EP1203511B1 - Infrared heater with electromagnetic induction and its uses - Google Patents

Infrared heater with electromagnetic induction and its uses Download PDF

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Publication number
EP1203511B1
EP1203511B1 EP00938420A EP00938420A EP1203511B1 EP 1203511 B1 EP1203511 B1 EP 1203511B1 EP 00938420 A EP00938420 A EP 00938420A EP 00938420 A EP00938420 A EP 00938420A EP 1203511 B1 EP1203511 B1 EP 1203511B1
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Prior art keywords
emitter according
emitter
infrared
layer
plate
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German (de)
French (fr)
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EP1203511A1 (en
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Normand Bedard
Michel Dostie
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Hydro Quebec
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Hydro Quebec
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
    • H05B6/105—Induction heating apparatus, other than furnaces, for specific applications using a susceptor
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
    • H05B6/105—Induction heating apparatus, other than furnaces, for specific applications using a susceptor
    • H05B6/106—Induction heating apparatus, other than furnaces, for specific applications using a susceptor in the form of fillings

Definitions

  • the invention relates to an infrared transmitter with electromagnetic induction. More particularly, the invention relates to a device for the emission of infrared radiation, which device is electrically powered by means of an inductor, and characterized by a choice of material for the transmitter which makes it possible to high temperatures and achieve high densities of medium-type radiation power.
  • the emission temperature of gas radiants is between 900 and 1150 ° C: the radiation is therefore of the "average" type, that is to say in the wavelengths identified with the average infrared (more than 85% of the power radiated between 1 and 6 ⁇ m). They offer radiation power densities of 100 to 160 kW / m 2 .
  • the lamp-type electric emitters (whose filament is increased to 2200 ° C) radiate more in the short type of infrared (more than 85% of the radiated power between 0 and 2.5 ⁇ m) and offer power densities that may exceed 300 kW / m 2 .
  • an infrared source consists of a solid body which is heated to a temperature such that it emits infrared-type electromagnetic radiation.
  • Electrical infrared emitters involve passing a direct current through a resistor, usually a wire. The heating is done by Joule effect (direct electrical conduction).
  • the power density of an emitter made of wire is limited for several reasons.
  • the wires have a low electrical resistivity and can not exceed a temperature of 1300 ° C.
  • the service life decreases sharply with the diameter of the wire: it is therefore preferable to increase the length of the wire, which is achieved by shaping a pudding.
  • a certain distance between turns of the same coil and between the rows of rolls must be respected at the risk of producing hot spots. This requirement further limits the power density.
  • the rods In addition, it is often imperative to cover the rods with a material isolating them from the environment, both from the thermal point of view (in order to limit the losses by convection with ambient air) and the electrical one (for reasons of security).
  • the corrugated son are then embedded or inserted in a material transparent or not to infrared radiation.
  • the power density of embedded infrared sources embedded in plates or inserted in quartz tubes is the highest among medium-type electric infrared sources but remains below 100 kW / m 2 , providing less than 80 kW / m 2 in radiation.
  • the sources with short infrared lamps are characterized by a very high power density, because the tungsten wire with the inside of the lamps is raised to a very high temperature (2200 ° C): but as we have seen, this temperature level implies that the emission is rather of short type, which brings the disadvantages already mentioned.
  • the tungsten wire must be enclosed in a sealed tube to prevent rapid oxidation.
  • Another way of increasing the power density is to enlarge the actual emission area by using an extended surface and no longer a coil wire.
  • a full and wide plate configuration makes it possible to increase the emission area. Theoretically, if a solid surface of Kanthal A1 at 1300 ° C could be heated relatively uniformly, the radiation power density would be very high (above 300 kW / m 2 ). The difficulty is to pass the current everywhere in this surface. In direct conduction, it is very difficult to achieve uniform heating because the current passes through the shortest "electric" path. To pass the current everywhere between the voltage terminals, it is necessary to cut several lines in the plate, which poses problems of mechanical resistance and local concentration of current. Some means have been evaluated and tested by the applicant but several problems have led to questioning the use of direct electrical conduction: heating uniformity, supply voltage, thermal expansion, mechanical strength, thermal losses by the contacts, and other.
  • the applicant proposes to involve the electromagnetic induction: rather than passing the current directly into a resistor, heating can then be carried out by eddy currents induced by a driver physically decoupled from the material heated.
  • the material in which these currents are developed may be other than the metal constituting the coil wire of conventional infrared sources.
  • the choice of the material constituting the emitting surface constitutes the determining aspect. This material must be able to withstand very high temperatures, far beyond the Curie point of all materials with magnetic properties. Only resistivity intervenes electromagnetically. On the other hand, the Applicant has been able to identify a resistivity range of materials and supply frequencies resulting in excellent electrical efficiency and a relatively good power factor, two conditions for induction to be used as a heating means. at the base of an infrared system. It is possible to transfer a very high power (above 50 kW for a 0.16 m 2 plate) by generating a typical electric field at a reasonable supply voltage.
  • the heating is relatively uniform, although the currents generated in the heating plate are in the image of the configuration of the inductor, which is in a circular shape ("pancake"): the four corners of the plate are therefore colder, than the center.
  • this concept makes it possible to avoid problems of hot spots and losses by the connections associated with direct electrical conduction.
  • the material constituting the emitting surface must be able to withstand very high temperatures and thermomechanical stresses.
  • the metals constituting the resistive wires of infrared sources are characterized by very weak mechanical properties in the vicinity of 1300 ° C. They could not therefore constitute the radiant plate.
  • CMC Ceramic Matrix Composite
  • CFRC Continuous Fiber Ceramic Composites
  • CFCC is therefore a solution to the traditional problem of fragility of ceramics. They can operate at high temperatures, undergo thermal shocks, and have a long service life. These assets make them ideal candidates to serve as a basis for a high power density infrared system. In contrast, most CFCCs do not conduct electricity, and therefore are not likely to be heated by electromagnetic induction. The Applicant has found that CFCCs comprising carbon fibers in a matrix of silicon carbide (C / SiC) conduct enough electricity to be effectively heated by electromagnetic induction.
  • C / SiC silicon carbide
  • Belgian Patent No. 497,198 discloses a low frequency induction heating apparatus comprising a thin metal shell surrounding a vessel which is heated by a solenoid. However, this document does not describe an apparatus capable of emitting infrared radiation of high power density.
  • the invention provides an infrared emitter using electromagnetic induction to heat a surface of a material having characteristics to bring it to a high temperature so as to produce a high power density of medium type infrared radiation. .
  • Another object of the invention is to use an electromagnetic induction of a few tens of kilohertz, which allows the use of non-metallic materials and to obtain a good electrical efficiency.
  • the object of the invention is also to reach a higher limit temperature than that of Fe - Cr - A - based metals, which is 1300 ° C., and even to pass beyond 1400 ° C.
  • Another object of the invention is to use a composite material having a relatively low electrical resistivity in order to respond to induction heating.
  • Another object of the invention is to achieve power densities of more than 200 kW / m 2 in the mean infrared using an emitter according to the invention.
  • the object of the invention is also to use a material that responds to electromagnetic induction and is capable of supporting the mentioned operating conditions, in particular in order to respond to induction heating.
  • an infrared transmitter comprising an electrically conducting surface (5) made of a composite ceramic material comprising fibers or composite / carbon covered with a outer layer preventing oxidation, at least one thickness of thermal insulator abutting said surface (5), an inductor (2) adjacent to said at least one thickness of thermal insulation and separated from said surface (5) by the latter , and a field concentrator (1) juxtaposed or adjacent to the inductor, said surface being characterized in that it emits a infrared radiating means type and having a higher power density to 200 kW / m 2 when heated by Foucault currents using said inductor.
  • the surface responding to the induction is in the form of a plate, which may be chosen from ceramic composite materials, in particular of the CFCC type.
  • the plate may also be a composite material of carbon / carbon type covered with a layer of silicon carbide.
  • the surface responding to the induction may be a thin layer contiguous to a plate.
  • the surface must be capable of being heated to a temperature of at least 1300 ° C, and generating a radiation power density exceeding 250 kW / m 2 .
  • the insulation consists of a thickness of a low temperature insulator and a thickness of a high temperature insulator.
  • the inductor may comprise an inductor consisting of a copper tube cooled with water, or may also comprise Litz cables.
  • the field concentrator is juxtaposed with the inductor.
  • the plate has a thickness of between about 1 mm and 5 mm.
  • the inductor is wound on itself in a plane.
  • a field concentrator 1 is juxtaposed with the spiral tubing (FIG. 2). As will be seen in FIG. 2, the infrared transmitter is placed to transmit radiation onto a sheet of paper 6.
  • a CFCC comprising carbon fibers makes it possible to obtain a high temperature extended plate producing an infrared radiation of medium type at a high power density.
  • Tests have found that carbon fibers, which are within a matrix of silicon carbide; allow induction heating at frequencies of a few tens of kilohertz. Simulation tests and tests on a prototype have shown that it would be possible to transfer power with very good electrical efficiency. Thermomechanically, it has been found that this composite has excellent properties.
  • a plate manufactured in CFCC from AlliedSignal Composites showed perfect flatness and a good appearance of uniformity. Induction heating of a very demanding nature has led to no breakage, deformation or reduction of mechanical rigidity. Electromagnetic coupling has also been confirmed excellent.
  • the invention consists in heating a plate of a specific material by electromagnetic induction, which plate is heated to high temperature and, consequently, emits infrared radiation.
  • the main temperature of the plate is about 1300 ° C, making it a medium-infrared type source, thus suitable for paper coating drying.
  • the radiation power density exceeds 250 kW / m 2 , which would more than double the radiation power density of most current gas radiants.
  • This very high power density is the essential asset of such a system. This translates into a occupied area halved for the same installed power.
  • the concept is characterized by a very small vertical space compared to current gas and electric technologies: this is due to the absence of combustion air and gas supply lines (with reference to gas radiants) or cooling air connectors (in reference to short tube infrared technology).
  • the new concept therefore allows the reduction of space occupied both horizontally and vertically.
  • the reduced vertical footprint can make it possible to place high density IRHD infrared sources on either side of the sheet of paper, which would further increase the power density.
  • IRHD High Density technology could also find very interesting applications in the field of metallurgy and glass.
  • the high temperature furnaces currently heated by radiating tubes could be advantageously replaced by induction heated plates. These plates would then cover the internal walls of the oven and allow a very large heating capacity, and therefore production.
  • the power density in medium-type infrared is highly sought after.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Resistance Heating (AREA)
  • General Induction Heating (AREA)
  • Glass Compositions (AREA)

