TW202037425A - Control method for continuous casting machine, control device for continuous casting machine, and method for manufacturing slab - Google Patents

Abstract

A control unit 10 for a continuous casting machine according to an embodiment of the present invention is provided with: a molten steel flow state estimation unit 11 that uses an operation condition of the continuous casting machine 1 and temperature data about a molten steel inside a cast mold, to estimate online the flow state of the molten steel inside the cast mold; a molten steel flow index calculation unit 12 that calculates online a molten steel flow index serving as a cause for infiltration of impurities into a cast slab inside the cast mold on the base of the flow state of the molten steel estimated by the molten steel flow state estimation unit 11; and an operation condition control unit 13 that controls the operation condition of the continuous casting machine 1 so that the molten steel flow index calculated by the molten steel flow index calculation unit 12 is within an appropriate range.

Description

Control method of continuous casting machine, control device of continuous casting machine, and manufacturing method of cast piece

The present invention relates to a control method of a continuous casting machine, a control device of a continuous casting machine, and a manufacturing method of cast slabs.

In recent years, the requirements for high-quality castings such as slabs manufactured on continuous casting machines have become higher. Therefore, technology to control the condition of molten steel in the mold of the continuous casting machine was developed. For example, Patent Document 1 describes a method of applying a magnetic field to molten steel in a mold. By applying a magnetic field to the molten steel in the mold to control the flow of molten steel, the quality of the cast piece can be stabilized. However, even if a magnetic field is applied to molten steel, it is difficult to completely control the flow of molten steel due to unexpected operation changes. Therefore, the technology of controlling the operation by using the temperature measurement results of the molten steel produced by the temperature measurement element embedded in the mold copper plate is proposed. For example, Patent Document 2 describes a method in which the molten steel flow in the mold is corrected based on the copper plate temperature data in the mold to estimate the molten steel flow with high accuracy.

As one of the qualities required for the cast slab, there are few defects caused by impurities such as bubbles and inclusions mixed in the vicinity of the surface of the cast slab. In a continuous casting machine, molten steel poured into a mold through an immersion nozzle is solidified in a shell shape from the mold wall (hereinafter, the steel that solidifies in a shell shape is referred to as a "solidified shell"). With the progress of casting, the thickness of the solidified shell gradually increased. There will be bubbles and inclusions suspended in the molten steel poured into the mold. If these bubbles and inclusions are captured by the solidification shell and the solidification progresses as it is, it will become the above-mentioned defect.

Bubbles and inclusions suspended in the molten steel, the faster the flow rate of the molten steel at the solidification interface, the less likely it is to be captured by the solidified shell. Based on this point of view, the technology to appropriately control the flow of molten steel in the mold is also known Developed. For example, Patent Document 3 discloses a technique to prevent the occurrence of defects due to insufficient molten steel flow rate at the solidification interface when the casting speed is relatively slow at around 1.6 m/min. Specifically, this technique is to apply a moving magnetic field to the molten steel discharged from the immersion nozzle to impart a braking force to perform continuous casting, and to adjust the position of the immersion nozzle's discharge port relative to the position where the moving magnetic field is applied. The discharge angle is set in an appropriate range. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 10-305353 [Patent Document 2] JP 2016-16414 A [Patent Document 3] Japanese Patent Application Publication No. 2005-152996

[The problem to be solved by the invention]

Although Patent Document 2 describes a method for estimating the molten steel flow in the mold with high accuracy, it does not disclose or suggest at all that it is estimated that the molten steel flow index which is the main cause of the inclusion of impurities in the cast slab in the mold, and the molten steel The flow index is controlled within an appropriate range. In order to produce high-quality cast slabs, it is presumed that the molten steel flow index which is the main cause of mixing impurities into the cast slab in the mold, and it is necessary to control the molten steel flow index within an appropriate range. Therefore, according to the method described in Patent Document 2, it is difficult to produce high-quality cast slabs.

On the other hand, although Patent Document 3 describes a method of controlling the flow rate of molten steel at the solidification interface within an appropriate range, the appropriate range is only defined by the geometric relationship of the equipment. However, in actual continuous casting, there are fluctuations in the flow rate of molten steel, such as the adhesion of inclusions in the nozzle hole of the dipping nozzle, and the occurrence of drift. Even if such a fluctuation occurs, it must be adjusted according to the fluctuation. The flow rate of molten steel at the solidification interface is controlled within an appropriate range. In other words, the main reason for mixing bubbles, inclusions and other impurities into the cast slab in the mold, that is, the decrease in the flow rate of molten steel at the solidification interface, is used as an indicator of molten steel flow, and the operating conditions of the continuous casting machine and the internal mold The temperature data of the molten steel is estimated, and the flow index of the molten steel is controlled within an appropriate range based on the estimated result, so as to produce higher-quality cast pieces.

