EP0081400A1 - Magnetic induction-heating device for rectangular metallic flat products moving lengthwise - Google Patents

Magnetic induction-heating device for rectangular metallic flat products moving lengthwise Download PDF

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Publication number
EP0081400A1
EP0081400A1 EP82401998A EP82401998A EP0081400A1 EP 0081400 A1 EP0081400 A1 EP 0081400A1 EP 82401998 A EP82401998 A EP 82401998A EP 82401998 A EP82401998 A EP 82401998A EP 0081400 A1 EP0081400 A1 EP 0081400A1
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EP
European Patent Office
Prior art keywords
inductor
pole
axis
heating device
polar
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Granted
Application number
EP82401998A
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German (de)
French (fr)
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EP0081400B1 (en
Inventor
Jean Maurice
Roger Travers
Jean-Paul Camus
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Alstom SA
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Compagnie Electro Mecanique SA
Alstom SA
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Publication of EP0081400A1 publication Critical patent/EP0081400A1/en
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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
    • H05B6/101—Induction heating apparatus, other than furnaces, for specific applications for local heating of metal pieces
    • H05B6/102—Induction heating apparatus, other than furnaces, for specific applications for local heating of metal pieces the metal pieces being rotated while induction heated
    • 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
    • H05B6/36—Coil arrangements
    • H05B6/365—Coil arrangements using supplementary conductive or ferromagnetic pieces

Definitions

  • the present invention relates to a device for heating by magnetic induction of flat rectangular metal products running in the direction of their length, of the type comprising at least one inductor capable of producing a magnetic field of constant intensity, but adjustable, oriented substantially perpendicular to a large face of the metal product to be heated, said inductor being rotatably mounted about an axis perpendicular to said large face of the metal product and comprising at least two magnetic poles having polar surfaces oriented towards said large face are parallel to these, and scanning an annular area when the inductor rotates.
  • the magnetic poles can be formed by permanent magnets, electromagnets or a combination of permanent magnets and electromagnets.
  • the inductor (s) can be placed outside a tunnel made of refractory material and permeable to the magnetic field, inside which pass the metallic products to be heated.
  • the previously known magnetic induction heating devices have been relatively little used until now for heating metallic products such as slabs or blanks, that is to say slabs before already undergoing several rolling passes in the roughing stands of a rolling mill, but not yet passed through the finishing stands of the rolling mill. Indeed, experience has shown that with previously known heating devices, it is difficult to obtain a temperature profile. regular erasure in the transverse direction of the metal products to be heated. This problem is further complicated if we consider that the metal products to be heated can have widths varying over a wide range of. values.
  • the present invention therefore aims to solve this problem by providing an improved device for magnetic induction heating to improve the uniformity of the heating in the transverse direction of the metal products running in the direction of their length, and this whatever the width of metal products within a given width range.
  • the magnetic induction heating device is characterized in that the pole surface of each pole has the shape of a curvilinear triangle having a vertex directed towards the axis of rotation of the inductor, two concave sides which are symmetrical with respect to a straight line passing through said vertex and perpendicular to said axis, and a convex side in an arc centered on said axis and whose radius of curvature is substantially equal to the outside radius of the annular zone swept by polar surfaces of the poles.
  • the conventional magnetic induction heating device which is shown diagrammatically in FIG. 1 and to which the present invention can be applied comprises, for example, two inductors 1 and 2 arranged respectively above and below the metal product 3 to be heated, for example a slab, facing the large faces of the slab 3, the latter being animated with a continuous movement in a direction perpendicular to the plane of the figure, that is to say in the direction of its length.
  • each of the two inductors comprises several magnetic poles, for example two magnetic poles 4.
  • the poles 4peuvent be constituted by permanent magnets, by p oles coils whose windings are supplied with direct current (solenoid), or by permanent magnets surrounded by windings which can be supplied with direct current.
  • the intensity of the direct current can be adjusted in a known manner in order to adjust the intensity of the magnetic field produced by the magnets and, consequently, the intensity of the heating produced by the eddy currents induced in the metallic product 3 to be heated.
  • the poles 4 have a section of circular shape (this shape corresponds to a maximum magnetic flux for a given length of conductor and therefore for given Joule losses in the case of wound poles).
  • At least one of the inductors 1 and 2 is rotated about the vertical axis z by known means not shown in Figure 1, the other inductor can be rotated synchronously either by the same means of drive, or by the magnetic field produced by the first inductor.
  • the speed of rotation of inductors 1 and 2 is usually clear much greater than the speed of advance of the metal product 3.
  • the pole surfaces of the poles 4 which are located opposite the large faces of the metal product 3 scan an annular zone 5 as shown in the figure 2. This zone 5 roughly corresponds to the zone of action of the inductors on the metal product 3 to be heated.
  • the heat energy which is brought to it by the Joule effect of the eddy currents induced in its mass would be relatively homogeneous in the annular zone 5.
  • the calorific energy provided at any point P located at a distance d from the longitudinal median axis of the product 3 is proportional to the length of stay of point P in the annular action zone 5 of the inductors, this length of stay being itself proportional to the length of the segment AB shown in FIG. 2.
  • the heating profile C which is obtained with such a heating device in the transverse direction of the metal product 3. As can be seen from the profile.
  • a heater such as that shown in Figure 1 and having dimensions such that the outside diameter of its annular action zone 5 corresponds substantially to the width of the metal product 3 to be heated does not not allow to obtain a homogeneous heating over the whole width of the product 3 while this one advances.
  • a heating device the dimensions of which are such that the outside diameter of its annular zone of action5 is significantly greater than the maximum width of the metallic products 3 to be heated, so as to operate in the middle part of the heating profile C. It is therefore necessary to use heating devices which are large in relation to the width of the metal products 3 to be heated. Under these conditions, it will be noted that the magnetic flux produced by the inductors is not fully used for heating, since it does not act on the metal product 3 to be heated when, during their rotation, the magnetic poles are found beyond the longitudinal sides of product 3, hence a lower yield.
  • the present invention overcomes this by -Providing a so'rait dimensions of the device such that the diameter of its area of action is only slightly greater than the maximum width of the products metal-li q ues moving heating , and making it possible to heat said products substantially homogeneously over their entire width with good efficiency.
  • this result can be obtained by using one or two inductors arranged like those of FIG. 1, but whose magnetic poles, constituted for example by electromagnets, have polar surfaces in the shape of a curvilinear triangle.
  • FIG. 3 shows by way of example, in front view, an inductor according to the present invention comprising four magnetic poles 4 of identical shapes and of alternating polarities.
  • Each magnetic pole 4 may comprise a magnetic core 6, for example of circular cross section, around which is arranged an excitation winding (not shown) supplied with direct current.
  • Each core 6 is provided with a pole shoe or pole piece 7 which is an integral part of the core 6 or which is fixed to the end of the core which is adjacent to the metal product to be heated.
  • Each pole shoe 7 has a planar pole surface parallel to one of the large faces of the metal product to be heated.
  • each bloom 7 has the shape of a curvilinear triangle which has a vertex 8 directed towards the axis of rotation z of the inductor, two concave sides 9 and 10, which are symmetrical with respect to a straight line passing through the apex 8 and perpendicular to the z axis, and a convex side 11 in an arc of a circle centered on the z axis and whose radius of curvature is substantially equal to the outside radius R of the annular zone 5 swept by the polar surfaces.
  • equation (1) The solution of equations (5) and (6) is provided by equation (1). Indeed, taking into account equations (1) and (3), equation (5) can be written: from where : from where : which gives E independent of d.
  • the variation in time of the magnetic field B seen by the point P, of polar coordinates r, ⁇ (figures 3 and 5) during the rotation of the induc tor can be represented by a succession of alternately positive and negative slots as shown in Figure 6.
  • Each slot corresponds to the passage of a pole 4 in front of point P and has a width which corresponds to the length of the polar arc ⁇ ( Figure 3) of each pole 4 at the distance r at which point P is located.
  • This waveform of the magnetic field B seen by point P can be broken down into Fourier series and expressed by the relation:
  • each of the pole shoes 7 the shape of a curvilinear triangle whose concave sides 9 and 10 are arcs of a circle having a profile which approaches the determined ideal profile.
  • the convex side 11 of which is an arc of a circle having a radius of curvature substantially equal to the outside radius of the annular zone swept by the poles 4, this outside radius itself being slightly larger than half the maximum width of the metal products to be heated.
  • each polar surface in the shape of a curvilinear triangle is preferably symmetrical with respect to the straight line passing through its apex 8 and through the center 0 of the rotating inductor, in order to obtain better balancing of the rotating masses.
  • the apex 8 of each curvilinear triangle is preferably curved to avoid leakage of magnetic flux between the poles 4 of opposite polarities.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Induction Heating (AREA)