Abstract

The invention concerns a heater made of a material (5) responsive to induction and capable of sustaining high temperatures. It further comprises at least an insulating thickness with low thermal conductivity, in particular a low temperature insulation (3) and a high temperature insulation (4), said thickness being fixed at the back of the material. A field winding (2) is adjacent to the insulating thickness and separated from the material (5) by the latter.

Description

DOMAINE TECHNIQUETECHNICAL AREA

L'invention concerne un émetteur infrarouge à induction électromagnétique. Plus particulièrement, l'invention est relative à un dispositif permettant l'émission de rayonnement infrarouge, lequel dispositif est alimenté à l'électricité au moyen d'un inducteur, et caractérisé par un choix de matériau pour l'émetteur qui permet de soutenir de hautes températures et d'atteindre de hautes densités de puissance de rayonnement de type moyen.The invention relates to an infrared transmitter with electromagnetic induction. More particularly, the invention relates to a device for the emission of infrared radiation, which device is electrically powered by means of an inductor, and characterized by a choice of material for the transmitter which makes it possible to high temperatures and achieve high densities of medium-type radiation power.

ART ANTÉRIEURPRIOR ART

Dans la plupart des nombreuses applications de l'infrarouge électrique, la densité de puissance requise par le procédé est relativement faible. Par contre, certains procédés comme le séchage de papier couché dans le secteur des pâtes et papiers requièrent l'utilisation de technologies à très haute densité de puissance. Cet impératif vient du fait que les machines font défiler la feuille de papier à de grandes vitesses et que la charge d'évaporation est relativement élevée.In most of the many applications of electric infrared, the power density required by the process is relatively low. On the other hand, some processes such as coated paper drying in the pulp and paper sector require the use of very high power density technologies. This is because the machines scroll the paper at high speeds and the evaporation load is relatively high.

La grande part des applications de l'infrarouge en pâtes et papiers concerne le séchage d'enductions. L'infrarouge est utilisé pour le séchage de couches sur la feuille de papier principalement depuis 1985 [Bédard, N., Evaluation of the Performance of Electric Emitters and Radiant Gas Burners, CEA report n° 9321 U 986, 1996]. Le système infrarouge est placé directement en aval de la coucheuse, ce qui permet de "saisir" la sauce sur son support de papier. Cette technique constitue maintenant la norme car elle permet une excellente qualité de produit et des vitesses de défilement élevées. La haute densité de puissance permet aussi de réaliser des installations sur des machines existantes, où l'espace est limité.The vast majority of pulp and paper infrared applications are in the drying of coatings. Infrared is used for the drying of layers on the paper sheet mainly since 1985 [Bédard, N., Evaluation of the Performance of Electric Emitters and Radiant Gas Burners, CEA report No. 9321 U 986, 1996]. The infrared system is placed directly downstream of the coater, which makes it possible to "grasp" the sauce on its paper support. This technique is now the norm because it allows for excellent product quality and high scrolling speeds. The high power density also allows for installations on existing machines, where space is limited.

La quasi-totalité des premiers systèmes infrarouges installés sur des machines à "coucher" le papier étaient alimentés à l'électricité: ils étaient essentiellement constitués de lampes à haute intensité (émettant une lumière blanche très vive). Mais peu à peu, une technologie infrarouge gaz concurrente a émergé et est venue prendre une part toujours grandissante du marché. Aujourd'hui, la majorité des nouveaux systèmes infrarouges installés dans le secteur des pâtes et papiers sont alimentés au gaz naturel. Différentes technologies sont offertes : plaquettes céramiques trouées, matrices de fibres céramiques ou de fibres métalliques, céramique réticulée et autres.Virtually all the first infrared systems installed on paper machines were powered by electricity: they consisted mainly of high intensity lamps (emitting a very bright white light). But little by little, competing infrared gas technology emerged and took an ever-increasing share of the market. Today, the majority of new infrared systems installed in the pulp and paper sector are powered by natural gas. Different technologies are offered: perforated ceramic plates, ceramic fiber or metal fiber matrices, reticulated ceramic and others.

