fig.l

[0035] [Fig.l] shows a diagram of a section along a plane perpendicular to the floor comprising a sandwich panel according to the prior art. Fig. 2

[0036] [Fig.2] shows a diagram of a section along a plane perpendicular to the panel in sandwich according to one embodiment. Fig. 3

[0037] [Fig.3] shows a simplified diagram of a top view of a path of the cavity of a sandwich panel according to one embodiment, the resistive cable winding along the path homogeneously over the surface of the panel, with a period of the undulations of the path of constant value along a direction of the panel. Fig. 4

[0038] [Fig.4] shows a simplified diagram of a top view of a cavity path of a sandwich panel according to one embodiment, the resistive cable winding along the path, in a heterogeneous manner, the period of the undulations of the path at two edge zones of the panel being of a value lower than the period value of the undulations at an intermediate central portion between the two edge zones.

[0039] Description of the embodiments

[0040] According to a first aspect, the invention proposes a sandwich panel comprising: - a thermally conductive upper skin and a lower skin; - a core arranged between the upper skin and the lower skin and - a resistive heating cable; said panel being remarkable in that the resistive cable is single-conductor, the core comprises one or more cavities, the single-conductor resistive heating cable being housed in one or more cavities of the core and in that the coverage rate is greater than 70%.

[0041] By "sandwich panel" is meant an assembly comprising at least three layers, in this case a structure having an intermediate layer, hereinafter called core, between two external layers, hereinafter called upper skin and lower skin.

[0042] The panel has a coverage rate greater than 70%, preferably greater than 75%, more preferably greater than 80%, or even greater than 85%. The panel has a coverage rate between 70% and 99%, preferably between 75% and 95%, more preferably between 80 and 90%.

[0043] Thermally conductive upper skin

[0044] The thermally conductive upper skin ensures the homogeneous radiation of the heat produced by the resistive cable and mechanical resistance while providing sealing properties.

[0045] By "thermal conductor" we mean a material which is characterized by its capacity to diffuse heat in the media without macroscopic movement of matter. It is the ratio of the thermal energy (quantity of heat) transferred per unit of time (therefore homogeneous to a power, in watts) and surface to the temperature gradient. Thermal conduction can take place quickly or slowly, or even very slowly.

[0046] The material constituting the upper skin may be chosen so as to diffuse heat evenly. This material may, for example, have good heat conductivity and possess good thermal inertia. Good thermal inertia means a rapid rise in temperature and slow diffusion of heat by radiation.

[0047] The upper skin may be a skin made of aluminum, steel, stainless steel, plastic (for example acrylonitrile butadiene styrene ABS, polycarbonate, etc.) or plywood or similar, or an assembly thereof obtained by thermosetting or thermoplastic bonding. The upper skin may be a single-ply or multi-ply composite material comprising glass, flax, carbon, basalt fibers or a mixture thereof, the constituent parts of said composite material being bonded by thermosetting or thermoplastic resins. This list is not exhaustive and the person skilled in the art will be able to choose the appropriate material for the upper skin according to their needs.

[0048] The upper skin may be made of aluminum, for example an aluminum sheet.

[0049] The upper skin may have a thickness of at least 0.1 mm, preferably between 0.3 mm and 5 mm, preferably between 0.3 mm and 3 mm.

[0050] According to one embodiment, the upper skin is an aluminum sheet. having a thickness of at least 0.1 mm.

[0051] The person skilled in the art will know how to choose the properties of the upper skin according to the field of application of the floors or partitions comprising this panel.

[0052] Lower skin

[0053] The lower skin may be the same or different from the upper skin.

[0054] The lower skin provides mechanical resistance and can also provide a homogeneous radiation of the heat produced by the resistive cable.

