JP2003500218A - Method and apparatus for measuring and adjusting the flow rate of liquid metal in a continuous casting ingot mold - Google Patents

Abstract

SUMMARY OF THE INVENTION The present invention relates to a method and apparatus for measuring and adjusting the flow rate of a metal liquid in an ingot mold equipped with an electromagnetic brake having a sliding field (9). According to the present invention, it is possible to measure the voltage or current of at least one power supply of the electromagnetic brake and to derive the flow velocity from the information.

Description

Detailed Description of the Invention

The present invention relates to metallurgical equipment, and more particularly to equipment for continuous casting of liquid metal in ingot molds.

FIG. 1 very schematically and partly shows, in perspective view, the inlet part of a continuous metallurgical casting ingot mold 1. The ingot mold essentially comprises a mold 2, both ends of which are open for continuous casting. The nozzle 3 immersed in the liquid metal and submerged in the mold 2 throws the liquid metal into the ingot mold. The nozzle 3 has a sideways port 4 which aims to give a horizontal component to the velocity of the liquid metal at the nozzle 3 outlet.

FIG. 2 is a simplified cross-sectional view of a conventional ingot mold 1, with arrows illustrating the movement of liquid metal at the inlet portion of the mold 2. As shown in FIG. 2, the horizontal component in the velocity of the liquid metal provided by the port 4 of the nozzle 3 limits the vertical penetration depth of the metal feed stream into the mold 2. The liquid metal 1 comes, for example, from a crucible (eg blast furnace type) 5. In the example shown in FIG. 2, the crucible 5 comprises in its lower part an opening 6 associated with a controllable closing means 7 for controlling the liquid metal injected into the nozzle 3. In conventional equipment, the velocity of the liquid metal at the nozzle 3 outlet can reach several meters per second. Therefore, it is important to be able to control the penetration of the liquid metal in the cast metal. In fact, the too deep penetration of this liquid metal presents several problems. Of these problems, it should be noted that it draws in non-metallic particles coming from the powder or skin (not shown) that covers the ingot 8 cast in the mold 2. These particles are trapped within the resulting metal. Too deep penetration of liquid metal also results in hot gradient reversal, as hot liquid metal affects the deeper areas of the cast metal, and especially in at least partially solidified ingots. It leads to local remelting in the deep part of, which also adversely affects product quality.

Brake systems, and in particular electromagnetic brake systems, are used to limit the velocity of liquid metals.

The first type of electromagnetic brake uses a DC magnetic field in a direction perpendicular to the flow of metal, which magnetic field produces an induced current. The induced current interacts with the applied magnetic field to generate an electromagnetic force, which is the braking force aimed at zeroing the velocity that caused the induced current. Such DC magnetic field systems generally consist of electromagnets that surround all or part of the ingot mold and generate a magnetic field across the liquid metal. Such a system has the disadvantage of being passive, i.e. the magnetic field has a spatial arrangement and position set only once, so that braking efficiency is reduced if it deviates from a predetermined operating point. Therefore, as the feed conditions (speed, nozzle geometry, nozzle port immersion depth, etc.) change, this braking is likely to be inadequate.

The second category, so-called sliding field electromagnetic brakes, uses an alternating magnetic field generated by a polyphase power supply acting on an inductor exhibiting a tailored spatial distribution. Therefore, the magnetic field is given a rotating or transitional movement depending on whether the shape of the inductor is cylindrical or planar. Such a magnetic field can accelerate or slow the flow of liquid metal in continuous metallurgical casting. The system is therefore active because the mechanical effects induced in the liquid metal are independent of the liquid velocity and controllable by the operator.

The present invention more specifically relates to a continuous casting facility equipped with a sliding field electromagnetic braking system.

In practice, in an industrial continuous metallurgical casting facility, the sliding field electromagnetic brake consists of four sliding field inductors associated in pairs on each side of the mold 2 of the ingot mold. . In FIG. 1, two of these inductors are schematically illustrated and designated by the reference numeral 9. In FIG. 2, two inductors are illustrated by dotted lines. On the same side of the ingot mold, two inductors are placed on either side of the nozzle 3, symmetrically about the axis of the nozzle 3, as illustrated in FIG. 1, to balance the metal distribution.

