EP3122492B1 - Semi-continuous casting of a steel ingot - Google Patents

Description

Field of engineering

The present invention relates to a method for the semi-continuous continuous casting of a strand, preferably a billet, made of steel in a continuous casting machine and a suitable continuous casting machine.

State of the art

The majority of the total steel produced today is cast into strands in continuously operated continuous casting machines with high throughput. Only about 5% of the total amount of steel is cast into billets (Engl. Ingots). The Vorblockgießen is described, for example, in the ASM Handbook, Volume 15: Casting, chapter "Steel Ingot Casting", pp. 911-917, DOI: 10.1361 / asmhba0005295 , Although the proportion of liquid steel poured over the so-called ingot route into blooms is small, the ingot route is very profitable because of its suitability for special steel grades and formats.

• Hohe Flexibilität in den Produktabmessungen, günstig bei kleinen Losgrößen, einzigartig bei großen Formaten;
• Eignung für spezielle Stahlsorten (z.B. für Kaltformstähle CHQ; HSLA Stähle; hochlegierte Stähle mit ca. 5% Legierungsanteilen, wie Cr, Ni, Mo; Kettenstähle; Automatenstähle mit einem hohen Anteil von S, Pb, Bi; Lagerstähle mit ca. 1% C, 1,2% Cr, 0,25% Ni, 0,25% Mo; etc.); und
• höhere Qualität in punkto Vermeidung von Zentrumsseigerung und Porosität, insbesondere von Fadenporosität im Zentrum des Strangs.

Advantages of pre-block casting are:

• High flexibility in product dimensions, favorable for small batch sizes, unique for large formats;
• Suitable for special steel grades (eg for cold forming steels CHQ, HSLA steels, high-alloyed steels with about 5% alloying parts, such as Cr, Ni, Mo, chain steels, free-cutting steels with a high content of S, Pb, Bi, bearing steels with about 1% C) , 1.2% Cr, 0.25% Ni, 0.25% Mo, etc.); and
• Higher quality in terms of avoiding Zentrsesseigerung and porosity, especially of thread porosity in the center of the strand.

• langsame aber nur unzureichend kontrollierbare Abkühlgeschwindigkeiten in der Vorblockkokille;
• höhere Ausbringverluste durch das Abtrennen des Kopf-und Fußteils des Vorblocks;
• höhere Betriebskosten; und
• geringere Gefügesymmetrie und Reinheit.

Disadvantages of the Vorblockgießens are:

• slow but insufficiently controllable cooling rates in the pre-block mold;
• higher application losses due to the separation of the head and foot part of the billet;
• higher operating costs; and
• less structural symmetry and purity.

Summary of the invention

Applicant's investigations have shown that the higher quality of pre-bloom casting in terms of center segregation and porosity is mainly due to the slow solidification rate and the solidification in the center region of the billet from strand start to strand end. The solidification in the center is globular or with an axially oriented solidification front, so that any occurring dendrites are avoided, which form bridges in the center and obstruct the suction of the melt. A yarn porosity in the center is thus largely excluded. In contrast, the properties of continuous casting are exactly the opposite. Extremely low cooling rates, as in the case of pre-block casting, can not be achieved in continuously operated continuous casting machines because the machine length is limited for economic reasons. Due to the higher cooling rate associated with the more radially directed from outside to inside solidification in continuous casting a dendritic solidification and thus Zentrumsseigerung and porosity is caused. Therefore, in the prior art, large formats that are substantially free of center segregations and porosities, particularly of filament porosities, are made via the ingot route. The higher operating costs, lower output and disadvantages in the structural symmetry and purity of the billet are accepted.

• Gießstart der Stranggießmaschine, wobei flüssiges Metall 6 in die Durchlaufkokille gegossen wird und das flüssige Metall einen teilerstarrten Strang ausbildet;
• Ausziehen des teilerstarrten Strangs aus der Durchlaufkokille; und
• Abkühlen des teilerstarrten Strangs in der Sekundärkühlzone.

Die Aufgabe der Erfindung ist es, die Nachteile des Stands der Technik zu überwinden und ein Verfahren zum semi-kontinuierlichen Stranggießen eines Strangs, vorzugsweise eines Vorblocks, aus Stahl darzustellen, bei dem der Strang

• eine geringe Zentrumsseigerung und Porosität aufweist, und
• dennoch rasch, d.h. mit hohem Durchsatz, vergossen werden kann. Dadurch soll der semi-kontinuierlich vergossene Strang einerseits ähnliche bzw. sogar bessere metallurgische Eigenschaften wie ein durch die klassische Ingotroute hergestellter Vorblock haben; andererseits soll der Strang aber mit einem ähnlich hohen Durchsatz produziert werden können wie in einer kontinuierlich betriebenen Stranggießmaschine.

