JP2018114548A - Method and apparatus for measuring molten-steel flow rate in immersion nozzle, continuous casting tundish, and method for continuously casting bilayer cast piece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow rate measuring method and apparatus for measuring noncontact a flow rate in an immersion nozzle supplying molten steel from a tundish to an interior of a mold, in which upon producing a bilayer cast piece whose component composition is different between a surface layer and an internal layer of a cast piece, the flow rate of molten steel for a cast piece different in component compositions between the surface layer and the internal layer is controlled correctly.SOLUTION: An injection nozzle for supplying molten steel from a continuous casting tundish to an interior of a mold has an upper nozzle, a sliding nozzle, and an immersion nozzle. An alternating magnetic field crossing over a molten steel flow 6 in the upper nozzle is excited by an exciting coil 2, and a magnetic field parallel in direction with a flow direction of the molten steel flow 6 or a change in time of the magnetic field is detected with detectors 3 (detection coils 3a) at one or more locations. On the basis of a detected signal, the flow rate of molten steel in a nozzle 4 is calculated. In supplying molten steel different in compositions from two immersion nozzles and continuously casting a bilayer cast piece, the flow rate of molten steel is controlled by a flow-rate measuring apparatus 1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and an apparatus for measuring a flow rate of molten steel in an immersion nozzle provided in a tundish for continuous casting, a tundish for continuous casting, and a continuous casting method for multi-layer slabs.

  Normally, molten steel is supplied from the tundish into the mold using a single immersion nozzle, and the amount of molten steel supplied into the mold is controlled so that the level of the molten metal is constant. Therefore, it is not necessary to directly measure the molten steel flow rate in the immersion nozzle.

  Attempts to produce multi-layered slabs having different surface layer and inner layer composition have been made for a long time. For example, the method disclosed in Patent Document 1 can be mentioned. In Patent Document 1, two immersion nozzles having different lengths are inserted into a pool of molten metal in a mold, each discharge port is provided at a position having a different depth, and a DC magnetic field is provided between different types of molten metal. A method for producing a multilayer slab while preventing the mixing of both metals is disclosed.

  Non-Patent Document 1 discloses that the surface layer / inner layer can be separated by applying a magnetic field of 0.2 to 0.3 T as a DC magnetic field.

  However, since the above method uses two types of molten steel having different component compositions, the two types of molten steel are separately melted at the same timing, transported to a continuous casting process, and used as an intermediate holding container for each molten steel. Each dish needs to be prepared. In addition, since the injection flow rate is greatly different between the surface layer molten steel and the inner layer molten steel, the amount of molten steel required for each heat is greatly different, which is difficult to realize in a normal steelmaking factory.

Patent Document 2 discloses a flow velocity measuring method and apparatus capable of measuring the flow velocity of a moving conductive measurement object (for example, a high-temperature liquid metal) stably and accurately even when the measurement object surface has ripples. It is disclosed. A magnetic field perpendicular to the surface of the moving object to be measured is excited (excitation winding P), and the surface of the object to be measured and the magnetic field in the direction parallel to the moving direction are detected in two ranges (detection) Windings S ₁ and S ₂ ), and when the flow velocity of the measurement object is calculated from the detected magnetic field signal, the measurement object is moved in two ranges outside the detection range of the detection windings S ₁ and S _2. The magnetic field in the direction parallel to the direction is detected (detection windings S ₃ and S ₄ ), and the flow velocity of the measurement object calculated based on the information related to the inclination of the surface of the measurement object obtained based on the detected magnetic field signal Correct.

JP 63-108947 A Japanese Patent Laid-Open No. 11-211741

E. Takeuchi, M. Zeze, H. Tanaka, H. Harada and S. Mizoguchi: Ironmaking and Steelmaking, 24 (1997), 257.

  A continuous casting method has been proposed in which molten steel for continuous casting is supplied with one ladle and one tundish, and a multi-layer continuous cast slab in which the alloy element concentration of the slab surface layer is different from the inside is cast. ing. In the tundish used in the method, a tundish weir having an opening is provided in the molten steel pool of the tundish, and the molten steel pool is divided into two zones. Of the two molten steel pools, two types consisting of different components in the pools on both sides of the tundish weir by continuously adding predetermined elements to the pool far from the ladle molten steel injection flow and adjusting the concentration Hold the molten steel. An immersion nozzle is arranged at the bottom of each molten steel pool. In the strand below the mold, a DC magnetic field band is formed in the strand by a DC magnetic field generator arranged over the entire width in the strand width direction, and the strand in the casting direction is divided into an upper side and a lower side of the DC magnetic field band. Of the two immersion nozzles provided at the bottom of the tundish, from the immersion nozzle on the side added with additional elements (immersion nozzle for surface layer molten steel), the molten steel is supplied to the upper molten steel pool in the DC magnetic field zone, and the ladle molten steel injection flow side The immersion steel (immersion nozzle for inner layer molten steel) supplies molten steel to the lower molten steel pool of the DC magnetic field zone. Since the components of the molten steel supplied from the respective immersion nozzles are different, it is possible to manufacture a multilayer slab having different component compositions of the surface layer and the inner layer of the slab.

  In the case of normal continuous casting using one immersion nozzle per mold, when adjusting the amount of molten steel injected into the mold from the tundish via the immersion nozzle, adjust the molten metal surface position in the mold to be constant. By doing so, it is possible to automatically supply an amount of molten steel equal to the casting amount. On the other hand, when supplying molten steel from two immersion nozzles per mold, it is necessary to adjust the balance of the molten steel supply amount from each immersion nozzle.

  On the other hand, for at least one of the two immersion nozzles, if the molten steel flow rate supplied through the immersion nozzle can be measured, the other is controlled so that the mold surface level in the mold is constant. It is preferable because the flow rate can be controlled so that the flow rate results from the respective immersion nozzles more accurately match the target molten steel flow rate.

  The present invention provides a method for measuring the flow rate of molten steel in a submerged nozzle that supplies molten steel from a tundish into a mold in a non-contact manner, a flow rate measuring device for the molten steel in the submerged nozzle, and a tundish for continuous casting using the same. The purpose is to do. It is another object of the present invention to provide a method for producing a multilayer slab in which the component composition of the surface layer and the inner layer of the slab is different using the method for measuring the flow rate of molten steel in the immersion nozzle and the flow rate measuring device.