The present invention was developed in view of the above problems, and its purpose is to provide a control method for a continuous casting machine that can produce high-quality cast slabs, a control device for a continuous casting machine, and a manufacturing method for cast slabs. [Technical means to solve the problem]

The control method of the continuous casting machine of the present invention includes a molten steel flow state estimation step, a molten steel flow index calculation step, and a working condition control step. The molten steel flow state estimation step uses the working conditions and molds of the continuous casting machine The temperature data of the molten steel in the mold is estimated online, and the molten steel flow index calculation step is based on the flow state of the molten steel estimated in the aforementioned molten steel flow state estimation step Calculate on-line the molten steel flow index which is the main reason for the inclusion of impurities in the cast slab. This operation condition control step is to make the molten steel flow index calculated in the aforementioned molten steel flow index calculation step into an appropriate range The way to control the operating conditions of the aforementioned continuous casting machine.

The aforementioned molten steel flow index may include: the area of the region where the flow velocity is below a predetermined value in the stirring flow generated by the electromagnetic stirring magnetic field.

The aforementioned molten steel flow index may include: the speed or flow state of the molten steel surface.

The aforementioned molten steel flow index may include an area where the flow velocity of the solidification interface becomes less than a predetermined value.

The aforementioned molten steel flow index may include: the maximum value of the surface flow rate of molten steel.

The aforementioned molten steel flow index may include: the maximum value of turbulent flow energy on the molten steel surface.

The aforementioned temperature data of the molten steel in the mold may be temperature data including the measured value of a temperature sensor installed in the mold.

The operating conditions of the aforementioned continuous casting machine may include at least one of the casting speed, the magnetic flux density of the electromagnetic stirring magnetic field, and the nozzle immersion depth.

The aforementioned operation condition control step may include: estimating the flow state of the molten steel when at least one of the casting speed, the magnetic flux density of the electromagnetic stirring magnetic field, and the nozzle immersion depth is slightly changed in each control cycle, thereby calculating Steps for the sensitivity of molten steel's flow state to changes in operating conditions.

The aforementioned operation condition control step may include the step of calculating and controlling the mutual interference among the casting speed, the magnetic flux density of the electromagnetic stirring magnetic field, and the nozzle immersion depth in an explicit method.

The control device of the continuous casting machine of the present invention is provided with a molten steel flow state estimation section, a molten steel flow index calculation section, and a working condition control section. The molten steel flow state estimation section uses the working conditions of the continuous casting machine and the mold The temperature data of the molten steel in the mold is estimated online; the molten steel flow index calculation section is based on the flow state of the molten steel estimated by the aforementioned molten steel flow state estimation section. Calculate the molten steel flow index, which is the main cause of the inclusion of impurities in the cast slab in the mold; this operating condition control unit is to make the molten steel flow index calculated by the aforementioned molten steel flow index calculation unit fall within an appropriate range Control the operating conditions of the aforementioned continuous casting machine.

The manufacturing method of the cast slab of the present invention includes the step of manufacturing the cast slab under the control of the continuous casting machine using the control method of the continuous casting machine of the present invention. [Effects of Invention]

According to the control method of the continuous casting machine, the control device of the continuous casting machine, and the manufacturing method of cast slabs of the present invention, high-quality cast slabs can be manufactured.

Hereinafter, with reference to the drawings, the structure and operation of a control device for a continuous casting machine according to an embodiment of the present invention will be described.

[Structure of continuous casting machine] First, referring to FIG. 1, a configuration example of a continuous casting machine used in the present invention will be described.

Fig. 1 is a schematic diagram showing a structural example of the continuous casting machine used in the present invention. As shown in Fig. 1, the continuous casting machine 1 has a casting mold 4 placed vertically below the feed trough 3 filled with molten steel 2 and at the bottom of the feed trough 3: a supply port for molten steel 2 to the mold 4 The dipping mouth 5. The molten steel 2 is continuously poured into the casting mold 4 from the feed tank 3, cooled by the casting mold 4 with a cooling water channel inside, and pulled out from the lower part of the casting mold 4 to become a flat blank. At this time, in order to make the weight of the molten steel 2 injected into the mold 4 coincide with the weight of the drawn flat blank, a sliding gate (not shown) provided directly above the dipping nozzle 5 is used in accordance with the drawing speed. nozzle) and so on to adjust the opening of the dip nozzle 5. A plurality of temperature sensors are provided on the F surface and the B surface at the two ends of the thickness direction of the flat blank to be cast in the mold 4. Each temperature sensor measures the temperature of the molten steel 2 at each installation position. In addition, a coil (not shown) that generates an electromagnetic stirring magnetic field is installed in the mold 4 to induce a stirring flow in the molten steel 2 in the mold 4.

