EP1453626B1 - Tundish for production of a metal strip of high purity - Google Patents

Description

The invention relates to an intermediate vessel with a refractory lining for the production and transfer of molten metal of high purity from a ladle into the mold of a continuous casting plant.

In metal continuous casting, in particular in the continuous casting of steel, an intermediate vessel is usually inserted between the ladle and the continuous casting mold in order to compensate for fluctuations in the supply of melt and at the withdrawal speed of the metal strand from the continuous casting plant. Especially in sequence casting, it is necessary to stock a sufficient amount of molten metal in the tundish to bridge the period of ladle change.

The transfer of the melt from the tundish into the mold of a continuous casting plant is usually carried out by a drain opening in the tundish bottom, which is associated with a controllable closure member such as a slide or a stopper, and further by a submersible pouring tube or a pouring nozzle. The mold may be of various types, for example an oscillating tube or plate mold, a mold formed by a single casting roll or two co-operating casting rolls and side plates or a mold formed by circumferential bands or beads.

In multi-strand casting this intermediate vessel is designed as a distribution vessel and supplies several juxtaposed Schmelzenauslässe several juxtaposed continuous casting molds. In two-strand casters V-shaped distribution vessels are known.

The tundish usually also serves to calm the molten metal flowing from the ladle and, during the residence time of the molten metal in the tundish, is intended to enable the separation of slag particles and other non-metallic inclusions. To ensure this to a sufficient extent, the flow behavior of the molten metal is often due to flow-conducting internals in the Intermediate vessel specifically influenced. Such shaped trough-shaped intermediate vessels are already known, for example, from EP-B 804 306 and EP-A 376 523.

Considering the flow and temperature behavior in a trough-shaped intermediate vessel, as it has been used for decades in conventional steelmaking and continuous casting, more precisely, liquid steel from the ladle is introduced via a shadow tube in a distribution or intermediate vessel. The induced steel jet flows in the direction of the intermediate vessel bottom and there impinges on the flat bottom of the intermediate vessel or a device for the flow deflection which deflects the liquid jet in the direction of the bath mirror surface and removes kinetic energy by dissipation. In the inlet region, the flow usually returns to the surface of the bath mirror, migrates along it and emerges again along the narrow rear wall and along the side walls of the trough-shaped intermediate vessel. As a result, depending on the shape of the vessel, essentially two oppositely directed recirculation rollers (upward flow in longitudinal central section) are induced, which migrate in the direction of the outlet opening. The temperature of the steel decreases as a result of heat loss via the side walls and the bath mirror surface in the direction of the outlet opening, wherein the temperature loss between feed and outlet point depends on the throughput.

On the one hand, the foreign substances in the molten metal to be separated as efficiently as possible come from the steelmaking process and are flushed out of the ladle into the intermediate vessel when the molten metal is transferred. On the other hand, foreign substances are also introduced into the molten metal in the tundish. These come from the refractory lining material of the tundish or from the most commonly used liquid steel cover slag and are on the one hand eroded and flooded by mechanical erosion due to wall shear stresses or by chemical erosion due to reoxidation. On the other hand, slag inclusions arise due to resuspension because of high bath mirror velocities and increased surface turbulence.

The object of the present invention is therefore to avoid the disadvantages described and to propose an intermediate vessel for producing a metal strand, in which the particle introduction into the molten metal within the intermediate vessel is minimized and, overall, the highest possible Separation rate of all inclusions contained in the molten metal is achieved and so the mold is fed a melt with the highest possible purity.

ergibt, zwischen 3,83 und 4,39 liegt.This object is achieved in an intermediate vessel according to the invention with a refractory lining in that a bricked interior of the tundish in response to an operating-Badspiegelhöhe (h) satisfies the condition that a dimensionless ratio (κ) of the wetted by the molten metal lined surface (A _Ref ) bounded by this walled surface and the badspiegelhöhenabhängigen free surface (A _Top ) bounded filling volume (V), which results from the relationship $\kappa =\frac{A_{\mathrm{ref}}}{{\left(V\right)}^{\frac{2}{3}}}$

yields between 3.83 and 4.39.

