EP0053060A1 - Inductor with travelling field and orientated flux for a stirrer for continuous casting slabs - Google Patents

Abstract

A translating field inductor for the stirring roller of a continuous slab caster includes a grooved arbor carrying flat magnetic sheets disposed parallel to the axis of the arbor, the latter and the sheets being notched by a series of circumferential grooves spaced over the length of the arbor and housing circular induction coils. In order to concentrate the magnetic flux on the moving slab in the course of the continuous casting, the arbor is stationary and is made of a nonmagnetic metal with good electrical conductivity. It has a longitudinal groove with a wide transverse cross section housing a single packet of sheets, which constitutes the magnetic core of the inductor. The arbor forms a screen for the magnetic flux generated by the induction coils with the entire assembly being such that the magnetic flux is oriented in a fixed, prescribed direction.

Description

The present invention relates to a device for setting in motion a molten metal in a continuous casting installation and during the cooling of the cast product.

It relates more particularly to the casting of large flat products, generally designated under the name of slabs.

Devices are already known for setting in motion a liquid metal by means of sliding or rotating magnetic fields, these fields being produced by inductors housed in the guide and support rollers of the continuously cast product. Such devices are for example described in French patent n ° 72/20546, published under n ° 2.187.467 and in its first and second certificates of addition n ° 73 / 19.399 and 73 / 19.400, respectively published under numbers 2,231,454 and 2,231,455. French patent 2,187,467, without going into the details of construction of the inductor itself, provides that it can either be made integral with the roller and rotate with it, or be kept fixed inside the rotating roller. The first addition certificate No. 2.231.454 describes an embodiment of a sliding field inductor, which is integral in rotation with the hollow body of revolution in which it is housed. The inductor includes a magnetic core in the form of a magnetic stainless steel shaft, which has deep longitudinal grooves extending over the entire length of the shaft and evenly spaced in the circumferential direction. In the grooves are embedded packets of flat magnetic sheets parallel to the axis of the shaft. The latter and the sheets are notched by a series of annular grooves spaced along the length of the shaft and housing circular induction coils.

The disadvantage of the devices described in the above-mentioned prior documents is their lack of power. We can think that this lack of power comes from the fact that the emission of the magnetic field produced by the inductor is distributed in azimuth in all directions around the axis of the roller. As a result, the density of the magnetic flux emitted in the useful direction, that is to say towards the zone of contact between the roller and the slab, is low, since the magnetic flux disperses unnecessarily in the other directions, particularly in the direction opposite to the slab and in the direction of the adjacent rollers situated upstream and downstream of the roll considered with respect to the direction of continuous casting.

The object of the present invention is to provide a sliding field inductor for a roll-brewer for continuous slab casting, making it possible to concentrate the magnetic flux towards the contact zone between the roll and the slab and to greatly reduce the magnetic leaks in the others. directions, in order to best use the magnetic capacity of the inductor core.

To this end, the inductor according to the present invention, comprising a grooved shaft which carries flat magnetic sheets and parallel to the axis of the shaft, the latter and the sheets being notched by a series of annular grooves spaced along the length of the shaft and housing circular field coils, is characterized in that the shaft is fixed, in a manner known per se, and is made of a non-magnetic metal which is a good conductor of electricity and comprises, a longitudinal groove of large cross section housing a single packet of magnetic sheets which alone constitutes the magnetic core of the inductor, while the shaft constitutes a screen for the magnetic flux generated by the inductor coils, the assembly being such that this magnetic flux is oriented in a privileged fixed direction.

In service, the inductor according to the intention is kept in a fixed orientation relative to the continuous casting, inside the roller which is mounted rotating so as to guide and support the continuously cast product. The inductor is mounted in a fixed orientation such that the lamination plane of the pack of magnetic sheets forming the core is perpendicular to the surface of the continuously cast slab and the free edge of the magnetic sheets is located opposite the area of contact between the roller and the slab. Each inductor completely surrounds the inductor, passing in front of the magnetic core formed by the pack of sheets, and behind the non-magnetic metal shaft which is a good conductor of electricity. Due to the fact that the magnetic core is embedded in the groove of the non-magnetic, electrically conductive metal shaft, the three faces of the core which are not opposite the contact area between the roller and the slab are protected _. against flow losses by the shielding effect resulting from the currents induced in the non-magnetic metal shaft which is a good conductor of electricity. The result is that, in service, the magnetic flux is essentially directed towards the contact zone between the roller and the slab.