Abstract

Dispositif de chauffage par induction magnétique de produits métalliques rectangulaires plats comprenant au moins un inducteur (1, 2) apte à produire un champ magnétique d'intensité constante, mais réglable perpendiculairement à la grande face du produit à chauffer. L'inducteur (1, 2) est rotatif autour d'un axe (z) perpendiculaire à la grande face du produit métallique et comporte au moins deux pôles magnétiques (4) dont les surfaces polaires sont orientees parallelement vers la grande face du produit métallique. La surface polaire de chaque pôle à la forme d'un triangle curviligne ayant un sommet (8) dirigé vers l'axe de rotation (z) de l'inducteur (1, 2), deux côtés concaves (9, 10) et un côté convexe (11) en arc de cercle centré sur l'axe (z) et dont le rayon de courbure (R) est sensiblement égal au rayon extérieur de la zone annulaire (5) balayée par les surfaces polaires des pôles (4).Magnetic induction heating device for flat rectangular metal products comprising at least one inductor (1, 2) capable of producing a magnetic field of constant intensity, but adjustable perpendicular to the large face of the product to be heated. The inductor (1, 2) is rotatable about an axis (z) perpendicular to the large face of the metal product and comprises at least two magnetic poles (4) whose polar surfaces are oriented parallel to the large face of the metal product . The polar surface of each pole has the shape of a curvilinear triangle having a vertex (8) directed towards the axis of rotation (z) of the inductor (1, 2), two concave sides (9, 10) and a convex side (11) in an arc centered on the axis (z) and whose radius of curvature (R) is substantially equal to the outside radius of the annular zone (5) swept by the pole surfaces of the poles (4).

Description

La présente invention concerne un dispositif de chauffage par induction magnétique de produits métalliques rectangulaires plats défilant dans le sens de leur longueur, du type comprenant au moins un inducteur apte à produire un champ magnétique d'intensité constante, mais réglable, orienté sensiblement perpendiculairement à une grande face du produit métallique à chauffer, ledit inducteur étant monté rotatif autour d'un axe perpendiculaire à ladite grande face du produit métallique et comportant au moins deux pôles magnétiques ayant des surfaces polaires orientées vers ladite grande face sont parallèles à celles-ci, et balayant une zone annulaire quand l'inducteur tourne.The present invention relates to a device for heating by magnetic induction of flat rectangular metal products running in the direction of their length, of the type comprising at least one inductor capable of producing a magnetic field of constant intensity, but adjustable, oriented substantially perpendicular to a large face of the metal product to be heated, said inductor being rotatably mounted about an axis perpendicular to said large face of the metal product and comprising at least two magnetic poles having polar surfaces oriented towards said large face are parallel to these, and scanning an annular area when the inductor rotates.