That is, the gist of the present invention is as follows.
(1) A method for measuring a molten steel flow rate in an immersion nozzle for supplying molten steel into a mold from a continuous casting tundish, wherein the upper nozzle is provided with a sliding nozzle and an upper nozzle above the immersion nozzle. An alternating magnetic field intersecting the inner molten steel flow is excited, a magnetic field in a direction parallel to the flow direction of the molten steel flow or a time change of the magnetic field is detected at one or more locations, and the molten steel flow rate in the submerged nozzle based on the detected signal A method for measuring the flow rate of molten steel in an immersion nozzle, characterized in that
(2) The excitation of the alternating magnetic field is performed by an exciting coil, and the diameter D of the exciting coil and the frequency f of the alternating magnetic field to be excited are determined by the following equations (1) and (2). Of measuring the flow rate of molten steel in a submerged nozzle.
D ≧ 2W (1)
f ≦ (1-0.2aH) ² /(0.04πμσH ² ) (2)
Where W: inner radius in the coil width direction of the upper nozzle at the exciting coil position (m), H: inner radius in the exciting magnetic field direction of the upper nozzle at the exciting coil position (m), μ: permeability of vacuum (N / A ² ) , Σ: electric conductivity of molten steel (S / m), a: constant determined by exciting magnetic field distribution in upper nozzle exciting magnetic field when molten steel does not pass (m ⁻¹ )
(3) Two pairs of excitation coils for exciting the alternating magnetic field and detectors for detecting the magnetic field or the time change of the magnetic field are installed, and each pair is installed relative to the upper nozzle, and two sets of detections are made. The molten steel flow rate in the immersion nozzle according to (1) or (2), wherein the molten steel flow rate in the immersion nozzle is calculated based on the result.
(4) A molten steel flow measuring device in an immersion nozzle for supplying molten steel into a mold from a continuous casting tundish, comprising a sliding nozzle above the immersion nozzle and an upper nozzle above the upper nozzle, the upper nozzle Based on an excitation coil that excites an alternating magnetic field intersecting the inner molten steel flow, a detector that detects a magnetic field in a direction parallel to the flow direction of the molten steel flow or a time change of the magnetic field at one or more locations, and a detected signal An apparatus for measuring a molten steel flow rate in an immersion nozzle, comprising an arithmetic unit for calculating the flow rate of molten steel in the immersion nozzle.
(5) The molten steel flow rate measuring device in the submerged nozzle according to (4), wherein the diameter D of the exciting coil and the frequency f of the alternating magnetic field to be excited are determined by the following formulas (1) and (2).
D ≧ 2W (1)
f ≦ (1-0.2aH) ² /(0.04πμσH ² ) (2)
Where W: inner radius in the coil width direction of the upper nozzle at the exciting coil position (m), H: inner radius in the exciting magnetic field direction of the upper nozzle at the exciting coil position (m), μ: permeability of vacuum (N / A ² ) , Σ: electric conductivity of molten steel (S / m), a: constant determined by exciting magnetic field distribution in upper nozzle exciting magnetic field when molten steel does not pass (m ⁻¹ )
(6) Two pairs of the excitation coil and the detector are installed, and each pair is installed relative to the upper nozzle, and the sliding nozzle sliding direction and the excitation coil axial direction are orthogonal to each other. The calculation device calculates the flow rate of molten steel in the immersion nozzle based on two sets of detection results. The apparatus for measuring the flow rate of molten steel in the immersion nozzle according to (4) or (5).
(7) A tundish for continuous casting, wherein the upper nozzle connected to the tundish is provided with the molten steel flow rate measuring device in the immersion nozzle according to any one of (4) to (6).
(8) Two immersion nozzles are connected to the tundish, and the molten steel flow rate measuring device in the immersion nozzle according to any one of (4) to (6) is installed on at least one immersion nozzle. A tundish for continuous casting, characterized in that
(9) A tundish weir having an opening in the tundish is provided, and the ladle molten steel injection side divided by the tundish weir is the first region, and the opposite side is the second region. The first region and the second region Hold the molten steel of different component composition on the side, arrange the immersion nozzle for inner layer molten steel at the bottom of one region of the tundish, and arrange the immersion nozzle for molten steel at the bottom of the other region,
A DC magnetic field generator that applies a DC magnetic field in the thickness direction over the entire width in the mold width direction is arranged, and the upper molten steel pool and the lower molten steel pool at the upper part of the strand across the DC magnetic field zone formed by the DC magnetic field generator. And supplying molten steel from the surface layer molten steel immersion nozzle to the upper molten steel pool, supplying molten steel from the inner layer molten steel immersion nozzle to the lower molten steel pool,
An injection nozzle having at least one of a surface layer molten steel immersion nozzle and an inner layer molten steel immersion nozzle is provided with the molten steel flow rate measuring device in the immersion nozzle according to any one of (4) to (6),
When supplying the amount of molten steel consumed by solidification in each molten steel pool from each of the two immersion nozzles into the mold, the immersion nozzle supplies molten steel in the immersion nozzle on the side provided with the molten steel flow measuring device. The molten steel flow rate is adjusted so that the molten steel flow rate is commensurate with the amount of molten steel consumed by solidification, and the molten steel flow rate is controlled so that the mold surface level in the mold is constant in the other immersion nozzle. A continuous casting method for multilayer slabs.

  Exciting an alternating magnetic field that intersects the molten steel flow in the upper nozzle above the immersion nozzle that supplies molten steel from the continuous casting tundish into the mold, and changes the magnetic field in the direction parallel to the flowing direction of the molten steel or the time variation of the magnetic field at one location By detecting at the above locations and calculating the molten steel flow rate in the upper nozzle based on the detected signal, the molten steel flow rate in the immersion nozzle can be detected in a non-contact manner.

  In addition, when supplying molten steel for continuous casting with one ladle and one tundish, and casting a multi-layer continuous cast slab in which the alloy element concentration of the slab surface layer portion is different from the inside, the present invention By using this molten steel flow rate measurement, it is possible to accurately control the molten steel flow rate in which the component composition of the surface layer and the inner layer of the slab is different, and to manufacture a multilayer slab.

It is a figure which shows the molten steel flow rate measuring method and apparatus of this invention, (A) is AA arrow plane sectional drawing, (B) is BB arrow side sectional drawing, (C) is CC arrow view. FIG. It is a figure which shows a molten steel flow rate measurement mechanism, (A) is an arrow view, (B) is side surface sectional drawing. It is a figure which shows the molten steel flow volume measuring method and apparatus of this invention. It is a figure which shows the radial direction molten steel flow velocity distribution in a nozzle. It is a figure which shows the radial direction molten steel flow velocity distribution in a nozzle. It is a figure which shows the molten steel flow rate measurement principle in a nozzle, (A) is an excitation magnetic field strength distribution in a nozzle, (B) is the relationship between the distance x and a sensor signal parameter | index, (C) is distance x and a sensor signal parameter | index total. It is a figure which shows the relationship. It is a figure which shows the molten steel flow rate measurement principle in a nozzle, (A) is an excitation magnetic field strength distribution in a nozzle, (B) is the relationship between the distance x and a sensor signal parameter | index, (C) is distance x and a sensor signal parameter | index total. It is a figure which shows the relationship. It is a figure which shows the relationship between molten steel flow ratio and a sensor integration signal index | exponent. It is a plane sectional view showing the relation between the molten steel flow rate measuring device of the present invention and an upper nozzle. It is sectional drawing which shows the relationship between the molten steel flow volume measuring apparatus of this invention, and an upper nozzle, (A) is an AA arrow cross-section side view of FIG. 9, (B) is a BB arrow cross-section front view. . It is a figure which shows the condition which continuously casts a multilayer cast piece. It is sectional drawing which shows the molten steel flow volume measuring apparatus of this invention accommodated in the case. It is a figure which shows the relationship between a molten steel flow rate actual value and the sensor signal by the molten steel flow rate measuring apparatus of this invention.

  As a flow meter for measuring the flow rate of a conductive fluid flowing in a pipe, an electromagnetic flow meter that measures an induced electromotive force generated when the conductive fluid moves in a DC magnetic field by providing an electrode in the pipe is generally used. However, when the fluid to be measured is molten steel, since the molten steel is at a high temperature, there is no material having both electrical conductivity and resistance to melting and corrosion. On the other hand, it is known as the “velocity effect of the magnetic field” that the magnetic field is distorted by the induced magnetic field formed by the induced current generated when the conductive fluid moves in the magnetic field. There has been disclosed a method and an apparatus for measuring a flow velocity that measure the flow velocity and the like of the surface of a molten steel flow in a mold in which molten steel is cast in a continuous casting process.

