JPH07108441B2 - Injection amount control method in continuous casting of multi-layer slab - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for appropriately controlling the injection amount of molten metal supplied from a tundish to a mold when the molten metal is supplied to a continuous casting mold for multi-layer slabs.

[0002]

2. Description of the Related Art When a molten metal is supplied to a continuous casting mold for casting, as a method for controlling the injection amount of the molten metal supplied from the tundish to the mold, for example, a multi-layer cast process control system shown in FIG. A method for casting a multi-layer cast product by a two-nozzle method using a load cell, which is shown in the schematic diagram, is adopted.

In FIG. 4, 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 level 35 of the molten metal in the mold 30 is the molten metal in contact with the atmosphere in ordinary 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 shell 36a of the cast slab is determined by the thickness of the solidified shell grown between 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 multiplied by the inner layer pouring amount controller FC2 and the surface layer pouring amount controller FC1 by a constant ratio α. The flow rate setting value Q1r is input.

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 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-mentioned conventional control method, as a method of measuring the molten steel pouring amount, the weight of a tundish or the like is measured by a load cell, and the flow rate is calculated from the time change (change speed) of the weight. Calculate

In this method, the change in weight, for example, for one second is generally very small compared to the measured weight. Therefore, if the flow rate is calculated from the weight difference per second, this flow rate signal cannot be used for control because the flow rate signal is very small compared to the noise inevitably generated in the mechanical system or the control circuit. There is.

Therefore, in order to suppress this noise to be smaller than the flow rate signal, it is necessary to calculate from the weight difference in a larger time interval, which causes a flow rate detection delay, which results in a large continuous casting facility. In that case, there is a time delay of 5 to 10 seconds, which adversely affects the control and is not preferable in terms of the quality of the cast multi-layer cast piece.

The present invention solves the above problems and provides a pouring amount control method for accurately and promptly grasping and controlling the flow rate of molten metal supplied from a tundish to a mold in continuous casting of multi-layer cast pieces.

[0014]

According to the present invention for solving the above-mentioned problems, molten metal is injected from the surface and inner layer tundish into each mold through each injection nozzle, and each injected molten metal is controlled by an electromagnetic brake. Power and mold
A boundary layer formed inside separates the upper and lower layers of metal.
In continuous casting to cast a multi-layer cast piece, the surface layer injection amount measured by the electromagnetic flow meter attached to the injection nozzle on the surface layer tundish side, and the set value was calculated by the surface layer shell thickness and casting speed. Compare with the surface flow rate setting value ,
Adjust the surface layer injection amount by opening and closing the stopper of the surface layer injection nozzle so that the two agree with each other, and calculate the set value from the surface level detected by the surface level gauge, the surface shell thickness and the casting speed. Compared with the set value of the molten metal level , the inner layer injection amount is adjusted by opening and closing the stopper of the inner layer injection nozzle so that the two agree with each other. It is a control method.

[0015]

[Operation] An electromagnetic flow meter is an electromotive force induced by electromagnetic induction in a direction perpendicular to the magnetic field direction when the molten metal passes through a magnetic field when measuring the flow rate of the molten metal flowing in a pipe with a fixed diameter. Is a flow meter that uses as an index. Therefore, the flow rate of the molten metal flowing down through the injection nozzle is immediately measured, and the control can be performed quickly and accurately without causing a time delay or the like.

It is better to use an alternating current type electromagnetic flowmeter. The reason is that when using direct current, there is a phenomenon of so-called zero-point fluctuation, which is a problem peculiar to an electromagnetic flow meter, in which a noise component is added to a true flow signal due to physical influence, and the flow signal does not become zero at zero flow rate. In this case, the AC magnetic field is 50 ~
The flow rate signal can be accurately detected by using at a relatively high frequency of 16 Hz and canceling noise.

Next, the operation of the present invention will be described with reference to FIG.

Based on the material balance, the molten metal level L1 in the mold and the boundary layer level L2 are expressed by the following equations.

[0019]

[Equation 1]

[0020]

[Equation 2]

[0021]

[Equation 3] S1 = WB

[0022]

## EQU00004 ## S2 = (W-0.2d) (B-0.2d)

[0023]

[Equation 5]

In the above formulas 1 to 5, L1 melt level (mm) L2 boundary layer level (mm) Q1 surface layer injection amount (kg / sec) Q2 inner layer injection amount (kg / sec) V casting speed (m / min) ) W mold width (cm) B mold thickness (cm) ρ molten steel density (g / cm ³ ) S1 mold cross-sectional area (cm ² ) S2 boundary layer cross-sectional area (cm ² ) d surface shell thickness (mm) K solidification constant n Solidification index τ Surface solidification time (sec) L1r Liquid level setting value (mm) Q1r Surface layer flow rate setting value (kg / sec).

In the calculation method of the surface layer flow rate set value Q1r, when the process is stable, both L1 and L2 do not fluctuate. Like

[0026]

[Equation 6]

[0027]

[Equation 7]

If Q2 is obtained from the equation 7 and is substituted into the equation 6 and the equations 3 and 4 are used, Q1 becomes the equation 8.