• La figure 1 montre deux rouleaux-brasseurs disposés de part et d'autre d'une brame en cours de coulée continue et équipés chacun d'un inducteur conforme à la présente invention, l'un des deux rouleaux étant vu en coupe transversale suivant la ligne A-A de la figure 2, l'autre étant vu en coupe transversale suivant la ligne B-B de la figure 2.

An embodiment of the present invention will now be described, by way of purely indicative and in no way limitative, with reference to the appended drawings in which:

• Figure 1 shows two brewer rollers arranged on either side of a slab during continuous casting and each equipped with an inductor according to the present invention, one of the two rollers being seen in cross section along the line AA in FIG. 2, the other being seen in cross section along line BB in FIG. 2.

Figures 2 and 3 show one of the two brewer rollers of Figure 1, in axial section along the line CC of Figure 1, and the spectrum of the magnetic flux lines, respectively at two instants of excitation separated by a quarter period of alternating current, in the case of a bipolar two-phase inductor.

FIG. 4 represents the winding diagram of the inductor shown in FIGS. 2 and 3.

In Figures 1 to 3, we can see part of a slab 1 during continuous casting, with its outer crust 2 of metal already solidified and its core 3 of metal still in fusion. The slab 1 during casting is guided and supported by a number of rollers such as rollers 4 to 9. As is known, some of the rollers are mounted to rotate freely, while others can be rotated. As is also known, certain rollers, for example the rollers 6 and 7, are hollow and house an inductor 10 for stirring the core 3 of molten metal. These latter rollers are usually called "brewer rollers".

Each brew roller 6 or 7 has a hollow cylindrical casing 11, made of non-magnetic stainless steel, at the ends of which are fixed two ends of hollow shafts, respectively 12 and 13, by screws such as 14. Bearings (not shown) allow the rotation of the assembly 11, 12, 13 about its axis.

Inside the cylindrical casing 11 is the inductor 10. This comprises a magnetic core 15 constituted by a single pack of thin magnetic sheets suitably insulated from each other in a known manner by an insulator not shown. The laminated magnetic core 15 is embedded in a wide and deep longitudinal groove 16 which is hollowed out in a solid shaft 17 made of non-magnetic metal and a good conductor of electricity, for example aluminum alloy or copper alloy. The magnetic core 15 is held in place in the longitudinal groove 16 by several bolts 18 cooperating with keys 19 housed in transverse grooves with a dovetail section, hollowed out in the face of the magnetic core 15 which faces the bottom of the the longitudinal groove 16. The free face 20 of the magnetic core 15 is flush with the cylindrical surface of the shaft 17 and is oriented towards the adjacent face of the slab 1.

The shaft 17 and the magnetic core 15 are notched by a series of large annular grooves 21 spaced along the length of the shaft 17 and housing inductor coils 22 to 26 of cylindrical shape. The coils 22 to 26 are for example constituted by turns of flat conductor insulated in copper and are suitably insulated with respect to the magnetic core 15 by insulators placed in the bottom of the annular grooves 2] and on the sides thereof.

The ends of the shaft 17 pass, with a certain radial clearance, respectively through the ends of hollow shafts 12 and 13 and are supported and rigidly fixed to a frame (not shown) so that the shaft 17 remains stationary when the assembly 11, 12, 13 rotates around its axis.

Two narrow longitudinal grooves 27 and 28 (Figure 1), extended over the entire length of the shaft 17 and slightly deeper than the annular grooves 21, and passages 29, 30, 31 and 32 (Figure 2), formed in the two ends of the shaft 17, are provided to house the conductors 33 and 34 (FIG. 4) for supplying current to the coils 22 to 26.