La raison première du succès de la technologie infrarouge gaz est naturellement le prix brut de cette source d'énergie. Le rapport entre le prix du gaz et celui de l'électricité dans les grandes entreprises est d'environ 1 à 3 au Québec et peut aller jusqu'à 1 à 5 et même davantage aux États-Unis. La robustesse physique des radiants à gaz est aussi appréciée face aux lampes à haute intensité, réputées assez fragiles.The primary reason for the success of gas infrared technology is of course the raw price of this energy source. The ratio of gas and electricity prices in large companies is about 1 to 3 in Quebec and can go as high as 1 to 5 and even more in the United States. The physical robustness of gas radiants is also appreciated by high-intensity lamps, which are known to be quite fragile.

Souvent, le prix plus élevé de l'électricité face au gaz est compensé par une meilleure efficacité des technologies électriques. Si on ne considère que le rendement de rayonnement, c'est-à-dire la puissance de rayonnement total sur la puissance consommée, on pourrait conclure que c'est le cas dans le domaine de l'infrarouge appliqué aux pâtes et papiers. En effet, ce rendement est typiquement de 80% pour les unités à infrarouge court et de 45% pour les radiants à gaz. Ces valeurs ont d'ailleurs été précisément mesurées sur un même banc d'essai dans le cadre d'un important projet de l'Association Canadienne de l'Électricité [idem]. Mais ce rendement ne considère pas ce qui se passe au niveau du papier, car la part vraiment utile de la puissance consommée est ce qui se retrouve effectivement à l'intérieur du papier couché. Les propriétés d'absorption du papier et de la sauce d'enduction doivent donc être prises en considération. Or, ces propriétés varient selon certaines gammes de longueurs d'onde.Often, the higher price of electricity compared to gas is offset by better efficiency of electric technologies. If we consider only the radiation yield, ie the total radiation power on the power consumed, we could conclude that this is the case in the field of infrared applied to pulp and paper. Indeed, this yield is typically 80% for short infrared units and 45% for gas radiants. These values were measured precisely on the same test stand as part of a major project of the Canadian Electricity Association [idem]. But this performance does not consider what happens to the paper, because the really useful part of the power consumed is what is actually found inside the coated paper. The absorption properties of paper and sauce coatings must therefore be taken into consideration. However, these properties vary according to certain ranges of wavelengths.

La température d'émission des radiants à gaz se situe entre 900 et 1150°C: le rayonnement est donc de type "moyen", c'est-à-dire dans les longueurs d'ondes identifiées à l'infrarouge moyen (plus de 85% de la puissance rayonnée entre 1 et 6 µm). Elles offrent des densités de puissance de rayonnement de 100 à 160 kW/m2. Les émetteurs électriques à lampe (dont le filament est porté à 2200°C) rayonnent davantage dans l'infrarouge de type court (plus de 85% de la puissance rayonnée entre 0 et 2.5 µm) et offrent des densités de puissance pouvant dépasser 300 kW/m2.The emission temperature of gas radiants is between 900 and 1150 ° C: the radiation is therefore of the "average" type, that is to say in the wavelengths identified with the average infrared (more than 85% of the power radiated between 1 and 6 μm). They offer radiation power densities of 100 to 160 kW / m 2 . The lamp-type electric emitters (whose filament is increased to 2200 ° C) radiate more in the short type of infrared (more than 85% of the radiated power between 0 and 2.5 μm) and offer power densities that may exceed 300 kW / m 2 .

Il est généralement reconnu que l'infrarouge de type « moyen » est mieux adapté au séchage du papier et des sauces de couchage à cause du couplage approprié de leurs propriétés d'absorption spectrales avec le spectre d'émission [Pettersson M., Stenstrom S., Absorption of Infrared Radiation and the Radiation Transfer Mechanism in Paper, Part II: Application to Infrared Dryers., Journal of Pulp and Paper Science: Vol. 24 N° 11, November 1998]. L'avantage du meilleur rendement de rayonnement des systèmes électriques à lampes est donc diminué, et conséquemment celui de la densité de puissance.It is generally recognized that "medium" type infrared is better suited for drying paper and coating colors due to the proper coupling of their spectral absorption properties with the emission spectrum [Pettersson M., Stenstrom S Absorption of Infrared Radiation and Radiation Transfer Mechanism in Paper, Part II: Application to Infrared Dryers., Journal of Pulp and Paper Science: Vol. 24 No. 11, November 1998]. The advantage of the better radiation efficiency of the electric lamp systems is therefore reduced, and consequently that of the power density.

La réponse évidente à ce problème est bien sûr l'infrarouge électrique de type moyen (donc avec une température de rayonnement autour de 1100°C), déjà très utilisé dans de nombreux domaines (textile, plastique, agro-alimentaire). Mais la technologie actuelle ne permet pas d'atteindre la densité de puissance de rayonnement des radiants à gaz : au plus 80 kW/m2 du côté électrique comparé à 150 kW/m2 du côté gaz. Cette absence de compétition de type à rayonnement moyen du côté électrique laisse toute la place aux systèmes gaz. Ce faisant, la technologie à gaz accapare le marché important du séchage infrarouge en pâtes et papiers au niveau nord-américain (300 MW en 1995) et mondial (plus de 1000 MW). Une technologie infrarouge électrique permettant d'atteindre des densités de puissance équivalentes aux radiants gaz dans l'infrarouge moyen serait donc la bienvenue. Qui plus est, le marché est en demande de densités de puissance encore supérieures: l'émergence d'une technologie électrique infrarouge de type moyen de très haute densité de puissance ouvrirait des horizons particulièrement attrayants. La disponibilité d'une telle technologie serait d'autant plus intéressante que le rendement des radiants à gaz diminue avec la température d'émission, donc avec la densité de puissance, de façon inextricable [Douspis, M., Robin, J.-P., « Les brûleurs radiants à gaz », document CERUG 86.05]: une technologie électrique d'une densité de puissance de rayonnement d'au-delà de 200 kW/m2 serait alors très compétitive (à une densité de puissance équivalente, les radiants à gaz ont un rendement de rayonnement de moins de 35%).The obvious answer to this problem is of course the medium-type electric infrared (so with a radiation temperature around 1100 ° C), already widely used in many areas (textile, plastic, food). But the current technology does not allow to reach the radiation power density of the gas radiation: at most 80 kW / m 2 of the electrical side compared to 150 kW / m 2 on the gas side. This lack of competition of average radiation type on the electrical side leaves room for gas systems. In doing so, gas technology is capturing the important market for pulp and paper infrared drying in North America (300 MW in 1995) and worldwide (over 1000 MW). A electric infrared technology to achieve power densities equivalent to gas radiants in the mid-infrared would be welcome. What's more, the market is in demand for even higher power densities: the emergence of medium-power infrared electric technology with very high power density would open up particularly attractive horizons. The availability of such a technology would be all the more interesting that the efficiency of gas radiants decreases with the emission temperature, so with the power density, inextricably [Douspis, M., Robin, J.-P ., "Radiant gas burners", CERUG document 86.05]: an electrical technology with a radiation power density of more than 200 kW / m 2 would then be very competitive (at an equivalent power density, the gas radiants have a radiation efficiency of less than 35%).