[0029]

[Equation 8]

The surface layer flow rate set value Q obtained by Q1 of the equation 8
It is 1r. On the other hand, the surface level set value L1r is
Calculate with 0. However, when the process is stable, that is, when L1 and L2 are constant, L1 (t-τ) of the equation 5 becomes the equation 9.

[0031]

## EQU9 ## L1 (t-.tau.) = L1 (t)

[0032]

[Equation 10] L1 = L2 + V · (d / K) ^{1 / n}

That is, as shown in Expression 10, this L1 is the required molten metal surface level set value L1r. At this time, L2 is generally used as the target value at the center level of the electromagnetic brake band.

If L1r calculated by the above equation 10 is used, the boundary layer is always maintained at the target level in the electromagnetic brake zone even if the casting speed V and the surface layer thickness d change, and the separation of the inner layer is effective. To be done.

[0035]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic diagram of a multi-layer slab process control system suitable for carrying out the present invention.

In FIG. 1, the continuous casting equipment is the same as the equipment described in the conventional example, and the surface layer tundish 1a,
It is injected into the mold 10 from the inner layer tundish 1b through the surface layer injection nozzle 2a and the inner layer injection nozzle 2b. Each of the injected molten steels receives a molten steel braking force by the boundary layer 4 formed by the electromagnetic brake 3, and is vertically separated in the mold to start solidification.

First, the method of controlling the flow rate on the surface layer side will be described. An electromagnetic flow meter 11 is mounted in the middle of the surface layer injection nozzle 2a on the surface layer tundish 1a side.
At 1, the molten steel for the surface layer flowing down the nozzle is measured and output as the surface layer injection amount Q1.

Further, the surface layer flow rate set value Q1r obtained by calculating the set value by the surface layer shell thickness d and the casting speed V which are separately set and the surface layer injection amount Q1 are inputted to the flow rate controller QC.

In the flow rate controller QC, the stopper drive unit 1 is compared by comparing the surface layer injection amount Q1 with the surface layer flow rate set value Q1r.
4a is driven, and the stopper 15a is opened and closed so that Q1 coincides with Q1r to adjust the flow rate.

In the flow rate control method on the inner layer side, first, the molten metal level L1 is detected by the molten metal level gauge 16 and is input to the molten metal level controller LC. At the same time, the molten metal level set value L1r calculated by calculating the set value from the surface shell thickness d and the casting speed V is input to the molten metal level controller LC.

In the melt level controller LC, the melt level L1
And the molten metal level set value L1r are compared, the stopper drive device 14b is driven, and the stopper 15b is opened and closed so that L1 coincides with L1r to adjust the flow rate.

FIG. 3 is a drawing in which the influence of the flow rate calculation delay is measured with the horizontal axis representing time, with respect to the fluctuations in the molten metal level and the boundary layer level.

FIG. 3 (A) shows an embodiment carried out by the equipment shown in FIG. 1, and at t = 50 sec, the molten metal level is -100 mm.
This is the case when the setting is changed from to -90 mm. Also (B)
Is the result of the conventional equipment shown in FIG.
In c, the casting speed was changed from 1.0 m / min to 0.8 m / min. As can be seen from this result, quick and stable setting change is possible in the present embodiment.

[0045]

As described above, according to the present invention, in particular, the control method using the AC electromagnetic flowmeter is used, so that the problem of zero fluctuation due to noise is solved, and accurate and prompt control and level adjustment are possible. It becomes possible, and stable operation and quality improvement of the slab can be achieved.

[Brief description of drawings]

FIG. 1 is a side view showing a main part of a continuous casting apparatus suitable for carrying out the present invention.

FIG. 2 is a schematic view of a mold for explaining the action of the present invention.

FIG. 3 is a drawing showing the results of the molten surface control stability test of Example (A) and Comparative Example (B).

FIG. 4 is a schematic diagram of a conventional multi-layer cast process control system.

[Explanation of symbols]

 1a Surface layer tundish 1b Inner layer tundish 2a Surface layer immersion nozzle 2b Inner layer immersion nozzle 3 Electromagnetic brake 4 Boundary layer 5 Surface level 6a Surface layer shell 6b Inner layer shell 10 Mold dish outflow part 11 Electromagnetic flow meter QC Flow controller LC Level adjuster 14a, 14b Stopper drive device 15a, 15b Stopper 16 Level gauge

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Shiroki 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Stock Development Department

Claims (1)

[Claims] 1. A molten metal is injected from the surface and inner layer tundish into each mold through each injection nozzle, and a braking force is applied to each injected molten metal by an electromagnetic brake.
The inner layer metal is given by the boundary layer formed in the mold.
In continuous casting in which a multi-layer cast piece is separated into upper and lower parts, in the surface layer injection amount measured by the electromagnetic flow meter attached to the injection nozzle on the surface layer tundish side, the set value is calculated by the surface layer shell thickness and the casting speed. Comparing the obtained surface layer flow rate setting value , the stopper of the surface layer injection nozzle is opened and closed so that the two agree with each other to adjust the surface layer injection amount, and on the other hand, the molten metal level detected by the molten metal level meter, Level of molten metal obtained by calculating the set value from the surface shell thickness and casting speed
A method for controlling an injection amount in continuous casting of a multi-layer cast product, which comprises comparing a set value and opening and closing a stopper of an injection nozzle for an inner layer so that the two match.