As shown in Figure 4, the coils 22 to 26 are divided into two groups of coils, constituted respectively by the coils 22, 24 and 26 and by the coils 23 and 25. The coils 22, 24 and 26 are wound in alternating directions , are electrically connected in series and are connected by the conductors 33 to two external terminals 35 which are themselves connected to one of the two phases of a two-phase alternating current supply source (not shown). Similarly, the coils 23 and 25 are wound in opposite directions, are electrically connected in series and are connected by the conductors 34 to two other external terminals 36 themselves connected to the second phase of the two-phase alternating current source. It will also be noted that the end coils 22 and 26 have approximately twice as few turns as the coil 24 and that the coils 23 and 25 each have approximately the same number of turns as the coil 24.

It follows that the magnetic flux generated by the inductor 10 when the current is maximum in the first phase and zero in the second phase, has the shape shown in Figure 2, with a north pole between the coils 22 and 24 and a south pole between the coils 24 and 26. It can be noted in FIG. 2 that the flux is closed in the laminated magnetic core 15 where the flux lines are very tight, which can lead to magnetic saturation of the laminated core . We can also see that the presence of the metal shaft 17 non-magnetic and good conductor of electricity constitutes a very effective screen which prevents the magnetic flux from exiting towards the rear face of the inductor 14 as a result of the currents induced in the shaft 17, which oppose the passage of the magnetic flux. As a result, the capacity of the magnetic core 15 until saturation will be devoted almost entirely to the passage of the useful magnetic flux.

The same observation can be made at the moment when the current reaches its maximum in the second phase and is zero in the first phase, that is to say when the coils 23 and 25 are excited by forming a north pole between them and two south poles at the ends. In this case, the saturation of the magnetic core 15 is maximum at the location of the coils 23 and 25, but leakage of magnetic flux towards the rear is still avoided thanks to the shaft 17 forming a screen.

In addition, as is more particularly visible in FIG. 1, the shaft 17 and the induced currents which arise therein also oppose magnetic flux leakage on the sides of the magnetic core 15. As a result, the magnetic flux is mainly concentrated in a dihedral of angle a, which represents the useful mixing angle.

When the two phases are supplied successively and periodically, at low frequency, a magnetic field is obtained sliding in the axial direction of the brewing roll whose flow lines sweep the core 3 of the slab 1 producing a stirring of the molten metal.

From the above, it is clear that the inductor according to the present invention therefore makes it possible to make maximum use of the magnetic capacity of the laminated core 15 to produce a useful stirring flux. It makes it possible to obtain a useful stirring power 5 to 6 times greater than that obtained with the previously known inductors.

Although the embodiment which has been described above relates more particularly to the case of a bipolar two-phase inductor, it is clear that the same design could be applied to a polyphase inductor having any number of poles. However, the two-phase and bipolar solution presents advantages of simplicity and efficiency which can be exploited thanks to the present invention.

It is moreover of course understood that the embodiment which has been described above has been given by way of purely indicative and in no way limitative example, and that numerous modifications can be made by those skilled in the art without however, depart from the scope of the present invention.

Claims (3)

1.- Sliding field inductor for roll-brewer for continuous slab casting, comprising a grooved shaft (17) which carries flat magnetic sheets and parallel to the axis of the shaft, the latter and the sheets being notched by a series of annular grooves (21) spaced along the length of the shaft and housing circular field coils (22 to 26), characterized in that the shaft (17) is fixed, in a manner known per se, and is in one non-magnetic metal that is a good conductor of electricity and has a longitudinal groove (16) with a large cross section accommodating a single packet of magnetic sheets which alone constitutes the magnetic core (15) of the inductor (10), while the shaft (17) constitutes a screen for the magnetic flux generated by the induction coils (22 to 26), the assembly being such that this magnetic flux is oriented in a preferred fixed direction. 2. Inductor according to claim 1, characterized in that narrow longitudinal grooves (27 and 28), extending over the entire length of the shaft (17) and slightly deeper than the annular grooves (21), and passages (29, 30, 31, 32) formed in the two ends of the shaft (17) are provided for the conductors (33 and 34) for supplying alternating current to the coils (22 to 26). 3. Inductor according to claim 1 or 2, characterized in that the coils (22 to 26) are connected so as to form a bipolar two-phase inductor.

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