Sandwich panels incorporating 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 an assembly, floor, or partition incorporating it.

Description

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 with 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 construction sector for heating homes or common areas. In order to control the temperature inside the enclosures and ensure thermal comfort, sandwich panels can integrate a heating function.

[0003] Current composite panels include heating devices, usually electrical. For example, heating elements configured as heating films are glued to conventional floor panels installed in railway vehicle passenger compartments and covered with flooring. These heating films, especially those with an IP rating of at least 66 (minimum IP66 rating), are not hermetically sealed, so penetrating moisture can damage them. The IP rating indicates the degree of protection of the device against the penetration of solid objects (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 as 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 the Fig. 1. The floor 1 may 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 floor covering 16, carpet for example. 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, being located between it and an insulating wool 11. The heating film 12 is self-adhesive, it is stuck 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 may be underheated or not heated at all, as 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 of the panel, or at least more controlled, presenting a high coverage rate and this without particular constraints imposed by the geometry of the panel.

[0008] Although efficient, heating films 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 film architecture. In turn, any change in the internal architecture of heating films (for example, the arrangement of heating elements inside the film) requires a change in tooling, which implies additional costs and delays during the manufacturing process. Its production process is therefore not flexible, and therefore not very attractive.

[0009] Documents US 2012 / 234819, CN 106 714 346, FR 2 610 098, US 5 740 858, EP 1 055 087 describe the use of cables having a heating function, these cables being, in a conventional manner for a person skilled in the art, double-conductor heating cables. To the knowledge of the Applicant, the heating cables used for floors in the transport sector are exclusively double-conductor cables. Double-conductor cables, generally composed of one conductor for the current and one for earthing or return, are known for their ability to manage high surface power and to be able to be deployed over long distances, with few sizing constraints.According to the inventor's findings, due to their relatively large diameter, the integration of bi-conductor cables into the various layers of the floors is not ideal in that it affects their mechanical strength by creating weak points within the panel. Therefore, there remains a search for a sandwich panel easily integrating a heating function, said panel allowing homogeneous heat distribution and a good coverage rate, while minimizing heat losses, particularly at the lateral edges and providing good mechanical strength. The present 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 core structure, it is possible to place the heating means, the single-conductor resistive cable, possibly by pressure, before adding the skins to make the panel. This new heating system will allow the heat to be selectively distributed through the panel skins. 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 presenting 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. For example, the cavities can be arranged so as to bypass an obstacle that could pass through the panel.

[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] Although thinner than a bi-conductor cable, a single-conductor resistive heating cable imposes specific sizing constraints on its incorporation. Indeed, the thinner and longer a wire is, the greater its electrical resistance. To maintain at least an equivalent surface power, without being bound by a theory, the inventors have noted that the uniformity of heating over the entire panel is improved with the increase in the heated area and, in order to ensure uniform heating, it is estimated, according to the invention, that the coverage rate is greater than 70%. The linear resistance of the cable can then be adjusted according to the supply voltage and the thermal power to be provided.

[0016] By homogeneous heating or homogeneous heat distribution we mean a good distribution of temperature on the panel, the temperature gradient between the hottest point and the coldest point of the panel is less than 7°C, preferably less than 5°C.

[0017] 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.

[0018] 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 unit; Press the unit for a period of more than 20 minutes.

[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 a railway 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 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.

[0021] 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.

[0022] The features set out in the following paragraphs may, optionally, be implemented, independently of each other or in combination with each other: 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; two adhesive layers may be located on either side of the core so as to connect the upper face of the core to the upper skin and the lower face of the core to the lower skin; the upper and lower skins may be made of aluminum; the core may be a foam, preferably a polymeric foam; the diameter of the cavity may be between 0.2 mm and 5.5 mm, preferably between 0.5 mm and 5.5 mm, or preferably between 0.2 mm and 4 mm; the panel may have a total thickness, measured from the upper skin to the lower skin, of between 5 mm and 100 mm, preferably between 10 mm and 50 mm;the resistive cable may wind along the path on the surface of the panel, with a period of the undulations of the path of value D along a direction of the panel, the value D being between 25 and 80 mm, preferably between 35 and 70 mm; the panel may be devoid of a metal layer, such as an aluminum foil, disposed between the resistive heating cable and the core; the panel may be devoid of a thermally conductive layer disposed between the heating means and the thermally insulating layer; the cable may extend along the length of the cavity or each of the cavities, the cavity or cavities being grooves having a cross-section of depth PC between 2 mm and 8 mm and width between 1 mm and 5.5 mm; the single-conductor resistive heating cable may comprise a resistive conductor and an electrically insulating jacket; 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;the cavity or cavities have a groove entry width greater than the diameter of the cable, said cavity may be sized to allow the insertion of the cable by elastically deforming the groove entry or entries of said cavity or cavities; the core may comprise one or more cavities provided opening onto at least one of the faces of the core, 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, optionally on each of the faces and therefore each integrating at least one cable; 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

