JPH09262653A - Method for estimating surface layer thickness of plural layer cast slab - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously estimate the thickness of a surface layer in real time at the time of continuously casting a complex layer cast slab. SOLUTION: Molten metals for surface layer and for inner layer are poured into a mold through each of a pouring nozzle 3s opened to the one side and a pouring nozzle 3i opened to the other side in two ranges divided in range which braking force of an electromagnetic brake intensely acts, in the mold 1 fitting the electromagnetic brake 6. Then, the solidified layer thickness DC of the molten metal for the surface layer and a boundary level L2C between the molten metals for surface layer and for inner layer are calculated with a mass flow model and a solidifying speed model by using at least one side of flow rates Q1C, Q2C of the molten metals for surface layer and for inner layer, molten metal surface level L1J in the mold, casting speed VJ and mold widths W, B at two directions of the drawing direction and the crossing direction at the right angle during the continuous casting forming the solidified shell 7s of the molten steel for surface layer and the solidified shell 7i of the molten steel for inner layer in the inside thereof in the inner surface of the mold. Then, the surface layer thickness D is calculated by applying a decrement correction with a remelting model and a thermo-shrinkage model to this solidified thickness DC by using the boundary level L2C, the temp. T2 of the molten metal for inner layer and the mold length ML in the drawing direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to continuous casting of a multi-layer slab in which a plurality of types of molten steel are injected into a mold and the surface layer and the inside have different component concentrations, and more particularly, to control the surface layer thickness during continuous casting. Regarding surface thickness estimation.

[0002]

2. Description of the Related Art In continuous casting of a slab formed of a plurality of layers (for example, a multi-layer slab in which the surface layer is made of stainless steel and the inner layer is made of ordinary steel), different molten steels stored in a plurality of tundish are melted. By pouring each region into the mold using each pouring nozzle and controlling the pouring amount from both tundish to the mold, that is, controlling the injection flow rate of each different molten steel, the interface between the surface layer and the inner layer is clear and the surface layer thickness is A slab with the desired value is produced. In this pouring amount control, the molten steel weight in the tundish is detected by a load cell, the level of the molten metal inside the mold is detected by a level meter, and the reduction amount of the molten steel in the tundish (injection flow rate into the mold) and the target weight are detected. In order to eliminate the deviation from the decrease amount (target injection flow rate) and the deviation between the detected molten metal level and the target molten metal level, the opening adjustment means such as a stopper provided at the pouring tuyere of both tundishes is opened. To adjust the molten steel pouring amount to the mold.

In this type of continuous casting, it is important to minimize the fluctuation of the pouring flow rate from the surface layer pouring nozzle and the inner layer pouring nozzle with respect to the target pouring flow rate. If this is not achieved, A mixed layer is formed between the molten steel for the surface layer and the molten steel for the inner layer in the mold, and this mixed layer deteriorates the quality of the multilayer slab.

As a conventional pouring amount control method for minimizing the variation of the pouring flow rate with respect to the target pouring flow rate, (1) the molten metal pouring flow rate for the surface layer is kept constant, and the molten steel pouring flow rate for the inner layer Method for controlling the level of molten metal, (2) Method for controlling the level of molten metal inside the mold by the molten metal pouring flow rate for the surface layer while keeping the molten steel pouring flow rate for the inner layer constant, and (3) Surface layer and inner layer There is a method in which the level of the molten steel pouring flow rate is kept constant and the level of the molten metal inside the mold is controlled by the sum of the pouring flow rates of the molten steel for the surface layer and the inner layer.

In order to know the state of each layer of the cast slab having a plurality of layers cast in this way, conventionally, a test slab is cut from a product, and the components of the cut surface are divided into layers. The distribution (particularly the surface layer thickness) was confirmed.

[0006]

However, since the state confirmation of each layer by the above method is carried out by batch processing, it takes time, and the surface layer thickness can be confirmed only in the cut cross section of the cast slab. .

There is also a problem that the cost is high. Therefore, during the operation of the continuous casting equipment, it was impossible to perform real-time control according to the state of the surface layer thickness, and it was also impossible to guarantee the surface layer thickness over the entire slab.

The first object of the present invention is to estimate the surface layer thickness continuously and in real time during casting of a multi-layer cast product, and to improve the accuracy of the surface layer control and to guarantee the surface layer of the entire cast product. The second purpose is to do so.

