EP3705202B1 - Conversion of a continuous casting plant for billet or bloom strands - Google Patents

Description

field of technology

The present invention relates to the technical field of continuous casting. Today, the majority of the world's annual steel production is cast into strands with different cross-sections (slabs, billets, blooms, sections, etc.) in continuously operated continuous casting plants.

Continuous casting machines for continuously casting molten steel into a strand with billet (engl. Billet) or Vorblockquerschnitt (engl. Bloom) are known.

On the one hand, the present invention relates to a method for converting a continuous casting installation for the continuous casting of a strand with a billet or bloom cross section.

On the other hand, the invention relates to the continuous casting plant converted by the method for converting a continuous casting plant for continuous casting of a strand with a billet or bloom cross section for continuous casting of a strand with a billet or bloom cross section.

State of the art

The conversion of an existing continuous caster for continuous casting of a strand with a billet or bloom cross-section in order to increase the productivity of the continuous caster and/or the quality of the strands produced is often difficult, time-consuming and expensive due to the prevailing general conditions. On the one hand, the radius of curvature of the strand routing cannot simply be changed due to structural conditions (e.g. the height of the hall or existing foundations) or financial limitations. With existing continuous casting plants the solidification point of the strand is typically in the area of the pull-out units. Increasing the casting speed shifts the solidification point backwards in the casting direction. If the solidification point is not to be shifted significantly, this requires either greater secondary cooling of the strand in the strand guide or a reduction in the casting speed. Stronger or harder cooling has a negative effect on the internal quality of the strand; a reduction in casting speed reduces productivity. On the other hand, there is the possibility of increasing productivity by increasing the strand cross section. However, this measure requires that the strand guide or the segments thereof have to be adapted to the changed strand cross section, which greatly increases the costs. In addition, the operator often does not want a format change because that would change the product mix or other processing units.

From the article

• eine Kokille zum Vergießen von flüssigem Stahl in einen Strang mit Knüppelquerschnitt;
• eine bogenförmige Strangführung zum Stützen, Führen und Abkühlen des Strangs;
• eine Auszugseinheit mit je einer an den Strang anstellbaren angetriebenen Strangführungsrolle zum Ausziehen des Strangs aus der Kokille;

aufweisend den Verfahrensschritt: Einbau zumindest einer Soft-Reduktions-Einheit in einen Freiraum nach der Auszugseinheit, wobei jede Soft-Reduktions-Einheit eine Anstelleinrichtung und eine durch die Anstelleinrichtung anstellbare Strangführungsrolle zur Dickenreduktion des Strangs aufweist. Ralf Thome et al.: "Principles of Billet Soft-reduction and Consequences for Continuous Casting", ISIJ International, Vol. 46, No. 12, 1 January 2006 (2006-01-01), pages 1839-1844, XP055300002 a method for converting a billet caster S4 is known, the billet caster comprising before the conversion:

• a mold for casting liquid steel into a strand of billet cross-section;
• an arcuate strand guide for supporting, guiding and cooling the strand;
• an extraction unit, each with a driven strand guide roller, which can be placed against the strand, for extracting the strand from the mold;

having the method step: installation of at least one soft reduction unit in a free space after the pull-out unit, each soft reduction unit having an adjustment device and a strand guide roller that can be adjusted by the adjustment device for reducing the thickness of the strand.

• eine Kokille zum Vergießen von flüssigem Stahl in den Strang;
• eine bogenförmige Strangführung zum Stützen, Führen und Abkühlen des Strangs;
• eine am hinteren Ende der bogenförmigen Strangführung angeordnete Auszugseinheit; und
• eine nach der Auszugseinheit angeordnete Soft-Reduktions-Einheit, wobei jede Soft-Reduktions-Einheit eine Anstelleinrichtung und eine durch die Anstelleinrichtung anstellbare Strangführungsrolle zur Dickenreduktion des Strangs aufweist.

