EP3437756A1 - Continuous casting of a metallic strand - Google Patents

Abstract

The invention relates to a method and a plant for continuous casting of a metallic strand (1) in a continuous casting machine. The object of the invention is to modify known continuous casting so that the formation of voids or cracks in the strand (1) is prevented. This object is achieved by the method according to claim 1, wherein the strand (1) in the Tertiärkühlzone (5) by a thermal insulation (9) is thermally insulated and a heat transfer coefficient U of the heat insulation (9) in the casting direction (G) is increasingly adjusted.

Description

Field of engineering

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

• Einführen eines Kaltstrangs in die Kokille;
• Halten des Kaltstrangs in der Kokille, wobei 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 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 continuous casting, preferably for semi-continuous casting, a strand in a continuous casting machine, wherein the continuous casting a mold with a primary cooling, casting in the following direction a strand guide with several, preferably engageable with the strand, strand guide rollers for guiding and a Secondary cooling for cooling the strand, and in turn subsequently a Tertiärkühlzone for controlled or controlled cooling of the strand, comprising the steps of:

• Introducing a cold strand into the mold;
• Holding the cold strand in the mold, wherein a head of the cold strand fluid-tightly closes the mold;
• Casting the continuous casting machine, wherein molten metal is poured into the mold and forms in the mold a casting mirror and a partially solidified strand;
• Beginning to pull the cold strand out of the mold, pulling the cold strand out of the mold;
• Supporting and guiding the semi-solid strand in the strand guide, wherein the semi-solid strand is supported by the strand guide rollers, guided and cooled by cooling nozzles of the secondary cooling; and
• Controlled or controlled cooling of the partially solidified strand until the solidification of the strand in the tertiary cooling zone.

• eine Kokille mit einer Primärkühlung,
• in Gießrichtung nachfolgend eine Strangführung mit mehreren, vorzugsweise an den Strang anstellbaren, Strangführungsrollen zum Führen und Stützen des Strangs, sowie eine Sekundärkühlung zum Abkühlen des Strangs, und
• wiederum nachfolgend eine Tertiärkühlzone zum gesteuerten oder geregelten Abkühlen des Strangs aufweist.

Moreover, the invention relates to a continuous casting machine for continuous casting, preferably for semi-continuous casting, of a metallic strand, wherein the continuous casting machine

• a mold with a primary cooling,
• in the casting direction below a strand guide with several, preferably engageable with the strand, strand guide rollers for guiding and supporting the strand, and a secondary cooling to cool the strand, and
• in turn subsequently has a Tertiärkühlzone for controlled or controlled cooling of the strand.

State of the art

The generic method and a suitable system are from WO 2015/079071 known. Through the tertiary cooling zone with adjustable insulation panels, the cooling rate of the strand can be fine-tuned from bottom to top. As a result, the formation of cavities in the strand is prevented, so that liquid molten steel can compensate for the solidification-induced volume jumps between the solid and liquid phase. The internal quality of the strand is thereby significantly improved. How the inner quality of the strand can be further improved, is not apparent from the Scriptures.

Summary of the invention

The object of the invention is to modify known continuous casting processes so that cavities or cracks in the strand are prevented even more consistently. This should further 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 of the dependent claims.

Specifically, the solution is carried out by a generic method, wherein the strand is thermally insulated in the Tertiärkühlzone by a thermal insulation and a heat transfer coefficient U of the heat insulation in the casting direction is increasingly adjusted. The heat insulation can either be preset statically or set dynamically during casting or solidification.

By this measure, a strand, typically a steel strand or a strand of a so-called superalloy (see https://de.wikipedia.org/wiki/Superlegierung, for example, a nickel-based alloy), produced with a pronounced V-shaped configuration of the strand shells. In other words, forms in the Tertiärkühlzone a strand whose strand shell is much thicker at the beginning of the strand than at the strand end. As a result, liquid molten steel can directly fill up any voids caused by the solidification, which improves the internal quality of the strand.

A simple way to achieve a heat transfer coefficient U of the heat insulation, which increases in the casting direction, is to make a thickness of the U of the heat insulation in the casting direction decreasing.

A heat transfer coefficient U of the heat insulation which increases in the casting direction can also be achieved by decreasing the degree of coverage of the heat insulation of the surface of the strand in the casting direction. This can e.g. be done by insulation panels whose degree of coverage is preset statically or dynamically adjusted during casting.