[0009]

[MEANS FOR SOLVING THE PROBLEMS] In a mold (1) having an electromagnetic brake (6) mounted therein, the mold is opened in one of two regions divided by a region where the braking force of the electromagnetic brake strongly acts. The molten metal for the surface layer and the inner layer was injected into the mold through the pouring nozzle (3s) and the pouring nozzle (3i) opened on the other side, and the solidified shell of the molten metal for the surface layer ( 7s) during the continuous casting in which the solidified molten metal shell (7i) for the inner layer is formed, the flow rates of the molten metal for the surface layer and the inner layer are Q1C and Q2.
At least one side of C, the molten metal level L1 in the mold
J, casting speed VJ, and mold widths W and B in two directions orthogonal to the drawing direction, using a mass flow model and a solidification rate model, the solidified layer thickness DC of the molten metal for the surface layer and the melting for the surface layer and the inner layer The boundary level L2C of the metal is calculated, and the solidification layer thickness DC is decremented by the remelting model and the heat shrinkage model using the boundary level L2C, the temperature T2 of the molten metal for the inner layer and the mold length ML in the drawing direction. The surface layer thickness D is calculated after correction. In addition, in order to facilitate understanding, the symbols of the corresponding elements in the embodiments shown in the drawings and described later are added in the parentheses for reference.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION First, an example of a process for continuously casting a multi-layer cast piece will be described with reference to FIG. 1, and then the principle of the surface layer thickness estimating method according to the present invention applied to this process will be described.

FIG. 1 shows an outline of equipment for continuously casting multi-layer cast slabs. Above the mold (mold) 1 are a tundish 4s for molten steel in the surface layer and a tundish 4i for molten steel in the inner layer. The mold 1 is equipped with an electromagnetic brake 6 that applies a braking force to the movement of the molten steel in the height direction of the mold 1 (longitudinal direction of the plane of FIG. 1: drawing direction of cast slab). The molten steel of the tundish 4s for surface molten steel is injected into the mold 1 through the surface nozzle 3s, and the pouring port in the mold of the surface nozzle 3s is a level LD where the electromagnetic brake 6 exerts a braking force.
It is higher than MB. Tundish 4 for inner layer molten steel
Although the molten steel of i is injected into the mold 1 through the inner layer nozzle 3i, the pouring port in the mold of the inner layer nozzle 3i is located at a position lower than the level LDMB at which the electromagnetic brake 6 exerts the braking force.

That is, the inner layer nozzle 3i extends below the region across the region where the electromagnetic brake 6 exerts the braking force.

The pouring flow rate from the tundish 4s for surface molten steel to the mold 1 is substantially determined by the position (opening) of the stopper 5s that opens and closes the pouring tuyere of the tundish 4s and the level of the molten metal in the tundish. Stopper driver 15s
Drive the stopper 5s up and down (open and close). The weight scale 11s detects the weight of the tundish 4s for surface molten steel. The flow velocity calculator 12s reads the detection value of the weighing scale 11s in a predetermined cycle, calculates the flow rate Q1C (flow velocity: the amount of change in weight during the last one cycle of the predetermined period), and always calculates the latest flow rate Q1C. Holds the data representing the.

The pouring flow rate from the tundish 4i for the inner layer molten steel to the mold 1 is substantially determined by the position of the stopper 5i that opens and closes the pouring tuyere of the tundish 4i and the level of the tundish internal molten metal. The stopper driver 15i drives the stopper 5i up and down. Tundish 4i for inner layer molten steel
Is weighed by the scale 11i. Flow velocity calculator 12i
Reads the detected value of the weighing scale 11i at a predetermined cycle, calculates the flow rate Q2C, and always holds the latest data representing the calculated flow rate Q2C.

An electric signal of a level corresponding to the upper surface level (melt level) of the molten metal in the mold 1 is generated by the molten metal level detecting end 13, and the level meter 14 removes noise from the electric signal and calibrates it ( (Amplification) processing is performed and converted into data representing the molten metal level L1J at a predetermined cycle, and the latest data representing the molten metal level L1J is always held.

The thermometer 24 removes noise and calibrates (amplifies) the temperature signal (electrical signal) generated by the temperature detecting end 23.
In addition to the signal processing circuit for performing the processing of FIG.
Is driven down through a temperature sensor driver (not shown) until the lower end thereof is lower than the molten metal level L1J by a predetermined distance or more, and the temperature signal processed by the signal processing circuit is digitally converted and read. Includes a temperature measurement controller that latches (holds) the digital data T2 at the time when the change (rise) of the temperature is saturated and that drives the temperature detection end 23 to the retracted position via the temperature sensor driver. Yes,
This temperature measuring controller is a computer 3 which will be described later.
When there is a temperature data request from 0 (FIG. 2), the above temperature measurement operation is executed once, and the obtained temperature data T2 is transferred to the computer 30.

A measuring roll 8 is in contact with a cast piece pulled out from the mold 1 at a position downstream of the mold 1.
This rotates due to the movement of the slab. A rotary encoder 9 is connected to the roll 8, and this encoder 9
Generates an electric pulse for each rotation of the roll 8 by a predetermined small angle and supplies it to the speed calculator 10. The speed calculator 10 clears the counter and counts up the electric pulse for a predetermined time. When the predetermined time elapses, the count data is fetched into the output latch to clear the counter, and again the predetermined time is reached. The counting process of starting the count-up of the electric pulse during the period is repeated. As a result, the output latch always holds the latest casting speed VJ (the number of electric pulses generated during the predetermined time).