Preferably, these values for the dimensionless ratio κ are between 3.83 and 4.2.

und der Geometrie eines stehenden Kreiszylinders, bei dem der Radius der kreisförmigen Grundfläche gleich der Höhe des Zylinders ist (κ = 3π^1/3 ≡ 4,39).The dimensionless ratio κ, which defines a volumetric wetting degree, indicates that the contact surface between lining and molten metal should be kept as small as possible in relation to the amount of molten metal in the intermediate vessel. At the same time, however, it must not be disregarded that a corresponding separation surface is necessary for maximum particle separation. Analyzes of various types of intermediate vessels have shown that optimum particle separation rates can be achieved with vessel shapes in which the ratio κ lies in the claimed range. The specified range limits result from the geometry of a hemisphere $\left(\mathrm{\kappa }=\frac{\mathrm{Second}\pi }{{\left(\frac{2}{3}\pi \right)}^{2/3}}\cong 3.83\right)$

and the geometry of a stationary circular cylinder in which the radius of the circular base is equal to the height of the cylinder (κ = 3π ^1/3 ≡ 4.39).

A high particle separation occurs when, in addition, the bricked-up interior of the tundish as a function of the operating-Badspiegelhöhe (h) satisfies the condition that the ratio (ζ) of the free surface (A _Top ) to the wet molten surface of the molten metal surface (A _ref ) is between 0.45 and 1.0. The dimensionless ratio ζ, which relates the free surface, which acts as a particle deposition surface, to the wetted lining surface, referred to as Particle generation surface acts, can be seen that in the preferred range, a balance in the opposite effects occurs. A favorable particle separation rate sets in at a ratio ζ between 0.5 and 0.8.

The κ and ζ values determined above do not take into account additional intermediate vessel installations such as flow deflectors, weirs etc.

To ensure a high particle separation, it is expedient that the operating bath level is between 0.5 m and 1.5 m.

The requirement for high particle separation from the molten metal in the tundish is ensured in sequence casting during the phase of ladle change, if the filling volume of the interior of the tundish contains at least 5 times, preferably at least 7 times the amount of molten metal per minute in normal operation is shed.

In order to realize favorable deposition rates, the filling volume of the interior of the tundish is at least 0.75m ³ , but preferably at least 1.0 m ³ . This ensures a sufficient residence time of the melt in the tundish at casting rates of 60 to 100 t steel / h. For higher casting rates, higher minimum volumes are recommended.

• eine maximale Partikelabscheidungsrate, die eine möglichst große Abscheidungsfläche bzw. Badspiegeloberfläche impliziert,
• eine minimale mit Metallschmelze benetzte Angriffsfläche aus Feuerfestmaterial, die die Entstehung von zusätzlichen Einschlüssen minimiert,
• eine Minimierung der Badspiegelgeschwindigkeiten und Oberflächenturbulenzen, durch die die Entstehung von Schlackeneinschlüssen reduziert wird,
• eine minimale Absenkung des Badspiegels bei instationärem Betriebsverhalten, wie beispielsweise Sequenzguss,
• eine Reduzierung der Wärmeverluste im Vergleich zu konventionellen Zwischengefäßen nach dem Stand der Technik,
• ermöglicht einen Kurzschlussbetrieb, d. h. ein überwiegender Teil der Metallschmelze durchströmt das Zwischengefäß auf möglichst kurzem Weg zwischen Schmelzenzulauf und Auslassöffnung.

The inventively claimed possible embodiments of a tundish combine the following conflicting requirements:

• a maximum particle deposition rate, which implies the largest possible deposition surface or bath mirror surface,
• a minimum refractory material attacked with molten metal which minimizes the formation of additional inclusions,
• a minimization of the bath mirror velocities and surface turbulence, which reduces the formation of slag inclusions,
• a minimal lowering of the bath level with unsteady operating behavior, such as sequence casting,
• a reduction of heat losses in comparison to conventional intermediate vessels according to the prior art,
• allows a short-circuit operation, ie a predominant part of the molten metal flows through the intermediate vessel on the shortest possible path between the melt inlet and outlet opening.