From the CH712937A2 discloses a soft reduction unit for a continuous casting plant for producing a strand with a billet or bloom cross-section, the continuous casting plant comprising:

• a mold for pouring liquid steel into the strand;
• an arcuate strand guide for supporting, guiding and cooling the strand;
• an extraction unit arranged at the rear end of the arcuate strand guide; and
• a soft-reduction unit arranged after the pull-out unit, each soft-reduction unit having an adjustment device and a strand guide roller, which can be adjusted by the adjustment device, for reducing the thickness of the strand.

the DE 10236368 A1 discloses a continuous casting plant for continuously casting a strand with a billet cross section, comprising a mold for casting liquid steel into the strand, an arcuate strand guide with a plurality of strand guide rollers arranged on both sides of the strand, the strand being cooled by cooling nozzles, and a soft reduction unit, wherein each soft-reduction unit has an adjustment device and a strand guide roller, which can be adjusted by the adjustment device, for reducing the thickness of the strand.

The state of the art does not show how the conversion of an existing continuous casting plant for the continuous casting of a strand with a billet or bloom cross section can be carried out with regard to low conversion costs, short conversion times and a high reusability of existing components and, moreover, the metallurgical quality of the produced strands can be increased out.

Summary of the Invention

The object of the invention is to find a method for converting an existing continuous casting plant for continuously casting a strand with a billet or bloom cross section, so that the conversion can be carried out with low conversion costs, a short conversion time and a high degree of reusability of existing components. In addition, the metallurgical quality of the strands produced is to be increased.

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

• eine Kokille zum Vergießen von flüssigem Stahl in einen Strang mit Knüppel- oder Vorblockquerschnitt und eine Oszilliereinheit zum Oszillieren der Kokille;
• eine bogenförmige Strangführung zum Stützen, Führen und Abkühlen des Strangs mit mehreren beiderseits des Strangs angeordneten Strangführungsrollen, wobei der Strang in der Strangführung durch Kühldüsen abgekühlt wird;
• zumindest eine Auszugseinheit mit je einer an den Strang anstellbaren angetriebenen Strangführungsrolle zum Ausziehen des Strangs aus der Kokille;
• eine Brennschneidemaschine zum Abschneiden des Strangs in Strangabschnitte; und
• einen Auslaufbereich zum Ablegen der Strangabschnitte auf einem Rollgang;
  aufweisend die Verfahrensschritte:
  1. i) Versetzten der Brennschneidemaschine in Gießrichtung, sodass zwischen der letzten Auszugseinheit und der versetzten Brennschneidemaschine ein Freiraum entsteht;
  2. ii) Einbau zumindest einer Soft-Reduktions-Einheit in den Freiraum, wobei jede Soft-Reduktions-Einheit eine Anstelleinrichtung und eine durch die Anstelleinrichtung anstellbare Strangführungsrolle zur Dickenreduktion des Strangs aufweist.

In concrete terms, the technical problem is solved by a method for converting a continuous caster for the continuous casting of a strand with a billet or bloom cross section, the continuous caster comprising before the conversion:

• a mold for casting liquid steel into a billet or bloom cross-section strand and an oscillating unit for oscillating the mold;
• an arcuate strand guide for supporting, guiding and cooling the strand, having a plurality of strand guide rollers arranged on both sides of the strand, the strand being cooled in the strand guide by cooling nozzles;
• at least one pull-out unit, each with a driven strand guide roller that can be placed against the strand, for pulling the strand out of the mold;
• a flame cutting machine for cutting the strand into strand sections; and
• an outlet area for depositing the strand sections on a roller table;
  having the process steps:
  1. i) shifting the cutting machine in the direction of casting so that there is a free space between the last extraction unit and the shifted cutting machine;
  2. ii) installation of at least one soft reduction unit in the free space, each soft reduction unit having a throw-on device and a throw-on device that can be thrown on Has strand guide roller for thickness reduction of the strand.

The conversion method according to the invention can increase the productivity of the continuous casting installation by increasing the casting speed, while the mold, at least parts of the strand guide, the pull-out unit and the outlet area can remain completely unchanged. Only the flame cutting machine is shifted horizontally in the casting direction, so that at least one soft-reduction unit can be used in the resulting free space between the last extraction unit in the casting direction and the offset flame-cutting machine. The soft reduction unit presses the two shells of the partially solidified strand together, which improves the internal quality of the strand. In this case, at least one strand guide roller of the soft reduction unit is placed against the strand by an adjusting device (typically a hydraulic cylinder), as a result of which the thickness of the strand is reduced. If, in addition to increasing the casting speed, the cross-section of the billet or bloom strand is also increased, the mold and the strand guide must be adapted to the changed cross-section.

