EP2346631B1 - Method and device for controlling the solidification of a cast strand in a continuous casting plant at startup of the casting process - Google Patents

Description

The invention relates to a method for casting a cast strand in a continuous casting machine equipped with a process computer having at least one casting machine, wherein the process computer comprises a first software which calculates in real time and regulates the casting process.

From the WO 2000 05014 A1 is a casting mill with a computing device known to be handled with the various production orders. For this purpose, the sequence of slabs belonging to the production orders is determined within the sequences with the computing device by a "genetic" algorithm, and the cast roll plant is controlled by the computing device according to the determined sequence. The "genetic" algorithm should be able to "take into account the technical and order constraints in an optimized way to allow optimized operation of the casting mill.

The WO 2004 048016 A2 discloses a method and apparatus for continuously casting slab, thin slab, billet, pre-profile, billet strands and the like of liquid metal, particularly steel material. There is a system control with a computer, to which the respective local measured values of the cooling medium, the cooling medium quantity, the cooling medium pressure of the secondary cooling zone and the measured values of the setting forces of the support roll stand and the surface temperature at the bottom end of the metallurgical strand length are fed online on the input side.

The WO 1996 28772 A1 relates to a control system for a plant of the raw materials or the processing industry, in particular for a metallurgical plant. In such a control system, a better production success should be achieved, in particular in the strip casting of metal strips. For this purpose, a control system is used, which is based on entered input prior knowledge, automatically provide situation-specific instructions for safe and optimal (optimal) process control.

According to one embodiment of the control system is provided that the control system has a basic functional system for the system components, which the instructions from the computational, z. B. from a process model, preferably a process overall model, knowledge gained, safely implemented in the plant management.

From the US Pat. No. 6,564,119 B1 there is a method of monitoring the operation of a continuous casting process using a multivariate statistical model that also uses process parameters measured outside the production process to represent the normal operation of the casting plant. This should also be able to predict breakthroughs in a casting mold. The occurrence of undesirable solidification of the steel in the casting mold based on a multivariate statistical model of normal function is predicted.

In the WO 2005 120747 A1 discloses a method for continuously casting a metal strand with a continuous casting mold and a downstream strand support device. To form a specific microstructure in the cast strand, continuous casting is carried out on the basis of a thermomechanical calculation model describing the stress on the metal during casting and during the solidification process taking place, with which the stress state of the strand is calculated online. The variable influencing the material load, such as the specific cooling amount provided for cooling the strand, is set during the ongoing casting process. In this case, a calculation model describing the crack-sensitivity of the microstructure and the crack-formation energy stored in the structure of the microstructure is used to form the desired crack-free microstructure.

In the WO 2004 080628 A1 describes a cast rolling mill for producing a steel strip in which all components of the plant are guided by technological control loops. For integrated adjustment of technological The system comprises control circuits based on mathematical models, which interconnect the liquid steel device, the liquid steel adding device, the casting device, the reduction device, the deflection device, the rolling mill and the coiler of the casting rolling mill. The individual parts of the system are coordinated with each other in terms of their interaction in coordination such that take into account the effects of the control steps of a part of the plant on following in mass flow direction plant parts.

In the continuous casting of steel, the solidification is achieved by the primary cooling of the steel in the mold and the secondary cooling in the region of the strand guide. Within the strand guide water or a water-air mixture is injected under pressure in the remaining between the strand guide rollers areas directly on the strand shell; As a result, heat is removed from the strand. The course of the solidification can be divided into different phases. In the mold initially a thin strand shell solidifies with a thickness of a few millimeters, which is characterized by a fine-grained structure. Due to the high solidification rate, differences in the chemical composition due to diffusion can not be compensated practically. Therefore, the composition of the alloying elements in the strand shell deviates from the proportions of the respective elements in the melt. For example, some elements accumulate in the melt.