Preferred forms of the tundish arise when the bricked interior of the tundish is formed essentially by a generator rotating about a vertical vessel axis. This creates rotationally symmetrical vessel interiors.

wobei h der Betriebs-Badspiegelhöhe und R dem Badspiegelradius entspricht.
Für den Fall h/R = 1 liegt eine Halbkugelgeometrie vor und es gilt ζ = 0,5. Verringert man z.B. das Verhältnis h/R auf 0,6, so vergrößert sich bei gleichbleibendem Verteilervolumen das Verhältnis von Badspiegelfläche zu der mit Flüssigstahl benetzten Ausmauerungsfläche auf ζ = 0,73. Wählt man für ein bestimmtes Zwischengefäßvolumen daher eine Kugelsegmentgeometrie (h/R<1), so ist mit einer zusätzlichen Steigerung der Reinigungswirkung zu rechnen.The optimum shape, which for a given tundish volume has a maximum surface area for the deposition of inclusions in the bath covering slag and at the same time forms a minimal molten metal wetted attack surface for mechanical and chemical erosion, is formed by a hemisphere or a hemisphere segment. For the hemisphere segment shape, a generally valid relationship for the theoretically ideal area ratio of bath mirror surface to wetted refractory lining can be stated: $$\zeta =\frac{1}{1+{\left(\frac{H}{R}\right)}^2}\mathrm{With}H/R\le 1$$

where h is the operating bath level and R is the bath mirror radius.
For the case h / R = 1, there is a hemispherical geometry and ζ = 0.5. If, for example, the ratio h / R is reduced to 0.6, the ratio of the bath level surface to the wall surface wetted with liquid steel increases to ζ = 0.73, assuming the distribution volume remains the same. If, therefore, a spherical segment geometry (h / R <1) is selected for a particular intermediate vessel volume, an additional increase in the cleaning effect is to be expected.

Further possible shapes result when the bricked-up interior of the intermediate vessel is essentially formed by a generator rotating about a vertical vessel axis with changing, preferably harmoniously pulsating distance (r) from the vertical vessel axis. Thus, normal to the vertical vessel axis elliptical cross sections, but also cross sections with any other outer contour, such as a square cross section with large radii of curvature or polygonal cross sections are possible.

Favorable forms for the tundish arise when the tundish at least partially has a hemispherical, frusto-conical, drehparaboloidförmigen or cylindrical interior and in this case the cross section of the tundish interior is at least partially circular or elliptical formed in a normal plane to the vertical vessel axis cutting plane.

In order to make optimal use of the entire interior space of the intermediate vessel for the particle separation, a dip tube projecting into the intermediate vessel is provided for the supply of melt, a flow guide and the outlet opening at the intermediate vessel bottom below the dip tube a flow guide and the outlet at a location of the tundish bottom spaced from the flow guide and at least half the bottom diameter arranged.

The intermediate vessel according to the invention can also be operated in short-circuit operation, whereby in particular the entry of harmful particles from the Zwischengefäßausmauerung is kept low. Short-circuit operation is understood to mean a procedure in which the molten metal flowing from the ladle into the intermediate vessel or the interior of an intermediate vessel flows through it over a short path and out through the outlet opening of the intermediate vessel or the interior of the intermediate vessel. In this case, a flow path in this interior, in which a large proportion of the inflowing molten metal is not subject to Umwälzströmungen in the tundish, but undergoes little flow deflections on the largely direct path from the melt inlet to the melt outlet. This is achieved by setting the horizontal distance between the molten metal jet entering the melt volume substantially vertically and the molten metal jet emerging essentially vertically from the melt volume to less than half the bottom diameter of the interior space.

