ES2279430T3 - INSTALLATION OF CONTINUOUS COLADA FOR AN ELECTROMAGNETIC ROTATION POSITION OF THE LIQUID METAL IN TRANSIT IN THE COLADA NOZZLE. - Google Patents

Abstract

Installation of continuous casting of metals, of steel in particular, in which the submerged nozzle (8) by which the melting metal to be cast arrives at the ingot from a distributor located above is surrounded by an annular electromagnetic inductor (1) of rotating magnetic field around the casting axis intended to drive the molten metal with axial rotation, said inductor (1) of the multi-phase time of the passing magnetic field provided with a pair of poles (3) per phase and of which each pole (3) is formed by a winding electric winding (6) around a polar tooth (3) protruding inwards and ending with a polar face (4) arranged in front of the nozzle (8), the polar teeth being joined between yes by an outer peripheral magnetic cylinder head (5a, 5b) for closing the magnetic flux, characterized in that each polar tooth (3) has, at the end of its protruding part, a lateral narrowing (12) that increases the d istancia that separates the polar faces (4) from each other.

Description

Continuous casting installation for laying in electromagnetic rotation of the liquid metal in transit in the wash nozzle

The present invention relates to laundry continuous of metals, of steel in particular, which uses a submerged casting nozzle that dips into an ingot arranged below. More precisely, the invention relates to the axial rotation of a liquid metal in transit within of said nozzle between the casting dispenser and the ingot.

It is known that the axial rotation of the metal already inside the casting nozzle is a recognized medium of control of the flows in the ingot mold modifying the distribution of gas bubbles and inclusions present in the liquid metal before your arrival at the bullion. It gets like this to:

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     reduce, even eliminate, deposits of inclusions throughout of the inside wall of the nozzle as well as, in case of nozzle with side outlet nozzles for rim casting, level of its nozzles and its bottom bucket;

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     greatly reduce the penetration depth of the bubbles of gas and inclusions in the liquid well of the product in progress of laundry, therefore also the risk of its entrapment on the face intrados of curved machine cast products,

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     reduce the speed of circulation of the liquid metal under the meniscus as well as its level fluctuations;

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     limit flow instabilities, of type jet balances, in the ingot box generated a "gyroscopic" effect on the nozzle flows.

The rotation of the flows in the casting nozzle appears as well as an effective means to fight against the appearance of surface appearance defects, of type blisters and exfoliations, on cold rolled sheets of steel alloys for automobile and steel applications for packing This technique therefore allows the reduction of scalping operations in continuous castings (reduction and even suppression of surface defects on exfoliation type plates), the suppression of declassifications and litigation for blister defects, as well as the increase of productivity of the machines by the sequence lengthening and increasing speeds of wash.

The rotation of the liquid metal in the casting nozzle has already been proposed using different types of actuators. You can schematically distinguish two types of actuators: the "passive" actuators and the "assets".

The "passive" actuators are among others Design modifications to the internal wall of the nozzle (for example: spirals), organs such as propeller, nozzle internal helical, etc ... that are implanted in the body itself of the nozzle, or the modifications of the upper part of the nozzle at the junction with the distributor (for example: cone of acceleration) or also the modifications of the organ itself of metal flow regulation at the nozzle. Main disadvantages of this type of actuators are to generate a rotation speed directly dependent on metal flow that passes through the nozzle and set up a few places privileged deposits of inclusions in the nozzle, of what a potential increase in the risk of plugging results.

The "active" actuators are essentially electromagnetic in nature: an inductor static annular electromagnetic of the polyphase type around the nozzle at a small distance in a part of its length and generates a magnetic field that rotates around the axis of the laundry intended to drag in axial rotation with it the liquid metal present in the mouthpiece Will be found if necessary some examples described in documents JP 06 023498 or JP 07 108355 or also in JP 07 148561.

However, electromagnetic devices so far proposed are, for the most part, based on the technology of linear tangential rotating field stators operating at low, even very low frequency (<10 Hz). These devices present in particular the drawbacks from:

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     generate rotation speeds often too weak, having take into account the current frequencies used to obtain the desired effects (for example, at 4 Hz three-phase usable for a 80mm internal diameter of nozzle, rotation speed theoretical maximum is 80 turns / min.),

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     generate a very concentrated force field in the liquid target of the inner wall of the nozzle, which results in create a high depression zone in the central part of the nozzle where the metal is then accelerated in the vertical direction falling;

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     have to operate with high electrical currents intensity (> 300-500 A), which leads to about important size devices in order to ensure your cooled, therefore not easy to use in a machine continuous casting and also need the use of a generator Very expensive electrical.