Ainsi que nous le verrons plus loin la présente technologie électrique en infrarouge de type moyen est limitée en densité de puissance et la présente invention a donc pour objet de repousser ces limitations.As we will see later, the present electrical technology in the middle type of infrared is limited in power density and the object of the present invention is therefore to overcome these limitations.

Typiquement, une source infrarouge est constituée d'un corps solide qui est porté à une température telle qu'il émet un rayonnement électromagnétique de type infrarouge. Les émetteurs infrarouges électriques impliquent le passage d'un courant direct dans une résistance, habituellement un fil métallique. Le chauffage est donc effectué par effet Joule (conduction électrique directe).Typically, an infrared source consists of a solid body which is heated to a temperature such that it emits infrared-type electromagnetic radiation. Electrical infrared emitters involve passing a direct current through a resistor, usually a wire. The heating is done by Joule effect (direct electrical conduction).

La densité de puissance d'un émetteur constitué d'un fil métallique est limitée pour plusieurs raisons. Les fils métalliques ont une faible résistivité électrique et ne peuvent dépasser une température de 1300°C. Pour obtenir une résistance adéquate (i.e. suffisamment élevée pour impliquer des courants raisonnables), il faut diminuer le diamètre ou augmenter la longueur du fil. Or la durée de vie diminue fortement avec le diamètre du fil : il faut donc préférablement augmenter la longueur du fil, ce qui est réalisé en façonnant un boudin. Mais alors, une certaine distance entre spires d'un même boudin et entre les rangées de boudins doit être respectée sous peine de produire des points chauds. Cette exigence limite derechef la densité de puissance.The power density of an emitter made of wire is limited for several reasons. The wires have a low electrical resistivity and can not exceed a temperature of 1300 ° C. To obtain adequate strength (ie high enough to involve reasonable currents), it is necessary to decrease the diameter or increase the length of the wire. But the service life decreases sharply with the diameter of the wire: it is therefore preferable to increase the length of the wire, which is achieved by shaping a pudding. But then, a certain distance between turns of the same coil and between the rows of rolls must be respected at the risk of producing hot spots. This requirement further limits the power density.

De plus, il est souvent impératif de recouvrir les boudins d'une matière les isolant de l'environnement, tant du point de vue thermique (afin de limiter les pertes par convection à l'air ambiant) qu'électrique (pour des raisons de sécurité). Les fils boudinés sont alors encastrés ou insérés dans une matière transparente ou non au rayonnement infrarouge.In addition, it is often imperative to cover the rods with a material isolating them from the environment, both from the thermal point of view (in order to limit the losses by convection with ambient air) and the electrical one (for reasons of security). The corrugated son are then embedded or inserted in a material transparent or not to infrared radiation.

Lorsqu'il s'agit d'une matière opaque à l'infrarouge, la chaleur doit se transmettre du fil métallique interne à l'enveloppe externe par conduction directe. C'est alors cette enveloppe qui émet le rayonnement infrarouge et celle-ci se maintient obligatoirement à plus basse température que le fil interne lui-même. Dans le cas des tubes rayonnants ("tubular heaters"), une matière non-conductrice de l'électricité (habituellement un oxyde) doit être insérée entre la résistance et l'enveloppe, ce qui limite le transfert de chaleur et crée un fort gradient de température. La densité de puissance est donc davantage limitée que pour un boudin à nu.In the case of an infrared material, the heat must be transmitted from the inner wire to the outer shell by direct conduction. It is then this envelope that emits the infrared radiation and it is necessarily maintained at a lower temperature than the inner wire itself. In the case of tubular heaters, an electrically non-conductive material (usually an oxide) must be inserted between the resistor and the shell, which limits the heat transfer and creates a strong gradient temperature. The power density is therefore more limited than for a naked coil.

Lorsqu'une matière transparente au rayonnement infrarouge (habituellement du quartz) est utilisée pour contenir le boudin, le rayonnement provient du boudin lui-même mais passe directement au travers du quartz. Le boudin métallique se trouve alors protégé des mouvements de l'air environnant: les pertes par convection sont donc diminuées. La densité de puissance des sources infrarouges à fils boudinés encastrées dans des plaques ou insérés dans des tubes de quartz est la plus élevée parmi les sources infrarouges électriques de type moyen mais demeure en deçà de 100 kW/m2, procurant moins de 80 kW/m2 en rayonnement.When a material that is transparent to infrared radiation (usually quartz) is used to contain the flange, the radiation comes from the flange itself but passes directly through the quartz. The metal coil is then protected from the movements of the surrounding air: the convective losses are therefore reduced. The power density of embedded infrared sources embedded in plates or inserted in quartz tubes is the highest among medium-type electric infrared sources but remains below 100 kW / m 2 , providing less than 80 kW / m 2 in radiation.

Pour leur part, les sources à lampes à infrarouge court sont caractérisées par une très forte densité de puissance, car le fil de tungstène à l'intérieur des lampes est porté à très haute température (2200°C): mais comme nous l'avons vu, ce niveau de température implique que l'émission est plutôt de type court, ce qui amène les désavantages déjà mentionnés. De plus, le fil de tungstène doit être enfermé dans un tube scellé pour éviter son oxydation rapide.For their part, the sources with short infrared lamps are characterized by a very high power density, because the tungsten wire with the inside of the lamps is raised to a very high temperature (2200 ° C): but as we have seen, this temperature level implies that the emission is rather of short type, which brings the disadvantages already mentioned. In addition, the tungsten wire must be enclosed in a sealed tube to prevent rapid oxidation.

Il est à noter que parmi tous les métaux, aucune technologie actuelle ne permet d'aller au-delà de 1300 °C en atmosphère oxydante sur une période de temps très longue (en termes d'années). Le seul alliage métallique capable de relativement bien soutenir ce niveau est composé de Fer-Chrome-Aluminium et est manufacturé principalement par la société Kanthal (sous le nom Kanthal AI). D'ailleurs, ses propriétés mécaniques sont très affaiblies à cette température.It should be noted that among all metals, no current technology allows to go beyond 1300 ° C in an oxidizing atmosphere over a very long period of time (in terms of years). The only metal alloy capable of supporting this level is Iron-Chrome-Aluminum and is mainly manufactured by Kanthal (under the name Kanthal AI). Moreover, its mechanical properties are very weak at this temperature.

Un autre moyen d'augnenter la densité de puissance est d'agrandir la surface réelle d'émission en utilisant une surface étendue et non plus un fil boudiné. Une configuration en plaque pleine et étendue permet d'augmenter la surface d'émission. Théoriquement, si on parvenait à chauffer une surface pleine de Kanthal A1 à 1300°C de façon relativement uniforme, la densité de puissance de rayonnement serait très élevée (au-delà de 300 kW/m2). La difficulté est de faire passer le courant partout dans cette surface. En conduction directe, il est très difficile de réaliser un chauffage uniforme, car le courant passe par le chemin «électrique» le plus court. Pour faire passer le courant partout entre les bornes de tension, il faut découper plusieurs traits dans la plaque, ce qui pose des problèmes de tenue mécanique et de concentration locale de courant. Certains moyens ont été évalués et testés par la demanderesse mais plusieurs problèmes ont amené à remettre en question l'utilisation de la conduction électrique directe: uniformité de chauffage, tension d'alimentation, dilatation thermique, solidité mécanique, pertes thermiques par les contacts, et autres.Another way of increasing the power density is to enlarge the actual emission area by using an extended surface and no longer a coil wire. A full and wide plate configuration makes it possible to increase the emission area. Theoretically, if a solid surface of Kanthal A1 at 1300 ° C could be heated relatively uniformly, the radiation power density would be very high (above 300 kW / m 2 ). The difficulty is to pass the current everywhere in this surface. In direct conduction, it is very difficult to achieve uniform heating because the current passes through the shortest "electric" path. To pass the current everywhere between the voltage terminals, it is necessary to cut several lines in the plate, which poses problems of mechanical resistance and local concentration of current. Some means have been evaluated and tested by the applicant but several problems have led to questioning the use of direct electrical conduction: heating uniformity, supply voltage, thermal expansion, mechanical strength, thermal losses by the contacts, and other.

