Metallurgical furnace monitored by electrical reflectometry

Abstract

The invention relates to a metallurgical furnace comprising a time- or frequency-domain electrical reflectometry monitoring device for monitoring the metallurgical furnace using an array of wire electromagnetic waveguides, wherein each waveguide comprises a measurement portion extending in parallel to the hot face and wherein the measurement portion is provided with a plurality of discontinuities, referred to as "base discontinuities", - which are distributed randomly at least along the measurement portion of the waveguide, and - are capable of generating echoes having an amplitude greater than 0.5%, preferably greater than 1% and less than 30%, of the amplitude of the back echo reflected by the output end of the waveguide, referred to as "base secondary echoes", or are formed by raised portions or by raised portions resulting from irregular segmentation of a dielectric material positioned between the first and second electrical conductors, or local variations in the distance between the first and second electrical conductors or in the distance between, on the one hand, the first electrical conductor and / or the second electrical conductor and, on the other hand, a dielectric material of a support, or variations in the structure and / or the composition of the environment surrounding the first and second electrical conductors or between the first and second electrical conductors, the number of base discontinuities, per metre of the measurement portion of the waveguide, being greater than 10.

Description

[0001] METALLURGICAL FURNACE MONITORED BY ELECTRICAL REFLECTOMETRY

[0002] Domain

[0003] The present invention relates to a metallurgical furnace, in particular a foundry furnace, more particularly an induction furnace, equipped with a device for monitoring the state of a part of such a furnace, in particular the state of the refractory lining of the furnace enclosure.

[0004] It also relates to a manufacturing method and a method for measuring the condition of the refractory lining of such a furnace.

[0005] State of the art

[0006] The technology of metal melting furnaces, particularly by induction, is known.

[0007] Figure 1 schematically represents in cross section, a crucible 8 of an induction furnace of a metallurgical furnace. This crucible comprises a side wall 10 which extends, substantially vertically, from a bottom 41 delimiting an enclosure 9. The side wall 10 of the crucible conventionally comprises, from the outside to the inside of the crucible:

[0008] - a surrounding or supporting layer 11, generally made of concrete, in which the inductor 16 is fixed;

[0009] - at least one layer of thermal insulation 17;

[0010] - at least one layer of electrical insulation 19;

[0011] - a refractory coating 22 of rammed earth which may comprise an unconsolidated region 28, preferably in the form of a compacted powder, and a consolidated region 29 in metal contact, defining the interior surface 28 of the crucible.

[0012] The order of the layers of thermal insulation 17 and electrical insulation 22 is not limiting.

[0013] The electrical insulating layer 22 is made of a dielectric mineral material, for example mica, and has the function of electrically insulating the inductor and the refractory coating.

[0014] The thermal insulation layer 17 may in particular be a ceramic fibrous mat, in particular made of an aluminosilicate. Advantageously, it makes it possible to compensate for the effect of thermal expansion of the refractory coating 22 during heating and / or to protect the electrical insulation layer.

[0015] The bottom or "floor" 41 conventionally comprises, from the outside to the inside of the crucible: a first layer of refractory blocks 13, substantially horizontal; - a refractory coating 22' itself comprising an unconsolidated layer 28', preferably in the form of a compacted powder, and a consolidated layer 29', defining the interior surface, or hot face 37 of the crucible.

[0016] The 22 or 22' refractory lining is also called the "first layer". The other layers form the "back layer" and can each be considered "sub-layers" of the back layer.

[0017] The furnace can be fixed but is usually mobile so that the molten metal it contains can be poured into different tanks or foundry molds.

[0018] To improve the monitoring of this type of furnace, US5139671 describes an array of electrodes placed in the thermal insulation layer between the inductor and the refractory layer in contact with the molten metal. This technology involves an impedance that may interact with the inductor and disrupt the operation of the furnace. In addition, this technology is expensive due to the large number of electrodes and the numerous connections it requires.

[0019] W02004 / 015349A2 describes a non-resistive device comprising optical waveguides. This technology has the advantage of avoiding any electrical interaction but is not sufficiently reliable due to the fragility of optical fibers, even when protected by a fiber mat. In addition, in service, the performance of this device is limited in temperature.

[0020] JPH11264706A or JP3395886B2 also discloses a device for measuring the residual thickness of a blast furnace lining, positioned within the thickness of the lining. This device is highly invasive and significantly increases the risk of the lining being breached. In addition, its spatial resolution is very low.

[0021] EP0065583A1 describes a metallurgical furnace equipped with an electrical reflectometry device for determining a residual thickness by measuring the travel time of a reflected wave in a waveguide placed perpendicular to a hot face. Documents US3078707A, US3532797, US3307401 or US3512413 cited by EP0065583A1 envisage the measurement of the residual thickness of a furnace lining by the variation in resistance or electrical potential of a network of electrical conductors oriented perpendicular to the hot face or of an electrically conductive plate perpendicular to the hot face. DE2461804, also cited by EP0065583A1, relates to a device comprising a waveguide and a reflector positioned between a target part whose thickness is measured by injecting, with an electromagnetic radiation generator, two signals of different high frequencies.

[0022] There is a continuing need for a robust, easy-to-implement solution that can continuously and in real time assess the condition of the refractory lining of a metallurgical furnace for all areas of the furnace with good spatial resolution, without weakening the lining, particularly in the case of electrical heating, and without increasing the risk of electrical interaction with the furnace heating system.

[0023] One aim of the invention is to meet, at least partially, this need.

[0024] Summary of the invention

[0025] According to the invention, this aim is achieved by means of a metallurgical furnace, preferably a foundry furnace, preferably an induction furnace, comprising:

[0026] - a metal melting chamber 9 having a hot face exposed towards the inside of the chamber;

[0027] - a device for monitoring, by time or frequency electrical reflectometry, the state of a part of the furnace, preferably a part of said enclosure, called “target”, said device comprising:

[0028] - a network of at least one wired waveguide, preferably a plurality of wired electromagnetic waveguides, each waveguide comprising, between an input end and an output end, first and second electrical conductors, preferably metallic, electrically insulated from each other, preferably by a dielectric material,

[0029] - a measuring part of the waveguide comprising a plurality of impedance discontinuities and extending parallel to the hot face and at a depth (distance behind said hot face relative to the interior of the enclosure) greater than 10 cm, preferably greater than 15 cm, or greater than 20 cm; preferably less than 200 cm, preferably less than 100 cm;

[0030] - an interrogator electrically connected to the input end and configured to inject an interrogation signal through said input end, receive a response signal reflected by said waveguide in response to said injection, analyze the response signal and emit a message on the state of the target based on said analysis. The inventors have discovered that this arrangement of the waveguide relative to the target offers an excellent compromise between robustness, resolution capacity and reliability, which makes it possible to evaluate the state of the refractory in real time throughout the life of the furnace, without weakening said coating and without increasing the risk of electrical interaction with the heating system, for example an inductor.

[0031] The waveguide network also makes it possible to track a target of any size in a metallurgical furnace.

[0032] The target preferably comprises the monolithic refractory lining 22, 22' of rammed earth defining the hot face of the side wall of the furnace crucible.

[0033] According to a first main embodiment, said impedance discontinuities comprise “basic discontinuities”:

[0034] - which, in particular when the length of the measuring part is less than 10 meters, are capable of generating, in response to the injection of the interrogation signal, echoes having an amplitude greater than 0.5%, preferably greater than 1%, and preferably less than 30% of the amplitude of the bottom echo reflected by the output end of the waveguide, called “basic secondary echoes”, and / or

[0035] - are made up of

[0036] - reliefs resulting from a texturing of the outer surface of the waveguide and / or of a dielectric material interposed between the first and second electrical conductors and / or of at least one of the first and second electrical conductors, and / or

[0037] - reliefs resulting from an irregular segmentation of said dielectric material, preferably by means of cleats made of a dielectric material, the cleats preferably having a length of less than 10 cm, preferably less than 5 cm, preferably less than 3 cm, more preferably less than 2 cm and / or greater than 0.5 cm, and / or

[0038] - local variations in the distance between the first and second electrical conductors; and / or

[0039] - variations in the distance between the first electrical conductor and / or the second electrical conductor on the one hand, and a dielectric material of a support, preferably made of a ceramic matrix composite, on the other hand; and / or

[0040] - variations in the structure and / or composition of the environment around the first and second electrical conductors or between the first and second electrical conductors, preferably variations in the structure and / or composition of a dielectric material of a support, preferably a ceramic matrix composite, preferably by the random dispersion of particles and / or fibers of a dielectric material within the support, and in particular within the matrix of the ceramic matrix composite, or between the first and second electrical conductors.

[0041] Remarkably, the inventors discovered that the analysis of basic secondary echoes by electrical reflectometry TDR (Time Domain Reflectometry) or FDR (Frequency Domain Reflectometry) allows monitoring of the target's state in real time and continuously, over a long period of time and in a precise and reliable manner.

[0042] The basic discontinuities are capable of generating basic secondary echoes in response to the injection of the interrogation signal, i.e. in service, to track the state of the target. To ensure this tracking, the amplitudes of the echoes are preferably measured under conditions similar or identical to those experienced by the measuring part in the service position, preferably at a temperature above 500°C, preferably above 600°C, preferably above 700°C, preferably above 800°C and / or below 1300°C, preferably below 1200°C, more preferably below 1100°C.

[0043] Preferably, the basic discontinuities are randomly distributed at least along the measurement portion of the waveguide, or even along the entire length of the waveguide. Advantageously, the random distribution avoids interference resonance phenomena.

[0044] Preferably, the basic discontinuities are:

[0045] - reliefs resulting from texturing of the outer surface of the waveguide and / or of a dielectric material interposed between the first and second electrical conductors and / or of at least one of the first and second electrical conductors, for example by abrasion and / or chemical attack, and / or

[0046] - reliefs resulting from an irregular segmentation of said dielectric material, preferably by means of cleats (for example in the form of beads or cylinders, preferably with a circular base) made of a dielectric material, the cleats preferably having a length of less than 10 cm, preferably less than 5 cm, preferably less than 3 cm, more preferably less than 2 cm and / or greater than 0.5 cm, and / or - local variations in the distance between the first and second electrical conductors.

[0047] The conductors may be sandwiched between two textiles made of a ceramic matrix composite or may be attached to the surface of a ceramic matrix composite textile, a dielectric material, for example in the form of a regular pattern, preferably extending over a surface of one or both of said textiles. The dielectric material may, for example, result from depositing a slip and then curing the slip.

[0048] In one embodiment, the aforementioned sandwiches have a thickness greater than 5 mm, greater than 8 mm, greater than 10 mm and / or less than 50 mm.

[0049] In one embodiment, a textile, preferably each of the aforementioned textiles, has a thickness greater than 0.5 mm, greater than 1 mm, and / or less than 10 mm, less than 5 mm, or less than 2 mm.

[0050] Preferably, the basic discontinuities generated by texturing generate more than 80% of said basic secondary echoes.

[0051] The cleat(s) are preferably arranged less than 1 mm from the first and / or second electrical conductor, preferably in contact with the first electrical conductor and / or the second electrical conductor.

[0052] Preferably, the cleat(s) are threaded, in the measuring part, onto the first electrical conductor and / or onto the second electrical conductor.

[0053] In one embodiment, bead-shaped lugs made of a dielectric material are threaded, in the measurement portion, onto the first electrical conductor and / or the second electrical conductor, and the lugs are arranged to together form a segmented protective sheath extending throughout the measurement portion of the waveguide.

[0054] The cleat(s) are preferably spacers made of a dielectric material, arranged to keep the first electrical conductor away from the second electrical conductor.

[0055] In one embodiment, the cleat(s) are movable relative to the first electrical conductor and / or the second electrical conductor. Preferably, the cleat(s) are made of a thermally and electrically insulating material.

[0056] The thermally insulating material preferably has a thermal conductivity of less than 30 W / mK, less than 20 W / mK, less than 10 W / mK, or even less than 5 W / mK, at a temperature between 20°C and 1000°C.

[0057] Preferably, the cleat(s) have a melting point greater than 300°C, greater than 500°C, or greater than 1000°C, and preferably are made of a material selected from mica, mica derivatives, titanium, barium, mullite, cordierite and alumina.

