EP3733323A1 - Method and continuous casting plant for casting a cast strand - Google Patents

Abstract

The invention relates to a continuous casting plant (110) and a method for casting a cast strand (100). For this purpose, the continuous caster (110) comprises a mold (112) with a lower opening (113) which is formed on an underside of the mold (112), and a supporting strand guide (116) which is located at the lower opening (113) of the The mold (112) is connected, the cast strand (100) being movable along the supporting strand guide (116). Adjustable support rollers or pairs of rollers (118) are arranged along the supporting strand guide (116), with which a thickness reduction for the cast strand (100) takes place. The supporting strand guide (116) comprises a selected area (120) for a sump tip of the cast strand (100), the adjustable support rollers or roller pairs (118) being arranged exclusively in the selected area (120) of the strand guide (116).

Description

The invention relates to a method for casting a cast strand according to the preamble of claim 1, and a continuous casting plant according to the preamble of claim 12.

When operating continuous casting plants, it corresponds to the state of the art to cool the cast strand after exiting the mold in the so-called secondary cooling of a supporting strand guide of such plants until the cast strand has completely solidified. This cooling process plays an important role in the resulting quality of the cast strand and the products made from it. The complete solidification of the cast strand should lie within the supporting strand guides, which support the cast strand with a still liquid core.

The operation of the secondary cooling of a continuous casting plant is usually realized with spray or cooling water, whereby the amount of water that is applied to the surfaces of the cast strand is set by specifying setpoint temperature curves. The course of these target temperature curves can vary depending on the material of the material to be potted, and z. B. vary depending on certain cooling zones of the supporting strand guide and / or the casting speed. Depending on the material and the selected casting speed, an operator of the continuous caster then selects a target temperature curve and thus sets the secondary cooling for applying the spray or cooling water to the surfaces of the cast strand to be cooled. For example, higher (= warmer) target temperature curves can be used at low casting speeds. Conversely, lower (= colder) target temperature curves should generally be used at higher casting speeds in order to achieve a stronger cooling of the cast strand so that it still solidifies within the supporting strand guide.

In continuous casting, a target temperature curve determines the target values for the surface temperature to be achieved that the strand reaches within the supporting strand guide, e.g. B. at the end of individual cooling zones that are part of this supporting strand guide. The amount of splash water from the secondary cooling is regulated in such a way that these target values are achieved.

As already explained above, when operating a continuous caster it is of great importance that the cast strand solidifies completely within the supporting strand guide and does not run out of this supporting strand guide with its sump tip. For this reason, a selected area is provided for the supporting strand guidance, in which the sump tip of the cast strand should lie.

During the casting of slabs, blooms, billets, etc. there can be constant changes in parameters such as casting temperature, water supply temperature, heat dissipation in the mold, which influences the casting process and thus makes temperature and position control necessary, as there are no stationary conditions.

With increasing slab thickness, the area of the central segregation increases, with the number of pores increasing, so that their removal by soft or hard reduction requires special attention.

In order to achieve maximum production or improved internal quality through soft reduction, position control is advantageous. For position control in continuous casting, secondary cooling and the casting speed can be used as manipulated variables.

In the continuous casting of large slab thicknesses, however, it is problematic to use the secondary cooling water manipulated variable to influence the position of the sump tip of the cast strand in order to keep the sump tip in a defined area of the supporting strand guide. The effectiveness of the secondary cooling decreases with increasing slab thickness. The thicker the strand shell of the cast strand, the greater the energy to be dissipated so that the strand shell grows. At the same time, this means that the strand surface temperature is lowered. With the same sump tip position, but with a different cooling intensity, different temperature profiles are then established over the strand thickness.

According to the prior art, it is also known that slabs with a thickness of 400 mm or more are cast at a casting speed of up to 6 m / min.

A position control in relation to the sump tip of a casting strand by means of secondary cooling is associated with the disadvantage that with a major change in the casting temperature it is necessary either to reduce the amount of water very much or to increase it very much. If the amount of water is greatly reduced, there is a risk of bulging. On the other hand, there is a risk of surface cracks with a large increase or increase in the amount of water, because the surface of the cast strand is (too) cooled down. Another disadvantage, due to the high temperatures and long dwell times, is the heavy build-up of scale, which affects the surface temperature of the cast strand. This can falsify a measurement of the surface temperature of the cast strand.

Out EP 2 346 631 B1 a method and a device for controlling the solidification of a cast strand in a continuous caster when starting the casting process are known. Here, a continuous caster is equipped with a process computer on which a first software and a second software are installed. The first software calculates in real time and regulates, in a known way, the casting process that is carried out with the continuous caster. By means of the second software, for which a higher calculation speed is set compared to the first software, during the initial phase of a new casting process or when the parameters of the currently running casting process are changed on the basis of processing of currently obtained data from the running casting process and / or on Correction factors are initially generated on the basis of data stored in a database, the second software then generating corrected target data for the casting process using these correction factors and transferring them to the first software.

In the above technology according to EP 2 346 631 B1 The second software is used primarily to determine a casting speed or corrected setpoint data for this purpose, so that after this data is mirrored to the first software and a corresponding control by the first software, the position of the sump tip of the cast strand is transferred to the target or The target position is placed. In the course of this, it should be emphasized that the corrected soldiers calculated by the second software are taken over directly by the first software and are thus immediately taken into account in the control carried out by the first software. Furthermore, such an operating mode of the second software only takes place at the point in time from which the casting process is completely represented with the data calculated in real time, so that the first software then regulates the casting process exclusively with this data.

The invention is based on the object of creating a technology for the continuous casting of metals with which the position of the sump tip of a cast strand, in particular with a large cast thickness, can be held more reliably at a certain target position or in a certain target range of the supporting strand guide and a thickness of the produced cast strand with simple and inexpensive means is set and the soft reduction can take place in a certain area

This object is achieved by a method with the features of claim 1 and by a device with the features of claim 12. Advantageous further developments of the invention are defined in the dependent claims.