[0055] The lower skin may be a skin made of aluminum, steel, stainless steel, plastic (for example acrylonitrile butadiene styrene ABS, polycarbonate, etc.) or plywood or similar, or an assembly thereof obtained by thermosetting or thermoplastic bonding. The lower skin may be a single-ply or multi-ply composite material comprising glass, flax, carbon, basalt fibers or a mixture thereof, the constituent parts of said composite material being bonded by thermosetting or thermoplastic resins. This list is not exhaustive and the person skilled in the art will be able to choose the appropriate material for the lower skin according to their needs.

[0056] The lower skin may be made of aluminum, for example an aluminum sheet, thus ensuring the mechanical strength of the panel.

[0057] The lower skin may have a thickness of at least 0.1 mm, preferably between 0.3 mm and 5 mm, preferably between 0.3 mm and 3 mm.

[0058] According to one embodiment, the lower skin is an aluminum sheet having a thickness of at least 0.1 mm.

[0059] The person skilled in the art will know how to choose the properties of the lower skin according to the field of application of the floors or partitions comprising this panel.

[0060] Soul

[0061] The core is disposed between the upper skin and the lower skin. The core has an upper face that can be adjacent to the thermally conductive upper skin and a lower face that can be adjacent to the lower skin.

[0062] For the purposes of the invention, the term "core" means a layer incorporating the resistive cable, this layer being located between the upper skin and the lower skin of the panel, but the upper and lower faces of the core are not necessarily adjacent to each of the skins.

[0063] The core can be rigid, resistant to bending.

[0064] The panel may comprise other additional layers between the core and at least one of the upper and lower skins, such as an acoustic insulation layer. The panel may also comprise a repeating pattern between the two upper and lower skins, this repeating pattern being able to be formed of one or more cores alternating with other additional layers.

[0065] The core may also comprise one or more reinforcements extending between the upper and lower skins of the panel so as to reinforce the mechanical properties thereof. Indeed, thanks to its flexible manufacturing process, the cavity or cavities of the panel can be arranged so as to bypass the reinforcements. Such an architecture is difficult to achieve, or even impossible, with heating films according to the prior art.

[0066] The core may be thermally insulating, made of a material having low thermal conductivity, i.e. capable of opposing the thermal flow passing through it with high thermal resistance.

[0067] The core is chosen so as to limit the heat losses generated by the single-conductor cable. The core plays a dual role: to limit heat losses and to contribute to the mechanical resistance of the panel.

[0068] The core may be in the form of a foam, for example a polymeric foam. The foam may have open or closed cells with homogeneous or variable density.

[0069] The core has good water and air tightness and good mechanical properties, particularly in bending. The core can protect against shocks and vibrations and also offers significant performance in acoustic insulation.

[0070] The core is chosen so as to be able to form cavities either on its surface or in its core.

[0071] The material constituting the core may be chosen from an aluminum or synthetic honeycomb (for example: aramid, polypropylene, etc.), rock wool, glass wool, polyurethane, polyethylene terephthalate (PET), polyethylene (PE), expanded polyethylene, polyetherimide (PEI), polyamide (PA), a core of biosourced origin, such as plywood, wood, cork, bamboo, or mixtures thereof. This list is not exhaustive and the person skilled in the art will be able to choose the appropriate material for the core according to their needs.

[0072] The core may have a density of between 1 and 1000 kg / m3, preferably between 20 and 350 kg / m3, more preferably between 80 and 150 kg / m3.

[0073] The core comprises one or more cavities for housing the single-conductor resistive cable.

[0074] The core may comprise one or more cavities provided opening onto one of its faces, the resistive heating cable being housed in one or more cavities. A face of the core having cavities provided may be adjacent to one of the skins of the panel.

[0075] Indeed, the core may comprise one or more cavities provided opening either on its upper face or on its lower face or on both its upper and lower faces.

[0076] The core may comprise one or more cavities provided without opening onto any of its upper or lower faces.

[0077] The cavity(ies) are sized and arranged so as to furrow the core and to make it possible to obtain a panel having a coverage rate greater than 70%.