[Structure of control device] Next, referring to Fig. 2, the structure of a control device for a continuous casting machine according to an embodiment of the present invention will be described.

Fig. 2 is a block diagram showing the structure of a control device of a continuous casting machine according to an embodiment of the present invention. As shown in FIG. 2, the control device 10 of the continuous casting machine of one embodiment of the present invention is constituted by an information processing device such as a computer, and the internal components of the CPU (Central Processing Unit) The arithmetic processing device executes a computer program and functions as the molten steel flow state estimation unit 11, the molten steel flow index calculation unit 12, and the work condition control unit 13.

The molten steel flow state estimation unit 11 uses known techniques such as the method for estimating the flow state of molten steel described in Patent Document 2 to estimate the flow state of the molten steel 2 in the mold 4 on-line. Specifically, the molten steel flow state estimation unit 11 uses a physical model such as computational fluid dynamics that takes the turbulent flow mode into consideration, and is based on the operating conditions of the continuous casting machine 1 and the measured value of the temperature sensor installed in the mold 4 To estimate the flow state of the molten steel 2 in the mold 4 online. As the operating conditions of the continuous casting machine 1, the casting width, the casting speed, the magnetic flux density of the electromagnetic stirring magnetic field, the immersion depth of the dipping nozzle 5 (nozzle immersion depth), and the like can be exemplified.

The molten steel flow index calculation section 12 uses the data of the flow state of the molten steel 2 estimated by the molten steel flow state estimating section 11, which will be the main reason for the inclusion of impurities in the flat blank (slab) in the mold 4 The molten steel flow index is estimated online. Here, the impurities mixed into the flat embryo include inclusions derived from mould powder. The casting powder is a lubricant that is always supplied to the upper surface of the molten steel injected into the mold 4 to prevent sand burning of the mold 4 and the flat blank, and also has the thermal insulation effect of the molten steel 2 and so on. At the uppermost part of the molten steel 2 in the mold 4, the molten cast powder contacts the molten steel 2 and the molten steel 2 flows at a certain flow rate. Here, in the present invention, the flow velocity of the molten steel 2 at the contact position with the casting powder is referred to as the surface flow velocity of the molten steel 2. Therefore, if the surface flow rate of the molten steel 2 is too large, the molten cast powder may be caught in the molten steel 2 and become an inclusion defect. In addition, inclusions such as alumina, together with bubbles such as argon (Ar) supplied from the immersion nozzle 5, rise with the flow of molten steel, and are absorbed by the molten cast powder layer to clean the molten steel 2. However, when the flow rate of the solidification interface is slow, inclusions and bubbles may be trapped on the side of the solidification shell and become the cause of surface defects in the product. Here, the flow velocity of the solidification interface refers to the flow velocity of the molten steel in the vicinity of the solidified shell in the mold.

Therefore, the molten steel flow index which is the main reason for the inclusion of impurities in the flat blank in the mold 4 can be exemplified: the maximum value of the molten steel surface flow rate in the mold 4 (the maximum flow rate of the molten steel surface) and the solidification interface flow rate below the predetermined value The area (low velocity area), the maximum value of turbulent flow energy on the molten steel surface. Specifically, the molten steel flow index calculation unit 12 calculates the molten steel at the uppermost part of the mold 4 (meniscus: the height position of the molten steel level) based on the data of the flow state of the molten steel 2 The flow state calculates the maximum value of the molten steel flow rate of the grid (the entire area of the width direction and the thickness direction) as the maximum flow rate of the molten steel surface. In addition, the molten steel flow index calculation unit 12 calculates based on the data of the molten steel 2 flow state: the molten steel flow state calculation grid (width direction) at a predetermined position in the height direction (casting direction) and thickness direction of the mold 4 For the entire area), the area of the grid is calculated for the molten steel flow state where the molten steel flow rate is below the predetermined value. For example, the molten steel flow index calculation unit 12 calculates the molten steel flow state at least from the meniscus position to 200 mm below it in the entire width direction and the mold height direction. The area of the mesh is added up on each side of the mold's long side, and this value is regarded as the area of low flow velocity. In addition, the molten steel flow index calculation unit 12 calculates the turbulent flow of the molten steel flow state calculation grid (the entire width direction and thickness direction) at the uppermost part of the mold 4 based on the flow state data of the molten steel 2 The maximum energy is used as the maximum turbulence energy on the molten steel surface.