An example of an electromagnetic brake in a metallurgical casting facility is, for example, European patent application 055.
0785, the contents of which are incorporated herein by reference.

The problem posed is that the spatial arrangement of the ports 4 of the nozzle 3 varies with time, in particular due to the erosion of these ports by the rapid flow of liquid steel in the nozzle. This erosion does not necessarily evolve symmetrically, and the stronger flow on one side of the nozzle 3 than on the other side results in hydrodynamic asymmetry in the ingot mold. Such an imbalance not only results in the introduction of non-metallic particles derived from the liquid metal crust, but also results in different solidification periods on one side and the other side of the ingot being formed, resulting in a finished product. Is adversely affecting the quality of.

Therefore, it is desirable to be able to identify the action of the sliding field inductor 9 and restore the balanced injection into the ingot mold.

For this purpose, it would be conceivable to supply the four inductors separately to provide many combinations in organizing the behavior of the liquid metal. Then, in particular, the braking of the liquid metal flow on one side of the nozzle 3 or on the other side could be carried out individually.

However, theoretically individualizing the effects of different inductors on the cast metal is a practical problem, especially because in that case it is necessary to know the actual speed at a given time. To raise. In addition, the current metal injection rates on both sides of the nozzle 3 must be known.

Conventional methods of adjusting the sliding electromagnetic field in an ingot mold of the type illustrated in FIGS. 1 and 2 model the excitation frequency of the inductor, for example, by modeling the flow in a test structure using water. Consists of making a decision. Such a method is described in particular in the above mentioned European patent application 0550785.

Obviously, in such a method, it is not possible to know in real time the velocity of the flow through both ports 4 of the nozzle 3, and more specifically to be able to detect imbalances in this flow. Can not.

The first solution to know this velocity would be to use a stress gauge mounted on a rod immersed in liquid ingot mold steel. Detecting any flow asymmetry by measuring the signal associated with the hydrodynamic force exerted by the liquid steel on the rod, thus adjusting and correcting the power injected into the inductor 9. You can However, the use of rods, such as alumina rods, poses some problems.

The first problem is that such a rod forms a penetrating element in the ingot mold, especially by erosion of the rod by cast liquid metal, which results in contaminants in the resulting product. There is a risk of introducing it.

Another drawback is that the erosive wear of these measuring rods makes this solution practically infeasible from an economic point of view due to the high wear of the alumina rods in the industrial process. .

The present invention aims to overcome the drawbacks of conventional continuous metallurgical casting equipment. More specifically, the invention aims at individual control of inductors in a sliding field electromagnetic brake of such an installation.

The invention also aims to provide a solution which does not lead to contamination of the liquid metal during casting.

The invention also aims to provide a solution which is particularly economical and does not require replacement of potentially wear-out materials.

The invention also aims to provide a solution which is particularly adapted to the individual control of the power injected into the inductor and which generates the sliding field.

To achieve these objects, the invention is equipped with a sliding-field electromagnetic brake, which consists of measuring the voltage or current of at least one electromagnetic brake power supply and deriving the flow velocity from this measurement. A method for measuring the flow rate of liquid molten metal in an ingot mold is provided.

According to an embodiment of the invention, the method is applied to an electromagnetic brake in which at least one inductor of the electromagnetic brake comprises two batches of several conductors in the vertical direction, and for each conductor: The relationship gradV = −i (ω−vk) A−ρj. In the above equation, ω represents an AC excitation pulse in the sliding field, v represents the velocity of the metal, k represents the wave number of the inductive sliding magnetic field, A represents the vector potential,
ρ represents the resistivity of the metal, j represents the excitation current density of the inductor, and V represents the voltage across the inductor.

According to one embodiment of the invention, the velocity measurement is used to servo the excitation of the inductor to a predetermined value.

The present invention also comprises the use of voltage or current measurements of each inductor to control the voltage or current of at least one power supply of a sliding field electromagnetic brake including several inductors. -Providing a method for controlling the continuous casting rate of molten metal in a mold.