Il est connu depuis longtemps d'utiliser des inducteurs tournants produisant un champ magnétique d'intensité constante, mais réglable, pour chauffer des produits métalliques destinés à être façonnés à chaud (voir par exemple les brevets français n° 916 287 et.1 387 653). Les pôles magnétiques peuvent être constitués par des aimants permanents, des électro-aimants ou une combinaison d'aimants permanents et d'électro-aimants. Le ou les inducteurs peuvent être placés à l'extérieur d'un tunnel en matériau réfractaire et perméable au champ magnétique, à l'intérieur duquel défilent les produits métalliques à chauffer.It has long been known to use rotating inductors producing a magnetic field of constant, but adjustable intensity, for heating metal products intended to be shaped hot (see for example French patents Nos. 916 287 and 1 387 653 ). The magnetic poles can be formed by permanent magnets, electromagnets or a combination of permanent magnets and electromagnets. The inductor (s) can be placed outside a tunnel made of refractory material and permeable to the magnetic field, inside which pass the metallic products to be heated.

Toutefois, les dispositifs de chauffage par induction magnétique antérieurement connus ont été relativement peu utilisés jusqu'à présent pour réchauffer des produits métalliques tels que des brames ou des ébauches, c'est-à-dire des brames avant déjà subi plusieurs passes de laminage dans les cages dégrossisseuses d'un laminoir, mais n'étant pas encore passées à travers les cages finisseuses du laminoir. En effet, l'expérience a montré qu'avec les dispositifs de chauffage antérieurement connus, il est difficile d'obtenir un profil de température régulier dans le sens transversal des produits métalliques à réchauffer. Ce problème se complique encore si l'on considère que les produits métalliques à chauffer peuvent avoir des largeurs variant dans une large gamme de . valeurs.However, the previously known magnetic induction heating devices have been relatively little used until now for heating metallic products such as slabs or blanks, that is to say slabs before already undergoing several rolling passes in the roughing stands of a rolling mill, but not yet passed through the finishing stands of the rolling mill. Indeed, experience has shown that with previously known heating devices, it is difficult to obtain a temperature profile. regular erasure in the transverse direction of the metal products to be heated. This problem is further complicated if we consider that the metal products to be heated can have widths varying over a wide range of. values.

La présente invention a donc pour but de résoudre ce problème en fournissant un dispositif perfectionné de chauffage par induction magnétique permettant d'améliorer l'homogénéité du chauffage dans le sens transversal des produits métalliques défilant dans le sens de leur longueur, et ceci quelle que soit la largeur des produits métalliques dans une gamme de largeur donnée.The present invention therefore aims to solve this problem by providing an improved device for magnetic induction heating to improve the uniformity of the heating in the transverse direction of the metal products running in the direction of their length, and this whatever the width of metal products within a given width range.

A cet effet, le dispositif de chauffage par induction magnétique selon la présente invention est caractérisé en ce que la surface polaire de chaque pôle a la forme d'un triangle curviligne ayant un sommet dirigé vers l'axe de rotation de l'inducteur, deux côtés concaves qui sont symétriques par rapport à une droite passant par ledit sommet et perpendiculaire audit axe, et un côté convexe en arc de cercle centré sur ledit axe et dont le rayon de courbure est sensiblement égal au rayon extérieur de la zone annulaire balayée par les surfaces polaires des pôles.To this end, the magnetic induction heating device according to the present invention is characterized in that the pole surface of each pole has the shape of a curvilinear triangle having a vertex directed towards the axis of rotation of the inductor, two concave sides which are symmetrical with respect to a straight line passing through said vertex and perpendicular to said axis, and a convex side in an arc centered on said axis and whose radius of curvature is substantially equal to the outside radius of the annular zone swept by polar surfaces of the poles.

L'invention sera -mieux comprise à la lecture de la description qui va suivre et qui est donnée en référence aux dessins annexés sur lesquels :

  • La figure 1 montre schématiquement, en coupe transversale, un dispositif conventionnel de chauffage par induction magnétique.
  • La figure 2 montre la zone annulaire d'action du dispositif de chauffage de la figure 1 sur le produit métallique à chauffer, ainsi que le profil de chauffage obtenu dans le sens transversal du produit métallique.
  • La figure 3 montre la forme des surfaces polaires des pôles magnétiques d'un dispositif de chauffage conforme à la présente invention.
  • La figure 4 est un diagramme montrant la loi idéale de variation de la puissance surfacique induite par le dispositif de chauffage dans le produit métallique à chauffer en fonction de la distance à l'axe de rotation du ou des inducteurs pour obtenir un chauffage homogène sur toute la largeur du produit métallique.
  • La figure 5 est un diagramme permettant d'expliquer comment on obtient la loi de la figure 4.
  • La figure 6 est un diagramme montrant comment varie au cours du temps le champ magnétique à une distance donnée de l'axe de rotation du ou des inducteurs du dispositif de chauffage.
The invention will be better understood on reading the description which follows and which is given with reference to the appended drawings in which:
  • Figure 1 shows schematically, in cross section, a conventional magnetic induction heating device.
  • FIG. 2 shows the annular zone of action of the heating device of FIG. 1 on the metal product to be heated, as well as the heating profile obtained in the transverse direction of the metal product.
  • FIG. 3 shows the shape of the polar surfaces of the magnetic poles of a heating device according to the present invention.
  • FIG. 4 is a diagram showing the ideal law of variation of the pfd induced by the heating device in the metallic product to be heated as a function of the distance to the axis of rotation of the inductor (s) to obtain uniform heating over the entire width of the metal product.
  • FIG. 5 is a diagram making it possible to explain how the law of FIG. 4 is obtained.
  • FIG. 6 is a diagram showing how the magnetic field varies over time at a given distance from the axis of rotation of the inductor or inductors of the heating device.