The others are through magnetic field, by both with outstanding poles wound with a pair of poles per phase facing each other on either side of the axis of the nozzle. The invention falls into this category. The same allow you to get rid of some of the above mentioned inconveniences previously, in particular the phenomenon of central depression. Without However, the requirement of the point allied to an electric power installed necessarily high, as well as the decrease sought of the air gap by approximation between the polar tooth protruding inwards exceeding the winding and the nozzle to maximize electromagnetic coupling, lead inevitably indeed a deterioration of energy efficiency at the same time as to a certain degree of possible disorganization of the rotational movements of the metal as a result, in Particular risk of parasitic bridges of magnetic flux between too close poles that belong to different phases of The power supply.

The object of the present invention is to propose a solution to an electromagnetic rotation of the metal liquid inside a pouring nozzle that does not have Disadvantages of known solutions.

To this end, the invention aims at a continuous casting of metals, of steel in particular, in which the submerged nozzle by which the metal in Casting fusion arrives at the ingot mold from a casting distributor above it is surrounded by an electromagnetic inductor static magnetic mobile field ring that rotates around the axis casting designed to drag the metal in axial rotation in fusion, said polyphase field type inductor being magnetic intern provided with a pair of poles per phase and therefore each pole is formed by a winding electric winding around a protruding inward polar tooth that ends by a polar face arranged front and in the vicinity of the mouthpiece, the teeth being joined together by a cylinder head outer peripheral magnetic magnetic flux closure, installation characterized because each polar tooth has a lateral narrowing (a bevel for example) at the end of its protruding part, which increases the distance between the faces polar to each other.

According to an advantageous variant, the ring inductor It consists of two pivoting articulated half-shells that It can be closed around the nozzle.

As will undoubtedly be understood, the invention uses a magnetic field called "intern", that is to say passes through the axis of the nozzle without noticeable weakening of its intensity between the edge and the center of it.

Thanks to the technological base considered, to know that of a pair of poles per phase of power supply that feeds a multi-phase ring inductor with protruding poles windings spread around the nozzle, the magnetic field Swivel produced is of the type "interns" sought. Said of otherwise, at every moment, the casting axis is at the center of the inductor air gap and the field produced thrives in this air gap through the pouring shaft to, from a pole given magnetic, reach the sign's magnetic pole opposite located opposite and not by your side as would be the case with a pole inductor distributed with several pairs of poles by phase.

Remember that this type of technology is not New in itself. It is even quite widely used for rotating a cast liquid metal, not within a nozzle, but in the same ingot, therefore in the case of Induced spinning (liquid metal column) diameter much larger than the metal jet in the nozzle and with a requirement of angular rotation speed correlatively much smaller (see for example USP 4 462 458). However, contrary to the ideas received, it turns out that the transfer of this technology from the ingot to the pouring nozzle can, without necessarily allowing a decrease in installed power marked, accompanied by a reduction of inductor size compatible with mounting the last around and closer to a casting nozzle provided character is preserved "intern", in all cases essentially "intern", of magnetic field produced, and this without harming then its necessary cooled.

Now, it is precisely here that find the basic idea of the invention: arrive, without penalizing inductor characteristics, to preserve this character "intern" of the field despite the compactness of the inductor and the minimization of the air gap allowing a slight loss of mass magnetic located at selected points of the poles outstanding, namely the edges of active faces, to counteract the natural tendency of the magnetic field of spread in the air gap according to the less reluctant roads forming loops between adjacent poles next to each other others.

Some tests on steel have confirmed the ability of said inductor to rotate the metal flowing in a submerged nozzle under the conditions of laundry much more severe than those that will be found in the industrial machines of blooms or llantones. These tests have they have been carried out with a straight type nozzle (nozzle single axial opening at the bottom) in which the metal flows to a  average speed of the order of 3.5 to 4.2 m / s, knowing that in a llantones casting nozzle, the average speeds that they supply are rather between 1.5 and 2.0 m / s.