[0058] In one embodiment, discontinuities, preferably basic discontinuities, are created by making said measuring portion integral with a said support. In particular, the support may surround the measuring portion, in the manner of a sheath, or sandwich the measuring portion. In particular, the measuring portion may be sandwiched between two textiles, preferably woven, stiffened by a ceramic matrix. The irregularities of the textiles and the matrix of such a ceramic matrix composite advantageously and unexpectedly make it possible to create basic discontinuities.

[0059] Preferably, the impedance discontinuities are spaced apart from each other by a distance, measured along the waveguide, at least 10 times, preferably at least 15 times, preferably at least 20 times less than the reference wavelength, equal to the propagation speed of the interrogation signal, of approximately 200,000 km / s for an electromagnetic wave, divided by the frequency of the highest peak of the frequency spectrum of the interrogation signal.

[0060] The invention further relates to a method for manufacturing a furnace according to the first main embodiment, said method comprising the following steps: i) modification of a measuring part of at least one waveguide, preferably of a coaxial cable, so as to create basic discontinuities randomly distributed along the waveguide; ii) integration of said at least one modified waveguide obtained in or against a wall of an enclosure of a glassmaking furnace; iii) connection of a said interrogator to an input end of said at least one modified waveguide, said at least one modified waveguide constituting a said wired electromagnetic waveguide, so as to obtain a glassmaking furnace according to the first main embodiment. The person skilled in the art knows how to modify a waveguide, and in particular a coaxial cable, to create basic discontinuities.By simple tests, it can easily check whether the echoes returned by discontinuities constitute basic secondary echoes and adapt said discontinuities, for example by reinforcing the texturing if the discontinuities return echoes of insufficient amplitude for said echoes to be basic secondary echoes.

[0061] Preferably, step i) comprises, preferably consists of, modifying the outer surface of a waveguide, preferably a coaxial cable, preferably by texturing the outer surface of the waveguide and / or segmenting, for example by threading cleats.

[0062] The waveguide that is the subject of the modification in step a) may be a commercial waveguide.

[0063] Step i) may be replaced by a step i') in which the basic discontinuities are created simultaneously with the manufacture of the waveguide. They may be created, in particular, by texturing the outer surface of the waveguide and / or segmentation, for example by threading cleats onto the waveguide, but also by modifying the composition of the dielectric interposed between the first and second electrical conductors and / or by modifying the composition of at least one of the first and second electrical conductors, and / or by creating reliefs on the surface of said dielectric material and / or at least one of the first and second electrical conductors.

[0064] According to a second main embodiment, the furnace further comprises one or more of the following optional features, preferably all of the following optional features: a) the measuring part of each of the waveguides of said network extends parallel to the hot face and at a distance adapted so that in service, that is to say when the furnace is in normal operation, said measuring part is at a temperature above 500°C, preferably above 600°C, preferably above 700°C, preferably above 800°C and / or below 1300°C, preferably below 1200°C, more preferably below 1100°C; b) the maximum distance between two measuring parts of any two waveguides of the network is greater than 20 cm, preferably greater than 30 cm, preferably greater than 50 cm, preferably greater than 70 cm, preferably greater than 90 cm, and preferably less than 500 cm;c) at least one, preferably each waveguide of the array is inserted into a hole in the target, the hole being configured to provide a thermal expansion space for the waveguide; d) the equivalent diameter of the measuring portion of at least one, preferably each waveguide of the array is greater than 0.6 mm, preferably greater than 0.8 mm, preferably greater than 1 mm and less than 50 mm, preferably less than 20 mm, preferably less than 10 mm, preferably less than 5 mm; e) the distance between the first and second electrical conductors of the measuring portion of at least one, preferably each waveguide of the array, is greater than 0.3 mm, preferably greater than 0.4 mm, preferably greater than 0.5 mm and less than 30 mm, preferably less than 10 mm, preferably less than 5 mm, preferably less than 3 mm, which improves reliability and spatial resolution;f) said measuring part has a number of bends:;

[0065] - less than 2 per meter of length of measuring part if the length of said measuring part is less than 3 meters;

[0066] - less than 1 bend per meter, preferably less than 0.5 bends per meter, more preferably less than 0.1 bend per meter of measuring part, if the length of said measuring part is greater than or equal to 3 meters, which improves the integration of the waveguide while minimizing the risk of breakage of the waveguide during its installation in the oven, the measuring part of the measuring part of a waveguide, preferably of each waveguide, preferably not having a bend;

[0067] - the maximum curvature of the measuring part is such that its radius of curvature is at least 3 times, preferably at least 5 times, preferably at least 10 times, greater than the equivalent diameter of said measuring part, which reduces the mechanical stresses on the measuring part.

[0068] Preferably, the measuring part of at least one waveguide, preferably of each waveguide, is slidably mounted relative to the target and / or relative to the support. The inventors have discovered that this combination of characteristics, which results from research on a multitude of parameters, provides a solution adapted to the specific constraints of a metallurgical furnace. In particular, it allows:

[0069] - an installation limiting the risk of deterioration of the waveguides,

[0070] - tracking a large target, such as the cylinder of a foundry furnace

[0071] - great robustness in service;

[0072] - good spatial resolution;

[0073] - high measurement reliability;

[0074] - real-time monitoring throughout the life of the furnace, without weakening the target and without increasing the risk of electrical interaction with the heating system.

[0075] According to a third main embodiment, the first and second conductors are fixed to or integrated into a support, preferably in the form of a plate, preferably made of a ceramic matrix composite, preferably are fixed by means of an interfacing layer or refractory tapes, staples or wires or are integrated into said composite. By "integrated" is meant that they are incorporated into the composite, for example by being weft or warp threads of the textile of the composite.

[0076] Fixing the conductors in or on a support allows them to be protected. The support is preferably arranged between the first layer and the backing layer (which preferably includes a heating system, for example an inductor).

[0077] According to a first preferred configuration, the support preferably comprises, and is made of, a ceramic matrix composite, and the first and second conductors are integrated within the textile of the ceramic matrix composite, preferably. The conductive threads, preferably arranged substantially parallel at a predetermined distance, may for example constitute part of the weft threads. The other threads of said textile (other than the first and second conductors) are preferably made of a dielectric material, so as to avoid any electrical contact or short circuit between said conductive threads.

[0078] In one embodiment, the other wires of a dielectric material (or "non-conductive wires") may be randomly modified, for example by abrasion or chemical etching to generate random base discontinuities. In a further or alternative embodiment, the first and second conductors are randomly modified, for example by abrasion or chemical etching to generate random base discontinuities.

[0079] In one embodiment, at least one of the first and second conductors is physically associated with one or more wires of a dielectric material, for example randomly wound to generate random base discontinuities.

[0080] In one embodiment, yarns of a dielectric material are added to the textile in a random manner.

[0081] In one embodiment, in order to generate discontinuities, in particular random basic discontinuities, the first and second conductors are integrated into the textile by weaving so that the distance between said conductors is variable along the conductors. Preferably, the distance between two said basic discontinuities is then less than 10 cm, preferably less than 5 cm and / or greater than 0.5 cm, preferably greater than 1 cm. Preferably, the distance between two successive points of passage of the first and second conductors over or under the sheet of weft threads or the sheet of warp threads of the woven textile, possibly overlapping several weft or warp threads, preferably the distance between two successive picks, is less than 10 cm, preferably less than 5 cm and / or greater than 0.5 cm, preferably greater than 1 cm.

[0082] In one embodiment, in order to generate random basic discontinuities, particles and / or fibers of random size and / or random shape and / or random dimensions and / or randomly spatially distributed are arranged in contact with said textile before impregnation with the matrix precursor. An irregularly textured fabric web can also be used as a textile.

[0083] According to a second configuration, the first and second conductors are fixed to the surface of the support and, preferably, the support comprises, preferably is constituted by a ceramic matrix composite.

[0084] According to one possible embodiment, the conductors, preferably the measuring part, of at least one waveguide, preferably of each waveguide, are fixed to the support by means of an interface layer. An interface layer is a layer made of a material having a coefficient of thermal expansion (CTE) intermediate between that of the support, in particular that of the ceramic matrix of the support, and that of the material constituting the conductors. Preferably, the interface layer comprises, or is even made of, a NiCrAlY.

[0085] According to another possible embodiment, the conductors, preferably the measuring part, of at least one waveguide, preferably of each waveguide are attached or fixed to the support, preferably in the form of a plate, by means of refractory tapes, staples or wires.

[0086] In one embodiment, the measuring part is protected by a sheath made of a dielectric material, preferably polymer or even more preferably ceramic, said sheath surrounding the conductors, the conductors preferably being separated by a dielectric material. Said sheath can be straight or curved. It can be flexible, or rigid to give a shape to the measuring part, or even to the transmission part.

[0087] In one embodiment, the measuring part is protected by a sheath, made of polymer or preferably ceramic in a dielectric material, said sheath surrounding the conductors preferably separated by a dielectric material. Said sheath can be straight or curved. It can be flexible, or rigid to give a shape to the measuring part, or even to the transmission part. In one embodiment, as shown in Figure 7, a support precursor, preferably consisting of a ceramic matrix composite precursor 40', conventionally a prepreg, is wound around the first and second conductors, at least in the measuring part. Before or after hardening of the matrix precursor, the instrumented support precursor or the instrumented support is preferably inserted into a protective sheath 27, preferably ceramic.

[0088] Attaching to or embedding the measuring portion of a waveguide in a ceramic matrix composite is particularly advantageous, not only because the ceramic matrix composite protects the measuring portion, but also because, by construction, even when the ceramic matrix composite includes a woven textile, it has an irregular microstructure that generates many basic discontinuities.

[0089] According to a fourth main embodiment, the measuring part of at least one waveguide, preferably of each waveguide, is movable so that its dimensions can change under the effect of a temperature variation in service. Preferably, the measuring part is slidably mounted relative to the target, preferably slidably in a housing, in particular an orifice, provided in the target or, preferably in the support.

[0090] More preferably, the housing provides a thermal expansion space, preferably generated by removing a sacrificial material around which at least a portion of the target or support has been formed.

[0091] Sliding can also result from the presence of a solid lubricant, preferably graphite, around the measuring part.

[0092] The lack of adhesion of the measuring part to the wall of the housing may also result from an incompatibility between the material of the target or the support defining the housing on the one hand, and the measuring part on the other hand, for example from a high porosity of the material of the target defining the housing.

[0093] Sliding can also result from the insertion of the measuring part into a protective sheath, preferably not segmented. The segmentation of a protective sheath by the succession of dielectric beads along the measuring part tends to increase the attenuation of the signals.

[0094] The invention also relates to a method of manufacturing an oven according to the invention, said method comprising, for at least one, preferably for each waveguide of the network, the following successive steps:

[0095] 1) interposition of a sacrificial material between

[0096] - the measuring part of the waveguide and

[0097] - the target or a precursor of the target, or a support, in particular a ceramic matrix composite or a support precursor, then

[0098] 2) after or simultaneously with the manufacture of the target or the support for the case where the sacrificial material has been interposed in a precursor of the target or in a precursor of the support, respectively, elimination of the sacrificial material so as to create a so-called expansion space for the measuring part.

[0099] In one embodiment, the sacrificial material is the material of a sacrificial sheath sheathing the measuring portion, and, to interpose the sacrificial material,

[0100] - the target or support is manufactured around the measuring part, preferably by casting and then sintering a precursor of the target around the measuring part, or by inserting the measuring part into a precursor of the support and then sintering the support precursor around the measuring part;

[0101] - a housing is provided, in the form of a groove or a hole (or "orifice"), passing through or not, in the target or in a precursor of the target or in the support or in the support precursor, then the measuring part is inserted into the housing, then the housing is filled with an unshaped refractory product (i.e. a powder or a paste) containing a binder, preferably a hydraulic binder, preferably a cement, and capable of setting into mass by activation of the binder, preferably a refractory concrete, then the unshaped refractory product is hardened.