In an advantageous embodiment, a first insulation tunnel for thermal insulation of the strand is used between the rear end of the strand guide or the last segment of the strand guide in the casting direction and the pull-out unit.

In addition, it is advantageous if a second insulation tunnel for thermal insulation of the strand is used between the extraction unit and the first soft reduction unit in the casting direction.

In both cases, the solidification point of the strand is shifted in the direction of casting, so that the strand enters the exit zone at a higher temperature.

It is advantageous if the casting speed and/or the cooling intensity of the converted continuous casting plant is adjusted by a plant control system so that the solidification point of the strand is between the axis of rotation of the roller of the first soft reduction unit and the axis of rotation of the roller of the last soft reduction unit located. As a result, the change in cross section of the strand in the soft reduction units can take place using moderate forces. Ideally, the solidification point of the strand is in the middle of the last soft reduction unit.

In general, it is possible for a dummy bar extraction unit arranged after the last extraction unit to continue to be used without being offset after the conversion to the continuous casting plant.

It has turned out to be advantageous that the strand leaves _{the mold already bent with a radius of curvature R 1 .} Such molds are referred to as arc molds.

The following applies to the radius of curvature R ₁ of the strand in the mold 0,9.R ₁ ≤ R ≤ 1,1.R _1, preferably R = R _1, where R is the radius of curvature of the strand guide and R ₁ is the radius of curvature of the strand in the mold is.

The object of the invention is also achieved by a continuous casting plant according to claim 9. Preferred embodiments are subject of the dependent claims.

• eine Kokille, vorzugsweise eine Bogenkokille, zum Vergießen von flüssigem Stahl in einen Strang mit Knüppel- oder Vorblockquerschnitt und eine Oszilliereinheit zum Oszillieren der Kokille;
• eine bogenförmige Strangführung zum Stützen, Führen und Abkühlen des Strangs mit mehreren beiderseits des Strangs angeordneten Strangführungsrollen, wobei der Strang in der Strangführung durch Kühldüsen abgekühlt wird;
• zumindest eine Auszugseinheit mit je einer an den Strang anstellbaren angetriebenen Strangführungsrolle zum Ausziehen des Strangs aus der Kokille, wobei die Auszugseinheit nach dem hinteren Ende der bogenförmige Strangführung angeordnet ist;
• eine Kaltstrangauszugseinheit zum Ausziehen eines Kaltstrangs aus der Kokille;
• zumindest eine Soft-Reduktions-Einheit mit einer Anstelleinrichtung und ein durch die Anstelleinrichtung anstellbare Strangführungsrolle zur Dickenreduktion des Strangs, wobei die zumindest eine Soft-Reduktions-Einheit in einen Freiraum zwischen der an ihrer ursprünglichen Position verbleibenden letzten Auszugseinheit und der, in Auslaufrichtung des Stranges versetzten, neuen Position der Brennschneidmaschine angeordnet ist;
• eine Brennschneidemaschine zum Abschneiden des Strangs in Strangabschnitte; und
• einen Auslaufbereich zum Ablegen der Strangabschnitte auf einem Rollgang, wobei zwischen dem hinteren Ende der Strangführung und einer ersten Auszugseinheit ein erster Isolationstunnel zur thermischen Isolation des Strangs angeordnet ist, und zwischen der letzten Auszugseinheit und der ersten Soft-Reduktions-Einheit ein zweiter Isolationstunnel zur thermischen Isolation des Strangs angeordnet ist.

Specifically, the solution is made by a continuous casting plant for the continuous casting of a strand with a billet or bloom cross-section produced by a method according to the invention Conversion of a continuous caster for the continuous casting of a strand with a billet or bloom cross section, comprising:

• a mould, preferably an arc mould, for casting liquid steel into a strand with a billet or bloom cross-section and an oscillating unit for oscillating the mould;
• an arcuate strand guide for supporting, guiding and cooling the strand, having a plurality of strand guide rollers arranged on both sides of the strand, the strand being cooled in the strand guide by cooling nozzles;
• at least one pull-out unit, each with a driven strand guide roller that can be placed against the strand, for pulling the strand out of the mold, the pull-out unit being arranged after the rear end of the curved strand guide;
• a dummy bar extraction unit for extracting a dummy bar from the mold;
• at least one soft reduction unit with an adjustment device and a strand guide roller, which can be adjusted by the adjustment device, for reducing the thickness of the strand, the at least one soft reduction unit extending into a free space between the last extraction unit remaining in its original position and the one in the discharge direction of the strand offset, new position of the cutting machine is arranged;
• a flame cutting machine for cutting the strand into strand sections; and
• an outlet area for depositing the strand sections on a roller table, with a first insulation tunnel for thermal insulation of the strand being arranged between the rear end of the strand guide and a first extraction unit, and a second insulation tunnel for thermal insulation between the last extraction unit and the first soft reduction unit Isolation of the strand is arranged.

According to the invention, both the rear end of the strand guide or the last segment in the casting direction and a first extraction unit is a first isolation tunnel and A second insulation tunnel for thermal insulation of the strand is arranged between the last extension unit and the first soft reduction unit.

In addition, it is advantageous if a radius of curvature R of the curved strand guide is between 8 m and 12 m, preferably between 9 m and 11 m.

In order to reliably enable the thickness reduction even at different casting speeds, it is advantageous if the converted continuous casting plant has between 4 and 6 soft reduction units.

Brief description of the drawings

• Fig 1 eine Darstellung einer Stranggießanlage zum Stranggießen eines Strangs mit Knüppel- oder Vorblockquerschnitt vor dem Umbau
• Fig 2 eine Darstellung der Stranggießanlage nach Fig 1 nach dem Umbau
• Fig 3 ein Detail zu Fig 2 mit der Darstellung der Strangführung
• Fig 4 ein weiteres Detail zu Fig 2 mit der Darstellung des Bereichs zwischen der Auszugseinheit und der Brennschneidemaschine
• Fig 5 eine Aufrissdarstellung der Soft-Reduktions-Einheit 8 aus den Figuren 2 und 4

Further advantages and features of the present invention result from the following description of non-limiting exemplary embodiments, with the following figures showing:

• figure 1 a representation of a continuous casting plant for the continuous casting of a strand with a billet or bloom cross section before the conversion
• figure 2 a representation of the continuous caster figure 1 after the remodel
• figure 3 a detail to figure 2 with the representation of the strand guidance
• figure 4 one more detail too figure 2 with the representation of the area between the extension unit and the flame cutting machine
• figure 5 an elevation view of the soft reduction unit 8 of FIGS figures 2 and 4

Description of the embodiments

In figure 1 a continuous casting plant 1 for the continuous casting of strands with billet or bloom cross sections is shown schematically. A ladle turret with one ladle is shown in the upper left area of the figure. The continuous casting plant 1 is supplied with molten steel by means of the ladle via a crane shown at the top. From the ladle, the molten steel is conducted in and of itself in a known manner via a shroud tube into the distributor and from there typically via a dip tube (engl. SEN) filled in the mold 2. A constant meniscus and a partially solidified strand with a liquid core and two solidified strand shells form in the cooled mold 2 . In order to prevent the strand shells from sticking to the mold 2, casting powder is applied to the meniscus and the mold 2 is oscillated essentially in the vertical direction by means of an oscillating unit 2a. The partially solidified strand is supported and guided in the curved strand guide 3 following the mold 2 and further cooled by cooling nozzles. In the figure 1 is a segment for supporting and guiding the strand 4 with several strand guide rollers arranged on both sides of the strand. The curved strand is pulled out of the mold 2 by the pull-out unit 5 with at least one driven strand guide roller, here two or three pairs of driven pull-out rollers, and straightened in the horizontal direction. In order to enable the so-called "bottom feeding" of the dummy bar, a dummy bar pull-out unit 13 is present, which can accommodate the also arc-shaped dummy bar after the continuous casting installation 1 has been cast on. The strand is then transported on a roller table to the flame cutting machine 6 and cut there into strand sections. The strand sections are either deposited in the discharge area 7 or further processed by the discharge area 7 downstream rolling mills into wires, profiles or similar products.