Le dispositif conventionnel de chauffage par induction magnétique qui est représenté schématiquement sur la figure 1 et auquel peut être appliquée la présente invention comporte par exemple deux inducteurs 1 et 2 disposés respectivement au-dessus et au-dessous du produit métallique 3 à chauffer, par exemple une brame, en regard des grandes faces de la brame 3, celle-ci étant.animée d'un mouvement continu dans une direction perpendiculaire au-plan de la figure, c'est-à-dire dans le sens de sa longueur. Comme montré sur la figure 1, chacun des deux inducteurs comporte plusieurs pôles magnétiques, par exemple deux pôles magnétiques 4. Selon.l'intensité de chauffage que l'on désire obtenir et selon la température ambiante au voisinage des inducteurs 1 et 2, les pôles 4peuvent être constitués par des aimants permanents, par des pôles bobinés dont les enroulements sont alimentés en courant continu (électro-aimant), ou par des aimants permanents entourés de bobinages pouvant être alimentés en courant continu. Dans le cas où on utilise des électro-aimants ou des aimants permanents munis de bobinages, l'intensité du courant continu peut être réglée de façon connue afin de régler l'intensité du champ magnétique produit par les aimants et, par suite, l'intensité du chauffage produit par les courants de Foucault induits dans le produit métallique 3 à chauffer. Habituellement, les pôles 4 ont une section de forme circulaire (cette forme correspond à un flux magnétique maximal pour une longueur de conducteur donnée et donc pour des pertes Joule données dans le cas de pôles bobinés) .The conventional magnetic induction heating device which is shown diagrammatically in FIG. 1 and to which the present invention can be applied comprises, for example, two inductors 1 and 2 arranged respectively above and below the metal product 3 to be heated, for example a slab, facing the large faces of the slab 3, the latter being animated with a continuous movement in a direction perpendicular to the plane of the figure, that is to say in the direction of its length. As shown in FIG. 1, each of the two inductors comprises several magnetic poles, for example two magnetic poles 4. Depending on the heating intensity which it is desired to obtain and according to the ambient temperature in the vicinity of the inductors 1 and 2, the poles 4peuvent be constituted by permanent magnets, by p oles coils whose windings are supplied with direct current (solenoid), or by permanent magnets surrounded by windings which can be supplied with direct current. In the case where electromagnets or permanent magnets with coils are used, the intensity of the direct current can be adjusted in a known manner in order to adjust the intensity of the magnetic field produced by the magnets and, consequently, the intensity of the heating produced by the eddy currents induced in the metallic product 3 to be heated. Usually, the poles 4 have a section of circular shape (this shape corresponds to a maximum magnetic flux for a given length of conductor and therefore for given Joule losses in the case of wound poles).

