EP1604551B1 - Device for heating by induction of metal strip - Google Patents

Abstract

The device has a choke coil (B) surrounding a zone of a metallic band (A) transversally to longitudinal direction (D) of the band. The coil has a set of single concave loops (1) whose average plan (P) is orthogonal to longitudinal direction of the band. The loops are arranged in parallel or series among themselves, where each loop has two larger and smaller sides in relation to width and thickness of the band.

Description

The invention relates to a device for heating electromagnetic induction of one or more metal strips, which device comprises at least one inductive coil which surrounds an area of the strip (s) transversely to the longitudinal direction of the ( tapes).

EP 0 385 571 discloses an induction heating device for steel strips, comprising an inductive coil which surrounds an area of the steel strip, the coil comprising four turns.

US 4,778,971 discloses an induction heating device comprising a pair of heating coil units arranged in parallel to allow passage of a room between the heating coil units. Each heating coil unit comprises a main coil comprising transverse conductors and a secondary coil comprising longitudinal conductors.

EP 0 407 660 discloses an inductive heating device for steel strips, comprising an inductor coil with a plurality of turns fed by a high frequency power source for periodically changing the frequency of the charging current and the charging voltage of said source of power. high frequency power supply.

EP 1 063 305 discloses an induction heating device comprising a multi-turn inductance for inductively heating a steel piece having an induced current limiting unit constituted by an iron core.

EP 0 589 087 discloses an induction heating device for steel strips, comprising an inductive coil which surrounds an area of the steel strip, the coil comprising a plurality of turns having longitudinal conductive segments.

Such a heater is used, for example, in metal strip processing lines, in particular for the drying of a coating such as a paint layer, or the heating before galvanization or the heating before annealing applied to the strip which passes through the inductor coil or coils, in its longitudinal direction.

The object of the invention is, above all, to provide a heating device which makes it possible to reduce or eliminate the defects in the coating of the strip which may occur with the heating devices known to date. This problem is solved by a heating device according to claim 1.

With such an arrangement, the electromagnetic field produced has no transverse component in the strip, unlike the state of the art in which the turns of the coil are inclined to the longitudinal direction of the strip. The removal of this transverse component makes it possible to avoid the circulation of parasitic induced currents in the band which are at the origin of potential differences between the band and the rollers located upstream and downstream of the inductor. These differences in potential sparks, which affects the coating and the surface condition of the strip. In addition, the transverse temperature homogeneity (median edges) is improved with respect to a zigzag inductor.

The coil may comprise several monospires whose average planes are orthogonal to the longitudinal direction of the strip. Monospires can be connected together in series, or in parallel, or in series-parallel.

Each monospire may have two long sides in relation to the width of the strip and two small sides in relation to the thickness of the strip. The current supply can be performed on a long side or a small side.

Preferably, the length of the long sides of the monospire is greater than the width of the web by a value such that an accentuated heating effect at the edge of the web is avoided.

The distance between the long sides of the monospire can increase towards the ends of the long sides so that the accentuated heating effect at the edge of the band is avoided. The monospire may have towards the ends of its long sides a trapezoidal outline whose large base constitutes a small outer side. Alternatively, the monospire may have towards the ends of its long sides a substantially circular convex outward contour.

Advantageously, the heating device comprises, at each longitudinal end of the monospiral inductive coil, a short-circuit monospire closed on itself and whose average plane is orthogonal to the longitudinal direction of the strip.

The device may include an electromagnetic shield to contain the magnetic field substantially in a direction orthogonal to the plane of the band.

The device may comprise a field deflector for correcting the temperature at the bank relative to the median zone of the strip.

• Fig.1 est une vue schématique en perspective d'un dispositif de chauffage avec monospire selon l'invention, traversé par une bande métallique.
• Fig.2 est une coupe schématique verticale d'une monospire avec la bande métallique à l'intérieur.
• Fig.3 montre une variante de monospire, sans représentation de la bande.
• Fig.4 montre une autre variante de monospire, semblablement à Fig.3.
• Fig.5 et 6 montrent, en coupe verticale deux variantes de réalisation de monospire entourant une bande qui se déplace horizontalement.
• Fig.7 est un schéma en perspective d'une bobine comportant trois monospires reliées en parallèle avec à chaque extrémité longitudinale une spire de court-circuit.
• Fig.8 est le schéma électrique du branchement en parallèle des monospires de Fig.7.
• Fig.9 est un schéma en perspective d'une bobine composée de trois monospires branchées en série.
• Fig.10 est le schéma électrique du branchement de Fig.9.
• Fig.11 est un schéma en perspective de quatre monospires branchées deux à deux en série-parallèle.
• Fig.12, enfin, est le schéma électrique du branchement de Fig.11.
• En se reportant à Fig.1 on peut voir un dispositif de chauffage par induction électromagnétique d'une bande d'acier A, ou plus généralement d'une bande métallique. Dans l'exemple de Fig.1 la bande A défile verticalement suivant sa direction longitudinale verticale D représentée par une flèche. Le dispositif de chauffage comprend au moins une bobine inductrice B qui entoure une zone de la bande A transversalement à la direction longitudinale D.