The invention will be better anyway understood and other aspects and advantages will appear in view of the description that follows given as an example of embodiment and with reference to the attached plans, in which:

- Figure 1 is a scheme representing, Seen in a straight section, the inductor in two half-shells arranged edge to edge provided with its internal thermal screen that borders the air gap;

- Figure 2 is a scheme similar to previous but intended to show the propagation of the lines well of force of the passing magnetic field in the air gap such as the afigadas at any given moment of the operation of the inductor;

- Figure 3 is a functional scheme of principle that shows the articulation of the two half-shells constitutive of the inductor;

- Figure 4 shows the map of the speeds of the liquid metal that rotates inside the nozzle of casting under the effect of the magnetic field in a section plane straight nozzle;

- Figure 5 shows the evolution of the intensity B of the magnetic field in the air gap along a diameter D of the nozzle taken in a plane located at medium height of the inductor;

- Figure 6 shows, in correspondence with the representation of figure 5, the correlative evolution of field of magnetic forces F_ along a diameter D of the nozzle according to a radial profile R and according to an orthoradial profile OR.

In the figures, the same elements are designated by identical references.

As seen referring to figures 1 to 3 together, inductor 1 is a linear motor stator closed on itself, constituted to this end by two parts equal independent semi-tubular 2a and 2b, (the half-shells). Each half-shell comprises three protruding winding poles 3 whose polar face 4 is turned inwards, these poles being magnetic iron plates stacked together, classically connected to each other by an external peripheral semi-tubular cylinder head 5a, 5b. The set is sized so that the two cylinder heads rigged pass through the ends in the joint plane J when the inductor is in closed working position represented in the Figures 1 and 2.

A shell 7a, 7b, also semi-tubular corresponding internally covers the polar faces of each half-face and form, once the inductor in closed position, a thermal protection screen 7 that surrounds the small distance wash nozzle This thermal protection is desirable for electric windings 3 of the inductor with respect to the radiation emitted by the casting nozzle 8 represented in the Figure 3 and which channels the flow of molten metal towards the ingot Some details about the possible constitution of this screen will be given below.

The electric winding 6 of each pole winding 3 is connected to a phase of a power supply three-phase (not shown) intended to provide the current inductor primary. With the inductor in the closed position, a outstanding pole any of one of the half-shells 2a is diametrically facing an outstanding pole of the other half-face 2b. These two poles form a "pair of poles" in the sense that both are connected to the same phase of the power supply, but in an opposition (for example through in a different winding direction) so that, in each Instantly, their active faces are of opposite signs. This condition is necessary for the magnetic field produced to be of intern type

Poles 3 and cylinder heads 5a, 5b return Magnetic flux are laminated in Fe-Si sheets of oriented grains of initial thickness 0.3 mm so as to minimize hysteresis losses. Its operating height (around the active face 4) is between 50 (minimum value) and 500 mm, function of the space available between the dealer and the upper part of the ingot mold between which the inductor will be placed. its internal diameter (air gap diameter) is of the order of external diameter of the casting nozzle increased by a dozen of mm just to preserve a separation but so that ensures the best possible inductive coupling.

Primary windings 6 are constituted by a large number (several hundreds) of turns of copper wires of very small diameter that support densities of high current (> 10 A / mm2). They are provided inside of copper heat extractors cooled by water circulation (not represented).

These windings are fed with currents three-phase medium frequency ranging from 50Hz to 600Hz. In the Proposed technology, it will be noted that operate frequently high, higher 50 or 60 Hz, allows, at constant intensity of currents, increase torque than forces Electromagnetic exerts on the metal that flows through the nozzle. However, this option requires the use of converter frequency contrary to the operation of the frequency of the network (50 or 60 Hz).

As shown in the diagram in Figure 5, this static motor that constitutes the inductor 1 can generate in its air gap occupied by the nozzle an electromagnetic field high intensity intern (called intern) (between 1000 and 1500 gauss) for low values of inductive currents (some tens of amps).

This field, as seen in the diagram, is almost uniform in the central part of the air gap. This feature essential of the invention allows generating in the liquid metal a uniformly decreasing force field from the wall to the center, as depicted in the diagram in figure 6. This allows, as the speed map of Figure 4, rotate the liquid metal with a speed which perishes important even in the axial part of the nozzle. This specificity is necessary to avoid depression too large in the central part of the nozzle where the metal would have tendency then to "run away" and suffer a strong acceleration descending vertical, thus canceling a part of the beneficial effect of The rotation.