Here, the turbulent flow energy is a value representing the intensity of the turbulent flow, and is obtained based on the deviation of the flow velocity with time variation at a certain spatial position from the time average value. Specifically, the turbulence energy is expressed by the mathematical formula shown below.

k代表亂流能量，U代表在某個空間位置之流體的流速之瞬間值，U_ave 代表在某個空間位置之流體的流速之時間平均值，U_i 代表在某個空間位置之流體的流速之相對於時間平均值的偏差。

k represents the turbulent flow energy, U represents the instantaneous value of the fluid velocity at a certain spatial location, U _ave represents the time average of the fluid velocity at a certain spatial location, U _i represents the fluid velocity at a certain spatial location The deviation from the time average.

Because the fast flow of molten steel at the solidification interface of the flat blank has the effect of reducing impurities (bubbles, inclusions) captured by the solidified shell from the molten steel 2, the low flow rate area becomes an effective index. The flow rate that should be judged to be a low flow rate here can be set individually according to the steel grade composition, the required quality level and the mold size, etc., and it does not need to be set to a certain value. According to the investigation by the inventors of the present invention, as a criterion for determining the low flow velocity, less than 0.05 m/s can be adopted. In addition, the area of low flow velocity, for example, when the unit area of the molten steel flow state calculation grid is set to 1cm ² (0.0001m ² ), when one of the long sides of the mold is judged to have 100 grids for the unit grid of low flow velocity , The low velocity area is 0.01m ² . In addition, the appropriate value of the low flow velocity area is also set individually according to the steel grade composition, the required quality level, and the mold size, etc., and does not need to be set to a fixed value. And according to the investigation of the present inventors, the quality standards required stringent conditions, may be employed as a standard 0.01m ² or less; the required quality level is not as stringent conditions, may be employed as the standard 0.02m ² or less. Since the slow flow of molten steel on the surface of the molten steel has the effect of suppressing the entrapment of casting powder into the molten steel 2, the maximum flow velocity on the surface of the molten steel becomes an effective index. In addition, the maximum value of the turbulent flow energy on the molten steel surface is an effective index for the same reason as the maximum flow velocity on the molten steel surface.

The operating condition control unit 13 controls the casting speed, the magnetic flux density of the electromagnetic stirring magnetic field, and the magnetic flux density of the electromagnetic stirring magnetic field in accordance with the molten steel flow index in order to control the molten steel flow index calculated by the molten steel flow index calculation unit 12 within an appropriate range. Operating conditions such as the depth of mouth immersion. For example, when the area where the flow velocity of the solidification interface becomes below a predetermined value exceeds a preset value, the operating conditions are controlled to increase the magnetic flux density of the electromagnetic stirring magnetic field to increase the electromagnetic stirring force. This is because as long as the flow rate of molten steel in the mold is further imparted by electromagnetic stirring force, the flow rate of molten steel can be increased even at the position where the flow rate of the solidification interface becomes below a predetermined value. In addition, even if the magnetic flux density of the electromagnetic stirring magnetic field is increased, the area where the flow velocity of the solidification interface is below the predetermined value still exceeds the value set in advance, and the location where the flow velocity of the solidification interface is below the predetermined value is close to the surface of the molten steel. The way the depth of the dipping nozzle becomes shallower controls the operating conditions. This is because if the depth of the dipping nozzle becomes shallow, the influence of the molten steel spit out from the dipping nozzle will appear on the side of the molten steel surface, and the flow rate of the molten steel on the molten steel surface will increase. On the other hand, by increasing the magnetic flux density of the electromagnetic stirring magnetic field, although the area where the flow velocity of the solidification interface falls below the predetermined value does not reach the predetermined value, the surface velocity of the molten steel and/or the surface turbulence energy of the molten steel exceeds the predetermined value. In the case of the value, the working conditions can be controlled so that the depth of the immersion nozzle becomes deeper while the magnetic flux density of the electromagnetic stirring magnetic field is increased. This is because if the depth of the dipping nozzle becomes deeper, the influence of the molten steel spit out from the dipping nozzle will not easily appear on the molten steel surface side, and the molten steel surface velocity and/or the molten steel surface turbulent flow energy will be reduced.

