EP3437759B1 - Continuous casting of a metallic strand - Google Patents

Description

field of technology

The present invention relates to continuous casting, preferably semi-continuous continuous casting, of a metal strand in a continuous casting machine.

• Einführen eines Kaltstrangs in die Kokille;
• Halten des Kaltstrangs in der Kokille, sodass ein Kopf des Kaltstrangs die Kokille fluiddicht verschließt;
• Angießen der Stranggießmaschine, wobei Metallschmelze in die Kokille gegossen wird und sich in der Kokille ein Gießspiegel und ein teilerstarrter Strang ausbildet;
• Beginnen des Ausziehens des Kaltstrangs aus der Kokille, wobei der Kaltstrang mit einer ersten Ausziehgeschwindigkeit v₁ aus der Kokille ausgezogen wird;
• Stützen und Führen des teilerstarrten Strangs in der Strangführung, wobei der teilerstarrte Strang durch die Strangführungsrollen gestützt, geführt und durch Kühldüsen der Sekundärkühlung abgekühlt wird; und
• gesteuertes oder geregeltes Abkühlen des teilerstarrten Strangs bis zur Durcherstarrung des Strangs in der Tertiärkühlzone.

Specifically, the invention relates to a method for the semi-continuous continuous casting of a strand in a continuous casting machine, wherein the continuous casting machine has a mold with a primary cooling system, downstream in the casting direction a strand guide with a plurality of strand guide rollers, preferably adjustable against the strand, for guiding and secondary cooling for cooling the strand , and in turn subsequently has a tertiary cooling zone for the controlled or regulated cooling of the strand, comprising the process steps:

• Inserting a dummy bar into the mold;
• Holding the dummy bar in the mold so that a head of the dummy bar closes the mold in a fluid-tight manner;
• Casting on the continuous casting machine, with molten metal being poured into the mold and a meniscus and a partially solidified strand forming in the mold;
• beginning the extraction of the dummy bar from the mold, the dummy bar being extracted from the mold at a first extraction speed v ₁ ;
• supporting and guiding the partially solidified strand in the strand guide, wherein the partially solidified strand is supported by the strand guide rollers, guided and cooled by cooling nozzles of the secondary cooling; and
• Controlled or regulated cooling of the partially solidified strand until solidification of the strand in the tertiary cooling zone.

State of the art

The generic method and a suitable system are from WO 2015/079071 known. Thanks to the tertiary cooling zone with adjustable insulation panels, the cooling speed of the strand can be finely adjusted from bottom to top. This prevents the formation of cavities in the strand, so that liquid steel melt can compensate for volume jumps between the solid and liquid phase caused by solidification. This significantly improves the internal quality of the strand. The disadvantage of this is that continuous casting takes a very long time until it has completely solidified. The document does not reveal how continuous casting can be accelerated without adversely affecting the internal quality of the strand.

From the DE 3937752 A1 and the U.S. 2004/172153 A1 it is known to begin with a relatively low extraction speed at the start of continuous casting and then to continuously increase the speed.

From the publication Y.Zhang et al. / Control Engineering Practice 14 (2006) 1357-1375 a gradual increase in the extraction speed is also known.

Summary of the Invention

The object of the invention is to change known continuous casting processes in such a way that a strand is cast quickly and the formation of cavities or cracks in the strand is nevertheless prevented. This is intended to increase profitability and improve the internal quality of the cast strand.

The output according to the invention is solved by the subject-matter of claim 1. Advantageous embodiments are the subject matter of the dependent claims.

• einer chemischen Zusammensetzung der Metallschmelze,
• der Primärkühlung in der Kokille,
• der Sekundärkühlung des Strangs in der Strangführung, ständig das Ist-Temperaturfeld des Strangs einschließlich der Ist-Phasengrenzen zwischen den festen, teigigen und flüssigen Phasen im Strang berechnet, wobei die Ausziehgeschwindigkeit v des Kaltstrangs aus der Kokille in Abhängigkeit des Ist-Temperaturfelds und/oder der Ist-Phasengrenzen, insbesondere der Ist-Position der Sumpfspitze, eingestellt wird.