The present invention is also a continuous casting facility of the type that uses a sliding field electromagnetic brake to control the flow of liquid metal supplied from the two ports of the nozzle, with each inductor of the electromagnetic brake having an individual inductor. Powering by means of a circuit, and the installation comprising means for adjusting the supply voltage or current of each inductor in order to maintain a balanced liquid metal flow rate between the two ports. provide.

According to an embodiment of the invention, each supply circuit of each inductor comprises its own means for adjusting the electromagnetic excitation force of this inductor.

According to one embodiment of the invention, the installation comprises a central station for controlling the supply circuits of the different inductors to regulate the liquid metal flow rate.

The above objects, features, and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments with reference to the accompanying drawings.

The same components in different drawings are designated with the same reference numerals. For clarity, only the components necessary for understanding the present invention are shown in the drawings and described hereafter. Since the invention does not modify the structure of conventional equipment, reference can be made to the literature, in particular to European patent application 0550785, for the construction of continuous casting equipment with active sliding field electromagnetic brakes.

A feature of the present invention is to utilize the individual power supplies of different inductors in a sliding field electromagnetic brake to derive information about the flow velocity of liquid metal in the ingot mold from the electrical characteristics of the inductor power supplies. Is.

The invention takes advantage of the fact that the current induced by a conducting liquid metal depends, inter alia, on the flow velocity of the liquid metal. In particular, we consider that the system is stabilized against the velocity of the metal corresponding to the permanent liquid metal flow conditions, and any disturbance that causes fluctuations in this velocity will cause the impedance of the inductor to respond to the corresponding induced current. Consider as fluctuation. Therefore, according to the invention, a steady-state power supply at either current or voltage is used to supply the inductor and the possible variation of the other variable (voltage or current) is investigated to determine the liquid metal Derive variations in flow velocity. Furthermore, due to the fact that the inductors are powered separately from each other,
This speed can be locally limited. In a preferred embodiment, this information is used as feedback for the power control system of the different inductors, and a predetermined speed reference value calculated based on modeling, for example as described in European patent application 0550785. The metal flow velocity can be controlled by the equilibrium point corresponding to.

FIG. 3 very schematically illustrates four inductor positions in a continuous casting facility. For simplicity, an inductor 9 and a parallelogram representing the liquid metal 1 between these inductors are shown.

Conventionally, each inductor 9 is composed of several imbricate turns adapted to be supplied from different phases. Figure 3
In the above example, a two-phase electromagnetic brake system is assumed. Thus, each inductor 9 consists of an electrically conductive, interlocking turn 2 in the magnetic yoke 12, facing the metal 1 with respect to the plane xz in which the electrically conductive circuits 10 and 11 are inscribed.
Two circuits, 10 and 11, respectively. The first conductive circuit 11 corresponding to the first phase is composed of conductors 13, 14, and 15 in 3 packs (bundle). The number of conductors in the central pack 15 is twice the number of conductors in the packs 13 and 14 surrounding the two pack conductors 16 and 17 of the second circuit 10 to be supplied from the second phase of the two-phase power supply. . The conductor batches are phase by phase, at their one end, and at their other end via a power supply (not shown in FIG. 3), so that there are matched ampere turns.
Connect directly to each. Therefore, the vertical axis z is in the casting direction, and the horizontal axes x, y respectively correspond to the alignment of the ports (4, FIG. 1) of the injection nozzle, the direction in which the liquid metal 1 is maximum and the liquid metal 1 In the example of FIG. 3 in which the is minimized, the conductor packs of the different inductors are oriented in the vertical direction z. The conductor packs are, for example, directly connected at their respective lower ends. By connecting the conductor pack, a current flows through the turn, but the current is
In the vertical part, the opposite is true, depending on whether the conductor 13, 14 or 15 for the first circuit 11 is associated or the conductor 16 or 17 for the second circuit 10 is associated. To illustrate this opposite flow, one example of current flow is marked with a “.” Or “x” depending on the direction of flow in the vertical section, and FIG.
Is shown in.

The current flow shown in FIG. 3 is conventional and will not be described in further detail. The present invention is
Although it can be carried out in a system containing a larger number of phases, for example, in a three-phase system or a multi-phase system, the fact that the phases are usually entangled with each other is only to obtain a multiphase sliding field. It should be noted. As illustrated by the display of the current flow direction in FIG. 3,
It should also be noted that the axis x corresponds to the longitudinal axis of symmetry, which axis of symmetry is actually the antisymmetric axis for the two inductors 9 facing each other.

