Multimaterial rod with insulating film

Abstract

The present invention relates to a multimaterial rod (10) comprising: - a core (16), extending in a direction of extension (AX), made of a composite material (12) based on carbon fibre, or formed of an assembly comprising a core made of a composite material (12) based on carbon fibre and a layer made of a composite material (14) based on glass fibre that surrounds the core; and - an outer shell (18) providing the core with electrical and / or UV and / or moisture insulation, wherein this outer shell (18) coating the core (16) along the direction of extension and being formed of a varnish that adheres mechanically and / or chemically to this core (16); wherein the shell (18) has an elongation at break that is substantially equal to or greater than the elongation at break of the core (16).

Description

[0001] DESCRIPTION

[0002] Title of the invention: Multi-material rod with insulating film

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] The present invention relates to the field of multi-material assemblies, and more specifically to a multi-material rod comprising a core including a carbon fiber-based composite material. Such a rod finds its application in various fields such as civil engineering for the manufacture of high-voltage cables.

[0005] TECHNICAL BACKGROUND

[0006] With the continued increase in demand for electricity, due in particular to the electrification of mobility and heating, and the emergence of new modes of production and consumption, the modernization of the existing electricity network will become a particularly critical issue to ensure the routing of electrical energy.

[0007] Currently, a substantial portion of existing high-voltage overhead power lines, generally composed of conductor cables suspended from supports such as pylons or poles, are already reaching their capacity limits for transmitting electrical energy. The cables of these lines are usually formed by combining a steel core, providing mechanical strength, and a conductive layer of stranded aluminum surrounding the core.

[0008] In this context of increasing the capacity of electrical transit through cables, it was proposed to replace the steel core with a core comprising a composite material formed from carbon fibers.

[0009] Carbon fiber composite has a higher stiffness for the same mass as steel, and a coefficient of thermal expansion that is significantly lower than that of steel. On this basis, its use as a substitute for steel to form the core of electric cables makes it possible in practice to increase the cross-section of the stranded aluminum layer surrounding it. By making it possible to increase, at the same cable mass, the proportion of the conductive aluminum layer compared to conventional steel-core cables, the energy transport potential of these carbon fiber composite core cables is increased.

[0010] This results in the possibility of directly replacing electrically undersized steel core cables with these carbon fiber composite core cables to improve the transit capacity of power lines without requiring replacement of the supports, which would otherwise lead to additional development costs.

[0011] One of the manufacturing constraints of these high-voltage cables lies in the need to electrically insulate the aluminum layer from the carbon fiber-based material to prevent the occurrence of galvanic corrosion, which can quickly lead to deterioration of the cable.

[0012] One of the solutions adopted is to coat the carbon fiber-based material with a layer of glass fiber composite material to form a multi-material rod. The conductive aluminum layer is thus added around the insulating layer of glass fiber composite material during the development of the cable.

[0013] Even though the development of such a rod structure has reached a certain degree of maturity, supported by the establishment of a breakdown voltage integrity control process, known from document FR3122498B1, a physicochemical instability of the layer of glass fiber-based material has been observed in the presence of humidity or exposure to UV. This particularity induces the risk that the layer of glass fiber-based composite material will not guarantee sufficient electrical insulation throughout the service life of the cable.

[0014] As an extension of the continuous development of high voltage cables, the aim is to propose a multi-material rod structure to overcome this identified instability without compromising the implementation of the above-mentioned breakdown voltage diagnostic method.

[0015] STATEMENT OF THE INVENTION

[0016] The invention relates to a multi-material rod comprising: - a core, extending in a direction of extent, made of a composite material based on carbon fibers or formed from an assembly comprising a core made of a composite material based on carbon fibers and a layer of composite material based on glass fibers which surrounds the core; and

[0017] - an outer envelope providing electrical and / or UV and / or moisture insulation of the core, this outer envelope coating the core along the direction of extension by being formed of a varnish which adheres mechanically and / or chemically to this core; in which the envelope has an elongation at break which is substantially equal to or greater than the elongation at break of the core.

[0018] The invention also relates to a multi-material rod thus defined, in which the outer envelope has a thickness, measured radially to the direction of extension of the core, which is equal to or less than 300 microns.

[0019] The invention also relates to a multi-material rod thus defined, in which the thickness of the outer envelope is equal to or less than 100 microns.