[0078] Figures 3 and 4 show simplified diagrams of a top view of a path of the cavity of a sandwich panel according to two embodiments.

[0079] According to the first embodiment of [Fig.3], the resistive cable 5 winds along the path which comprises undulations along a direction of the panel, and in a homogeneous manner over the surface of the panel, namely that the period of the undulations of the path of constant value along a direction of the panel. According to such an embodiment, a temperature gradient may appear in use during heating and along the direction of the undulations, and due to edge losses; the temperature of the panel measured at the two edge zones of the panel may be lower than the temperature measured at an intermediate central zone.

[0080] It is possible to smooth this gradient by the design of the second embodiment according to [Fig.4], the resistive cable 5 winding along the path, in a heterogeneous manner, the period of the undulations of the path at two edge zones of the panel being of a value lower than the period value of the undulations at an intermediate central portion between the two edge zones.

[0081] Generally, the sandwich panel may have a higher resistive cable coverage density at two edge areas of the panel, and compared to an intermediate portion of the panel between the two edge areas.

[0082] By "coverage density" is meant the ratio of the length of the resistive cable per unit area of ​​the sandwich panel.

[0083] It is preferably sought to limit the temperature difference between the edge zones and the central portion to less than 4°C, preferably less than or equal to 2°C.

[0084] In addition to the upper and lower faces, the core has a slice defined by its thickness EA. By "total thickness of the core EA" is meant the thickness of the core measured on its untreated portion, as illustrated in [Fig.2].

[0085] The core has a total thickness EA and one or more cavities has a depth PC, the depth PC being less than the total thickness EA of the core.

[0086] The depth of the cavity may be between 2 mm and 8 mm. The width of the cavity may be between 1 mm and 5.5 mm.

[0087] The core may have a total thickness greater than 8 mm, preferably between 8 and 50 mm.

[0088] One or more cavities have a depth. By "depth" is meant the depth of a cavity measured along a single plane perpendicular to the panel.

[0089] For example, a depth PC, as illustrated in [Fig.2], corresponds to the distance between the groove entrance EG of a cavity and the bottom of a cavity FC when the latter is arranged to open onto one of the faces of the core.

[0090] By “groove entrance” we mean the perimeter of a cavity when it is arranged to open onto one of the faces of the core.

[0091] When one or more cavities are provided inside the core without opening onto one of the faces, then the depth of such a cavity corresponds to the maximum distance of this cavity measured along a single plane perpendicular to the panel.

[0092] When one or more cavities are provided inside the core without opening onto one of the faces and one or more cavities are provided to open onto one of the faces of the core on the same panel, each of them has a depth depending on the location of the core where it is located. However, the sum of the depths of the cavities along a single plane perpendicular to the panel remains less than the total thickness EA of the core. When these are provided along different planes perpendicular to the panel, then the sum of the depths of the cavities may exceed the total thickness EA of the core, as long as the sum of the depths of the cavities along a single plane perpendicular to the panel remains less than the total thickness EA of the core.

[0093] A cavity depth of less than 1 mm would be insufficient to hold the heating means in place. Conversely, too great a cavity depth in a single plane would constitute points of weakness in the structure of the core, which would harm the mechanical strength of the panels.

[0094] The cable may extend along the length of the cavity or each of the cavities, the cavity or cavities being grooves having a section of depth PC between 2 mm and 8 mm and of width between 1 mm and 5.5 mm.

[0095] By “width” we mean the maximum distance between the sides of a cavity measured along a plane parallel to the panel.

[0096] It is noted that all of the dimensions given relating to the panel described above are given in the final panel when it is already pressed and assembled. However, within the meaning of the invention, the core retains its thickness before and after assembly.

[0097] The core may be arranged to form cavities opening onto its upper face by additive manufacturing or by etching. According to the invention, the cavities may be preformed grooves, for example by machining / etching or by hot wire cutting, in the foam before the integration of the cable or grooves formed during the integration of the cable under pressure, by pressing. Preferably, the cavities are preformed grooves.