The invention consists, apart from the arrangements set out above, in a number of other provisions which will be more explicitly discussed below with reference to exemplary embodiments described with reference to the accompanying drawings, but which are in no way limiting. On these drawings:

• Fig.1 is a schematic perspective view of a heating device with monospire according to the invention, crossed by a metal strip.
• Fig.2 is a schematic vertical section of a single-spoke with the metal band inside.
• Fig.3 shows a variant of monospire, without representation of the band.
• Fig.4 shows another variant of monospire, similarly to Fig.3 .
• Fig.5 and 6 show, in vertical section two variants of realization of monospire surrounding a band that moves horizontally.
• Fig.7 is a perspective diagram of a coil having three monospires connected in parallel with each longitudinal end a short-circuit turn.
• Fig.8 is the wiring diagram for the parallel connection of single-core Fig.7 .
• Fig.9 is a perspective diagram of a coil composed of three monospires connected in series.
• Fig.10 is the circuit diagram of the connection of Fig.9 .
• Fig.11 is a perspective diagram of four parallel-connected two-to-two connected monospheres.
• Fig.12 , finally, is the electrical diagram of the connection of Fig.11 .
• Referring to Fig.1 we can see a device for electromagnetic induction heating of a steel strip A, or more generally a metal strip. In the example of Fig.1 the band A scrolls vertically in its vertical longitudinal direction D represented by an arrow. The heating device comprises at least one inductor coil B which surrounds an area of the band A transversely to the longitudinal direction D.

The coil B, according to the invention, comprises at least one monospire 1 whose average plane P is orthogonal to the longitudinal direction D of the band A.

according to Fig.1 , the monospire 1 is constituted by a flat conductor forming a rectangular contour whose long sides 1a, 1b, are parallel to the large faces of the strip, and the short sides 1c, 1d, parallel to the edge of the strip.

The current supply is carried out on a large side 1b according to Fig.1 . This large side 1b is open substantially at mid-length and has two lamellae L1, L2 folded at right angles outwardly with respect to the plane of the side 1b to allow connection to the power supply.

Because of the arrangement of the average plane P orthogonal to the direction D, the inductor coil B does not produce parasitic current in the band A, unlike conventional multispiral coils which are not orthogonal to the direction D. According to the invention, the temperature homogeneity in the width of the strip is improved.

Fig.2 shows a similar layout to Fig.1 with a band A that moves horizontally instead of the vertical displacement of Fig.1 .

Fig.3 illustrates a variant embodiment according to which the current supply and the lamellae L1, L2 are provided in the central zone of a short side, for example 1c. The metal strip A is not represented on Fig.3 .

Fig.4 shows a variant of the monospire according to which the current supply is provided by lamellae L1, L2 provided at one end of a short side, for example 1c.

Although the drawings illustrate a monospire made with a flat conductor, it is clear that other types of conductor for example circular or rectangular section or combination of several conductors of circular or rectangular section can be used to make the single-sided.

The length H ( Fig.2 ) of the long sides of the monospire 1 is greater than the width h of the band by a value such as an accentuated heating effect at the edge of the band, that is to say along the banks Ac, Ad is avoided. As an indication H may be greater than about 25% to h, with equal distribution of the difference in dimensions on either side of the longitudinal axis of the band A.

Fig.5 illustrates an alternative embodiment in which the distance E between the long sides of the monospire increases towards the ends of these long sides so that the accentuated heating effect in edge Ac, Ad of the band is even better avoided.

according to Fig.5 the monospire 1 has towards the ends of its long sides a trapezoidal contour Td, Tc whose large base constitutes the small outer side 1c, 1d, while the small base of the trapezium corresponds to the distance between the long sides of the monospire in the central region.

According to the variant of Fig.6 , the ends of the long sides of the monospire have a substantially circular contour Cd, Cc convex outwards, also favorable to the limitation or suppression of the heating effect accentuated edge Ac, Ad.