Specifically, the solution is provided by a generic method, wherein after the start of the extraction, the extraction speed v of the dummy bar from the mold is increased to a second extraction speed v ₂ , where v ₂ > v ₁ , and a thermal calculation model during continuous casting as a function

• a chemical composition of the molten metal,
• the primary cooling in the mold,
• the secondary cooling of the strand in the strand guide, constantly calculates the actual temperature field of the strand including the actual phase boundaries between the solid, pasty and liquid phases in the strand, with the extraction speed v of the cold strand from the mold depending on the actual temperature field and/or the actual phase boundaries, in particular the actual position of the sump tip, is set.

This measure produces a strand, typically a steel strand or a strand made from a so-called superalloy (see https://de.wikipedia.org/wiki/Superalloy, e.g. a nickel-based alloy), with a pronounced V-shaped formation of the strand shells. In other words, the thickness of the strand shells increases rapidly in the casting direction, so that the strand shell is significantly thicker at the lower end of the strand than at the upper end. As a result, liquid molten metal can immediately fill up any cavities caused by the solidification, which improves the internal quality of the strand. Increasing the casting speed also has an advantageous effect on the economics of the continuous casting process.

In order to achieve a pronounced V-shape of the strand shells, it is advantageous if the extraction speed v is increased as a function of time or the strand length. Limiting the extraction speed v upwards with v _max ensures that the strand shell has a minimum thickness at the upper end of the strand. This can prevent escaping.

In order to prevent shocks in the system, it is favorable if the extension speed v is gradually increased, preferably continuously differentiable at least once.

Alternatively, the extension speed v can also be increased discontinuously, e.g. in discrete steps.

• einer chemischen Zusammensetzung der Metallschmelze,
• der Primärkühlung in der Kokille,
• der Sekundärkühlung des Strangs in der Strangführung, ständig das Ist-Temperaturfeld des Strangs einschließlich der Ist-Phasengrenzen zwischen den festen, teigigen und flüssigen Phasen im Strang, wobei die Ausziehgeschwindigkeit des Kaltstrangs aus der Kokille in Abhängigkeit des Ist-Temperaturfelds und/oder der Ist-Phasengrenzen, insbesondere der Ist-Position der Sumpfspitze, eingestellt wird.

According to the invention, a thermal calculation model calculates as a function during continuous casting

• a chemical composition of the molten metal,
• the primary cooling in the mold,
• the secondary cooling of the strand in the strand guide, constantly the actual temperature field of the strand including the actual phase boundaries between the solid, pasty and liquid phases in the strand, with the extraction speed of the dummy bar from the mold depending on the actual temperature field and/or the actual -Phase boundaries, in particular the actual position of the sump tip, is set.

The calculation of the actual temperature field is, for example, from the WO 2009/141205 A1 known. Details are incorporated into this application by reference. Due to the embodiment according to the invention, the extraction speed of the dummy bar from the mold can be set, for example, in such a way that the actual position corresponds as closely as possible to a time-dependent target position of the sump tip.

In addition to changing the extraction or casting speed during the casting process, it is advantageous to adjust the intensity of the cooling capacity of the cooling nozzles in the secondary cooling as a function of the actual temperature field and/or the actual phase boundaries, in particular the actual position of the sump tip.

In addition, it is extremely favorable to have a heat transfer coefficient U of the insulation in the Set tertiary cooling zone depending on the actual temperature field and / or the actual phase boundaries, in particular the actual position of the sump tip.

The last two measures also have a very positive effect on the V-shaped design of the strand shell.

In general, it is advantageous if the intensity of the cooling capacity of the cooling nozzles in the secondary cooling decreases over time or over the strand length s and/or the strand in the tertiary cooling zone is thermally insulated by insulation, with a heat transfer coefficient U of the insulation increasing in the casting direction . As a result, the lower end of the strand, i.e. the strand head, is cooled more than the upper end of the strand, i.e. the strand foot.

A further improvement in the internal quality of the strand can be achieved if the continuous casting machine includes a strand stirrer that can be moved in the casting direction, with the strand stirrer electromagnetically stirring the region of the sump tip of the strand during the extraction and after the extraction of the dummy bar from the mold.