A method according to the present invention is used to cast a cast strand in a continuous casting plant equipped with a process computer with at least one casting machine. Here, the process computer includes at least a first piece of software that calculates in real time and regulates the casting process. In addition to this, the process computer includes a second additional software that calculates faster than in real time and thus has a calculation speed greater than the first software. With the second software, on the one hand, in association with a specific casting length and, on the other hand, depending on the currently obtained process parameters from the ongoing casting process, in particular in the area of the mold and / or from at least one process parameter stored in a database, the position for a sump tip of the cast strand is calculated the specific casting length along a supporting strand guide of the continuous caster would currently be available. The second software compares this calculated sump tip position with a target position or a target range for the sump tip and continuously calculates a casting speed correction value on the basis of this. Instead of the sump tip, a solid fraction or a strand shell spacing can also be used. Following this, the casting speed correction value calculated by the second software is transferred to the first software, with the first software regulating the sump position with the aid of the casting speed in real time and only the casting speed correction value calculated by the second software in association with the specific casting length taken into account with a delay resulting from a distance between the target position or the target area for the sump tip and the last in Real time set casting speed results. As a result, a sump tip position of the cast strand in the ongoing casting process is always found within a predetermined or selected area along the supporting strand guide or the sump tip of the cast strand is kept in this predetermined area.

The invention and the associated method are based on the essential knowledge that the second software runs continuously or makes calculations during the course of the casting process. In other words, the second software runs permanently in parallel with the actual speed control, which is carried out by means of the first software. In this way, effects of disturbance variables such as casting temperature, heat dissipation in the mold and / or changes in the water inlet temperatures (e.g. in the secondary cooling or the primary or mold cooling) can be separately taken into account by the second software and corresponding casting speed correction values can be calculated in this regard which are then transferred to the first software. In this context, it is important that the calculation speed for the second software is selected to be greater than for the first software. After these casting speed correction values have been received by the first software, the first software can determine the sump length (i.e. the position of the sump tip of the cast strand) with the aid of the casting speed, which is used as a manipulated variable, and taking into account the casting speed calculated by the first software. Regulate or adjust correction values.

Another "whistle" for the method according to the invention is that the casting speed correction values calculated by the second software, after they have been transferred or sent to the first software, are then not immediately delayed by the first software, but rather only delayed, ie with a time delay must be taken into account, which is dependent on the currently set casting speed and the target position or the target range for the sump tip of the cast strand. Exactly this delayed consideration of the Casting speed correction values calculated by the second software and by the first software make it possible to bring or keep the position of the sump tip in the predetermined or selected area of the supporting strand guide, ie in the target area.

In the method according to the invention, the sump tip is preferably used as the controlled variable. Here the sump tip for the cast strand is to be understood as a position along the supporting strand guide at which the strand center of the cast strand has solidified, ie the solid fraction (= "Solid Fraction") has the value of 1 (in other words: Solid Fraction = 1) .

In addition and / or alternatively, a defined solidification fraction in the center of the strand, which has a solid fraction fraction of <1, can be used as a controlled variable for the method according to the invention.

In addition and / or alternatively, the strand shell spacing can also be used as a controlled variable for the method according to the invention.

Because the calculation speed for the second software is set higher than that for the first software, the method according to the invention makes it possible to “look into the future” with regard to the casting process and its further course. For this, the following example: If the first software, which controls the casting process in real time, has a calculation time of 20 minutes, for example, the same sequence of the casting process can be performed in a much shorter time using the second software, e.g. B. can be simulated or calculated in just 30 seconds. Accordingly, by means of the calculation of the second software, compared to the calculation by means of the first software, it is possible at a significantly earlier point in time to gain knowledge about the further course of the casting process.

At this point it is emphasized separately that the feature “obtained” can be a setting or a measurement. This means that "obtained" process parameters in the context of the present invention are those that have either been set in a targeted manner (possibly on the basis of a previous calculation) or have been obtained as the result of a measurement.

• Schnelle Auswirkung auf die Positionsänderung der Sumpfspitze bei Änderung der Gießgeschwindigkeit;
• Keine großen Änderungen der Oberflächentemperaturen, somit auch nur geringe Änderung der Oberflächentemperatur im Richtbereich;
• Bei steigender Gießgeschwindigkeit steigt die Wassermenge durch eine geschwindigkeitsproportionalen Sekundärkühlung und verringert die Gefahr von Bulging;
• Bei reduzierter Gießgeschwindigkeit sinkt die Wassermenge durch eine geschwindigkeitsproportionalen Sekundärkühlung und verringert die Gefahr von Rissen im Richtbereich.

In the method according to the invention, the casting speed (= manipulated variable) is used as the manipulated variable for the position control of the sump tip or a defined solidification fraction in the center of the strand or a predetermined distance between the strand shells on the loose and fixed side, the setpoints for the secondary water quantities being adapted to this in proportion to the speed. The target position for the sump tip of the cast strand is set in the predetermined or selected area of the supporting strand guide, preferably within narrowly defined limits, within the supporting strand guide. The advantages of such a position control in relation to the sump tip are as follows:

• Rapid effect on the change in position of the sump tip when changing the casting speed;
• No major changes in surface temperatures, so only minor changes in surface temperature in the directional area;
• As the casting speed increases, the amount of water increases due to secondary cooling proportional to the speed and reduces the risk of bulging;
• When the casting speed is reduced, the amount of water decreases due to secondary cooling proportional to the speed and reduces the risk of cracks in the straightening area.

The disadvantage that otherwise exists in the prior art that long dead and control times (target position / casting speed) or the risk of instability of the control can occur is, as already explained above, with the present invention through the permanent use or operation of the encountered second software, whereby z. B. a long dead time can be greatly reduced.