As it clearly appears in Figure 2, it is thanks to the narrowed shape of the radial magnetic teeth 3 at its free end 4 (the polar faces) that, at any time, the lines of force of the magnetic field in the air gap unite essentially the diametrically opposite poles and that only one residual part of the field loops between nearby poles. This result, indispensable for the use of the invention, is obtains, despite the necessary compactness of the inductor, thanks to this narrowed shape of the end of the poles, which makes despite its mutual approach as it moves towards the center, the distance that separates its free ends two by two it remains sufficient to avoid an important bridging of the lines  from field to each other. This is what, in the case of the compact inductor of Small size, it is guarantee of the relative high intensity of the magnetic field on the axis (see figure 5), in other words the imperatively "intern" character of this field without which The invention does not produce the desired effects. As seen in the figure 1 and more visibly in figure 2, this narrowing of shape of radial teeth 3 is obtained thanks to a precut in bevel 12 of the ends of the plates for form them The angle of the bevel must be adjusted according to the outside diameter of the nozzle to surround. It is considered however that the polar face 4 must not be, on the surface, less than half of the straight section of tooth 3 and that the bevel start of narrowing 12 on the tooth body can be initiated only at two thirds of the length. It is not necessary to start before and it is even desirable to do it as late as possible in order to maximize the magnetic mass of the inductor.

Feeding the inductor through a circuit resonant, the intensity of the primary currents can be greatly increased. The proposed technique allows, in effect, in a wide range of the intensity of the primary currents, greatly increase the intensity of the electromagnetic field in the air gap, increasing the intensity of these currents to about values well beyond the threshold intensity corresponding to the magnetic saturation of the cylinder head 5. This allows channeling the magnetic field lines and increase, in the engine air gap, the intensity of this magnetic field until the latter reaches its saturation value in the stock. Beyond this value of threshold, is the magnetic field generated, by the inductor directly in the air that contributes to the increase in intensity from the field in the engine air gap,

In operation, the inductor is very close (approximately 5 mm away) from the casting nozzle 8 whose outside temperature is of the order of 1,100 to 1,200 ° C. its thermal protection, with respect to the radiation emitted by the nozzle, is then secured by the segmented screen of copper 7, thin, cooled by water circulation and transparent to the electromagnetic field thanks to this segmentation.

The constitution of inductor 1 in two parts semi-tubular independent 5a and 5b easily allows your placement around the nozzle and its removal in any moment without any modification of the standard procedure of wash. Referring again to Figure 3, it is seen that, for the placement around the casting nozzle 8, the inductor is advantageously supported by a support constituted by two arms 9 articulated around a pivot shaft 10. The arms are animated by some cats 11 that ensure their closing-opening and allow to exert a force of sufficient contact (greater than 200 kgf.) between cylinder heads 5a and 5b of the two semi-tubular parts 2a and 2b once you are on end to end as shown in figure 1. On the other hand, a close contact between the cylinder heads 5a and 5b is necessary for a good loop formation of magnetic field lines between two constituent parts of the inductor and therefore of good electromagnetic performance Moreover, an important force Closing of the two half-pipes is necessary to prevent vibrations that would inevitably be generated by the forces oscillating electromagnetic.

Of course, the invention could not be limited. to the described embodiment example but it extends to multiple variants and equivalents to the extent that it is respected its definition given by the appended claims.

Claims (6)

1. Installation of continuous casting of metals, of steel in particular, in which the submerged nozzle (8) by which the melting metal to be cast arrives at the ingot from a distributor located above is surrounded by an annular electromagnetic inductor (1 ) of rotating magnetic field around the casting axis intended to drive the molten metal in axial rotation with it, said inductor (1) of the multi-phase time of passing magnetic field provided with a pair of poles (3) per phase and of which each pole (3) is formed by a winding electric winding (6) around a polar tooth (3) protruding inwards and ending with a polar face (4) arranged in front of the nozzle (8), the polar teeth being joined together by an outer peripheral magnetic cylinder head (5a, 5b) for closing the magnetic flux, characterized in that each polar tooth (3) has, at the end of its protruding part, a lateral narrowing (12) that increases at a distance that separates the polar faces (4) from each other. 2. Continuous casting installation according to claim 1, characterized in that the submerged nozzle (8) is a nozzle with lateral outlet nozzles. 3. Continuous casting installation according to claim 1, characterized in that the inductor (1) comprises on its inner periphery a thermal protection screen (7) surrounding the nozzle at a distance. 4. Continuous casting installation according to claim 1, characterized in that the annular inductor (1) is formed by two pivoting articulated half-shells (2a, 2b). 5. Continuous casting installation according to claim 1, characterized in that it further comprises a resonant electrical circuit in which the inductor is mounted in series with a capacity
adjustable. 6. Continuous casting installation according to claim 4, characterized in that the inductor (1) is mounted on the end of supporting support arms (9) in position, this support arm being retractable and provided with mandated means (11) which they activate each half-pin (2a, 2b) in pivoting.