JPH06589A - Boundary layer level measurement method and boundary layer level control method of molten metal in continuous casting of multi-layer slab - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a method for measuring the level of a molten metal boundary layer injected into a mold and a method for controlling the level in continuous casting of a multi-layer slab. [Structure] Two bubbler tubes 6a, 6b are inserted so that their tips are located in the surface molten steel above and below the boundary layer 3 and in the inner molten steel, and these two bubbler tubes are foamed to form This is a method for measuring the boundary layer level of molten metal in which the back pressure at a position is measured and the boundary layer level is obtained based on the measured back pressure value. [Effect] Even if there is a change in the flow of molten metal in the upper and lower layers at the start of casting, the boundary layer level can be returned to the normal position and settled in a short time, avoiding the problem of molten metal mixing, and reducing the boundary layer level. The accuracy of the surface shell that is stably formed is also improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boundary layer-level measuring method and a boundary layer-level controlling method for separating a molten metal injected into a mold into upper and lower parts in continuous casting of multi-layer cast pieces.

[0002]

2. Description of the Related Art When a molten metal is supplied to a continuous casting mold to cast a multi-layer slab, a method of controlling the amount of the molten metal injected into the mold is, for example, a multi-layer slab shown in the schematic view of FIG. There is a process control method. This employs a method of casting a multi-layer cast product by a two-nozzle method using a load cell.

In FIG. 5, separately manufactured molten steels having different compositions are injected into the mold 30 from the surface layer tundish 31a and the inner layer tundish 31b through the surface layer injection nozzle 32a and the inner layer injection nozzle 32b, respectively.

Each of the injected molten steels receives a molten steel braking force by the boundary layer 34 formed by the electromagnetic brake 33, and is separated into upper and lower parts in the mold to start solidification. The molten metal level 35 in the mold 30 is a molten metal surface in contact with the atmosphere in normal continuous casting, and the boundary layer 34 corresponds to the separation position between the surface layer and the inner layer, that is, the solidification start point of the inner layer.

Therefore, the thickness of the surface layer shell 36a of the slab is
It is determined by the solidified shell thickness that grows between these two layers, the molten steel level 35 and the boundary layer 34. Therefore, in order to obtain a multi-layer cast product having a surface layer with a uniform thickness, it is necessary to accurately control the injection amount from each of the tundishes 31a and 31b. In the figure, 36b indicates the generation of the inner layer shell.

Each of the above tundish 31a, 3
In the conventional method as a technique for controlling the injection amount from 1b,
First, the molten metal level L1 is detected by the molten metal level gauge 41, which is input to the molten metal level controller LC, and compared with the molten metal level set value L1r to output the flow rate set value Q2r.

FC1 is a surface layer pouring amount controller, FC2 is an inner layer pouring amount controller, and the flow rate set value Q2r is shown in the inner layer pouring amount controller FC2 and the surface layer pouring amount controller FC1.
A constant value is multiplied by the determined surface layer flow rate / inner layer flow rate ratio α and is input as the flow rate set value Q1r.

At the same time, the load cells 4 attached to the surface tundish 31a and the inner tundish 31b.
Based on the weight of the molten metal in the tundish detected by 2a and 42b, this is input into the flow rate calculators 43a and 43b, and the flow rates Q1 and Q of the tundishes 31a and 31b are input.
2 is calculated, and this value is used as the surface layer pouring amount controller FC1
And the inner layer pouring amount controller FC2.

In the surface layer pouring amount controller FC1, the flow rate set value Q
1r and the flow rate Q1, and in the inner layer pouring amount controller FC2, the flow rate set value Q2r and the flow rate Q2 are compared, and both are compared to drive the stopper drive devices 44a and 44b to open and close the stoppers 45a and 45b, respectively. Above flow rate Q
1 and Q2 are adjusted so as to match the flow rate setting values Q1r and Q2r.