[0023] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which: Fig. 1 [ Fig. 1 ] shows a diagram of a section along a plane perpendicular to the floor comprising a sandwich panel according to the prior art. Fig. 2 [ Fig. 2 ] shows a diagram of a section along a plane perpendicular to the sandwich panel according to one embodiment. Fig. 3 [ 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 [ Fig. 4] 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, 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. Fig. 5 [ Fig. 5 ] shows a diagram of a section along a plane perpendicular to the sandwich panel according to an embodiment illustrating the period between two undulations. Fig. 6 [ Fig. 6 ] shows a simplified diagram of a top view of a path of the cavity of a sandwich panel according to the embodiment of a single-phase connection. Fig. 7 [ Fig. 7 ] shows a simplified diagram of a top view of a path of the cavity of a sandwich panel according to one embodiment of a three-phase star connection. Fig. 8 [ Fig. 8 ] shows a simplified diagram of a top view of a path of the cavity of a sandwich panel according to an embodiment of said assembly comprising a three-phase delta electrical supply and its connection to the heated sandwich panel, the three-phase delta connection made by electrical wires not integrated into the sandwich panel. Fig. 9 [ Fig. 9 ] shows a simplified diagram of a top view of a path of the cavity of a sandwich panel according to one embodiment, and of a three-phase delta connection having electrical wires integrated into the sandwich panel. Description of the embodiments

[0024] According to a first aspect, the invention provides 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%.

[0025] By "sandwich panel" is meant an assembly comprising at least three layers, in this case a structure having an intermediate layer, hereinafter called the core, between two external layers, hereinafter called the upper skin and lower skin.

[0026] 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%. Thermally conductive upper skin

[0027] The thermally conductive upper skin ensures the homogeneous radiation of the heat produced by the resistive cable and mechanical resistance while providing sealing properties.

[0028] A "thermal conductor" is a material characterized by its ability to diffuse heat in environments without macroscopic movement of matter. It is the ratio of thermal energy (amount of heat) transferred per unit of time (therefore homogeneous to a power, in watts) and surface area to the temperature gradient. Thermal conduction can occur quickly or slowly, or even very slowly.

[0029] By "thermal insulator" we mean a material which is defined in opposition to a "thermal conductor" material.

[0030] Preferably, the thermal conductivity of a thermally conductive layer of the panel is at least 5 times greater than the thermal conductivity of a thermally insulating layer of the panel, preferably at least 10 times greater.

[0031] The material used for the upper skin can be chosen to distribute heat evenly. This material can, for example, have good heat conductivity and good thermal inertia. Good thermal inertia means a rapid temperature rise and slow heat diffusion by radiation.

[0032] The upper skin may be a skin made of aluminum, steel, stainless steel, plastic (for example, acrylonitrile butadiene styrene ABS, polycarbonate, etc.) or plywood, wood or the like, 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.

[0033] The upper skin may be made of aluminum, for example aluminum sheet or a composite material comprising glass fibers, or basalt fibers or a mixture thereof.

[0034] 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.

[0035] According to one embodiment, the upper skin is an aluminum sheet having a thickness of at least 0.1 mm.

[0036] 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. Lower skin

[0037] The lower skin may be the same or different from the upper skin.

[0038] The lower skin provides mechanical strength and can also ensure homogeneous radiation of the heat produced by the resistive cable.

[0039] The lower skin may be a skin made of aluminum, steel, stainless steel, plastic (for example, acrylonitrile butadiene styrene ABS, polycarbonate, etc.) or plywood, wood or the like, 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.

[0040] The lower skin can be made of aluminum, for example an aluminum sheet, thus ensuring the mechanical strength of the panel.