In a sliding field as illustrated in the above figures, the potential vector A, the current density j, and the electric field E have a single component along the vertical axis z and are induced metal. It can be considered that the velocity v of V has a single component along the longitudinal axis x and the magnetic induction B has two components along the horizontal axes x and y.

The synchronous velocity v _S of the sliding electromagnetic field is equal to the product of the two-phase AC excitation operating frequency f and the wavelength λ of the sliding field wave. It should be noted that the actual metal velocity v is the inverse of this synchronous velocity, and the actual velocity v also has only one component along the longitudinal axis x.

The equations that determine the behavior of the electromagnetic field in the inductor, in the atmosphere, in the magnetic yoke, and in the metal receiving the induction can be expressed as follows, projected on the vertical axis z. In these equations, the only unknown value is the potential vector

[Outer 1] Is the component A along the O _z of.

[0040]   In the inductor, it can be expressed as:

[Equation 1] In the above equation, J _i represents the current density imposed on the inductor by the power supply,
μ ₀ represents the magnetic permeability of vacuum.

[0041]   In air, it can be expressed as:

[Equation 2]

[0042]   In a magnetic yoke, it can be expressed as:

[Equation 3] In the above equation, μ _r is the relative magnetic permeability of the magnetic medium.

[0043]   For an induced metal, it can be expressed as:

[Equation 4] In the above equation, ω represents the electric pulse (ω = 2πf) of the AC power source, and ρ represents the resistivity of the liquid metal.

As a first approximation, the potential vector A is
It can be regarded as a sliding wave due to an infinitely long inductive sheet that follows the longitudinal direction x. Then, the only component A of the vector potential along the vertical axis z
It can be considered that can be expressed as:

[Equation 5] In the above equation, k represents the wave number (k = 2π / λ) of the inductive sliding magnetic field.

By this approximation, the aforementioned relationship in metals undergoing induction is projected onto the vertical axis,
Can be expressed as equivalent to:

[Equation 6]

[0046]   Introducing synchronous speed into this equation gives:

[Equation 7]

All of the above equations show that when applying a current, the only variable quantities are the potential A and the velocity v of the liquid metal.

It should be noted that the current density must be set rather than the current. However, the number of conductors per pack (i.e., the number of turns) has no effect since the voltage variations of each phase relative to the velocity variations of the metal are compared in a relative manner.

Therefore, the voltage gradient gradV can be calculated on the basis of the potential vector A, the imposed current density j, and the respective values of the relationships defined above.

[0050]   By projecting the following Maxwell equation on the vertical axis z,

[Equation 8] The equation connects the values of j, gradV, and A, and

[Equation 9] By replacing ivkA with ivkA, we obtain the following relationship which gives each conductor a voltage gradient: gradV = -i (ω-vk) A-ρj.

Therefore, by summing the values obtained for all conductors in each pack,
Sufficient to determine the total voltage of each phase. If desired, this voltage can be divided by the current imposed by the current sources 31 and 32 to determine the impedance, rather than the voltage of each phase.

As a specific example, consider for each conductor pack a rectangle 160 × 100 mm ² (excluding the end packs 13 and 14 corresponding to rectangle 80 × 100 mm ² respectively) and its current density is 6.75 × 10 ^6. Ampere rms / m ² . The wavelength λ of the sliding field is about 1.3 m, assuming a serrative permeability μ _r 1000. For an operating frequency, for example 0.65 Hz, the sync speed v _S is 84.5 cm /
Seconds.

[0053] In simplified fashion, the metal undergoing induction, certain resistivity [rho = 100.10 ^- is an ⁸ [Omega] m solid (which corresponds to the conductivity 1.10 ^{6 (Ωm) -1,} i.e. (Corresponding to the conductivity of substantially liquid steel), the respective total voltage values for the conductor packs can be calculated for the two modules at liquid metal velocities of 10 and 9 cm / sec. For example, for batches 16 and 17 consisting of 40 conductors having a square cross-sectional area of 20 × 20 mm ² in series, one would consider each of the 40 spiral batches to carry a current of 2700 amps rms,
A voltage of 38.66 volts at rates for 10 and 9 cm / sec, respectively.
And 36.74 volts are obtained. Therefore, the rate of the corresponding phase voltage is reduced by about 2/38, or about 5%. Regarding the impedance of the corresponding phase,
The fluctuation is still in the 5% range for the same metal speed fluctuation.