[0010]

By the way, in the above injection amount control method, when there is a large change in the flow of the molten metal in the upper and lower layers, such as when the casting is started or when the casting speed and the injection amount are changed during casting. The boundary layer level fluctuates up and down.

This boundary layer is a separation position between the surface layer and the inner layer and corresponds to the solidification start point of the inner layer. When the boundary layer changes, the solidification shell thickness of the surface layer changes with the change of the solidification start point of the inner layer. However, when the limit of the molten steel braking force due to the boundary layer is exceeded, the molten metal in the surface layer and the molten metal in the inner layer are mixed together.

The boundary layer 34 is preferably located at the center of the electromagnetic brake 33 for effective separation of the surface layer and the inner layer. Therefore, it is necessary to stabilize the boundary layer as soon as possible at the start of casting, etc., and control it so that the boundary layer level does not change during operation.

However, in practice, it is difficult to accurately measure the boundary layer level position inside the molten metal injected into the mold. Therefore, the conventional control system controls the molten metal level. However, it has not been possible to accurately measure the boundary layer level and continuously control it.

The present invention has solved the above-mentioned problems, and in the continuous casting of a multi-layer slab, the boundary layer level for separating the molten metal in the mold into upper and lower parts can be quickly and accurately measured, and the boundary layer level can be stabilized. A continuous control method is provided.

[0015]

The measuring method of the present invention is to inject molten metal into the mold from the surface and inner layer tundish through each injection nozzle, and apply a braking force to each injected molten metal by an electromagnetic brake. In continuous casting, in which the surface and inner layer metals are separated vertically by the boundary layer formed in the mold to cast a multi-layer slab, two bubbler pipes are provided in the surface molten steel above and below the boundary layer. Insert it so that it is located in the molten steel, foam the two bubbler tubes, measure the back pressure at each position of each bubbler tube, and use the value of this measured back pressure as the boundary according to the following equation (1). It is a method for measuring a boundary layer level of molten metal in continuous casting of a multi-layer slab, which is characterized by obtaining a layer level.

[0016]

[Equation 2]

However, H1 and H2 position of each bubbler pipe P1 and P2 back pressure of each bubbler pipe ρ1 and ρ2 molten steel densities of surface and inner layers L2 boundary layer level.

The first of the control methods of the present invention is to inject molten metal into the mold from the surface and inner layer tundish through each injection nozzle, and apply a braking force to each injected molten metal by an electromagnetic brake, In the continuous casting equipment that separates the surface and inner layer metal into upper and lower parts by the boundary layer formed in the continuous casting equipment, the surface molten steel flow rate measuring device,
It has an inner layer molten steel flow rate measuring device, a surface / inner layer flow rate ratio adjusting device, a molten metal level meter and a molten metal level adjusting device, and a boundary layer level measuring device and boundary layer level adjusting device for the surface and inner layer tundish. In addition to the level control and the surface / inner layer flow rate control performed by adjusting the stopper or sliding nozzle opening provided, it is possible to automatically adjust the surface / inner layer flow rate ratio so that the boundary layer level matches the target value. It is a boundary layer level control method for molten metal in continuous casting of a multi-layer slab.

In the second control method of the present invention, molten metal is injected into the mold from the surface and inner layer tundish through each injection nozzle, and a braking force is applied to each injected molten metal by an electromagnetic brake. A continuous casting facility that separates the surface and inner layer metal into upper and lower parts by a boundary layer formed in the mold to cast multi-layer slabs, a melt level meter and a melt level controller, and a boundary layer level measuring device and boundary. With a bed level adjusting device, the opening level of a stopper or sliding nozzle provided on the surface or inner layer tundish is controlled so that the molten metal level matches the target value, while the inner layer or surface tundish is controlled. The boundary layer level is adjusted to the target value by adjusting the opening of the stopper or sliding nozzle provided on the The boundary layer level control method of the molten metal in continuous casting of multilayer slab, wherein a Gosuru.

[0020]

[Operation] The boundary layer level measuring method of the present invention will be described in detail below.