Brief description of the drawings

• Fig 1a bis 1h die Verfahrensschritte bei der Durchführung des Verfahrens,
• Fig 2a ein stranggegossener Strang nach dem Stand der Technik,
• Fig 2b ein stranggegossener Strang, der gemäß der Erfindung hergestellt wurde,
• Fig 3a ein Verlauf einer Ausziehgeschwindigkeit eines Strangs aus einer Kokille über der Zeit t,
• Fig 3b ein Verlauf einer Ausziehgeschwindigkeit eines Strangs aus einer Kokille über der Stranglänge s,
• Fig 4a ein Verlauf einer Durchflussrate Q eines Kühlmittels durch eine Kühldüse über der Zeit t,
• Fig 4b ein Verlauf einer Durchflussrate Q eines Kühlmittels durch eine Kühldüse über der Stranglänge s,
• Fig 5 ein Darstellung einer auf einen Strang akkumulierten Kühlmittelmenge,
• Fig 6 eine Darstellung einer variablen Isolierung in der Tertiärkühlzone,
• Fig 7a eine Darstellung einer variablen Wärmeisolation in der Tertiärkühlzone durch verschwenkbare Isolierklappen,
• Fig 7b eine Darstellung einer variablen Wärmeisolation in der Tertiärkühlzone durch verschiebbare Isolierklappen,
• Fig 8a eine Darstellung einer nicht erfindungsgemäßen Stranggießmaschine mit einer Steuer- und Regeleinrichtung zur Einstellung der Auszugsgeschwindigkeit v,
• Fig 8b eine Darstellung einer nicht erfindungsgemäßen Stranggießmaschine mit einer Steuer- und Regeleinrichtung zur Einstellung der Intensität der Sekundärkühlung,
• Fig 8c eine Darstellung einer nicht erfindungsgemäßen Stranggießmaschine mit einer Steuer- und Regeleinrichtung zur Einstellung der Wärmeisolierung in der Tertiärkühlzone,
• Fig 9a bis 9e eine Darstellung von Verfahrensschritten auf einer alternativen Stranggießmaschine zu den Fig la...lh,
• Fig 10 eine Darstellung einer Kopfisolierung, und
• Fig 11 eine Darstellung der Position der Sumpfspitze im Strang über der Zeit gemäß dem Stand der Technik und der Erfindung.

Other advantages and features of the present invention emerge from the description of non-limiting exemplary embodiments. The following diagrammatic figures show:

• Figures 1a to 1h the procedural steps in the implementation of the procedure,
• Figure 2a a continuously cast strand according to the prior art,
• Figure 2b a continuously cast strand made according to the invention,
• Figure 3a a course of a pull-out speed of a strand from a mold over time t,
• Figure 3b a course of a withdrawal speed of a strand from a mold over the strand length s,
• Figure 4a a course of a flow rate Q of a coolant through a cooling nozzle over time t,
• Figure 4b a course of a flow rate Q of a coolant through a cooling nozzle over the strand length s,
• figure 5 a representation of a quantity of coolant accumulated on a strand,
• figure 6 a representation of a variable insulation in the tertiary cooling zone,
• Figure 7a a representation of a variable thermal insulation in the tertiary cooling zone by pivoting insulating flaps,
• Figure 7b a representation of a variable thermal insulation in the tertiary cooling zone by means of sliding insulating flaps,
• Figure 8a a representation of a continuous casting machine not according to the invention with a control and regulating device for setting the extension speed v,
• Figure 8b a representation of a continuous casting machine not according to the invention with a control and regulating device for adjusting the intensity of the secondary cooling,
• Figure 8c a representation of a continuous casting machine not according to the invention with a control and regulating device for adjusting the thermal insulation in the tertiary cooling zone,
• Figures 9a to 9e a representation of process steps on an alternative continuous casting machine to FIGS.
• figure 10 an illustration of head insulation, and
• figure 11 Figure 12 shows the position of the sump tip in the strand versus time according to the prior art and the invention.