[0020] The invention also relates to a multi-material rod thus defined, in which the varnish forming the outer envelope corresponds to one of: an epoxy resin, an acrylic resin, a urethane acrylate resin, a polyamide resin, polyurethane, a silicone, a phenolic copolymer.

[0021] The invention also relates to a multi-material rod thus defined, in which the elongation at break of the varnish is between 2% and 20% elongation and preferably between 2.5 and 10% elongation.

[0022] The invention also relates to a multi-material rod thus defined, in which the elongation at break of the core is between 0.5% and 2.5%.

[0023] The invention also relates to a multi-material rod thus defined, in which the film has an adhesion which satisfies a hold on the core up to a tear stress of 40 MPa.

[0024] The invention also relates to a multi-material rod thus defined, in which the outer envelope has an adhesion which satisfies a hold on the core for a tearing stress value of between 15 and 20 MPa. Method of manufacturing a multi-material rod comprising the following steps of:

[0025] - provision of a core extending in a direction of extent, made of a carbon fiber composite material or formed of an assembly comprising a core made of a carbon fiber composite material and a layer of glass fiber composite material which surrounds the core;

[0026] - depositing a varnish on the core followed by drying this varnish to form an outer envelope which adheres mechanically and / or chemically to the core along the direction of extension, this outer envelope providing electrical and / or UV and / or humidity insulation of the core, in which the envelope has an elongation at break which is substantially equal to or greater than the elongation at break of the core.

[0027] Method of manufacturing a multi-material rod thus defined, in which the varnish is deposited by spraying it onto the core or by dipping the core in a varnish bath.

[0028] Process for manufacturing a multi-material rush as defined above, in which the varnish is dried by applying heat or by UV radiation.

[0029] Method of manufacturing a multi-material rod thus defined, comprising a preliminary step of manufacturing the core by pultrusion.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0032] - [Fig.1] is a schematic perspective view of a multi-material rod according to the invention, comprising a carbon-glass rod core which is formed from a core made of carbon fiber-based composite material and an insulating layer made of glass fiber-based composite material which coats the core, and an outer envelope which surrounds the core;

[0033] - [Fig.2] is a longitudinal sectional view of the multi-material rod of figure 1; - [Fig.3a] illustrates a behavior of a multi-material rod not in accordance with the invention, marked by a resistance of the core and a rupture of the outer envelope under stress;

[0034] - [Fig.3b] illustrates another behavior of multi-material rod not in accordance with the invention, marked by a rupture of the core and maintenance of the outer envelope under stress;

[0035] - [Fig.3c] illustrates the behavior of a multi-material rod in accordance with the invention, marked by simultaneous rupture of the core and the outer casing under stress;

[0036] - [Fig.4] is a schematic perspective view of a multi-material rod according to an alternative embodiment of the invention, comprising a core formed from a carbon fiber-based composite material, and an outer casing which surrounds the core;

[0037] - [Fig.5] is a longitudinal sectional view of the multi-material rod of Figure 4.

[0038] DETAILED DESCRIPTION OF THE INVENTION

[0039] The present application aims to propose a rod provided with a core including a carbon fiber composite material, which guarantees electrical insulation of the core as satisfactory as possible to fully justify its use in the development of high voltage cables.

[0040] It is known from the state of the art to form multi-material rods in which a carbon fiber composite material is coated with a layer of glass fiber composite material to electrically insulate it from the outside.

[0041] Such a multi-material rod structure equipped with a carbon fiber composite core and an insulating layer made of a glass fiber composite material, hereinafter referred to as "carbon-glass rod", is developed in particular by the applicant using a pultrusion manufacturing process. This process is based on the successive production of the core and then the insulating layer by impregnation and bonding, using the same polymer matrix, of carbon and glass fibers deployed from bundles. In practice, the implementation of this manufacturing process, as well as the packaging and transport of the manufactured carbon-glass rods, are subject to various hazards and disturbances. The same applies during the manufacturing operations of high-voltage cables using these carbon-glass rods and during the installation of the cables to form the high-voltage lines.

[0042] For example, fiber misalignment, insufficient impregnation, or cracks generated during firing can occur during manufacturing. Also, the rods can be subjected to unexpected impacts or severe environmental conditions during their packaging and transport. These hazards and disturbances generate non-conformity, i.e. can significantly alter the properties of the carbon-glass rods to the point of no longer meeting the properties set by the specifications.