From the DE 2042546 A1 is a method for continuously casting a metallic strand 2 in one Continuous casting machine, wherein the continuous casting machine comprises a cooled continuous casting mold 3 for the primary cooling of the strand, a secondary cooling for cooling the strand and Ausziehwalzen 4, comprising the method steps:

• Casting start of the continuous casting machine, wherein liquid metal 6 is poured into the continuous casting mold and the liquid metal forms a partially solidified strand;
• Extracting the partially solidified strand from the continuous casting mold; and
• Cooling the partially solidified strand in the secondary cooling zone.

The object of the invention is to overcome the disadvantages of the prior art and a method for semi-continuous Continuous casting of a strand, preferably a billet, of steel, in which the strand

• has a low center segregation and porosity, and
• nonetheless can be shed quickly, ie with high throughput. As a result, the semi-continuously cast strand should on the one hand have similar or even better metallurgical properties than a bloom produced by the classical ingot route; On the other hand, however, the strand should be able to be produced with a similarly high throughput as in a continuously operated continuous casting machine.

Finally, a suitable continuous casting machine should be specified.

This object is achieved by a method according to claim 1, advantageous embodiments are the subject of the dependent claims.

• Gießstart der Stranggießmaschine, wobei flüssiger Stahl in die durch einen Kaltstrang verschlossene Durchlaufkokille gegossen wird und der flüssige Stahl mit dem Kaltstrang einen durcherstarrten Stranganfang und nachfolgend einen teilerstarrten Strang ausbildet;
• Ausziehen des teilerstarrten Strangs aus der Durchlaufkokille;
• Stützen und Führen des teilerstarrten Strangs in der Strangführung, wobei der teilerstarrte Strang durch die Sekundärkühlung abgekühlt wird;
• Gießende der Stranggießmaschine, wobei das Vergießen von flüssigem Stahl in die Durchlaufkokille beendet wird und sich ein Strangende ausbildet;
• Ausziehen des Strangendes aus der Durchlaufkokille;
• Beenden des Ausziehens, sodass das Strangende außerhalb der Durchlaufkokille (d.h. im Bereich der Sekundärkühlzone oder der Tertiärkühlzone der Stranggießmaschine) liegt;
• Beenden der Sekundärkühlung;
• gesteuertes oder geregeltes Abkühlen des teilerstarrten Strangs bis zur Durcherstarrung des Strangs in der Tertiärkühlzone der Stranggießmaschine, wobei das Abkühlen am Stranganfang stärker und zum Strangende hin abnehmend eingestellt wird;
• Ausfördern des Strangs aus der Stranggießmaschine.

According to the invention, in the method for semi-continuous casting of a strand, preferably a billet, made of steel in a continuous casting machine, wherein the continuous casting a chilled continuous mold for primary cooling of the strand, followed by a strand guide for supporting and guiding the strand with a - typically comprising a plurality of cooling nozzles - Secondary cooling to cool the strand, and in turn below a tertiary cooling for further cooling of the strand, the following process steps carried out:

• Casting start of the continuous casting machine, wherein liquid steel is poured into the sealed by a cold strand continuous casting mold and the liquid steel with the dummy strand forms a solidified Stranganfang and then a partially solidified strand;
• Extracting the partially solidified strand from the continuous casting mold;
• Supporting and guiding the partially solidified strand in the strand guide, wherein the partially solidified strand is cooled by the secondary cooling;
• Casting end of the continuous casting machine, wherein the casting of liquid steel is completed in the continuous mold and forms a strand end;
• Extracting the strand end from the continuous casting mold;
• Terminating the extraction so that the strand end is outside the continuous casting mold (ie in the area of the secondary cooling zone or the tertiary cooling zone of the continuous casting machine);
• Terminating the secondary cooling;
• Controlled or controlled cooling of the partially solidified strand until the solidification of the strand in the tertiary cooling zone of the continuous casting machine, wherein the cooling is set at the strand beginning stronger and decreasing towards the strand end;
• Extracting the strand from the continuous casting machine.

The continuous casting machine used is divided into three parts. The chilled continuous casting mold for primary cooling of the strand, which is typically made of copper or a copper alloy, is followed by a strand guide for supporting and guiding the strand with a secondary cooling, typically comprising a plurality of single-material (mostly so-called water-only nozzles) and / or multi-substance nozzles (mostly so-called. airmist nozzles) to cool the partially solidified strand shell and a tertiary cooling zone to further cool the strand.

In order to avoid the bending or the bending back of the strand, it is advantageous if the continuous casting machine is designed as a vertical continuous casting machine with a vertical mold, a vertical strand guide and a vertical Tertiärkühlzone.