FIG. 1 is a sectional view (a) and a schematic view (b) of a continuous casting apparatus for a multi-layer cast piece for explaining the boundary layer level measuring method of the present invention.

In the boundary layer level measuring method using the present casting apparatus, molten steels having different compositions are first prepared separately from the tundish through the surface layer injection nozzle and the inner layer injection nozzle (the injection nozzle is omitted in FIG. 1). Injected into 1.

Each of the injected molten steels receives a molten steel braking force by the boundary layer 3 formed by the electromagnetic brake 2, and is separated into upper and lower parts in the mold to start solidification. The level 4 in the casting mold 1 is the level of the molten metal in contact with the atmosphere in normal continuous casting, and the boundary layer 3 is the separation position between the surface layer and the inner layer.
That is, it corresponds to the solidification start point of the inner layer. 5a
Is a surface layer shell, and 5b is an inner layer shell.

Further, in the present casting apparatus, the two bubbler tubes 6a and 6b are inserted at predetermined positions in the surface molten steel above and below the boundary layer 3 and in the inner molten steel. A pressure reducing valve 7 for supplying an inert gas such as Ar and constant flow rate devices 8a, 8b and pressure transmitters 9a, 9b are attached to the bubbler tube. Reference numeral 10 is an arithmetic unit, and pressure transmitters 9a and 9b
Boundary layer level is calculated by receiving the pressure signal from.

Next, a constant flow rate of an inert gas is fed from the supply side through a pressure reducing valve to foam the two bubbler tubes 6a and 6b, and first, the back pressure at each position of each tube is set by the pressure transmitters 9a and 9b. P1 and P2 are measured. Back pressure P
1 and P2 are represented by the following equations (2) and (3).

[0026]

## EQU00003 ## P1 = .rho.1 (L1-H1) (2)

[0027]

## EQU00004 ## P2 = .rho.1 (L1-L2) +. Rho.2 (L2-H2) (3)

Next, the values of the back pressures P1 and P2 are input to the arithmetic unit 10, and the arithmetic unit 10 calculates the equations (2) and (3) as simultaneous equations, and the solution thereof is the boundary layer level L.
2 is obtained as in (4) below.

[0029]

[Equation 5]

However, in the above formulas (2), (3) and (4), the positions of the bubbler pipes inserted into the H1 and H2 surface layers and the inner layers P1 and P2 The back pressure of each bubbler pipe ρ1 and ρ2 Surface and inner layer molten steel densities L2 It is at the boundary layer level. Here, the values of H1, H2, ρ1 and ρ2 are known, and the values of P1 and P2 are measured values.

As described above, the boundary layer level L2 can be obtained from the equation (4).

[0032]

EXAMPLE A method for controlling a boundary layer level of molten metal in continuous casting of a multi-layer cast piece will be described as an example of the present invention.

FIG. 2 is a diagram showing an example of an apparatus for explaining a boundary layer level control method. This device uses a load cell to measure the pouring amount. In this method, the weights of the inner layer and the surface layer tundish are measured with a load cell, and the amount of molten metal poured into the surface layer is calculated from the time change rate of the weight. The present apparatus is provided with a boundary layer arithmetic unit 10 for transmitting a boundary layer level L2 signal given by the equation (4) calculated from the back pressure of a bubbler tube inserted into the molten metal. .

Molten steels having different compositions, which are separately melted, are supplied from the surface tundish 21a and the inner layer tundish 21b to the surface layer injection nozzle 22a and the inner layer injection nozzle 22, respectively.
It is injected into the mold 20 via b.

Each of the injected molten steels receives a molten steel braking force by the boundary layer 24 formed by the electromagnetic brake 23, and is separated into upper and lower parts in the mold to start solidification. The molten metal level 25 in the mold 20 is the molten metal level in contact with the atmosphere in normal continuous casting, and the boundary layer 24 corresponds to the separation position between the surface layer and the inner layer, that is, the solidification start point of the inner layer.