[0098] The cross-section of the cavity may have a rounded, circular, rectangular shape. tangular, U-shaped, omega Q-shaped, or any other shape that allows the heating means to be integrated. The shape of the cavities will be chosen by the person skilled in the art according to their needs so that they are sized to allow the heating means to be integrated. In the case of engraving, the person skilled in the art will know how to choose the shape of the head of the frieze adapted to obtain cavities adapted to their needs.

[0099] The cavity(ies) have a groove entry width greater than the maximum width of the cavity. This allows for better retention of the cable inside the cavity(ies).

[0100] The cavity(ies) may have a groove entry width greater than the diameter of the cable, said cavity being able to be sized to allow the insertion of the cable by elastically deforming the groove entry(s) of said cavity(ies).

[0101] Single-conductor resistive heating cable

[0102] The resistive heating cable is a single-conductor resistive cable.

[0103] The resistive heating cable may have a round cross-section.

[0104] Resistive heating cable means a cable with a resistance value in ohms high, preferably between 1 and 4000 Q / m.

[0105] The diameter of the single-conductor resistive heating cable may be between 1 mm and 5 mm, preferably between 1.2 mm and 3 mm.

[0106] The single-conductor resistive heating cable may comprise a resistive conductor and an electrically insulating jacket. The single-conductor resistive heating cable may contain therein a spiral system for generating heat from a power supply. The resistive conductor may be spirally disposed around an electrically non-conductive central core serving as a mechanical support for said conductor.

[0107] The electrically insulating envelope may have a thickness between 0.2 and 0.4 mm. It may be made of a polymeric material, such as a fluorinated ethylene propylene resin.

[0108] Preferably, the heating means is not a double-conductor cable.

[0109] Single-core heating cables are cables in which heat is released by the Joule-Lenz effect when the electric current passes through the heating core. The cable is designed so that a complete drop in the applied voltage occurs in the heating core, but the cable elements do not overheat beyond the permissible values. Cables of this type may have a heating core having a linear or spiral shape. This cable is connected at each of the ends, hence the need to form a continuous circuit.

[0110] The person skilled in the art will know how to choose the architecture of the cavities engraved in the core so as to homogenize the heat distribution at a given surface power.

[0111] For example, in the case of a simple 230V connection, the single-core cable has a single-phase connection, it is composed of a single conductor and the power supply is also single-phase. In this case, the cable will be installed in a serpentine pattern, necessarily making a round trip to the connection point. The upper face of the core is therefore etched accordingly. Such an embodiment is illustrated in [Fig.4]. This schematically illustrates a view of the upper face of the core 4. The heating means 5 is an electric cable which follows a serpentine circuit.

[0112] Another example, this time in the case of a three-phase connection, the single-core cables will be mounted in a star configuration. The upper face of the core is therefore etched accordingly. Each cable will be connected to each of the phases on one side and to the other two cables on the other. The sum of the lengths of the 3 cables would be equal to the length of the cable that would have covered the surface of the panel alone, the lengths of each of the cables being equal. The connection point of the 3 cables will be connected to ground (neutral).

[0113] The heating means is chosen so as to have a surface power of between 100 and 700 W / m2, preferably between 200 and 350 W / m2.

[0114] The resistive heating cable can be connected to an electricity supply source through a power cable, in particular having a diameter greater than that of the cable. The connection can therefore be made by connectors.

[0115] The resistive heating cable may comprise two ends. In order to ensure the connection, at least one stripped end of the resistive heating cable and one stripped end of a power cable may be connected by an electrical connector. Such a connector may be a mechanical crimping sleeve or a heat-shrinkable terminal consisting of a heat-shrinkable sheath and a tin ring. This sheath acts as a sleeve. By heating the sleeve, the tin melts to weld the two wires and the sheath shrinks to ensure sealing.