Therefore, in industrial terms, it can be considered that a 10% variation in the velocity of the metal results in a 5-6% variation in the voltage and in the impedance. This variation is substantially sufficient to be used in the control of the regulation circuit to bring the speed back to its average standard value or to zero the distance between the two values.

FIG. 4 illustrates the respective electrical connections according to the invention of the two-phase inductor illustrated in FIG. 3 on the upper surface of the ingot mold. For example, the direct connection between the different conductor packs at the bottom of the system is indicated by the dotted line.

In the top view of FIG. 4, the nozzle 3 is roughly at the center of the mold 2. Each inductor 9 has its magnetic yoke 12 and two packs 16 and 17 having the same number of conductors in the vertical direction, and packs 13 and 14 having a central pack 15 at its end
2 consisting of three packs 13, 14, 15 having twice as many conductors as
Shown by two conductive circuits 10, 11.

As shown so far, the parts 16 and 17 of each circuit 10 are directly connected by a cable 18 underneath them. Similarly, packs 13 and 14 are connected to pack 15, respectively, by cables 19 and 20, respectively. On top of the vertical conductor pack, said packs are connected at their ends to the supply means. According to the invention, the conductive circuits 10 and 11 of each inductor 9 are individually connected to the supply circuit 21 specified for the associated inductor. Therefore, packs 13 and 14, pack 15, pack 16, and pack 17 are connected to circuit 21 by respective cables 22, 23, 24, and 25.

According to the invention, all circuits 21 have exactly the same structure, which will be described hereinafter in connection with FIG. Each circuit is individually connected to the central control station 26, for example by a cable 27. The cable 27 is illustrated as carrying each supply circuit 21 with a number of independent conductors carrying different required AC power phases and, if necessary, the appropriate control signals provided by the central station 26. ing. However, only the control signals can be individualized and the polyphase supply leads can be common to different circuits 21, in which case the circuits will supply their respective powers to their respective inductors. It should be noted that it is a role.

For clarity, the different reference numbers for the inductor 9 are shown only once in FIG. 4, but each inductor has a similar structure and, as illustrated in FIG. Only the direction of flow differs from the others.

FIG. 5 shows very schematically the structure of the supply circuit 21 of the inductor according to the invention.

In the example of FIG. 5, each phase of the inductor is supplied with a low frequency alternating current and a signal for which the effective current value is set to a predetermined value according to the nominal braking characteristics desired for the ingot mold. Is assumed. Therefore, the circuit 21 of FIG.
Includes two current sources 31 and 32, which supply, for example, cables 23 and 25 associated with conductor packs 15 and 16, respectively, illustrated in FIG. According to the invention, the current sources 31 and 32 are controllable by signals provided by control circuits, respectively 35 and 36, respectively 33 and 34. Each circuit 35, 36 measures the voltage between conductors 22 and 23 and the voltage between conductors 24 and 25, respectively. These voltage measurements attempt to determine the velocity of the liquid metal facing the corresponding inductor.

In the embodiment illustrated in FIG. 5, each controller 35, 36 includes a control station 2
6 (FIG. 4) receives reference values 37, 38 and serves to control the current provided by the power supplies 31 and 32, allowing a constant, balanced velocity in the ingot mold. However, it is also possible for the central station 26 to provide and provide the regulation directly, or a regulation of the voltage is provided which can be used to calculate the speed and utilize it in the central control room 26.

Of course, it is also possible to supply the inductor with a controllable voltage of a predetermined value, and also to make a measurement of the current, in which case the variation of the current will be speed-dependent and thus the supply voltage. Feedback to the power supply is possible.