The process according to the invention proceeds as follows: During the casting start of the continuous casting machine, liquid steel is produced (typically from a metallurgical vessel, such as a ladle or pouring spreader) into the cold-run through mold, the liquid steel having the cold strand forming a solidified strand and a semi-solid strand following it (ie, a solidified strand shell and a liquid core) formed. The flow from the metallurgical vessel into the continuous casting mold can be adjusted, for example, via a slide closure or a plug drive. Subsequently, the partially solidified strand is drawn out of the continuous casting mold, wherein the casting level in the mold, which is adjusted by the inflow of liquid steel into the mold and the extraction of the partially solidified strand by driven strand guide rollers, is kept approximately constant. The partially solidified strand is supported by the continuous casting mold in the strand guide, guided and further cooled by the secondary cooling. Especially at higher casting speeds, it is advantageous if the secondary cooling has a plurality of cooling nozzles; at slow casting speeds, however, cooling by radiation may already be sufficient to form a viable strand shell. The cooling intensities in the primary and secondary cooling are adjusted depending on the pull-out speed so that the shell of the partially solidified strand can withstand the maximum occurring ferrostatic pressure in the continuous casting machine. When the strand has reached the desired length or weight, the casting process is terminated, for example by closing the metallurgical vessel. As a result, a strand end of the strand, which is typically not completely solidified, forms. The strand end is now at least as far removed from the continuous casting mold, that it comes to rest in the area of secondary cooling or tertiary cooling of the continuous casting machine. At the latest when the strand end has passed the secondary cooling zone, the secondary cooling is terminated. The partially solidified strand is now - compared to continuous casting - slow, controlled or regulated in the Tertiary cooling zone of the continuous casting machine cooled to complete solidification. The cooling takes place in a controlled manner - decreasing more in the foot area (ie in the area of the strand start) of the strand and towards the strand head, ie in the region of the strand end). This causes a bottom-up solidification front in the center area. In the center of the partially solidified strand, either a globular or dendritic microstructure appears with only extremely small segregations and porosities. In dendritic solidification, the dendrites in the strand center can not grow together, thus avoiding the thread porosity in the strand center. Finally, the solidified strand is discharged from the continuous casting machine.

The cooling of the partially solidified strand in the tertiary cooling zone is either controlled or regulated. The setpoint value for the cooling may be the surface temperature of the strand, or preferably a microstructure composition in the center of the strand calculated in real time in a 2- or 3-dimensional model including the heat equation for the strand and optionally taking into account the processes during structural transformation be used. As a result, the cooling and the structure formation in the strand can be set very accurately. In tertiary cooling, the strand is cooled primarily by thermal radiation and possibly by convection; spray cooling is typically not required.

Due to the slow cooling of the strand, any necessary annealing treatments of the strand for the purpose of stress relief and further structural improvement can already be carried out in the tertiary cooling zone of the continuous casting machine.

1. a) Beeinflussung der Wärmeisolation des Strangs,
2. b) Heizung des Strangs,
3. c) Oberflächenkühlung des Strangs.

Advantageously, the slow, controlled or controlled cooling of the strand is influenced by at least one of the following measures:

1. a) influencing the heat insulation of the strand,
2. b) heating the strand,
3. c) surface cooling of the strand.

By deliberately influencing the heat insulation, the cooling at the start of the strand can be set more strongly than at the end of the strand without additional energy. By targeted heating of the strand, this can be ensured with additional energy. Finally, a - possibly only locally - present - too slow cooling of the strand can be remedied by a surface cooling of the strand.

In order to prevent too rapid cooling of the partially solidified strand in the tertiary cooling zone, it is advantageous if the partially solidified strand, preferably its lateral surface, in the tertiary cooling zone is heated by a, preferably inductive, heating device. Alternatively, the strand can also be heated by burners.

Although too slow a cooling of the partially solidified strand according to the invention should not occur, a locally too slow cooling can be prevented when the partially solidified strand is cooled in the tertiary cooling zone by a, preferably movable, cooling device.

It is particularly advantageous if the heating device can be moved in the extension direction of the continuous casting machine. As a result, the temperature of the strand can only be influenced by a single heating device without the need for distributed devices.

For setting the solidification, it is particularly advantageous if the partially solidified strand is protected in the tertiary cooling zone by a thermal insulation against rapid cooling. It is advantageous if the heat insulation is preheated before the casting start. A particularly effective heat insulation which also promotes the degassing of the not yet solidified melt and also before Scaling protects, is to keep the strand in a vacuum or in an atmosphere of inert gas.