[0041] 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.

[0042] According to one embodiment, the lower skin is an aluminum sheet having a thickness of at least 0.1 mm.

[0043] The lower skin can be thermally conductive or insulating.

[0044] 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. Soul

[0045] 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.

[0046] 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.

[0047] The core can be rigid, resistant to bending.

[0048] The panel may include 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 include a repeating pattern between the two upper and lower skins, this repeating pattern being formed of one or more cores alternating with other additional layers.

[0049] The core may also include one or more reinforcements extending between the upper and lower skins of the panel so as to enhance its mechanical properties. 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.

[0050] The core may be thermally insulating, made of a material having low thermal conductivity, i.e. capable of opposing the heat flow passing through it with a high thermal resistance. For example, the thermal conductivity of the thermally conductive upper skin is at least 5 times greater than the thermal conductivity of the thermally insulating core, preferably at least 10 times greater.

[0051] The core is chosen to limit heat loss generated by the single-core cable. The core plays a dual role: to limit heat loss and to contribute to the mechanical strength of the panel.

[0052] 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.

[0053] The core can have 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.

[0054] The soul can be chosen so as to be able to form cavities either on its surface or in its core.

[0055] The material constituting the core can 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 bio-sourced origin, such as plywood, 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.

[0056] The core may have a density of between 1 and 1000 kg / m 3, preferably between 20 and 350 kg / m3, more preferably between 80 and 150 kg / m3.

[0057] The core comprises one or more cavities for housing the single-conductor resistive cable. For the purposes of the invention, the same cavity can house a single-conductor resistive cable along a single plane perpendicular to the panel, while the panel in its entirety can house one or more single-conductor resistive cables.

[0058] 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.

[0059] In fact, the core may include one or more cavities opening either on its upper face or on its lower face or on both its upper and lower faces.

[0060] The core may include one or more cavities provided without opening onto any of its upper or lower faces.

[0061] The cavity(ies) are sized and arranged so as to furrow the core and to produce a panel with a coverage rate greater than 70%.

[0062] The core may be impregnable, for example it may have through holes or may be porous, so as to allow the passage of an impregnating material, such as a resin.

[0063] THE Figures 3 and 4 show simplified diagrams of a top view of a cavity path of a sandwich panel according to two embodiments.

[0064] According to the first embodiment of figure 3, the resistive cable 5 winds along the path which includes 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.

[0065] It is possible to smooth this gradient by designing the second embodiment according to the figure 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 a central portion intermediate between the two edge zones.

[0066] 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. Such an arrangement ensures a more homogeneous distribution of the generated heat, avoiding insufficient heat generation in the edge areas.

[0067] By "coverage density" we mean the ratio of the length of the resistive cable per unit area of ​​the sandwich panel.

[0068] It is preferable 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.

[0069] In addition to the upper and lower faces, the core has a section 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 the Figure 2 .

[0070] 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. The depth PC corresponds to the distance between the throat entrance EG of a cavity and the bottom of a cavity FC.

[0071] The depth of the cavity can be between 2 mm and 8 mm. The width of the cavity can be between 1 mm and 5.5 mm.

[0072] The core may have a total thickness greater than 8 mm, preferably between 8 and 50 mm.

[0073] One or more cavities have a depth. "Depth" means the depth of a cavity measured along a single plane perpendicular to the panel.

[0074] For example, a PC depth, as shown in the Figure 2 , corresponds to the distance between the throat 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.

[0075] By "groove entrance" we mean the perimeter of a cavity when it is designed to open onto one of the faces of the core.

[0076] 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.

[0077] 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 place on 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.

[0078] A cavity depth of less than 1 mm would be insufficient to hold the heating medium in place. Conversely, a cavity depth that was too great in a single plane would create weak points in the core structure, which would affect the mechanical strength of the panels.

[0079] The panels according to the invention are therefore sufficiently resistant to wear over time.

[0080] The cable may extend along the length of the cavity or each of the cavities, the cavity(ies) being grooves having a PC depth section between 2 mm and 8 mm and a width between 1 mm and 5.5 mm.

[0081] By "width" we mean the maximum distance between the sides of a cavity measured along a plane parallel to the panel.

[0082] It is noted that all 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.

[0083] 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.