Alternatively or additionally, it is advantageous if the tertiary cooling zone comprises a plurality of dynamically adjustable during operation Isolierpanele, wherein an opening angle an insulating panel relative to the vertical in the casting direction is increasingly adjusted.

In order to obtain a pronounced V-shaped strand shell, it is favorable if, after the start of the extraction, the withdrawal speed v of the cold strand from the mold is increased. Thus, the Stranganfang is pulled out of the mold slower than the Stranggende, whereby the Stranganfang is much thicker than the strand end.

In this case, it is favorable if the raising of the pull-out speed v takes place as a function of the time t or the strand length s. Thus, the strand beginning is pulled out more slowly than the strand end of the mold, so that the strand end has a thinner strand shell.

It is particularly preferred if the increase is piecewise continuous, preferably continuously differentiable at least once. As a result, shocks are prevented in the continuous casting machine.

To achieve a pronounced V-shaped strand shell, it is further favorable if the intensity of the secondary cooling over the time or the strand length is set decreasing.

This can be done by adjusting a pressure p and / or a flow rate Q of a coolant introduced onto the strand by a cooling nozzle over time or the strand length decreasing.

• einer chemischen Zusammensetzung der Metallschmelze,
• der Primärkühlung in der Kokille,
• der Sekundärkühlung des Strangs in der Strangführung,
• optional einer Auszugsgeschwindigkeit des Strangs aus der Kokille,

ständig das Ist-Temperaturfeld des Strangs einschließlich der Ist-Phasengrenzen zwischen den festen, teigigen und flüssigen Phasen im Strang berechnet, wobei eine Wärmeisolation des Strangs in der Tertiärkühlzone in Abhängigkeit des Ist-Temperaturfelds und/oder der Ist-Phasengrenzen, insbesondere der Ist-Position der Sumpfspitze, eingestellt wird.It is particularly advantageous if a thermal calculation model during continuous casting in dependence

• a chemical composition of the molten metal,
• the primary cooling in the mold,
• the secondary cooling of the strand in the strand guide,
• optionally an extraction speed of the strand from the mold,

continuously calculates the actual temperature field of the strand including the actual phase boundaries between the solid, doughy and liquid phases in the strand, wherein a thermal insulation of the strand in the tertiary cooling zone as a function of 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 eg from the DE 4417808 C3 or the WO 2009/141205 A1 known. Details are included in this application by reference. By this embodiment, the heat insulation can be adjusted, for example, so that the actual position of a time-dependent desired position of the sump tip corresponds as possible.

In addition to changing the heat insulation during the casting process, it is advantageous to set an intensity of 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.

A further improvement in the internal quality of the strand can be achieved if the continuous casting machine comprises a strand-movable in the casting direction, the strand agitator during the extraction and after completing the extraction of the cold strand from the mold, the region of the sump tip of the strand is electromagnetically stirred.

The object of the invention is also achieved by a continuous casting plant according to claim 12. Advantageous embodiments are the subject of the dependent claims.

Specifically, the solution is carried out by a generic continuous casting machine, which has a control or regulating device for controlling or regulating a heat transfer coefficient U of the heat insulation in the Tertiärkühlzone.

It is advantageous if the control or regulating device realizes a time or length-dependent control or regulation of the heat transfer coefficient U.

• einer chemischen Zusammensetzung der Metallschmelze,
• der Primärkühlung in der Kokille,
• der Sekundärkühlung des Strangs,
• optional einer Auszugsgeschwindigkeit des Strangs aus der Kokille,

ständig das Ist-Temperaturfeld des Strangs einschließlich der Ist-Phasengrenzen zwischen den festen, teigigen und flüssigen Phasen im Strang zu berechnen, wobei die Wärmeisolation in Abhängigkeit des Ist-Temperaturfelds und/oder der Ist-Phasengrenzen, insbesondere der Ist-Position der Sumpfspitze, eingestellt werden kann.Moreover, it is advantageous if the control or regulating device comprises a thermal calculation model which is suitable during continuous casting in dependence

• a chemical composition of the molten metal,
• the primary cooling in the mold,
• the secondary cooling of the strand,
• optionally an extraction speed of the strand from the mold,

constantly calculate the actual temperature field of the strand including the actual phase boundaries between the solid, doughy and liquid phases in the strand, the thermal insulation depending on the actual temperature field and / or the actual phase boundaries, in particular the actual position of the sump tip, can be adjusted.

It is particularly advantageous if an extraction speed of the strand from the mold and / or an intensity of the secondary cooling can be set as a function of the actual temperature field and / or the actual phase boundaries, in particular the actual position of the sump tip.