Description of the embodiments

In the figures la...lh the continuous casting, specifically the so-called semi-continuous continuous casting, of a strand 1 made of steel is shown. The continuous casting machine is designed as a vertical system and has as its main components a water-cooled mold 2, a strand guide 3 comprising several strand guide rollers 3a that can be set against the strand 1 and a secondary cooling system 4 with several cooling nozzles 4a, as well as a tertiary cooling zone 5 with thermal insulation 9 and several insulation panels 9a on. The machine head of the continuous casting machine, comprising the mold 2 and the strand guide 3, can be moved relative to the tertiary cooling zone 5, so that a single machine head can supply strands to several tertiary cooling zones. The strand guide rollers 3a do not necessarily have to be adjustable against the strand 1 via an actuator. It is sufficient if these can be adjusted mechanically, e.g. using washers or so-called shims.

In Figure 1a shows the situation before casting on the continuous casting machine. A dummy bar 6 was introduced into the mold 2 so that the stationary dummy bar 6 seals the mold in the casting direction G in a fluid-tight manner.

In Figure 1b the casting of the continuous casting machine is shown. A steel melt or a melt of a so-called. Superalloy is either directly or in the mold 2 supplied via a tundish, so that a meniscus M forms in the mold 2 and a strand 1 forms due to the primary cooling of the mold 2 . After a somewhat constant liquid level M has been established, the dummy bar 6 is started to be pulled out of the mold 2 . Initially, the extraction takes place relatively slowly with a first extraction speed v ₁ of 0.12 m/min (see Figure 3a ). The extraction speed v is increased according to the invention (see Figure 3a ), so that a strand 1 is formed with a pronounced V-shape of the strand shells (see Figure 2b ). In contrast, the strand 1 in continuous casting according to the prior art (see Figure 2a ) does not have a pronounced V-shape, which leads to poor internal quality (such as cracks, cavities, etc.). Due to the pronounced V-shape of the strand shells 11 of strand 1 (see Figure 2b ) during cooling in the tertiary cooling zone 5, the strand 1 can suck in liquid melt from the upper region of the partially solidified strand 1b, so that any cavities or cracks caused by the solidification are refilled with melt. A thin strand shell 11 at the upper strand end 1c facilitates this significantly. The mold 2 is oscillated in the vertical direction by an unillustrated oscillator. A stirring coil, also not shown, below the mold 2 stirs the partially solidified strand. Both details are customary and eg from the WO 2015/079071 known.

In Figure 1c When the continuous casting has progressed further, the strand 1 is supported and guided in the strand guide 3 by the strand guide rollers 3a and further cooled by the cooling nozzles 4a of the secondary cooling system 4. According to the solid line of Figure 3a is the extraction speed at the time of Figure 1c at about 0.2 m/min.

In Figure 1d shows the point in time during continuous casting at which the feeding of molten steel into the mold has just stopped. The extraction speed v corresponds to second extraction speed v ₂ of 0.36 m/min. This extraction speed of strand 1 is maintained until the end of the extraction process (see Figure 3a ).

After the supply of molten steel has stopped, the liquid level G in mold 2 drops (see Fig Fig. 1e ). At this point in time, the strand 1 has a strand length L of typically 6 to 12 m. The diameter of the strand 1 is 600 mm.

the Fig 1f shows the situation after the strand end 1c has passed the strand guide 3 and the secondary cooling 4 has been switched off. The partially solidified strand 1b is then in the tertiary cooling zone 5 and is slowly cooled there in a controlled or regulated manner.

In the Figures 1g and 1h is the cooling of the partially solidified strand 1b shown in the tertiary cooling zone 5, the time of Fig. 1g before the time of Fig 1h is. As already indicated above, the machine head can serve several tertiary cooling zones 5 and can be moved, for example, in a horizontal direction to a further tertiary cooling zone 5 . In order to further delay the solidification of the strand end 1c, the strand end 1c can be heated by a head heater 13 instead of the secondary cooling 4. The head heating 13 can take place, for example, inductively or by means of an exothermic powder (the process is referred to as "hot topping"), with the powder generating heat energy with the liquid molten steel. Since the partially solidified strand 1b is particularly prone to form cracks or cavities in the region of the sump tip, it is advantageous if a strand stirrer 14 stirs this region in particular electromagnetically.

the Figure 2a shows a continuously cast, partially solidified billet 1b according to the prior art. The strand end is almost completely solidified, so that any cavities or Cracks in the strand can no longer be filled with liquid melt 12.