Au moins l'un des inducteurs 1 et 2 est entraîné en rotation autour de l'axe vertical z par des moyens connus non montrés sur la figure 1, l'autre inducteur pouvant être entraîné en rotation en synchronisme soit par les mêmes moyens d'entraînement, soit par le champ magnétique produit par le premier inducteur. La vitesse de rotation des inducteurs 1 et 2 est habituellement nettement plus grande que la vitesse d'avance du produit métallique 3. Au cours de ce mouvement de rotation, les surfaces polaires des pôles 4 qui sont situées en regard des grandes faces du produit métallique 3 balayent une zone annulaire 5 comme montré sur la figure 2. Cette zone 5 correspond en gros à la zone d'action des inducteurs sur le produit métallique 3 à chauffer.-Si ce produit 3 était immobile, l'énergie calorifique qui lui est apportée par l'effet Joule des courants de Foucault induits dans sa masse serait relativement homogène dans la zone annulaire 5. Cependant, comme le produit métallique 3 se déplace, l'énergie calorifique apportée en un point quelconque P située à une distance d de l'axe médian longitudinal du produit 3 est proportionnelle à la durée de séjour du point P dans la zone annulaire d'action 5 des inducteurs, cette durée de séjour étant elle-même proportionnelle à la longueur du segment AB montré dans la figure 2. Dans le bas de la figure 2, on a représenté le profil de chauffage C qui est obtenu avec un tel dispositif de chauffage dans le sens transversal du produit métallique 3. Comme on peut le voir d'après le profil. de chauffage C montré sur la figure 2, un dispositif de chauffage tel que celui représenté sur la figure 1 et ayant des dimensions telles que le diamètre extérieur de sa zone annulaire d'action 5 corresponde sensiblement à la largeur du produit métallique 3 à chauffer ne permet pas d'obtenir un chauffage homogène sur toute la largeur du produit 3 pendant que celui-ci avance. Dans la pratique, pour obtenir un chauffage à peu près homogène, on est conduit à utiliser un dispositif de chauffage dont les dimensions sont telles que le diamètre extérieur de sa zone annulaire d'action5 soit nettement plus grand que la largeur maximale des produits métalliques 3 à chauffer, de façon à opérer dans la partie médiane du profil de chauffage C. On est donc conduit à utiliser des dispositifs de chauffage de grande dimension par rapport à la largeur des produits métalliques 3 à chauffer. Dans ces conditions, on notera que le flux magnétique produit par les inducteurs n'est pas pleinement utilisé pour le chauffage, puisqu'il n'agit pas sur le produit métallique 3 à chauffer lorsque, au cours de leur rotation, les pôles magnétiques se trouvent au-delà des côtés longitudinaux du produit 3, d'où un rendement plus faible.At least one of the inductors 1 and 2 is rotated about the vertical axis z by known means not shown in Figure 1, the other inductor can be rotated synchronously either by the same means of drive, or by the magnetic field produced by the first inductor. The speed of rotation of inductors 1 and 2 is usually clear much greater than the speed of advance of the metal product 3. During this rotational movement, the pole surfaces of the poles 4 which are located opposite the large faces of the metal product 3 scan an annular zone 5 as shown in the figure 2. This zone 5 roughly corresponds to the zone of action of the inductors on the metal product 3 to be heated. If this product 3 was stationary, the heat energy which is brought to it by the Joule effect of the eddy currents induced in its mass would be relatively homogeneous in the annular zone 5. However, as the metal product 3 moves, the calorific energy provided at any point P located at a distance d from the longitudinal median axis of the product 3 is proportional to the length of stay of point P in the annular action zone 5 of the inductors, this length of stay being itself proportional to the length of the segment AB shown in FIG. 2. At the bottom of FIG. 2, the heating profile C which is obtained with such a heating device in the transverse direction of the metal product 3. As can be seen from the profile. heater C shown in Figure 2, a heater such as that shown in Figure 1 and having dimensions such that the outside diameter of its annular action zone 5 corresponds substantially to the width of the metal product 3 to be heated does not not allow to obtain a homogeneous heating over the whole width of the product 3 while this one advances. In practice, in order to obtain almost homogeneous heating, one is led to use a heating device the dimensions of which are such that the outside diameter of its annular zone of action5 is significantly greater than the maximum width of the metallic products 3 to be heated, so as to operate in the middle part of the heating profile C. It is therefore necessary to use heating devices which are large in relation to the width of the metal products 3 to be heated. Under these conditions, it will be noted that the magnetic flux produced by the inductors is not fully used for heating, since it does not act on the metal product 3 to be heated when, during their rotation, the magnetic poles are found beyond the longitudinal sides of product 3, hence a lower yield.

La présente invention permet de remédier à cela en -fournissant un dispositif de chauffage'ayant des dimensions telles que le diamètre de sa zone d'action ne soit que très légèrement supérieur à la largeur maximale des produits métal- liques en mouvement à chauffer, et permettant de chauffer lesdits produits de manière sensiblement homogène sur toute leur largeur avec un bon rendement. Selon la présente invention, ce résultat peut être obtenu en'utilisant un ou deux inducteurs disposés comme ceux de la figure 1, mais dont les pôles magnétiques, constitués par exemple par des électro-aimants, ont des surfaces polaires en forme de triangle curviligne. La figure 3 montre à titre d'exemple, en vue de face, un inducteur conforme à la présente invention comportant quatre pôles magnétiques 4 de formes identiques et de polarités alternées. Chaque pôle magnétique 4 peut comporter.un noyau magnétique 6, par exemple de section transversale circulaire, autour duquel est disposé un enroulement d'excitation (non montré) alimenté en courant continu. Chaque noyau 6 est muni d'un épanouissement polaire ou pièce polaire 7 qui fait partie intégrante du noyau 6 ou qui est fixé à l'extrémité du noyau qui est adjacente au produit métallique à chauffer. Chaque épanouissement polaire 7 a une surface polaire plane et parallèle à l'une des grandes faces du produit métallique à-chauffer. Comme montré dans la figure 3, la surface polaire de chaque épanouissement 7 a la forme d'un triangle curviligne qui comporte un sommet 8 dirigé vers l'axe de rotation z de l'inducteur, deux côtés concaves 9 et 10, qui sont symétriques par rapport à une droite passant par le sommet 8 et perpendiculaire à l'axe z, et un côté convexe 11 en arc de cercle centré sur l'axe z et dont le rayon de courbure est sensiblement égal au rayon extérieur R de la zone annulaire 5 balayée par les surfaces polaires.The present invention overcomes this by -Providing a chauffage'ayant dimensions of the device such that the diameter of its area of action is only slightly greater than the maximum width of the products metal-li q ues moving heating , and making it possible to heat said products substantially homogeneously over their entire width with good efficiency. According to the present invention, this result can be obtained by using one or two inductors arranged like those of FIG. 1, but whose magnetic poles, constituted for example by electromagnets, have polar surfaces in the shape of a curvilinear triangle. FIG. 3 shows by way of example, in front view, an inductor according to the present invention comprising four magnetic poles 4 of identical shapes and of alternating polarities. Each magnetic pole 4 may comprise a magnetic core 6, for example of circular cross section, around which is arranged an excitation winding (not shown) supplied with direct current. Each core 6 is provided with a pole shoe or pole piece 7 which is an integral part of the core 6 or which is fixed to the end of the core which is adjacent to the metal product to be heated. Each pole shoe 7 has a planar pole surface parallel to one of the large faces of the metal product to be heated. As shown in Figure 3, the pole surface of each bloom 7 has the shape of a curvilinear triangle which has a vertex 8 directed towards the axis of rotation z of the inductor, two concave sides 9 and 10, which are symmetrical with respect to a straight line passing through the apex 8 and perpendicular to the z axis, and a convex side 11 in an arc of a circle centered on the z axis and whose radius of curvature is substantially equal to the outside radius R of the annular zone 5 swept by the polar surfaces.

