EP0022711B1 - Process and agitating means for ameliorating the quality of continuous cast metals - Google Patents

Abstract

1. A process for rabbling a continuous flow of metal by the action of a rotating magnetic field on the metal which is cooling, characterised in that in an inductor (4) is caused to rotate and produces a fixed magnetic field in relation to the inductor about an axis parallel to at least one of the surfaces of the cast product (1, 21).

Description

The invention relates to a method and a stirring device intended to improve the quality of a continuously cast metal.

The quality standards of metals, steel in particular, becoming more and more strict, it is necessary, to avoid quality downgrading or scrap, to obtain a regularity of quality in the production of greater and greater. This is in particular the aim, in the production by continuous casting, of devices for stirring the metal during casting, that is to say in the ingot mold, and during solidification at levels situated below the ingot mold. where an area still liquid, frequently called liquid well, is in the middle of the ingot when cooling. Such mixing makes it possible on the one hand to reduce the length of the crystals during solidification, on the other hand to distribute the impurities which would not have risen to the surface above the ingot mold.

Electromagnetic stirring devices for billets or blooms are known which operate by the action of a rotating magnetic field passing through the billet in the course of solidification, the magnetic field being created by inductor coils arranged in the mold or below it. this. Such a device is described for example in the French patent application of the Applicant published under No. 2,355,392, or in the patent USA 3153820.

There are also known stirring devices for the continuous casting of slabs.

One of these devices described in French patent of the Applicant No. 2 231 454, comprises an inductor arranged inside a roll for guiding the slab below the ingot mold, and creating around it a sliding field in a direction parallel to the axis of the roll and perpendicular to the axis of the casting, so as to create a lateral movement of the part still liquid located behind the cooled crust.

There is also known a device for mixing slabs in a continuous casting ingot mold which was the subject of the French patent application by the Applicant published under No. 2,393,632 and which comprises an inductor located in the ingot mold and creating a sliding field. either in the lateral direction to create a horizontal movement of the liquid metal during casting, or in the vertical direction to create an upward or downward movement of the liquid metal.

The methods described above all have the disadvantage, because supplied with alternating current and because the magnetic field created must pass through a considerable air space, of requiring considerable magnetizing power for a reduced active power demand.

This results in considerable losses in copper, low efficiency, and important equipment for the power supply.

The subject of the invention is a method and a device intended to improve the quality of a continuously cast metal which have, for the same effects as described above, a clearly higher yield and an increased stirring movement.

The method is characterized in that an inductor rotating produces a fixed magnetic field with respect to the inductor about an axis parallel at least to one of the surfaces of the cast product.

Depending on the case, the relative displacement will be a rotational displacement around an axis perpendicular to the pouring axis or an axis parallel thereto.

The devices corresponding to this process will therefore include means for producing a constant magnetic field consisting of permanent magnets or electromagnets, the magnetizing power therefore being provided in this second case by a direct current as in a rotor of a synchronous machine. .

Furthermore, the devices for rotating these devices are provided so as to create the relative movement of the magnets and thus to cause eddy currents in the liquid metal and to give rise to forces for the circulation of the liquid metal.

• La figure 1 représente en coupe diamétrale un dispositif de brassage pour coulée continue de billettes ou blooms.
• Les figures 2, 3 et 4 représentent un dispositif de brassage pour coulée continue de brames.
• La figure 2 représente une brame en cours de coulée continue.
• La figure 3 représente schématiquement le principe du brassage.
• La figure 4 donne le détail d'un rouleau brasseur.

The attached figures, relating to two variants of devices according to the method, will help to understand the invention, among which:

• Figure 1 shows in diametrical section a stirring device for continuous casting of billets or blooms.
• Figures 2, 3 and 4 show a stirring device for continuous casting of slabs.
• Figure 2 shows a slab during continuous casting.
• Figure 3 shows schematically the principle of mixing.
• Figure 4 shows the detail of a brew roller.