[0084] The cross-section of the cavity may have a rounded, circular, rectangular, U-shaped, omega Ω, or any other shape allowing 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.

[0085] The cavity(ies) have a groove entry width greater than the maximum cavity width. This allows for better retention of the cable inside the cavity(ies).

[0086] 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 insertion of the cable by elastically deforming the groove entry(s) of said cavity(ies). Single-conductor resistive heating cable

[0087] The resistive heating cable is a single-conductor resistive cable.

[0088] The resistive heating cable can have a round cross-section.

[0089] Resistive heating cable means a cable with a high resistance value in ohms, preferably between 0.1 Ω / m and 4000 Ω / m, preferably between 0.1 Ω / m and 1000 Ω / m or between 1 Ω / m and 4000 Ω / m.

[0090] The diameter of the single-conductor resistive heating cable may be between 0.1 mm and 5 mm, preferably between 0.2 mm and 5 mm, preferably between 0.5 mm and 5 mm, 1 mm and 5 mm, preferably between 1.2 mm and 3 mm, or preferably between 0.1 mm and 1.5 mm, or preferably between 0.1 mm and 1 mm. Due to its reduced diameter, the cavities formed in the core to receive the single-conductor resistive heating cable have reduced sizes which do not affect the mechanical strength of the panel.

[0091] The resistive cable winding along a path on the surface of the panel, has a period of the path undulations of value D along a direction of the panel, the value D being between 25 and 80 mm, preferably between 35 and 70 mm. The minimum value of D allows to guarantee a minimum bending radius (D / 2) so as not to alter the structure of the cable while above the upper limit, the heating homogeneity can be negatively impacted.

[0092] 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 arranged around an electrically non-conductive central core serving as a mechanical support for said conductor.

[0093] The electrically insulating jacket may have a thickness between 0.01 mm and 0.4 mm, preferably between 0.01 and 0.2 mm or between 0.2 mm and 0.4 mm. It may be made of a polymeric material, such as a fluorinated ethylene propylene resin.

[0094] Preferably, the heating means (resistive heating cable) is not a double-conductor cable.

[0095] Dual-core cables have a larger diameter than single-core cables, requiring an increase in the size of the cavities which would affect the mechanical strength of the entire panel.

[0096] 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 can have a heating core with a linear or spiral shape. This cable is connected at each end, hence the need to form a continuous circuit.

[0097] The person skilled in the art will know how to choose the architecture of the cavities engraved in the core in order to homogenize the heat distribution at a given surface power.

[0098] The single-core cable can be supplied using a single-phase, two-phase or three-phase connection.

[0099] 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 engraved accordingly. Such an embodiment is illustrated in figure 6 . This schematically illustrates a view of the upper face of the core. The heating means 5 is the single-conductor electrical cable which follows a serpentine circuit.

[0100] Generally, the panel may include one or more single-conductor cables distributed over its surface. The description of the single-conductor cable above or below applies to each of the cables. The single-conductor cables may be identical or different, chosen so that each has the same resistance. An embodiment has been described with a single cable over the entire surface of the panel which may be suitable for a single-phase power supply. The panel may include several cables, particularly when the power supply is three-phase.

[0101] According to one embodiment, the panel is configured for a three-phase power supply, comprising: a first single-conductor resistive heating cable 51 extending over a first surface portion of the panel, a second single-conductor resistive heating cable 52 extending over a second surface portion of the panel, a third single-conductor resistive heating cable 53 over a third surface portion of the panel.

[0102] According to one aspect, the invention relates to an assembly comprising the panel described above and a three-phase star power supply, comprising: a first phase PH1 of the three-phase power supply connected to a first end of the first single-conductor resistive heating cable 51, a second phase PH2 of the power supply connected to a first end of the second single-conductor resistive heating cable 52, a third phase PH3 of the power supply connected to a first end of the third single-conductor resistive heating cable 53, a cable respectively connecting a second end of the first single-conductor resistive heating cable, a second end of the second single-conductor resistive heating cable, and a second end of the third single-conductor resistive heating cable configured to form a neutral N of the three-phase power supply.

[0103] Such an embodiment is illustrated in figure 7 .

[0104] 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).