[0102] The target precursor may be a preform intended to be sintered or a powder mixture capable of setting by chemical reaction. The support precursor may be a ceramic matrix composite precursor comprising a textile and a matrix precursor impregnating the textile, or "prepreg".

[0103] The measuring portion provided with the sacrificial sheath may be embedded in the target or support precursor at the time of its manufacture. Alternatively, a housing may be provided in the target or target precursor or support or support precursor, and the measuring portion provided with the sacrificial sheath may be embedded in the unshaped refractory material.

[0104] In one embodiment, the sacrificial material is a filling material independent of the waveguide, i.e. which, unlike a sacrificial sheath, is not initially integral with the waveguide and, to interpose the sacrificial material,

[0105] - a housing is provided, in the form of a groove or a hole, through or not, in the target or in a precursor of the target or in a support or in a precursor of a support, then

[0106] - insert the measuring part into the housing, then

[0107] - the housing is filled with the filling material so as to drown the measuring part, the quantity of filling material being adapted to provide the expansion space, then

[0108] - the housing is filled with a so-called unshaped refractory product, preferably refractory concrete, then

[0109] - the unshaped refractory product is hardened. In step 2), the sacrificial material is preferably removed by heat treatment, preferably by consolidation heat treatment of the target precursor or the support, preferably by sintering. The sacrificial material is preferably removed by heat during quenching of the furnace and / or during sintering of the unshaped refractory product or the target precursor or the support precursor at a temperature preferably between 400°C and 1200°C. Sintering may result from quenching of the furnace.

[0110] Removal of the sacrificial material can be accomplished by vaporization or combustion.

[0111] The sacrificial material thus leaves room for thermal expansion.

[0112] Preferably, the sacrificial material is an organic material, preferably a polymer. By degrading, such a sacrificial material advantageously generates residual carbon which limits the oxidation of the first and second conductors, which allows its use in an oxidizing atmosphere.

[0113] The manufacturing process may further include one or more of the following optional and preferred features:

[0114] - step 1) and / or step 2) are carried out in situ, i.e. at the location of the furnace at which the measuring part is intended to be used in the furnace;

[0115] - the housing is provided in the support or in a precursor of the support, but it can also be provided in a rear layer of the target or in a precursor of the rear layer;

[0116] - the sacrificial sheath of a waveguide, preferably of each waveguide, is made of a polymer, preferably a polymer comprising no halogen and / or no nitrogen and / or no silicon, preferably a polyalkylene, preferably a polyethylene or one of its derivatives;

[0117] - the filling material is a resin;

[0118] - the removal of the sacrificial material is simultaneous with a hardening of the precursor of the target or of the support leading to said target or said support, respectively.

[0119] In one embodiment, step 1) comprises the following steps:

[0120] - placing the network precursor in the operating position, i.e. placing the measuring part(s) in the desired operating position during operation of the furnace;

[0121] - preparation of a starting charge having the desired composition for the target or support, considering only the refractory oxides;

[0122] - deposition of the starting charge in order to drown the network precursor and obtain the precursor of the target or support.

[0123] In one embodiment, at least one, preferably each, measuring part is protected by a protective sheath, preferably ceramic. The sacrificial sheath then covers the protective sheath.

[0124] According to a fifth main embodiment, the waveguide comprises a protective sheath for the first and second electrical conductors.

[0125] The protective sheath may be rigidly secured to the conductors provided that it is segmented, or constitute a rigid sheath serving as a housing for the waveguide. The waveguide may be inserted into the sheath after the sheath has been placed in the service position. In particular, the sheath may be included in the target at the time of manufacture of said target, for example placed in position before being embedded in a concrete constituting the target.

[0126] Preferably, the waveguide can move freely within the sheath. The protective sheath may also provide an expansion space as described above.

[0127] A rigid sheath can advantageously guide the waveguide to give it a predetermined shape, for example straight or bent, or guide it over a long length during its insertion.

[0128] Preferably, the waveguide is protected by two protective sheaths, namely a segmented protective sheath, preferably consisting of several cleats placed end to end, and a rigid protective sheath serving as a housing for the waveguide. The segmented protective sheath may, for example, result from a threading of a multitude of beads.

[0129] The invention also relates to a method for manufacturing a metallurgical furnace according to the invention, said method comprising, for at least one waveguide of the network, preferably for each waveguide of the network, the following steps:

[0130] A) preparing a precursor of a ceramic matrix composite comprising a ceramic matrix precursor, preferably in the form of a plate, and integrating the measuring part of the waveguide into or onto the ceramic matrix composite precursor so as to obtain an instrumented support precursor;

[0131] B) hardening and / or firing, preferably sintering, said instrumented support precursor, preferably during the temperature rise of the furnace, so as to obtain said instrumented support by consolidation of the ceramic matrix precursor, preferably in the form of an instrumented plate;

[0132] C) installation of the instrumented support if step C) is subsequent to step B) or installation of the instrumented support precursor if step C) is prior to step B), preferably between a rear layer defining the hot face and a furnace heating system, preferably substantially parallel to said hot face.

[0133] Preferably, step A) preferably comprises the following steps: a) preparation of the ceramic matrix precursor in the form of a slip comprising ceramic particles and / or precursors of ceramic particles, the material of said ceramic particles having a dielectric constant or relative electrical permittivity with respect to vacuum at 25°C and at atmospheric pressure, preferably measured at 1 MHz, greater than 3 and / or less than 30, preferably less than 15;b) independently of step a), fixing or integrating the first and second electrical conductors of said measuring part to a textile, preferably in the form of one or more fabrics or sheets of wires, preferably ceramic wires, the material of said textile having a material with a dielectric constant or relative electrical permittivity with respect to vacuum at 25°C and atmospheric pressure, preferably measured at 1 MHz, greater than 3 and / or less than 30, preferably less than 15; c) impregnation of the textile with said slip.;

[0134] Before or preferably after step B), a connector is installed capable of electrically connecting said conductors to an interrogator.

[0135] In one embodiment, the measuring part, or even the transmission part, is protected by a said sheath, before fixing or integration into the support.

[0136] In one embodiment, in step B), the baking is such that the temperature of the instrumented support precursor is between 400 and 1200°C.

[0137] In a particular embodiment, step B) is carried out, prior to step C), in an oven or furnace, preferably in air and preferably in a controlled atmosphere. In one embodiment, in step C), an instrumented support precursor is installed on or in a target precursor, and in step B), the instrumented support precursor is simultaneously consolidated by transforming the ceramic matrix precursor into a ceramic matrix and the target precursor to transform it into said target.

[0138] In one embodiment, in step C), the instrumented support or instrumented support precursor, preferably in the form of a plate, is disposed between

[0139] - said measuring part and

[0140] - the target or a precursor of the target.

[0141] Of course, the characteristics of the different main aspects can be combined. They are preferably combined.

[0142] Regardless of the main embodiment, the waveguide network of a metallurgical furnace according to the invention may also include one or more of the following optional and preferred features:

[0143] - the waveguide network extends at least partially, preferably completely, within

[0144] - a refractory rear layer extending behind a first layer consisting of an assembly of refractory blocks defining the hot face of the target or

[0145] - a refractory underlayer of said rear layer;

[0146] - the measuring portion of a waveguide, preferably of each waveguide, extends into said back layer or into a sub-layer of said back layer, preferably behind the barrier sub-layer;

[0147] - said underlayer is a thermally insulating underlayer in contact with the cold face of the target, intended to define the thermal profile of the coating, or7preferably, an electrically insulating underlayer intended to electrically insulate the first layer, or even, and preferably when the target is the sole, between the thermally insulating underlayer and the electrically insulating underlayer;

[0148] - the measuring portion of a waveguide of the array, preferably of each waveguide of the array, extends into a housing, preferably in the form of an orifice, provided in the target and defining a thermal expansion space for said waveguide;

[0149] - the thermal expansion space is adapted so that in service, the measuring part of the waveguide is not compressed by the target under the effect of dimensional changes of the target and of said measuring part resulting from temperature variations;

[0150] - preferably, the ratio of the equivalent diameter of the housing to the equivalent diameter of the measuring part is greater than 1.05, preferably greater than 1.10, preferably greater than 1.20, and / or less than 3.00, preferably less than 2.50;

[0151] - said housing is an orifice, the diameter of the orifice being less than the thickness of said layer or sub-layer in which said measuring part is placed;

[0152] - the diameter of said orifice is less than 70%, or even less than 50% of the thickness of said layer or sub-layer;

[0153] - the measuring part of a waveguide, preferably of each waveguide, except the bends, extends at least partially, preferably completely parallel to the measuring part of another waveguide;

[0154] - the measuring part of at least one waveguide, preferably of each waveguide of the network, is free of bends;

[0155] - the maximum distance between the measuring parts of any two waveguides is less than 200 cm;

[0156] - measuring parts of the waveguides together form a sheet extending along a curved or flat surface, preferably flat;

[0157] - the measuring parts of said sheet are separated from each other by a distance greater than 1 cm, greater than 5 cm, greater than 10 cm, greater than 20 cm, and / or less than 100 cm, less than 80 cm, or less than 50 cm;

[0158] - said measuring parts of the sheet extend parallel to each other or cross without touching;

[0159] - the furnace comprises more than 1, more than 2, preferably more than 3, preferably more than 5 said layers, said layers being preferably parallel to each other, preferably parallel to the hot face, and preferably regularly spaced apart in a direction perpendicular to the hot face, the distance between two successive layers being preferably less than 10 cm, 5 cm, or 2 cm, which, advantageously, makes it possible to evaluate thermal fluxes through the target;

[0160] - at least one measuring part, preferably more than half of the measuring parts of the network extend in a direction perpendicular to the direction of flow of the molten metal in service; - the radius of curvature of the measuring part of a waveguide, preferably of each waveguide of the network is at any point at least 3 times, preferably at least 5 times, preferably at least 10 times, greater than the equivalent diameter of said measuring part;

[0161] - the waveguide, preferably each waveguide of the network opens onto a cold face of the target, opposite the hot face, or onto a lateral face of the target (in particular when the target is the bottom of the furnace) colder than said hot face.

[0162] The skilled person knows how to determine the dimensions of a housing for a measuring part in order to reserve a suitable thermal expansion space. For example, for a sole, he will take into account the thermal gradient in the sole, the coefficient of thermal expansion of the slabs and the measuring part, as well as their dimensions.

[0163] The housing is also sized so that the target and the waveguide can expand independently of each other, and in particular so that an elongation or a shrinkage of the target does not cause stresses on the waveguide, and vice versa.

