EP2480356B1 - Process and device for casting liquid metal in a continuous casting machine - Google Patents

Description

The present invention relates to a method and apparatus for casting metallic melt into continuously cast precursors in a continuous casting machine.

• Einbringen der Schmelze in eine Kokille, wobei ein Gießspiegel der Schmelze in der Kokille und wenigstens eine Strömung der Schmelze in der Kokille in Form eines Einfachwirbels oder eines Doppelwirbels ausgebildet wird;
• Abkühlen der Schmelze in der Kokille unter Ausbildung einer festen Strangschale;
• Ausziehen eines zumindest teilerstarrten Strangs aus der Kokille;
• Führen, Stützen und Kühlen des ausgezogenen Strangs in einer Strangstützeinrichtung;

Eine Vorrichtung zum Vergießen von metallischer Schmelze zu stranggegossenen Vorprodukten in einer Stranggießmaschine umfasst im Wesentlichen

• eine Kokille in der die Schmelze eingebracht wird, wobei in der Kokille ein Gießspiegel und ein teilerstarrter Strang ausgebildet werden;
• eine Strangstützeinrichtung zum Führen, Stützen und Kühlen des Strangs, wobei der zumindest teilerstarrte Strang aus der Kokille ausgezogen wird; und
• mehrere stabförmige Einbauteile im Bereich des Gießspiegels der Schmelze in der Kokille.

Specifically, the invention relates to a method for casting metallic melt into continuously cast precursors with the following steps

• Introducing the melt into a mold, wherein a casting level of the melt in the mold and at least one flow of the melt in the mold in the form of a single vortex or a double vortex is formed;
• Cooling the melt in the mold to form a solid strand shell;
• Extracting an at least partially solidified strand from the mold;
• Guiding, supporting and cooling the drawn strand in a strand support device;

An apparatus for casting metallic melt into continuously cast precursors in a continuous casting machine essentially comprises

• a mold in which the melt is introduced, wherein in the mold a casting mirror and a partially solidified strand are formed;
• a strand support device for guiding, supporting and cooling the strand, wherein the at least partially solidified strand is pulled out of the mold; and
• several rod-shaped mounting parts in the region of the casting level of the melt in the mold.

• DAUBY, P. H. und KUNSTREICH, S.: Electromagnetic stirring in slab caster molds: What and why. Iron & steelmaker, vol. 30, no11, pp. 21-29, ISSN 0275-8687, 2003 .

entnommen werden.It is known to a person skilled in the art of continuous casting to cast metallic melt in a continuous casting machine into continuously cast precursors, the melt being melted either by a free jet casting process (see US Pat eg WO 0010741 A1 . US 3,833,050 . US 3,840,062 and the JP 48-9251 A ) or by means of a pouring tube (English submerged entry nozzle, short SEN ) is placed in a mold. In both cases, a casting level of the melt is formed in the mold, wherein in the first case, the melt is introduced without guidance through a pouring tube in free fall and in the second case, the melt from one or more outlet openings in the SEN in the mold. Regardless of the way in which the melt is introduced into the mold, at least one flow in the form of a single or double vortex is formed in the mold. In the case of the single vortex, the melt flows below the casting mirror in the direction of the casting mirror, wherein this flow is deflected either in the region of the casting level or below the casting level in the direction of the strand movement (downwards); in the case of the double vortex, the melt flows below the casting mirror in the direction of a mold wall, where it is divided at a stagnation point in a flow in the direction of the casting mirror (upward) and in a flow in the direction of strand movement (downward). Further details on the single and double whirls can eg the publication

• DAUBY, PH and KUNSTREICH, S .: Electromagnetic stirring in slab caster molds: What and why. Iron & steelmaker, vol. 30, no11, pp. 21-29, ISSN 0275-8687, 2003 ,

be removed.

After cooling the melt in the mold to form a solid strand shell, an at least teilerstarrter strand is pulled out of the mold, which is guided in a, the mold in the strand downstream, strand support means, supported and further cooled.

The characteristic formation of the flow of the melt in the mold in the form of a single or double vortex significantly affects the quality of the continuously cast precursor (eg thin slabs, slabs or ingots), since these Flow for the stability of the casting mirror, the uniform solidification of the strand, the melting and distribution conditions of the casting powder and for the deposition behavior of particles in the melt is responsible. By a transient behavior of this flow, moreover, variations in the casting level or inadequate lubrication of the strand can be caused. Gießschwankungenschwankungen have negative effects on the surface quality; the insufficient strand lubrication, due to insufficiently melted casting powder, can lead to so-called strand plugs, which can result in a strand breakage or a casting demolition. The stationary behavior of this flow is thus of particular importance for the continuous casting process.