[0105] According to one aspect, the invention relates to an assembly comprising the panel described above and a three-phase delta power supply, comprising: a first phase PH1 of the three-phase power supply connected to a second end of the first resistive cable 51 and to a first end of the second resistive single-conductor heating cable 52, a second phase PH2 of the power supply connected to a second end of the second resistive cable 52 and to a first end of the third resistive single-conductor heating cable 52, a third phase PH3 of the power supply connected to a second end of the third resistive cable 53 and to a first end of the first resistive single-conductor heating cable 51.

[0106] Such three-phase delta connections are illustrated in figures 8 And 9 , these allow to avoid overlapping cables and thus better control the total thickness of the panel.

[0107] There figure 8illustrates an embodiment in which the panel comprises a three-phase delta supply, the connection being located outside the panel while the figure 9 illustrates an embodiment in which the panel includes a three-phase delta supply, with the three phases electrically connected to a connector 54 located within the panel. These example connections can also be advantageous in that they provide users with the freedom to adapt the connectors to the power source according to their needs.

[0108] The heating means, the single-conductor resistive heating cable, is chosen so as to have a surface power of between 100 and 700 W / m 2< , preferably between 200 and 350 W / m 2< .

[0109] The resistive heating cable can be connected to a power supply source through a power cable, in particular one having a diameter larger than that of the cable. The connection can therefore be made by connectors.

[0110] The resistive heating cable may have two ends. 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 a seal.

[0111] Alternatively, one stripped end of the resistive heating cable and one stripped end of a power cable can be mechanically crimped.

[0112] The cable can be in direct contact with the core, inside the cavities, without adding any additional foil between the cable and the core. This helps limit unnecessary heat loss.

[0113] Preferably, the cable is not in direct contact with the upper skin. Adhesive layers

[0114] The panel may further comprise two adhesive layers adjacent to the top and bottom skins. These adhesive layers may connect the core to the skins of the panel. The adhesive layers are thermally conductive and can survive at temperatures above 60°C, preferably above 80°C, for example between 60°C and 160°C without their adhesive properties being negatively impacted.

[0115] The adhesive layers can be the same or different.

[0116] Adhesion can be ensured by various 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.

[0117] The skilled person 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.

[0118] 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.

[0119] 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%.

[0120] Each of the constituent elements of the panel can be the same as those described above.

[0121] There figure 2schematically 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.

[0122] The resistive cable winds around the panel with a period of path ripples of value D along a direction of the panel, as shown in Figure 5 This value D is between 25 and 80 mm, preferably between 35 and 70 mm.

[0123] The invention also relates to a floor or a partition comprising such a panel. The floor may further comprise acoustic insulation layers or surface covering layers. In the present application, the term upper skin, as opposed to lower skin, means the skin which is heated by the single-conductor cable when the sandwich panel is used as a floor (typically horizontally). In the case of a partition, the core comprises one or more cavities provided opening onto both the upper and lower faces of the core. The single-conductor resistive heating cable may therefore be housed in one or more cavities of the core on each of the upper and lower faces, the upper face being adjacent to the upper skin and the lower face being adjacent to the lower skin.When used as a partition, the panel is typically arranged vertically: in such a case in the present application, reference may be made generally to a "first skin," instead of "upper skin," and to a "second skin," instead of "lower skin."

[0124] 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; Cover the faces of the core with the skins to form an assembly; Press the assembly to form the panel.

[0125] Among the techniques that can be used to manufacture the panel according to the first aspect, are cited: draping of pre-pregs, infusion of LRI resin (Liquid Resin Infusion in English), contact molding (or contact lamination), wet compression molding (wet compression molding in English), etc.

[0126] Preferably, the method comprises 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 unit; Press the unit for a period of more than 20 minutes.

[0127] The pressing can be carried out at a temperature above 50°C, preferably between 65°C and 100°C, for a period 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 period of more than 20 minutes, preferably between 2 hours and 24 hours.

[0128] The assembly can be hot pressed to be assembled. It must therefore withstand a temperature between 50°C and 170°C for 180 minutes.

[0129] According to one embodiment, the method of manufacturing a sandwich panel according to the first aspect is a a prepreg draping process , 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 one or more layers of fabric impregnated with a thermosetting or thermoplastic resin on each of the faces of the core, so as to form a unit, Press the unit for a period of more than 20 minutes.