As shown in FIG. 2 (A), the molten steel flow 6 in a magnetic field B _E moves across the magnetic field B _E in speed _{v, E V = v × B} E becomes the speed electromotive force is a magnetic field B in the molten steel It occurs in a direction perpendicular to both _E and velocity v. By this speed electromotive force E _V , an induced current J _V is induced in the molten steel, and an induced magnetic field B _V resulting from the induced current is generated. The present invention uses this principle to measure the flow rate of molten steel flowing in the immersion nozzle in a non-contact manner.

FIG. 3 shows a situation where the molten steel filling the nozzle 4 forms a molten steel flow 6 directed downward. As shown in FIG. 3, in the flow velocity measuring method and measuring apparatus of the present invention, an alternating magnetic field _BE intersecting the molten steel flow 6 is excited with respect to the molten steel flow 6 in the nozzle 4. Excitation of the alternating magnetic field B _E is performed by the excitation coil 2. It is most preferable to arrange the exciting coil so that the central axis 51 is orthogonal to the molten steel flow 6 to excite the magnetic field. Hereinafter, taking the case where the central axis 51 of the exciting coil is arranged so as to be orthogonal to the molten steel flow 6, the exciting magnetic field _BE at an arbitrary point on the central axis 51 of the exciting coil in the molten steel flow is taken as an example. The operation will be described.

Since the molten steel in a magnetic field B _E flows across the magnetic field B _E in speed v, is in the molten steel, the induced current J _V in a direction perpendicular to both the velocity v and the magnetic field B _E is induced (FIG. 2 ( A)). Induced magnetic field B _V due to the induced current J _V forms a concentric magnetic field around the induction current J _V, it can be observed outside the nozzle 4. Since the main direction of the induced magnetic field B _V is parallel to the flow direction of the molten steel flow 6 outside the nozzle 4, the detector 3 detects the magnetic field in the direction parallel to the flow direction of the molten steel flow 6 or the time of the magnetic field. A change will be detected. As the detector 3 for detecting the induced magnetic field B _V , the magnetic field itself or the detector 3 for detecting the time change of the magnetic field can be used. Preferably, by using the detection coil 3 a as the detector 3, it is possible to detect a time change of the magnetic field. It is preferable that the direction of the central axis 52 of the detection coil and the direction of the molten steel flow 6 is parallel or nearly parallel. Thereby, the time change of the magnetic field of the direction parallel to the flow direction of the molten steel flow 6 is detectable. Hereinafter, the case where the detector 3 is the detection coil 3a will be described as an example.

  The installation position of the detection coil 3 a is preferably installed between the excitation coil 2 and the nozzle 4 so that the central axis 52 of the detection coil is parallel to the molten steel flow 6 of the nozzle 4. The number of detection coils 3a may be one, or a sum signal of detection signals may be collected after a plurality of detection coils 3a are installed.

Here, an alternating exciting current is supplied to the exciting coil 2 to excite a magnetic field _BE perpendicular to the molten steel flow 6 of the nozzle 4. Then, an induced current J _V flows in the molten steel flow. FIG. 2B illustrates two induced currents (J _V1 and J _V2 ) in the molten steel flow. The induced magnetic fields Bv ₁₁ and Bv ₁₂ due to the induced current J _V1 are shown. An induced magnetic field Bv ₂ by the induced current J _V2 is illustrated. The induction magnetic fields Bv ₁₂ and Bv ₂ are parallel to the molten steel flow 6 at the position of the detection coil 3 a immediately below the exciting coil 2, and these induction magnetic fields B _V are arranged in parallel to the molten steel flow 6. Detect with. Since the detected magnetic field or the magnitude of the time change of the magnetic field corresponds to the flow velocity of the molten steel flow 6, the flow velocity of the molten steel flow 6 can be measured from this. In practice, as shown in FIG. 3, the output signal of the detection coil 3a is detected by using a lock-in amplifier 17 or the like and a component having a phase shifted by -90 ° from the excitation current, and a flow velocity source signal that is a source of flow velocity measurement. And Here, the detection coil 3a is used for the detection of the magnetic field, and the signal detected by the detection coil 3a is the time change of the magnetic field _BE , so that the excitation magnetic field _BE by the excitation coil 2 and the detection voltage of the detection coil 3a are used. Since there is a phase difference of −90 °, a phase component shifted by −90 ° is detected.

  As shown in FIG. 3, the circuit of the molten steel flow rate measuring device 1 generates a sine wave by a waveform generator 15 and supplies an excitation current to the excitation coil 2 via a power amplifier 16. Here, the excitation frequency was 3 Hz. The detection signal in the detection coil 3a is phase-shifted by −90 ° with respect to the excitation current to the excitation coil 2 by the lock-in amplifier 17 after the noise signal in the unnecessary band is removed in advance by a band-pass filter having a predetermined bandwidth. Are detected. This reference phase signal for detection is supplied from the waveform generator 15 to the lock-in amplifier 17. A signal after detection by the lock-in amplifier 17 is a flow velocity source signal that is a source of flow velocity measurement. The flow velocity source signal is sent to a computer 18 serving as an arithmetic unit 14, and the molten steel flow rate in the nozzle 4 is calculated.

  The exciting magnetic field by the exciting coil intersects the molten steel flow that fills and passes through the molten steel passage in the nozzle. Of the molten steel flow in the nozzle, the molten steel flow at each position within the range where the exciting magnetic field penetrates from the side closer to the exciting coil to the far side forms an induced current, and the sum of the induced magnetic fields formed by the induced current at each position Is detected by the detection coil. Here, how the phenomenon at each position in the direction of the central axis of the exciting coil is detected by the detection coil is verified based on the calculation.

  Here, as shown in FIG. 2A, the direction of the central axis 51 of the exciting coil is named “depth direction 61”. A direction perpendicular to both the depth direction 61 and the height direction 62 is named “width direction 60”.

  As shown in FIG. 3, the case where the radius R of the molten steel flow path 5 in the nozzle 4 is 60 mm and the magnetic field frequency f of the exciting coil 2 is 3 Hz was examined. The detection coil 3a is installed between the exciting coil 2 and the outer wall of the nozzle 4, and the center axis 52 direction of the detection coil is set to the height direction 62 and is arranged in parallel to the molten steel flow direction. The depth direction distance 61 in the flow path was set to x = 0 on the inner wall 19 on the side close to the exciting coil 2, and the center position in the depth direction 61 of the molten steel flow path 5 was set to x = R = 60 mm.

The molten steel flow 6 that fills and passes through the molten steel flow path 5 of the nozzle 4 forms a boundary layer in the vicinity of the inner wall 19 of the nozzle, and has a flow velocity of 0 at a position (x = 0) in contact with the inner wall 19. In other parts, the flow velocity is close to the average flow velocity. The molten steel flow in the nozzle for pouring molten steel from the tundish into the mold has a Reynolds number of 3000 or more and is in a turbulent state. Therefore, the flow velocity distribution of the molten steel flow in the nozzle in the turbulent state was obtained by numerical calculation. FIG. 4 shows the calculation results with the horizontal axis representing the distance ratio from the nozzle inner wall x _r = x / R and the vertical axis representing the flow velocity ratio v _r = (flow velocity at x) / (flow velocity at the center of the nozzle). As apparent from FIG. 4, the boundary layer portion velocity ratio v _r becomes smaller, the distance ratio x _r of the nozzle inner wall is within the range of about 0 to 0.1, the nozzle inner wall (x _r = 0) It was found that the molten steel flow rate in the molten steel flow channel of the nozzle can be measured with sufficient reproducibility if the flow velocity of the molten steel flow up to the distance ratio x _r = 0.2 (x = 0.2R) can be measured.