For a method according to the present invention, it is also important that a temperature field is determined, preferably calculated, for the cast strand along its conveying direction within the supporting strand guide, so that the associated temperature is known for each calculated node of the cast strand, namely at a specific point of the cast strand or the system length, in particular within the supporting strand guide and its cooling segments. An exact position of the sump tip for the cast strand can then be determined from this.

In an advantageous further development of the invention it can be provided that for the calculation of the casting speed correction value by means of the second additional software at least one process parameter of the casting process is selected from the group of chemical composition of the material of the cast strand, current casting temperature, current casting speed, water supply temperature for secondary cooling, or water supply temperature for the mold primary cooling and / or the set casting length is taken into account. This advantageously means that current values or parameters of the current casting process and the type of metal processed in this connection are included in the calculations by the second software or are taken into account accordingly by the second software.

In an advantageous development of the invention, it can be provided that the casting speed correction value is calculated by means of the second software on the basis of process parameters stored in the database and is used by the first software at the beginning of the casting process as a manipulated variable to control it. This is particularly advantageous when starting the casting process at the beginning of a production process or after an interruption in operation.

In an advantageous development of the invention, it can be provided that the casting speed correction value is calculated by means of the second software as a function of currently obtained process parameters from the ongoing casting process. This casting speed correction value is then used by the first software to regulate the casting speed of the casting process if there are deviations between the target and actual values in relation to the temperature of the cast strand in the course of the casting process. The advantage here is that the second software, as already explained, is permanently "running" or switched on during the ongoing casting process. This ensures that the casting speed correction values calculated by the second software, which are then transferred from the second software to the first software to control the real casting process, can be responded to appropriately to possible deviations that may occur during the ongoing casting process.

In an advantageous development of the invention it can be provided that when calculating the casting speed correction value by means of the second software, a reference position along the supporting strand guide between the bath level and the target position or the target area for the sump tip is selected. In the course of this, it can be provided that all target speeds calculated by the second software are used one after the other. In this case, there is a kind of average value formation with regard to the formation of the sump length, since the sump length results integratively from the history of the casting speeds. In this case, the reference position can expediently lie at a point on the supporting strand guide which is between 40% and 70% of the distance between the bath level and the desired position of the sump tip. This reference position can preferably be located at at least 60% of the distance between the bath level and the target position of the sump tip.

In an advantageous development of the invention, it can also be provided that the calculation of the casting speed correction value by means of the second software is based on the fact that the current target speed is averaged from all positions along the casting length up to the position of the sump tip. This means that all casting length positions that are currently in the supporting strand guide have been successively assigned a target speed by the second software in the course of time or the calculations. Such an assignment can be understood to mean that the calculated values of the second software, i.e. the casting speed correction values calculated by means of the second software from the previous period are used for the current definition of the target casting speed in the first software in order to control the position of the sump tip of the cast strand in the future period. Since the current casting speed affects the strand cross-sections along the supporting strand guide at all positions from the meniscus to the sump tip, it is useful to use all these target speeds z. B. to be taken into account in the form of an average value for determining the current target speed. Values that are most frequently represented - regardless of which position they are assigned to - are represented more strongly by the average value than values that rarely occur (e.g. outliers).

The present invention also provides a continuous caster for casting a cast strand. Such a continuous casting plant comprises a mold with a lower opening which is formed on an underside of the mold, a supporting strand guide which is connected to the lower opening of the mold, the cast strand being movable along the supporting strand guide. Furthermore, in the continuous caster according to the invention, adjustable support rollers or pairs of rollers are arranged along the supporting strand guide, with which a thickness reduction for the cast strand takes place. The supporting strand guide has a selected area in which a sump tip of the cast strand is to lie, with support rollers or pairs of rollers that allow a soft reduction adjustment have, are arranged exclusively in the selected area of the strand guide.

The "whistle" of the above-mentioned continuous caster is that the support rollers or pairs of rollers that can be adjusted for soft reduction and are provided for the supporting strand guide are arranged exclusively in the selected area in which the sump tip of the cast strand should also be located. In other words, when this continuous caster is in operation, it is provided that the target position for the sump tip of the cast strand comes to lie in said selected area of the supporting strand guide. In this way it is possible to carry out a targeted soft reduction for the cast strand by means of the adjustable support rollers or roller pairs of the selected area of the supporting strand guide. All other support rollers or pairs of rollers, which - viewed in the conveying direction of the cast strand - are usually upstream of the selected area, can thus be of conventional design, namely without a soft-reduction adjustment function. With these conventional support rollers, only the thermal shrinkage of the cast strand 100 is followed.

In an advantageous further development of the continuous casting plant according to the invention, it can be provided that the support rollers or pairs of rollers are combined to form roller segments. This facilitates both the assembly and disassembly of the individual support rollers when they are installed or removed in or from the continuous caster, as well as a possible common control for the purpose of performing a desired soft reduction for the cast strand.

The above-mentioned method according to the invention is also suitable for operating a continuous caster according to the present invention, in the sense that it brings the position of the sump tip of the cast strand specifically into the selected area of the supporting strand guide or - in the event of changes in the casting process - is also held therein .

The present invention is expediently used in the production of cast strands which - in the case of the production of slabs or similar products - have a casting thickness of at least 250 mm, more preferably even greater casting thicknesses (e.g. 300 mm, preferably 350 mm, or 400 mm, or more). Such products are also known under the name "thick slabs". Because the inventive control or regulation of the casting process by changing or setting the casting speed has a direct effect on all sections of the cast strand along the supporting strand guide, this means that the invention is also suitable for such "thick slabs" or comparable products.

If long products (for example billets or blooms) are produced using the method according to the invention, the cast strand has a cast thickness or a diameter of at least 150 mm.