Especially in the case when the intermediate vessel according to the invention several juxtaposed strand conductors of a continuous casting plants are to be supplied with melt and the melt is thus distributed over several molds, the intermediate vessel comprises a melt feed basin and at least one melt-discharge basin, each melt discharge basin by a transport channel, preferably an overflow, is separated from the melt supply tank and each melt-discharge basin defines an interior of the intermediate vessel. This type of intermediate vessel, in which the melt flows through two tanks arranged in series, not only spatially but also structurally separates the region of the melt feed from the casting ladle from the region of the melt discharge into the mold and thus allows an additional continuity in the flow behavior. The connection area between the melt supply basin and the melt discharge basin can be provided by an overflow or by a transport channel, which can also be arranged below the bath level. The above-described geometric conditions for the design of the interior must be fulfilled at least by the melt discharge basin. A reduction in the introduction of foreign substances from the lining of the tundish is additionally contributed if the melt supply basin delimits an interior of the tundish and satisfies the conditions of the dimensionless ratio (κ) and optionally also the dimensionless ratio (ζ). The melt feed basin is a Flow control arm and the melt discharge basin is at least one outlet opening zugeorgnet.

For easy manipulation of the tundish according to the invention, in particular its preparation for the casting and its exact positioning over dre mold opening, the tundish is supported on a preferably lifting and / or tilting distribution van having a traction drive and on a roadway between an operating position and a Waiting position procedure is formed.

Fig. 1

eine schematische Darstellung einer Stranggießanlage mit dem erfindungsgemäßen Zwischengefäß,

Fig.2a, 2b

das erfindungsgemäße Zwischengefäß in Grund- und Aufriss nach einer ersten Ausführungsform,

Fig. 3a, 3b

das erfindungsgemäße Zwischengefäß in Grund- und Aufriss nach einer zweiten Ausführungsform,

Fig. 4a, 4b

das erfindungsgemäße Zwischengefäß für eine zweisträngige Gießanlage in Grund- und Aufriss

Fig. 5

das erfindungsgemäße Zwischengefäß auf einem Verteilerwagen

Fig. 6

das erfindungsgemäße Zwischengefäß im Kurzschlussbetrieb.

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

Fig. 1

a schematic representation of a continuous casting with the intermediate vessel according to the invention,

2a, 2b

the intermediate vessel according to the invention in plan and elevation according to a first embodiment,

Fig. 3a, 3b

the intermediate vessel according to the invention in plan and elevation according to a second embodiment,

Fig. 4a, 4b

the intermediate vessel according to the invention for a two-strand casting in basic and elevation

Fig. 5

the intermediate vessel according to the invention on a distribution truck

Fig. 6

the intermediate vessel according to the invention in short-circuit operation.

From Fig. 1, the arrangement of an inventive tundish 1 in its operating position between a ladle 2 and a mold 3 in a continuous casting plant, which is indicated by the mold 3 and the outflowed from her casting 13, shown schematically. The ladle 2 is deposited in fork arms 4 of a ladle turret, which is indicated by the vertical turret axis 5. A submersible pouring tube 6, which adjoins the outlet opening 7 of the ladle 2 and projects into the intermediate vessel 1, flows molten metal from the ladle 2 into the intermediate vessel 1 and exits there below the bath level 8. From here, the molten metal is passed through an outlet opening 9 and another immersion pouring tube 10 into the mold 3 and exits there below the mold bath level 11. The melt flow in the immersion casting tube 10 is controlled by a controllable closure member 12, for example a slide. In the cooled mold 3, the molten metal solidifies into a cast strand 13, which is continuously conveyed out in a roll guide, not shown, of a continuous casting plant.

The tundish 1 consists, as shown in FIGS. 2a and 2b, of a steel tub 15, which forms an outer stable vessel frame and a refractory lining 16 as an insulating layer whose inner surface forms the contact surface to the molten metal 17 and forms the interior 14 of the tundish. From the intermediate vessel bottom 18, the intermediate vessel wall 19 protrudes upwards about a vertical vessel axis 20 and forms a spherical-segment-shaped interior space 14. The interior space 14 is geometrically formed by a generator E rotating at a constant distance r around the vertical vessel axis 20. At the intermediate vessel bottom 18 is at the greatest possible distance from the vertical vessel axis 20 a Flow guide 21 is arranged below the immersion casting tube 6. At the opposite edge of the tundish bottom 18 there is an outlet opening 9, to which, attached to the steel trough 15 of the tundish, designed as a controllable slide closure member 12 and then a Tauchgießrohr 10 connects. The flow guide 21 and the outlet opening 9 are therefore as far away as possible from each other.