Generally speaking, the flow state of the molten steel 2 in the casting mold 4 changes according to the difference in the operating state of the continuous casting machine 1. For example, as shown in Figure 3, the dipping nozzle 5 used has two outlets 5a on the left and right. If inclusions such as alumina adhere to the outlet 5a on one side, the molten steel in the mold 4 The discharge flow of 2 produces a left-right difference (drift). This bias flow occurs even if the operating conditions such as the casting width, casting speed, and magnetic flux density of the electromagnetic stirring magnetic field are the same. By using the temperature sensor set in the mold 4, the measured value will include the flow state of the molten steel with the bias flow. It is reproduced with high accuracy, and the flow index of molten steel can be estimated online with high accuracy.

That is, the calculation condition of the molten steel flow index calculation unit 12 is corrected in a manner corresponding to the measured value of the temperature sensor installed in the mold 4, and the calculated value is updated successively, thereby making it possible to estimate more accurately online Flow index of molten steel. In addition, the number of temperature sensors, the pitch, and the sampling interval of the measured value can be set within a possible range according to the environment in which the present invention is implemented. According to the investigation by the inventors, if the temperature sensors are arranged at a pitch of 50 mm or less and a pitch of 100 mm or less in the casting direction and the width direction, and the measured values are sampled at 1 second intervals or less, the molten steel can flow The calculation accuracy of the index calculation unit 12 is further improved. By estimating the molten steel flow index online, it can be grasped whether the operation is carried out in an appropriate range with low risk of defect generation, and the molten steel flow index can be controlled within an appropriate range by changing the operating conditions. As a result, high-quality flat embryos can be manufactured.

In the present embodiment, although the low-velocity area is considered to be the area where the solidification interface flow velocity becomes less than a predetermined value, the molten steel flow index is not limited to the flow velocity of the solidification interface itself. As long as there is a region with a low flow rate in the molten steel flow (stirring flow) generated by the electromagnetic stirring magnetic field, etc., such a region will adversely affect the trapping of bubbles and inclusions on the solidification interface, so it can be regarded as Used as a flow index for molten steel. In this way, the area of low flow velocity is not limited to the flow velocity of the solidification interface, but can be defined in various ways. Similarly, the maximum value of the surface velocity of the molten steel and the maximum value of the turbulence energy on the surface of the molten steel indicate the surface state of the molten steel, which is related to the incorporation of casting powder as mentioned above. Therefore, the molten steel flow index is not limited to these maximum values, and the speed or flow state of the molten steel surface can be appropriately specified as the molten steel flow index.

In addition, the flow index of molten steel should be controlled based on the following two points. The first point is that the flow phenomenon of molten steel is nonlinear. That is, if the original operating conditions are different, even if the changes in operating conditions are the same, the changes in molten steel flow index are still different. Figure 4 (a), (b) shows the relationship between the change in the magnetic flux density of the electromagnetic stirring magnetic field and the change in the maximum flow rate of the molten steel surface under the two conditions of different magnetic flux densities of the electromagnetic stirring magnetic field. Under the conditions shown in Fig. 4(a), even if the magnetic flux density of the electromagnetic stirring magnetic field is changed, the maximum flow velocity on the molten steel surface hardly changes. In contrast, under the conditions shown in Fig. 4(b), if the magnetic flux density of the electromagnetic stirring magnetic field increases, the maximum flow velocity on the surface of the molten steel also increases. Furthermore, as described above, regardless of the operating conditions, a drift will occur in the spit flow of molten steel. Therefore, relative to the change of operating conditions, the sensitivity of the molten steel flow index may change all the time. If the established sensitivity is set in advance, it will be difficult to control the molten steel flow index within an appropriate range. Happening.

The second point is that there is mutual interference between operating conditions and molten steel flow indicators. For example, if the casting speed is increased, although the area with low flow velocity decreases, the maximum flow velocity on the surface of molten steel increases. In addition, by changing the immersion depth of the immersion nozzle, the maximum flow velocity on the molten steel surface and the maximum turbulence energy on the molten steel surface can be changed. In order to control all molten steel flow indicators within an appropriate range, it is necessary to implement control that combines several operating conditions and takes interference into account. However, if the amount of change in operating conditions is to be obtained by implicit calculation using iterative computation, the calculation time will be longer and dynamic control will be difficult. Therefore, it is advisable to consider interference and calculate the amount of change in operating conditions with an explicit method, and let it be reflected in the operating conditions of the next control cycle.

Fig. 5 is a flowchart showing the flow of the operating condition control process performed by the control device of the continuous casting machine according to one embodiment of the present invention. In the flowchart shown in FIG. 5, every time the molten steel flow index is calculated by the molten steel flow index calculation unit 12, it starts, and the operation condition control process proceeds to the process of step S1. In the case described below, the operating conditions A, B, and C are changed in order to control the low-velocity area S, the maximum flow velocity V of the molten steel surface, and the maximum value E of the turbulent flow energy on the molten steel surface as an index of molten steel flow.