An analysis of the flow conditions of the melt in the mold shows that the flow in the form of a single or double vortex behaves unsteadily and has a great tendency to periodic oscillations. Especially shortly after the casting start, this flow is very unstable and takes a certain amount of time (typically several minutes) to settle into a quasi-stationary state.

From the JP 02-015852 It is known to use heat pipes in the region of the casting mirror during continuous casting. By means of these elements heat is deliberately removed from the metallic melt, so that the solidification of the melt in the mold is accelerated and the productivity of the plant can be increased. The manner in which the flow of the melt in the mold can be stabilized is not shown in the document.

From the JP 11-104789 A is a continuous casting mold with two "unidirectional flow weirs 9" known, which can be considered in the broadest sense as rod-shaped built-in parts. These can be raised and lowered manually via rail guides 12 in order to influence the flow in the mold.

From the JP 2-015852 A and the JP S54-43832A is a mold with a rod-shaped, oscillating in the horizontal direction cooling device known.

• wodurch die Stabilität des Gießspiegels erhöht wird;
• das Abscheideverhalten von Partikel in der Kokille verbessert wird; und
• gleichmäßigere Aufschmelz- und Verteilbedingungen für das Gießpulver erzielt werden.

The object of the invention is to provide a method and a device of the aforementioned type with which a more stable flow of the melt in the mold in the form of a single or double vortex can be achieved,

• whereby the stability of the casting mirror is increased;
• the deposition behavior of particles in the mold is improved; and
• More uniform melting and distribution conditions for the casting powder can be achieved.

Another object is to reduce the settling time of the flow of the melt in the mold in the form of a single or double vortex, whereby the time can be reduced from the casting start to normal operation with quasi-stationary conditions of a continuous casting.

This object is achieved by a method of the type mentioned, in which the flow of the melt in the form of a single vortex or a double vortex is stabilized by a plurality of rod-shaped mounting parts in the region of the casting mirror. In this case, the flow in the form of a single or double vortex (hereinafter also called circular flow) through at least two rod-shaped mounting parts, which are sunk by a, possibly different per insertion part, immersion depth in the melt in the mold, and. braked to the left and right of the SEN, stabilizing the transient flow so that the resulting stabilized flow can be considered stationary. This stabilization leads to a calming of the casting level and to an improved separation behavior of particles. In addition, this uniform melting and distribution conditions for the casting powder is achieved, resulting in an improved surface quality of the strand and the formation of strand connectors and thus the penetration risk counteracts. Due to the improved separation behavior, electromagnetic stirring or braking devices can be dispensed with, which on the one hand reduces investment costs and, on the other hand, reduces energy costs during operation.

In one embodiment, the melt is introduced into the mold either by free jet casting or by means of a pouring tube introduced, wherein in the latter form, the melt exits below the pouring mirror from the pouring tube through one or more outlet openings.

• Erfassen eines Messwerts von einem Messwertaufnehmer durch ein Messen einer Zustandsgröße des Stranggießverfahrens;
• Ermitteln eines zeitlich veränderlichen Stellsignals mit Hilfe einer Steuerung unter Berücksichtigung des Messwerts;
• Beaufschlagen eines Aktuators mit dem Stellsignal, wobei der Aktuator entweder eine Eintauchtiefe wenigstens eines stabförmigen Einbauteils gegenüber dem Gießspiegel oder eine Position eines stabförmigen Einbauteils gegenüber einer Seitenwand der Kokille verändert.

Mittels dieser Ausführungsform wird entweder die Eintauchtiefe oder die Position wenigstens eines stabförmigen Einbauteils mittels einer Steuerung (z.B. einer Kennfeldsteuerung) in Abhängigkeit eines Messwerts eingestellt.An adaptation to different operating conditions (for example, different pullout extension speeds or strand cross-sections) is possible in a simple form by the following steps:

• Detecting a measurement value from a transducer by measuring a state quantity of the continuous casting method;
• Determining a time-varying control signal by means of a control taking into account the measured value;
• Actuation of an actuator with the actuating signal, wherein the actuator changes either a depth of immersion of at least one rod-shaped component relative to the casting mirror or a position of a rod-shaped component relative to a side wall of the mold.