[0043] To ensure the conformity of carbon-glass rods, a quality control process specifically adapted to this type of bi-composite assembly has been developed based on the measurement of the "breakdown voltage". This process, described in document FR3122498B1, makes it possible to highlight the presence of a structural defect in the rod by passing an electric current and detecting a breakdown at a voltage level below a threshold value. The breakdown voltage, also called "disruptive voltage", corresponds to the minimum electrical voltage making a portion of an electrical insulator such as the glass fiber composite material conductive.

[0044] Although this carbon-glass rod structure is recognized as particularly suitable for conforming electrical cables meeting the new capacity requirements of high-voltage lines, under guarantee of its conformity established by the aforementioned quality control, a physicochemical instability of the layer of composite material based on glass fibers has been noted. This physicochemical instability, appearing in the event of exposure to humidity or UV radiation, risks hindering the insulation properties of this layer of composite material based on glass fibers. For example, a tendency for the matrix of the insulating layer to plasticize by absorption of humidity has been noted. This results in a risk of uncontrolled galvanic corrosion of high-voltage cables manufactured on the basis of these carbon-glass rods.

[0045] The invention is part of a logic of improving carbon-glass rods to satisfy the dual conditions of:

[0046] - eliminate the risk of physicochemical instability of the insulating layer made of composite material based on glass fibers; and

[0047] - maintain control over the quality of the rods manufactured by guaranteeing the applicability of the quality control process based on the measurement of the breakdown voltage.

[0048] In this respect, the idea behind the invention is based on the formation of a multi-material rod based on the addition of an external protective envelope around the carbon-glass rod to supplement the insulating layer of composite material based on glass fibers.

[0049] In detail, as illustrated in FIG. 1, a multi-material rod 10 according to the invention comprises a carbon-glass rod formed from the combination of a carbon fiber-based composite material 12 and a glass fiber-based composite material 14 which coats the carbon fiber-based composite material 12 in the form of an electrical insulation layer.

[0050] This carbon-glass rod, advantageously formed by pultrusion, defines a core 16 extending in a direction of extent, noted AX, which is centered on the carbon fiber-based composite material 12 forming its core.

[0051] According to the invention, an outer envelope 18 is formed around this core 16, by coating the electrical insulation layer 12 in carbon fiber-based composite material to form, together with the core 16, the multi-material rod 10.

[0052] In the context of the invention, this outer envelope 18 is recommended to protect the core 16, and more specifically the insulating layer 14 of the core 16 made of composite material based on glass fibers, from humidity and / or UV radiation.

[0053] To both satisfy the compatibility of the multi-material rod 10 with the quality control process based on the measurement of the breakdown voltage, and maintain effective protection of the core 16 by the outer casing 18, it is necessary to ensure that the behavior of the casing 18 matches that of the core 16. In detail, it is necessary to ensure both compliance with:

[0054] - a first criterion according to which the envelope 18 can withstand the stresses admissible by the core 16 during its operating life, in particular in tension exerted along the direction of extension AX; and

[0055] - a second criterion which imposes a rupture of the envelope 18 in response to a rupture of the core 16, namely according to which the envelope 18 must not remain intact if the integrity of the core 16 is lost.

[0056] The first criterion stated must be respected insofar as it conditions the capacity of the envelope 18 to guarantee adequate protection of the insulating layer 14 within the predefined operating limits of the rod.

[0057] It is well understood that if the envelope 18 is not capable of withstanding the maximum stresses and deformations that the core 16 can withstand in its specifications, it is likely to break unexpectedly, no longer allowing satisfactory guarantee of the desired UV and / or humidity protection. Figure 3a illustrates such a situation which is not admissible within the framework of the invention, for which a rupture, noted H, of the outer envelope 18 occurs in the event of tensile stress F of the multi-material rod which does not, however, induce a rupture of the core. This rupture H would then allow passage through humidity or UV radiation towards the core 16.