In contrast, shows Figure 2b a strand according to the invention. The strand end 1c is still largely liquid, so that any cavities or cracks in the strand can be filled with liquid melt 12. As a result, the strand has a better internal quality.

As stated above, the Figure 3a the

Extraction speed v over time t. The diagram shows that the extension speed v does not necessarily have to be increased linearly, but also, for example, under- or over-linearly (see dashed lines). An increase in discrete steps (not shown) would also be conceivable and could be useful.

the Figure 3b shows another diagram for the extraction speed v, where v does not depend on the time t but on the strand length s. This ensures that the beginning of the strand 1a is cooled more than the end of the strand 1c, regardless of any interruptions in the casting process.

In both cases, increasing the extraction speed v not only increases the internal quality of the strand 1, but also improves the economics of the continuous casting process, since more strands can be cast within the same time.

The internal quality of the strand can also be adjusted by adjusting the intensity of the secondary cooling 4 depending on the time or the strand length s (see Figure 1c ) take place. In both cases, this means that the beginning of the strand 1a is cooled more in the secondary cooling system 4 than the end of the strand 1c. This measure can be taken in addition to increasing the extraction speed v of the dummy bar 6 from the mold 2 or instead of it.

In the event that the intensity of the secondary cooling 4 is adjusted in addition to changing the extraction speed v, the description of FIG Figures 1a-1h still fully valid. In addition, the intensity of the secondary cooling is varied depending on the time t or the strand length s. The time-dependent change in the intensity of the secondary cooling due to a change in the flow rate Q through the cooling nozzles 4a of the secondary cooling 4 is in Figure 4a shown. The decrease in the flow rate Q or the intensity of the secondary cooling 4 can be linear (continuous line) but also less than or more than linear (see dashed lines). Alternatively, the intensity of the secondary cooling can also be varied depending on the strand length s (see Figure 4b ). In this case, the strand length s is recorded or calculated during casting and the intensity of the secondary cooling 4 according to the characteristic of Figure 4b set.

In the event that the intensity of the secondary cooling 4 is adjusted instead of changing the extraction speed v, the description of the Figures 1a-1h to be modified in such a way that the extension speed v remains constant. The strand 1 pulled out of the mold 2 is cooled in the secondary cooling zone 4 with variable intensity either as a function of time or strand length, so that the beginning of the strand 1a is cooled more than the end of the strand 1c.

In figure 5 is a schematic of the amounts of coolant accumulated in the different areas of a partially solidified strand 1b when the intensity of the secondary cooling is adjusted as a function of time or strand length (see Fig Figure 4a or 4b ) shown. A high accumulated amount of coolant, such as at the lower end of the strand 1a, was finely rasterized and a low accumulated amount of coolant, such as at the upper end of the strand 1c, was shown as a coarse raster. By changing the flow rate as a function of time or line length Q or a change in the pressure p of the coolant that is dependent on time or strand length, the intensity of the secondary cooling is changed so that the beginning of the strand is cooled more than the end of the strand.

In figure 6 another possibility for improving the internal quality of the strand is shown. In this case, the thermal insulation 9 in the tertiary cooling zone 5 is adjusted as a function of the strand length L, with a heat transfer coefficient U of the thermal insulation 9 in the casting direction G increasing. In other words, the start of the strand 1a is cooled more in the tertiary cooling system 5 than the end of the strand 1c. This measure can be taken either in addition to or instead of increasing the extraction speed v of the dummy bar 6 from the mold 2 . It would also be possible for the thermal insulation 9 in the tertiary cooling zone 5 to be changed in addition to or instead of adjusting the intensity of the secondary cooling 4 . The change in the heat transfer coefficient U of the thermal insulation 9 is in figure 6 represented by a variable thickness of insulation.

In Figure 7a the strand length-dependent change in the thermal insulation 9 in the tertiary cooling zone 5 is shown by insulation panels 9a. In order to cool the start of the strand 1a more than the end of the strand 1c, the pivotable flaps of the insulation panels are set differently, with the upper flaps being largely closed and the lower flaps being largely open. As a result, a heat transfer coefficient U of the thermal insulation 9 in the casting direction G increases. The change in the opening angle of the flaps can either be preset statically or dynamically, for example via pivoting drives for pivoting the flaps, during the cooling in the tertiary cooling zone 5 .

the Figure 7b shows an alternative to Figure 7a , the degree of coverage of the insulating flaps 9a of the strand being higher at the end of the strand 1c than at the beginning of the strand. Also because of that the heat transfer coefficient U of the heat insulation 9 in the casting direction G increases.