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 eine 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 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 1a...1h,
• 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.

Further advantages and features of the present invention will become apparent from the description of non-limiting embodiments. The following schematically illustrated figures show:

• Fig 1a to 1h the process steps in carrying out the process,
• Fig. 2a a continuous casting strand according to the prior art,
• Fig. 2b a continuously cast strand made according to the invention,
• Fig. 3a a course of a withdrawal speed of a strand from a mold over the time t,
• Fig. 3b a course of a withdrawal speed of a strand from a mold over the strand length s,
• Fig. 4a a profile of a flow rate Q of a coolant through a cooling nozzle over the time t,
• 4b a profile of a flow rate Q of a coolant through a cooling nozzle over the strand length s,
• Fig. 5 a representation of an accumulated on a strand coolant amount,
• Fig. 6 a representation of a variable insulation in the tertiary cooling zone,
• Fig. 7a a representation of a variable heat insulation in the tertiary cooling zone by means of pivotable insulating flaps,
• Fig. 7b a representation of a variable heat insulation in the tertiary cooling zone by sliding insulating flaps,
• Fig. 8a a representation of a non-inventive continuous casting machine with a control and regulating device for adjusting the pull-out speed v,
• Fig. 8b a representation of a non-inventive continuous casting machine with a control and regulating device for adjusting the intensity of the secondary cooling,
• Fig. 8c a representation of a continuous casting machine according to the invention with a control and regulating device for adjusting the thermal insulation in the Tertiärkühlzone,
• 9a to 9e a representation of process steps on an alternative continuous casting machine to the Fig. 1a ... 1h .
• FIG. 10 a representation of a head insulation, and
• Fig. 11 a representation of the position of the sump tip in the strand over time according to the prior art and the invention.

Description of the embodiments

In the FIGS. 1a ... 1h is the continuous casting, specifically the so-called semi-continuous continuous casting, a strand 1 shown in steel. The continuous casting machine is designed as a vertical installation and has as main components a water-cooled mold 2, a strand guide 3 comprising a plurality of strand guide rollers 3a engageable with the strand 1 and a secondary cooling 4 with a plurality of cooling nozzles 4a and a tertiary cooling zone 5 with a 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, are movable 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 need not necessarily be adjustable via an actuator to the strand 1. It is sufficient if these can be adjusted to the strand mechanically, for example via washers or so-called shims.

In Fig. 1a the situation is shown before casting the continuous casting machine. A cold strand 6 was introduced into the mold 2, so that the stationary cold strand 6, the mold in the casting direction G fluid-tight seals.

In 1b is the casting of the continuous casting machine shown. A molten steel or a melt of a so-called superalloy is fed into the mold 2 either directly or via a distributor vessel, so that a casting level M is formed in the mold 2 and a strand 1 due to the primary cooling of the mold 2. After a somewhat constant pouring M has been set, is started with the extraction of the cold strand 6 from the mold 2. Initially, the drawing off takes place relatively slowly with a first drawing speed v ₁ of 0.12 m / min (see Fig. 3a ). The extraction speed v is increased (see Fig. 3a ), so that already outside the tertiary cooling zone 5, a strand 1 with a pronounced V-shape of the strand shells is formed (see Fig. 2b ). In contrast, the strand 1 in prior art continuous casting processes (see Fig. 2a ) does not have a pronounced V-shape, resulting in poor internal quality (such as cracks, voids, etc.). Due to the pronounced V-shape of the strand shells 11 of the strand 1 (see Fig. 2b ), the strand 1 during cooling in the Tertiärkühlzone 5 molten liquid melt from the upper portion of the partially solidified strand 1b so that any caused by the solidification cavities or cracks are refilled by melt. A thin strand shell 11 at the upper end of the strand 1c facilitates this crucial. The mold 2 is oscillated by an oscillator, not shown, in the vertical direction. A stirring coil, also not shown below the mold 2 stirs the partially solid strand. Both details are customary and eg from the WO 2015/079071 known.

In Fig. 1c the continuous casting is more advanced, wherein 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 4. According to the solid line of Fig. 3a is the extraction speed at the time of Fig. 1c in about 0.2 m / min.

In Fig. 1d is the time in continuous casting shown, in which the supply of molten steel was just stopped in the mold. The drawing speed v corresponds to the second drawing speed v ₂ of 0.36 m / min. This pull-out speed of the strand 1 is maintained until the end of the pull-out operation (see Fig. 3a ).