By means of this embodiment, either the immersion depth or the position of at least one rod-shaped built-in component is adjusted by means of a controller (eg a map control) as a function of a measured value.

In a preferred embodiment, the measured value used is a pultrusion speed, a temperature of a side wall of the mold or a mass flow of the melt introduced into the mold. The measured value is preferably determined by permanent measuring in real time and based on the control.

• Erfassen eines Messwerts von einem Messwertaufnehmer durch ein Messen einer Zustandsgröße des Stranggießverfahrens;
• Ermitteln einer zeitlich veränderlichen Stellgröße mit Hilfe einer Regeleinrichtung unter Zuhilfenahme eines Regelgesetzes und unter Berücksichtigung eines Sollwerts des Messwerts;
• Beaufschlagen eines Aktuators mit der Stellgröße, wobei der Aktuator entweder eine Eintauchtiefe wenigstens eines stabförmigen Einbauteils gegenüber dem Gießspiegel oder eine Position eines stabförmigen Einbauteils gegenüber einer Seitenwand der Kokille verändert.

Mittels dieser Ausführungsform wird entweder die Eintauchtiefe oder die Position wenigstens eines stabförmigen Einbauteils mittels einer Regelung so eingestellt, dass durch eine Veränderung der Eintauchtiefe bzw. der Position mindestens eines stabförmigen Einbauteils der Messwert im Wesentlichen beim Sollwert gehalten wird.A highly accurate and robust adaptation to different operating conditions is further possible by the following steps:

• Detecting a measurement value from a transducer by measuring a state quantity of the continuous casting method;
• Determining a temporally variable manipulated variable by means of a control device with the aid of a Control law and taking into account a reference value of the measured value;
• Actuation of an actuator with the manipulated variable, wherein the actuator either an immersion depth of at least one rod-shaped insert relative to the casting mirror or a position of a rod-shaped insert relative to a side wall of the mold changed.

By means of this embodiment, either the immersion depth or the position of at least one rod-shaped built-in component is adjusted by means of a control so that the measured value is essentially kept at the desired value by a change in the immersion depth or the position of at least one rod-shaped component.

In a preferred embodiment, the measured value used is a temperature of a side wall of the mold or a flow velocity of the melt, preferably substantially parallel to the casting mirror, in the mold. The measured value is preferably determined by permanent measuring in real time and based on the control.

In a preferred embodiment, a free jet of the melt at the outlet from the pouring tube is recessed by the rod-shaped built-in parts. This ensures in a simple manner that the melting of the casting powder is not endangered by the thermal energy of the flow or a freezing of the casting mirror is prevented.

A further preferred embodiment is that the melt is cooled by at least one rod-shaped component, the rod-shaped component is in communication with a cooling circuit. Here, the cooling circuit is preferably carried out as a thermosiphon or heat pipe, whereby on the one hand a large amount of the heat of fusion of the liquid metal is removed, whereby the quality of the precursors can be improved.

In order to enable the most direct implementation of the method according to the invention, which solves the underlying problem of the invention, at least one rod-shaped insert has an actuator for changing a depth of immersion of the rod-shaped insert relative to the casting mirror or an actuator for changing a position of the rod-shaped insert relative to a Side wall of the mold, wherein the device additionally comprises at least one transducer for measuring a state variable of the continuous casting machine and an associated control or regulating device, wherein the actuator is respectively connected to the controller and the rod-shaped fixture such that the control or regulating device taking into account the measured value determines a control signal that can be supplied to the actuator, so that the immersion depth relative to the casting mirror or the position relative to a side wall of the coke ille of at least one rod-shaped insert can be changed.

By means of the latter embodiment, the automatic, i.e. automatic, adaptation of the immersion depth and / or the position of a rod-shaped component to various operating conditions possible.

In one embodiment, the rod-shaped fixtures cover less than 50% of the surface of the mold level of the mold, i. the sectional area of all rod-shaped installation parts with the casting mirror is less than 50% of the surface of the casting mirror.

In one embodiment, a rod-shaped component has a round, oval, lenticular or polygonal cross section.

In a further advantageous embodiment, a rod-shaped built-in part to a cooling circuit. This makes it possible to improve the quality of the precursors.

In one embodiment, the actuator is designed as a pressure medium cylinder or as an electric actuator. Both the pressure cylinder and the electric actuator are well suited as actuators for a control or regulation.

Advantageously, the device according to the invention or the method according to the invention is used in a continuous casting machine in the production of precursors from melt, preferably slabs or thin slabs made of steel, for stabilizing a flow of the melt in the form of a single vortex or a double vortex in a mold.