[0164] Regardless of the primary embodiment, a waveguide, preferably each waveguide of the array may further comprise one or more of the following optional and preferred features:

[0165] - the waveguide satisfies the Rayleigh scattering condition, which facilitates the localization of the regions having reflected the basic secondary echoes;

[0166] - at least one spacer, made of an electrically insulating material and more deformable than the material of the cleats, is arranged between two adjacent cleats, preferably between the cleats of each pair of two adjacent cleats, at least in the measuring part;

[0167] - said spacer, preferably each said spacer:

[0168] - is made of an elastically compressible material, like a spring and / or

[0169] - comprises and / or is made of an organic material, preferably a polymer material, for example based on polyethylene or silicone, preferably chosen from elastomers, thermoplastic materials and heat-shrinkable materials, for example in the form of a foam or a mastic;

[0170] - the length of the measuring part and / or the waveguide is greater than 1 meter, preferably greater than 2 meters, preferably greater than 3 meters, or even greater than 10 meters and / or less than 30 meters, preferably less than 20 meters;

[0171] - the length of the transmission part is preferably greater than 0.1 m and / or less than 5 meters, or even less than 2 meters;

[0172] - the first and second electrical conductors are parallel, which provides robustness, efficiency and reduced cost;

[0173] - the first and second electrical conductors are coaxial, which limits the size and reinforces the stability of the inter-conductor distance, the dielectric material holding the two coaxial conductors in position;

[0174] - the first and second electrical conductors are straight, which facilitates integration into the target;

[0175] - the equivalent diameter of said first and second conductors is greater than 0.4 mm, greater than 0.5 mm, preferably greater than 1 mm and / or less than 50 mm, preferably less than 20 mm, preferably less than 10 mm, preferably less than 5 mm, which makes it possible to improve the quality of the signal (low attenuation) while reducing the risk of weakening or breaking the target;

[0176] - the first and second electrical conductors are separated from each other by a dielectric material belonging to the target, for example an electrically insulating layer;

[0177] - the first and second electrical conductors comprise, preferably are made of a refractory metal, for example F Silver usable up to 800°C, for example Inconel (for example alloys 625 and 690), usable up to 1100°C, Kanthal of the FeCr type, for example KANTHAL APM, usable up to 1425°C or a noble metal, preferably chosen from Platinum, Tungsten, F Gold, Palladium, Rhodium, Ruthenium, iridium, or an alloy of these elements, the Platinum being able to be doped, preferably with 0.001% to 5% of zirconium, hafnium, calcium, magnesium or yttrium oxide;

[0178] - a dielectric material comprising, preferably consisting of an oxide of at least one element chosen from Al, Zr, Mg and Si, separates said first and second conductors;

[0179] - the material constituting the first and second electrical conductors has an electrical resistivity of less than 10 micro-ohm.m in the temperature range of the environment of the measuring part in service, preferably between 20 and 1000°C;

[0180] - the dielectric material which separates the first and second conductors has a dielectric constant or relative electrical permittivity with respect to vacuum at 25°C and atmospheric pressure, preferably measured at 1 MHz, greater than 3 and / or less than 30, preferably less than 15;

[0181] - the dielectric material comprises an oxide of at least one element chosen from Al, Zr, Mg, Ca, Ti and Si;

[0182] - at least a fraction of the measuring part, preferably at least in a region of the part of the waveguide which comes out of the target, is protected by a protective part, for example in the form of a tube or a pierced or grooved brick, preferably a protective sheath, preferably ceramic, partially, preferably completely surrounding said measuring part;

[0183] - said protective sheath is made of an oxide material of at least one element chosen from Al, Zr, Mg, Ca Ti and Si;

[0184] - the waveguide is connected to an interrogator at each of its two ends;

[0185] - the waveguide opens onto a cold face of the target, opposite the hot face, or onto a lateral face of the target colder than said hot face;

[0186] - the first and second conductors are fixed to a plate-shaped support, preferably made of a ceramic matrix composite, preferably by means of an interfacing layer or refractory tapes, staples or wires or are integrated into said composite.

[0187] Regardless of the main embodiment, at least one spacer made of a material more deformable than the material of the cleats is preferably arranged between two adjacent cleats. Preferably, a spacer is arranged between the cleats of each pair of adjacent cleats, at least in the measuring portion. Preferably, the material of the spacers is elastically compressible, in the manner of a spring. A spacer, preferably each spacer, preferably has the shape of a spring or the shape of a washer. A spacer, preferably each spacer, comprises or is made of an organic material, preferably a polymer material, preferably thermoplastic or heat-shrinkable, or a polymer foam.

[0188] Preferably, the spacers are threaded, in the measuring part, onto the first electrical conductor and / or onto the second electrical conductor.

[0189] Inserting spacers between the cleats advantageously ensures a minimum spacing between said cleats, particularly when said waveguide is curved. In particular, the spacers limit the risk of breakage when winding the waveguide, for example onto a mandrel or a reel, for transport, and when placing it in the service position.

[0190] Regardless of the primary embodiment, the interrogator may further include one or more of the following optional and preferred features:

[0191] - the interrogator is configured to determine, based on the analysis of the response signals, a temperature, a wear level and / or a wear rate of the target;

[0192] - the interrogator is configured to predict the occurrence of a breakthrough or infiltration of the target by molten metal, or of a sudden movement or degradation of the coating;

[0193] - the furnace preferably comprises at least one thermocouple arranged less than 10 cm from a waveguide, preferably any waveguide, for example in an area of ​​the furnace at a temperature between 500°C and 1500°C when the furnace is in operation, in order to calibrate said waveguide for indirect temperature measurement.

[0194] The invention also relates to a method for monitoring the state of a target of a metallurgical furnace according to the invention, said method comprising the following steps: a. manufacturing a metallurgical furnace according to the invention; b. for each waveguide, controlling the interrogator to which the waveguide is connected, so that it injects an interrogation signal through the input end of said waveguide; c. analyzing the response signal so as to determine information relating to the state of the target in the region of the measurement part of said waveguide.

[0195] According to a particular mode, the information relating to the state of the target is the residual thickness of refractory or a temperature at one or more points of the target.

[0196] Brief description of the figures

[0197] Other characteristics and advantages of the invention will become apparent upon reading the detailed description which follows and upon examining the attached drawing in which:

[0198] - [Fig 1] Figure 1 represents a schematic half-cross section of an induction metallurgical furnace;

[0199] - [Fig 2] Figure 2 schematically represents an example of a tracking device according to the invention, in a service position; - [Fig 3] Figure 3 illustrates different possible embodiments for a waveguide comprising beads;

[0200] - [Fig 4] Figure 4 illustrates, in cross-section, an arrangement of a waveguide in an induction metallurgical furnace in a first, preferred embodiment;

[0201] - [Fig 5] Figure 5 illustrates a support in the form of a plate, integrating a measuring part according to a first embodiment according to the invention;

[0202] - [Fig 6] Figure 6 illustrates a support in the form of a plate, integrating a measuring part according to another embodiment according to the invention;

[0203] - [Fig 7] Figure 7 illustrates the manufacture of a support by winding a support precursor around a measuring part;

[0204] - [Fig 8 ] Figure 8 represents an example of a response signal.

[0205] In the various figures, identical references are used to designate identical or similar organs.

[0206] Definitions

[0207] The term "target" refers to a refractory part of the furnace equipped with a tracking device. The target is preferably an element of the refractory lining of the furnace or "first layer" (seen from the inside of the furnace), conventionally obtained by assembling blocks or by ramming refractory rammed earth, for example an element of the refractory lining of a side wall of a crucible, a wall, a vault or a hearth. The first refractory layer is conventionally made of a molten material or a dense sintered material in order to resist the temperature but also corrosion by the molten metal or its slag.

[0208] The "hot face" is the face of a target that is exposed to a space in the furnace that, in use, contains molten metal or is intended to contain molten metal. The hot face may be in contact, or is intended to be in contact with molten metal and / or its slag. The hot face is thus the face of the target that is subjected or is intended to be subjected to the highest temperatures. All the hot faces of the blocks or rammed earth of the side wall of the metal melting crucible may also, by extension, be referred to as the "hot face". The upper surface of the hearth may also be referred to as the "hot face". The adjective "hot" is used for clarity.

[0209] Conventionally, the "thickness" of a target is its dimension measured in a direction perpendicular to its hot face, or "depth" direction. For example, for a side block of a crucible in a metallurgical furnace in contact with molten metal, the thickness is measured in a substantially horizontal direction directed towards the molten metal bath. For a hearth, the thickness is measured in a vertical direction.

[0210] Two objects have “substantially the same composition” when at least 80%, preferably at least 90% of their components are identical.

[0211] Concrete is typically made up of a set of coarse grains, with a size greater than 50 pm, typically between 50 pm and 25 mm, bound by a matrix, said matrix ensuring a substantially continuous structure between the coarse grains. The matrix is ​​made up of “matrix particles” with a size less than or equal to 50 pm.

[0212] Activation is the process of setting fresh concrete into a mass. It typically results from moistening a particulate mixture containing a hydraulic binder with water or another liquid, preferably by adding more than 3% water by mass. To be shaped, fresh concrete is preferably poured, vibro-cast if the mixture is not self-flowing, or even sprayed.

[0213] A "hydraulic binder" means a binder that, upon activation, generates hydraulic setting and hardening, generally at room temperature. A cement is a hydraulic binder. An aluminous cement is an example of a cement. A calcium aluminate cement is an example of an aluminous cement.

[0214] A refractory "rammed earth" is a refractory mixture containing a chemical and / or ceramic and / or organic binder, conventionally shaped after possible humidification, by tamping or compacting or beading, by hand or using appropriate mechanical means. Preferably, the particulate mixture is not humidified ("dry" implementation) or humidified with less than 3% water, in mass percentage).

[0215] The "support" is a part added to the target and on which or in which the measuring part of one or more waveguides is arranged. The support physically protects the measuring part, preferably creates basic discontinuities and preferably allows sliding of the measuring part, in particular under the effect of temperature.

[0216] The support or support precursor is sometimes referred to as "instrumented" when it carries the measuring part of at least one waveguide. A plate typically has two large faces that are substantially parallel, the thickness between the two large faces typically being less than 1 / 2, or even less than 1 / 3, or even less than 1 / 5, or even less than 1 / 10, or even less than 1 / 100 of the width of the large faces. A plate may be flat or curved. The shape of a plate-shaped support is preferably adapted to match the shape of the target to which it is intended to be attached.

[0217] By "Ceramic Matrix Composite", or "CMC", we conventionally mean a product composed of fibers and / or threads bonded together by a ceramic matrix, preferably representing at least 30% of the ceramic matrix composite by volume. The fibers and / or threads are chosen according to the environment in which the ceramic matrix composite is to be placed, in particular according to the conditions of temperature, corrosion, thermal cycling, expansion, and according to the nature of the target to be equipped.

[0218] The arrangement of the fibers and / or wires, which constitute the reinforcing structure for the matrix, is chosen according to the desired shape for the ceramic matrix composite, and the ease of fixing the waveguide to it. For example, a stack of woven or fiber sheets is well suited for simple plates, a filament winding is well suited for plates with a geometry of revolution, a filament placement is well suited for complex shapes of large dimensions.

[0219] A ceramic matrix composite is conventionally manufactured by heating, preferably above 600°C, preferably above 700°C, preferably by sintering.

[0220] The fibers and / or threads are typically in the form of a textile. The ceramic matrix composite can then be referred to as a “ceramic matrix textile”.

[0221] A textile can be:

[0222] - an organized two-dimensional structure of fibers or yarns, including a knit, braid, fabric, or

[0223] - a random two-dimensional structure of fibers or threads, this random structure not being preferred.

[0224] A textile is distinguished in particular from a fibrous mat, in which the organization of the fibers or threads is random in the three dimensions of space. ZI

[0225] A "fiber" is a filament whose length is greater than 5 times its equivalent diameter. The "diameter" of a fiber is the diameter of a disk with the same area as its cross-section at mid-length.

[0226] A "yarn" is an assembly of fibers which, in cross-section, contains more than 10 and preferably less than 500,000 fibers, and whose length is greater than 5 times the diameter.

[0227] By "wire" is meant "having the general shape of a wire." For example, a cable has a wire shape. A narrow strip, or "ribbon," is considered wire. An object having a wire shape preferably has a length greater than 10 times, 100 times, 1,000 times, or 10,000 times its width (i.e., its largest dimension in a plane perpendicular to the direction of its length).

[0228] By "waveguide" is meant a wire transmission line, different from the target, capable of guiding an electromagnetic wave originating from a very high frequency electrical signal in order to carry out a measurement by time or frequency electrical reflectometry. A waveguide conventionally comprises at least two electrical conductors electrically insulated from each other and which extend along the length direction of the waveguide. The interrogation signal is conventionally a variation in the electrical potential difference between said electrical conductors. The interrogation signal is injected at the input end of the waveguide, then propagates in the form of an electromagnetic wave. A variation in electrical impedance causes a partial reflection of this wave. The reflected response signal is also a temporal variation in the potential difference between the electrical conductors.

[0229] The part of a response signal that is returned is called an "echo":

[0230] - by a discontinuity (secondary echo),

[0231] - through the input end of the waveguide, at the connector (transmission echo) or

[0232] - through the output end of the waveguide (bottom echo 4 - see figure 8).

[0233] A secondary echo is thus a response of a discontinuity to the interrogation signal, the secondary echoes can be "noise" secondary echoes 5, "basic" secondary echoes 6 and or "clear" secondary echoes 7 (figure 8).

[0234] Secondary noise echoes are secondary echoes that have an amplitude less than or equal to 0.5% of the amplitude of the background echo and preferably greater than 0.0001%, preferably greater than 0.01%, preferably greater than 0.1% of the amplitude of the background echo. They are conventionally generated by “noise” discontinuities resulting from imperfections in the waveguide, generated in particular during the manufacture of the waveguide.