Suite à cette remise en question, la demanderesse propose de faire intervenir l'induction électromagnétique: plutôt que de faire passer le courant directement dans une résistance, le chauffage peut alors s'effectuer par courants de Foucault induits par un conducteur physiquement découplé de la matière chauffée. De plus, le matériau dans lequel ces courants sont développés peut être autre que le métal constituant le fil à boudins des sources infrarouges conventionnelles.Following this questioning, the applicant proposes to involve the electromagnetic induction: rather than passing the current directly into a resistor, heating can then be carried out by eddy currents induced by a driver physically decoupled from the material heated. In addition, the material in which these currents are developed may be other than the metal constituting the coil wire of conventional infrared sources.

L'utilisation de l'induction plutôt que la conduction directe permet donc de régler de nombreux problèmes techniques.The use of induction rather than direct conduction thus makes it possible to solve many technical problems.

Le choix du matériau constituant la surface émettrice constitue l'aspect déterminant. Ce matériau doit d'être en mesure de supporter des températures très élevées, bien au-delà du point de Curie de tous les matériaux ayant des propriétés magnétiques. Seule la résistivité intervient donc sur le plan électromagnétique. D'autre part, la demanderesse a pu identifier une gamme de résistivité de matériaux et de fréquences d'alimentation résultant en un rendement électrique excellent et un facteur de puissance relativement bon, deux conditions pour que l'induction puisse être utilisée comme moyen de chauffage à la base d'un système infrarouge. Il est possible de transférer une puissance très élevée (au-delà de 50 kW pour une plaque de 0,16 m2) en générant un champ électrique typique, à une tension d'alimentation raisonnable. Le chauffage est relativement uniforme, quoique les courants générés dans la plaque chauffante soient à l'image de la configuration de l'inducteur, qui est en forme circulaire ("pancake"): les quatre coins de la plaque sont donc plus froids, ainsi que le centre. Toutefois, ce concept permet d'éviter les problèmes de points chauds et de pertes par les connexions associés à la conduction électrique directe.The choice of the material constituting the emitting surface constitutes the determining aspect. This material must be able to withstand very high temperatures, far beyond the Curie point of all materials with magnetic properties. Only resistivity intervenes electromagnetically. On the other hand, the Applicant has been able to identify a resistivity range of materials and supply frequencies resulting in excellent electrical efficiency and a relatively good power factor, two conditions for induction to be used as a heating means. at the base of an infrared system. It is possible to transfer a very high power (above 50 kW for a 0.16 m 2 plate) by generating a typical electric field at a reasonable supply voltage. The heating is relatively uniform, although the currents generated in the heating plate are in the image of the configuration of the inductor, which is in a circular shape ("pancake"): the four corners of the plate are therefore colder, than the center. However, this concept makes it possible to avoid problems of hot spots and losses by the connections associated with direct electrical conduction.

Le matériau constituant la surface émettrice se doit d'être en mesure de supporter des températures et des contraintes thermomécaniques très grandes. Les métaux constituant les fils résistifs des sources infrarouges se caractérisent par des propriétés mécaniques très affaiblies au voisinage de 1300 °C. Ils ne pourraient donc constituer la plaque rayonnante.The material constituting the emitting surface must be able to withstand very high temperatures and thermomechanical stresses. The metals constituting the resistive wires of infrared sources are characterized by very weak mechanical properties in the vicinity of 1300 ° C. They could not therefore constitute the radiant plate.

Une solution étudiée a été d'utiliser des céramiques conduisant l'électricité, notamment le carbure de silicium de type « réaction bounded ». Certaines variantes de ce matériau contiennent une certaine part de silicium libre permettant un chauffage par induction électromagnétique à quelques dizaines de kilohertz. Le chauffage par induction de plaques d'un pied carré a montré un bon couplage électromagnétique mais a systématiquement conduit à des bris de nature thermomécanique. Il apparait que matériaux céramiques de type monolithique ne sont pas appropriés : d'une part parce que les contraintes thermomécaniques engendrées par un chauffage intense et imparfaitement uniforme sont de l'ordre de leur résistance mécanique ultime ; d'autre part, les procédés actuels de fabrication de grandes plaques en céramique monolithique engendrent des contraintes résiduelles importantes.One solution studied has been to use electrically conducting ceramics, particularly silicon carbide of the "bounded reaction" type. Some variants of this material contain a certain amount of free silicon allowing heating by electromagnetic induction to a few tens of kilohertz. Induction heating of one-foot square plates has shown good electromagnetic coupling but has consistently led to thermomechanical breakage. It appears that ceramic materials monolithic type are not appropriate: firstly because the thermomechanical stresses generated by intense heating and imperfectly uniform are of the order of their ultimate mechanical strength; on the other hand, the current processes for manufacturing large monolithic ceramic plates generate significant residual stresses.

En définitive, la demanderesse a constaté, comme d'autres, que les céramiques même les plus performantes comme le carbure de silicium souffrent de fragilité aux chocs mécaniques et thermomécaniques.In the end, the plaintiff has found, like others, that ceramics, even the most efficient ones, such as silicon carbide, suffer from fragility due to mechanical and thermomechanical shocks.

Une solution relativement récente à ce problème traditionnel est d'insérer des fibres dans la matrice de céramique, pour constituer une « Ceramic Matrix Composite » (CMC). Le fait d'incorporer des fibres permet d'accroître la force du matériau et réduit le danger de brisure selon un processus catastrophique: les fibres empêchent le développement rapide de microfissures [Wessel J.K., Breaking Tradition With Ceramic Composites Offer New Features that Traditional Ceramics Lack), Chemical Engineering, pp 80 - 82, October 1996].A relatively recent solution to this traditional problem is to insert fibers into the ceramic matrix to form a "Ceramic Matrix Composite" (CMC). The incorporation of fibers increases the strength of the material and reduces the danger of breakage in a catastrophic process: the fibers prevent the rapid development of microcracks [Wessel JK, Breaking Tradition With Ceramic Composites Offer New Features that Traditional Ceramics Lack ), Chemical Engineering, pp 80-82, October 1996].

Dans un effort d'amélioration, il y a quelques années, on a développé un type particulier de composite céramique, soit les "Continuous Fiber Ceramic Composites" (CFCC), dont la fabrication implique des techniques comme le CVI (Chemical Vapor Infiltration) et le CVD (Chemical Vapor Deposition).In an effort to improve, a few years ago, we developed a particular type of ceramic composite, the "Continuous Fiber Ceramic Composites" (CFCC), whose manufacture involves techniques such as CVI (Chemical Vapor Infiltration) and CVD (Chemical Vapor Deposition).