It was assumed that an alternating magnetic field was applied perpendicularly to the nozzle surface with an inner diameter of 120 mm (R = 60 mm). The magnetic field _BE excited in the molten steel flow path 5 filled with molten steel by the exciting coil 2 decreases as the distance from the coil increases. Regarding the magnetic field B _E excited in the molten steel flow path, the excitation magnetic field on the inner wall 19 of the nozzle is set as B _E0 . Here, first, the shape of the exciting coil 2 was selected so that B _E / B _E0 = 1 / e (e is the base of natural logarithm) at a distance x = 0.2R. The magnetic field frequency is 3 Hz as described above.

According to the numerical calculation, the molten steel flow velocity distribution in the nozzle radial direction is estimated as a flow velocity distribution as shown in FIG. Next, when the excitation magnetic field B _E / B _E0 at each position from x = 0 to x = 60 mm was calculated, it was as shown in FIG. At a distance x = 12 mm, which is 0.2R from the inner wall 19, B _E / B _E0 = 1 / e. Then, the induced magnetic field B _E and the induced magnetic field B _V based on the molten steel flow having the distribution shown in FIG. 5 are detected by the detection coil 3a installed in the vicinity of the outer wall of the nozzle as a sensor signal index, and the induced magnetic field B the vertical axis of the sensor signal index obtained by calculation for each value of x the underlying induced current J _V of _V is located, the illustrated abscissa the x, is as shown in FIG. 6 (B). In the vicinity of x = 0, the sensor signal index has a slope that rises to the right due to the molten steel flow velocity distribution. On the center side of the boundary layer, the sensor signal index decreases as x increases. At a distance x = 12 mm which is 2R, the sensor signal index resulting from the molten steel flow 6 is also a sufficiently large value, and the induced magnetic field B _V due to the molten steel flow velocity from x = 0 to x = 0.2R is sufficient. It is clear that it can be detected. In actual detection, the signal for each position of x cannot be collected, and the integrated value of all signals becomes the sensor signal. FIG. 6C shows the contribution of each part.

Next, the shape of the exciting coil 2 was selected so that B _E / B _E0 = 1 / e (e is the base of natural logarithm) at a distance x = 0.5R. The magnetic field frequency is also 3 Hz. In this case, the distribution of the excitation magnetic field B _E / B _E0 is shown in FIG. 7A, and B _E / B _E0 = 1 / e at a distance x = 30 mm, which is 0.5 R from the inner wall 19. FIG. 7B shows the distribution of the sensor signal index, and FIG. 7C shows the contribution of each part. Compared with the case of FIG. 6, as a result of selecting the condition that the excitation magnetic field _BE penetrates deeper in the molten steel flow path, the flow velocity of the molten steel flow up to a deeper position can be reflected in the integrated value. .

Further, in the case of FIG. 6 (x = 0.2R and B _E / B _E0 = 1 / e) and FIG. 7 (x = 0.5R and B _E / B _E0 = 1 / e), Varying the molten steel flow rate in the nozzle, the flow velocity distribution in the x direction at each molten steel flow rate is calculated, the sensor signal index is calculated according to the calculated flow velocity distribution, and the integrated value (sensor integrated signal index) of the sensor signal index is calculated. Calculated. When calculating the sensor signal index, the same value was used as the reference sensor signal intensity under all conditions. As shown in FIG. 8, the relationship between the molten steel flow rate (relative ratio) and the sensor integrated signal index is in a linear relationship passing through the origin, so that it is understood that the molten steel flow rate can be measured by the sensor integrated signal index. .

  The molten steel accommodated in the tundish flows out from the bottom of the tundish and is supplied into the molten steel in the mold via the immersion nozzle. In adjusting the amount of molten steel supplied into the mold, there are cases where a stopper is used and a sliding nozzle is used. Here, the case where a sliding nozzle is used will be described with reference to FIGS. The tundish bottom portion 13 is provided with an upper nozzle 9 for allowing molten steel to flow out, and a sliding nozzle 10 is disposed below the upper nozzle 9 and an immersion nozzle 12 is disposed below the sliding nozzle 10. Here, the assembly of the upper nozzle 9, the sliding nozzle 10, and the immersion nozzle 12 is collectively referred to as an injection nozzle 8. The sliding nozzle 10 has a plurality of sliding nozzle plates 11. In the example shown in FIGS. 9 and 10, the sliding nozzle 10 is provided with three sliding nozzle plates 11 including an upper plate 11a, a center plate 11b, and a lower plate 11c. Each plate has a molten steel passage, and the upper plate 11a and the lower plate 11c are fixed and the center plate 11b is slid to adjust the position of the molten steel passage of the three plates. The amount of molten steel injection is adjusted by changing the area of 50.

  The molten steel flow 6 in the injection nozzle 8 may be in a state where the molten steel is filled in the injection nozzle (full flow 48), while the space in the injection nozzle is not filled with the molten steel, and is discrete. In some cases, the molten steel falls into a state (non-full flow 49). In the injection nozzle 8 having the sliding nozzle 10, as shown in FIG. 10, there is a seam between the upper nozzle 9 of the tundish bottom 13 and the injection nozzle discharge hole 47, and in particular, the sliding nozzle 10 has a plurality of seams. From the joint portion, air or an inert gas sprayed around the joint portion flows into the injection nozzle. Therefore, an unfilled flow 49 is continuously formed in the injection nozzle below the sliding nozzle 10 during continuous casting. On the other hand, in the upper nozzle 9 above the sliding nozzle 10, there is no unfilled flow, and a full flow 48 is formed as shown in FIG.

  In the present invention, when the molten steel flow 6 is the non-full flow 49 in the portion of the injection nozzle 8 where the molten steel flow rate is measured, the measurement accuracy becomes insufficient. Therefore, in order to improve the measurement accuracy, It is preferable to perform flow measurement at the part. And as mentioned above, since the full flow 48 is formed about the molten steel flow path in the upper nozzle 9 above the sliding nozzle 10, in the present invention, the molten steel flow formed in the molten steel flow path 5 in the upper nozzle 9. The flow rate of molten steel was to be measured. Thereby, the position where the magnetic field is excited by the exciting coil 2 also becomes the full flow 48, and the molten steel flow rate measurement of the present invention can be performed with sufficient accuracy. In this case, it is necessary not to blow gas into the upper nozzle. Gas blowing may be performed below the sliding nozzle 10.