[0235] Since secondary noise echoes are of low amplitude, they are quickly attenuated. In many cases, they do not allow for accurate monitoring of measurement changes, for example when the temperature rises or when the humidity is high.

[0236] Basic secondary echoes are secondary echoes generated by "basic" discontinuities generally resulting from intentional modifications made to the waveguide, for example by texturing or adding cleats. They preferably have an amplitude lower than the amplitude of the bottom echo, preferably less than 90%, preferably less than 70%, preferably less than 50%, preferably less than 30% of the amplitude of the bottom echo. When the length of the measurement part is less than 10 meters, they preferably have an amplitude greater than 0.5%, preferably greater than 1% and less than 30% of the amplitude of the bottom echo.

[0237] The amplitude of the secondary backbone echoes can be greater than 2%, 3%, or 5%, or even 10% of the amplitude of the backbone echo reflected from the output end of the waveguide.

[0238] Sharp secondary echoes are secondary echoes that have an amplitude greater than or equal to 30% of the amplitude of the background echo. They are generally isolated and generated by "sharp" discontinuities, typically resulting from a significant or sudden variation in the structure of the waveguide, for example resulting from unintentional degradation of the waveguide, for example by cracking (without breakage). Such sharp, local discontinuities do not allow, by analyzing the sharp secondary echoes, to measure disturbances or changes in the environment elsewhere than at the locations of the sharp discontinuities. They therefore do not allow measurement variations to be located over the entire length of the measurement section.

[0239] Recent studies carried out by the inventors have however demonstrated that frank secondary echoes generated by discontinuities can constitute basic secondary echoes usable for monitoring, by time or frequency electrical reflectometry, the state of a part of the furnace if the number of discontinuities which generate them, per meter of waveguide measurement part, is greater than 10, greater than 15, greater than 20, greater than 30, greater than 40, greater than 50, and preferably less than 10,000, and if these discontinuities are distributed randomly.

[0240] A "discontinuity" or "impedance discontinuity" is a part of the waveguide capable of returning a specific echo in response to an interrogation signal, preferably in the form of a small variation in electric potential. This echo is modified when the impedance of the discontinuity varies, in particular when it is subjected to a modification of a property of its local environment (i.e. in the region of the discontinuity). The impedance of a discontinuity may in particular be modified when the shape and / or the local temperature of the waveguide, and / or the nature of the local environment, i.e. around the discontinuity, is / are modified. If only one of the modification factors of the discontinuity is modified, for example the local temperature, there is consequently a link between the impedance, and therefore the echo, and the value of this factor.

[0241] The discontinuity may in particular result from a local variation in the structure and / or composition of the waveguide, and in particular of one of the conductors of the waveguide and / or of a dielectric arranged between said conductors.

[0242] By "sacrificial sheath" is meant a sheath capable of decomposing, at least partially, preferably by heat treatment.

[0243] For the sake of clarity, a distinction is made between the protective sheath intended to be kept in service, and the sacrificial, or "temporary" sheath, which is used to provide thermal expansion space for the waveguide, and which is therefore intended to be eliminated.

[0244] The equivalent diameter of a waveguide or measuring part or conductor or housing is the largest of the cross-sectional diameters of that waveguide or measuring part or conductor or housing, respectively, considering all cross-sections (i.e. perpendicular to the length direction) along that waveguide or measuring part or conductor or housing, respectively, a cross-sectional diameter measured for a cross-section being the diameter of a disk having the same surface area as that cross-section.

[0245] When the cross-section is constant, the equivalent diameter is therefore equal to the transverse diameter regardless of the cross-section considered. A "bend" is a region of the measuring part in which said measuring part changes direction by more than 45° over a length of less than 80 cm.

[0246] A "precursor" of an element is an object that, during furnace manufacturing, transforms into that object. For example, a target preform is a precursor of the target, which transforms into the target during sintering.

[0247] By "preform" is meant a part shaped or prefabricated from a particulate mixture such as, for example, concrete (conventionally by pouring and vibration) or rammed earth (conventionally by tamping) and intended to be consolidated by heat treatment, for example by sintering. The methods for manufacturing a preform are well known to those skilled in the art. Conventionally, the particles of a refractory powder are mixed with a temporary binder and the mixture is put into the desired shape.

[0248] The adjectives "first" and "second" are used for clarity only.

[0249] Unless otherwise specified, "conductor" means the first or second electrical conductor of a waveguide.

[0250] "Local" or "locally" is used to describe a characteristic or action that only affects a fraction of the waveguide, for example, a fraction less than 5 cm, 1 cm, or 1 mm in length. A "local" variation of a property thus means that the value of this property varies in this fraction, for example, by more than 5% or more than 10%. This variation can be, for example, less than 500%.

[0251] The term "ceramic material" is conventionally understood to mean a material that is neither metallic nor organic. In a preferred embodiment, an oxide glass and carbon (in various forms, crystallized or not) are considered to be ceramic materials.

[0252] “Behave,” “present,” or “include” should be interpreted broadly and not exhaustively. detailed

[0253] The invention uses the well-known principles of electrical time domain reflectometry or electrical frequency domain reflectometry (E-TDR or E-FDR, respectively). Conventionally, a transmitter emits an interrogation signal, in the form of a pulse, into the electrically conductive medium. The latter returns a reflected response signal, which is then analyzed to deduce information about the conductive medium.

[0254] In particular, a measuring part is subjected to a temperature which depends on the target's environment, in particular the molten metal or its vapors, but also on the thickness of the material which separates it from this environment. When this thickness decreases at a location on the target, the measuring part can modify its reaction locally to the reception of the interrogation signal.

[0255] This local reaction allows the interrogator to be informed of a reduction in the thickness of the target, or even of a breakthrough by the molten metal in the target at this location.

[0256] Tracking device

[0257] Electromagnetic waveguide

[0258] The waveguide 12 (Figure 2) has the shape of a transmission line, for example the general shape of a strip or cable, which extends from an input end 12e to an output end 12s. It comprises:

[0259] - a measurement part 14, which includes the discontinuities used for the measurement, and

[0260] - a transmission part 15, which is used to connect the measurement part 14 to an interrogator 18.

[0261] The measuring part is designed to withstand the temperatures to which it is subjected in service, preferably to withstand a temperature of 200°C, preferably a temperature of 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, or 1200°C.

[0262] The length of the waveguide, and preferably of the measuring part, is preferably greater than 1 m, preferably greater than 2 m, preferably greater than 5 m, preferably greater than 10 m, greater than 15 m, greater than 20 m, and / or less than 200 m, or even less than 100 m, preferably less than 50 m.

[0263] Preferably one conductor, preferably each conductor, or even the waveguide

[0264] - has an equivalent diameter or,

[0265] - for a conductor or waveguide having the shape of a strip, has a thickness less than 10 millimeters, less than 5 mm, and / or preferably greater than 0.4 mm, preferably greater than 0.5 mm, preferably greater than 1 mm.

[0266] The waveguide comprises first and second electrical conductors, 12i and 122 respectively, for example in the form of a cable comprising one or more wires, a cable assembly or a strip.

[0267] Each driver includes:

[0268] - an input end (i.e. at the input end of the waveguide) electrically connected to a respective terminal of the interrogator 18, and,

[0269] - at the output end of the waveguide, a free output end.

[0270] The output ends are not electrically connected to each other, so the conductors do not form an electrical circuit, as in a resistive measuring device, in which direct or alternating current flows.

[0271] The material of the conductors is preferably a conductive metal such as Al, Cu or a steel or a metal alloy. It can also be a ceramic or a cermet. In particular, for application in a high temperature environment, the conductors can be

[0272] - in inconel (for example alloys 625 and 690), usable up to 1100°C,

[0273] - in platinum,

[0274] - in Kanthal type FeCr, for example KANTHAL APM, usable up to 1425 °C,

[0275] - tungsten,

[0276] - in rhodium,

[0277] - in ruthenium,

[0278] - in palladium,

[0279] - in iridium

[0280] A conductor made of a metal coated with conductive refractory oxide of SnCL or Spinel Cr2O3-MgO or perovskite or metalloid or metal carbide may be suitable for very high temperatures.

[0281] Preferably, the material of the conductors is a noble metal, preferably chosen from Platinum, Gold, Palladium, Rhodium, iridium. The electrical resistivity of the first and second conductors is preferably less than 10 micro-ohm. m in the temperature range of the environment, preferably between 20°C and 1000°C.

[0282] According to a first embodiment, each conductor is formed of a cable formed of one or more wires. The first and second conductors are non-coaxial and kept at a distance from each other by a dielectric insulator, preferably having an electrical resistivity greater than 10, 50, 100 or 1000 times that of the conductors.

[0283] According to a second embodiment, which is preferred, the waveguide is formed from a coaxial cable, for example of BNC type connection, comprising an internal wire or sleeve forming the first conductor and an external sleeve forming the second conductor, the two sleeves being separated by a separator in the form of an electrically insulating intermediate sleeve. Preferably, the material of the intermediate sleeve preferably comprises an oxide of at least one element chosen from Al, Zr, Mg, Ca, Ti and Si.

[0284] In one embodiment, said waveguide is formed of at least two linear conductors, preferably platinum wires, for example FKS platinum wires supplied by Ogussa, parallel and spaced apart by a distance greater than 1 mm, preferably greater than 2 mm, and / or preferably less than 20 mm. Refractory beads, preferably alumina beads, are threaded onto the conductors, preferably by first and second through-holes through which the first and second conductors pass.

[0285] The length of the waveguide, and preferably of the measuring part, is preferably greater than 1 m, preferably greater than 2 m, preferably greater than 3 m, or even greater than 10 m, and / or less than 30 m, or even less than 20 m.

[0286] The two conductors are preferably parallel except, possibly, in the areas of discontinuities. Local defects of parallelism can be provided to create discontinuities, and in particular basic discontinuities.

[0287] Preferably, in particular before fixing or integration into a support, preferably in the form of a plate, the waveguide and / or each conductor can be inserted into a protective sheath, possibly segmented, in order to protect the conductors during installation of the waveguide.

[0288] The protective sheath may be made of ceramic, particularly alumina, particularly for an environment at a temperature above 400°C.

[0289] The protective sheath is preferably made of a material having a coefficient of thermal expansion substantially identical to that of the material of the conductors.

[0290] Preferably, the coefficient of thermal expansion of the waveguide, preferably at least of the measuring part, is substantially identical to that of the part of the target which receives the measuring part (+ / -20%, preferably + / -10%).

[0291] Said protective sheath can be straight or curved, and extends around the measuring part. This sheath can be useful for giving a curved shape to the measuring part, or even to the transmission part.

[0292] The waveguide, and in particular at least the measuring part, can also be fixed on a support 40 (see figure 5 or 2), preferably in the form of a plate, itself in contact with the target 30.

[0293] A single support, particularly in the form of a plate, can support several measuring parts, or even all of the measuring parts of the waveguide network.

[0294] The support is preferably at least partly made of a material consisting of threads and / or fibers bonded together by a ceramic matrix, called a “ceramic matrix composite”.

[0295] The fibers and / or wires and the ceramic matrix will be chosen according to the environment where the ceramic matrix composite is to be placed, in particular according to the conditions of temperature, corrosion, thermal cycling, expansion, and according to the nature of the target to be monitored.

[0296] The coefficient of thermal expansion of the ceramic matrix composite can be adjusted by techniques well known to those skilled in the art, in particular by adapting the composition of the ceramic matrix composite.

[0297] Preferably, the ceramic matrix composite has a 3-point bending breaking strength, measured according to standard ASTM C 1341-13, greater than 3 MPa, preferably greater than 6 MPa, preferably greater than 10 MPa. Advantageously, the mechanical strength, in particular its impact resistance, is improved.

[0298] For example, a stack of woven fabrics or sheets of fibers or yarns is well suited for simple plates, filament winding is well suited for plates with a geometry of revolution, filament placement is well suited for complex shapes of large dimensions.