In Figure 8a a non-inventive continuous casting machine with a control or regulating device 10 for controlling or regulating the extension speed v is shown. The control or regulating device 10 calculates the temperature field and the sump tip in the cast strand 1, taking into account the chemical composition 15 of the metal melt, the primary cooling 2a in the mold 2, the secondary cooling 4 and the strand length s, and sets the extraction speed of the motor 16 as a function of the swamp peak on. Optionally, it would also be possible to take other parameters into account, such as the position of the insulating panels 9a in the tertiary cooling zone.

the Figure 8b shows a continuous casting machine not according to the invention with a control or regulating device 10 for controlling or regulating the intensity of the secondary cooling 4 depending on the strand length s. The control or regulating device 10 calculates taking into account the chemical composition 15 of the molten metal and the primary cooling 2a in the mold and the strand length s the temperature field and the sump peak in the cast strand 1 and adjusts the intensity of the secondary cooling 4 depending on the sump peak. The sump tip is calculated in real time in a thermal calculation model.

the Figure 8c also shows a continuous casting machine not according to the invention with a control or regulating device 10 for controlling or regulating a heat transfer coefficient U of the heat insulation 9 in the tertiary cooling zone 5. The control or regulating device 10 calculates taking into account the chemical composition 15 of the molten metal and the primary cooling 2a in the Mold the temperature field and the sump tip in the cast strand 1 and sets the opening angle of the insulating panels 9a depending on the sump tip. the Sump tip is calculated in real time in a thermal calculation model.

In the Figures 9a to 9e an alternative continuous casting machine for carrying out the method according to the invention is shown. In Figure 9a we cast a strand 1 in the mold 2 and pulled out of the mold with a variable extraction speed v. The strand 1 is supported and guided in the strand guide 3 and cooled by the secondary cooling. In Figure 9b the casting in the mold has ended and the strand 1 is in a radiation area 17 where it can radiate heat to the environment for a certain time. On the way to the tertiary cooling zone 5, the strand passes through a stirring coil 14 and is stirred electromagnetically by it, see FIG Figure 9c . The strand is then introduced into the tertiary cooling zone 5, where it is cooled in a controlled or regulated manner by the thermal insulation 9. Since the strand end 1c in particular is particularly sensitive, it is again particularly thermally insulated by a cover, see Figures 9d and 9e .

In figure 10 a head insulation 18 of a strand 1 is shown schematically. The head insulation has thermal insulation 9 for the strand end 1c of the strand 1, so that the strand end 1c remains liquid longer. In addition to the thermal insulation 9, an exothermic powder 19 can be applied to the liquid strand end 1c, which additionally heats the strand 1.

In figure 11 the result of the time- or distance-dependent setting of the extension speed v and/or the time- or path-dependent setting of the intensity of the secondary cooling and/or the setting of a heat transfer coefficient U of the thermal insulation 9 is shown schematically. All of these measures have the effect of slowing down the solidification of the partially solidified strand (see the dashed line indicating the position of the sump tip in the strand over time). In contrast, the solid line indicates the comparison with the prior art. As stated above, these measures lead to the strand according to the invention has a pronounced V-shape of the strand shell (see figure 11 right) in contrast to strands according to the prior art without a pronounced V-shape of the strand shell (see figure 11 Left).

Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention as defined in the appended claims.