LC1 is a molten metal level controller, which receives a level signal L1 from the molten metal level. FC1 is a surface layer pouring amount controller, FC2 is an inner layer flow rate controller, LC2 is a boundary layer level controller, and α is a signal instructing a ratio of surface layer flow rate / inner layer flow rate.

The melt level controller LC1 is a melt level meter 2
The flow rate set value Q2r of the inner layer flow rate controller FC2 is output so that the molten metal level signal L1 from 5a matches the set value L1r. At the same time, the flow rate set value Q2r is multiplied by the ratio α in the calculator X, and the resulting Q1r is given as the set value of the surface layer pouring amount controller FC1.

The surface layer pouring amount controller FC1 and the inner layer flow rate controller FC2 are stopper driving devices so that the flow rates Q1 and Q2 calculated by the flow rate calculators 27a and 27b from the weights of the load cells 26a and 26b match the set values Q1r and Q2r, respectively. 28a, 28b are driven to stop 29a, 2
Adjust the opening of 9b.

On the other hand, the boundary layer arithmetic unit 10 outputs the boundary layer level L2 given by the equation (4). The boundary layer level adjuster LC2 adjusts the magnitude of the signal α that commands the surface layer flow rate / inner layer flow rate ratio so that the boundary layer level signal L2 matches the set value L2r.

When the boundary layer level L2 fluctuates in this way, the α value is adjusted by comparing with the set value L2r,
As a result, the opening degree of the stopper 29a is adjusted by the surface layer pouring amount controller FC1 so that the boundary layer 24 sets the set value L2r.
The boundary layer level control is performed by adjusting the amount of molten steel injected from each of the injection nozzles 22a and 22b so as to coincide with.

FIG. 3 shows the actual molten metal level L1 and boundary layer level L2 when the molten metal level set value L1r is changed stepwise at the time of 60 seconds in the apparatus shown in FIG.
Shows the fluctuation of. The molten metal level L1 is settled in a short time when the control by the boundary layer level adjuster LC2 is ON or OFF for the changed level of −238 mm.

However, the boundary layer level L2 is -6 which is the target value.
When the control is OFF for 90 mm, it largely deviates from the target value and returns to the target value due to the self-balancing property of the process, but it takes a long time. On the other hand, when the boundary layer level control is ON, the settling is performed within a short time.

By incorporating the boundary layer level control in this way, it is possible to avoid or minimize the problem that the boundary layer is disengaged from the electromagnetic brake zone and the surface inner layer is mixed.

FIG. 4 is a diagram showing an example of an apparatus for explaining a boundary layer level control method of a direct level control method having a simple structure. In this device, the level controller LC1 is
The inner layer stopper 29b opening is adjusted so that the molten metal level L1 matches the target value L1r.

Further, the boundary layer level adjuster LC2 adjusts the opening degree of the surface layer stopper 29a so that the boundary layer level L2 output from the boundary layer arithmetic unit 10 matches the target value L2r. This method has the features that the apparatus configuration is the simplest and that no molten steel flow rate measuring device such as a load cell or flow rate calculator is required.

[0046]

EFFECTS OF THE INVENTION According to the boundary layer level measuring method and level controlling method of the present invention, there are large fluctuations in the flow of the molten metal in the upper and lower layers, such as changes in the casting speed and the injection amount at the start of casting and during casting. Even if there is, the boundary layer level of the molten metal can be returned or settled to the normal position in a short time, the problem that the molten metal of the surface layer and the inner layer is mixed can be avoided, and the boundary layer level can be stabilized. The accuracy of the formed surface shell thickness is also improved.

Further, according to the present invention, since the molten metal level and the boundary layer level are always controlled to be in the normal positions,
A flow meter is not necessary for injecting the molten metal, and the device can be simplified.

[Brief description of drawings]

FIG. 1 is a sectional view (a) and a schematic view (b) of a continuous casting apparatus for a multi-layer cast for explaining a boundary layer level measuring method of the present invention.
Is.