From the molten metal 17, a filling volume (V) is filled in the interior 14 of the intermediate vessel 1, wherein the free surface (A _Top ) of the molten metal forms the bath level 8, which is at the operating level of the bath level (h) and covered by a slag layer 22 is, in which from the molten metal continuously foreign particles are deposited. In the intermediate vessel 1, a portion of the surface of the refractory lining 16 is wetted by molten metal 17 and this wetted bricked surface (A _ref ) is exposed to particularly high thermal stress and chemical and mechanical erosion. Particles are continuously flushed out of the lining 16 into the molten metal 17 and released again with the melt flow at the transition to the dead zone 22.

FIGS. 3a and 3b show a further embodiment of a possible intermediate vessel, in which each cross-sectional area normal to the vertical vessel axis 20 is formed by an ellipse as can be seen in the plan view. The inner contour results geometrically by rotation of a generatrix (E) around the vertical vessel axis 20, wherein the radius distance (r) of the generatrix of the vertical vessel axis as a function of the rotation angle (φ) varies. Again, the flow guide 21 and the outlet opening 9 are as far away as possible from each other to create favorable flow conditions in the interior 14 and to ensure a high Partikelabscheiderate.

The intermediate vessel may also be formed by a plurality of receiving tanks for molten metal. FIGS. 4a and 4b show in plan and elevation an intermediate vessel or distribution vessel for a two-strand casting installation, wherein the two casting taps 23 are indicated by dashed lines. The intermediate vessel is formed in plan V-shaped by three contiguous receiving basin. A Schmetzen feed basin 25 is centrally located and connected to two melt diverters 26 to form a unit.

In the melt feed basin 25, a flow guide 21 is embedded in the bottom of the refractory lining. The intermediate vessel is in this case, as shown in Fig. 1, during operation so positioned that the immersion nozzle 6 of the ladle 2 is located exactly above the flow control arm 21. Each melt discharge basin 26 is penetrated at the bottom of the vessel by an outlet opening 9, which is positioned above the mold 3 in the casting operation. In this case, the submersible pouring tube 10 adjoining the outlet opening 9 projects into the mold cavity of the mold 3. The vertical section through the intermediate vessel along the line AB shows an overflow 27 formed by a refractory lining between the melt feed basin 25 and the melt drainage basin 26. The bath level 8 of the molten metal 17 projects beyond the overflow 27, so that the molten metal pre-soaked in the melt feed basin 25 can flow in a slow flow into the melt discharge basin 26 and there can be further particle separation before the molten metal flows through the outlet opening 9 into the continuous casting mold 3 , Both the melt supply tank 25 and the two melt discharge basins 26 form a spherical segment-shaped interior 14.

As is usual in conventional continuous casting plants, the intermediate vessel according to the invention, like conventional intermediate vessels hitherto, is height-adjustable and possibly also tiltably supported on a distribution truck 30 by means of lifting and / or tilting devices 31 and between an operating position in which the immersion casting tube protrudes into the mold. and a maintenance position in which the intermediate vessel is heated and prepared for its use, usually rail-bound on a roadway 32 movable (Fig. 5). The distribution truck 30 is equipped with a travel drive 33.

The intermediate vessel is usually closed with a lid to largely prevent cooling of the melt by thermal radiation. If necessary, additional internals are possible in the tundish, which favorably influence the melt flow. The passing of the molten metal between the adjacent melting tanks can also be done below the bath level of the filled melts through one or more tubular transport channels, with the advantage that the slag layer is subject to a flow movement only to a very small extent.