[0299] More preferably, the ceramic matrix composite, in particular in the form of a ceramic matrix textile, has a very high compressive strength of greater than 5 MPa, preferably greater than 10 MPa, which improves the stability of the sensor. This compressive strength is notably greater than that of layers made of fiber mats ("insulating mats" in English).

[0300] Preferably, the ceramic matrix composite has a melting or sublimation temperature greater than 800°C, preferably greater than 1000°C.

[0301] The thermal conductivity of the ceramic matrix composite is preferably less than 2.0 Wm^.K' 1 , between 20°C and 500°C.

[0302] Preferably, the ceramic matrix composite comprises, in mass percentage, more than 80%, more than 90%, more than 95%, or even substantially 100% of one or more of the following oxides: AI2O3, Z1O2. HfCL, CnCh, MgO, CaO, SiCL.

[0303] In one embodiment, the ceramic matrix composite has a chemical composition, in mass percentage based on oxides, such that AI2O3 + SiCL > 80%, preferably greater than 85%, preferably greater than 90%, or even greater than 95%.

[0304] In one embodiment, the matrix comprises, preferably consists of, more than 80%, more than 90%, more than 95%, preferably substantially 100% of its mass, one or more compound(s) chosen from the group formed by AI2O3, Z1O2, Cr2O3, MgO, CaO and SiO2.

[0305] Preferably, the volume of the fibers or yarns represents more than 25%, preferably more than 30%, preferably more than 40%, preferably more than 50%, preferably more than 60% and / or less than 70% of the volume of the material of the ceramic matrix composite, that is to say without taking into account its porosity, the remainder to 100% being constituted by the ceramic matrix binding said fibers together. The diameter of the fibers, measured at mid-length of the fibers and on average over the set of fibers, is preferably between 3 and 30 micrometers, preferably between 5 and 25 micrometers.

[0306] Preferably, the support is in the form of a plate, flat or non-flat, and has, between its large faces, an average thickness which is preferably constant, preferably less than 40 mm, preferably less than 32 mm, preferably less than 28 mm, preferably less than 22 mm, preferably less than 20 mm, or even less than 18 mm or 15 mm or 10 mm, and / or preferably greater than 1 mm, preferably greater than 2 mm, or even greater than 3 mm, or greater than 5 mm.

[0307] The surface area of ​​a large face of the support is preferably greater than 100 cm 2 , preferably greater than 200 cm 2 , preferably greater than 300 cm 2 , preferably greater than 400 cm 2 , and / or less than 20,000 cm 2 , preferably less than 15,000 cm 2 or even less than 10000 cm 2 .

[0308] In one embodiment, the support is in the form of a roll before being placed against the target. In one embodiment, the support is fixed to a cold face of the target and, preferably, the support comprises an openwork area, i.e. crossed by a plurality of orifices in order to facilitate thermal exchanges with the cold face.

[0309] A support is particularly useful when the target belongs to or constitutes the side wall of the crucible. The target can be in particular a first layer consisting of dense, fused or sintered blocks.

[0310] In one embodiment, the support is bonded to the cold face of the target. Preferably, the adhesive used to fix the waveguide to the support and / or the support to the target is selected from mixtures of ceramic powders and binders, preferably applied in a liquid form.

[0311] Preferably, the powders are alumina and / or silica and / or mullite powders. Preferably, the binders are chosen from colloidal silica, sodium silicate, organic resins, organic glues and mixtures thereof. The adhesive used may also be a commercial adhesive such as Fixwool FX adhesives from Unifrax.

[0312] In one embodiment, the measuring portion of the waveguide is embedded within the ceramic matrix composite or the precursor of said ceramic matrix composite, preferably sandwiched between two textiles of said composite. According to a first particular embodiment, the measuring portion of the waveguide is fixed to the support by means of an interfacing layer. The interfacing layer may be, in particular if the temperature of the face of the target which receives the support, in particular the cold face, is less than or equal to 400°C, an adhesive comprising a thermosetting, thermoplastic or elastomeric polymer.

[0313] In one embodiment, the measuring portion of the waveguide is attached to the support using refractory tapes, staples, or wires.

[0314] In an embodiment illustrated by Figure 6, the first and second conductors of the measuring part are integrated into the arrangement of threads of the ceramic matrix composite or the precursor of said ceramic matrix composite, for example as a weft thread, a warp thread or a knitting thread. They extend substantially parallel and at a predetermined distance. Preferably, the distance separating the conductors is greater than 0.3 mm, preferably greater than 0.4 mm, preferably greater than 0.5 mm and less than 30 mm, preferably less than 10 mm, preferably less than 5 mm, preferably less than 3 mm.

[0315] In order to maintain a distance between the two conductors, at least one wire, or even a plurality of wires made of a dielectric material, may be interposed between the first and second conductors of the waveguide.

[0316] In one embodiment, a single support may support multiple measurement portions of different waveguides.

[0317] In one embodiment, the measuring portion is housed in a ceramic protective sheath incorporated into the support during its manufacture, or in a channel formed in the support during or after the manufacture of said support.

[0318] Whatever the embodiment, the absence of direct electrical contact between the two conductors can be facilitated by the interposition of a dielectric insulator 25, or “separator”, for example made of mica, a mica derivative, titanium, barium, mullite, cordierite or alumina.

[0319] The dielectric insulator may be a single piece or may consist of an assembly of several dielectric cleats. Preferably, the dielectric cleats are interposed between the conductors, the cleats preferably having the form of beads threaded onto at least one of the conductors, preferably onto both conductors.

[0320] The cleats are described in more detail later in the description.

[0321] The predetermined distance between the two electrical conductors is preferably substantially constant.

[0322] When the first and second conductors are integrated into the textile of a ceramic matrix composite and constitute threads constituting the textile, for example weft or warp threads, the separator may consist of threads made of a dielectric material also constituting the textile. For example, if the first and second conductors are weft or warp threads, they may be separated by one or more other weft or warp threads, respectively made of a dielectric material (thread 25 in FIG. 6).

[0323] Discontinuities

[0324] The number of discontinuities, in particular basic discontinuities, per meter of waveguide measuring portion is preferably greater than 10, greater than 15, greater than 20, greater than 30, greater than 40, greater than 50, and / or less than 10000, less than 1000, less than 500, less than 100. Advantageously, it is thus possible to evaluate the property of the environment of the measuring portion substantially over its entire length, and with good precision.

[0325] Preferably, the distance between any two discontinuities 24, in particular any two basic discontinuities, successive along the waveguide 12, is less than 1 / 100 of the wavelength of the interrogation signal (equal to the propagation speed of the interrogation signal, approximately 200,000 km / s for an electromagnetic wave, divided by the frequency of the highest peak of the frequency spectrum of the interrogation signal).

[0326] This distance is preferably greater than 10 mm, 15 mm or 20 mm and / or less than 100 mm or 50 mm.

[0327] The sensitivity of the information provided by the interrogator is thus advantageously improved.

[0328] The use of discontinuities returning a small variation in electrical potential makes it possible to avoid having to create strong discontinuities, which are likely to strongly dampen the interrogation signal, and therefore prevent tracking over the entire length of the measurement part of the waveguide. Preferably, more than 50%, preferably more than 80%, preferably more than 90% of the discontinuities return secondary basic echoes and / or noise, preferably secondary basic echoes.

[0329] The exploitation of these small random variations in electric potential runs counter to the developments of electrical reflectometry, as these variations are considered detrimental. Preferably, discontinuities are added randomly in the waveguide.

[0330] The discontinuities are variable, that is, they do not all return the same echo when they receive the same interrogation signal. Preferably, the variation of the discontinuities, particularly the basic discontinuities, is random.

[0331] The discontinuities 24, in particular the basic discontinuities, can be obtained by modification of the surface and / or the constituent material of one or both conductors and / or the dielectric insulator, for example by a surface modification by abrasion, by a chemical attack, by the addition of a dopant in the material, or by the addition of cleats.

[0332] In one embodiment, the waveguide is formed from a coaxial cable, for example a BNC type connection, comprising a wire forming the first conductor and an outer sleeve forming the second conductor, the two sleeves being separated by an electrically insulating intermediate sleeve. It is possible to create discontinuities 24, in particular basic discontinuities, by modifying the surface condition of the insulating sleeve, for example by creating roughness. Another way consists of creating random discontinuities, in particular basic discontinuities, on the outer sleeve, for example by abrasion (without stopping the electrical conduction within the outer sleeve).

[0333] In one embodiment, discontinuities, particularly base discontinuities, are surface irregularities on the separator, preferably provided opposite the connectors, preferably in at least one area of ​​the separator in contact with the connectors. Texturing said area advantageously makes it possible to generate random discontinuities.

[0334] It is also possible to create discontinuities 24, in particular basic discontinuities, preferably random, by modifying the surface state of the dielectric insulator 25 (texturing), for example by creating roughness, for example by abrasion. Preferably, the texturing comprises the creation of reliefs with a height greater than 0.05 mm, preferably greater than 0.1 mm, preferably greater than 0.2 mm, preferably greater than 0.4 mm, preferably greater than 0.5 mm, or even greater than 0.8 mm, and / or less than 3 mm, less than 2 mm or less than 1 mm.

[0335] The density in reliefs, in number of reliefs relative to the textured surface (in particular relative to the surface of the dielectric material and / or to the surface of at least one of said first and second electrical conductors) is preferably greater than 1 / 10000 mm 2 , preferably greater than 1 / 1000 mm 2 , preferably greater than 0.5 / 100 mm 2 (or 0.5 / cm 2 ) and / or less than 10 / mm 2 , preferably less than 1 / mm 2 , preferably less than 1 / 10 mm 2 (or 10 / cm 2 ).

[0336] The predetermined distance between the two electrical conductors is preferably substantially constant. The two conductors are preferably parallel except, possibly, in the areas of discontinuities. Local parallelism defects may be provided to create discontinuities, and in particular basic discontinuities.

[0337] Preferably, to create a basic discontinuity by varying the distance

[0338] - between the two electrical conductors or

[0339] - between the first electrical conductor and / or the second electrical conductor on the one hand, and a dielectric material of a said support on the other hand, this distance is varied by more than 0.1 mm to less than 2 mm, preferably less than 1 mm, along the measuring part.

[0340] Preferably, to create discontinuities, dielectric cleats are arranged in contact with the first and second conductors.

[0341] Dielectric cleats, and in particular beads, may have a length, measured along the length of the waveguide, greater than 10 mm, 15 mm or 20 mm and / or less than 100 mm or 50 mm.

[0342] The dielectric cleats, and in particular the beads, preferably have a width, i.e. a largest dimension in a plane transverse to the direction of their length, greater than 1 mm, 2 mm or 3 mm and / or less than 10 mm or 5 mm. Figure 3 illustrates different possible embodiments for dielectric cleats.

[0343] In particular, it illustrates embodiments in which:

[0344] - beads 23 are threaded onto only one of the first and second conductors (3E) or onto both the first and second conductors (3A-3D);

[0345] - beads 23 are threaded to form a segmented protective sheath 27 (3A, 3C-3E) or not (3B), on the two first and second conductors (3A-3D), for one (3E) or for the two conductors;

[0346] - 23 beads of identical (3 A, 3D) or different (3B, 3C, 3E) shapes are threaded;

[0347] - beads 23 having surfaces textured in the same way (3A-3C, 3E) or not (3D) are threaded;

[0348] - one or more of the conductors extend symmetrically with respect to the axis of each bead 23 (3 A, 3B, 3C, 3D) or not (3E);

[0349] - one or more of the conductors extend parallel to the axis of each bead 23 (3A- 3E) or not.

[0350] The cleats also facilitate the identification of regions generating secondary basic echoes, and can therefore serve as identification marks.

[0351] Preferably, to create a basic discontinuity, it is also possible to modify the composition and / or structure of a support near or around the first and second electrical conductors or between the first and second electrical conductors. In particular, the composition and / or structure of the support may vary by more than 10% over less than 1 mm along the measurement portion. For example, it is possible to locally deform the structure of the support to create depressions or bumps, for example mechanically or by local melting, and / or to vary the composition of the support.

[0352] The support may be a support integral with the waveguide, for example a support in a CMC.