After the supply of molten steel has been stopped, the pouring mirror G in the mold 2 drops (see Fig. 1e ). At this time, the strand 1 has its final strand length L of typically 6 to 12m. 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 solided strand 1b is then in the Tertiärkühlzone 5 and is slowly controlled or controlled cooled.

In the Fig. 1g and 1h the non-inventive cooling of the partially solidified strand 1b is shown in the Tertiärkühlzone 5, wherein 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, for example, can be moved in a horizontal direction to a further tertiary cooling zone 5. In order to further delay the solidification of the strand end 1 c, instead of the secondary cooling 4, the strand end 1 c can be heated by a head heater 13. The head heater 13 can be made, for example, inductively or by an exothermic powder (the process is referred to as "hot topping"), wherein the powder generates heat energy with the liquid molten steel. Since the partially solidified strand 1b in the region of the sump tip is particularly susceptible to cracks or cavities, it is advantageous if a strand agitator 14 in particular electromagnetically stirs this region.

The Fig. 2a shows a continuous cast semi-solid strand 1b according to the prior art. The strand end is almost completely solidified, so that any voids or cracks in the strand can not be filled by liquid melt 12.

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

As stated above, the shows Fig. 3a the extraction speed v over time t. It can be seen from the diagram that the pull-out speed v does not necessarily have to be increased linearly, but also, for example, under- or over-linear (see dashed lines). Even an increase, not shown, in discrete stages would be conceivable and could be useful.

The Fig. 3b shows another diagram for the extraction speed v, where v depends not on the time t but on the strand length s. This ensures that the strand beginning 1a is cooled more strongly than the strand end 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 economy of the continuous casting process, since more strands can be cast within the same time.

The inner quality of the strand can also be adjusted by adjusting the intensity of the secondary cooling 4 as a function of time or the strand length s (see Fig. 1c ) respectively. In both cases, this means that the strand beginning 1a is cooled more strongly in the secondary cooling 4 is called the strand end 1c. This measure can be done in addition to increasing the Ausziehgeschwindigkeit v of the dummy bar 6 from the mold 2 or instead of it.

In the event that the adjustment of the intensity of the secondary cooling 4 takes place in addition to the change of the withdrawal speed v, the description of the Figures 1a-1h still fully valid. In addition, the intensity of the secondary cooling is varied as a function of the time t or the strand length s. The time-dependent change in the intensity of the secondary cooling by a change in the flow rate Q through the cooling nozzles 4a of the secondary cooling 4 is in Fig. 4a shown. The decrease of the flow rate Q or the intensity of the secondary cooling 4 can be linear (continuous line) but also sub-linear or superlinear (see dashed lines). Alternatively, the intensity of the secondary cooling can also be varied as a function of the strand length s (see 4b ). In this case, the strand length s during casting is calculated and the intensity of the secondary cooling 4 is determined according to the characteristic of 4b set.

In the event that the adjustment of the intensity of the secondary cooling 4 takes place instead of the change of the withdrawal speed v, the description of the Figures 1a-1h modify so that the extraction speed v remains constant. The drawn out of the mold 2 strand 1 is cooled in the secondary cooling zone 4 either time or strand length dependent variable intensity, so that the strand beginning 1a is cooled more than the strand end 1c.

In Fig. 5 schematically shows the accumulated on the different areas of a teilerstarrten strand 1b amounts of coolant in the time or strand length-dependent adjustment of the intensity of the secondary cooling (see Fig. 4a or 4b ). A high accumulated amount of coolant, as at the lower strand beginning 1a, was finely screened and a Low accumulated refrigerant amount, as at the upper strand end 1c, has been roughly rastered. Due to the time or strand length-dependent change in the flow rate Q or a time or strand length-dependent change in the pressure p of the coolant, the intensity of the secondary cooling is changed so that the strand start is cooled more than the strand end.

In Fig. 6 a possibility according to the invention for improving the internal quality of the strand is shown. In this case, the heat insulation 9 is set in the tertiary cooling zone 5 as a function of the strand length L, wherein a heat transfer coefficient U of the heat insulation 9 in the casting direction G increases. In other words, the strand beginning 1a is cooled more strongly in the teritary cooling 5 than the strand end 1c. This measure can be done in addition to increasing the Ausziehgeschwindigkeit v of the dummy bar 6 from the mold 2. It would also be possible for the change in the thermal insulation 9 in the tertiary cooling zone 5 to be carried out in addition to the adjustment of the intensity of the secondary cooling 4. The change in the heat transfer coefficient U of the heat insulation 9 is in Fig. 6 represented by a variable thickness of the insulation.

