JP2006527661A - Continuous casting machine that electromagnetically rotates molten metal moving in the nozzle - Google Patents

Abstract

The invention relates to a continuous casting apparatus for metals, in particular steel. The submerged nozzle (8) is surrounded by an annular electromagnetic inductor (1), the magnetic field rotates around the casting axis, and the molten metal rotates around that axis. A feature of the present invention is that the inductor is a multiphase type through which a magnetic field passes, and includes a pair of projecting poles (3) for each phase. Furthermore, lateral narrow details (12) that increase the distance between the magnetic pole tips (4) are provided at the ends of each protruding magnetic pole facing the nozzle. In this way, the inductor is extremely compact and extremely powerful and can supply a strong transverse magnetic field to the center of the nozzle using a high frequency primary current to produce effective rotation of the molten metal flowing in the nozzle. . The invention is particularly suitable for continuous casting of slabs using submerged nozzles with outlets on the sides.

Description

  The present invention relates to continuous casting of metal, in particular steel, using a submerged casting nozzle immersed in a mold located below. More particularly, the invention relates to inducing axial rotation in liquid metal flowing through the nozzle between a puddle for casting and a mold.

Inducing axial rotation in the metal in the casting nozzle is a recommended means of controlling the flow to the mold by modifying the distribution of inclusions and bubbles present in the liquid metal before it enters the mold. It is known that by this,
Adherence of contaminants along the inner wall of the nozzle, and in the case of nozzles with lateral outlets for slab casting, adhesion of contaminants at these outlets and the bottom of the nozzle can be reduced and possibly eliminated. Can
It is possible to greatly reduce the mixture depth of the liquid reservoir and the penetration depth of the bubbles during casting, and thus the risk of these being captured by the internal curved surface of the product cast on the curved casting machine,
Reduce the flow rate of the liquid metal just below the meniscus and reduce this meniscus level fluctuation,
Based on the “gyro” effect of the flow in the nozzle, the jet swing flow instability in the mold can be limited.

  Therefore, inducing rotation in the flow in the casting nozzle can cause the appearance of visible surface flow, such as blistering and peeling, on cold-worked strips of various grades of steel and packaging steel for automotive applications. It can be said that it is an effective means to stop. Therefore, this technique means that repair operations with few cracks on continuous cast slabs (with little or no stripping surface flow on the strip), blistering flow, no quality degradation or clogging, and It is long and the casting speed is faster, so the productivity of the casting machine is high.

  Inducing rotation in the liquid metal in the casting nozzle has been proposed using various actuators. There are basically two types of actuators: “passive” actuators and “active” actuators.

  Passive actuators are, among other things, designed at the top of the nozzle at the junction with the nozzle inner wall (eg, a helix), a propeller tailored to the nozzle body, the design of components such as the helix inner nozzle, or the puddle. Use corrections, corrections in the actual components that control the metal flow rate in the nozzle. An important drawback of this type of actuator is that the generated rotational speed is directly dependent on the flow rate of the metal through the nozzle, and that a position where contaminants are likely to adhere is formed in the nozzle, and therefore the risk of clogging the nozzle. There is a possibility of increase.

  Active actuators are electromagnetic in nature, and a multi-phase annular static electromagnetic inductor surrounds the nozzle over part of its length, generating a magnetic field that rotates around the casting axis, The liquid metal existing in the nozzle is rotated. See JP06-023498A, JP07-108355A and JP07-148561A.

However, most electromagnetic devices submitted to date are based on the technology of linear stators that generate a tangential rotating magnetic field that operates at low or very low frequencies (<10 Hz). In particular, these devices have the following defects.
Due to the current frequency used, the rotational speed generated is often too low to achieve the desired result (for example, for a 4 Hz three-phase current that can be used for a nozzle inner diameter of 80 mm, the theoretical rotational speed is up to 80 rpm. ).
The creation of a highly concentrated force field in the liquid metal close to the inner wall of the nozzle results in a large pressure drop at the center of the nozzle where the metal is thus accelerated vertically downwards.
The operation requires a high current (> 300 to 500 A), and the apparatus becomes large to the extent that it is necessary to control it. Therefore, it is not easy to adapt to a continuous casting machine, and an extremely expensive generator is used. Need arises.