In the molten steel flow rate measurement according to the present invention, it is preferable that the molten steel flow 6 in as many portions as possible in the cross section of the molten steel flow path 5 of the nozzle is the target of flow rate measurement. Therefore, preferable measurement conditions were examined in relation to the shape of the molten steel flow channel of the nozzle. In the above-described examination, the molten steel flow path is circular with a radius R, but the actual molten steel flow path is not necessarily circular. Therefore, it was decided to define preferable conditions including the case where the cross section of the molten steel channel is not circular.
First, the width direction 60 of the nozzle 4 (horizontal direction perpendicular to the excitation nozzle central axis 51) will be considered. As shown in FIG. 1A, W is half of the inner diameter 60 in the width direction 60 of the nozzle 4 at the position of the exciting coil 2 (the horizontal direction perpendicular to the central axis 51 of the exciting coil as described above). If the molten steel channel 5 is a circle having a radius R, W = R. When the diameter of the exciting coil 2 is D,
D ≧ 2W (1)
Is preferable. The magnetic field excited by the excitation coil 2 is formed with a width wider than at least the excitation coil diameter D. Therefore, when the expression (1) is satisfied, excitation is performed over the entire area of the inner radius W of the nozzle 4 in the coil width direction. Since it receives a magnetic field and the molten steel flow of the whole width direction becomes the object of a flow velocity measurement, it is preferable.

  Next, the excitation magnetic field direction (depth direction 61) of the nozzle 4 will be examined. Let H be the inner radius of the nozzle in the depth direction 61 at the exciting coil position. If the molten steel channel 5 is a circle having a radius R, H = R. Similarly to the above, the depth direction 61 distance x in the molten steel flow path 5 is set to x = 0 on the inner wall 19 near the exciting coil 2, x = 2H = 2R on the inner wall 19 far from the exciting coil, and the molten steel flow path 5. The center position in the depth direction 61 is set to x = H = R (see FIGS. 1 and 3).

Due to the distribution of the lines of magnetic force outside the exciting coil 2, the intensity of the magnetic field excited at the position where the nozzle is disposed becomes weaker as the distance from the exciting coil 2 increases. When the strength of the magnetic field is expressed by the distance x in the state where the molten steel is not circulating in the nozzle, the strength of the magnetic field ∝exp (−ax) (2a)
It can be expressed as. a is a constant. The value of the constant a is determined by the inner diameter, the outer shape, the number of turns, the distance from the coil center and the like of the exciting coil 2, and can be obtained by approximating the magnetic field analysis result and the magnetic field measurement result with an exponential function.

In a situation where molten steel exists in the molten steel flow path 5 of the nozzle 4, the excited alternating magnetic field is attenuated in the molten steel, and the degree of attenuation at the distance x depends on the skin depth δ exp (−x / δ) (2b )
It is represented by

In summary, the magnitude of the excitation magnetic field _BE at a position x from the inner wall 19 of the nozzle 4 can be expressed as follows, assuming that it is proportional to the product of the two factors.
B _E ∝exp (−ax) × exp (−x / δ)
= Exp (-(a + 1 / δ) x) (3)
Where the skin depth δ is
δ = √ (1 / (πσμf)) (4)
It is represented by σ: electrical conductivity, μ: permeability of vacuum, f: frequency of exciting magnetic field.

To evaluate the molten steel flow in the nozzle 4 as accurately as possible is, x = 0.2H, i.e. the magnitude of the excitation magnetic field B _E of 0.2H position from the inner wall 19 of the nozzle 4 in the depth direction 61, x = 0 Is preferably larger than 1 / e of the magnitude of the excitation magnetic field B _E0 at (e is the base of the natural logarithm). And in order to ensure such a condition, from said Formula (3) and Formula (4),
(a + 1 / δ) (0.2H) ≦ 1 (5)
Then, by substituting δ in equation (4) into this equation and solving for frequency f,
f ≦ (1-0.2aH) ² /(0.04πσμH ² ) (2)
Is obtained. That is, by appropriately selecting the excitation frequency f and the constant a indicating the magnetic field distribution of the excitation coil so as to satisfy the above expression (2), the inner radius H of the inner diameter H of the nozzle 4 in the depth direction 61 at the position of the excitation coil 2 is 0.2. It is preferable because detection can be performed with sufficient accuracy including the excitation magnetic field _BE at the double position.

The induced current J _V flows based on the exciting magnetic field _BE attenuated in the depth direction 61 and the molten steel flow. Induced current J _V induced magnetic field B _V by is also attenuated in the molten steel, about attenuation in the molten steel of the distance x is also exp (-x / δ) (6 )
It is represented by As described above, by selecting the conditions that ensure the excitation magnetic field B _E to the depth of 0.2H in the depth direction of the molten steel flow path, the molten steel up to the depth of 0.2H is also detected for the induced magnetic field B _V. It is possible to ensure sufficient strength for detecting the flow velocity.

  As described above, by determining the excitation frequency f so as to satisfy the above expression (2), an induction magnetic field caused by the molten steel flow 6 up to a depth of 0.2H in the depth direction 61 of the nozzle 4 at the excitation coil position is detected. can do. Therefore, when the molten steel flow velocity is to be detected as much as possible in the cross section of the molten steel flow path 5 of the nozzle 4, as shown in FIGS. 9 and 10, the exciting coil 2 for exciting the alternating magnetic field and the magnetic field or time of the magnetic field Two pairs of detectors 3 for detecting changes are installed, each set is installed relative to the nozzle (upper nozzle 9), and the flow rate of molten steel in the immersion nozzle is calculated based on the two sets of detection results. This is preferable.

  Note that when the flow velocity measurement is performed with the molten steel flow in the upper nozzle 9 disposed above the sliding nozzle 10, the flow velocity in the molten steel passage may not be rotationally symmetric with respect to the center of the molten steel passage. That is, when the opening 50 is formed only in a part of the cross section of the molten steel passage of the upper nozzle due to the overlap of the molten steel passage ports of the sliding nozzle plate 11, the opening is formed in the molten steel flow path of the upper nozzle 9. It is conceivable that the flow velocity on the side on which 50 is formed increases and the flow velocity decreases on the opposite side of the position. Therefore, in the present invention, as shown in FIG. 9, it is preferable that the sliding nozzle sliding direction 63 is arranged at an angle of 90 degrees with the central axis 51 of the exciting coil 2 with the central axis of the upper nozzle 9 as the rotation axis. . Thereby, the non-uniformity of the molten steel flow velocity in the upper nozzle is eliminated as much as possible, and a value close to the average molten steel flow velocity in the upper nozzle can be obtained. When arranging two pairs of excitation coils and detectors, it is preferable to arrange them so as to sandwich the upper nozzle.

  By applying the molten steel flow rate measuring method described above, a molten steel flow rate measuring device 1 in an immersion nozzle for supplying molten steel from a continuous casting tundish into a mold, the sliding nozzle 10 is provided above the immersion nozzle 12, and further There is an upper nozzle 9 at the top, an exciting coil 2 that excites an alternating magnetic field that intersects the molten steel flow in the upper nozzle 9, and a magnetic field in a direction parallel to the flow direction of the molten steel flow or a time variation of the magnetic field at one or more locations. It can be set as the molten steel flow volume measuring apparatus 1 in an immersion nozzle characterized by having the detector 3 detected in a location, and the calculating device 14 which calculates the molten steel flow volume in an immersion nozzle based on the detected signal.

  As the exciting coil 2 and the detection coil 3a, in addition to an air core type in which a coil is wound around a ceramic bobbin, a magnetic core type in which a coil is wound around a magnetic body such as ferrite may be used. Further, as the detector 3 for detecting the induction magnetic field or the time change of the magnetic field, another magnetic sensor such as a Hall element may be used instead of the detection coil 3a. Further, in addition to a method of processing with software on a computer as the arithmetic device 14, processing may be performed using hardware (for example, an appropriate analog circuit) instead of software. In addition to using a lock-in amplifier to detect the signal from each detection coil, it may not be a lock-in amplifier as long as it can detect the phase component desired for each signal, for example, a synchronous detector instead. May be used.