Before the start of casting, the lower opening of the mold 1 is damaged.
It is closed with a ba. Tundish 4s to Mold 1
And / or after starting injection of molten steel from 4i, mold 1
When the level of the molten metal in the inside reaches around the first predetermined level, the extraction of the dame bar is started, the molten steel is injected into the mold from both the tundish 4s and 4i, and the level of the molten metal in the mold 1 becomes the second level. When the braking current is applied to the electromagnetic brake 6 when the level is around a predetermined level, and when the molten metal surface level in the mold 1 is close to the target level, the tundish 4s and 4i for setting the surface layer thickness of the slab to the target value. The molten steel flow rate control into the mold 1 is started from each of the above. FIG. 1 shows a stable steady state after starting the flow rate control.

Immediately after starting the extraction of the dummy,
Although the molten steel for the surface layer and the molten steel for the inner layer, which have been injected into the container 1, are in a mixed state, after braking by the electromagnetic brake 6, as the molten steel descends due to the lowering of the dame bar, the electromagnetic brake -By the braking force of the key 6, the electromagnetic brake 6
For the molten steel for the surface layer injected above the region (level LDMB) exerting a strong braking force, braking is applied to the downward movement, and for the inner layer injected below the region (LDMB). The upward movement of the molten steel is braked, and the mixing of the molten steel for the surface layer and the molten steel for the inner layer is suppressed at the boundary (LDMB).

The molten steel for the surface layer injected into the mold 1 gradually solidifies from the inner surface of the mold to form the surface layer solidified shell 7s, and the molten steel for the inner layer gradually solidifies inside the surface layer solidified shell 7s. To form the inner layer solidified shell 7i. In this way, the molten steel is drawn downward while forming the shell, and all the molten steel in the inner layer is solidified downstream.

The boundary between the surface molten steel and the inner molten steel in the region of the mold 1 where the electromagnetic brake 6 exerts a strong braking force is called a boundary layer. The surface solidified shell 7s, which is the surface layer of the multi-layer cast slab, begins to grow from the molten metal level L1J,
Since the inner layer solidified shell 7i, which is the inner layer, starts to grow from the boundary layer, the inner layer solidified shell 7i is located below the boundary layer.
There is no growth. That is, the inner layer solidified shell 7i has the maximum thickness in the boundary layer. Temperature of molten steel injected, Mold 1
If the casting conditions such as the cooling conditions, molten steel injection flow rate, slab drawing speed, and braking force of the electromagnetic brake 6 are constant, the surface layer thickness becomes constant in time series (the maximum thickness). That is, the surface layer thickness of the manufactured slab becomes constant.

However, in reality, various disturbances disturb the balance of the flow rate ratio between the surface layer and the inner layer, and the boundary layer fluctuates up and down. This variation is the variation of the surface layer thickness. in addition,
The surface solidified shell 7s once solidified may be remelted and reduced in thickness when it comes into contact with the hotter inner layer molten steel.
Moreover, when mixing of the surface molten steel and the inner molten steel occurs in a part,
In the vicinity of the boundary layer, a concentration gradient of the component called the transition layer (direction perpendicular to the surface) is created, and the effective surface shell thickness decreases.

In general, a slab is reduced in thickness and width (for example, 3%) between hot and cold (for example, 20 ° C.).
Therefore, the thickness of the surface layer solidified shell 7s in the boundary layer does not directly become the surface layer thickness of the cast product.

In view of the above-mentioned phenomenon, the present invention estimates and calculates the surface layer thickness of the cast product obtained by the current continuous casting operation. First, the hot theoretical surface layer thickness is obtained by the mass flow model, Dissolution correction, transition layer correction, and heat shrinkage correction are added to obtain the estimated cold surface layer thickness.
The contents of these will be described below.

1. Calculation of hot theoretical surface layer thickness DC and boundary layer level L2C The boundary position between the surface molten steel and the inner layer molten steel, that is, the boundary layer level in the vertical direction is near the level LDMB at the center of the braking force region of the electromagnetic brake 6, The boundary layer level cannot be used to calculate the surface layer thickness because there is no practical method for direct measurement. Therefore, in the present invention, specifically, based on the mass flow model and the solidification rate model, specifically, the following equation (1) for calculating the moving speed (estimated value) of the boundary layer level L2C, the inner layer cross-sectional area at the boundary layer level is calculated. Calculate S2 (estimated value)
Formula (2), formula (3) for calculating the hot surface layer thickness DC (estimated value of the inner layer thickness at the boundary layer level), and the surface layer solidification time TAU
Using equation (4) for calculating (estimated value), these are treated as simultaneous equations, and the hot surface layer thickness DC and the boundary layer level L2C are calculated.
Is calculated.