In the case of thermal insulation, it is advantageous if the insulation effect is preset either statically or controlled or regulated during operation. The setting may e.g. done by swiveling insulation lamellae. During the tertiary cooling phase, the insulation lamellae can be adjusted over the length of the strand to different, but static, swivel angles. The swivel angle can also be adjusted dynamically depending on the production program during the cooling phase. For example. For example, the swivel angles at the bottom - i. in the area of the strand beginning - are set larger than above, whereby the strand area is cooled more slowly than the strand start area.

In order to increase the throughput in the semi-continuous casting operation, it is extremely advantageous if, after the strand end has passed the secondary cooling, the cooled continuous casting mold, preferably the continuous casting mold and the secondary cooling zone, are separated from the tertiary cooling zone (for example lifted off) and the separated components transverse to the extension direction of the continuous casting machine to another casting station, ie to a further Tertiärkühlzone be moved. At the further tertiary cooling zone, another strand may be poured, during which time the previously produced strand in the tertiary cooling zone is slowly cooled. These measures combine the high quality of pre-block casting with the high productivity of continuous casting.

After separating the cooled Durchlaufkokille, or the continuous mold with the secondary cooling zone, from the tertiary cooling zone, it is advantageous if the strand end is protected by a thermal insulation against rapid cooling.

Furthermore, it is advantageous if the strand end is heated by a heating device, in particular an inductive heating device, an electric arc furnace, a plasma heater or by the burning of exothermic covering powder.

By isolating and heating the strand end of the upper portion of the strand is held until the solidification end with liquid sump and the suction of the melt ensured in the strand center. By these measures, a high quality is achieved and a too large funnel formation avoided in the strand end. Similar measures are also possible in the lower part of the strand. Through these measures, the Ausbringverluste be reduced, since only a shorter section from Stranganfang and end must be separated.

To achieve a uniform internal structure, a stirring device such as a stirring coil is advantageous. This is conveniently movable along the string axis. Alternatively, the semi-solidified strand in the tertiary cooling zone may be alternately rotated clockwise and counterclockwise about its own axis. By reversing the direction of a particularly intimate mixing is ensured inside the strand.

So that the cast strand obtains a stable shell as quickly as possible and thereby the length of the secondary cooling can be kept as short as possible, it is advantageous if the strand has a round cross-section. A similar effect can also be achieved with a strand having a three-round, four-round, etc. cross section.

The object of the invention is also achieved by a device according to claim 10. Advantageous embodiments are the subject of the dependent claims.

• eine Einrichtung zum Ausziehen eines Strangs aus einer Durchlaufkokille und eine Einrichtung zum Ausfördern des Strangs aus der Stranggießmaschine,
• die gekühlte Durchlaufkokille zur Primärkühlung des Strangs, nachfolgend
• eine Strangführung zum Stützen und Führen des Strangs mit einer Sekundärkühlzone, typischerweise umfassend mehrere Kühldüsen, zum Abkühlen des Strangs, und wiederum nachfolgend
• eine Tertiärkühlzone zum weiteren Abkühlen des Strangs, dadurch gekennzeichnet,

dass die Tertiärkühlzone eine, vorzugsweise induktive, insbesondere in die Auszugsrichtung der Stranggießmaschine verfahrbare, Heizvorrichtung zum gesteuerten oder geregelten Abkühlen des teilerstarrten Strangs aufweist.The continuous casting machine according to the invention comprises

• a device for extracting a strand from a continuous casting mold and a device for conveying the strand from the continuous casting machine,
• the cooled through mold for the primary cooling of the strand, below
• a strand guide for supporting and guiding the strand with a secondary cooling zone, typically comprising a plurality of cooling nozzles, for cooling the strand, and again subsequently
• a tertiary cooling zone for further cooling of the strand, characterized

the tertiary cooling zone has a, preferably inductive, heating device, which can be moved, in particular in the drawing-out direction of the continuous casting machine, for the controlled or controlled cooling of the partially solidified strand.

Instead of the heating device movable in the tertiary cooling zone, the continuous casting machine according to the invention may also have a statically presettable or dynamically (i.e., during operation) controlled or adjustable heat insulation.

By the heater, the lateral surface of the strand can be heated, whereby the cooling (and thus the microstructure formation) in the center region of the partially solidified strand in the tertiary cooling zone of the continuous casting machine can be adjusted very accurately.

In order to enable the slow cooling of the partially solidified strand with a low energy consumption for the heating device, it is advantageous if the tertiary cooling zone has a, in particular statically adjustable or dynamically controlled or regulated adjustable, heat insulation.

It is expedient if the continuous casting mold, the secondary and the tertiary cooling zone are arranged in one row (so-called in-line).