With increasing thickness of the strand shell, the heat transfer from the liquid steel in the strand core through the strand shell deteriorates to the outside. A phase of directional dendritic solidification begins with the major axes of the dendrites aligned along the heat flow direction. Again, the solidification rate is still so high that some alloying elements continue to accumulate in the residual melt. Part of the enriched melt remains between the dendrite arms, so that the chemical composition of the solidified strand shell can change within short distances. Depending on the fluidity of the solidifying residual melt prevent the geometric relationships between the growing strand shells from a certain time, ie when reaching the so-called critical sump diameter, the further exchange of the melt. With the method of soft reduction, the so-called "soft reduction", as for example, already from the EP 0 450 391 B1 However, a method for reducing unwanted segregation effects is available. Here, the strand thickness is reduced in the field of Enderstarrung by external forces in addition to the thermal shrinkage, so as to compensate for the increased volume reduction of the liquid strand core and to prevent the suction of enriched residual melt.

From the essay " Soft reduction of billets on the continuous casting plant S0 of Saarstahl AG "(Stahl und Eisen 127 (2007) Nr. 2, pages 43 - 50 , A method is known by which the effect of soft reduction, ie the soft reduction, can be assessed on the internal quality of the casting strand with little effort. For this purpose, in the area of secondary cooling, all those rollers that are involved in the soft reduction or behind the area of soft reduction are raised. From this article, it is also known, with the help of mathematical-physical models, the temperature, the sump tip or the position of the critical sump diameter to control. Control variables for the control processes are the water quantity of the secondary cooling and the casting speed.

It is the object of the invention to improve the productivity in the production of a cast strand by already after only a few meters of a slab, a billet or billet of a metal strand have been poured, the desired material conditions are met.

According to the invention this object is achieved in a method of the aforementioned Art solved by the fact that a second additional, fast computing software in the process computer, the casting process during the initial phase of a new incipient casting process or a parameter change of the casting strand to be cast during the current process influenced by the second software currently obtained data from the current casting process and / or processes stored data from a database and generates correction factors with which the second software generates corrected target data for the casting process, up to the time when the casting process with the data calculated in real time is completely displayed and the first software exclusively with these Data governs the casting process.

In this way, it is possible to reduce the length of the usually rejected as unusable strand material, especially in the start-up phase of the casting process. Conventionally, a strand length of up to 25 m of a slab or a billet often can not be used. Taking into account that in many cases up to six strands of billets or two strands of slabs are poured and straightened in parallel, this results in the prior art loss of a total billet length of 150 m, which is avoided by the invention.

However, since at least the length of the secondary cooling area of the cast strand is required in the start-up phase until the first software of the system computer used for the regular determination of the target data, for example the amount of cooling water, can calculate the controlled variable in real-time, and others Time passes until the controlled variable can be maintained, according to the invention, a second software is used in the same system calculator in order to be able to supply the required control parameters from the outside, so that in contrast to the prior art almost from the beginning of the casting process, ie from the emergence of a cast strand below the casting mold, no unusable strand material more accumulates. By the invention, the productivity is increased by already in the first cast meters can be given the values or ranges of values of the cast strand specified for the current operation. This is achieved by installing additional software parallel to the real-time compute first software, the second high-speed software to generate the setpoint data at the start of the process or when changing process parameters such as the thickness and width of the casting strand.

The task of the second software is to use the process parameters and the nominal values (target temperature, nominal position of the critical sump diameter or the target sump tip) to determine the necessary quantities of coolant (quantities of water) at the start of casting or when switching on the control. This is particularly important because the setpoints are strongly influenced by the current process parameters such as the actual analysis, the superheat of the melt, the current coolant temperature of the coolant (water) of the secondary cooling and the heat dissipation in the mold.

Advantageous developments of the invention will become apparent from the dependent claims, the description and the single FIGURE.

Preferably, the second software uses both process parameters and nominal sizes of the casting process.