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

The Fig. 7b shows an alternative to Fig. 7a , wherein the degree of coverage of the insulating flaps 9a of the strand at the strand end 1c is higher than at the strand beginning. This also increases the heat transfer coefficient U of the heat insulation 9 in the casting direction G.

In Fig. 8a is a non-inventive continuous casting machine with a control or regulating device 10 for controlling or regulating the pullout speed v shown. The control unit 10, taking into account the chemical composition 15 of the molten metal, the primary cooling 2a in the mold 2, the secondary cooling 4 and the strand length s calculates the temperature field and the sump tip in the cast strand 1 and sets the withdrawal speed of the dummy strand via the motor 16 depending on the sump tip. The sump tip is calculated in real time in a thermal calculation model. Optionally, it would also be possible to consider other parameters such as the position of the insulating panels 9a in the tertiary cooling zone.

The Fig. 8b also shows a non-inventive continuous casting machine with a control or regulating device 10 for controlling or regulating the intensity of the secondary cooling 4 as a function of the strand length s. The controller 10 calculates, considering 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 tip in the cast strand 1 and adjusts the intensity of the secondary cooling 4 as a function of the sump tip. The sump tip is calculated in real time in a thermal calculation model.

The Fig. 8c Finally shows a continuous casting machine 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 Tertiärkühlzone 5. The control or regulating device 10th In consideration of the chemical composition 15 of the molten metal and the primary cooling 2a in the mold, the temperature field and the sump peak in the cast strand 1 are calculated and adjusts the opening angles 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 9a to 9e an alternative continuous casting machine is shown. In Fig. 9a we poured a strand 1 in the mold 2 and pulled out with variable withdrawal speed v from the mold. The strand 1 is supported and guided in the strand guide 3 and cooled by the secondary cooling. In Fig. 9b the casting in the mold was stopped and the strand 1 is located in a radiation area 17, where it can radiate heat to the environment over a certain time. On the way to the tertiary cooling zone 5, the strand passes through a stirring coil 14 and is electromagnetically stirred by this, see Fig. 9c , The strand is then introduced into the tertiary cooling zone 5, where it is cooled or controlled by the thermal insulation 9. Since, in particular, the strand end 1 c is particularly sensitive, it is again thermally insulated by a lid, see 9d and 9e ,

In FIG. 10 schematically a head insulation 18 of a strand 1 is shown. The head insulation has a heat 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 Fig. 11 is schematically the result of the time- or distance-dependent adjustment of the extraction speed v and / or the time- or path-dependent adjustment of the intensity of the secondary cooling and / or the setting of a heat transfer coefficient U of the heat insulation. 9 shown. All of these measures have the effect of slowing the solidification of the partially solidified strand (see the dashed line indicating the increase in temperature over time). In contrast, the solid line indicates the comparison with the prior art. As stated above, these measures result in the strand having a pronounced V-shape of the strand shell (see Fig. 11 right) in contrast to strands without pronounced V-shape of the strand shell (see Fig. 11 Left).

While the invention has been further illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

LIST OF REFERENCE NUMBERS

1

strand

1a

train early

1b

partially solid strand

1c

strand end

2

mold

2a

primary cooling

3

strand guide

3a

Strand guide rolls

4

Secondary cooling, secondary cooling zone

4a

cooling nozzle

5

Tertiary cooling, tertiary cooling zone

6

dummy bar

7

computer model

8th

crater tip

9

thermal insulation

9a

insulation panel

10

Control or regulating device

11

strand shell

12

liquid area of the strand

13

Heating head

14

Strangrührer

15

chemical composition

16

engine

17

radiation range

18

head insulation

19

exothermic powder

G

casting

L

strand length

M

meniscus

Q

Flow rate

S

strand length

t

Time

U

Heat transfer coefficient

v

Extraction speed, casting speed

Claims (15)