The productivity of the semi-continuous continuous casting machine is substantially increased if the continuous casting machine has a plurality of transverse cooling zones offset transversely to the drawing machine direction, wherein the machine head of the continuous casting machine, comprising the continuous casting mold and preferably the secondary cooling zone, is connectable and separable with a tertiary cooling zone and at least the Machine head is movable transversely to the extension direction. As described above, a single machine head can serve multiple tertiary cooling zones so that high throughput is achieved despite the slow cooling of the partially solidified strands.

Preferably, the machine head is moved to another tertiary cooling zone during which the strand is stationary. As a result, the controlled or controlled, slow cooling in the center region of the strand is not disturbed. Alternatively, but also the strand, possibly with the Tertiärkühlung be moved away from the machine head.

When adjusting the heat insulation, it is advantageous if the adjustable heat insulation at least one - advantageously several - insulation panel (also called lamella), that in the extension direction of the continuous casting machine is displaced or pivotable to the extension direction. As a result, the cooling rate of the partially solidified strand can be passive, i. without additional input of energy.

Multiple strands of small size can be created simultaneously if the machine head of the continuous casting machine has a plurality of cooled continuous molds and a plurality of strand guides with secondary cooling zones arranged behind them.

A simple and robust continuous casting machine has a strand withdrawal carriage for pulling out the strand, wherein the strand withdrawal carriage in the extension direction, for example by spindle, rack or cylinder drives, is movable.

The strand beginning is supported by the cold strand on the strand withdrawal trolley.

In one embodiment of the continuous casting machine according to the invention the strand withdrawal carriage is connected to the machine head, wherein the strand withdrawal carriage with the machine head is movable transversely to the extension direction. In this case, the cast strand after the pouring end, e.g. parked on a pedestal on the hall floor and moved the machine head with the pullout trolley to another Tertiärkühlung. The slow cooling of the parked strand may e.g. be ensured by a pulled over the strand thermal hood.

Alternatively, it would also be possible that the machine head is stationary and the cast strand is movable transversely to the extension direction. Here the cast strand is e.g. parked on a pedestal, wherein the pedestal can be moved together with the strand to another tertiary cooling zone.

Brief description of the drawings

• Fig 1 mit den Teilfiguren 1a...1f zeigen schematisch die Verfahrensschritte beim semi-kontinuierlichen Stranggießen eines Vorblocks aus Stahl.
• Fig 2a und 2b zeigen zwei alternative Ausführungsformen einer Tertiärkühlung für das semi-kontinuierlichen Stranggießen eines Vorblocks aus Stahl.
• Fig 3 zeigt den zeitlichen Verlauf eines Heizaggregats zum Erwärmen eines Vorblocks in einer Tertiärkühlung.
• Fig 4 zeigt die Temperaturen bei der Abkühlung des Strangs 1 in der Tertiärkühlzone 5.
• Fig 5 zeigt die Temperaturverläufe über der Zeit zu Fig 4.
• Fig 6a und 6b zeigen eine erfindungsgemäße Stranggießmaschine in einem Auf- und einem Kreuzriss.
• Fig 7 zeigt einen Maschinenkopf einer erfindungsgemäßen Stranggießmaschine in zwei Rissen.
• Fig 8a, 8b zeigen schematisch das Ausfördern eines durcherstarrten Strangs aus einer Tertiärkühlzone.

Further advantages and features of the present invention will become apparent from the following description of non-limiting embodiments, wherein the figures show:

• Fig. 1 with the subfigures 1a ... 1f show schematically the process steps in semi-continuous continuous casting of a billet made of steel.
• FIGS. 2a and 2b show two alternative embodiments of tertiary cooling for the semi-continuous casting of a billet of steel.
• Fig. 3 shows the time course of a heating unit for heating a billet in a tertiary cooling.
• Fig. 4 shows the temperatures during the cooling of the strand 1 in the tertiary cooling zone. 5
• Fig. 5 shows the temperature curves over time Fig. 4 ,
• Fig. 6a and 6b show a continuous casting machine according to the invention in an up and a cross crack.
• Fig. 7 shows a machine head of a continuous casting machine according to the invention in two cracks.
• 8a, 8b schematically show the discharge of a solidified strand from a Tertiärkühlzone.

Description of the embodiments

In the Fig. 1a ... 1f the process steps in the semi-continuous casting of a strand 1 in a continuous casting machine are shown.