  Other devices are based on a transverse magnetic field and thus on a wound-type projecting magnetic pole, which is a pair of magnetic poles facing each other on each side of the nozzle shaft. The present invention falls within this category. They eliminate some of the above disadvantages, especially the central pressure drop phenomenon. However, to maximize the space associated with high stored power and electromagnetic coupling, it is desirable to reduce the air gap by reducing the distance between the inner protruding pole teeth protruding beyond the winding and nozzle. Thus, especially due to the risk of spurious bridging of magnetic flux between the magnetic poles corresponding to different power supply phases that are too close, energy efficiency is reduced and at the same time, some disturbance in the rotational movement of the metal is inevitable.

  The object of the present invention is to propose a solution that electromagnetically induces the rotation of a liquid metal in the casting nozzle, without the disadvantages of the known solutions.

  For this purpose, the subject of the present invention is that a submerged nozzle that allows the molten metal to be cast to reach the mold from the upper puddle is surrounded by an annular electromagnetic inductor having a magnetic field that rotates around the casting axis. , Rotating the molten metal in its axial direction, the inductor is a multiphase transverse magnetic field type, has a pair of magnetic poles for each phase, and each magnetic pole ends inwardly with a magnetic pole face located facing the nozzle A continuous casting device of metal, in particular steel, formed by electrical windings wound around pole teeth and connected to each other by a peripheral magnetic yoke for closing the magnetic flux, each pole tooth having its pole teeth The continuous casting apparatus is characterized by having a side taper (for example, a bevel) that increases a distance separating magnetic pole faces from each other at the end of the protrusion.

  According to an advantageous embodiment, the annular inductor is formed as two articulated half-shells that are pivotable so that both close around the nozzle.

  As will be appreciated, the present invention uses a so-called “transverse” magnetic field, ie a magnetic field that passes through the axis of the nozzle and does not have a clear reduction in strength between the edge and center of the nozzle.

  Generated because of the technical means employed, i.e. a pair of magnetic poles are provided for each phase of the power supply supplying power to the annular multi-phase inductor having the protruding magnetic pole with windings distributed around the nozzle The rotating magnetic field is the desired “lateral” type. In other words, at each moment, the casting axis is in the center of the inductor's air gap, and the magnetic field generated is from a given magnetic pole, as in the case where the inductor has a distributed magnetic pole or several pairs of magnetic poles per phase. The air gap is filled so as to pass through the casting shaft so as to return to a pair of magnetic poles which are opposed to each other but are not adjacent to each other.

  It will be recalled that this kind of technology is not new in itself. It is a rotor that has an apparent diameter much larger than that of the metal jet in the nozzle, not in the nozzle, and therefore with a much lower angular rotational speed. In the case of (ie, liquid metal columns), it is even used quite extensively to induce rotation in the cast liquid metal (see, eg, US Pat. No. 4,462,458). Now, contrary to the accepted view, when this technique is transferred from the mold to the casting nozzle, the “transverse”, at least essentially “transverse” characteristics of the generated magnetic field are maintained, thus not compromising its necessary cooling. In doing so, it has been found that there is a reduction in bringing the size of the inductor as close as possible to the casting nozzle without necessarily a substantial reduction in the power introduced.

  The idea that forms the basic principle of the present invention is exactly this point, that is, by making a loop between the magnetic poles closest to each other, the magnetic field propagates in the air gap along the path having the minimum magnetoresistance. Regardless of the compactness of the inductor and the minimization of the air gap by counteracting the natural tendency of the magnetic field, by making some loss of magnetic mass at selected parts of the projecting pole, i.e. at both edges of the working surface This is to maintain the “transverse” characteristics of the magnetic field without impairing the performance of the inductor.

  Tests performed on steel have confirmed that the inductor can induce rotation in the metal flowing through the submerged nozzle, even under conditions that are much more severe than those encountered in industrial machines that cast blooms or slabs. These tests were performed with a straight type nozzle (single axial outlet opening at the bottom) in which the metal flows at an average speed of about 3.5 to 4.2 m / s. Note that for slab casting nozzles, the average output speed is 1.5-2.0 m / s or higher.

  The invention will be more clearly understood and further embodiments and advantages thereof will emerge from the following description, given by way of example with reference to the accompanying drawings.

  In the accompanying drawings, the same parts are represented by the same symbols.