In Figure 1 is shown in 1 a billet being cooled below the mold, the still liquid metal being shown in 2. A stirring device 3 is placed around the billet. It comprises an inductor 4 comprising a cylindrical yoke 5 in which are fixed two inductor poles 6 made of magnetically hard material so as to create a uniform field crossing the cylindrical space partially occupied by the billet. To facilitate the realization, these poles can be executed by stacking elements relatively thin 7 arranged according to generatrices and glued together.

A particularly well suited material for making such a stack is magnetic rubber, which can be arranged in a uniform layer, either pre-magnetized or magnetizable after installation, for example by placing an alternator rotor inside the available cylindrical space. in which a suitable shock current will be sent.

The cylinder head 5 is arranged in two mounting elements 8 and 9 and the assembly of the inductor 4 is placed in a casing 10 of steel which has a lower disc part 11 and a cylindrical lateral part 12, so that the inductor 4 can rotate inside the housing 10.

To this end, rollers 13a and 13b are provided rotating around axes linked to the mounting elements 8 and 9 and rolling on tracks 14 and 15 integral with the casing 10.

The frame 8 has a toothed wheel 16 which allows the inductor to be driven by the electric motor 17 and the gear 18.

A cover 19 of ordinary steel makes it possible to serve as a magnetic screen for the leakage flows as well as the wall 11.

The assembly of the inductor 4 and the casing 10 is capped by a water jacket 20, of stainless steel for example, comprising a vertical double-walled tube 20a and a double-walled disc 20b, so as to protect the inductor against radiation from the billet and metal splashes from the ingot mold. This shirt will be crossed by a stream of water.

The operation is as follows: the rotation of the inductor 4, under the action of the motor 17, makes it possible to rotate the magnetic field created and which crosses the billet so that the eddy currents generated therein cause by action on this field an energetic rotational movement of the still liquid part 2.

One could, of course, instead of poles made of hard magnetic materials, make the latter out of magnetically soft steel surrounded by an inductor winding traversed by a direct current: In this case electrical contacts with wipers must be provided between the windings in a rotating system and the fixed part where the electric current is brought.

A device with permanent magnets as described above lends itself remarkably well to its installation in a mold. In this case the rotating assembly will preferably be placed in an O-ring casing partially formed by the ingot mold and if necessary filled with water. Only the watertight drive shaft of the drive gear will pass through.

Compared to solutions with a fixed electromagnetic inductor supplied with alternating current, the proposed system has, on the one hand, the advantage of greater simplicity and, on the other hand, makes it possible to produce fields of higher intensity and not require reactive power other than that requested by the motor which will only supply the power necessary for stirring, mechanical losses and eddy current losses in the solidified part of the billet and in the fixed parts (screens and jacket of 'water).

As a variant, it is planned to give the inductive poles 4 diametrically opposite a helical shape so that the electric currents generated in the billet by the rotation of the inductors are inclined relative to the casting axis and generate forces which have a component parallel to the casting axis, either in the upward direction or in the downward direction, so as to create a helical stirring, which gives an improvement in the quality of the metal greater than that given by simple rotary stirring.

FIG. 2 which schematically represents a slab 21 during continuous casting in the part located below the ingot mold, as well as the pairs of guide rollers 22 of this slab, certain pairs of rollers have been shown such as 221, 222, 223, 224 which represent the particularity of being provided at each of their ends with inductors with cylindrical permanent magnets 23 and 24 on either side of the slab and magnetized transversely in a homogeneous manner so that the lines of force of the magnetic field are perpendicular to a diametral plane.

The magnetic axes of the cylindrical permanent magnets 23 and 24 are oriented relative to each other as shown in Figure 3 and rotate. the same speed, different from that of the guide rollers and their arrangement inside the guide roller will be described later.