Exemplary embodiments of the invention are described in detail below with reference to a schematically simplified drawing.

Fig. 1

eine schematisch vereinfachte Seitenansicht einer erfindungsgemäßen Stranggießanlage, mit der auch ein Verfahren nach der vorliegenden Erfindung durchführbar ist,

Fig. 2

ein Flussdiagramm zur Veranschaulichung einer Schrittabfolge eines Verfahrens nach der vorliegenden Erfindung,

Fig. 3

ein Diagramm für eine Gießgeschwindigkeit und für die Position einer Sumpflänge als Funktion der Zeit, die mit einem erfindungsgemäßen Verfahren erzielt werden,

Fig. 4, 5

jeweils ein Diagramm zur Darstellung der Wechselbeziehung zwischen einer Änderung der dies Temperatur und einer daraus resultierenden Position der Sumpfspitze eines Gießstrangs, auch unter Berücksichtigung eines erfindungsgemäßen Verfahrens, und

Fig. 6

eine schematisch vereinfachte Seitenansicht einer erfindungsgemäßen Stranggießanlage analog zu Fig. 1, für die beispielhafte Gießlängen für den erzeugten Gießstrang symbolisch gezeigt sind.

Show it:

Fig. 1

a schematically simplified side view of a continuous caster according to the invention, with which a method according to the present invention can also be carried out,

Fig. 2

a flowchart to illustrate a sequence of steps of a method according to the present invention,

Fig. 3

a diagram for a casting speed and for the position of a sump length as a function of time, which are achieved with a method according to the invention,

Fig. 4, 5

each a diagram to illustrate the interrelationship between a change in this temperature and a position of the sump tip of a cast strand resulting therefrom, also taking into account a method according to the invention, and

Fig. 6

a schematically simplified side view of a continuous caster according to the invention analogous to FIG Fig. 1 , for which exemplary casting lengths for the cast strand produced are shown symbolically.

With reference to the Figs. 1 to 6 Preferred embodiments for a continuous casting installation 110 and a method are explained with which a cast strand 100 is produced from metal by means of continuous casting. The same features in the drawing are each provided with the same reference symbols. At this point it is pointed out separately that the drawing is only shown in a simplified manner and, in particular, without a scale.

Fig. 1 FIG. 10 shows a side view of the continuous caster 110 according to the invention in a simplified, principally simplified manner.

At this point it is pointed out separately that the terms cast strand and metal strand are optionally used as synonyms for the following description.

The continuous caster 110 after Fig. 1 comprises a mold 112, which has a lower opening 113 and thereby a vertical exit downwards. Liquid metal, for example steel or a steel alloy, is poured into the mold 112 up to a casting level or bath level 114.

In the area of a secondary cooling system 130, the continuous caster 110 comprises a supporting strand guide 116, which adjoins the lower opening 113 of the mold. Thus, the supporting strand guide 116 is arranged immediately downstream of the mold 112 or downstream thereof. In operation of the continuous caster 110 and when a corresponding method according to the invention is carried out, a cast or metal strand 100 emerges downward from the lower opening 113 of the mold 112 and is then moved or transported along the supporting strand guide 116 in a conveying direction F.

The secondary cooling 130 comprises along the supporting strand guide 116 (unspecified) individual cooling segments through which the application of a cooling medium, in particular in the form of water e.g. is ensured by spray nozzles on both sides of the metal strand 100 to cool the metal strand 100 in a targeted manner. These cooling segments are each fed with cooling liquid via lines (not shown) and are each equipped with spray nozzles. Accordingly, it is possible to apply cooling liquid to the surfaces of the metal strand 100 through the spray nozzles of the individual cooling segments, namely on its upper side and / or lower side.

The continuous caster 110 is a thick slab system with which a cast strand 100 with a thickness of preferably 250 mm, or possibly even greater cast thicknesses, can be produced. The continuous caster 110 comprises, for example, a total of one hundred and twenty pairs of support rollers, which are divided into twenty physical segments or cooling segments 1-20. Here, the crack-critical straightening area is located within the supporting strand guide 116 in the cooling or straightening segments with the numbers 8 and 9, which can be equipped with their own control circuits for the coolant supply so that the specified target temperatures can be achieved.

The continuous casting plant 110 comprises a control or regulation unit 122, which is connected to the cooling segments of the supporting strand guide 116 for signaling purposes via a signal path 124. This signal path 124 can be wired or wireless, for example by a radio path or the like.

The control or regulation unit 122 comprises a process computer 123 on which a first software I and a second additional software II are set up. The meaning and function of these two software packages I, II are explained separately below.

The control or regulation unit 122 is connected to a data memory 126 in which the required process data for the continuous casting plant 110 are stored. To this extent, this data memory 126 forms a database. Via an interface (not shown) it is possible to input or read individual process data PD into the data memory 126. This input option is in the Fig. 1 symbolized by an arrow with "PD".

The continuous caster 110 is equipped with at least one (unspecified) temperature sensor, or a plurality of such sensors, which is or are arranged adjacent to the supporting strand guide 116. The temperature of the metal strand 100 can be determined by means of such a sensor or a plurality of such sensors in order, for example, to compare the previously calculated temperature of the metal strand 100 with the measurement. The temperature data from the sensor or sensors are first fed to a data acquisition system 128 and from there sent to the control or regulation unit 122 via the signal path 124.

Values or parameters are stored in the data memory 126, on the basis of which setpoint temperatures can be set or determined for the individual cooling segments along the supporting strand guide 116. These variables may include a first target temperature, a second target temperature and a predetermined distance from the mold level 114. These variables are dependent on a specific material or a specific group of materials from which the metal strand 100 is produced, and in any case independent of a specific continuous casting plant.

Using the above-mentioned parameters, which are stored in the data memory 126, the control and regulation unit 122 can be used for the individual cooling segments along the strand guide 116 in the area of the secondary cooling 130 of a specific continuous casting plant, for example the continuous casting plant 110 from Fig. 1 , Target temperatures can be set or determined.