[0130] In this case, the skins correspond to fabrics pre-impregnated with a thermosetting or thermoplastic resin. The core can be impregnable, for example it can have through holes or can be porous, so as to allow the passage of the resin.

[0131] According to one embodiment, the method of manufacturing a sandwich panel according to the first aspect is a n contact lamination process , the method comprising the following steps: Provide two skins and a core with one or more cavities provided; House a single-conductor resistive heating cable inside the cavities; Apply one or more layers of fabric by contact lamination on each of the faces of the core, each of the layers of fabric being coated with a thermosetting or thermoplastic resin, so as to form an assembly, Press the assembly for a period of more than 20 minutes.

[0132] In this case, the skins correspond to the unimpregnated fabrics. The core can be impregnable, for example it can have through holes or can be porous, so as to allow the resin to pass through.

[0133] According to one embodiment, the method of manufacturing a sandwich panel according to the first aspect is wet compression molding, 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 one or more layers of fabric to each side of the core, Apply a thermosetting or thermoplastic resin to each of the layers of fabric to form a whole, Heat and press the whole for a period of more than 20 minutes.

[0134] In this case, the skins correspond to the unimpregnated fabrics. The core can be impregnable, for example it can have through holes or can be porous, so as to allow the resin to pass through.

[0135] According to one embodiment, the method of manufacturing a sandwich panel according to the first aspect is a resin infusion, 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; Vacuum inject a thermosetting or thermoplastic resin so as to pass through the core and create bridges between each of the faces of the core, so as to form an assembly, Press the assembly for a period of more than 20 minutes.

[0136] In this case, the skins correspond to the resin itself. The core can be impregnable, for example it can have through holes or can be porous, so as to allow the resin to pass through.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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 Thermal camera

[0141] Every body emits infrared radiation. A thermal imaging camera captures this radiation and creates an image that displays the radiation intensity of different parts of the body. The hotter a body is, the higher the intensity of its radiation.

[0142] 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 the hottest and coldest points of the body using this software, but also to plot a histogram illustrating a temperature gradient if one exists. Thermocouples

[0143] Thermocouples are used to measure the temperature at a specific point on the body. 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 junction (junction between two wires of different metals) which will be connected to a measuring device equivalent to a voltmeter. The junction point is the temperature detection point. Placing several thermocouples on different parts of the body allows a graph of temperature versus 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 on a specific point.

[0144] In this case, three acquisition devices are used, each with 8 thermocouples, for a total of 24 possible measurement points. The devices are then connected to measurement software to interpret the measurements.

[0145] The electrical bench allows you to power the heating system (in this case, the resistive cable) but also to integrate additional controls into the assembly such as a switch or a probe.

[0146] Heating is provided through the power supply by an electric bench. This heating allows the proper functioning of the heating means to be checked after gluing.

[0147] As for testing, this heating can be useful to see the maximum temperature that a heating cable can reach. Heating generally requires a power supply and a ground connection.

[0148] The homogeneity of the heat as well as the inertia of the heating system are evaluated during this test. Example 1 - manufacturing a panel according to the invention

[0149] A panel comprising two aluminum sheets of thickness 1 mm and 1.5, respectively and a PET foam core with 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. Example 2 - mechanical properties

[0150] The results of the breaking stress measurements are shown in Table 1. Test 1 tests a panel according to Example 1 with an adhesive weight of 250g / m2. Test 2 tests a panel according to Example 1 with an adhesive weight of 250g / m2 but in which the resistive cable has not been added. [Table 1] Essay Bending stress Flexural modulus (MPa) Breakup mode (MPa) 1 with resistive cable 19 Cohesive PET foam 2 without resistive cable 19.2 3118 Cohesive PET foam

[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: Speed: 10 mm / min Upper support: 30 mm diameter Lower supports: 20 mm diameter Maximum crosshead movement: 15 mm Distance between lower supports: 300 mm

[0154] Tests 3 to 6 are carried out on panels according to Example 1.

[0155] Test 3 tests a new panel with the cable heated to room temperature. Test 4 tests a new panel with the cable heated to 40°C.

[0156] 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.