Avec les surfaces polaires en forme de triangle curviligne qui ont été décrites ci-dessus, il est possible d'obtenir un profil de chauffage dans le sens transversal plus uniforme qu'avec les pôles magnétiques à surfaces polaires circulaires ou carrées qui étaient utilisés dans les dispositifs de chauffage antérieurement connus. Ceci peut être expli- qué de la manière suivante. En première approximation, si on néglige les effets de longueur et de largeur finies, on peut considérer que la puissance surfacique induite par l'inducteur tournant en un point quelconque P du produit métallique à chauffer n'est fonction que de la distance r dudit point à l'axe de rotation z de l'inducteur. Pour obtenir.un chauffage homogène du produit métallique en mouvement, dont la demi- largeur peut être comprise entre 0 et R (R étant le rayon maximal d'action de l'inducteur, c'est-à-dire le rayon extérieur de la zone annulaire balayée par les pôles magnétiques 4), on peut démontrer qu'il faut que la puissance surfacique soit une fonction croissante (figure 4) de la distance r sus-mentionnée, cette fonction pouvant être exprimée par la relation suivante:

Figure imgb0001
dans laquelle k1 est une constante.With the polar surfaces in the shape of a curvilinear triangle which have been described above, it is possible to obtain a more uniform transverse heating profile than with the magnetic poles with circular or square polar surfaces which were used in the previously known heating devices. This can be explained q ated as follows. As a first approximation, if we neglect the effects of finite length and width, we can consider that the surface power induced by the inductor rotating at any point P of the metal product to be heated is only a function of the distance r from said point to the axis of rotation z of the inductor. To obtain a homogeneous heating of the moving metal product, the half width of which can be between 0 and R (R being the maximum radius of action of the inductor, i.e. the outside radius of the annular zone swept by the magnetic poles 4), it can be demonstrated that the surface power must be an increasing function (FIG. 4) of the distance r mentioned above, this function being able to be expressed by the following relation:
Figure imgb0001
 where k 1 is a constant.

En effet, en partant de l'hypothèse sus-mentionnée, l'énergie moyenne Em(d) induite au point P qui se déplace le long du segment AB à une distance d de l'axe Oy (figure 5) est proportionnelle à :

Figure imgb0002
avec :
Figure imgb0003
Figure imgb0004
soit :
Figure imgb0005
 Indeed, starting from the aforementioned hypothesis, the average energy E m (d) induced at point P which moves along the segment AB at a distance d from the axis Oy (Figure 5) is proportional to :
Figure imgb0002
 with:
Figure imgb0003
Figure imgb0004
 is :
Figure imgb0005

Pour obtenir un chauffage homogène en largeur, il faut que l'énergie moyenne Em induite à la distance d ne dépende pas de cette distance d :

Figure imgb0006
To obtain a uniform heating in width, the average energy E m induced at the distance d must not depend on this distance d:
Figure imgb0006

La solution des équations (5) et (6) est fournie par l'équation (1). En effet, en tenant compte des équations (1) et (3), l'équation (5) peut s'écrire :

Figure imgb0007
d'où :
Figure imgb0008
d'oü :
Figure imgb0009
ce qui donne bien E indépendant de d.The solution of equations (5) and (6) is provided by equation (1). Indeed, taking into account equations (1) and (3), equation (5) can be written:
Figure imgb0007
 from where :
Figure imgb0008
 from where :
Figure imgb0009
 which gives E independent of d.

Sur la figure 4 on a tracé la courbe représentative de la fonction f (r) définie par l'équation (1) pour r compris entre -R et +R. D'après cette courbe on peut voir que pour obtenir un chauffage homogène sur toute la largeur d'un produit métallique ayant une largeur égale à 2 R, c'est-à-dire égale au diamètre de la zone annulaire d'action de l'inducteur, la puissance surfacique induite devrait théoriquement avoir une valeur infinie à la périphérie de ladite zone annulaire, ce qui est bien entendu impossible à réaliser en pratique. Dans la pratique, pour une largeur maximale donnée des produits métalliques à chauffer, il suffira de dimensionner l'inducteur de telle façon que son rayon d'action R soit légèrement plus grand que la moitié de ladite largeur maximale donnée et que la courbe représentative des variations de la puissance surfacique induite en fonction de la distance r ait une allure semblable à celle de la courbe de la figure 4, mais avec des valeurs finies de la puissance pour les' valeurs de r voisines de R.In Figure 4 we have drawn the curve representative of the function f (r) defined by equation (1) for r between -R and + R. From this curve it can be seen that to obtain homogeneous heating over the entire width of a metal product having a width equal to 2 R, that is to say equal to the diameter of the annular zone of action of l 'inductor, the induced surface power should theoretically have an infinite value at the periphery of said annular zone, which is of course impossible to achieve in practice. In practice, for a given maximum width of the metal products to be heated, it will suffice to size the inductor so that its radius of action R is slightly greater than half of said given maximum width and that the curve representative of the variations in the induced pfd as a function of the distance r has a shape similar to that of the curve in FIG. 4, but with finite values of the power for the 'values of r close to R.