[0116] Alternatively, a stripped end of the resistive heating cable and a stripped end of a power cable may be mechanically crimped.

[0117] The cable can be in direct contact with the core, inside the cavities, without adding any additional sheet between the cable and the core. This helps to limit unnecessary heat losses.

[0118] Preferably, the cable is not in direct contact with the upper skin.

[0119] Adhesive layers

[0120] The panel may further comprise two adhesive layers adjacent to the upper and lower skins. These adhesive layers may connect the core to the skins of the panel. The adhesive layers are thermally conductive and may persist at temperatures above 60°C, preferably above 80°C, for example between 60°C and 160°C without their adhesive properties being negatively impacted.

[0121] The adhesive layers may be the same or different.

[0122] Adhesion may be provided by different types of adhesives, such as glues. The adhesive may have a melting point of at least 60°C, preferably at least 65°C. The adhesive may have a melting point below 200°C, preferably at least 170°C. Adhesives effective at room temperature for "cold" pressing may also be used, for example two-component epoxy or polyurethane adhesives.

[0123] The person skilled in the art will know how to choose the appropriate glue so that, on the one hand, the cable is not damaged during the gluing procedure and, on the other hand, the glue itself is not damaged during use of the panel.

[0124] The adhesive layers may comprise an adhesive selected from at least one of an olefin-based adhesive, a urethane-based adhesive, an acrylic-based adhesive, an epoxy-based adhesive, a polyamide-based adhesive, a phenolic adhesive, or a mixture thereof.

[0125] According to one embodiment, the sandwich panel consists of a thermally conductive upper skin and a lower skin; a core arranged between the upper skin and the lower skin and a resistive heating cable, the resistive cable being single-conductor, the core comprising one or more cavities, the single-conductor resistive heating cable being housed in one or more cavities of the core and the coverage rate being greater than 70%.

[0126] Each of the constituent elements of the panel may be the same as those described above.

[0127] [Fig. 2] schematically illustrates a panel 1 according to an embodiment in a perpendicular section. The skins 2 and 3 are arranged on either side of the upper and lower faces of the core 4, each connected by adhesive layers 6 and 7. The cable 5 is located at the upper face of the core 4, inside the cavities 8.

[0128] The invention also relates to a floor or partition comprising such a panel. The floor may further comprise acoustic insulation layers or surface covering layers.

[0129] The invention also relates to a method of manufacturing a sandwich panel according to the first aspect, the method comprising the following steps: - Provide two skins and a core with one or more cavities provided; - Place a single-conductor resistive heating cable inside the cavities; - Apply an adhesive layer to each of the two faces of the core; - Cover the faces of the core with the skins so as to form a together ; - Press the whole thing for more than 20 minutes.

[0130] The pressing can be carried out at a temperature above 50°C, preferably between 65°C and 100°C, for a duration of more than 20 minutes, preferably between 30 minutes and 2 hours. According to an alternative method, the pressing can be carried out at room temperature, between 20 and 25°C, called “cold” pressing, for a duration of more than 20 minutes, preferably between 2 hours and 24 hours.

[0131] The assembly can be hot pressed to be assembled. It must therefore withstand a temperature between 50°C and 1170°C for 180 minutes.

[0132] According to one aspect, the invention relates to the use of a panel according to the first aspect or obtained according to the above method in a railway vehicle as a heating panel by circulation of an electric current in the resistive cable.

[0133] According to one aspect, the invention relates to the use of a panel according to the first aspect or obtained according to the above method in an aeronautical vehicle as a heating panel by circulation of an electric current in the resistive cable.

[0134] According to one aspect, the invention relates to a floor comprising a panel according to the first aspect or obtained according to the above method.

[0135] According to one aspect, the invention relates to a partition comprising a panel according to the first aspect or obtained according to the above method. Examples Means of measurement

[0136] Thermal camera

[0137] Every body emits infrared radiation. The thermal camera captures this radiation and creates an image showing the radiation intensity of different parts of the body. The hotter a body is, the higher the intensity of its radiation.