[0157] The maximum temperature is reached between 25 and 30 minutes. To ensure that the maximum temperature is reached: wait 30 minutes before starting the test. [Table 2] Essay Maximum effort (N) Flexural strength (N / mm 2< ) State / temperature (°C) Breakup mode Gap Comment(s) 3 1 545 30.3 New / Ambient Cohesive PET foam + punching of aluminum sheet sup / Compliant 4 1 448 28.4 New / 40°C Cohesive PET foam + punching of aluminum sheet sup -6.2% compared to reference 5 1 490 29.2 Aged D3 / ambient Cohesive PET foam + punching of aluminum sheet sup -2.0% compared to reference 6 1 479 29.0 Aged D3 / 40°C Cohesive PET foam + punching of aluminum sheet sup -2.7% compared to reference

[0158] Furthermore, a polyurethane adhesive was tested instead of an epoxy adhesive. The results in terms of mechanical strength are similar.

[0159] The results are within ±10% of stress (N) and flexural strength (N / mm2). No degradation in the aged state was observed and all failure modes are as expected. The results are as expected. Example 3 - homogeneity of diffused heat

[0160] A panel according to example 1 was tested. The cables are connected by a parallel circuit. The circuit is then supplied with a supply voltage of 230 V.

[0161] Check: A thermal photo is taken with the bare panel to ensure all cables are functional.

[0162] 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 points 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.

[0163] The homogeneity of the heat generated by the heated floor was measured using two methods: thermocouples and a thermal imaging camera. The results show that the expected homogeneity is met.

[0164] This disclosure is not limited to the examples described above, only as an example, but it encompasses all the variations that a person skilled in the art may envisage within the framework of the protection sought.

Claims

1. Sandwich panel (1) comprising: - a thermally conductive upper skin (2) and a lower skin (3); - a core (4) arranged between the upper skin and the lower skin and - a resistive heating cable (5); said panel (1) being characterized in that the resistive cable is single-conductor, the core (4) comprises one or more cavities (8), the single-conductor heating resistive cable (5) being housed in one or more cavities (8) of the core (4) 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 (8) has a depth PC, the depth PC being less than the total thickness EA of the core (4).

3. Panel according to one of the preceding claims, characterized in thatthe 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 consists of 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 upper skin (2) which is thermally conductive and a lower face adjacent to the lower skin (3) and in that the core comprises one or more cavities (8) 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 higher at two edge areas 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 polymer foam.

9. Panel according to one of the preceding claims, characterized in that the resistive cable winds along a path on the surface of the panel, with a period of the path undulations of value D along a direction of the panel, the value D being between 25 and 80 mm.

10. Panel according to one of claims 1 to 9, configured for a three-phase power supply, comprising: - a first resistive cable (51), single-conductor, extending over a first surface portion of the panel, - a second resistive cable (52) single-conductor, extending over a second surface portion of the panel, - a third resistive cable (53) single-conductor, over a third surface portion of the panel.

11. Method for manufacturing a panel according to one of claims 1 to 10, 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; - 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.

12. Method for manufacturing a panel according to one of claims 1 to 10, 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 (6, 7) 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.

13. Use of a panel according to one of claims 1 to 10, or obtained according to the method according to claim 11 or 12, in a railway or aeronautical vehicle as a heating panel by circulation of an electric current in the resistive cable.

14. Floor or partition comprising a panel according to one of claims 1 to 10, or obtained according to the method according to claim 11 or 12.

15. Assembly comprising a panel according to claim 10 and a three-phase star power supply, comprising: - a first phase (PH1) of the three-phase power supply connected to a first end of the first single-conductor resistive cable (51), - a second phase (PH2) of the power supply connected to a first end of the second single-conductor resistive cable (52), - a third phase (PH3) of the power supply connected to a first end of the third single-conductor resistive cable (53), - a cable respectively connecting a second end of the first resistive cable, a second end of the second resistive cable, and a second end of the third resistive cable configured to form a neutral (N) of the three-phase power supply.

16. An assembly comprising a panel according to claim 10 and a three-phase delta power supply, comprising: - a first phase (PH1) of the three-phase power supply connected to a second end of the first resistive cable (51) and to a first end of the second resistive cable (52) single-conductor heating, - a second phase (PH2) of the power supply connected to a second end of the second resistive cable (52) and to a first end of the third resistive cable (52) single-conductor heating, - a third phase (PH3) of the power supply connected to a second end of the third resistive cable (53) and to a first end of the first resistive cable (51) single-conductor heating.

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