Referring to Figure 3 which schematically gives the orientation of the magnetic axes of the magnets 24 located on one side of the slab and designated by 241a, 241b, 242a, 242b, 243a, 243b, 244a, 244b, the straight arrows passing by the center of the rollers indicate at a given instant the direction of the magnetization and the curved arrows located in the circles representing the magnets give the directions of rotation printed to these magnets. We see that all the magnets 241 a, 242a, 243a, 244a rotate in one direction and that the magnets 241 b etc ... facing them rotate in the other direction.

It can also be seen that from a magnet 241 to a magnet 242 the directions of the magnetic axes are offset by a quarter of a turn in the direction of rotation of the corresponding magnets going from left to right.

By rotating the previously oriented magnets in synchronism as shown in Figure 3, a sliding field is created and the liquid metal located in the middle part of the slab is drawn in the direction of the arrow F (Figures 2 and 3). If the same operation is carried out on the other side of the slab with the inductors 23 but by rotating them in the opposite direction, the liquid metal will circulate in the direction of the arrow F ′, so that circulation will be created. in closed circuit following contours such as C.

FIG. 4 gives the detail of a stirring roller such as 22 in the vicinity of one of its ends which contains a cylindrical magnet 24. The hollow guide roller 22 rotates in bearings 25 located at its two ends. It is made in three parts, a central part 22a and two end caps 22b. The central part is located so as to receive at each of its ends the cylindrical magnets 24 located inside a cylindrical sheath 26 of non-magnetic steel. The magnets are rotated by a shaft 27 and rotate in roller bearings 29 and 30 housed in the parts 22a and 22b. A cooling air circulation is provided between the axis and the plug 22b, and countersinks 32 and 33 allow the arrival area in the annular cylindrical space 34 located between the sheath 26 and the guide roller 22 and to come out to go to the other end of it by a central channel 28. Arrows 35 to 38 materialize the circulation of cooling air.

The magnet can be constituted by a stack of ferrite washers in the sheath 26. It can also be made from a ferrite powder mixed with thermosetting resin then injected and hardened.

Claims (10)

1. A process for rabbling a continuous flow of metal by the action of a rotating magnetic field on the metal which is cooling, characterised in that in an inductor (4) is caused to rotate and produces a fixed magnetic field in relation to the inductor about an axis parallel to at least one of the surfaces of the cast product (1,21).

2. A device for rabbling a metal in the course of solidification in a continuous casting installation for carrying out the process as claimed in Claim 1, characterised in that it comprises means (16-18) for creating a rotary movement of the inductor (4) in such a manner as to create a magnetic field rotating about the flow.

3. A device as claimed in Claim 2, characterised in that the means (4) for producing the magnetic field consist of permanent magnets (6).

4. A device as claimed in Claim 2, characterised in that the means (4) for producing the magnetic field consist of electromagnets.

5. A device as claimed in Claim 2, adapted for the rabbling of billets or blooms (1), characterised in that two magnetic poles (6) of opposite polarity are disposed in a diametrically opposite manner inside a cylindrical magnetic yoke (5) rotating in a toric casing (10) which is at least partially non-magnetic and comprises cooling by water (20).

6. A device as claimed in Claim 5, characterised in that the poles (6) are disposed parallel to a generatrix of said magnetic yoke (5).

7. A device as claimed in Claim 5, characterised in that the poles (6) have a helicoidal shape.

8. A device as claimed in Claim 5, characterised in that said toric casing (10) consists partially of the chill mould.

9. A device for carrying out the process as claimed in Claim 1, adapted for the rabbling of slabs (21) and comprising guide rollers (22), characterised in that it comprises, at least at one of the ends and in the axis of said end of certain guide rollers (22), a generator of a magnetic field of constant intensity (23 or 24) set in rotation independent of that of the roller (22) by appropriate means.

10. A device as claimed in Claim 9, characterised in that a certain number of rollers (221-224) have, at one of their ends, inductors (23), the magnetic axes of which are offset in a regular manner to create a field sliding in the direction of the flow and, at the other end of the inductors (24), rotating in opposite directions in such a manner as to create a field sliding in the opposite direction.

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