Les CFCC constituent donc une solution au problème traditionnel de fragilité des céramiques. Ils peuvent fonctionner à haute température, subir des chocs thermiques, et ont une durée de vie importante. Ces atouts en font des candidats idéaux pour servir de base d'un système infrarouge à haute densité de puissance. Par contre, la plupart des CFCC ne conduisent pas l'électricité, et ne sont donc pas susceptibles d'être chauffés par induction électromagnétique. La demanderesse a constaté que les CFCC comportant des fibres de carbone dans une matrice de carbure de silicium (C/SiC) conduisent suffisamment l'électricité pour être efficacement chauffés par induction électromagnétique.CFCC is therefore a solution to the traditional problem of fragility of ceramics. They can operate at high temperatures, undergo thermal shocks, and have a long service life. These assets make them ideal candidates to serve as a basis for a high power density infrared system. In contrast, most CFCCs do not conduct electricity, and therefore are not likely to be heated by electromagnetic induction. The Applicant has found that CFCCs comprising carbon fibers in a matrix of silicon carbide (C / SiC) conduct enough electricity to be effectively heated by electromagnetic induction.

D'autre part, d'autres matériaux faisant l'objet de développements continuels sont les composites carbone/carbone, ayant eux aussi une très grande résistance aux chocs thermiques. Ils sont toutefois limités en température car ils s'oxydent au-delà de 600°C. Ils doivent donc être recouverts d'une couche protectrice externe, ce qui fait l'objet de beaucoup de travaux à travers le monde. La demanderesse a vérifié l'excellente réponse au chauffage par induction électromagnétique d'une plaque C/C recouverte d'une couche de carbure de silicium.On the other hand, other materials being continuously developed are the carbon / carbon composites, which also have a very high resistance to thermal shocks. They are however limited in temperature because they oxidize beyond 600 ° C. They must therefore be covered with an outer protective layer, which is the subject of much work around the world. The Applicant has verified the excellent response to electromagnetic induction heating of a C / C plate covered with a layer of silicon carbide.

Toutefois, la tenue du revêtement anti-oxydation à haute température des composites C/C sur une période prolongée (années) reste un problème technologique jusqu'à maintenant [Bédard N., Développement d'un émetteur infrarouge à haute densité de puissance - Rapport d'activités 1998, LTEE-RT-0096/1998]. La résolution de ce problème ouvrirait alors la porte sur un horizon immense, car ie composite C/C lui-même garde d'excellentes propriétés mécaniques jusqu'au delà de 2000 °C. Cette température impliquerait des densités de puissance dépassant le millier de kilowatt au mètre carré !However, the high-temperature anti-oxidation coating of C / C composites over a long period (years) remains a technological problem until now [Bédard N., Development of a high-power infrared emitter - Report 1998, LTEE-RT-0096/1998]. Solving this problem would open the door to an immense horizon, since the C / C composite itself retains excellent mechanical properties up to 2000 ° C. This temperature would imply power densities exceeding a thousand kilowatts per square meter!

Le brevet belge N° 497 198 décrit un appareil de chauffage par induction à basse fréquence comprenant une mince coquille métallique entourant un récipient qui est chauffé par un solénoïde. Cependant, ce document ne décrit pas un appareil pouvant émettre un rayonnement infrarouge de haute densité de puissance.Belgian Patent No. 497,198 discloses a low frequency induction heating apparatus comprising a thin metal shell surrounding a vessel which is heated by a solenoid. However, this document does not describe an apparatus capable of emitting infrared radiation of high power density.

DIVULGATION DE L'INVENTIONDISCLOSURE OF THE INVENTION

L'invention met à disposition un émetteur infrarouge utilisant l'induction électromagnétique afin de chauffer une surface constituée d'un matériau ayant des caractéristiques permettant de le porter à une température élevée de façon à produire une haute densité de puissance de rayonnement infrarouge de type moyen.The invention provides an infrared emitter using electromagnetic induction to heat a surface of a material having characteristics to bring it to a high temperature so as to produce a high power density of medium type infrared radiation. .

Un autre objet de l'invention est de recourir à une induction électromagnétique de quelques dizaines de kilohertz, ce qui permet d'utiliser des matériaux non métalliques et d'obtenir un bon rendement électrique.Another object of the invention is to use an electromagnetic induction of a few tens of kilohertz, which allows the use of non-metallic materials and to obtain a good electrical efficiency.

L'invention a aussi pour objet d'atteindre une température limite supérieure à celle des métaux à base de Fe - Cr - A, qui est de 1300° C, et même de passer au-delà de 1400° C.The object of the invention is also to reach a higher limit temperature than that of Fe - Cr - A - based metals, which is 1300 ° C., and even to pass beyond 1400 ° C.

Un autre objet de l'invention est d'utiliser un matériau composite possédant une résistivité électrique relativement faible, afin de répondre au chauffage par induction.Another object of the invention is to use a composite material having a relatively low electrical resistivity in order to respond to induction heating.

Un autre objet de l'invention est d'atteindre des densités de puissances de plus de 200 kW/m2 en infrarouge moyen en utilisant un émetteur selon l'invention.Another object of the invention is to achieve power densities of more than 200 kW / m 2 in the mean infrared using an emitter according to the invention.

L'invention a aussi pour objet d'utiliser un matériau répondant à l'induction électromagnétique et capable de soutenir les conditions d'opération mentionnées, notamment afin de répondre au chauffage par induction.The object of the invention is also to use a material that responds to electromagnetic induction and is capable of supporting the mentioned operating conditions, in particular in order to respond to induction heating.

Un autre objet de l'invention est de proposer comme matériau d'émetteur, des céramiques composites qui ne souffrent pas des désavantages des céramiques de type monolithique.
Afin de surmonter les désavantages décrits ci-dessus, la demanderesse a mis au point un émetteur infrarouge comprenant une surface (5) conduisant l'électricité et constituée d'un matériau en céramique composite comportant des fibres ou en composite/carbone recouvert d'une couche externe empêchant l'oxydation, au moins une épaisseur d'isolant thermique adossé à ladite surface (5), un inducteur (2) adjacent à ladite au moins une épaisseur d'isolant thermique et séparé de ladite surface (5) par cette dernière, et un concentrateur de champ (1) juxtaposé ou adjacent à l'inducteur, ladite surface étant caractérisée en ce qu'elle émet un rayonnement infrarouge de type moyen et ayant une densité de puissance supérieure à 200 kW/m2 lorsqu'elle est chauffée par courants de Foucault au moyen dudit inducteur.Another object of the invention is to propose, as emitter material, composite ceramics which do not suffer from the disadvantages of ceramics of the monolithic type.
In order to overcome the disadvantages described above, the Applicant has developed an infrared transmitter comprising an electrically conducting surface (5) made of a composite ceramic material comprising fibers or composite / carbon covered with a outer layer preventing oxidation, at least one thickness of thermal insulator abutting said surface (5), an inductor (2) adjacent to said at least one thickness of thermal insulation and separated from said surface (5) by the latter , and a field concentrator (1) juxtaposed or adjacent to the inductor, said surface being characterized in that it emits a infrared radiating means type and having a higher power density to 200 kW / m 2 when heated by Foucault currents using said inductor.