[0353] For example, the waveguide may be fixed to a support which is not a homogeneous mass of material but has variations due to the presence of pores, through or not, for example due to the fact that it comprises a woven textile. The irregular succession of wires creates random basic discontinuities. For example, the waveguide is fixed to or embedded in a support which comprises inclusions, each inclusion, for example in the form of a particle or a fiber, along the measurement part leading to a variation in the composition of said support.

[0354] Random distribution of discontinuities

[0355] Preferably, the discontinuities are not distributed regularly along the waveguide. Preferably, the discontinuities, particularly base discontinuities, are randomly distributed along the waveguide.

[0356] The random nature of the distribution or intensity of the discontinuities advantageously avoids the risk of creating an accumulation of secondary echoes of the same period, which could significantly dampen the interrogation signal.

[0357] Dielectric cleats may have the same or different shapes and / or dimensions and / or be made of the same or different materials. Even though dielectric cleats appear identical, no two cleats are completely identical.

[0358] Variations in the shape and composition of the cleats, particularly the beads, and variations in the positioning of the beads relative to the conductors make it possible to randomize the discontinuities they generate. It is thus possible to create basic discontinuities randomly.

[0359] To generate random discontinuities, in particular basic discontinuities, in the embodiment in which the first and second conductors of the measuring part are integrated into the yarn arrangement of a support made of a ceramic matrix composite, for example as a weft yarn, warp yarn or knitting yarn, the first and second conductors and / or the other yarns made of a dielectric material (or non-conductive yarns) can be randomly modified by e.g. abrasion or chemical etching. Yarns made of a dielectric material can also or alternatively be randomly wound around the first conductor and / or the second conductor. Yarns and / or fibers and / or particles made of a dielectric material can also or alternatively be randomly added to the textile.Particles of varying size or shape or placed unevenly may also be, in addition to or as an alternative to the other possibilities described above, placed in contact with said textile before impregnation. The choice of particle size or shape, texturing or fiber length makes it possible to create random discontinuities. The conductors may also or alternatively be placed in contact with an irregularly textured fabric or a mat of randomly arranged fibers, before impregnation with a matrix precursor and then hardening to form an instrumented support.

[0360] Rayleigh scattering condition

[0361] The waveguide preferably satisfies the Rayleigh scattering condition. Advantageously, the regions having reflected the basic secondary echoes can be easily located.

[0362] Preferably, the basic discontinuities 24 are spaced from each other by a distance, measured along the waveguide, at least 10 times, preferably at least 15 times, preferably at least 20 times less than the reference wavelength, equal to the propagation speed of the interrogation signal, of approximately 200,000 km / s for an electromagnetic wave, divided by the frequency of the highest peak of the frequency spectrum of the interrogation signal.

[0363] This distance can be defined in particular by the length of dielectric cleats, in particular beads threaded onto the waveguide. To generate sufficient basic secondary echoes, the length of the cleats is preferably adapted, as a function of the reference frequency (inverse of the reference wavelength), so as to respect the Rayleigh scattering condition.

[0364] For example, for a reference wavelength of about fifteen centimeters, cleats, for example beads, with a length of less than 3 cm, preferably less than 2 cm or 1 cm, are well suited. For example, for an interrogation signal with a frequency of 1 GHz, alumina beads with a length of less than 10 mm and threaded onto platinum wires produce secondary echoes of too low amplitude, while beads with a length of more than 100 mm produce clear secondary echoes.

[0365] With basic discontinuities and under Rayleigh scattering conditions, it is possible to perform accurate measurements over a length greater than 1 m, preferably greater than 2 m, preferably greater than 5 m, preferably greater than 10 m, greater than 15 m, or greater than 20 m, and / or less than 500 m, for example over the entire length of the measuring section.

[0366] Waveguide array Preferably, the array comprises a plurality of measuring portions, preferably parallel to each other and to the hot face of the target, such that the density of discontinuities, preferably the basic density of discontinuities, on the equipped surface is greater than 3, preferably greater than 10, preferably greater than 50, preferably greater than 100, preferably greater than 500, preferably greater than 800 discontinuities and / or less than 1,000,000, preferably less than 500,000, preferably less than 100,000, preferably less than 50,000, preferably less than 10,000, preferably less than 5000, preferably less than 2,000, per m 2 of the hot face surface. The reliability of the analysis by the interrogator is improved.

[0367] Preferably, the measuring parts form a sheet extending along a curved or flat surface, preferably flat, each waveguide being preferably connected to its own interrogator.

[0368] The waveguide network may comprise more than 1, more than 2, preferably more than 3, preferably more than 5 said sheets, said sheets being preferably parallel to each other and preferably regularly spaced from each other in a direction perpendicular to a surface of the assembly.

[0369] In one embodiment, at least two waveguides intersect at different depths, the depth being measured from the hot face, perpendicular to the hot face. The identity of the superimposed waveguides being known, it is thus advantageously possible to define a temperature profile along the direction of the depth, and / or to evaluate the extent of a reduction in the thickness of the target, for example of the sole, at each point of the hot face below which several waveguides are superimposed. For this purpose, a central computer can collect the messages from the different interrogators and, knowing the spatial distribution of the waveguides, deduce a wear profile therefrom.

[0370] The input ends of the electrical conductors of the waveguide are electrically connected to the interrogator 18, or "reflectometer". The interrogator is configured to:

[0371] - inject the interrogation signals by establishing a variation in the potential difference between the two conductors of the waveguide; and

[0372] - analyze the response signals reflected in response to the interrogation signals.

[0373] The interrogator 18 conventionally comprises a transmitter / receiver 21 and a control module 31 (FIG. 2). The control module 31 conventionally comprises a processor and a memory in which a computer program is loaded. Using this computer program, the processor can control the transmission of the interrogation signals and analyze the received reflected signals in order to identify the echoes returned by the discontinuities. In one embodiment, the analysis is carried out by an analysis computer 39 in communication with the interrogator.

[0374] The interrogator may be, for example, a voltage generator coupled to an oscilloscope allowing the reception and analysis of reflected signals. The interrogator may be a network analyzer provided with software such as "VNA software" for generating the interrogation signal and analyzing the reflected signal.

[0375] In a preferred embodiment, a first interrogator is connected to the input end of a waveguide. A second interrogator is connected to the output end of the waveguide.

[0376] The second interrogator therefore receives the parts of the interrogation signal injected by the first interrogator and which were not reflected by the different discontinuities of the waveguide. Preferably, the second interrogator can also send an interrogation signal. The presence of two interrogators advantageously makes it possible, in the event of a break in the waveguide, to obtain information on each side of the break zone. It therefore improves the robustness of the device.

[0377] Analysis

[0378] The analysis performed by an interrogator is based on electrical time domain reflectometry or electrical frequency domain reflectometry (E-TDR or E-FDR), which is a conventional technique for measuring changes in the state of a medium using a waveguide and an interrogator.

[0379] Each interrogation signal, preferably in the form of a pulse or "Dirac", is generated by establishing a variation in the potential difference between the two conductors of the waveguide. The latter returns a response signal, which is then analyzed in order to deduce information on the medium crossed by the pulse. In the presence of an impedance discontinuity, for example a significant physicochemical variation of the medium causing a local variation in impedance, part of the interrogation signal is reflected towards the interrogator, which makes it possible to identify and analyze this variation.

[0380] The interrogation signal may take the form of a periodic wave of any shape. The interrogation signal may be repeated. Preferably, the maximum amplitude of the interrogation signal is between 0.1 V and 100 V, preferably less than 10 V, preferably less than 1 V. The frequency of the highest peak in a frequency spectrum of the interrogation signal is preferably greater than 10 KHz, preferably greater than 100 KHz, preferably greater than 1 MHz, preferably greater than 100 MHz, preferably greater than 200 MHz, preferably greater than 500 MHz, preferably greater than 1 GHz, and / or less than 50 GHz, preferably less than 30 GHz, preferably less than 20 GHz, preferably less than 10 GHz, preferably less than 6 GHz, preferably less than 4 GHz.The interrogation signals may be sent in the form of signal trains preferably comprising a series of periodic signals of varying frequencies depending on the periodic signal in question.

[0381] The frequency of the interrogation signal is conventionally adapted to the length of the measuring part. The wavelength of the interrogation signal is conventionally less than the length of the measuring part of the waveguide. The ratio of the wavelength of the interrogation signal to the length of the measuring part of the waveguide is preferably between 0.1 and 0.9, preferably between 0.1 and 0.5, preferably between 0.1 and 0.3.

[0382] Preferably, the length of the measuring portion of the waveguide is not a multiple of the wavelength of the interrogation signal in order to avoid resonance problems.

[0383] For example, the frequency of the interrogation signal may be 1 GHz (corresponding to a wavelength of approximately 20 cm) for a length of the measuring part of the waveguide of between 10 and 15 m, for a measurement at 600°C or more.

[0384] Each interrogation signal propagates in the waveguide to the free end of the conductors. At each discontinuity, a portion of the interrogation signal, or "echo," is reflected back to the interrogator. All the returned echoes together constitute the response signal associated with the interrogation signal and which the interrogator analyzes.

[0385] In particular, we distinguish the emission echo returned by the input end of the waveguide, the bottom echo returned by the output end of the waveguide, and a set of discontinuity echoes returned by the discontinuities of the waveguide. The discontinuity echoes are of low amplitude, and are of various amplitudes and shapes.

[0386] The interrogator is programmed to analyze the reflected signals, and possibly compare them, so as to determine information relating to the state of the target in the region of the measurement part of the waveguide and, preferably, transmit a message accordingly.

[0387] All the techniques for analyzing response signals used in electrical time or frequency domain reflectometry can be implemented, and in particular those described in the article “Distributed temperature sensing with unmodified coaxial cable based on random reflections in TDR signal” by Baokai Chen et al, 2019 Meas. Sci. Technol. 30 015105 or the article “Electric time domain reflectometry distributed flow sensor” by Aurimas Dominauskas et al, in the journal Composites Part A 38(2007) 138-146.

[0388] Preferably, the message specifies:

[0389] - a value for the physical state of the target, and in particular a value for the residual thickness or an average temperature and / or a value representative of the temperature differences along the measurement part; and / or

[0390] - a value for an evolution of said value compared to a previous situation; and / or

[0391] - a location of defects or damage affecting said physical state of the target.

[0392] The message may be sent to a central computer and / or presented to an operator, for example on a screen and / or by activating a light and / or by emitting an audible signal.

[0393] In a preferred embodiment, at least a portion of the waveguides is capable of providing, in the response signal that it returns, a quantitative indication of the temperature that it is undergoing due to the wear of the target. As the thickness of the target part, for example the sole, reduces, the frequency of the response signal returned by the waveguide changes. This change advantageously makes it possible to determine the local change in temperature. Advantageously, it is thus in particular possible to detect an abnormal change in the temperature of a waveguide, and to intervene in order to repair the target, for example changing the refractory coating.

[0394] Target

[0395] The target 30 may be all or part of the metallurgical furnace, in particular a foundry furnace, comprising a hot face, in particular the side wall of the crucible or the hearth, or a block or a set of blocks belonging to the side wall of the crucible or to the hearth.

[0396] The target may have a back layer, for example the side wall of the crucible or the bottom.

[0397] The target can be in particular a first layer made up of refractory rammed earth or dense, melted or sintered blocks.

[0398] The use of a waveguide advantageously allows exposure to high temperature, for example, over 100°C, over 125°C, over 200°C or over 300°C. A metal waveguide sheathed in a polymer sheath, for example, allows tracking in an environment up to 300°C.

[0399] Manufacturing or assembly

[0400] Different techniques can be used to install the waveguides, especially in the back layer of the target. Preferably, the waveguides are placed in a thermal zone of the furnace at a temperature above 400°C, preferably above 500°C, preferably above 600°C and below 1300°C, preferably below 1200°C, more preferably below 1100°C.

[0401] According to a preferred embodiment, at least a part, preferably the entire measuring part of each waveguide is protected by a refractory support 40 in the form of a plate arranged between the hot face of the target and the rear layer, preferably between the first layer and the rear layer.