[0058] As regards the second criterion, it results directly from the correct implementation of the quality control method by measuring the breakdown voltage. Conventionally, the conformity of a carbon-glass rod, forming the core 16 of the multi-material rod 10 according to the invention, is admitted if and only if a breakdown in the form of an electric arc is not detected, between two electrodes, one of which is arranged on the surface of the insulating layer 14, when the passage of an electric current of predefined voltage is imposed. On this basis, it is indeed a question of avoiding non-compliance with the second criterion which leads to the non-compliant situation illustrated in FIG. 3b, for which the envelope 18 remains intact, namely without discontinuity, when the core 16 suffers conversely from a structural defect T in the second layer based on glass fibers 11.In such a case, the envelope 18 would be likely to form a barrier to the occurrence of breakdown, in particular by unexpectedly increasing the threshold value for which it appears. Such a situation would then lead to the critical case for which the multi-material rod would be wrongly considered as compliant, called a “false negative” in the breakdown voltage diagnosis, whereas it would on the contrary require the implementation of countermeasures such as the scrapping of the multi-material rod or the replacement of the cable equipped with it.

[0059] To satisfy the two aforementioned criteria, it is recommended in the present invention that the envelope 18 coating the core 16 along the direction of extension AX is in the form of a varnish film which:

[0060] - adheres to the insulating layer 16 made of composite material based on glass fibers; and additionally

[0061] - has an elongation at break which is substantially equal to or slightly greater than the elongation at break of the core 16.

[0062] This particularity of adhesion, which may designate a mechanical, chemical anchoring or a mechanical / chemical combination, imposes a rupture of the envelope 18 by propagation of a rupture of the core 16. Corolarily, the condition of elongation at rupture posed prevents the isolated rupture of the envelope 28 by allowing it to follow the elongation of the core 16 under stresses.

[0063] By synergistic effect {adhesion-elongation at break}, this results in the guarantee of a simultaneous breakage of the core 16 and the envelope 18 in response to a given stress F of the multi-material rod 10 according to the invention. This dynamic of concomitance of the breakages of the core 16 and the envelope 18 according to the invention, respectively denoted T and H, is illustrated in figure 3c. The multi-material rod 10 according to this first aspect of the invention is thus obtained by forming the outer envelope 18 by depositing and then drying varnish on a supplied carbon-glass rod, this carbon-glass rod being, in a non-limiting manner, previously formed by pultrusion.

[0064] The varnish may in particular be deposited by spraying it onto the core 16 or by dipping the core 16 into a varnish bath. Also, the varnish may in particular be dried by applying heat or by UV radiation depending on its nature.

[0065] In this regard, the varnish forming the outer envelope 18 can be chosen in particular from: an epoxy resin, an acrylic resin, a urethane acrylate resin, a polyamide resin, polyurethane, a silicone, a phenolic copolymer.

[0066] In the case where the aim is to provide increased resistance to humidity, the varnish is advantageously chosen from: epoxy resin, urethane acrylate resin or a silicone.

[0067] If UV resistance is preferred, acrylic varnish or silicone may be considered particularly suitable.

[0068] In practice, the fixed breaking elongation value of the outer casing 18 must allow it to break as soon as the core 16 is damaged. This breaking elongation value of the outer casing 18 is dependent on its adhesion to the insulating layer 16, it being understood that the greater the adhesion, the more the outer casing 18 can elongate; it is defined as equal to or, for safety, greater than the breaking elongation value of the core 16.

[0069] Thus, for an elongation at break of the core 16 of between 0.5% and 2.5%, the elongation at break of the outer casing 18 is advantageously set between 0.5% and 20%, and preferably defined between 2.5 and 10%.

[0070] With regard to the adhesion value, it is defined to satisfy a retention of the outer casing 18 on the insulating layer 14 made of composite material based on glass fibers up to a tearing stress of 40 MPa, exerted radially to the axis AX in accordance with the ASTM D4541 standard for characterizing adhesion by “pull off”. Advantageously, the outer casing 18 has an adhesion which satisfies a retention on the core 16 for a restricted tearing stress value of between 15 and 20 MPa.

[0071] From a dimensional point of view, the thickness of the outer envelope 18, measured radially to the direction of extension AX of the core 16, is advantageously equal to or less than 300 microns, and preferably defined is equal to or less than 100 microns.