  The continuous casting tundish, in which the molten steel flow rate measuring device 1 in the immersion nozzle of the present invention is installed on the injection nozzle 8 connected to the tundish 22, is continuously cast while measuring the molten steel flow rate passing through the injection nozzle 8. Can be performed.

  Next, molten steel for continuous casting is supplied by one ladle 21 and one tundish 22 to continuously cast a multi-layer continuous cast slab in which the alloy element concentration of the slab surface layer portion is different from the inside. In the casting method, an invention to which the molten steel flow measuring device 1 in the immersion nozzle of the present invention is applied will be described with reference to FIG.

First, the DC magnetic field generator 28 is arranged at a predetermined position below the meniscus 37 in the mold 23 to form a DC magnetic field band 34. In the DC magnetic field zone 34, a DC magnetic field in which the magnetic lines of force are directed in the thickness direction of the slab is applied, and the magnetic flux density is substantially uniform in the mold width direction. By forming such a DC magnetic field zone 34, an electromagnetic brake is applied to the molten steel attempting to pass through the DC magnetic field zone 34, and an upper molten steel pool 35 above the DC magnetic field zone 34 and a lower molten steel pool 36 below the It will be effectively blocked. The solidified shell solidified in the upper molten steel pool 35 forms the surface layer portion 44 of the slab, and the solidified shell 43 solidified in the lower molten steel pool forms the inner layer portion 45 of the slab. The thickness d of the solidified shell 43 in the DC magnetic field zone 34 corresponds to the thickness of the surface layer portion of the slab. Accordingly, the height h from the meniscus at which the DC magnetic field band 34 is arranged is determined based on the target surface layer thickness d, the solidification coefficient K in the mold, and the casting speed V _C.

  In addition, two immersion nozzles (25, 26) are installed to supply molten steel above and below the DC magnetic field zone 34, and the molten steel is supplied from each immersion nozzle by the amount of molten steel solidified in each molten steel pool. Thus, slabs having different component compositions of the surface layer and the inner layer can be cast. The magnetic flux density of the DC magnetic field zone 34 is selected so that the interchange of molten steel between the upper molten steel pool 35 and the lower molten steel pool 36 can be minimized. If the magnetic flux density of the DC magnetic field zone 34 is 0.3 T (Tesla) or more, the replacement of molten steel can be sufficiently suppressed.

  As shown in FIG. 11, the tundish 22 is divided into a plurality of regions by the tundish weir 24 having the opening 30, that is, the first region 31 that receives the first molten steel 41 from the ladle, and the first molten steel 41 has a wire or the like. Is divided into two regions, the second region 32, in which a predetermined element or an alloy thereof is added to adjust the components. In the example shown in FIG. 11, the ladle pouring flow 33 position and the inner layer molten steel immersion nozzle 25 are arranged in the first region 31, and the surface layer molten steel immersion nozzle 26 is arranged in the second region 32. The first molten steel 41 is injected into the lower molten steel pool 36 from the inner layer molten steel immersion nozzle 25. The second molten steel 42 is injected into the upper molten steel pool 35 from the surface molten steel immersion nozzle 26.

  By doing in this way, while the molten steel flow from the ladle injection flow 33 to the immersion nozzle 25 for inner-layer molten steel is formed in the 1st area | region 31 in a tundish, it is the 2nd area | region divided by the tundish dam 24 A predetermined element or alloy is continuously added to 32 by a wire or the like by means of a component addition device 27 to adjust the contained components, and the second molten steel 42 is produced. As a result, two types of molten steel: the first molten steel 41 and the second molten steel 42 can be held in one tundish.

In the present invention, in the example schematically shown in FIG. 11, the strand is divided into two of an upper molten steel pool 35 and a lower molten steel pool 36 by a DC magnetic field zone 34 that is formed over the entire mold width. The second molten steel 42 is injected from the surface layer molten steel immersion nozzle 26, and the first molten steel 41 is injected into the lower molten steel pool 36 from the inner layer molten steel immersion nozzle 25. Let Q _{1 be} the amount of molten steel supplied from the inner layer molten steel immersion nozzle 25 to the lower molten steel pool 36, and Q ₂ be the amount of molten steel supplied from the surface layer molten steel immersion nozzle 26 to the upper molten steel pool 35. Total molten steel amount Q is Q = Q ₁ + Q ₂
It is.

In the present invention, the molten steel flow rate is controlled by using the molten steel flow rate measuring device 1 of the present invention for _{one of} the molten steel amount Q ₁ and the molten steel amount Q ₂ . Here, first, the case where the molten steel flow rate control is performed using the molten steel flow rate measuring device 1 of the present invention for the molten steel amount Q ₂ of the second molten steel supplied to the upper molten steel pool 35 will be described.

At the position of the DC magnetic field zone 34, a solidified shell (upper molten steel pool solidified portion) formed by solidifying the molten steel of the first molten steel pool is formed on the surface side of the slab. Let S ₂ be the cross-sectional area of the solidified shell at the DC magnetic field band position. The solidified shell cross-sectional area S ₂ becomes the surface layer portion 44 area S ₂ of the cast after cast piece. Surface portion area S ₂ other portions of the slab surface area of the inner layer portion 45 area S _1, the value obtained by adding the S ₁ and S ₂ is the cast strip cross-sectional area.

The solidification coefficient K (mm / min ^0.5 ) in the mold in the continuous casting apparatus to be applied is confirmed in advance. By determining the height h from the meniscus 37 to the DC magnetic field zone 34 and the casting speed V _C , the solidified shell thickness d in the DC magnetic field zone 34 is d = K√ (h / V _C )
It is obtained as Using the obtained solidified shell thickness d in the DC magnetic field band, the solidified shell cross-sectional area S ₂ in the DC magnetic field band is determined, and the aforementioned S ₁ is determined by the difference from the slab cross-sectional area.
G ₂ = ρ ₂ S ₂ V _C
Since G ₂ is determined by
Q ₂ = G ₂
The molten steel amount Q ₂ from the immersion nozzle 26 for surface molten steel may be determined so that ρ ₂ is the density of the second molten steel 42. The molten steel flow measuring device 1 of the present invention installed in a surface layer of molten steel for immersion nozzle 26 top of on the nozzle 9, the molten steel flow actual value measured is the flow rate controlled so as to coincide with the amount of molten steel Q _2.

In addition, in the adjustment of the flow rate of the inner layer molten steel immersion nozzle 25 for supplying the first molten steel 41 whose components have been adjusted to the lower molten steel pool 36, the molten metal surface level measured by the molten metal surface level meter 46 is constant. The molten steel amount Q ₁ is controlled. As a result, the lower molten steel pool 36 in the mold balances the amount of molten steel supplied (Q ₁ ) and the transport amount per hour (G ₁ ) discharged as a solidified shell, and the upper molten steel pool 35 supplies The amount of molten steel (Q ₂ ) and the transport amount per hour (G ₂ ) discharged as a solidified shell are balanced. Therefore, there is no molten steel flow that mixes through the direct current magnetic field zone, so that the interface between the upper molten steel pool 35 and the lower molten steel pool 36 in FIG. 11 can be stably maintained. The interface between the upper molten steel pool 35 and the lower molten steel pool 36 determined by the balance between Q ₁ and Q ₂ is controlled within the range of the DC magnetic field zone.