Advantageously, the target casting speed, in particular for larger strand cross sections of the cast strand, the target temperature of the cast strand at a predetermined position or the setpoint temperatures at a plurality of predetermined positions, in particular on the surface, the desired position of the critical sump diameter (CMD ) (CMD = critical mushy diameter) and / or the desired sump tip of the casting strand in the region of the output of the casting machine used. Larger strand cross-sections are to be understood in particular those of more than 200 mm. Preferably, as a process parameter, the result of a steel analysis. Temperatures of the molten metal in the tundish, in the casting mold, amounts of cooling water for cooling the mold and the secondary cooling area and cooling water temperatures of the cooling water used to cool the mold and in the secondary cooling area.

Advantageously, it can also be provided that when either the first software and / or the second software are switched off, a third software for the data transfer between the continuous casting machine and the first and the second software causes after switching on the first and the second Software for a fixed period of time, the target data for the continuous casting process are generated exclusively using data stored in the database.

Likewise, it is advantageous if the second software comprises a database with stored process data which subsequently simulates the course of a casting process carried out by means of a simulation or replay function.

It is also advantageous if the second software uses a modified simulation or replay function to reduce the dead time until the first software is used.

In addition, it is advantageously provided that a device for measuring the strand length of the cast strand measures and that when a predetermined strand length is exceeded, the replay function can be switched on.

In general, the invention is realized as a software solution for improving the functions of a known per se computer of a continuous casting with at least one continuous casting mold. However, the invention may alternatively be in the form of an additional computer or one with additional memory equipped computer can be realized.

In this case, the invention also relates to a device for controlling the casting process in a continuous casting plant with a real-time controlling device for carrying out a method as described above.

The device according to the invention is characterized in that it has a high-speed computer for providing target data and process data in the initial phase of the casting process or when changing the metal to be cast or the metal alloy during the current casting process and that the controller instead of the real-time calculated data that of the Speed calculator provided data provided.

Preferably, the device comprises a database with stored process data, wherein the high-speed computer by means of a simulation function (replay function) subsequently simulates the course of a casting process performed. In addition, it is provided that the process data stored in the database can be used during the initial phase of the casting process or during a change within the current casting process by the control device.

Another advantage arises when the speed calculator uses a modified simulation function to reduce the dead time until the regular controller is used.

The invention will be explained in more detail in an embodiment with reference to the single figure. This shows in a schematic way the data transfer within the continuous casting plant.

To be able to perform the calculation as quickly as possible, be at the beginning a casting process of a software 1 (FIG. 1) for generating target data for the process for casting the cast strand simultaneously with the software 2 calculating in real time, supplying all process data 3 from a cast strand 4 via a data interface 5. However, the software 1 does not receive the actual casting speed, but the target casting speed and the target values stored, for example, in a cooling program that generates the data for cooling the strand. With this information, the software 1 simulates the continuous casting process much faster than in real time and controls the setpoints within the simulation by changing the manipulated variables such as water quantity and casting speed. This makes it possible to provide the coolant quantities necessary in the casting process to reach the setpoint values as quickly as possible. The software 1 determines a current correction factor 6 for the specific coolant application during the initial phase of the casting process; the correction factor 6 is forwarded via the interface 5 to the circuit part for calculation with the software 2. This then generates target data 7 for the amount of coolant, in particular the amount of water, and sends them via the interface 5 to the casting strand 4. All data is transmitted to a database 8.

From the database 8, the software 1 takes data 9 from earlier casting processes, which can be utilized for the control of the initial phase of the casting process currently taking place and which are delivered to the software 1 via the data interface 5. In particular, this is possible and necessary if, for example, due to an operating error, the computer system was not switched on for a while, with the exception of the data interface 5 and the software associated with the data interface 5. Then, when the computer is turned on, the software 2 first takes the necessary data from the database 8, which are provided via the data interface 5 available.

For larger strand cross sections is a control to a desired position of the critical sump diameter in Gießstrang with the help of the coolant not suitable, because this is the risk of low surface temperatures, leading to surface damage to the strand. In this case, a control of the casting speeds for the control of the critical sump diameter (CMD = critical mushy diameter) is more suitable.

Modified replay functions allow the operator of the continuous casting plant to simulate castings that have been carried out in the past. This is done by means of the stored in the database 8 process data.