Selon une réalisation préférée, la surface répondant à l'induction est sous forme de plaque, laquelle peut être choisie parmi les matériaux composites céramiques, notamment de type CFCC. La plaque peut être également un matériau composite de type carbone/carbone recouvert d'une couche de carbure de silicium. Selon ne autre réalisation préférée, la surface répondant à l'induction peut être une couche mince accolée à une plaque.According to a preferred embodiment, the surface responding to the induction is in the form of a plate, which may be chosen from ceramic composite materials, in particular of the CFCC type. The plate may also be a composite material of carbon / carbon type covered with a layer of silicon carbide. According to no other preferred embodiment, the surface responding to the induction may be a thin layer contiguous to a plate.

Selon une réalisation préférée, la surface doit être capable d'être portée à une température d'au moins 1300° C, et d'engendrer une densité de puissance de rayonnement dépassant 250 kW/m2.According to a preferred embodiment, the surface must be capable of being heated to a temperature of at least 1300 ° C, and generating a radiation power density exceeding 250 kW / m 2 .

Selon une autre réalisation, l'isolant est constitué d'une épaisseur d'un isolant basse température et d'une épaisseur d'un isolant haute température.In another embodiment, the insulation consists of a thickness of a low temperature insulator and a thickness of a high temperature insulator.

D'autre part, l'inducteur peut comporter un inducteur constitué d'un tube de cuivre refroidi à l'eau, ou peut aussi comporter des câbles de Litz.On the other hand, the inductor may comprise an inductor consisting of a copper tube cooled with water, or may also comprise Litz cables.

Selon une autre réalisation, le concentrateur de champ est juxtaposé à l'inducteur.In another embodiment, the field concentrator is juxtaposed with the inductor.

Selon une application pratique, la plaque possède une épaisseur se situant entre environ 1 mm et 5 mm.In a practical application, the plate has a thickness of between about 1 mm and 5 mm.

DESCRIPTION SOMMAIRE DE L'INVENTIONSUMMARY DESCRIPTION OF THE INVENTION

D'autres caractéristiques et avantages de l'invention ressortiront d'ailleurs d'une réalisation illustrée dans les dessins annexés, dans lesquels

  • la figure 1 est une vue en plan d'un émetteur infrarouge à induction, selon l'invention, et
  • la figure 2 est une coupe prise selon A'-A" de la figure 1.
Other features and advantages of the invention will emerge from an embodiment illustrated in the accompanying drawings, in which:
  • FIG. 1 is a plan view of an infrared induction transmitter, according to the invention, and
  • Figure 2 is a section taken along A'-A "of Figure 1.

DESCRIPTION DÉTAILLÉE DE L'INVENTIONDETAILED DESCRIPTION OF THE INVENTION

En se référant aux dessins, on verra que la configuration de base d'un émetteur selon l'invention est simple. On retrouve une surface rayonnante plane 5 d'un matériau répondant à l'induction et soutenant de hautes températures. Un matériau préféré constituant la surface rayonnante plane sera décrit en détail plus bas. Cette surface plane est adossée à un isolant thermique haute température 4. Surmontant cet isolant haute température 4, on retrouve un isolant basse température 3 Il est entendu que la nature des isolants 3,4 variera selon les besoins et le choix particulier des matériaux constituants sera laissé à l'homme de l'art. De l'autre côté des deux isolants 3,4 est placé un inducteur 2 constitué dans le cas illustré d'un tube de cuivre refroidi à l'eau, bien connu de l'homme de l'art. On pourrait tout aussi bien utiliser un câble de Litz ou tout autre inducteur, selon le choix de l'homme de l'art. L'inducteur est enroulé sur lui-même dans un plan. Enfin, un concentrateur de champ 1 est juxtaposé à la tubulure spiralée (figure 2). Comme on le verra sur la figure 2, l'émetteur infrarouge est placé pour transmettre un rayonnement sur une feuille de papier 6.Referring to the drawings, it will be seen that the basic configuration of a transmitter according to the invention is simple. We find a radiant surface plane 5 of a material responsive to induction and supporting high temperatures. A preferred material constituting the planar radiating surface will be described in detail below. This flat surface is backed by a high temperature thermal insulation 4. Overcoming this high temperature insulation 4, there is a low temperature insulation 3 It is understood that the nature of the insulators 3,4 will vary according to the needs and the particular choice of constituent materials will be left to the man of the art. On the other side of the two insulators 3,4 is placed an inductor 2 constituted in the illustrated case of a copper tube cooled with water, well known to those skilled in the art. One could equally well use a Litz cable or any other inductor, according to the choice of those skilled in the art. The inductor is wound on itself in a plane. Finally, a field concentrator 1 is juxtaposed with the spiral tubing (FIG. 2). As will be seen in FIG. 2, the infrared transmitter is placed to transmit radiation onto a sheet of paper 6.

La demanderesse a découvert qu'un CFCC comportant des fibres de carbone permet d'obtenir une plaque étendue à haute température produisant un rayonnement infrarouge de type moyen à une forte densité de puissance. Des essais ont permis de constater que les fibres de carbone, qui sont au sein d'une matrice de carbure de silicium; permettent un chauffage par induction à des fréquences de quelques dizaines de kilohertz. Des essais de simulation et des essais sur un prototype ont montré qu'il serait possible de transférer la puissance avec une très bonne efficacité électrique. Sur le plan thermomécanique, il a été possible de constater que ce composite possède des propriétés excellentes. Une plaque fabriquée en CFCC de la compagnie AlliedSignal Composites présentait une planéité parfaite et une bonne apparence d'uniformité. Un chauffage par induction de nature très exigeante n'a conduit à aucun bris, déformation ni réduction de la rigidité mécanique. Le couplage électromagnétique a aussi été confirmé excellent.Applicant has discovered that a CFCC comprising carbon fibers makes it possible to obtain a high temperature extended plate producing an infrared radiation of medium type at a high power density. Tests have found that carbon fibers, which are within a matrix of silicon carbide; allow induction heating at frequencies of a few tens of kilohertz. Simulation tests and tests on a prototype have shown that it would be possible to transfer power with very good electrical efficiency. Thermomechanically, it has been found that this composite has excellent properties. A plate manufactured in CFCC from AlliedSignal Composites showed perfect flatness and a good appearance of uniformity. Induction heating of a very demanding nature has led to no breakage, deformation or reduction of mechanical rigidity. Electromagnetic coupling has also been confirmed excellent.

En résumé, l'invention consiste à chauffer une plaque d'un matériau spécifique par induction électromagnétique, laquelle plaque est portée à haute température et, conséquemment, émet un rayonnement infrarouge. La température principale de la plaque est d'environ 1300°C, ce qui en fait une source de type à infrarouge moyen, donc appropriée au séchage d'enduction sur papier. A cette température, et tenant compte de l'émissivité du matériau constituant, la densité de puissance de rayonnement dépasse 250 kW/m2, ce qui ferait plus que doubler la densité de puissance de rayonnement de la plupart des radiants à gaz actuels.In summary, the invention consists in heating a plate of a specific material by electromagnetic induction, which plate is heated to high temperature and, consequently, emits infrared radiation. The main temperature of the plate is about 1300 ° C, making it a medium-infrared type source, thus suitable for paper coating drying. At this temperature, and taking into account the emissivity of the constituent material, the radiation power density exceeds 250 kW / m 2 , which would more than double the radiation power density of most current gas radiants.