Or as molten steel supply amount control method into the mold, the molten steel flow measuring device 1 of the present invention installed in a nozzle on the inner molten steel for immersion nozzle 25 upper, lower molten steel quantity to Q ₁ from the inner layer molten steel for immersion nozzle 25 The molten steel flow rate control is performed so that the molten steel pool solidification amount G ₁ is obtained, and the molten steel flow rate control of the submerged nozzle 26 for surface layer molten steel may be controlled so that the molten metal level in the mold becomes constant. Further, unlike the example shown in FIG. 11, the ladle pouring flow 33 position and the surface layer molten steel immersion nozzle 26 are disposed in the first region 31 of the tundish 22, and the inner region molten steel immersion nozzle 25 is disposed in the second region 32. It is good also as a form to arrange.

[Example 1]
The present invention was applied to casting a slab having a width of 1200 mm and a thickness of 250 mm using a slab continuous casting apparatus. As shown in FIGS. 9 and 10, the tundish bottom 13 has one injection nozzle 8 for each strand, and the molten steel in the tundish is poured into the mold through the injection nozzle 8. The injection nozzle 8 has an upper nozzle 9, a sliding nozzle 10, and an immersion nozzle 12 with an inner diameter of 120 mmΦ. The upper nozzle 9 (inner diameter 120 mm (inner radius R = 60 mm), outer diameter 150 mm) is connected to the tundish bottom 13 and immersed. The nozzle 12 is immersed in the molten steel in the mold. The sliding nozzle 10 has three sliding nozzle plates 11 (upper plate 11a, center plate 11b, and lower plate 11c), and controls the opening degree of the opening 50 by sliding of the center plate 11b of the sliding nozzle plate 11. To adjust the flow rate of molten steel.

As shown in FIG. 9, the molten steel flow rate measuring apparatus 1 is an exciting coil 2 in which a ceramic cylinder having an inner diameter of 120 mm is wound with 1.3 turns of a conductor of 1.3 mmΦ, and an excitation coil 2 is formed on the front surface of the ceramic cylinder of 10 mmΦ and a conductor of 0.1 mmΦ. The sensor coil 3a was wound with 1200 turns, and the set of coils was housed in a cylindrical case 7 made of stainless steel as a sensor. In addition, as shown in FIG. 12, a heat insulating material 20 is provided on the inner surface of the case 7 on the front and side surfaces of the sensor to completely block overheating due to radiant heat from the molten steel. Then, dry air is blown at a discharge pressure of 5 kg / cm ² to form an air flow 39 passing through the cylinder bottom of the exciting coil 2 and passing through the outer surface of the detecting coil 3a and exciting coil 2, thereby preventing overheating of the molten steel flow measuring device 1 did.

  Two sets of the molten steel flow rate measuring device 1 housed in the case 7 are prepared, and are arranged in a space between the tundish bottom 13 and the sliding nozzle 10 as shown in FIGS. Installed to face each other. The sliding nozzle plate 11 is arranged so that the sliding direction 63 is orthogonal to the direction of the central axis 51 of the exciting coil. At that time, a stainless steel cylindrical case 7 containing a sensor inside faces a position 30 mm away from the surface of the upper nozzle 9 while facing the upper nozzle.

  As shown in FIG. 3, a waveform generator 15, a power amplifier 16, a lock-in amplifier 17, and a computer 18 are connected to the molten steel flow rate measuring device 1. A 3 Hz alternating current (4 A) was applied to the exciting coil 2 using a power amplifier 16 (constant current amplifier), and an alternating magnetic field was applied perpendicularly to the nozzle surface. The voltage signal of the detection coil 3 a was subjected to noise removal through a 5 Hz low-pass filter, and only a frequency component of 3 Hz was detected using the lock-in amplifier 17. Note that the coil shape and frequency were set so that the excitation magnetic field penetrates the upper nozzle inner radius of 60 mm to a position 30 mm from the inner wall.

  During continuous casting, the molten steel injection from the ladle to the tundish is temporarily interrupted, the molten steel is injected into the mold from the injection nozzle, and the tundish mass at that time is measured. Was measured. The time change of the tundish mass is the actual molten steel flow rate. First, the correspondence between the molten steel flow rate into the mold and the signal from the molten steel flow rate measuring device 1 was measured at least once, and the signal from the molten steel flow rate measuring device was converted into the molten steel flow rate to obtain a molten steel flow rate index. Thereafter, the flow rate of the molten steel into the mold was variously changed, and the correspondence with the molten steel flow rate index was evaluated. As a result, as shown in FIG. 13, it was found that the signal (molten steel flow index) obtained using the molten steel flow rate measuring device 1 of the present invention showed a very good agreement with the molten steel flow rate obtained from the tundish mass change. . The temperature of the thermocouple provided on the front surface of the sensor was about 50 ° C. and was stable during the experiment. From the above, it was found that stable flow rate measurement can be performed without contact by using this method.

[Example 2]
In a continuous casting method in which molten steel for continuous casting is supplied by one ladle 21 and one tundish 22, and a multi-layer continuous cast slab having a different alloy element concentration in the slab surface layer compared to the inside is cast. The present invention was applied. This will be described with reference to FIG.
Immersion nozzles having different lengths (immersion nozzle 25 for inner layer molten steel and immersion nozzle 26 for surface layer molten steel) were arranged on the bottom surface of the tundish where two types of molten steel were held. The immersion nozzle for surface layer molten steel 26 for supplying the surface layer molten steel was connected to the tundish bottom portion 13 via the upper nozzle 9 and the sliding nozzle 10. Two sets of the molten steel flow rate measuring device 1 accommodated in the case 7 are prepared and arranged in a space between the sliding nozzle 10 connected to the surface layer molten steel immersion nozzle 26 and the tundish bottom 13 as shown in FIGS. And it installed so that the upper nozzle 9 might be opposed. The sliding nozzle plate 11 is arranged so that the sliding direction 63 is orthogonal to the direction of the central axis 51 of the exciting coil. As a flow rate adjusting mechanism of the inner layer molten steel immersion nozzle 25, either a method using a sliding nozzle or a method using a stopper may be adopted.

  The immersion nozzle for surface layer molten steel 26 is placed on the upper part (upper molten steel pool 35) of the molten steel pool in the mold divided by the electromagnetic brake (DC magnetic field generator 28), and the immersion nozzle 25 for inner layer molten steel is electromagnetic brake (DC magnetic field generator 28). It set so that molten steel might be discharged to the lower pool (lower molten steel pool 36) divided by (1).

  A tundish weir 24 is provided in the tundish 22, a first molten steel 41 having a predetermined composition is formed in the first region 31 in the tundish, and a second molten steel 42 having a composition different from that of the first molten steel is formed in the second region 32. Formed. The first molten steel 41 was supplied from the inner layer molten steel immersion nozzle 25 to the lower molten steel pool 36, and the second molten steel 42 was supplied from the surface layer molten steel immersion nozzle 26 to the upper molten steel pool 35. When supplying molten steel to the upper part (upper molten steel pool 35) of the molten steel pool divided by the electromagnetic brake (DC magnetic field generator 28), the inside of the immersion nozzle 26 for surface molten steel is used by using the molten steel flow measuring device 1 of the present invention. While measuring the flow rate of the molten steel passing therethrough, the molten steel flow rate was controlled by the sliding nozzle 10 so that the measured flow rate was the same as the amount of molten steel consumed by solidification in the upper molten steel pool 35. The flow rate of the molten steel passing through the inner layer molten steel immersion nozzle 25 was controlled using a molten metal level meter 46 provided in the mold so that the molten metal level was constant. As a result, since the amount of molten steel from each immersion nozzle could be controlled to be a predetermined amount during casting, the boundary position between the upper molten steel pool 35 and the lower molten steel pool 36 is always in the DC magnetic field zone 34. Could be kept within range. By applying a magnetic field having a magnetic flux density necessary for suppressing mixing as a magnetic flux density of the electromagnetic brake, a slab having a surface layer and an inner layer clearly separated was obtained.