In the process of step S1, the work condition control unit 13 determines whether or not all the molten steel flow indexes calculated by the molten steel flow index calculation unit 12 are within an appropriate range. As a result of the determination, when all the molten steel flow indexes are within the appropriate range (step S1: Yes), the work condition control unit 13 does not change the work conditions, and ends a series of work condition control processing. On the other hand, when at least one of the molten steel flow indexes is outside the proper range (step S1: No), the work condition control unit 13 advances the work condition control process to the process of step S2.

In the process of step S2, the work condition control unit 13 estimates the molten steel flow state in the case where the work conditions of the operation target are changed slightly, and calculates the molten steel flow index. In addition, if the amount of change in operating conditions is greatly changed from the original operating conditions, the estimation accuracy of the molten steel flow distribution may deteriorate, so it is better to change within 10% of the original operating conditions. Next, the working condition control unit 13 calculates the difference between the calculated molten steel flow index and the molten steel flow index calculated by the molten steel flow index calculation unit 12, and calculates the sensitivity of the molten steel flow index after each working condition is changed. The degree vector, thereby obtaining the sensitivity matrix X. The sensitivity matrix X shown in the following mathematical formula (1) is the sensitivity vector (∂S/∂A,∂V/∂A,∂E/) of the molten steel flow index obtained after the operating condition A is changed ∂A), the sensitivity vector of the molten steel flow index after changing the operating condition B (∂S/∂B, ∂V/∂B, ∂E/∂B), and the situation after changing the operating condition C The sensitivity vector (∂S/∂C, ∂V/∂C, ∂E/∂C) of the molten steel flow index. Thereby, the process of step S2 is completed, and the work condition control process proceeds to the process of step S3.

In the process of step S3, the working condition control unit 13 calculates the difference between the molten steel flow index calculated by the molten steel flow index calculation unit 12 and the respective appropriate range, thereby obtaining the deviation vector Y. In the case where the deviations of the low flow velocity area S, the maximum flow velocity V of the molten steel surface and the maximum value E of the turbulent flow energy on the molten steel surface are ΔS, ΔV, and ΔE respectively, the deviation vector Y is expressed by the following mathematical formula (2) . Thereby, the process of step S3 is completed, and the work condition control process proceeds to the process of step S4.

In the processing of step S4, the operating condition control unit 13 uses the sensitivity matrix X obtained by the processing of step S2 and the deviation vector Y obtained by the processing of step S3 to calculate the optimal operating conditions by the least square method The change vector Z=(ΔA,ΔB,ΔC). The following mathematical formula (3) represents the relationship between the sensitivity matrix X, the deviation vector Y, the change amount vector Z of the working conditions, and the error vector ε. The least square method is a method to find the change amount vector Z that minimizes the square sum of the error vector ε in the mathematical formula (3) as the optimal solution. The change amount vector Z for the optimal working condition can be as follows Mathematical formula (4) is calculated. In this way, the change amount vector Z of the optimal working condition is calculated by an explicit method based on the original working condition of the known quantity and the molten steel flow index calculated by the molten steel flow index calculation unit 12. In this way, the processing of step S4 is completed, and the job condition control processing proceeds to the processing of step S5.

In the processing of step S5, the operating condition control unit 13 reflects the change amount vector Z= (ΔA, ΔB, ΔC) of the optimal operating condition obtained by the processing of step S4 in the operating condition to create the next control cycle Operating conditions. Specifically, the work condition control unit 13 uses the work conditions A+ΔA, B+ΔB, C+ΔC in the next control cycle. In this way, the processing of step S5 is completed, and a series of work condition control processing ends. [Example]