  As can be seen from the overall FIGS. 1-3, the inductor 1 is a closed linear motor stator, and for this purpose consists of two independent identical half-cylindrical parts 2a and 2b (half-shell). Each half shell has three coiled projecting magnetic poles 3 whose pole faces 4 bend inward, and these magnetic poles consist of a laminated iron core of a soft iron laminate, usually semi-cylindrical outer yokes 5a, 5b. Are connected to each other. This system is such that when the inductor is in the abutting operation position shown in FIGS.

  The caps 7a and 7b are also corresponding semi-cylindrical shapes, which cover the inside of the magnetic pole surface of each half-shell and form a heat shield 7 that closely surrounds the casting nozzle when the inductor is in contact. This heat shield is desirable for the inductor electrical winding 3 against the radiation emitted by the casting nozzle 8 shown in FIG. Details of possible configurations of this shield will be described later.

  The electric winding 6 of each magnetic pole 3 is connected to one phase of a three-phase power source (not shown) that allows a primary current to flow through the inductor. When the inductor is in the closed position, any protruding pole of one half shell 2a completely faces the protruding pole of the other half shell 2b. These two poles form a “pair of magnetic poles” because they are connected to the same phase of the power supply and are opposite in phase (eg, different winding directions) so that their working surfaces have opposite signs at each moment This is because of the relationship. This condition is necessary because the generated magnetic field is in the landscape format.

  The magnetic pole 3 and the magnetic flux feedback yokes 5a and 5b are a laminate made of a directional particle type Fe—Si sheet having an initial thickness of 0.3 mm so as to minimize hysteresis loss. Their operating height (the height of the operating surface 4) is 50 mm (minimum value) to 500 mm, depending on the space used between the puddle for interposing the inductor and the upper part of the mold. Their inner diameter (air gap diameter) is barely sufficient to keep the separation, and is about 10 mm larger than the outer diameter of the cast nozzle made to ensure the best possible electromagnetic coupling.

The primary winding 6 is formed from a copper wire having a very small diameter of many (several hundreds) turns capable of supporting a high current density (> 10 A / mm ² ). Inside, a water-cooled copper heat sink (not shown) is provided.

  These windings are supplied with a three-phase current having an intermediate frequency of 50 Hz to 600 Hz. With the proposed technique, when operating at a high frequency exceeding 50-60 Hz, the motor torque that the electromagnetic force will exert on the metal flowing through the nozzle can be increased with a constant current intensity. However, according to this option, a frequency converter must be used, unlike operation at the main frequency (50 or 60 Hz).

  As shown in FIG. 5, the static motor formed by the inductor 1 generates a transverse magnetic field having a high strength (1000 to 1500 gauss) with respect to a low inductor value (several tens of amperes) in an air gap occupied by the nozzle. Can do.

  As can be seen from the figure, this magnetic field is substantially uniform at the center of the air gap. According to this very important feature of the present invention, a force field can be generated in the liquid metal that uniformly decreases from the wall to the center as shown in FIG. As clearly shown in the velocity map of FIG. 4, rotation can be induced in the liquid metal at a high velocity even in the shaft portion of the nozzle. This special feature is necessary to avoid excessive pressure drops in the center of the nozzle, where the metal tends to escape and be subject to high downward acceleration, thus destroying some of the beneficial effects of rotation. .

  As is apparent from FIG. 2, at any moment, the field line of the magnetic field in the air gap is substantially connected to two diametrically opposite magnetic poles, and the rest of the magnetic field connects between adjacent magnetic poles. It depends on the taper shape of the magnetic teeth in the radial direction on the magnetic pole surface. This result, which is essential for the implementation of the present invention, is obtained thanks to this taper shape at the end of the pole, although the inductor needs to be compact. This means that after being moved towards the center, they are close to each other, but the distance separating the paired free ends remains sufficient to prevent substantial bridging of the magnetic field lines between them. In the case of small and compact inductors, it is this that ensures the high relative strength of the magnetic field along the axis (see FIG. 5), in other words the “transverse” characteristic of this magnetic field without which the invention does not produce the desired effect. Is a point. As can be seen from FIG. 1 and clearly seen in FIG. 2, this taper shape of the radial teeth 3 is obtained by a bevel precut 12 at the end of the stack stacked for formation. The bevel angle should be adjusted according to the outer diameter of the enclosed nozzle. However, the pole face 4 should not have an area less than half of the cross section of the tooth 3 and the tapered bevel 12 on the tooth body can start at 2/3 of the length. It is not necessary to start before this, and it is desirable to start as late as possible to maximize the magnetic mass of the inductor.