FIG. 2 is a diagram showing an example of an apparatus for explaining a boundary layer level control method.

FIG. 3 is a diagram illustrating an effect of controlling a boundary layer level.

FIG. 4 is a diagram showing an example of an apparatus showing another example of the boundary layer level control method.

FIG. 5 is a drawing showing a conventional example of a process control system for continuous casting of multi-layer cast slabs.

[Explanation of symbols]

 1,20 Mold 2,23 Electromagnetic brake 3,24 Boundary layer 4,25 Liquid level 5a, 5b Surface layer, inner layer solidification shell 6a, 6b Bubbler tube 7 Pressure reducing valve 8a, 8b Constant flow rate device 9a, 9b Pressure transmitter 10 Boundary layer computing device 21a, 21b Tundish 22a, 22b Injection nozzle 25a Liquid level meter 26a, 26b Load cell 27a, 27b Flow rate calculator 28a, 28b Stopper driving device 29a, 29b Stopper LC1 Liquid level controller LC2 Boundary layer level Controller FC1 Surface layer pouring amount regulator FC2 Inner layer pouring amount regulator X Calculator

Front Page Continuation (72) Inventor Eiichi Takeuchi 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Co., Ltd.Technology Development Headquarters (72) Inventor Atsushi Jouki 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Company Technology Development Division

Claims (3)

[Claims] 1. A molten metal is injected into the mold from the surface layer and the inner layer tundish through each injection nozzle, and a braking force is applied to each of the injected molten metals by an electromagnetic brake, whereby a boundary layer formed in the mold is used. In continuous casting in which the front and inner layer metals are separated into upper and lower parts to cast a multi-layer slab, two bubbler tubes are inserted so that their tips are located in the surface molten steel above and below the boundary layer and in the inner molten steel. Two
The back pressure at each position of each bubbler tube is measured by expanding the bubbler tubes of this book, and the boundary layer level is obtained by the following equation 1 based on the measured back pressure value. Method for measuring boundary layer level of molten metal in continuous casting. [Equation 1] However, H1, H2 Position of each bubbler pipe P1, P2 Back pressure of each bubbler pipe ρ1, ρ2 Molten steel density of surface layer and inner layer L2 Boundary layer level 2. A molten metal is injected into the mold from the surface layer and the inner layer tundish through each injection nozzle, and a braking force is applied to each of the injected molten metals by an electromagnetic brake, whereby a boundary layer formed in the mold is used. For continuous casting equipment that separates the front and inner layer metal into upper and lower parts and casts multi-layer slabs
It has a surface molten steel flow rate measuring device, an inner layer molten steel flow rate measuring device, a surface / inner layer flow rate ratio adjusting device, a melt level meter and a melt level adjusting device, and a boundary layer level measuring device and boundary layer level adjusting device. In addition to the level control of the metal surface and the surface / inner layer flow rate ratio by adjusting the stoppers or sliding nozzle openings provided on the surface and inner layer tundish, the surface / inner layer flow rate is adjusted so that the boundary layer level matches the target value. A boundary layer level control method for molten metal in continuous casting of multi-layer slab, which is characterized by automatically adjusting a ratio. 3. A molten metal is injected into the mold from the surface and inner layer tundish through each injection nozzle, and a braking force is applied to each of the injected molten metals by an electromagnetic brake, whereby a boundary layer formed in the mold is used. For continuous casting equipment that separates the front and inner layer metal into upper and lower parts and casts multi-layer slabs
It has a molten metal level meter and a molten metal level adjusting device, and further a boundary layer level measuring device and a boundary layer level adjusting device,
By controlling the opening of the stopper or sliding nozzle provided on the surface or inner layer tundish, the molten metal level is controlled to match the target value, while the stopper or sliding nozzle on the inner layer or surface layer tundish is controlled. A method for controlling a boundary layer level of a molten metal in continuous casting of a multi-layer slab, wherein the boundary layer level is controlled so as to match a target value by adjusting an opening degree.