The continuous casting installation 110 comprises a selected or predetermined area 120 for the supporting strand guide 116 or along it, which area corresponds, for example, to the segments no. 17 and no. In any case, adjustable support rollers 118 are arranged in this selected area 120, each of which is present in pairs in the form of an upper support roller R1 and a lower support roller R2 opposite thereto.

In the representation of Fig. 1 For example, only two such pairs of rollers are labeled "R1" and "R2".

In the embodiment shown, each of the segments No. 17 and No. 18 consists of three such pairs of rollers R1, R2, and the associated support rollers 118 can be adjusted individually, i.e. in the direction of the cast strand 100 passed through between the support rollers 118. A soft reduction is carried out for the cast strand 100 by adjusting these support rollers.

A so-called soft reduction is possible for the cast strand 100 by means of the individual support rollers R1, R2 and their adjustment in the direction of the cast strand 100 passed through between the support rollers 118. In this case, both the upper support roller R1 and the lower support roller R2 are expediently employed, so that a reduction in thickness is achieved for the cast strand 100, both on its upper side and on its lower side. This is particularly true for a metal strand 100 in the form of a slab with a comparatively large size Casting thickness, ie ≥ 250mm particularly advantageous. The internal quality of the cast strand 100 can be improved by reducing the top and bottom sides.

A stronger construction of the adjustable support rollers 118 enables larger individual removals for a metal strand 100 and / or the service life of the soft reduction unit (i.e. segments no. 17 and no. 18) can be extended. Furthermore, the acceptance steps can be graded individually.

At this point it is emphasized separately that along the supporting strand guide 116 the supporting rollers, which have a soft-reduction adjustment function, are arranged solely in segments No. 17 and No. 18, i.e. in accordance with the selected area 120. This means that with the support rollers 118 which are arranged in the selected area 120, a soft reduction can be carried out for the cast strand 100.

The remaining support roller segments No. 1-16, and No. 19-20, are of conventional design and have no such soft-reduction adjustment function. Instead, they can only be used to the extent that the reduction in thickness caused by thermal shrinkage is followed. This allows the continuous caster 110 to be built more cost-effectively.

The selected or predetermined area 120 of the supporting strand guide 116 is to be seen in the context that the sump tip of the cast strand 100 should lie or be positioned therein during operation of the continuous caster 110. In other words, a target position or a target area for the sump tip of the cast strand 100 is located within this selected area 120. It is then possible to perform a targeted soft reduction for the cast strand 100 within the selected area 120 of the supporting strand guide 116 , finally through the explained adjustment of the support rollers 118.

Fig. 2 FIG. 11 shows a flow chart to illustrate the "architecture" of the control or regulation unit 122. Specifically, the process computer 123 (cf. Fig. 1 ) of this control or regulation unit 122 a first software I (also referred to as a simulation model “regulation”) and a second software II (also referred to as a simulation model “precontrol”).

In the diagram of Fig. 2 the control or regulation unit 122 is shown placed in the middle, and here also provided with the designation "communication simulation models and casting process". This expresses the fact that the control or regulation unit 122 is set up or has corresponding means to enable data exchange between the second software II and the first software I.

• Werkstoff
• Gießtemperatur
• IST-Wert der Gießgeschwindigkeit
• Sekundärkühlwasser (d.h. Menge und Temperatur)
• Gießlänge.

The control or regulating unit 122 receives the process data or process parameters of the current casting process from the continuous casting plant 110, which is indicated by a corresponding arrow pointing from the continuous casting plant 110 in the direction of the control or regulating unit 122. These process parameters include:

• material
• Casting temperature
• ACTUAL value of the casting speed
• Secondary cooling water (i.e. quantity and temperature)
• Casting length.

As explained, these process parameters PD can be entered into the data memory 126 via an interface and from there can be sent to the processor of the control or regulation unit 122 via the signal path 124. Subsequently, these process data are then forwarded by the control or regulation unit 122 both to the first software I (simulation model “precontrol”) and to the second software II (simulation model “regulation”).

As indicated by the arrow for “process parameters”, which is directed to the symbol for the second software II, the second software II also receives information from the control and regulation unit 122 with regard to the respective process parameters for the current casting process.

While the casting operation is running and is controlled by the first software I, the second software II runs permanently in the background. In this regard, it is emphasized separately that the second software II calculates much faster than in real time, at least faster than the first software I. In other words, the calculation speed for the second software II is set higher than that for the first software I.

Regarding the in the Fig. 2 The aforementioned “pouring length x” is specifically pointed out that according to the present invention the counting of a respective pouring length starts in the pouring or bath level 114.

A method according to the present invention now works as follows:
With the second software II, on the one hand, in association with a specific casting length ("x") and, on the other hand, depending on currently obtained process parameters from the ongoing casting process, in particular in the area of the mold 112 and / or from at least one process parameter stored in the database 126, is calculated or Simulates which position would currently be present for a sump tip of the cast strand 100 according to the determined casting length along the supporting strand guide 116 of the continuous caster 110.

In other words, the second software II calculates the position of the solidification or of a defined solidification fraction either in the center of the strand or at a predetermined distance between the strand shells much faster than in real time of the cast strand 100 on the loose and fixed side, with the control variable casting speed.

The second software II then compares this calculated sump tip position with the selected area 120, or with the target position for the sump tip, and on the basis of this a casting speed correction value (in Fig. 2 also referred to as "optimal speed for the casting length x"). This casting speed correction value corresponds to a target casting speed and is assigned to a certain casting length of the cast strand 100, based on the current process parameters of the casting process, such as casting temperature, chemical composition of the cast metal, heat dissipation in the mold and changes in the water supply temperatures (secondary cooling, primary or mold cooling).