Such continuous casting plants 1 are inexpensive to purchase and operate, but are unable to keep up with modern continuous casting plants either in terms of the productivity of the plant or the quality of the strands produced. Accordingly, there is a need to rebuild existing continuous casters in order to increase the quality of the strands produced and/or the productivity of the continuous caster.

Although modern continuous casting plants allow significantly higher casting speeds and qualities due to advances in the mold, the oscillating unit, the strand guide, better casting powder and last but not least through greatly improved strand cooling and plant automation, these advances cannot be directly transferred to existing continuous casting plants.

On the one hand, the solidification point of the strand in the strand guide shifts backwards in the material direction at higher casting speeds, i.e. in the direction of the outlet area 7. In order to reliably prevent a partially solidified strand from being cut off, either the strand would have to be cooled more intensively by strand cooling or the Arc radius of the strand guide can be increased. However, both measures are problematic because on the one hand more intensive strand cooling degrades the quality of the strand and on the other hand a larger arc radius increases the overall height of the continuous casting plant, which is very problematic in an existing hall with a given height.

According to the invention, the technical problem is solved in that the flame cutting machine 6 is moved backwards in the casting direction, so that a free space F is created between the last extension unit 5 and the displaced flame cutting machine 6, and at least one soft reduction unit 8 is installed in the free space F , wherein each soft reduction unit 8 has an adjustment device 9 and a strand guide roller 10, which can be adjusted by the adjustment device, for reducing the thickness of the strand.

These measures reliably prevent a partially solidified strand from being cut off and also increase the internal quality of the strand.

The converted continuous caster 1 is in figure 2 as well as in further details in the Figures 3 to 5 shown.

As in figure 1 represented by an arrow, the flame cutting machine 6 is displaced in the material flow direction in the direction of the outlet area 7 . By moving the flame cutting machine 6, a free space F (see figure 2 ) formed between the rear end of the extension unit 5 and the front end of the flame cutting machine 6. The soft reduction unit 8 or several such units 8a . . . 8e is inserted into this free space F. The soft reduction units 8 are typically inserted by a crane, as is the case with the soft reduction units 8b, 8c in figure 4 implied.

Due to the conversion method according to the invention, the pull-out unit 5 and the dummy bar pull-out unit 13 can typically be left in the same position (see figure 3 and 4 ), which further reduces the conversion time and effort. In order to move the solidification point of the strand even further in the direction of the outlet area 7, first and second insulation tunnels 11, 12 can be installed between the last segment 4 of the strand guide 3 and the extraction unit 5 and between the extraction unit 5 and the soft reduction unit 8 (please refer figure 2 ).

In the ideal case, the solidification point of the converted continuous caster is in the area between the first soft reduction unit 8a and the last soft reduction unit 8e. This is ensured during operation by a system control.

In practice, it has turned out to be favorable if the mold 2 is designed as a curved mold and the radius of the mold 2 and the radius R of the curved guide 3 are between 8 m and 12 m, preferably between 9 m and 11 m.

In figure 5 five soft reduction units 8a...8e are shown. Each reduction unit 8 has an adjustment device 9 (here a hydraulic cylinder) which can move an upper strand guide roller 10b in the direction of a lower strand guide roller 10a. By placing the upper strand guide roller 10b on the strand, which is not shown, the thickness of the strand is reduced. All reduction units 8a...8e are constructed identically and are connected to the foundation via a base frame. Further details on soft reduction units are not necessary, since these are, for example, from the WO 2009/144107 A1 are known.

Reference List

1

continuous caster

2

mold

2a

oscillating unit

3

strand guide

4

Segment of the strand guide

5

pull-out unit

6

flame cutting machine

7

outlet area

8.8a...8e

Soft reduction unit

9

queuing device

10,10a,10b

strand guide roller

11

first isolation tunnel

12

second isolation tunnel

13

Dummy leg extraction unit

f

free space

R, R1

radius of curvature

Claims (11)

1. Method for converting a continuous casting plant (1) for the continuous casting of a strand with a billet or bloom cross section, wherein the continuous casting plant (1) before the conversion comprises:

   - a mould (2) for casting liquid steel into a strand with a billet or bloom cross section and an oscillating unit (2a) for oscillating the mould (2);

   - an arcuate strand guide (3) for supporting, guiding and cooling the strand with a plurality of strand guiding rollers arranged on either side of the strand, wherein the strand in the strand guide (3) is cooled by cooling nozzles;