[0138] The camera used is a TESTO camera. The images taken by this camera will be analyzed by suitable software. It is therefore possible to determine on this software the hottest point and the coldest point of the body but also to plot a histogram illustrating a temperature gradient if one exists.

[0139] Thermocouples

[0140] Thermocouples allow the temperature to be measured at a point on the body in question. This device works by exploiting the Seebeck effect: the appearance of a potential difference following the temperature difference in contact between two conductive materials of different nature. Thus a thermocouple consists of a hot weld (junction between two wires of different metals) which will be connected to a measuring device equivalent to a voltmeter. The weld point is the temperature detection point. Placing several thermocouples on different parts of the body allows a graph of temperature as a function of time to be drawn and thus to have an idea of ​​the thermal behavior of the body. Thermocouples do not allow the distribution of heat to be visualized over the entire body but rather at a specific point.

[0141] In this case, three acquisition devices are used, each having 8 thermocouples, for a total of 24 possible measurement points. The devices are then connected to measurement software to interpret the measurements.

[0142] The electrical bench allows the heating system to be powered (in this case, the resistive cable) but also allows additional controls to be integrated into the assembly such as a switch or a probe.

[0143] Heating is provided through the power supply by an electric bench. This heating makes it possible to check the correct operation of the heating means after gluing.

[0144] As far as testing is concerned, this heating can be interesting to see the maximum temperature that a heating cable can reach. Heating generally requires a power supply and a ground connection.

[0145] The homogeneity of the heat as well as the inertia of the heating system are evaluated during this test.

[0146] Example 1 - manufacturing a panel according to the invention

[0147] A panel comprising two aluminum sheets of thickness 1 mm and 1.5, respectively and a PET foam core having a thickness of 15 mm, a weight of 100 kg / m3 and integrating a resistive cable of 1.5 mm diameter was manufactured. To do this, the core integrating the cable in the cavities machined on its upper face was coated on each of these faces with an epoxy adhesive. The assembly was pressed at 125 bar, at 70°C for one hour.

[0148] Example 2 - mechanical properties

[0149] The results of the breaking stress measurements are shown in Table 1. Test 1 tests a panel according to Example 1 with a glue weight of 250g / m2. Test 2 tests a panel according to Example 1 with a glue weight of 250g / m2 but in which the resistive cable has not been added. Test Bending stress Bending modulus Mode of failure (MPa) (MPa) 1 with resistive cable 19 Cohesive PET foam 2 without resistive cable 19.2 3118 Cohesive PET foam

[0150] [Table 1]

[0151] The results are consistent, 1% difference in bending stress between tests with resistive cable and without resistive cable.

[0152] The results of the bending strength measurements are shown in Table 2.

[0153] 3-point bending test:

[0154] - Speed: 10 mm / min

[0155] - Upper support: 30mm diameter

[0156] - Lower supports: 20mm diameter

[0157] - Maximum crossbar displacement: 15mm

[0158] - Distance between lower supports: 300mm

[0159] Tests 3 to 6 are carried out on panels according to Example 1.

[0160] Test 3 tests a new panel whose cable is heated to room temperature. Test 4 tests a new panel whose cable is heated to 40°C.

[0161] Test 5 tests an aged panel (carried out according to ISO 9142 following 7 type D3 cycles) whose cable is heated to room temperature. Test 6 tests an aged panel whose cable is heated to 40°C.

[0162] The maximum temperature is reached between 25 and 30 min. To ensure that the maximum temperature is reached: wait 30 min before starting the test.