[0026]

[Equation 1]

However, L2C boundary layer level estimated value (mm) calculated value (time variable) Q2C inner layer molten steel flow rate (Kg / sec) measured value S2 boundary layer cross-sectional area (cm ² ) calculated value (time variable) ρ2 Inner layer molten steel density (g / cm ³ ) Set value ・ VJ Casting speed (m / min) Measured value ・ W Mold width in long side direction (cm) Set value ・ DC hot theoretical surface layer thickness estimated value (mm) Calculated value (time variable) ・ B Short side direction mold width (cm) setting value ・ KC solidification coefficient setting value ・ L1J melt level actual (mm) measured value ・ TAU surface layer solidification time (sec) calculated value (time Variable) ・ NC Solidification index set value ・ * Multiplying symbol (×) Here, in the surface layer solidification time TAU, the slab is at the molten metal surface level L1.
It is the time (estimated value) required to travel the distance between J and the boundary layer level L2C. However, generally, the level L1J
Is kept constant within ± 5 to 10 mm with respect to the target level, so equations (3) and (4) are practical even if they are approximated by equations (5) and (6), respectively. There is no problem on the top.

[0028]

[Equation 2]

The solidification coefficient KC and the solidification index NC are values determined by the mold and steel type.

The boundary layer level L2C can be obtained by integrating equation (1) if an initial value is given at the start of calculation. Therefore, equations (1), (2), (5) and (6) are used. The theoretical hot surface layer thickness DC (estimated value) can be obtained based on the defined mass flow model and solidification rate model.

2. Remelting correction Surface layer molten steel solidification temperature TL1 (° C) and inner layer molten steel temperature T2
Based on the temperature difference from (° C), the redissolution amount (estimated value) DR, which is the thickness reduction, is empirically determined based on the following redissolution model.

1) When TL1 <T2 + δ, where: ・ Constant set value determined by δ steel type

[0033]

(Equation 3)

However, ・ DR remelted thickness (mm) calculated value (time variable) ・ RK remelted coefficient set value ・ T2 inner layer molten steel temperature (° C) measured value (set value is acceptable) ・ TL1 surface molten steel temperature (° C) set value-ML mold length (mm) set value-L2C boundary layer level estimated value (mm) calculated value (time variable) -VJ casting speed (m / min) measured value-Rn constant set value-RC Constant setting value.

2) When TL1≤T2 + δ, DR = 0 (8).

3. Transition layer correction Due to partial mixing of the surface molten steel 7s and the inner molten steel 7i, a concentration transition layer is generated between them, and as a result, the surface thickness DC is β.
(Mm) decrease. This β is a constant determined by the steel types of the surface layer and the inner layer, the strength of the braking force of the electromagnetic brake 6 and the casting speed VJ.

4. Correction of heat shrinkage According to the following calculation formula including a transition layer correction model and a heat shrinkage model, the above-mentioned hot theoretical surface thickness DC is corrected by the above-mentioned decrease β and the heat shrinkage by the temperature of the cast slab to room temperature. Calculate the surface layer thickness (estimated value) D of the room temperature slab by adding: D = (DC-DR-β) * (1-α) (9) However, ・ D Cold surface layer thickness (estimated value) ( mm) Calculated value (time variable) -α Heat shrinkage correction coefficient Set value α is a heat shrinkage coefficient determined by the hot temperature and cold temperature (normal temperature) determined by the steel type of the surface layer.

As described above, the surface layer thickness estimated value D of the cast product (cold slab) obtained by the present continuous casting conditions is calculated. This is repeated at regular intervals to obtain the surface layer thickness estimated value D (t) of the cast product obtained in the immediate future, that is, the surface layer thickness (estimated value) distribution in the drawing direction, obtained in the immediate future according to the casting conditions at each time. . This data can be used not only for quality judgment, quality assurance and history of cast products, but also for continuous casting control (for example, flow rate control of each molten steel).
In addition, it is possible to realize real-time surface layer thickness control by utilizing the same as feedback data.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of the equipment configuration around a mold for carrying out the present invention in one mode, and FIG. 2 shows a computer system connected to the equipment around the mold. The computer system is, in this embodiment, a first computer 20 for controlling the molten steel flow rate from the surface and inner layer tundish 4s and 4i to the mold 1, and a detector around the mold 1. The second computer 30 is mainly used to collect the detected values of 1 to calculate the surface layer thickness (estimated value) D.

The second computer 30 collects the detected values at the DT cycle for a predetermined time. At the detected value collection timing, the thermometer 24 is instructed to measure the temperature, and the flow velocity calculators 12s, 12i and the level meter are measured. 14, the speed calculator 10 and the thermometer 24 are sequentially requested to transfer the measured values, and then the surface layer molten steel flow rate data Q1C and the inner layer molten steel flow rate data are transmitted.
Data Q2C, melt level data L1J, casting speed data V
J and the temperature data T2 of the molten steel for the inner layer were sequentially obtained, and saved (written) in a register (one area of the internal memory of the computer) to calculate the surface layer thickness D and to collect the measured values. The data and the surface layer thickness D are updated and displayed on the CRT display 32, and these data are transferred to the first computer 20. Further, the floppy disk inserted in the floppy disk device incorporated in the computer 30 is written, and the printer 33 prints out on the recording sheet.