   - at least one extraction unit (5) with in each case one driven strand guiding roller, which can be adjusted on the strand, for extracting the strand from the mould (2);

   - a flame cutting machine (6) for severing the strand into strand portions; and

   - a run-out region (7) for laying down the strand portions; having the following method steps:

   i) offsetting the flame cutting machine (6) in the casting direction, with the result that between the last extraction unit (5) and the offset flame cutting machine (6) a free space (F) is produced;

   ii) installing at least one soft reduction unit (8, 8a, ..., 8e) in the free space (F), wherein each soft reduction unit (8) has an adjusting device (9) and a strand guiding roller (10), which can be adjusted by the adjusting device, for reducing the thickness of the strand.
2. Method according to Claim 1, characterized in that a first insulation tunnel (11) for thermally insulating the strand is inserted between the rear end of the strand guide (3) and the extraction unit (5).
3. Method according to Claim 2, characterized in that a second insulation tunnel (12) for thermally insulating the strand is inserted between the extraction unit (5) and that soft reduction unit (8, 8a) that is first in the casting direction.
4. Method according to one of the preceding claims, characterized in that the casting speed and/or the cooling intensity of the converted continuous casting plant is set by a plant regulating means, with the result that the point of solidification right through of the strand lies between the first soft reduction unit (8a) and the last soft reduction unit (8e).
5. Method according to one of the preceding claims, characterized in that a cold-strand extraction unit (13) arranged downstream of the last extraction unit (5) is reused after the conversion to the continuous casting plant.
6. Method according to Claim 5, characterized in that the cold-strand extraction unit (13) is not offset during the conversion.
7. Method according to one of the preceding claims, characterized in that the strand leaves the mould (2) of the continuous casting machine (1) in a curved shape with a radius of curvature (R₁).
8. Method according to Claim 8, characterized in that the following applies for the radius of curvature (R₁) of the strand in the mould (2): 0.9.R₁ ≤ R ≤ 1.1.R₁, preferably R = R₁, with R being the radius of curvature of the strand guide (3).
9. Continuous casting plant (1) for the continuous casting of a strand with a billet or bloom cross section, produced by a method for converting a continuous casting plant (1) for the continuous casting of a strand with a billet or bloom cross section according to one of the preceding claims, comprising:

   - a mould (2), preferably a curved mould, for casting liquid steel into a strand with a billet or bloom cross section and an oscillating unit (2a) for oscillating the mould (2);

   - an arcuate strand guide (3) for supporting, guiding and cooling the strand with a plurality of strand guiding rollers arranged on either side of the strand, wherein the strand in the strand guide (3) is cooled by cooling nozzles;

   - at least one extraction unit (5) with in each case one driven strand guiding roller, which can be adjusted on the strand, for extracting the strand from the mould (2), wherein the extraction unit (5) is arranged downstream of the rear end of the arcuate strand guide (3);

   - a cold-strand extraction unit (13) for extracting a cold strand from the mould (2);

   - at least one soft reduction unit (8) with an adjusting device (9) and a strand guiding roller (10), which can be adjusted by the adjusting device, for reducing the thickness of the strand, wherein the at least one soft reduction unit (8) is arranged in a free space (F) between the last extraction unit (5), which remains at its original position, and the new position, which is offset in the run-out direction of the strand, of the flame cutting machine (6);

   - a flame cutting machine (6) for severing the strand into strand portions; and

   - a run-out region (7) for laying down the strand portions,

   wherein a first insulation tunnel (11) for thermally insulating the strand is arranged between the rear end of the strand guide (3) and a first extraction unit (5), and a second insulation tunnel (12) for thermally insulating the strand is arranged between the last extraction unit (5) and the first soft reduction unit (8, 8a).
10. Continuous casting plant (1) according to Claim 9, characterized in that the following applies for a radius of curvature (R) of the arcuate strand guide: 12 m ≥ R ≥ 8 m, preferably 11 m ≥ R ≥ 9 m.
11. Continuous casting plant (1) according to either of Claims 9 and 10, characterized in that the converted continuous casting plant (1) has between 4 and 6 soft reduction units (8, 8a, ..., 8e) .

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