The actual regulation of the casting process is carried out by the first software I (simulation model "regulation") in real time. For this purpose, the first software I receives the necessary information relating to the individual process parameters from the control or regulation unit 122. Furthermore, the first software I also receives the casting speed correction values calculated by the second software II via the control or regulation unit 122, i. Values for the target casting speed that each belong to a relevant casting length. On the basis of this, the value for an associated target speed (meaning: target casting speed) is then sent back to the control or regulating unit 122 by means of the first software I and output from there to the relevant components of the continuous casting plant 110.

This means that the first software I regulates the sump position with the aid of the casting speed for the casting process carried out with the continuous caster 110 in real time and in this case the casting speed correction value calculated by the second software II in association with the determined Casting length only considered with a delay. This delay is determined from a distance between the selected area 120 or a target position for the sump tip and the casting speed last set in real time. As a result, the result is that a sump tip position of the cast strand 100 during the ongoing casting process is always located within the selected area 120 along the supporting strand guide 116 or the sump tip of the cast strand 100 is held in this predetermined area 120.

The regulation according to the invention can take place, for example, with a PI controller or a controller with similar properties. It is possible to use algorithms to search for the zero point ( _target position - _ACTUAL position = 0). Which controller or algorithm is selected for the zero point search can be parameterized.

The mode of operation of the present invention that has just been explained or of an associated method will first be explained below using a numerical example:
A casting operation is shown for the continuous casting plant 110 according to FIG Fig. 1 set in such a way that the position of the sump tip of the cast strand 100 should come to lie within the selected region 120. If the casting speed is set accordingly and the cooling (primary and secondary cooling) of the cast strand 100 is adapted to it, its sump tip is then located within the selected region 120.

For the present numerical example, it is assumed that the target position for the sump tip of the casting strand 100 is at a distance from the meniscus 114 of 20 meters, the casting speed set being 1 m / min

For the present numerical example, it is further assumed that the casting temperature in the area of the mold 112 or the casting level 114 is around 10 ° increases. Such a rise in temperature can be induced by using a new pan. According to a further assumption, this temperature increase takes place in the region of the mold 112 at a point in time t _n . At this point in time t _n , a casting length of N meters has already been cast, so that the new piece of the cast strand 100 is designated with the casting length "N".

Due to the higher casting temperature, the cast strand 100 has more heat, so that the calculated sump tip increases by approx. 1 meter. If the other process parameters, in particular the cooling of the cast strand 100 in the area of the secondary cooling 130, remained unchanged during the above-mentioned temperature increase and only the first software I for controlling the casting process were available, this would result in the position of the sump tip taking into account the The increase in length of about 1 meter mentioned - viewed in the conveying direction F of the cast strand 100 - is downstream (ie in the illustration of FIG Fig. 1 from left to right) and thereby "run out" of the selected area 120.

To compensate for the said temperature increase by 10 ° C. in the region of the mold 112, a corresponding casting speed correction value is calculated by means of the second software II. Taking into account the fact that the second software II calculates much faster than in real time, the new strand piece with the casting length "N" reaches the position of the previous solidification, i.e. in the simulation model "precontrol". Calculated 20 meters from the mold level 114, for example after 30 seconds. In comparison, with the parameters mentioned (casting speed = 1 m / min; sump position = 20 meters calculated from the mold level 114) the simulation time with the first software I, which calculates in real time, would have already increased or advanced by 20 minutes.

In any case, the casting speed correction value calculated by the second software II - initially in the model and theoretically - is used for the casting speed correction value 100 resulting casting speed can be reduced in the present numerical example in such a way that the position of the sump tip for the casting length "N" is again within the selected area 120 and thus reaches its target position.

The second software II - in view of the above-mentioned temperature rise in the area of the mold 112 - thus provides information to the first software I at any time about the factor (= casting speed correction value) by which the real casting speed of the casting process carried out with the continuous caster 110 It must be changed compared to the casting speed set up to now so that the sump tip of the cast strand 100 does not run out of the selected area 120 with the explained increase in length.

In the present numerical example, it is important for the functioning of the first software I that the first software I stores the casting speed correction value calculated by the second software II upon receipt. An essential feature for the method according to the invention is that the first software I does not reduce the real casting speed by the casting speed correction value immediately, but only after a time delay.

If the new piece of the casting strand 100 with the casting length "N" now reaches a position (e.g. 5 meters) in front of the current sump position (= 20 meters, calculated from the meniscus 114), the current casting speed is determined by the first software I. already reduced by the casting speed correction value calculated by the second software II. A position of e.g. B. 5 meters from the current or last sump position of z. B. corresponds to 20 meters - at a casting speed of 1 m / min, a period of 15 minutes that the new piece of the cast strand 100 with the casting length "N" has covered by then. This then amounts to the time for this example Delay with which the first software I adjusts or reduces the real casting speed, taking into account the casting speed correction value calculated by the second software II, to 15 minutes. As a result, the sump length is reduced by half of the value as it had increased in the simulation of the second software II, i.e. only by 0.5, until the warmer strand piece arrives, ie the new piece of the cast strand 100 with the casting length "N" m.

If now the strand piece with the higher casting temperature (= casting length "N") solidifies, the real sump length of the cast strand 100 also increases by approximately 1 meter. For this purpose, the assumption is made that the reference position for the casting length is 50%. This means that the casting speed is used by the second software II, which is approximately half the distance between the bath level 114 and the target position for the sump tip (this corresponds to FIG Fig. 6 the casting length L). However, since this sump length was previously reduced by 0.5 meters by reducing the casting speed, which has the same effect along the entire supporting strand guide 116, or - seen in the conveying direction F of the cast strand 100 - has been shifted in the upstream direction, If the result remains the position of the sump tip of the cast strand 100 in the target area, ie within the selected area 120. As a result, a hydraulic soft reduction can then continue to be carried out for the cast strand.