[0402] Example: induction foundry furnace

[0403] As shown in Figure 4, a metallurgical furnace according to the invention comprises a first layer 22 in contact with the molten metal, the shape of which is not limiting. After production or in place of the electrical insulating layer 19, the support 40 containing all or part of the measuring parts of the network, preferably in the form of a plate, is arranged parallel to the surrounding or support layer 11 comprising the inductor coil 16 of the heating system.

[0404] In one embodiment, prior to its installation in the metallurgical furnace, the support, preferably in the form of a plate, is sintered or baked in an oven or furnace, preferably in air and preferably in a controlled atmosphere.

[0405] In another embodiment, a precursor of the support is provided in the furnace, preferably in the form of a precursor of a ceramic matrix composite. The precursor of the support, preferably the precursor of the matrix of the ceramic matrix composite, is consolidated during heating of the metallurgical furnace to a temperature between 400 and 1200°C.

[0406] In one embodiment, the support replaces the electrical insulating layer 19.

[0407] The support advantageously protects the waveguide(s) during the construction of the first layer, typically in dry refractory rammed earth.

[0408] In one embodiment, one or more plate-shaped supports are provided to form layers of measuring parts, each layer consisting of several, for example more than 2, more than 5 or more than 10 measuring parts oriented parallel to each other, the layers being oriented differently so that the measuring parts of different layers intersect.

[0409] As is now clearly apparent, the invention provides a robust, easy-to-implement solution for assessing, for all areas of the furnace, continuously and in real time, the condition of the refractory lining of a metallurgical furnace. The waveguides can be in close contact with the target, which allows good heat exchange and limits the risk of infiltration of molten metal. The protection by the support finally limits the stresses on the waveguides. Finally, this solution offers good spatial resolution, without weakening said lining and, in particular in the case of electrical heating, without increasing the risk of electrical interaction with the furnace heating system.This solution makes it possible to evaluate, more precisely and in real time, the residual thickness or the temperature of a refractory part of a metallurgical furnace. Of course, the invention is not limited to the embodiments described and represented, provided for illustrative purposes only.

[0410] 5

Claims

CLAIMS 1. Metallurgical furnace, preferably foundry furnace, comprising: - a metal melting enclosure (8; 9) having a hot face (37) exposed towards the inside of the enclosure; - a device for monitoring, by time or frequency electrical reflectometry, the state of a part of the furnace, called “target” (30), said device comprising: - a network of at least one wired waveguide, preferably a plurality of wired electromagnetic waveguides (12), each waveguide comprising, between an input end and an output end, first and second electrical conductors (121, 122), electrically insulated from each other, - an interrogator (18) electrically connected to the input end (12e) and configured to inject an interrogation signal through said input end, receive a response signal reflected by said waveguide in response to said injection, analyze the response signal and transmit a message on the state of the target according to said analysis, the waveguide comprising, between the input and output ends of said waveguide, a measuring portion (14) extending parallel to the hot face (37) and at a depth greater than 10 cm, the measuring portion (14) comprising a plurality of discontinuities, called “basic discontinuities” (24), randomly distributed at least along the measuring portion of the waveguide, the number of basic discontinuities, per meter of measuring portion of the waveguide, being greater than 10, the basic discontinuities being: - capable of generating, in response to the injection of the interrogation signal, echoes having an amplitude greater than 0.5%, preferably greater than 1% of the amplitude of the bottom echo reflected by the output end of the waveguide, called “basic secondary echoes”, and / or - being constituted by - reliefs resulting from a texturing of the outer surface of the waveguide and / or of a dielectric material interposed between the first and second electrical conductors and / or of at least one of the first and second conductors electrical, and / or - reliefs resulting from an irregular segmentation of a dielectric material interposed between the first and second electrical conductors, and / or - local variations in the distance between the first and second electrical conductors; and / or - variations in the distance between the first electrical conductor and / or the second electrical conductor on the one hand, and a dielectric material of a support, preferably made of a ceramic matrix composite, on the other hand; and / or - variations in the structure and / or composition of the environment around the first and second electrical conductors or between the first and second electrical conductors.

2. Oven according to the immediately preceding claim, in which the basic discontinuities are - reliefs resulting from a texturing of the outer surface of the waveguide and / or of a dielectric material interposed between the first and second electrical conductors and / or of at least one of the first and second electrical conductors, and / or - reliefs resulting from an irregular segmentation of a dielectric material interposed between the first and second electrical conductors; and / or - local variations in the distance between the first and second electrical conductors.

3. Oven according to any one of the preceding claims, in which said reliefs have a height greater than 0.05 mm, preferably greater than 0.1 mm, preferably greater than 0.2 mm, preferably greater than 0.4 mm, preferably greater than 0.5 mm, or even greater than 0.8 mm, and less than 3 mm, less than 2 mm or less than 1 mm.

4. Oven according to any one of the preceding claims, comprising cleats (23) in the form of beads and made of a dielectric material are threaded, in the measuring part, onto the first electrical conductor and / or onto the second electrical conductor.

5. Oven according to the immediately preceding claim, in which the cleat(s) are arranged so as to together form a segmented protective sheath (27) extending along the entire measuring portion of the waveguide.

6. Oven according to any one of the two immediately preceding claims, in which the cleats have a length of less than 10 cm, preferably less than 5 cm, preferably less than 3 cm, more preferably less than 2 cm, and greater than 0.5 cm.

7. Oven according to any one of the preceding claims, wherein the waveguide satisfies the Rayleigh scattering condition.

8. Oven according to any one of the preceding claims, wherein: a) the measuring part of each of the waveguides of said array extends parallel to the hot face and at a distance adapted so that in use said measuring part is at a temperature above 500°C; b) the maximum distance between two measuring parts of any two waveguides of the array is greater than 20 cm; c) each waveguide of the array is inserted into an orifice of the target, the orifice being configured to provide a thermal expansion space for the waveguide; d) the equivalent diameter of the measuring part of each waveguide of the array is greater than 1 mm and less than 50 mm; e) the distance separating the first and second electrical conductors of the measuring part of each waveguide of the array is greater than 0.3 mm and less than 30 mm; f) said measuring part has a number of bends: - less than 2 per meter of length of measuring part if the length of said measuring part is less than 3 meters; - less than 1 elbow per meter if the length of said measuring part is greater than or equal to 3 meters.

9. Oven according to any one of the preceding claims, in which the waveguide network extends at least partially, preferably completely, within a rear layer extending behind a first layer consisting of refractory rammed earth defining the hot face of the target or in a sub-layer of said rear layer.

10. Oven according to any one of the preceding claims, in which the radius of curvature of the measuring part of each waveguide of the network is at any point at least 3 times greater than the equivalent diameter of said measuring part.

11. Oven according to any one of the preceding claims, in which: - the material constituting the electrical conductors is a refractory metal or a noble metal, preferably chosen from Platinum, Tungsten, Gold, Palladium, Rhodium, Ruthenium, iridium, or an alloy of these elements, and / or - said first and second electrical conductors are separated by a dielectric material comprising an oxide of at least one element chosen from Al, Zr, Mg, Si, and / or - at least a fraction of the measuring part of each waveguide of the network is protected by a ceramic sheath surrounding said measuring part.

12. Oven according to any one of the preceding claims, in which at least part of the measuring parts of the waveguides, except the bends, extend parallel to each other.

13. An oven according to any preceding claim, wherein each measuring portion of a waveguide of the array extends into a housing provided in the target and defining a thermal expansion space for said waveguide, the ratio of the equivalent diameter of the housing to the equivalent diameter of the measuring portion being greater than 1.05 and less than 3, the equivalent diameter of the measuring portion or the housing being the largest of the transverse diameters of said measuring portion or said housing, respectively, considering all the transverse sections along said measuring portion or said housing, respectively.

14. Oven according to any one of the preceding claims, wherein the first and second conductors are fixed to a said support (40), preferably in the form of a plate, constituted by a ceramic matrix composite and within which said first and second conductors are integrated or to the surface of which said first and second conductors are fixed.

15. An oven according to any preceding claim, wherein the measuring portion of the waveguide extends to a depth, measured from said hot face, of less than 200 cm.

16. Oven according to any one of the preceding claims, in which the measuring part of each of the waveguides of said network extends at a distance adapted so that in service, said measuring part is at a temperature greater than 700°C and less than 1300°C.

17. Oven according to any one of the preceding claims, wherein said secondary base echoes have an amplitude less than 30% of the amplitude of the bottom echo reflected by the output end of the waveguide.

18. Oven according to any one of the preceding claims, in which the measuring part of at least one waveguide is slidably mounted relative to the target and / or, when claim 14 applies, relative to the support (40).

19. The furnace of claim 16 wherein the first and second conductors are attached to said support (40) by means of an interfacing layer or refractory tapes, staples or wires, or are integrated into said support.

20. Method of manufacturing an oven according to any one of the preceding claims, said method comprising, for at least one waveguide of the network, the following successive steps: A) preparing a precursor of a ceramic matrix composite comprising a ceramic matrix precursor, preferably in the form of a plate, and integrating the measuring part of the waveguide into or onto the ceramic matrix composite precursor so as to obtain an instrumented support precursor; B) hardening and / or firing said instrumented support precursor so as to obtain said instrumented support by consolidation of the ceramic matrix precursor; C) installation of the instrumented support if step C) is subsequent to step B) or installation of the instrumented support precursor if step C) is prior to step B), preferably between a rear layer defining the hot face and a furnace heating system.

21. Method according to the immediately preceding claim, wherein step A) comprises the following steps: a) preparing the ceramic matrix precursor in the form of a slip comprising ceramic particles and / or precursors of ceramic particles, the material of said ceramic particles having a dielectric constant at 25°C and atmospheric pressure, preferably measured at 1 MHz, greater than 3 farad per meter and / or less than 30 farad per meter, preferably less than 15 farad per meter less than 10 farad per meter; b) independently of step a), fixing or integrating the first and second electrical conductors of said measuring part to a textile, the material of said textile having a material with a dielectric constant at 25°C and atmospheric pressure, preferably measured at 1 MHz, greater than 3 farad per meter and / or less than 30 farad per meter, preferably less than 15 farad per meter;c) impregnation of the textile with said slip; 22. Method of manufacturing an oven according to any one of claims 1 to 19, said method comprising the following successive steps: 1) interposition of a sacrificial material between - the measuring part of the waveguide and - the target or a precursor of the target, or a support (40), in particular a ceramic matrix composite or a support precursor, then 2) after or simultaneously with the manufacture of the target or the support for the case where the sacrificial material has been interposed in a precursor of the target or in a precursor of the support, respectively, elimination of the sacrificial material so as to create a so-called expansion space for the measuring part.

23. Method according to the immediately preceding claim, in which: - the sacrificial material is the material of a sacrificial sheath sheathing the measuring part, and, to interpose the sacrificial material, - we make the target around the measuring part, or - a recess, in the form of a groove or a hole, is provided in the target or in a precursor of the target, then the measuring part is inserted into the recess, then the recess is filled with an unshaped refractory product containing a binder, preferably a cement, and capable of setting into mass by activation of the binder, preferably a refractory concrete, then the unshaped refractory product is hardened; or - the sacrificial material is a filling material independent of the waveguide and, to interpose the sacrificial material, - a recess is provided, in the form of a groove or a hole, in the target or in a precursor of the target, then the measuring part is inserted into the recess, then the recess is filled with the filling material so as to embed the measuring part, the quantity of filling material being adapted to provide the expansion space, then the recess is filled with an unshaped refractory product containing a binder, preferably a cement, and capable of setting into mass by activation of the binder, preferably a refractory concrete, then the unshaped refractory product is hardened.

24. Method for monitoring the state of the target of a metallurgical furnace according to any one of claims 1 to 19, said method comprising the following steps: a. manufacturing the metallurgical furnace; b. for each waveguide, controlling the interrogator to which the waveguide is connected, so that it injects an interrogation signal through the input end of said waveguide; c. analyzing the response signal so as to determine information relating to the state of the target in the region of the measurement part of said waveguide.

25. Method according to the immediately preceding claim, in which the information relating to the state of the target is a residual thickness of refractory or a temperature at one or more points of the target.

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