[0163] [Tables2] Test Maximum force (N) Bending strength (N / mm2) State / temperature (°C) Failure mode Deviation Comment(s) Compliant 3 1 545 30.3 New / ambient Cohesive PET foam + punching of upper aluminum sheet / 4 1 448 28.4 New / 40°C Cohesive PET foam + punching of upper aluminum sheet -6.2% compared to reference 5 1 490 29.2 Aged D3 / ambient Cohesive PET foam + punching of upper aluminum sheet -2.0% compared to reference 6 1 479 29.0 Aged D3 / 40°C Cohesive PET foam + punching of upper aluminum sheet -2.7% compared to reference

[0164] Furthermore, a polyurethane glue was tested instead of an epoxy glue. The results in terms of mechanical resistance are similar.

[0165] The results are contained within an interval of ±10% in stress (N) and in flexural strength (N / mm2). No degradation in the aged state was observed and all failure modes are in line with expectations. The results are in line with expectations.

[0166] Example 3 - homogeneity of diffused heat

[0167] A panel according to Example 1 was tested. The cables are connected by a parallel circuit. The circuit is then powered by a supply voltage of 230 V.

[0168] Check: A thermal photo is taken with the bare panel to ensure that all cables are functional.

[0169] A thermocouple is placed in direct contact with the cable, then the aluminum sheet is placed on top and the temperature is recorded at different locations on the surface of the heating panel using thermocouples. The cable was first given time to reach its full potential (highest heating point), then the regulation was applied between 33.5°C and 34.5°C.

[0170] The homogeneity of the heat generated by the heated floor was measured by two means: thermocouples and a thermal camera. According to the results obtained, the expected homogeneity is respected.

[0171] The present disclosure is not limited to the examples described above, only by way of example, but it encompasses all the variants that a person skilled in the art may envisage within the framework of the protection sought.

Claims

Claims

1. Sandwich panel comprising: - a thermally conductive upper skin and a lower skin; - a core arranged between the upper skin and the lower skin and - a resistive heating cable; said panel being characterized in that the resistive cable is single-conductor, the core comprises one or more cavities, the single-conductor resistive heating cable being housed in one or more cavities of the core and in that the coverage rate is greater than 70%.

2. Panel according to claim 1, characterized in that the core has a total thickness EA and one or more cavities has a depth PC, the depth PC being less than the total thickness EA of the core.

3. Panel according to one of the preceding claims, characterized in that the cable extends along the length of the cavity or each of the cavities, the cavity or cavities being grooves having a section of depth PC between 2 mm and 8 mm and width between 1 mm and 5.5 mm.

4. Panel according to one of the preceding claims, characterized in that the single-conductor resistive heating cable comprises a resistive conductor and an electrically insulating jacket.

5. Panel according to one of the preceding claims, characterized in that the diameter of the single-conductor resistive heating cable is between 1 mm and 5 mm, preferably between 1.2 mm and 3 mm.

6. Panel according to one of the preceding claims, characterized in that the core has an upper face adjacent to the thermally conductive upper skin and a lower face adjacent to the lower skin and in that the core comprises one or more cavities provided opening onto at least one of the faces of the core.

7. Panel according to one of the preceding claims, said panel having an intermediate portion located between two edge zones, said panel being characterized in that the coverage density of the resistive cable is greater at the level of two edge zones of the panel compared to an intermediate portion.

8. Panel according to one of the preceding claims, characterized in that the upper and lower skins are made of aluminum and / or in that the core is a polymeric foam.

9. Method for manufacturing a panel according to one of claims 1 to 8, comprising the following steps: - Providing two skins and a core having one or more cavities provided; - Housing a single-conductor resistive heating cable inside the cavities; - Applying an adhesive layer to each of the two faces of the core; - Covering the faces of the core with the skins so as to form an assembly; - Pressing the assembly for a period of more than 20 minutes.

10. Use of a panel according to one of claims 1 to 8, or obtained according to the method according to claim 9, in a railway or aeronautical vehicle as a heating panel by circulation of an electric current in the resistive cable.

11. Floor or partition comprising a panel according to one of claims 1 to 8, or obtained according to the method according to claim 9.

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