On the basis of the functional instructions given herein above, it is appropriate to actually carry out the method according to the invention by forming an electronic circuit or by programming the calculation tools necessary for the calculation. Within the capabilities of the engineer in the field. It should be noted that for any conventional control, the complexity of this electronic circuit or of the programming calculations will depend on the desired accuracy of the control.

The advantages of the present invention are that, according to the invention, there is no physical contact with liquid metal,
The velocity of the liquid metal in the ingot mold can be measured.

Another advantage of the present invention is that it is particularly well suited for controlling continuous casting systems, as it is extremely easy to provide feedback to current or voltage in the inductor.

Another advantage of the present invention is that it does not require any modification of conventional continuous casting equipment with sliding field electromagnetic brakes, except for the control circuits of various inductors.

Of course, the present invention is susceptible to various changes, improvements and modifications that those skilled in the art will consider. In particular, the suitability of the method according to the number of phases of the sliding field electromagnetic braking system is within the capabilities of a person skilled in the art, depending on the application and on the executability of the functions presented herein above. Further, the numerical values shown in the above description are shown only for illustrating the industrial effectiveness of the present invention and for exemplification. Further, it should be noted that in any continuous casting system, whatever the shape of the ingot mold, it can be practiced if it uses an active sliding field electromagnetic braking system.

[Brief description of drawings]

1 is a perspective view showing an example of a continuous metallurgical casting facility of the type to which the present invention is applied, very schematically and partially showing an inlet portion of an ingot mold; FIG.

FIG. 2 is a simplified cross-sectional view of a conventional ingot mold, which is an example of a continuous metallurgical casting facility of the type to which the present invention is applied.

FIG. 3 is a diagram very schematically showing respective positions of inductors in a continuous casting facility to which the present invention is applied.

FIG. 4 is a top view of an ingot mold equipped with a casting speed control system according to the present invention.

[Figure 5]   FIG. 6 is a schematic diagram showing an embodiment of an inductor control circuit according to the present invention.

─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ernst Loran             France, F-38610 Giere,               Ryu Pasteur, No. 8 F-term (reference) 4E004 AA09 MB07 MB11 NB01 TB07

Claims (7)

[Claims] 1. An ingot mold (1) equipped with a sliding field electromagnetic brake.
A method for measuring the flow velocity of a liquid molten metal (1) in a method, comprising supplying current and voltage to an electromagnetic brake from at least one constant power source, respectively, and measuring the voltage of the power source (31, 32). , Measuring the current, and deriving the flow velocity from the variation of this measurement. 2. A method as applied to an electromagnetic brake, wherein at least one inductor (9) of the electromagnetic brake comprises several conductors of two packs (16, 17) in the vertical direction (z). Consists of applying the following relationship gradV = -i (ω-vk) A-ρj for each conductor, where ω is the AC excitation pulse of the sliding field and v is the velocity of the metal. Where k represents the wave number of the inductive sliding magnetic field, A represents the vector potential,
The method of claim 1, wherein ρ represents the resistivity of the metal, j represents the excitation current density of the inductor, and V represents the voltage across the inductor. 3. Method according to claim 1, characterized in that the measured speed value is used to servo the excitation of the inductor (9) to a predetermined value. 4. A method for adjusting the flow rate of molten metal in an ingot mold (1) equipped with a sliding field electromagnetic brake comprising several inductors (9), each method comprising at least one. A method comprising supplying a current, voltage to an electromagnetic brake from a constant power source, and controlling the voltage or current of the power source (31, 32) using the measured value of the voltage or current of each inductor. . 5. A continuous casting facility of the type that uses a sliding field electromagnetic brake to control the flow of liquid metal (1) supplied from two ports (4) of a nozzle (3), the electromagnetic being Powering each inductor (9) of the brake by a separate circuit (21), and its equipment controlling the supply voltage or current of each inductor to maintain a balanced liquid metal flow rate between the two ports. An installation characterized in that it comprises means (26, 35, 36) for 6. The supply circuit (21) of each inductor (9) comprises its own means (35, 36) for adjusting the electromagnetic excitation force of the inductor. Equipment described in. 7. Different inductors (9) for adjusting the liquid metal flow rate.
Installation according to claim 5, characterized in that it comprises a central station (26) for controlling the supply circuit (21) of the.