The first computer 20 is for the surface layer to make the deviations between the casting speed target value, the molten metal surface level target value and the surface layer thickness target value and these feedback values VJ, L1J and D zero. And a target value of the flow rate of the molten steel for the inner layer and a target value of the energizing current level of the electromagnetic brake are generated and given to the stopper controllers 17 and 18 and the brake controller 19. These controllers 17-19
Are these target values and feedback values Q1C, Q2C
And the stopper drivers 15s and 15i and the brake driver 16 are driven (controlled) so that the deviation from the actual energization current value becomes zero. The second computer 30 collects the measurement data as described above in the DT cycle to calculate the surface layer thickness D. If the latest time when this processing is performed is represented by K (time index is K) and the time when this processing is performed last time is represented by K-1, in this embodiment, the second computer is used.
In T30, TAU of equation (6), DC of equation (5), S2 of equation (2)
And the integrated value L2C of the equation (1) is calculated by the following equation (10),
The calculation program was set so as to calculate by the equations (11), (12), and (13). DT is a surface layer thickness calculation cycle (sec).

[0043]

(Equation 4)

The initial value (the value at the time of starting the integral calculation, that is, the value of L2C at the time of starting the calculation of the surface layer thickness D) is given by the equation (13) for calculating the integral value L2C of the equation (1). Is necessary but unknown. The boundary layer level L2C is an electromagnetic blur.
Since the braking force of the key 6 is near the central level LDMB, in this embodiment, the initial value L2C (0) of L2C is set to LDMB. That is, L2C (0) = LDMB (14).

The reduction amount DR of the surface layer thickness DC due to re-melting is
Surface layer molten steel solidification temperature TL1 (° C) and inner layer molten steel temperature T2
The temperature difference from (° C) is calculated as follows. This is empirically determined based on past casting results.

1) When TL1 <T2 + δ

[0047]

(Equation 5)

However, ・ δ constant set value determined by steel type ・ DR remelted thickness (mm) calculated value (time variable) ・ RK remelted coefficient set value ・ Rn constant set value ・ RC constant set value ・ ML mold length (Mm) Set value-TL1 Surface layer molten steel solidification temperature (° C) set value-T2 Inner layer molten steel temperature (° C) Measured value (setting value may be used). 2) DR (K) = 0 (16) when TL1 ≤ T2 + δ.

The transition layer correction is performed by the decrement β (m
This β is a constant determined by the steel grades of the surface layer and the inner layer, the strength of the braking force exerted by the electromagnetic brake 6 and the casting speed. The β access corresponding to each division is written in the computer 30 by using each steel type of the surface layer and the inner layer, the energization current value of the electromagnetic brake 6 and the casting speed as division parameters (addresses). There is a table (β data group memory), and the computer 30 uses the β derivation stage to determine the target value of the energizing current of the electromagnetic brake 6 obtained from the first computer 20 and its own The β value corresponding to each steel type of the surface layer and the inner layer to be held and the casting speed VJ is read from the β access table.

Thermal shrinkage correction is performed as follows to obtain the latest surface layer thickness (estimated value) D (K): D (K) = (DC (K) -DR (K) -β) * (1 -α) (17) However, ・ D Cold surface layer thickness (estimated value) Calculated value (time variable) ・ α Heat shrinkage correction coefficient Set value α is heat shrinkage determined by hot and cold temperatures determined by the steel type of the surface layer It is a coefficient. FIG. 3 shows an outline of the processing function of the second computer 30. When the power is turned on to itself, the computer 30 executes initialization (1) according to its own system program and waits for the user program to be turned on (step 1). In the following, in the parentheses, the word step is omitted, and the step No. Write only numbers.

The operator attaches the floppy disk in which the surface layer thickness management program has been written to the computer 30 and gives an instruction to read it. In response to this, the computer 30 executes the surface layer thickness management program.
When the reading is completed in the internal memory and the reading is completed, first, the initial input menu screen is displayed on the CRT display 32 according to the surface layer thickness management program on the memory (2).

On the initial input menu screen, the mold width W in the long side direction, the mold width B in the short side direction, and the mold length M are shown.
L, center level LDBM of electromagnetic brake 6, steel types of surface molten steel and inner molten steel, inner molten steel density ρ2, solidification coefficient K
Reference values of C, solidification index NC, constant δ, redissolution coefficient RK and constants Rn, RC, a sentence notifying the change and a start / stop input field for surface thickness calculation are displayed. When the above-mentioned display value (reference value) needs to be changed in the continuous casting to be started, the operator places a cursor on the corresponding display value and inputs the changed value. Upon receiving this change input, the computer 30 updates the display with the changed value (3 to 6).

On the other hand, when the first computer 20 completes the system startup, the reference values of the casting speed target value, the molten metal surface level target value and the surface layer thickness target value, and the sentence for issuing the change input, the automatic An initial input menu screen displaying a control start / stop input field and an input field for manually operating the stoppers 5s, 5i and the electromagnetic brake 6 is displayed on the CRT display 22. When the above-mentioned display value (reference value) needs to be changed in the continuous casting to be started, the operator places a cursor on the corresponding display value and inputs the changed value. Upon receiving this change input, the computer 20 updates the display with the changed value.