In Fig. 1a is poured from a pan distributor not shown separately liquid steel via a dip tube in a cooled continuous casting mold 2, wherein the casting mold 2, the continuous casting mold 2 is closed fluid-tight by the cold strand 6 during casting start of the continuous casting machine, so that in the mold a casting M (also called meniscus) adjusts. By connecting the liquid steel to the head of the dummy bar 6, a solidified strand beginning 1a is formed (see Fig. 1c ) out. As a result of the primary cooling of the cooled continuous casting mold 2, the partially solidified strand 1b following the solidified strand beginning 1a is not solidified in the opposite direction to the drawing direction A, but has only a thin strand shell and a liquid core. In order to keep the pouring M in the mold 2 in spite of the flowing over the dip tube liquid steel in about constant, the strand 1 is pulled out of the mold 2. For this purpose, the continuous casting machine on a Strangabzugswagen 11, the cold strand 6 itself, a threaded spindle 12, a Threaded nut 13 and a motor 14 for moving the strand extractor carriage 11 in the extension direction A includes. The motor 14 is connected via a gear and the threaded spindle 12 with the threaded nut 13 and has a drive-through for the threaded spindle 12.

In 1b was the strand 1 already pulled out of the continuous mold 2, wherein the strand 1 in the mold 2 subsequent strand guide 3 is supported by a plurality of strand guide rollers 3a, guided and cooled by a plurality of cooling nozzles 4a in the secondary cooling 4. The strand 1 forms a stable strand shell, which can withstand the ferrostatic pressure. Thus, a breakthrough of the strand 1 is prevented.

In Fig. 1c the strand beginning 1a has already passed the secondary cooling 3 of the continuous casting machine and has entered the tertiary cooling zone 5. In the tertiary cooling zone 5, the strand 1 is further controlled slowly or cooled controlled so that in the center of the partially solidified strand 1b, the solidification takes place with an upward direction. As a result, either a globular or at least one dendritic structure avoiding the yarn porosity is formed. In order to prevent too rapid cooling of the partially solidified strand 1b, the tertiary cooling zone 5 has a thermal insulation 9 and an in Fig. 1f shown heater 7. In the Fig. 2a an example of a thermal insulation 9 is shown for a Tertiärkühlung, wherein the atmosphere between the strand 1 and the heat hood 9 by a vacuum pump (here a jet pump 15) is evacuated. For this purpose, a pressure connection of the jet pump 15 is connected to a compressed air network and the suction connection of the jet pump 15 to the space inside the thermal insulation 9. This measure also prevents oxidation, ie scaling, of the strand 1; In addition, the not yet solidified melt in the train is degassed by the vacuum treatment. The heat insulation 9 has a plurality of insulation panels 9a, which are independent of each other closed (opening angle 0 °), opened (opening angle 90 °) or partially opened (90 °> opening angle> 0 °).

In Fig. 1d the casting in the continuous casting machine was finished so that a strand end 1c is formed. By pulling the strand end 1c out of the mold 2, the casting mirror M is located below the pouring mirror shown in dashed lines according to the process steps 1a-1c.

The Fig. 1e shows the situation after the strand end 1c of the strand 1 has passed the secondary cooling zone 3, the secondary cooling has ended and the strand end 1c is flush with the upper end of the tertiary cooling zone 5. In the tertiary cooling zone 5, the slow, controlled or controlled cooling of the partially solidified strand 1b is ensured by the heat insulation 9 and the heating of the strand by the movable in the extension direction A heater 7 (see Fig. 1f ). After separating and lifting the machine head, comprising the continuous casting mold 2, the strand guide 3 and the secondary cooling 4, from the tertiary cooling 5, the strand end 1c is heated by an inductive head heater 10, so that too rapid cooling of the strand end 1c is prevented.

According to the FIGS. 1a ... 1f a round steel strand 1 with a diameter of 1200 mm and a length of 10 m was produced. The pull-out speed of the strand 1 from the continuous casting mold 2 is 0.25 m / min. Due to the thermal insulation 9 and the reheating of the strand 1 by the movable heater 7, the complete solidification of the strand 1 is reached only after 13 h. The casting of the strand - without the slow cooling of the strand in the Tertiärkühlzone 5 - but was already completed after 46 min. Since potting, unlike slow solidification, is rapidly completed, it is advantageous to increase the throughput of the semi-continuous continuous casting process when the in-mold Fig. 1f not shown anymore Separate machine head of the Tertiärkühlzone 5 and is moved transversely to the extension direction A to another Tertiärkühlzone 5. There, a new strand can be shed, while the in Fig. 1f shown strand 1 is cooled further slowly. After slow cooling of the strand 1 until its complete solidification of the strand is discharged from the continuous casting machine, for example. By a device acc. the FIGS. 8a and 8b ,

In the Fig. 2a is a first alternative embodiment of the tertiary cooling zone 5 of Fig. 1 shown. The space between the strand 1 and the thermal insulation 9 is evacuated by a jet pump 15, whereby a good thermal insulation and a slow cooling is achieved. In addition, the surface of the strand 1 is protected from scaling and degassed the residual melt. The jet pump is simple and wear-free; its pressure connection is connected to a compressed air connection P and its suction connection to the space to be evacuated within the tertiary cooling zone. The blowing off can take place against ambient pressure U. The inductive head heater 10 is advantageous over plasma heating, since the magnetic field also acts through the thermal insulation of the strand end 1c.