As this embodiment, the present invention is applied to the continuous casting of extremely low carbon steel. The mold size is 1200mm in width and 260mm in thickness, and the steady-state casting speed is 1.6m/min. In this embodiment, the proper range of the low flow velocity area is set to 0.02 m ² or less, and the proper range of the maximum flow velocity on the molten steel surface is set to 0.05 to 0.30 m/s, and the work is performed. During the operation, because the low flow velocity area calculated in the operation of the continuous casting machine 1 becomes larger than the appropriate range, the magnetic flux density of the electromagnetic stirring magnetic field is increased by 5%. As a result, as shown in FIG. 6, the stirring force of molten steel in the mold 4 is increased, the flow velocity at the solidification interface increases, and the low flow velocity area decreases. However, due to this change in operating conditions, the stirring force of the molten steel is increased, as shown in Fig. 7, and the maximum flow velocity on the surface of the molten steel may exceed the appropriate range. Therefore, the nozzle immersion depth was increased by 30 mm. This is because the spit flow from the dipping nozzle 5 will become a reverse flow when it hits the copper plate of the mold. The reverse flow and the stirring flow overlap each other to increase the velocity of the molten steel surface. By increasing the immersion depth of the immersion nozzle 5, the reverse flow The turning flow becomes smaller, and the surface velocity of molten steel can be suppressed. With this change in operating conditions, as shown in Figure 8, the low flow rate area can be reduced and the maximum flow rate on the molten steel surface can be controlled within an appropriate range. In addition, by estimating the molten steel flow index (maximum flow rate of molten steel surface, low flow rate area, and maximum value of turbulent flow energy on molten steel surface) online, it is possible to control the operating conditions in order to make the molten steel flow index into an appropriate range. As shown in Fig. 9, the flat embryo quality index, that is, the defect mixing rate of flat embryos can be reduced. It is thus confirmed that the control method of the continuous casting machine according to the present invention can produce flat blanks of excellent quality.

The embodiment shown in Fig. 10(a)~(d) is confirmed by simulation. The virtual factory is created by artificially generating disturbances like clogging the nozzle. By operating the magnetic flux of the electromagnetic stirring magnetic field Whether the density and casting speed, the low flow rate area calculated from the virtual factory and the maximum flow rate of the molten steel surface can be controlled within an appropriate range by the control device of the continuous casting machine of an embodiment of the present invention. When disturbance occurs at the time t=t1 shown in Fig. 10(a)~(d), the area of low velocity calculated by the molten steel flow index calculation unit 12 and the maximum velocity of the molten steel surface, and the virtual factory An estimation error occurs between the area with low flow velocity and the maximum flow velocity on the molten steel surface. Next, when the molten steel flow state estimation process starts at the time t=t2 shown in Fig. 10(a)~(d), the low velocity area and molten steel calculated by the molten steel flow index calculation unit 12 The estimation error of the maximum surface velocity, the low velocity area of the virtual factory and the maximum velocity of the molten steel surface is reduced. Furthermore, when the working condition control process is started at the time t=t3 shown in Fig. 10(a)~(d), the magnetic flux density of the electromagnetic stirring magnetic field increases and the casting speed decreases, which can reduce the low flow rate of the virtual factory The area and the maximum flow rate of the molten steel surface are controlled to near the upper limit of the appropriate range. It was confirmed that by estimating the molten steel flow index online (maximum flow rate of molten steel surface, low flow rate area, and maximum value of turbulent flow energy on molten steel surface), it can be controlled at any time to make the molten steel flow index into an appropriate range. Operating conditions, and can produce high-quality flat embryos. 10(a)~(d), the dotted line L1 represents the low velocity area of the virtual factory, the line L2 represents the low velocity area calculated by the molten steel flow index calculation unit 12, and the dotted line L3 represents the molten steel of the virtual factory The maximum surface flow velocity, and the line L4 represents the maximum surface velocity of the molten steel calculated by the molten steel flow index calculation unit 12.

The foregoing is the description of the embodiment using the invention developed and completed by the inventors, but the present invention is not limited to the description and drawings that constitute a part of the disclosure of the present invention based on this embodiment. For example, in the embodiment shown in Fig. 10(a)~(d), although the magnetic flux density and casting speed of the electromagnetic stirring magnetic field were verified, the low flow rate area, molten steel surface flow rate, molten steel surface Flow indicators such as turbulence energy can also be controlled by operating the magnetic flux density of the electromagnetic stirring magnetic field. In this way, other embodiments, examples, and operating techniques that can be completed by a person having ordinary knowledge in the technical field to which this embodiment belongs are all included in the scope of the present invention. [Industrial Utilization]

According to the present invention, it is possible to provide a control method of a continuous casting machine capable of producing high-quality cast slabs, a control device of a continuous casting machine, and a manufacturing method of cast slabs.