Another way to reduce rejects or quality degradation of continuously cast material is to use a modified replay function if the software 1 and / or software 2 of the computer were turned on too late. The modified replay function makes it possible to reduce the dead time until the calculation process starts with the software 1, 2, in that the simulation is not performed in real time, but at maximum computing speed.

This is achieved by checking the current casting length when the software 1, 2 is switched on. If the casting length is greater than, for example, ten meters, the replay function is automatically switched on. The software is now not supplied with the current process data, but with the help of the replay function, the process data stored in the database 8 is transmitted. The software 1, 2 then calculates as quickly as possible, and only when the simulated casting length matches the current casting length, the software switches 1, 2 again in the normal control mode, in which the current process data is processed in real time.

LIST OF REFERENCE NUMBERS

1

software

2

software

3

process data

4

cast strand

5

Data Interface

6

correction factor

7

nominal data

8th

Database

9

Data from previous casting processes

Claims (13)

1. Method of casting a cast strip (4) in a continuous casting plant, which is equipped with a process computer, with at least one casting machine, wherein the process computer comprises first software (2) which computes in real time and regulates the casting process, characterised in that second, additional, software (1) in the process computer influences the casting process during the initial phase of a newly instituted casting process or in the case of parameter change of the cast strip, which is to be cast, during the current process in that the second software (1) processes instantaneous obtained data from the current casting process and/or stored data from a databank (8) and generates correction factors with the help of which the second software (1) produces corrected target data for the casting process up to a point in time from which the casting process is fully represented by the data computed in real time and the first software (2) regulates the casting process exclusively by these data.
2. Method according to claim 1, characterised in that the second software (1) employs not only process parameters, but also target variables of the casting process.
3. Method according to claim 1 or 2, characterised in that the target casting speed, the target temperature of the cast strip (4) at a predetermined position or the target temperatures at a plurality of predetermined positions, the target position of the critical liquid-phase diameter (CMD) (CMD = critical mushy diameter) and/or the target position of the liquid-phase end of the cast strip (4) in the region of the outlet of the casting machine or below the outlet is or are used as target variables.
4. Method according to claim 3, characterised in that the target casting speed in the case of greater strip cross-sections of the cast strip (4) is used as target variable.
5. Method according to claim 3 or 4, characterised in that the target casting speed in the case of strip cross-sections of more than 200 millimetres is used as target variable.
6. Method according to any one of claims 3 to 5, characterised in that the target temperatures at the surface are used.
7. Method according to any one of claims 1 to 6, characterised in that the result of a steel analysis, temperatures of the metal melt in the tundish, in the casting mould, cooling water quantities for cooling the mould and the secondary cooling region as well as cooling water temperatures of the cooling water for cooling the mould and in the secondary cooling region are used as process parameters.
8. Method according to any one of claims 1 to 7m, characterised in that if either the first software (2) or the second software (1) is switched off or if both the first software (2) and the second software (1) are switched off a third software (5) for data transfer between the continuous casting plant and the first and second software (2, 1) has the effect that after switching-on of the first and second software (2, 1) the target data for the continuous casting process are for a fixed period of time generated exclusively with use of data stored in the databank.
9. Method for using a device according to claim 12 or 13, characterised in that the regulating device during the current casting process uses, instead of the data computed in real time, data made available by the process computer.
10. Method of using a device according to claim 13, characterised in that the process computer subsequently simulates the course of a casting process, which is carried out, by means of a simulation function (replay function) and that the process data filed in the databank (8) are used by the regulating device during the initial phase of the casting process or in the case of a change within the current casting process.
11. Method according to claim 10, characterised in that the process computer uses a modified simulation function in order to reduce the dead time until use of the normal regulating device.
12. Device for controlling the casting process in a continuous casting plant with a regulating device, which computes in real time, for carrying out a method according to any one of claims 1 to 11, characterised in that it comprises a high-speed computer for providing target data and process data in the initial phase of the casting process or in the case of change of the metal to be cast or the metal alloy during the current casting process.
13. Device according to claim 12, characterised in that it comprises a databank (8) with filed process data.

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