  By supplying the inductor via a resonant circuit, the strength of the primary current can be greatly increased. According to the proposed technique, within a wide range of temporary currents, these currents are increased to a value sufficiently exceeding the threshold current corresponding to the magnetic saturation of the yoke 5, thereby increasing the strength of the magnetic field in the air gap. Can be greatly increased. Thereby, the lines of magnetic force can be concentrated, and the strength of the magnetic field in the air gap of the motor can be increased to the saturation value of the yoke. Beyond this threshold, it is the magnetic field generated by the inductor directly in the air that contributes to increasing the strength of the magnetic field in the motor air gap.

  In operation, when the inductor is in close proximity to the casting nozzle 8 (about 5 mm from the nozzle), the outside temperature of the nozzle is 1100-1200 ° C. Thus, the inductor is thermally protected from the radiation emitted from the nozzle by a thin divided copper shield 7 that is cooled by the circulation of water and is transparent to the electromagnetic field even with this division.

  According to the configuration of the inductor 1 with two independent semi-cylindrical parts 5a and 5b, the inductor can easily be mounted around the nozzle and removed at any time without changing the standard casting process. Referring again to FIG. 3, in order to mount the inductor around the casting nozzle, it is advantageous if the inductor is held by a support consisting of two arms 9 articulated around the pivot spindle 10. I understand. These arms open and close the arm, and when the two semi-cylindrical portions 2a and 2b are connected as shown in FIG. 1, the cylinder 11 exerts a sufficient contact force between the yokes 5a and 5b of the semi-cylindrical portions 2a and 2b. It is driven by. First, close contact between the yokes 5a and 5b is necessary for the looping of the magnetic field lines between the two component parts of the inductor and is therefore necessary for good electromagnetic efficiency. Secondly, a high clamping force between the two half-cylinders is necessary to prevent vibrations inevitably generated by the vibrating electromagnetic force.

  The present invention is not limited to the exemplary embodiments described, but it goes without saying that the invention extends to many alternative and equivalent embodiments when its definition according to the appended claims is respected.

FIG. 4 is a cross-sectional view of an inductor formed from two butt half shells and provided with an internal heat shield in contact with the air gap. FIG. 6 is a view similar to the previous figure showing the propagation of transverse magnetic field lines in the air gap taken at any moment during operation of the inductor. It is a functional diagram which shows the principle of the connection method of the joint of 2 component half shells of an inductor. Fig. 3 shows a velocity map in the cross section of a liquid metal rotating in a casting nozzle under magnetic field effects. The change in the strength D of the magnetic field in the air gap along the diameter D of the nozzle on the surface located at the intermediate height of the inductor is shown. FIG. 6 shows changes in the field of the magnetic force Fs along the nozzle diameter D in the radial profile R and the right-angle radial profile OR corresponding to the display of FIG.

Claims (6)

  A submerged nozzle (8) for allowing the molten metal to be cast to reach the mold from the upper puddle is surrounded by an annular electromagnetic inductor (1) having a magnetic field rotating around the casting axis. Rotating in the axial direction, the inductor (1) is of a multiphase transverse magnetic field type, and has a pair of magnetic poles (3) for each phase, and each magnetic pole (3) is located facing the nozzle (8). Formed by an electrical winding (6) wound around inwardly projecting pole teeth (3) ending at the pole face (4), the pole teeth are connected to each other by outer magnetic yokes (5a, 5b) for closing the magnetic flux A side taper (12) which increases the distance that each pole tooth (3) separates the pole faces (4) from each other at the end of its projection, comprising a continuous casting device of metal, in particular steel, Continuation characterized by comprising Forming apparatus.   The continuous casting apparatus according to claim 1, characterized in that the submerged nozzle (8) is a nozzle having an outlet on the side.   2. The continuous casting apparatus according to claim 1, further comprising a heat shield (7) surrounding the nozzle at a distance on the inner circumference of the inductor (1).   2. Continuous casting apparatus according to claim 1, characterized in that the annular inductor (1) is formed from two pivot joint half shells (2a, 2b).   The continuous casting apparatus of claim 1, further comprising a resonant electrical circuit in which the inductor is connected in series with the adjustable capacitor. An inductor (1) is provided at the end of the support arm (9) and maintains its position, the support arms can be retracted, and each half shell (2a, 2b) is actuated to pivot. 5. Continuous casting apparatus according to claim 4, characterized in that means (11) are provided.

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