Si l'on suppose que le champ magnétique est uniforme sous chaque pôle 4 de l'inducteur, que le produit métallique à chauffer est limité à la zone d'action de l'inducteur et que la réaction d'induit est négligeable, la variation dans le temps du champ magnétique B vu par le point P, de coordonnées polaires r,α (figures 3 et 5) au cours de la rotation de l'inducteur peut être représentée par une succession de créneaux alternativement positif et négatif comme montré sur la figure 6. Chaque créneau correspond au passage d'un pôle 4 devant le point P et a une largeur qui correspond à la longueur de l'arc polaire θ (figure 3) de chaque pôle 4 à la distance r à laquelle se trouve le point P. Cette forme d'onde du champ magnétique B vue par le point P peut être décomposée en série de Fourier et exprimée par la relation :

Figure imgb0010
If it is assumed that the magnetic field is uniform under each pole 4 of the inductor, that the metal product to be heated is limited to the zone of action of the inductor and that the armature reaction is negligible, the variation in time of the magnetic field B seen by the point P, of polar coordinates r, α (figures 3 and 5) during the rotation of the induc tor can be represented by a succession of alternately positive and negative slots as shown in Figure 6. Each slot corresponds to the passage of a pole 4 in front of point P and has a width which corresponds to the length of the polar arc θ ( Figure 3) of each pole 4 at the distance r at which point P is located. This waveform of the magnetic field B seen by point P can be broken down into Fourier series and expressed by the relation:
Figure imgb0010

Si on considère pour simplifier que la puissance surfacique induite au point P est proportionnelle au carré de l'amplitude de la composante fondamentale du champ magnétique, ceci peut être exprimé par l'équation suivante :

Figure imgb0011
où k2 est une constante de proportionnalité et AO est l'amplitude de la composante fondamentale du champ. A peut être tiré de l'équation (10) enfaisant p = 0, soit :
Figure imgb0012
L'équation (11) devientalors :
Figure imgb0013
ce qui peut encore s'écrire :
Figure imgb0014
avec :
Figure imgb0015
 If we consider for simplicity that the pfd induced at point P is proportional to the square of the amplitude of the fundamental component of the magnetic field, this can be expressed by the following equation:
Figure imgb0011
 where k 2 is a proportionality constant and A O is the amplitude of the fundamental component of the field. A can be taken from equation (10) doing p = 0, that is:
Figure imgb0012
 Then equation (11) becomes:
Figure imgb0013
 which can still be written:
Figure imgb0014
 with:
Figure imgb0015

D'après l'équation (14), on voit par conséquent que la la longueur de l'arc polaire θ de chaque pôle magnétique 4 à la distance r du centre O de l'inducteur est une fonction croissante de la distancé r, d'où la forme concave des côtés 9 et 10 de chacune des surfaces polaires 7 (figure 3).From equation (14), we therefore see that the length of the polar arc θ of each magnetic pole 4 at the distance r from the center O of the inductor is an increasing function of the distance r, d 'where the concave shape of the sides 9 and 10 of each of the pole surfaces 7 (Figure 3).

A l'aide des équations ci-dessus on peut déterminer, pour une largeur donnée des produits métalliques à chauffer et en négligeant les effets de bord, une forme théorique de la surface polaire permettant d'obtenir une homogénéité de chauffage sur toute la largeur des produits métalliques à chauffer. La prise en compte des effets de bord, qui dépendent de la vitesse de rotation de l'inducteur, du nombre et de la forme des pôles, des caractéristiques physiques du produit métallique à chauffer et de la valeur de l'entrefer est complexe. Les effets de bord peuvent être pris en compte en modifiant de manière itérative la forme théorique déterminée par le calcul pour une largeur donnée des produits métalliques. Pour des raisons de simplicité de fabrication, on peut adopter pour la surface polaire de chacun des épanouissements polaires 7 la forme d'un triangle curviligne dont les côtés concaves 9 et 10 sont des arcs de cercle ayant un profil qui se rapproche du profil idéal déterminé de la manière décrite plus haut, et dont le côté convexe 11 est un arc de cercle ayant un rayon de courbure sensiblement égal au rayon extérieur de la zone annulaire balayée par les pôles 4, ce rayon extérieur étant lui-même-légèrement plus grand que la moitié de la largeur maximale des produits métalliques à chauffer. En outre, chaque surface polaire en forme de triangle curviligne est de préférence symétrique par rapport à la droite passant par son sommet 8 et par le centre 0 de l'inducteur tournant, afin d'obtenir un meilleur équilibrage des masses en rotation. En outre, comme montré dans la figure 3, le sommet 8 de chaque triangle curviligne est de préférencetron- qué pour éviter les fuites de flux magnétique entre les pôles 4 de polarités opposées.Using the above equations, it is possible to determine, for a given width of the metallic products to be heated and neglecting the edge effects, a theoretical shape of the polar surface making it possible to obtain a homogeneity of heating over the entire width of the metal products for heating. Taking edge effects into account, which depend on the speed of rotation of the inductor, the number and shape of the poles, the physical characteristics of the metal product to be heated and the value of the air gap is complex. The edge effects can be taken into account by iteratively modifying the theoretical shape determined by the calculation for a given width of the metallic products. For reasons of simplicity of manufacture, it is possible to adopt for the pole surface of each of the pole shoes 7 the shape of a curvilinear triangle whose concave sides 9 and 10 are arcs of a circle having a profile which approaches the determined ideal profile. as described above, and the convex side 11 of which is an arc of a circle having a radius of curvature substantially equal to the outside radius of the annular zone swept by the poles 4, this outside radius itself being slightly larger than half the maximum width of the metal products to be heated. In addition, each polar surface in the shape of a curvilinear triangle is preferably symmetrical with respect to the straight line passing through its apex 8 and through the center 0 of the rotating inductor, in order to obtain better balancing of the rotating masses. In addition, as shown in FIG. 3, the apex 8 of each curvilinear triangle is preferably curved to avoid leakage of magnetic flux between the poles 4 of opposite polarities.