• Fig. 1 eine Schnittdarstellung einer Kokille zum Stranggießen von Brammen mit mehreren stabförmigen Einbauteilen Fig. 2 eine zu Fig. 1 zugehörige Draufsicht
• Fig. 3 eine Schnittdarstellung einer Kokille zum Stranggießen von Brammen mit einer unterschiedlichen Eintauchtiefe der stabförmigen Einbauteile

Further advantages and features of the present invention will become apparent from the following description of non-limiting embodiments, reference being made to the following figures, which show the following:

• Fig. 1 a sectional view of a mold for continuous casting of slabs with several rod-shaped components Fig. 2 one too Fig. 1 associated top view
• Fig. 3 a sectional view of a mold for continuous casting of slabs with a different immersion depth of the rod-shaped mounting parts

In Fig. 1 is a sectional view of a mold for continuous casting of steel slabs shown. In this case, a liquid molten steel flows from a distribution vessel, not shown, which is mounted above the mold 1, through a pouring tube 6 into the, from two narrow side walls 2 and two broad side walls 3 formed (see Fig. 2 ), Mold 1, where the melt cools and forms a solid strand shell. The thus forming, at least partially solidified, strand is pulled out of the mold 1 and guided in a strand support device, not shown, supported and further cooled. As shown in the figure, the melt flows below the casting mirror 5 through a plurality of, mutually opposite, outlet openings 7 from the pouring tube, wherein in each case forms a flow of the melt in the form of a double vortex. In each case, a free jet 8 flows in the direction of a narrow side wall 2 of the mold 1, wherein the free jet in the stagnation points 9 in a flow in the strand extraction direction (in the picture down) and in a flow in the direction of the casting mirror 5 (in the picture above). The flows in the direction of the casting mirror 5 are of particular importance, since they are responsible for the distribution conditions and the melting of the casting powder which is added to the casting mirror from above.

The circular flows in the form of a double vortex are determined by 30 rod-shaped mounting parts 10 (viewed from the casting distributor each 3 rows of 5 columns per left and right half-plane of the mold level of the mold 1, see. Fig. 2 ), wherein the flow velocities of the flows are reduced in the form of a double vortex, especially in the region of the casting mirror 5. The immersion depth of a rod-shaped built-in part 10 is adjusted by means of a - for reasons of clarity only for a rod-shaped insert - actuator 11, which is designed as a pressure medium cylinder, so that the exiting free jet 8 of the flow of the melt is recessed, ie that the melt in Essentially uninfluenced from the pouring tube 4 can escape into the mold 1. In an alternative embodiment, it would of course also be possible, instead of the immersion depth of a rod-shaped fixture relative to the casting mirror 5, to change the position of a rod-shaped fixture relative to a narrow side wall 2 or a broad side wall 3 of the mold 1.

The positions of the rod-shaped built-in parts 10 are set as a function of a measurement value designed as a pullout extension speed, the measured value (a Speed of a not shown, non-driven strand guide roller of the strand support device) by a transducer (a speed sensor) is detected and a control, not shown, is supplied. Taking into account the measured value, the controller ascertains a plurality of actuating signals, which are supplied to the actuators 11 by means of a characteristic map, so that the immersion depths of the rod-shaped built-in components 10 are changed relative to the casting mirror 5. In Fig. 3 is a schematic representation with different immersion depths of the rod-shaped mounting parts 10 shown (the illustration of the actuators 11 has been omitted for reasons of clarity).

LIST OF REFERENCE NUMBERS

1

mold

2

Narrow side wall

3

Wide side wall

4

casting tube

5

meniscus

6

central axis

7

outlet opening

8th

free jet

9

stagnation point

10

Rod-shaped built-in part

11

actuator

Claims (12)

1. Process for casting molten metal into continuously cast pre-products comprising the following steps

   - introducing the molten metal into a mould (1), a meniscus (5) of the molten metal in the mould (1) and at least one flow of the molten metal in the mould (1) being given the form of a single vortex or a double vortex;

   - cooling down the molten metal in the mould (1) and thereby forming a solid strand shell;

   - drawing out an at least partly solidified strand from the mould (1);

   - guiding, supporting and cooling the drawn-out strand in a strand-supporting device;

   characterized by

   - recording a measured value by means of a measured value sensor by measuring a state variable of the continuous casting process;