Method for continuous casting, preferably for semi-continuous casting, of a strand (1) in a continuous casting machine, wherein the continuous casting machine comprises a mold (2) with a primary cooling (2a), in the casting direction (G) subsequently a strand guide (3) with a plurality of strand guiding rolls (3) 3a) for guiding and a secondary cooling (4) for cooling the strand (1), and in turn subsequently a tertiary cooling zone (5) for the controlled or controlled cooling of the strand (1), comprising the method steps: - Introducing a cold strand (6) in the mold (2); - Holding the cold strand (6) in the mold (2), wherein a head of the dummy bar (6) the mold (2) closes fluid-tight; - Casting the continuous casting machine, wherein molten metal is poured into the mold (2) and in the mold (2) a casting mirror (M) and a teilerstarrter strand (1b) is formed ;, - Starting to pull out the cold strand (6) from the mold (2), wherein the cold strand (6) from the mold (2) is pulled out; Supporting and guiding the partially solidified strand (1b) in the strand guide (3), wherein the partially solidified strand (1b) is supported by the strand guiding rolls (3a) and cooled by cooling nozzles (4a) of the secondary cooling (4); - controlled or controlled cooling of the partially solidified strand (1b) until solidification of the strand (1) in the tertiary cooling zone (5); characterized in that the strand (1) in the Tertiärkühlzone (5) by a thermal insulation (9) is thermally insulated and a heat transfer coefficient U of the heat insulation (9) in the casting direction (G) is increasingly adjusted. A method according to claim 1, characterized in that a thickness of the U of the heat insulation (9) in the casting direction (G) to make decreasing. A method according to claim 1 or 2, characterized in that a degree of coverage of the heat insulation (9) of the surface of the strand (1) in the casting direction (G) is set decreasing. The method of claim 1 to 3, wherein the tertiary cooling zone (5) comprises a plurality of dynamically adjustable during operation Isolierpanele (9a), characterized in that an opening angle of a Isolierpanels (9) relative to the vertical in the casting direction (G) is increasingly adjusted. Method according to one of the preceding claims, characterized in that after the start of the extraction, the extraction speed v of the cold strand (6) from the mold (2) is increased. A method according to claim 5, characterized in that the raising of the extraction speed v as a function of the time t or the strand length s occurs. Method according to one of the preceding claims, characterized in that the intensity of the secondary cooling (4) over the time t or the strand length s is set decreasing. Method according to one of the preceding claims, characterized in that a thermal calculation model (7) during the continuous casting in dependence a chemical composition (15) of the molten metal, the primary cooling (2a) in the mold, - the secondary cooling (4) of the strand (1) in the strand guide (3), constantly calculating the actual temperature field of the strand (1) including the actual phase boundaries between the solid, doughy and liquid phases in the strand (1), wherein a thermal insulation (9) of the strand (1) in the tertiary cooling zone (5) as a function of Actual temperature field and / or the actual phase boundaries, in particular the actual position of the sump tip (8) is set. A method according to claim 8, characterized in that the heat insulation (9) is set such that the actual position of a time-dependent desired position of the sump tip (8) corresponds as possible. Method according to one of the preceding claims, characterized in that the intensity of the secondary cooling (4) as a function of the actual temperature field and / or the actual phase boundaries, in particular the actual position of the sump tip (8), is set. Method according to one of the preceding claims, wherein the continuous casting machine comprises a strand agitator (14) which can be moved in the casting direction (G), characterized in that the strand agitator (14) is withdrawn from the mold during removal and after completion of drawing out the cold strand (6). 2) the region of the sump tip (8) of the strand (1) is electromagnetically stirred. Continuous casting machine for carrying out the method according to one of the preceding claims, wherein the continuous casting machine a mold (2) with a primary cooling (2a), - In the casting direction (G) below a strand guide (3) with a plurality of strand guide rollers (3a) for guiding the strand (1) and a secondary cooling (4) and for cooling the strand (1), and - again below a Tertiärkühlzone (5) for controlled or controlled cooling of the strand (1), characterized by 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). Continuous casting machine according to claim 12, characterized in that the control or regulating device (10) realizes a time or strand length-dependent control or regulation of the heat transfer coefficient U. Continuous casting machine according to claim 12 or 13, characterized in that the control or regulating device (10) comprises a thermal calculation model (7) which is suitable during the continuous casting in dependence a chemical composition (15) of the molten metal, the primary cooling (2a) in the mold (2), - the secondary cooling (4) of the strand (1) in the strand guide (3), constantly calculating the actual temperature field of the strand (1) including the actual phase boundaries between the solid, doughy and liquid phases in the strand (1), the thermal insulation (9) depending on the actual temperature field and / or the actual phase boundaries , In particular, the actual position of the sump tip (8) can be adjusted. Continuous casting machine according to claim 14, characterized in that an extraction speed v of the strand (1) from the mold (2) and / or an intensity of the secondary cooling (4) in dependence of the actual temperature field and / or the actual phase boundaries, in particular the actual Position of the sump tip (8), can be adjusted.

Images