When starting the casting, the operator operates the input board 21 to give the computer 20 an instruction (opening input) to open the stoppers 5s and 5i, and the input board 21 and the computer 20 are opened. -Through the stopper 20, the stopper 5s,
Adjust the opening of 5i. From the instruction to open the stopper to the input of the automatic control start, the computer 20 requests the computer 30 to transfer data at a predetermined short cycle, and the computer 30 steps this. 3 to recognize the flow rate data Q1C of the molten steel for the surface layer, the flow rate data Q2C of the molten steel for the inner layer, the melt level data L1J and the casting speed data VJ, respectively, as flow velocity calculators 12s, 12i and level. Compute from the total 14 and speed calculator 10
To the data 20 (3 to 6). The computer 20 displays these data and the openings of the stoppers 5s and 5i on the CRT display 22.

With reference to this display, the operator grasps the pouring state of the mold 1 and adjusts the stopper opening.
When the level of the molten metal in the mold 1 reaches the level at which the upper molten steel / lower molten steel separation by the electromagnetic brake 6 functions effectively, the operator turns on the electromagnetic brake 6 to the computer 20. Give instructions (input). Then, when the casting level index such as the molten metal level reaches a value that enables stable automatic control,
The automatic control start is instructed (input) to the computer 20, and the computer 30 is operated via the operation board 31.
Instruct (input) the start of surface layer thickness calculation.

After the start of pouring (switching the stoppers 5s and 5i from closed to open), the surface molten steel and the inner molten steel are mixed in the mold 1 until the electromagnetic brake 6 is turned on. Yes, the component concentration of the surface layer solidified shell 7s is considerably deviated from the component concentration when it is in the surface layer tundish 4s. As the electromagnetic brake 6 is turned on and the extraction process proceeds, the component concentration of the surface layer solidified shell 7s changes as shown in FIG.

Referring again to FIG. When the surface layer thickness calculation start is instructed, the computer 30 requests the first computer 20 to transfer the energization current target value of the electromagnetic brake 6, and when the transfer is received, the brake is transmitted. The central level LDBM of the electromagnetic brake 6 being displayed on the CRT display 32 is written in the integration register L2C for writing in the current register and for storing the boundary level data L2C (7). Next, the timer DT for the DT time period is started (8), and the computer 30 sets data indicating "during thickness measurement" in the status register (9).

The computer 30 then performs "input reading".
Return to (3), wait for input on the operation board 31,
It also waits for the timer DT to time out (3-5).
10-11-3 grouping). When the operation board 31 receives an input, the corresponding processing is performed (6). When the reference value is changed, the reference value is changed to the input value.
When there is a stop input, "Thickness is being measured" there.
The data indicating "1" is erased from the status register and "input read" is performed.
Stay in (3).

Now, when there is no stop input and the timer DT is in the "thickness measuring" state, the computer 30 restarts the timer DT (11, 1).
2) Read the detected value (13). In reading the detected value, first, the thermometer 24 is instructed to measure the temperature. In response to this, the controller of the thermometer 24 drives the temperature detecting end 23 downward through a temperature sensor driver (not shown) until the lower end of the temperature detecting end 23 is below the molten metal level L1J by a predetermined distance or more. The temperature signal is digitally converted, and this is repeated to latch the temperature data T2 at the time when the temperature data is saturated (the detected temperature value has stopped changing), and the temperature detection end 23 is driven to the retracted position. Start the computer 30
The data transfer is notified by an interrupt to the latched temperature data
The computer T2 is transferred to the computer 30. Temperature detection end 23
When reaches the retracted position, the driving of the detection end 23 is stopped there.

Since it takes a considerable time from when the thermometer 24 receives the temperature measurement instruction until the temperature data T2 is transferred, the computer 30 issues the temperature measurement instruction to the thermometer 24, and then the thermometer 24 issues the temperature measurement instruction. Without waiting for the temperature data T2 to be transferred from 24, the flow rate data Q is supplied to the flow velocity calculator 12s.
Request 1C transfer. In response to this, the flow velocity calculator 12s transfers the stored latest flow rate data Q1C to the computer 30. The computer 30 saves the received flow rate data Q1C in a register, and then similarly obtains the flow rate data Q2C from the flow velocity calculator 12i. Next, the computer 30 similarly obtains the molten metal level data L1J from the level meter 14, and then similarly obtains the casting speed data VJ from the speed calculator 10 and stores them in the registers. Save. Then, it waits for the thermometer 24 to transfer the temperature data T2, and when there is the transfer, it saves it in the register (13).

Next, the computer 30 calculates the coagulation time TAU (k) according to the equation (10) (14). In the formula (10) used for this calculation, L1J (K) is the level data L1J
, L2C (k-1) has data L2C of the integration register L2C.
(Initial value is LDMB), VJ (k) is the casting speed data VJ
Is used. These data L1J and VJ were obtained in step 13.