[0072] This thickness limitation aims to guarantee a reliable assessment of the conformity of the multi-material rod 10 according to the invention by the quality control method by measuring the breakdown voltage. Indeed, too great a thickness of varnish could prevent the recognition of the breakdown by positioning an electrode on the outer casing 18, due to the excessively large spacing distance with the core 16

[0073] The invention has been described at this stage as an improvement of carbon-glass rods, defined as rods formed from a core 12 of carbon fiber-based composite material and an insulating layer 14 of glass fiber-based composite material. This improvement relates to the addition of varnish to a carbon-glass rod to form a multi-material rod 10 provided with an outer envelope 18 providing a barrier role to humidity and / or UV radiation for the insulating layer 14 of glass fiber-based composite material.

[0074] It should be noted, however, that the invention is not strictly limited to this particular arrangement. Given that the aforementioned types of varnish have good electrical insulation performance, it may be chosen, according to an alternative embodiment, to substitute the insulating layer 14 with the outer envelope 18.

[0075] According to this alternative embodiment, illustrated in Figures 4 and 5, the multi-material rod 10 can thus be formed from a core 16 made of a carbon fiber-based composite material 12 and an outer casing 18 which adheres to the core 16 by coating it. As understood, unlike the first arrangement described on the basis of Figures 1, 2 and 3c, the outer casing 18 is formed in this alternative directly around the carbon fiber-based composite material 12 to both insulate it from moisture and / or UV radiation, but also to insulate it electrically.

[0076] The values ​​of adhesion, elongation at break and thickness, as well as the types of varnish, defined within the framework of the improvement of carbon-glass rods, described with reference to figures 1, 2 and 3c, are also applicable in the case of this variant embodiment.

[0077] In view of the above, the multi-material rod 10 according to the invention can be defined generically as comprising:

[0078] - a core 16, extending in a direction of extent AX, consisting either of a composite material based on carbon fibers 12 or of an assembly comprising a core consisting of a composite material based on carbon fibers 12 and a layer of composite material based on glass fibers 14 which surrounds the core; and

[0079] - an outer envelope 18 providing electrical and / or UV and / or humidity insulation of the core 16, this outer envelope 18 coating the core 16 along the direction of extension by being formed of a varnish which adheres mechanically and / or chemically to this core 16; in which the envelope 18 has an elongation at break which is substantially equal to or greater than the elongation at break of the core 16.

Claims

CLAIMS 1. Multi-material rush (10) comprising: - a core (16), extending in a direction of extent (AX), formed of an assembly comprising a core made of a carbon fiber-based composite material (12) and a layer of glass fiber-based composite material (14) which surrounds the core; and characterized by - an outer envelope (18) providing electrical and / or UV and / or moisture insulation of the core, this outer envelope (18) coating the core (16) along the direction of extension by being formed of a varnish which adheres mechanically and / or chemically to the glass fiber-based layer (14); wherein the envelope (18) has an elongation at break which is substantially equal to or greater than the elongation at break of the core (16); the outer envelope (18) has a thickness, measured radially to the direction of extension (AX) of the core, which is equal to or less than 300 microns; and the outer envelope (18) has an adhesion which satisfies a hold on the core (16) for a tear-off stress value of between 15 and 20 MPa.

2. Multi-material rod (10) according to claim 1, wherein the thickness of the outer casing (18) is equal to or less than 100 microns.

3. Multi-material rod (10) according to any one of the preceding claims, in which the varnish forming the outer envelope (18) corresponds to one of: an epoxy resin, an acrylic resin, a urethane acrylate resin, a polyamide resin, polyurethane, a silicone, a phenolic copolymer.

4. Multi-material rod (10) according to any one of the preceding claims, in which the elongation at break of the varnish is between 2% and 20% elongation and preferably between 2.5 and 10% elongation; and in which the elongation at break of the core is between 0.5% and 2.5%.

5. Multi-material rod (10) according to any one of the preceding claims, in which the film has an adhesion which satisfies a hold on the core up to a tear stress of 40 MPa.

6. Method of manufacturing a multi-material rod (10) according to any one of the preceding claims, comprising the steps of: - supply of said core (16); - depositing said varnish on the core (16), which has been previously manufactured, followed by drying this varnish to form said outer envelope (18); in which the varnish is deposited by spraying it onto the core (16) or by dipping the core (16) in a bath of the varnish.

7. Method according to claim 6, in which the varnish is dried by adding heat or by UV radiation.

8. Method according to any one of claims 6 or 7, in which the core (16) is previously manufactured by pultrusion.

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