1: Continuous casting machine 2: molten steel 3: feeding trough 4: Mold 5: Dipping mouth 10: Control device 11: Molten steel flow state estimation section 12: Calculation of molten steel flow index 13: Working condition control department

[Fig. 1] is a schematic diagram showing a structural example of a continuous casting machine used in the present invention. [Fig. 2] is a block diagram showing the structure of a control device of a continuous casting machine according to an embodiment of the present invention. [Figure 3] is a schematic diagram showing a structural example of the dipping nozzle. [Figure 4 (a), (b)] shows the relationship between the change of the magnetic flux density of the electromagnetic stirring magnetic field and the change of the maximum flow velocity of the molten steel surface under the two conditions of different magnetic flux density of the electromagnetic stirring magnetic field. Fig. 5 is a flowchart showing the flow of operating condition control processing performed by the control device of the continuous casting machine according to one embodiment of the present invention. [Figure 6] shows an example of the change in the low-velocity area caused by the change in the magnetic flux density of the electromagnetic stirring magnetic field. [Figure 7] shows an example of the change in the maximum flow velocity of the molten steel surface caused by the change in the magnetic flux density of the electromagnetic stirring magnetic field. [Figure 8] shows an example of the change in the maximum flow velocity on the molten steel surface caused by changes in the magnetic flux density of the electromagnetic stirring magnetic field and the immersion depth of the nozzle. [Figure 9] It is an example of the change of the defect mixing rate of flat embryos caused by the control working conditions. [Fig. 10] is a sequence diagram showing an embodiment of work condition control processing.

1: Continuous casting machine

10: Control device

11: Molten steel flow state estimation section

12: Calculation of molten steel flow index

13: Working condition control department

Claims (12)

A control method of a continuous casting machine includes a step of estimating the flow state of molten steel, a step of calculating molten steel flow index, and a step of controlling operating conditions, The estimating step of the molten steel flow state is to use the operating conditions of the continuous casting machine and the temperature data of the molten steel in the mold to estimate the flow state of the molten steel in the mold online. This molten steel flow index calculation step is based on the molten steel flow state estimated in the aforementioned molten steel flow state estimation step, and calculates the molten steel flow index online, which is the main reason for the inclusion of impurities in the cast slab in the mold. This operating condition control step controls the operating conditions of the continuous casting machine so that the molten steel flow index calculated in the molten steel flow index calculation step falls within an appropriate range. The control method of a continuous casting machine as described in claim 1, wherein: The aforementioned molten steel flow index includes: the area of the region where the flow velocity is below a predetermined value in the stirring flow generated by the electromagnetic stirring magnetic field. The control method of the continuous casting machine according to claim 1 or 2, wherein: The aforementioned molten steel flow index includes: the speed or flow state of the molten steel surface. The method for controlling a continuous casting machine according to any one of claims 1 to 3, wherein: The aforementioned molten steel flow index includes the area where the solidification interface flow velocity becomes less than a predetermined value. The control method of the continuous casting machine described in claim 4, wherein: The aforementioned molten steel flow index includes: the maximum value of the surface flow velocity of molten steel. The control method of a continuous casting machine as described in claim 4 or 5, wherein: The aforementioned molten steel flow index includes: the maximum value of turbulent flow energy on the molten steel surface. The method for controlling a continuous casting machine according to any one of claims 1 to 6, wherein: The aforementioned temperature data of the molten steel in the mold includes the temperature data of the measured value of the temperature sensor set in the mold. The method for controlling a continuous casting machine according to any one of claims 1 to 7, wherein: The operating conditions of the aforementioned continuous casting machine include at least one of the casting speed, the magnetic flux density of the electromagnetic stirring magnetic field, and the nozzle immersion depth. The control method of a continuous casting machine according to claim 8, wherein: The aforementioned operating condition control steps include: Estimate the flow state of the molten steel when at least one of the casting speed, the magnetic flux density of the electromagnetic stirring magnetic field, and the nozzle immersion depth is slightly changed in each control cycle, thereby calculating the effect of the flow state of the molten steel on the operating conditions Steps to change the sensitivity. The control method of a continuous casting machine according to claim 8 or 9, wherein: The aforementioned operation condition control step includes the step of calculating and controlling the mutual interference among the casting speed, the magnetic flux density of the electromagnetic stirring magnetic field, and the nozzle immersion depth by an explicit method. A control device for a continuous casting machine is provided with a molten steel flow state estimation unit, a molten steel flow index calculation unit, and a working condition control unit, The molten steel flow state estimation unit uses the operating conditions of the continuous casting machine and the temperature data of the molten steel in the mold to estimate the flow state of the molten steel in the mold online; The molten steel flow index calculation unit is based on the molten steel flow state estimated by the aforementioned molten steel flow state estimating unit, and calculates on-line the molten steel flow index which is the main reason for the inclusion of impurities in the cast slab in the mold; The operating condition control unit controls the operating conditions of the continuous casting machine such that the molten steel flow index calculated by the molten steel flow index calculation unit falls within an appropriate range. A method for manufacturing cast slabs includes the step of manufacturing cast slabs under the control of the continuous casting machine using the control method of the continuous casting machine as described in any one of claims 1 to 10.

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