Next, according to the above equation (11), the hot surface layer thickness DC
(k) is calculated (15). Equation (11) used for this calculation,
For the coagulation coefficient KC, the one being displayed (reference value or operator input value) is used, and for TAU (k), the one calculated in step 14 is used.

Then, the boundary layer cross-sectional area is calculated according to the equation (12).
S2 (k) is calculated (16). In the equation (12) used for this calculation, the ones being displayed (reference value or operator input value) are used as the model widths W and B, and those calculated in step 15 are used as DC (k).

Next, according to the above equation (13), the boundary layer level
L2C (k) is calculated and the calculated value is written in the integration register L2C (17). In equation (13) used for this calculation, the data of the integration register L2C (previously calculated value: initial value is LDMB) is stored in L2C (k-1), and the flow rate obtained in step 13 is stored in Q2C (k). The data Q2C, the value calculated in step 16 for S2 (k), the displayed value for ρ2, the casting speed VJ obtained in step 13 for VJ (k), and DT for The time limit value DT of the timer DT is used.

Next, the reduction DR (k) of the surface layer thickness due to remelting is calculated (18). Here, first, T2 + δ is calculated and compared with TL1. T2 is the temperature data obtained in step 13, δ and TL1 are CRT display 3
This is the data displayed in 2.

When TL1 <T2 + δ, the reduction DR (k) of the surface layer thickness due to remelting is calculated based on the above equation (15).
(18). In equation (15) used for this calculation, RK is the displayed value and T2 (k) is the temperature data T2 obtained in step 13.
Is displayed on TL1 and ML, calculated on step 17 for L2C (k), and step 1 on VJ (k) for VJ (k).
The casting speed VJ obtained in No. 3 is used, and the RN and RC shown are used.

When TL1 ≧ T2 + δ, DR
Calculate (k) = 0.

Next, the surface layer thickness decrease β corresponding to the transition layer is derived (19). As described above, in the computer 30, the steel types of the surface layer and the inner layer, the current value of the electromagnetic brake 6 and the casting speed are set as the division parameters (address).
There is a β access table (β data group memory) in which the β value corresponding to each section is written. In this case, the computer 30 includes each of the steel types of the surface layer and the inner layer (in the display), the data of the break current register (the target value of the energization current of the electromagnetic brake 6).
And the V value corresponding to VJ (the value obtained in step 13) are read from the β access table and saved in the register.

Next, based on the equation (17), the surface layer thickness D (k) corrected for thermal shrinkage is calculated (20). In the formula (17) used for this calculation, DC (k) is calculated in step 15, D
R (k) is calculated in step 18, and β is calculated in step 19.
The value α derived from the above is the data being displayed.

As described above, a data representing the surface layer thickness (estimated value) in the cold (normal temperature) of the cast slab produced under the present casting conditions.
This means that DC (k) has been obtained.

The computer 30 then transfers the latest DC (k), Q1C, Q2C, L1J and VJ obtained in the above process to the computer 20, and the latest from the computer 20. Casting speed target value data, molten metal level target value data, surface layer thickness target value data, energization current target value data for electromagnetic brake 6, opening degree target value data for stopper 5s, and Upon receiving the transfer of the opening target value data of the stopper 5i, these are saved in the register (21). The target current value data of the electromagnetic brake 6 is written in the above-mentioned brake current register.

Next, the computer 30 adds the latest data obtained in the above process to the data being displayed on the CRT display 32, and adds the manufacturing date and time and the slab longitudinal direction index (corresponding value k). Generated data group and CR
Update display on the T display. When the first calculation is completed after the surface layer thickness calculation start, the entire data group is printed out by the printer 33 and registered in the floppy disk, but the second and subsequent calculations are performed. At the time of completion, the data group obtained this time is compared with the data of the previous data group table, and the output data in which only the items having different data and that data are extracted are compared. A group is generated, printed out by the printer 33, and registered in the floppy disk (22).

Upon completion of these output processes (22), the computer 30 returns to "input reading" (3) and the timer D
Wait for T to time over (3-5-10-11-
3).

When the timer DT time-overs,
Start the timer DT again and read the detected value.
(13) -Data output (22) is executed. That is, D
In the T cycle, one cycle of processing (12 to 22) from reading the detected value to calculating and outputting the surface layer thickness is repeated.

The first computer 20 sends the measured values Q1C, Q2C, L from the second computer 30 in the DT cycle.
1J and VJ and surface thickness (estimated) D (k) are given. While the "automatic control" is designated, the first computer 20 sets the casting speed target value, the molten metal surface level target value, the surface layer thickness target value, and these feedback values VJ, L.
The stopper controller 17 generates the flow rate target values of the molten steel for the surface layer and the inner layer and the energization current level target value of the electromagnetic brake for making the deviation from 1 J and D zero.
18 and a break controller 19. These controllers 17 to 19 have these target values and feelers.
The stopper drivers 15s and 15i and the brake driver 16 are driven (controlled) so that the deviations from the feedback values Q1C and Q2C and the actual energization current value become zero.