Reference List

1

strand

1a

start of strand

1b

partially solidified strand

1c

strand end

2

mold

2a

primary cooling

3

strand guide

3a

strand guide rollers

4

Secondary cooling, secondary cooling zone

4a

cooling nozzle

5

Tertiary cooling, tertiary cooling zone

6

dummy leg

7

calculation model

8th

swamp top

9

thermal insulation

9a

insulation panel

10

Control or regulating device

11

strand shell

12

liquid section of the strand

13

head heating

14

strand stirrer

15

chemical composition

16

engine

17

radiation range

18

head insulation

19

exothermic powder

G

pouring direction

L

strand length

M

casting level

Q

flow rate

S

strand length

t

time

u

heat transfer coefficient

v

extraction speed, pouring speed

Claims (10)

1. Method for the semi-continuous casting of a strand (1) in a continuous casting machine, wherein the continuous casting machine has a mould (2) with primary cooling (2a), followed in the casting direction (G) by a strand guide (3) with multiple strand guiding rollers (3a) for guiding purposes and secondary cooling (4) for cooling the strand (1), followed in turn by a tertiary cooling zone (5) for the controlled or regulated cooling of the strand (1), said method comprising the following method steps:

   - introducing a dummy bar (6) into the mould (2);

   - holding the dummy bar (6) in the mould (2), with the result that a head of the dummy bar (6) closes the mould (2) in a fluid-tight manner;

   - beginning casting in the continuous casting machine, wherein molten metal is cast into the mould (2) and a casting level (M) and a partially solidified strand (1b) are formed in the mould (2);

   - starting the extraction of the dummy bar (6) from the mould (2), wherein the dummy bar (6) is extracted from the mould (2) at a first extraction velocity v₁;

   - supporting and guiding the partially solidified strand (1b) in the strand guide (3), wherein the partially solidified strand (1b) is supported and guided by the strand guiding rollers (3a) and cooled by cooling nozzles (4a) of the secondary cooling (4);

   - performing controlled or regulated cooling of the partially solidified strand (1b) until the strand (1) has solidified right through in the tertiary cooling zone (5);

   characterized in that, after the extraction starts, the extraction velocity v at which the dummy bar (6) is extracted from the mould (2) is increased to a second extraction velocity v₂, wherein v₂ > v₁, and

   in that, during the continuous casting, a thermal calculation model (7) continuously calculates the actual temperature distribution of the strand (1), including the actual phase boundaries between the solid, pasty and liquid phases in the strand (1), depending on

   - a chemical composition (15) of the molten metal,

   - the primary cooling (2a) in the mould (2),

   - the secondary cooling (4) of the strand (1) in the strand guide (3),
   wherein the extraction velocity v at which the dummy bar (6) is extracted from the mould (2) is set depending on the actual temperature distribution and/or the actual phase boundaries, in particular the actual position of the liquidus tip (8).
2. Method according to Claim 1, characterized in that the extraction velocity v is increased depending on the time t or the strand length s.
3. Method according to Claim 2, characterized in that the extraction velocity v is increased continuously in some parts, preferably at least once in a continuously differentiable manner.
4. Method according to Claim 2, characterized in that the extraction velocity v is increased discontinuously, e.g. in discrete stages.
5. Method according to Claim 1, characterized in that the extraction velocity v of the dummy bar (6) is set in such a way that the actual position corresponds as far as possible to a temporally dependent setpoint position of the liquidus tip (8) .
6. Method according to Claim 1 or 5, characterized in that the intensity of the secondary cooling (4) is set depending on the actual temperature distribution and/or the actual phase boundaries, in particular the actual position of the liquidus tip (8).
7. Method according to one of Claims 1, 5 and 6, wherein the strand (1) is thermally insulated in the tertiary cooling zone (5) by heat insulation (9), characterized in that a heat transfer coefficient U of the heat insulation (9) is set depending on the actual temperature distribution and/or the actual phase boundaries, in particular the actual position of the liquidus tip (8).
8. Method according to one of the preceding claims, characterized in that the intensity of the secondary cooling (4) decreases over the time t or the strand length s.
9. Method according to one of the preceding claims, characterized in that the strand (1) is thermally insulated in the tertiary cooling zone (5) by heat insulation (9), wherein a heat transfer coefficient U of the heat insulation (9) increases in the casting direction (G).
10. Method according to one of the preceding claims, wherein the continuous casting machine comprises a strand stirrer (14) that is displaceable in the casting direction (G), characterized in that the strand stirrer (14) electromagnetically stirs the region of the liquidus tip (8) of the strand (1) while the dummy bar (6) is being extracted from the mould (2) and after said extraction has ended.

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