DESCRIPTION OF SYMBOLS 1 Molten steel flow measuring device 2 Excitation coil 3 Detector 3a Detection coil 4 Nozzle 5 Molten steel flow path 6 Molten steel flow 7 Case 8 Injection nozzle 9 Upper nozzle 10 Sliding nozzle 11 Sliding nozzle plate 11a Upper plate 11b Center plate 11c Lower plate 12 Immersion nozzle 13 Tundish bottom 14 Computing device 15 Waveform generator 16 Power amplifier 17 Lock-in amplifier 18 Computer 19 Inner wall 20 Insulating material B _E AC magnetic field B _V induction magnetic field 21 Ladle 22 Tundish 23 Mold 24 Tundish weir 25 Immersion for inner layer molten steel Nozzle 26 Surface layer molten steel immersion nozzle 27 Component addition device 28 DC magnetic field generator 29 Electromagnetic stirrer 30 Opening 31 First region 32 Second region 33 Ladle pouring flow 34 DC magnetic field zone 35 Upper molten steel pool 36 Lower molten steel pool 37 Menis Scan (molten metal surface)
38 Air Blowing Port 39 Air Flow 40 Molten Steel 41 First Molten Steel 42 Second Molten Steel 43 Solidified Shell 44 Surface Layer 45 Inner Layer 46 Molten Surface Level Meter 47 Discharge Hole 48 Filled Flow 49 Unfilled Flow 50 Opening 51 Central Axis of Excitation Coil 52 Detection coil central axis 60 Width direction 61 Depth direction 62 Height direction 63 Sliding direction

Claims (9)

  A method for measuring a molten steel flow rate in an immersion nozzle for supplying molten steel into a mold from a tundish of continuous casting, comprising a sliding nozzle above the immersion nozzle and an upper nozzle above the immersion nozzle, and the molten steel flow in the upper nozzle The magnetic field in the direction parallel to the flow direction of the molten steel flow or the time variation of the magnetic field is detected at one or more locations, and the molten steel flow rate in the immersion nozzle is calculated based on the detected signal. A method for measuring a flow rate of molten steel in an immersion nozzle. 2. The immersion nozzle according to claim 1, wherein the excitation of the alternating magnetic field is performed by an exciting coil, and the diameter D of the exciting coil and the frequency f of the alternating magnetic field to be excited are determined by the following equations (1) and (2). Method for measuring the flow rate of molten steel inside.
D ≧ 2W (1)
f ≦ (1-0.2aH) ² /(0.04πμσH ² ) (2)
Where W: inner radius in the coil width direction of the upper nozzle at the exciting coil position (m), H: inner radius in the exciting magnetic field direction of the upper nozzle at the exciting coil position (m), μ: permeability of vacuum (N / A ² ) , Σ: electric conductivity of molten steel (S / m), a: constant determined by exciting magnetic field distribution in upper nozzle exciting magnetic field when molten steel does not pass (m ⁻¹ )   Two pairs of an exciting coil for exciting the alternating magnetic field and a detector for detecting the magnetic field or the time change of the magnetic field are installed, and each pair is installed relative to the upper nozzle, and based on the two sets of detection results. The molten steel flow rate in the immersion nozzle according to claim 1 or 2, wherein the molten steel flow rate in the immersion nozzle is calculated.   An apparatus for measuring a flow rate of molten steel in an immersion nozzle for supplying molten steel from a continuous casting tundish into a mold, comprising a sliding nozzle above the immersion nozzle and an upper nozzle above the immersion nozzle, and the molten steel flow in the upper nozzle An excitation coil that excites an alternating magnetic field that intersects the flow direction of the molten steel, a detector that detects a magnetic field in a direction parallel to the flow direction of the molten steel flow, or a time change of the magnetic field at one or more locations, and an immersion nozzle based on the detected signal An apparatus for measuring a molten steel flow rate in a submerged nozzle, comprising an arithmetic unit for calculating a molten steel flow rate of the submerged nozzle. The apparatus for measuring the flow rate of molten steel in an immersion nozzle according to claim 4, wherein the diameter D of the exciting coil and the frequency f of the alternating magnetic field to be excited are determined by the following equations (1) and (2).
D ≧ 2W (1)
f ≦ (1-0.2aH) ² /(0.04πμσH ² ) (2)
Where W: inner radius in the coil width direction of the upper nozzle at the exciting coil position (m), H: inner radius in the exciting magnetic field direction of the upper nozzle at the exciting coil position (m), μ: permeability of vacuum (N / A ² ) , Σ: electric conductivity of molten steel (S / m), a: constant determined by exciting magnetic field distribution in upper nozzle exciting magnetic field when molten steel does not pass (m ⁻¹ )   Two pairs of the excitation coil and detector are installed, each pair is installed relative to the upper nozzle, and the sliding nozzle sliding direction and the excitation coil axial direction are arranged so as to be orthogonal to each other. 6. The apparatus for measuring the flow rate of molten steel in an immersion nozzle according to claim 4, wherein the apparatus calculates the flow rate of molten steel in the immersion nozzle based on two sets of detection results.   A tundish for continuous casting, comprising the upper nozzle connected to the tundish, and the apparatus for measuring a flow rate of molten steel in an immersion nozzle according to any one of claims 4 to 6.   Two immersion nozzles are connected to the tundish, and the molten steel flow rate measuring device in the immersion nozzle according to any one of claims 4 to 6 is installed in at least one immersion nozzle. Tundish for continuous casting characterized by A tundish weir having an opening in the tundish is provided, the ladle molten steel injection side divided by the tundish weir is the first region, the opposite side is the second region, and the first region and the second region side Holds molten steel of different component composition, arranges an immersion nozzle for inner layer molten steel at the bottom of one region of the tundish, and an immersion nozzle for molten steel at the bottom of the other region,
A DC magnetic field generator that applies a DC magnetic field in the thickness direction over the entire width in the mold width direction is arranged, and the upper molten steel pool and the lower molten steel pool at the upper part of the strand across the DC magnetic field zone formed by the DC magnetic field generator. And supplying molten steel from the surface layer molten steel immersion nozzle to the upper molten steel pool, supplying molten steel from the inner layer molten steel immersion nozzle to the lower molten steel pool,
An apparatus for measuring the flow rate of molten steel in an immersion nozzle according to any one of claims 4 to 6, is provided in an injection nozzle having at least one of an immersion nozzle for surface layer molten steel and an immersion nozzle for inner layer molten steel,
When supplying the amount of molten steel consumed by solidification in each molten steel pool from each of the two immersion nozzles into the mold, the immersion nozzle supplies molten steel in the immersion nozzle on the side provided with the molten steel flow measuring device. The molten steel flow rate is adjusted so that the molten steel flow rate is commensurate with the amount of molten steel consumed by solidification, and the molten steel flow rate is controlled so that the mold surface level in the mold is constant in the other immersion nozzle. A continuous casting method for multilayer slabs.

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