Fig.7 schematically shows in perspective a coil B1 comprising three identical monospires 1, 21 and 31 coaxial connected in parallel according to the electrical diagram of Fig.8 . Each monospire 1, 21, 31 has its mean plane orthogonal to the longitudinal direction of the metal strip (not shown in FIG. Fig.7 ) which scrolls inside the turns. The AC power supply, generally high frequency, is provided by conductors connected in parallel to the supply lamellae L1, L2 of each monospire.

Advantageously, there is provided at each longitudinal end of the coil B1 a short-circuit monospire 4, 5 closed on itself, whose average plane is orthogonal to the longitudinal direction of the strip. These monospires 4, 5 short-circuit can close the electromagnetic field lines, two of which are schematically represented in Mc and Md, shortly after their exit of the turns 4 and 5. It is thus avoided that the electromagnetic field propagates further along the longitudinal direction of the band, so that any disturbances created by this field on devices downstream or upstream of the coil B1 are avoided.

Fig.9 illustrates a coil B2 having three coaxial monospires 1, 21, 31 connected in series as illustrated by the circuit diagram of FIG. Fig.10 . The average plane of each monospire is orthogonal to the longitudinal direction D of the metal strip which is not represented on Fig.9 .

Of course, the number of monospires connected in parallel or in series may be different from three, for example equal to two or more than three.

Fig.11 schematically shows in perspective a series -parallel assembly of four monospires 1, 21, 31, 41 coaxial whose average plane is orthogonal to the longitudinal direction D of the steel strip not shown.

The monospires 1, 21 are connected in series as well as the monospires 31, 41. These two series groups are connected in parallel as illustrated schematically by Fig.12 .

Of course, the series-parallel connection can be made with a number of monospires different from that illustrated on Fig.11 and 12 .

In all the variants shown it is possible to provide short-circuit monospires placed at each end of the coil as in the case of Fig.7 .

It is also possible to provide an electromagnetic shielding, for example with a magnetic circuit with sheets or ferrites, or a shield made of copper sheet, in order to contain the magnetic field essentially in a direction orthogonal to the plane of the strip.

The heater may operate under controlled atmosphere or not.

Field deflectors may be provided in particular for correcting the temperature at the edge Ac, Ad, relative to the median zone of the strip.

One could also provide concave monospires in the longitudinal direction of the strip.

Claims (10)

1. Device for heating a metal strip (A) by electromagnetic induction, comprising at least one inducing coil (B) that surrounds an area of the strip transversely to the longitudinal direction (D) of the strip, where the coil (B) comprises several single turns (B1), the mid-planes of which are orthogonal to the longitudinal direction (D) of the strip, characterised in that the single turns are connected to each other in series, or in parallel, or in series-parallel, so that the electric current flows in the same direction around the strip (A) in all the single turns, the electromagnetic field produced not having any transverse component in the strip.
2. Device according to claim 1, in which each single turn has two large sides relating to the width of the strip and two small sides relating to the thickness of the strip, characterised in that the current feed (L1, L2) is effected on a large side (1b).
3. Device according to claim 1, in which each single turn has two large sides relating to the width of the strip and two small sides relating to the thickness of the strip, characterised in that the current feed (L1, L2) is effected on a small side (1c).
4. Device according to claim 2 or 3, characterised in that the length (H) of the large sides of the single turn is greater than the width (h) of the strip (A) by an amount such that an accentuated heating effect at the rim of the strip is avoided.
5. Device according to claim 2, 3 or 4, characterised in that the distance (E) between the large sides of the single turn increases towards the ends of the large sides so that the accentuated heating effect at the rim of the strip is avoided.
6. Device according to claim 5, characterised in that the single turn has, towards the ends of its large sides, a trapezoidal contour (Tc, Td) the large base of which constitutes an external small side (1c, 1d).
7. Device according to claim 5, characterised in that the single turn has, towards the ends of its large sides, a substantially circular contour (Cc, Cd) convex towards the outside.
8. Device according to one of the preceding claims, characterised in that it comprises, at each longitudinal end of the inducing coil, a short-circuit single turn (4, 5) closed on itself, the mid-plane of which is orthogonal to the longitudinal direction (D) of the strip.
9. Device according to any one of the preceding claims, characterised in that it comprises an electromagnetic screen in order to contain the magnet field essentially in a direction orthogonal to the plane of the strip.
10. Device according to one of the preceding claims, characterised in that it comprises at least one field deflector for correcting the temperature on the edge (Ac, Ad) with respect to the middle area of the strip.

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