Claims (4)

1.- Dispositif de chauffage par induction magnétique de produits métalliques rectangulaires plats (3) défilant dans le sens de leur longueur, comprenant au moins un inducteur (1,2) apte à produire un champ magnétique d'intensité constante, mais réglable, orienté sensiblement.perpendiculairement à une grande face du produit métallique (3) à chauffer, ledit inducteur (1,2) étant monté rotatif autour d'un axe (z) perpendiculaire à ladite grande face du produit métallique et comportant au moins deux pôles magnétiques (4) ayant des surfaces polaires orientées vers ladite grande face et parallèles à celle-ci, et balayant une zone annulaire (5) quand l'inducteur tourne, caractérisé en ce que la surface polaire de chaque pôle (4) a la forme d'un triangle curviligne ayant un sommet (8) dirigé vers l'axe de rotation (z) de l'inducteur (1,2), deux côtés concaves (9,10) qui sont symétriques par rapport à une droite passant par ledit sommet (8) et perpendiculaire audit axe (z), et un côté convexe (11) en arc de cercle centré sur ledit axe (z) et dont le rayon de courbure (R) est sensiblement égal au rayon extérieur de la zone annulaire (5) balayée par les surfaces polaires des pôles (4).1.- Magnetic induction heating device for flat rectangular metal products (3) running lengthwise, comprising at least one inductor (1,2) capable of producing a magnetic field of constant intensity, but adjustable, oriented substantially.perpendicular to a large face of the metal product (3) to be heated, said inductor (1,2) being rotatably mounted about an axis (z) perpendicular to said large face of the metal product and comprising at least two magnetic poles ( 4) having polar surfaces oriented towards and parallel to said large face, and scanning an annular zone (5) when the inductor rotates, characterized in that the polar surface of each pole (4) has the shape of a curvilinear triangle having a vertex (8) directed towards the axis of rotation (z) of the inductor (1,2), two concave sides (9,10) which are symmetrical with respect to a straight line passing through said vertex ( 8) and perpendicular to said axis (z), and a convex side ( 11) in an arc centered on said axis (z) and whose radius of curvature (R) is substantially equal to the outside radius of the annular zone (5) swept by the pole surfaces of the poles (4). 2.- Dispositif de chauffage selon la revendication 1, caractérisé en ce que lesdits côtés concaves (9,10) ont une forme en arc de cercle.2.- A heating device according to claim 1, characterized in that said concave sides (9,10) have a shape in an arc. , 3.- Dispositif de chauffage selon la revendication 1 ou 2, caractérisé en ce que ledit sommet (8) est tronqué., 3.- A heating device according to claim 1 or 2, characterized in that said top (8) is truncated. 4.- Dispositif de chauffage selon l'une quelconque des revendications 1 à 3, dans lequel chaque pôle (4) comporte un noyau (6) entouré d'une bobine et muni d'un épanouissement polaire (7), caractérisé en ce que ladite surface polaire en forme de triangle curviligne est la surface polaire de l'épanouissement polaire (7) du pôle (4) considéré.4. A heating device according to any one of claims 1 to 3, in which each pole (4) comprises a core (6) surrounded by a coil and provided with a pole shoe (7), characterized in that said polar surface in the shape of a curvilinear triangle is the polar surface of the polar expansion (7) of the pole (4) considered.
EP82401998A 1981-11-13 1982-10-28 Magnetic induction-heating device for rectangular metallic flat products moving lengthwise Expired EP0081400B1 (en)

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FR8121238A FR2516641A1 (en) 1981-11-13 1981-11-13 DEVICE FOR MAGNETICALLY INDUCING HEATER OF FLAT RECTANGULAR METAL PRODUCTS THROUGHOUT THEIR LENGTH

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US5483042A (en) * 1990-06-04 1996-01-09 Nordson Corporation Magnetic separator
US5847370A (en) * 1990-06-04 1998-12-08 Nordson Corporation Can coating and curing system having focused induction heater using thin lamination cores
US5529703A (en) * 1990-06-04 1996-06-25 Nordson Corporation Induction dryer and magnetic separator
DE69128096T2 (en) 1990-11-30 1998-02-26 Nordson Corp INDUCTION DRYER AND MAGNETIC CUTTER
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NZ282347A (en) * 1994-03-16 1999-01-28 Larkden Pty Ltd Converting rotational energy of shaft into heat, inducing eddy currents in graphite block
FR2733553B1 (en) * 1995-04-25 1997-07-11 Pem Sa Protection Electrolytiq LAMINATION DEVICE FOR SOLIDARIZING A METAL STRIP AND A STRIP OF INSULATING MATERIAL
DE102008014165A1 (en) * 2008-03-14 2009-09-24 Ab Skf Apparatus for heating and method for heating
WO2009126850A1 (en) * 2008-04-11 2009-10-15 The Timken Company Inductive heating using permanent magnets for hardening of gear teeth and components alike
KR20130139997A (en) * 2010-10-11 2013-12-23 더 팀켄 컴퍼니 Apparatus for induction hardening
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