The Fig. 2b shows a second alternative of the tertiary cooling zone 5 of Fig. 1 , The insulation lamellae 9a of the thermal insulation 9 are pivotable relative to the extension direction, so that the air exchange between the ambient air and the strand 1 in the interior of the tertiary cooling zone 9 is adjustable. Merely to illustrate the function of the insulation lamellae 9a, the insulation lamellae 9a on the right side of the strand 1 were closed and shown open on the left side by 10 ° to the extension direction A. The adjustment of the slats 9a can be done either manually or by actuators.

The Fig. 3 schematically shows the time course of the travel s of the inductive heating device 7 for Reheating the lateral surface of the strand 1. Here, the heater 7 is pulled through in the upper part of the strand 1 and shown in dashed lines in the lower area. Since the solidification front shifts during the cooling from bottom to top (ie, from strand start 1a to strand end 1c), also the travel s of the heating device 7 decreases over time. As an alternative to a movable heating device 7, a plurality of heating devices (eg burners) arranged distributed in the extension direction A over the length of the tertiary cooling zone 5 could also be used.

The Fig. 4 shows the temperatures in ° C of the according to Fig. 1 produced strand 1 in a sectional view 3h after casting start (part 1), 8.3h after casting start (part 2) and solidification of the strand 1, about 13h after casting start (part 3). The time course of the temperatures of the strand 1 at different positions on the surface and in the center of the strand are in Fig. 5 shown. It follows that the casting of the strand and thus also the primary and the secondary cooling is terminated 46 minutes after the casting start and then the strand 1 is cooled controlled only by the Tertiärkühlung 5.

In the FIGS. 6a . 6b a vertical strand casting machine according to the invention is shown in two views. The liquid steel is poured from a pan 30 via a shadow tube in the casting manifold 31, then the melt flows through a not shown immersion tube ( SEN ) in the continuous casting mold 2 a. Due to the primary cooling in the mold 2, a partially solid strand 1 forms with a stable strand shell. In the mold 2, the melt is further influenced by an optional stirring device 32. The strand 1 is supported in the strand guide 3, guided and further cooled in the secondary cooling zone 4. At least the continuous casting mold 2, the stirring coil 32, the strand guide 3 with the secondary cooling zone 4, and optionally also the tertiary cooling zone 5, are on a casting trolley 33 on the casting platform G movable. The strand 1 with the cold strand 6 is pulled out of the continuous casting mold 2 via the strand withdrawal carriage 11. For this purpose, the Strangabzugswagen 11 is driven by four threaded spindles 12 and guided by additional guide rails 34, wherein a motor via a gear and the threaded spindle 12 is connected to the threaded nut 13. After the casting process has ended and the strand 1 has been placed on the anvil 40, the casting trolley 33 can be moved transversely to the extension direction A to a further casting station, since the casting of the partially solidified strand, ie without the Tertiärkühlung the strand 1, much less time needed as the tertiary cooling of strand 1 until its solidification. In the tertiary cooling zone 5, the strand 1 is slowly cooled by the thermal insulation 9 and possibly by a heater, not shown here, so that the solidification takes place in the center of the strand with an upwardly oriented solidification front.

A more detailed representation of the machine head of the continuous casting machine from the Fig. 6a . 6b is in Fig. 7 shown.

The 8a, 8b schematically show an embodiment for discharging the solidified strand 1 from the Tertiärkühlzone. The strand 1 is laterally supported by two brackets 38, so that on the continuous casting machine also very different diameters (see plan of Fig. 8a ) can be shed. In Fig. 8a the strand 1 has already been swung out with respect to the vertical and rests against the brackets 38. In Fig. 8b the strand 1 is placed over the pivot drive 39 on a roller table 37, where it can be removed in the direction of the arrow.

Although 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 may occur to those skilled in the art be derived therefrom 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

Continuous casting mold, 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

heater

9

thermal insulation

9a

insulation panel

10

Heating head

11

Strand pulling carriage

12

screw

13

threaded nut

14

engine

15

jet pump

30, 30 '

pan

31

distribution trough

32

stirring coil

33

ladle

34

guide rail

35

oscillating

36

water wiper

37

roller table

38

hanger

39

Rotary actuator

40

anvil

A

extraction direction

G

casting platform

M

meniscus

P

Pressure in a compressed air network

s

traverse

U

ambient pressure

Claims (17)

1. Method for the semi-continuous casting of a strand (1) made of steel in a continuous casting machine, wherein the continuous casting machine has

   - a cooled open-ended mold (2) for the primary cooling of the strand (1), followed by