   - determining a time-variable actuating signal with the aid of a controller, while taking into account the measured value;

   - applying the actuating signal to an actuator (11), the actuator (11) changing either an immersion depth of at least one bar-shaped built-in part (10) relative to the meniscus (5) or a position of a bar-shaped built-in part (10) relative to a side wall (2, 3) of the mould (1), so that the flow of the molten metal is stabilized in the area of the meniscus (5) in the form of a single vortex or a double vortex by a plurality of bar-shaped built-in parts (10).
2. Process according to Claim 1, characterized in that a strand drawing-out rate, a temperature of a side wall (2, 3) of the mould (1) or a mass flow of the molten metal introduced into the mould (1) is used as the measured value.
3. Process for casting molten metal into continuously cast pre-products comprising the following steps

   - introducing the molten metal into a mould (1), a meniscus (5) of the molten metal in the mould (1) and at least one flow of the molten metal in the mould (1) being given the form of a single vortex or a double vortex;

   - cooling down the molten metal in the mould (1) and thereby forming a solid strand shell;

   - drawing out an at least partly solidified strand from the mould (1);

   - guiding, supporting and cooling the drawn-out strand in a strand-supporting device;

   characterized by

   - recording a measured value by means of a measured value sensor by measuring a state variable of the continuous casting process;

   - determining a time-variable actuating variable with the aid of a closed-loop control device while assisted by a set of control rules and taking into account a desired value of the measured value;

   - applying the actuating variable to an actuator (11), the actuator (11) changing either an immersion depth of at least one bar-shaped built-in part (10) relative to the meniscus (5) or a position of a bar-shaped built-in part (10) relative to a side wall (2, 3) of the mould (1), so that the flow of the molten metal is stabilized in the area of the meniscus (5) in the form of a single vortex or a double vortex by a plurality of bar-shaped built-in parts (10).
4. Process according to Claim 3, characterized in that a temperature of a side wall (2, 3) of the mould (1) or a flow rate of the molten metal, preferably substantially parallel to the meniscus (5), in the mould (1) is used as the measured value.
5. Process according to one of Claims 1 to 4, characterized in that a free jet (8) of the molten metal is left clear by the bar-shaped built-in parts (10) as it leaves the casting tube (4).
6. Process according to one of Claims 1 to 5, characterized in that the molten metal is cooled down by at least one bar-shaped built-in part (10), the bar-shaped built-in part (10) being in connection with a cooling circuit.
7. Device for casting molten metal into continuously cast pre-products in a continuous casting machine, having

   - a mould (1), into which the molten metal is introduced, a meniscus (5) and a partly solidified strand being formed in the mould (1);

   - a strand-supporting device for guiding, supporting and cooling the strand, the at least partly solidified strand being drawn out from the mould (1);

   - a plurality of bar-shaped built-in parts (10) in the area of the meniscus (5) of the molten metal in the mould (1);

   characterized in that at least one bar-shaped built-in part (10) has an actuator (11) for changing an immersion depth of the bar-shaped built-in part (10) relative to the meniscus (5) or an actuator (11) for changing a position of the bar-shaped built-in part (10) relative to a side wall (2, 3) of the mould (1), the device additionally having at least one measured value sensor for measuring a state variable of the continuous casting machine and a controller or closed-loop control device connected thereto, the actuator (11) being connected to the controller or closed-loop control device and the bar-shaped built-in part (10) in such a way that, while taking into account the measured value, the controller or closed-loop control device determines an actuating signal, which can be fed to the actuator (11), so that the immersion depth relative to the meniscus (5) or the position relative to a side wall (2, 3) of the mould (1) of the at least one bar-shaped built-in part (10) can be changed.
8. Device according to Claim 7, characterized in that the bar-shaped built-in parts (10) cover less than 50% of the surface of the meniscus (5) of the mould (1).
9. Device according to either of Claims 7 and 8, characterized in that a bar-shaped built-in part (10) has a round, oval, lenticular or polygonal cross section.
10. Device according to one of Claims 7 to 9, characterized in that the bar-shaped built-in part (10) has a cooling circuit.
11. Device according to one of Claims 7 to 10, characterized in that the actuator (11) is formed as a pressure medium cylinder or as an electrical servo drive.
12. Use of the device according to one of Claims 7 to 11 in a continuous casting machine in the production of pre-products from molten metal, preferably slabs or thin slabs of steel, for stabilizing a flow of the molten metal in the form of a single vortex or a double vortex in a mould (1).

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