Cette densité de puissance très élevée constitue l'atout essentiel d'un tel système. Cela se traduit en une surface occupée réduite de moitié pour une même puissance installée. En plus, le concept se caractérise par un encombrement vertical très réduit par rapport aux technologies gaz et électriques actuels : ceci est dû à l'absence de conduites d'amenée d'air de combustion et de gaz (en référence aux radiants à gaz) ou d'air de refroidissement des connecteurs (en référence à la technologie infrarouge court à lampes). Le nouveau concept permet donc la réduction de l'espace occupé à la fois horizontalement et verticalement. L'encombrement vertical réduit peut permettre de placer des sources IRHD Infrarouge Haute Densité de part et d'autre de la feuille de papier, ce qui augmenterait encore davantage la densité de puissance.This very high power density is the essential asset of such a system. This translates into a occupied area halved for the same installed power. In addition, the concept is characterized by a very small vertical space compared to current gas and electric technologies: this is due to the absence of combustion air and gas supply lines (with reference to gas radiants) or cooling air connectors (in reference to short tube infrared technology). The new concept therefore allows the reduction of space occupied both horizontally and vertically. The reduced vertical footprint can make it possible to place high density IRHD infrared sources on either side of the sheet of paper, which would further increase the power density.

Outre le domaine des pâtes et papiers, la technologie IRHD Infrarouge Haute Densité pourrait aussi trouver des applications très intéressantes dans le domaine de la métallurgie et du verre. En métallurgie, les fours à haute température présentement chauffés par des tubes rayonnants pourraient être avantageusement remplacés par des plaques chauffées par induction. Ces plaques tapisseraient alors les parois internes du four et permettraient une très grande capacité de chauffage, et donc de production. Dans l'industrie du verre, la densité de puissance en infrarouge de type moyen est très recherchée.In addition to the pulp and paper sector, IRHD High Density technology could also find very interesting applications in the field of metallurgy and glass. In metallurgy, the high temperature furnaces currently heated by radiating tubes could be advantageously replaced by induction heated plates. These plates would then cover the internal walls of the oven and allow a very large heating capacity, and therefore production. In the industry of glass, the power density in medium-type infrared is highly sought after.

Claims (17)

  1. Infrared emitter comprising a surface (5) that conducts electricity and is constituted of a ceramic composite material containing fibers or of a carbon/carbon composite covered with an external layer preventing oxidation, at least one layer of a thermal insulation applied against said surface (5), one inductor (2) adjacent to said layer with at least one layer of thermal insulation and separated from said surface (5) by the latter, and a field concentrator (1) juxtaposed or adjacent to the inductor, said surface being characterized in that it emits infrared radiation of medium type and has a power density greater than 200 kW/m2 when heated by Foucault currents using said inductor.
  2. Emitter according to claim 1, characterized in that the surface (5) is in the form of a plate.
  3. Emitter according to claim 2, characterized in that the material of said plate is a ceramic composite.
  4. Emitter according to claim 3, characterized in that the material of said plate is selected from among ceramic composite materials of type CFCC (Continuous Fiber Ceramic Composites).
  5. Emitter according to claim 4, characterized in that the material of said plate is selected from among CFCC (Continuous Fiber Ceramic Composites) materials containing carbon fibers in a silicon carbide matrix.
  6. Emitter according to claim 1, characterized in that the composite material is of the carbon/carbon type covered with a layer of silicon carbide.
  7. Emitter according to any one of claims 1 to 6, characterized in that the surface (5) responding to the induction is a thin layer applied to a plate.
  8. Emitter according to any one of claims 1 to 7, characterized in that the insulation is constituted of one layer of a low-temperature insulation (3) and one layer of a high-temperature insulation (4).
  9. Emitter according to any one of claims 1 to 8, characterized in that the inductor (2) contains a water-cooled copper tube.
  10. Emitter according to any one of claims 1 to 8, characterized in that the inductor contains a Litz cable.
  11. Emitter according to one of claims 2 to 10, characterized in that said plate has a thickness ranging from1 mm to 5 mm.
  12. Emitter according to claim 1, characterized in that said ceramic composite material is constituted of a matrix that allows for heating by induction and that contains carbon fibers.
  13. Infrared emitter according to any one of claims 1 to 12, characterized by a power density of greater than 250 kW/m2 at a temperature of at least 1300°C.
  14. Use of an emitter as defined in any one of claims 1 to 13 in the pulp and paper, metallurgy and glass industries.
  15. Use according to claim 14 that consists in the drying of coated paper.
  16. Heating device composed of an emitter as defined in any one of claims 1 to 13.
  17. Paper drying device composed of an emitter as defined in any one of claims 1 to 13.
EP00938420A 1999-07-16 2000-06-15 Infrared heater with electromagnetic induction and its uses Expired - Lifetime EP1203511B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
CA2277885 1999-07-16
CA002277885A CA2277885C (en) 1999-07-16 1999-07-16 Electromagnetic induction infrared heat system
PCT/CA2000/000722 WO2001006814A1 (en) 1999-07-16 2000-06-15 Infrared heater with electromagnetic induction

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EP1203511A1 EP1203511A1 (en) 2002-05-08
EP1203511B1 true EP1203511B1 (en) 2006-02-22

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EP (1) EP1203511B1 (en)
AU (1) AU5383000A (en)
CA (1) CA2277885C (en)
DE (1) DE60026139T2 (en)
NO (1) NO20021642D0 (en)
WO (1) WO2001006814A1 (en)

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Publication number Priority date Publication date Assignee Title
US20070210056A1 (en) * 2005-11-16 2007-09-13 Redi-Kwick Corp. Infrared oven
FR2906786B1 (en) * 2006-10-09 2009-11-27 Eurocopter France METHOD AND DEVICE FOR DEFROSTING AN AIRCRAFT WALL
US8043375B2 (en) * 2008-03-06 2011-10-25 MoiRai Orthopaedic, LLC Cartilage implants
EP2893854B1 (en) * 2014-01-10 2016-11-30 Electrolux Appliances Aktiebolag Induction cooker
WO2019163311A1 (en) * 2018-02-23 2019-08-29 Ｔｍｔマシナリー株式会社 Heating roller and spun yarn drawing device

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* Cited by examiner, † Cited by third party
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BE497198A (en)
US2635168A (en) 1950-11-04 1953-04-14 Pakco Company Eddy current heater
US5227597A (en) * 1990-02-16 1993-07-13 Electric Power Research Institute Rapid heating, uniform, highly efficient griddle
US5240542A (en) * 1990-09-06 1993-08-31 The Board Of Trustees Of The Leland Stanford Junior University Joining of composite materials by induction heating
US5528020A (en) * 1991-10-23 1996-06-18 Gas Research Institute Dual surface heaters

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EP1203511A1 (en) 2002-05-08
NO20021642L (en) 2002-04-05
CA2277885C (en) 2007-05-22
WO2001006814A1 (en) 2001-01-25
DE60026139D1 (en) 2006-04-27
US6858823B1 (en) 2005-02-22
AU5383000A (en) 2001-02-05
CA2277885A1 (en) 2001-01-16
DE60026139T2 (en) 2006-11-23
NO20021642D0 (en) 2002-04-05

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