FIG. 6 clearly shows the short-circuit operation already described above on the intermediate vessel. In the tundish 1, the molten metal flows through the immersion nozzle 6 of the ladle into the interior 14 and flows on a short path, which is indicated by flow lines 35, to the outlet opening 9 and leaves there again the intermediate vessel. The horizontal distance H between the entering in the vertical direction in the interior 14 and also again in the vertical direction from the interior 14 emerging molten metal is less than half the diameter d of the tundish 18th

Claims (14)

1. Tundish with a refractory lining (16) for producing and transferring high-purity metal melt, preferably steel melt, from a casting ladle (2) into the permanent mould (3) of a continuous-casting installation, characterized in that a refractory-lined interior space (14) of the tundish (1), as a function of an operating bath level (h), satisfies the condition that a dimensionless ratio (κ) of the refractory-lined surface area (A_ref) which is wetted by the metal melt (17) to the filling volume (V) which is delimited by this wetted surface area (A_ref) and the bath-level-dependent exposed surface area (A_Top) and results from the relationship $\kappa =\frac{A_{\mathit{ref}}}{{\left(V\right)}^{\frac{2}{3}}}$

   

   be between 3.83 and 4.39.
2. Tundish according to Claim 1, characterized in that the dimensionless ratio (κ) is between 3.83 and 4.20.
3. Tundish according to Claim 1 or 2, characterized in that the refractory-lined interior space (14) of the tundish, as a function of the operating bath level (h), satisfies the condition that the ratio (ζ) of the exposed surface area (A_Top) to the refractory-lined surface area (A_ref) which is wetted by the metal melt be between 0.4 and 1.0.
4. Tundish according to Claim 3, characterized in that the ratio (ζ) is between 0.5 and 0.8.
5. Tundish according to one of the preceding claims, characterized in that the filling volume (V) of the interior space (14) of the tundish comprises at least 0.75 m³, preferably at least 1.0 m³.
6. Tundish according to one of the preceding claims, characterized in that the refractory-lined interior space (14) of the tundish is substantially formed by a generatrix (E) which rotates about a vertical tundish axis (20).
7. Tundish according to one of the preceding claims, characterized in that the refractory-lined interior space (14) of the tundish is substantially formed by a generatrix (E) which rotates about a vertical tundish axis (20) at a fluctuating, preferably harmonically pulsating distance (r) from the vertical tundish axis (20).
8. Tundish according to one of the preceding claims, characterized in that the tundish, at least in sections, has an interior space (14) which is in the shape of a hemisphere, a truncated cone, a paraboloid of revolution or a cylinder.
9. Tundish according to Claim 7, characterized in that the cross section of the interior space (14) of the tundish, in a section plane taken normally to the vertical tundish axis (20), at least in sections, is circular or elliptical in form.
10. Tundish according to one of the preceding claims, characterized in that to supply the melt there is a submerged pipe (6) which projects into the tundish (1), in that a flow diverter (21) is arranged on the tundish base (18) beneath the submerged pipe (6), and in that the outlet opening (9) is arranged at a location of the tundish base (18) which is spaced apart from the flow diverter (21) by at least half the diameter (d) of the base.
11. Tundish according to one of the preceding claims, characterized in that the tundish (1) comprises a melt feed tank (25) and at least one melt discharge tank (26), in that each melt discharge tank (26) is separated from the melt feed tank (25) by a transfer passage, preferably an overflow (27), and each melt discharge tank (26) delimits an interior space (14) of the tundish (1).
12. Tundish according to Claim 11, characterized in that the melt feed tank (25) delimits an interior space (14) of the tundish.
13. Tundish according to claim 11 or 12, characterized in that a flow diverter (21) is assigned to the melt feed tank (25) and an outlet opening (9) is assigned to the melt discharge tank (26).
14. Tundish according to one of the preceding claims, characterized in that the tundish is supported on a distributor carriage (30), which preferably has lifting and/or tilting devices (31), has a movement drive (33) and is designed such that it can be displaced on a movement path (32) between an operating position and a waiting position.

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