   - a strand guide (3) for supporting and guiding the strand (1), having secondary cooling (4) for cooling the strand (1), followed in turn by

   - tertiary cooling (5) for cooling the strand (1) further,

   comprising the method steps:

   - start of casting in the continuous casting machine, wherein liquid steel is poured into the open-ended mold (2) closed off by a dummy bar (6) and the liquid steel forms with the dummy bar a fully solidified strand start (1a) and then a partially solidified strand (1b);

   - extracting the partially solidified strand (1b) from the open-ended mold (2);

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

   - end of casting in the continuous casting machine, wherein the pouring of liquid steel into the open-ended mold (2) is ended and a strand end (1c) forms;

   - extracting the strand end (1c) from the open-ended mold (2);

   - ending extraction, such that the strand end (1c) is located outside the open-ended mold (2);

   - ending secondary cooling (4);

   - controlled or regulated cooling of the partially solidified strand (1b) until full solidification of the strand (1) in the tertiary cooling zone (5) of the continuous casting machine, wherein the cooling takes place more strongly at the strand start (1a) and in a decreasing manner toward the strand end (1c);

   - discharging the strand (1) from the continuous casting machine.
2. Method according to Claim 1, characterized in that the cooling of the partially solidified strand (1b) in the tertiary cooling zone (5) is set by influencing at least one from the group of:

   - thermal insulation of the strand (1, 1b),

   - heating of the strand (1, 1b),

   - surface cooling of the strand (1, 1b).
3. Method according to Claim 2, characterized in that the partially solidified strand (1b) is heated in the tertiary cooling zone (5) by a heating device (7).
4. Method according to Claim 3, characterized in that the heating device (7) is displaceable in the extraction direction (A) of the continuous casting machine.
5. Method according to one of Claims 2 to 4, characterized in that the partially solidified strand (1b) is protected from cooling too rapidly in the tertiary cooling zone (5) by thermal insulation (9).
6. Method according to Claim 5, characterized in that the insulating effect of the thermal insulation (9) is set.
7. Method according to one of Claims 2 to 6, characterized in that the strand end (1c) is heated by head heating (10).
8. Method according to one of Claims 2 to 7, characterized in that the surface of the partially solidified strand (1b) is cooled by a cooling device (4a) in the tertiary cooling zone (5).
9. Method according to one of the preceding claims, characterized in that the partially solidified strand (1b) is stirred in the tertiary cooling zone (5) by a stirring coil (32) that is stationary or displaceable in the extraction direction (A), or the partially solidified strand (1b) is rotated about its own axis alternately in the clockwise direction and the counterclockwise direction in the tertiary cooling zone (5).
10. Continuous casting machine for carrying out the method according to one of Claims 1 to 9, having

    - a device for extracting a strand (1) from an open-ended mold (2) and a device (37, 38, 39) for discharging the strand (1) from the continuous casting machine,

    - the cooled open-ended mold (2) for the primary cooling of the strand (1), followed by

    - a strand guide (3) for supporting and guiding the strand (1), having a secondary cooling zone (4) for cooling the strand (1), followed in turn by

    - a tertiary cooling zone (5) for cooling the strand (1) further, characterized

    in that the tertiary cooling zone (5) has a heating device (8) for the controlled or regulated cooling of the partially solidified strand (1b).
11. Continuous casting machine according to Claim 10, characterized in that the tertiary cooling zone (5) has thermal insulation (9) that is statically settable or settable in a controlled or regulated manner.
12. Continuous casting machine according to either of Claims 10 and 11, characterized by a plurality of tertiary cooling zones (5) that are offset transversely to the extraction direction (A) of the continuous casting machine, wherein the machine head of the continuous casting machine, comprising the open-ended mold (2) and the secondary cooling zone (4) is connectable to and separable from a tertiary cooling zone (5).
13. Continuous casting machine according to Claim 12, characterized in that a plurality of tertiary cooling zones (5) are arranged one after another in an arcuate or linear manner.
14. Continuous casting machine according to one of Claims 11 to 13, characterized in that the adjustable thermal insulation (9) has at least one insulation panel (9a) which is displaceable in the extraction direction (A) or pivotable with respect to the extraction direction (A).
15. Continuous casting machine according to one of Claims 11 to 14, characterized in that the continuous casting machine has a strand extraction carriage (11) for extracting the strand (1), wherein the strand extraction carriage (11) is displaceable in the extraction direction (A).
16. Continuous casting machine according to Claims 11 and 15, characterized in that the strand extraction carriage (11) is connected to the machine head and both are displaceable transversely to the extraction direction (A).
17. Continuous casting machine according to one of Claims 11 to 15, characterized in that the machine head is stationary and the strand (1) is displaceable transversely to the extraction direction (A).

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