In short: For the numerical example mentioned, the first software I can, using the casting speed correction value calculated by the second software II and taking into account the said delay, reduce the real casting speed for the casting process in such a way that the sump length of the cast strand 100 continues to be within the selected Area 120 is or remains therein.

For the numerical example mentioned above, it should also be pointed out that the first software I and the second software II always receive the same process values or process parameters of the ongoing casting process.

To clarify the numerical example just explained, it should be pointed out that the mentioned reduction in the real casting speed is related to the assumption that a temperature increase is assumed in the region of the mold 112. If, in deviation from this example, the melting temperature in a ladle should drop, this would mean that the first software I would then increase the real casting speed of the casting process using a casting speed correction value calculated accordingly by the second software II, also in compliance with the explained time delay.

The mode of operation of the present invention or of an associated method is further illustrated by the illustrations in FIG Fig. 3 - 5 explained as an example:
The representation of Fig. 3 shows an example of a possible combination of second software II and first software I for the purpose of regulating the casting speed in order to achieve a target sump length or a target position for the tip of the sump of the cast strand 100.

In detail, the Fig. 3 two diagrams in which the casting speed (with a solid line) and the position of the sump length (with a dashed line) are plotted as a function of time. The upper diagram relates to the second software II (or the simulation model "feedforward control"). The lower diagram relates to the first software I (or the simulation model "control").

Both in the upper diagram and in the lower diagram of Fig. 3 the nominal swamp length is shown in each case with a dash-dotted line. The hatched area, within which the respective dash-dotted line runs, indicates a target area for the target position of the sump tip of the cast strand 100. Referring to the representation of Fig. 1 it should be noted that this hatched target area for the sump tip lies within the selected area 120 of the supporting strand guide 116.

At the top of the top diagram of Fig. 3 , which, as explained, applies to the second software II, two areas are marked which are marked with "A" and "B". These areas are of importance: - Area A: Calculation of a first target casting speed v1, with sump length = target sump length. - Area B: Adjustment of the target casting speed to changed process values.

The lower diagram of Fig. 3 which, as explained, applies to the first software I, is divided into a total of three areas by thin dashed vertical lines, the second and third areas being identified with the letters "C" and "D". These letters have the following meanings: - Area C: Use of the target casting speed calculated in the pre-control (= second software II) for the current casting length. - Area D: Internal control of the casting speed taking into account the target casting speed calculated in the pre-control (= second software II) for the current casting length.

A synopsis of the two diagrams from Fig. 3 makes clear that the quality of the control can be improved by the simulation model "precontrol", ie by using the second software II and taking into account the target casting speed (= casting speed correction value) calculated with it. The following consideration is given in detail:

Without signals from the pilot control, a sump peak control would only register a rise in the casting temperature when the first strand cross-section with the higher temperature has reached the solidification point. The resulting overshooting of the target position leads to a falling speed ramp through the PI control. By the time the drop in the casting speed has had its full effect on the shortening of the sump length, another strand must have covered the path from the meniscus 114 to the sump tip. If the regulation is set too strong, undesirable overshoots occur. If it is set weaker, the correction will take longer.

On the other hand, the control can determine very promptly from the values of the feedforward which setpoint speed would be suitable for which strand length. Since this target speed is usually not the same for all strand positions, an algorithm is used to calculate which casting speed provides the smallest deviations from the target value overall. This is done either by selecting a reference position for which the target speed is determined, or the current target speed is averaged from all positions up to the top of the sump (which is also done in Fig. 6 is shown, with three exemplary casting lengths K, L and M).

According to a further embodiment (not shown) it can be provided that the averaged target speed (ie an average value derived from the target casting speeds determined by the second software II for various Casting lengths is formed) can then be taken over directly by the first software I as the target speed, taking into account the time delay explained above. In addition and / or as an alternative, a PI control can also be used to superimpose the current deviation of the sump length from the target position in order to take into account the actual process history of all strand cross-sections separately.

The diagram of Fig. 4 contains a total of three graphs, the curves of which are understood as follows: - Upper solid line : = current casting temperature - lower solid line : = Casting speed - dashed line : = calculated swamp length

Furthermore, the diagram of Fig. 4 a dash-dotted horizontal line which marks the target value for the position of the sump tip of the cast strand 100.

The diagram of Fig. 4 shows that when the casting temperature changes by up to 20 ° C., the casting speed is regulated in such a way that the calculated sump length agrees well with the target value for the position of the sump tip of the cast strand 100.

The representation of Fig. 5 shows two diagrams, namely in the upper diagram a course of the casting temperature as a function of time, and in the lower diagram the resulting position of the sump tip as a function of time. In this regard, it should be understood that the timelines in the upper and lower diagrams of FIG Fig. 5 are chosen accordingly. This means that the course of the sump tip (shown in the lower diagram) results in each case as a reaction to the change in the casting temperature (shown in the upper diagram).

For the lower diagram of Fig. 5 it is additionally pointed out that here two curve courses are shown, namely with a solid line the curve course of a control according to the prior art, and with a dashed line the curve course that is established when the method according to the invention is carried out.

The lower diagram of Fig. 5 shows that - if there are significant fluctuations in the casting temperature - then the resulting position of the sump tip, which is established with the aid of the method according to the invention, has smaller deflections compared to the conventional curve shape and is significantly closer to the target value (indicated by an arrow to the left of the ordinate made) for the sump tip of the cast strand 100 is.

List of reference symbols

1-20

Support roller segments (of the supporting strand guide 116)

100

Cast strand / metal strand

110

Continuous caster

112

Mold

113

lower opening (of the mold 112)

114

Bath mirror / pouring mirror

116

supporting strand guide

118

Support rollers / pairs of rollers

120

predetermined or selected area (of strand guide 116)

122

Control or regulation unit

123

Process computer

124

Signal path or signal connection

126

Database or data storage

128

Data acquisition

130

Secondary cooling (of the continuous caster 114)

I.

first software (simulation model "control")

II

second software (simulation model "pre-control")

F.