When the automatic control stop is input, the first computer 20 enters the manual intervention mode, stops the above-mentioned automatic control, and the operator gives an opening instruction via the keyboard 21. Positioning the stoppers 5s and 5i each time (opening setting)
However, the current value of the electromagnetic brake 6 is also keyed by the operator.
The value is designated via the board 21. After the automatic control stop is input, while there is no operator input, the opening target values of the stoppers 5s and 5i and the energization current target value of the electromagnetic brake 6 are maintained at the values at the time of stop input, and there is no disturbance. As long as the stopper opening and the value of the energizing current do not change.

The above equation (1) is used for the inner layer molten steel Q2C.
And ρ2 is a calculation formula of the boundary level moving velocity d (L2C) / dt based on the mass balance principle regarding the inner layer cross section, which can also be expressed using the surface molten steel Q1C, ρ1: However, ・ Q1C surface molten steel flow rate (kg / sec) ・ ρ1 surface molten steel density (g / cm ³ ) In this case, the surface layer sectional area S1 is calculated instead of the boundary layer sectional area S2, and the formula (1) is calculated. Q2C to Q1C, ρ2
Is replaced with ρ1 and S2 is replaced with S1.

Therefore, in order to calculate the surface layer thickness, one of the surface layer molten steel flow rate Q1C and the inner layer molten steel flow rate Q2C may be detected and used for the surface layer thickness calculation. In the above embodiment, Q2
Computer 2 detects both C and Q1C.
This is because 0 is given a flow rate feedback value for automatic injection flow rate control.

As described above, the hot theoretical surface layer thickness is obtained from the mass flow model, and redissolution correction, transition layer correction and heat shrinkage correction are added to estimate the cold surface layer thickness.
That is, since it is possible to estimate the product surface layer thickness online and in real time, if the surface layer pouring amount is controlled based on the surface layer thickness estimated value, the surface layer thickness control accuracy can be improved, and the surface layer thickness of the entire slab can be improved. Guarantee becomes possible.

[Brief description of drawings]

FIG. 1A is a block diagram showing a main part of a continuous casting facility and additional equipment for carrying out the present invention in one embodiment. (B) is a sectional view taken along line BB of (a).

FIG. 2 is a block diagram showing an outline of a computer system connected to the device shown in FIG.

FIG. 3 is a flowchart showing an outline of functions of the second computer 30 shown in FIG.

[Fig. 4] After starting pouring into the mold 1 shown in Fig. 1, the component concentration of the surface solidification shell 7s converges to the component concentration corresponding value (100%) when it is in the surface tundish 4s. Is a time chart showing the change in density up to.

[Explanation of symbols]

1: Mold 2: Mold Copper Plate 3i: Inner Molten Steel Nozzle 3s: Surface Molten Steel Nozzle 4i: Inner Molten Steel Tundish 4s: Surface Molten Steel Tundish 5i: Inner Tundish Stopper 5s: Surface Tundish Stopper 6: Electromagnetic Break 7: Slab 7i: Inner layer solidified shell 7s: Surface layer solidified shell 8: Measuring roll 9: Rotary encoder 10: Velocity calculator 11i: Inner layer tundish weighing machine 11s: Surface layer tundish weighing machine 12i: Inner layer tundish Flow velocity calculator 12s: Surface layer tundish Flow velocity calculator 13: Melt level detector 14: Melt level meter 15i: Inner layer tundish stopper driver 15s: Surface layer tundish stopper driver 16: Break driver 17: Surface layer tundish stopper Controller 18: Inner Tundisi Stopper controller 19: Break controller 20: 1st computer 21: 1st computer operation board 22: 1st computer CRT display 23: Temperature detection end 24: Temperature 30: 2nd computer 31: 2nd computer operation board 32: 2nd computer CRT display 33: Printer B: Short side direction mold width DC: Hot theoretical surface layer thickness estimation Value LMBD: Electromagnetic brake braking center level L1J: Hot water level ML: Mold length W: Long side direction mold width

Claims (1)

[Claims] 1. A mold in which an electromagnetic brake is mounted is divided into two regions in which a strong braking force of the electromagnetic brake acts.
The molten metal for the surface layer and the inner layer is injected into the mold through each of the pouring nozzle opened to one of the regions and the pouring nozzle opened to the other, and the solidified shell of the molten metal for the surface layer is formed on the inner surface of the mold. During continuous casting to form a molten metal solidified shell for the inner layer inside, at least one of the flow rates Q1C and Q2C of the molten metal for the surface layer and the inner layer, the molten metal level in the mold L1J, the casting speed VJ And the mold width W in two directions orthogonal to the drawing direction,
Using B, the solidified layer thickness DC of the molten metal for the surface layer and the boundary level L2C of the molten metal for the surface layer and the inner layer are calculated by the mass flow model and the solidification rate model. The surface layer thickness of the multilayer cast product, in which the level L2C, the temperature T2 of the molten metal for the inner layer, and the mold length ML in the drawing direction are used to calculate the surface layer thickness D by decrement correction using the remelting model and the heat shrinkage model. Estimation method.