Direction of conveyance (for the cast strand 100)

K, L, M, N

Casting length (n)

PD

Process data

R1

upper support roller

R2

lower support roller

Claims (17)

A method for casting a cast strand (100) in a continuous casting plant (110) equipped with a process computer (123) and having at least one casting machine, the process computer (123) comprising at least one first software (I) that calculates in real time and regulates the casting process, wherein the process computer (123) comprises a second additional software (II) which calculates faster than in real time, so that the calculation speed for the second software (II) is greater than for the first software (I),
that the second software (II) is assigned on the one hand to a specific casting length (K; L; M) and on the other hand as a function of currently obtained process parameters from the ongoing casting process, in particular in the area of the mold (112) and / or from at least one in a database The stored process parameters calculate which position would currently be present for a sump tip of the cast strand (100) according to the determined casting length (K; L; M) along a supporting strand guide (116) of the continuous caster (110), the second software (II) having this calculated sump tip position compares with a target position or target range (120) for the sump tip and continuously calculates a casting speed correction value on the basis thereof, and
that the casting speed correction value calculated by the second software (II) is transferred to the first software (I), the first software (I) regulating the sump position with the aid of the casting speed in real time and the one calculated by the second software (II) The casting speed correction value in association with the specific casting length is only taken into account with a delay, which results from a distance between the target position or the target area (120) for the sump tip and the casting speed last set in real time, so that a sump tip position of the Cast strand (100) in the running The casting process is always located within a predetermined or selected area (120) along the supporting strand guide (116) or the sump tip of the cast strand (100) is kept in this predetermined or selected area (120). Method according to claim 1, characterized in that for the calculation of the casting speed correction value by means of the second software (II) at least one process parameter of the casting process is selected from the group of chemical composition of the material of the cast strand (100), current casting temperature, current casting speed, water supply temperature for the secondary cooling, or the water inlet temperature for the mold primary cooling and / or the set casting length is taken into account. Method according to claim 1 or 2, characterized in that the casting speed correction value is calculated by means of the second software (II) on the basis of process parameters stored in the database and used by the first software (I) at the beginning of the casting process as a manipulated variable to control it becomes. Method according to one of Claims 1 to 3, characterized in that the casting speed correction value is calculated by means of the second software (II) as a function of currently obtained process parameters (128) from the current casting process, this casting speed correction value if it is in the course of the casting process leads to deviations between target and actual values in relation to the sump length of the cast strand (100), is used by the first software (I) to set the casting speed of the casting process. Method according to one of the preceding claims, characterized in that a reference position along the supporting strand guide (116) between the bath level (114) and the target position or the target area (120) for the sump tip, from which the casting speed correction value is adopted. Method according to Claim 5, characterized in that the reference position is at a point on the supporting strand guide (116) which is between 40% and 70% of the distance between the bath level (114) and the target position of the sump tip, preferably the reference position is at least 60% of the distance between the bath level (114) and the desired position of the sump tip. Method according to one of the preceding claims, characterized in that the calculation of the casting speed correction value by means of the second software (II) takes place on the basis that from all positions (K; L; M) along the casting length up to the position of the sump tip the current Target speed is averaged. Method according to one of the preceding claims, characterized in that a defined solidification fraction in the center of the strand, which has a solid fraction fraction <1, is used as the controlled variable. Method according to one of the preceding claims, characterized in that a strand shell spacing is used as the controlled variable. Method according to one of the preceding claims, characterized in that slabs are produced therewith, the cast strand (100) having a casting thickness of at least 250 mm, preferably of at least 300 mm, more preferably of at least 350 mm, more preferably of at least 400 mm. Method according to one of Claims 1 to 9, characterized in that long products are produced therewith, the cast strand (100) having a cast thickness or a diameter of at least 150 mm A continuous casting plant (110) for casting a cast strand (100), comprising a mold (112) with a lower opening (113) which is formed on an underside of the mold (112), a supporting strand guide (116) which adjoins the lower opening (113) of the mold (112), the cast strand (100) being movable along the supporting strand guide (116), along the supporting strand guide (116) adjustable support rollers or pairs of rollers (118) are arranged with which a thickness reduction for the cast strand (100) takes place,
wherein the supporting strand guide (116) has a selected area (120) in which a sump tip of the cast strand (100) is to lie,
characterized,
that the support rollers or roller pairs (118), which have a soft-reduction adjustability, are arranged exclusively in the selected area (120) of the strand guide (116). Continuous casting plant (110) according to claim 12, characterized in that a pair of rollers (118) is formed from opposing support rollers (R1, R2), between which the cast strand (100) can be passed, the respective support rollers individually in the direction of the other support roller are employable. Continuous casting plant (110) according to Claim 12 or 13, characterized in that the support rollers or roller pairs (118) are combined to form roller segments (17; 18). Continuous casting plant (110) according to one of claims 12 to 14, characterized in that a position of a sump tip of the cast strand (100) can be set in particular by a method according to one of claims 1 to 8, so that the position of the sump tip within the selected area (120) of the supporting strand guide (116) lies. Continuous casting plant (110) according to one of claims 12 to 15, characterized in that the mold (112) and the supporting strand guide (116) are designed such that a cast strand (100) in the form of a long product with a casting thickness of at least 150 mm can be produced is. Continuous caster (110) according to one of claims 12 to 15, characterized in that the mold (112) and the supporting strand guide (116) are designed in such a way that a cast strand (100) in the form of a slab with a casting thickness of at least 250 mm, preferably of at least 300 mm, more preferably of at least 350 mm, more preferably of at least 400 mm.

Images