EP1106286B1 - Device for feeding molten metal from a tundish through a submerged tube in a continuous casting mould - Google Patents

Abstract

To promote more uniform flow in the continuous casting mold, and to prevent build-up of melt deposits on the inner wall (16) of the dip tube (15), the axial flow is induced to swirl. An Independent claim is included for suitable equipment carrying out the method.

Description

The invention relates to a device for the introduction of a melt from a distributor via a dip tube into a continuous casting mold, comprising a flow control for the melt in the distributor by means of a stuffing bar, wherein a swirl generator is arranged in the inlet region of the dip tube.

The prior art in the continuous casting of metals is the introduction of melt from a distributor into a mold through plug-controlled or slide-controlled pouring systems, wherein melt flows through refractory dip tubes into the mold. The flow conditions within the spout system and the mold are transient in nature, so that even in steady-state casting conditions asymmetric and non-uniform flow patterns occur. Depending on their intensity, these can have a negative effect on product quality. In addition, under certain conditions, deposits of dispersed non-metallic inclusions present in the steel can form on the walls of the throughflow system. This "clogging" can affect the flow formation within the mold and the bath level and lead to disturbances of the casting operation. In addition, broken deposits can get into the strand. Significant quality losses on the cast product can be the result.

The document DE 34 44 228 A1 describes a method and a device for generating a directed flow during the casting of a melt from a melt reservoir in a mold, in particular in a continuous casting mold. The melt is already displaced in the outlet region of the melt reservoir and / or in the feed region to the casting mirror in a direction of rotation in the feed direction. By means of the generated rotation of the melt jet, the melt in the mold is displaced in a direction of movement about the longitudinal axis of the casting, in particular around the strand axis.

An apparatus for carrying out the known method consists of a melt reservoir with Bodenausguß and from a projecting from the spout opening into the mold immersion nozzle. The inner surface of the spout has guide surfaces inclined to the casting direction. On the bottom of the melt reservoir plate-shaped refractory elements are arranged perpendicular to the ground in the immediate vicinity of the spout opening and associated with each other such that between each end face of an element and a side surface of an adjacent element remains a gap allowing the melt flow. However, it can not be avoided with certainty that results between the rotating inflowing melt in the manifold, in particular at a comparatively low melt height, a fluid coupling with higher melt areas, the self-enhancing verikkelt to the aforementioned vortex. Such a vortex would flush parts of the distributor cover mass into the mold, especially at low filling levels in the distributor, and thus impair the product quality. In addition, the inner surface of the immersion nozzle on the casting direction inclined guide surfaces.

It can be seen from the state of the art that the production of a swirling melt flow within the dip tube to prevent deposits of non-metallic inclusions on the dip tube wall has not been recognized and used up to now. Also about a positive influence of the Dralls on the uniformity of the flow, ie the reduction of transient flow conditions at the mold level, nothing is reported.

Swirl flows in molds or immersion nozzle systems can also be generated with electromagnetic alternating field, the technical complexity is very high due to the necessary electrical equipment.

Based on this finding, the invention has for its object to provide a device which in an uncomplicated way and by means of technically mature means the emergence of non-metallic deposits (clogging) on the dip tube inner wall as much as possible prevented and simultaneously reduces transient flow conditions in the mold in their intensity, without generating a Vorlexartiger vortex in the inflowing melt, in particular at low Verleiterfüllstand when using the swirl generator.

To solve the problem is proposed in an apparatus having the features of the preamble of claim 1 with the invention for preventing deposits of non-metallic inclusions of a melt on the Tauchrohrinneninnenwandung that the swirl generator is designed with a bottom plate and a cover plate, between which one or more in the inlet region opening flow channels are formed. Surprisingly, harmful deposits on the dip tube inner wall can hereby be substantially reduced or even completely avoided if the melt flows through the dip tube in rotation. This results in a promising measure for preventing the so-called "clogging", because the effect of the centripetal force on specific lighter particles as a melt deposition of these particles is much more difficult. At the same time, the swirl is used to stabilize the flow in the dip tube, so that the transient flow conditions that usually already occur when the flow out of the dip tube into the mold, be reduced.

In an embodiment of the device according to the invention it is proposed that both the bottom plate, and the cover plate are formed for the passage of the stuffing bar, each with an opening.

Further inventive embodiments of the device are provided according to the subclaims.

Details, features and advantages of the invention will become apparent from the following explanation of an embodiment schematically illustrated in the drawings.

Figur 1

im Schnitt einen Verteiler mit bodenseitig angeordnetem Tauchrohr und an dessen Einlaufbereich angeordnetem Drallerzeuger,

Figur 2a

den Drallerzeuger im Schnitt einer Schnittebene ∥-∥ in Fig. 2b;

Figur 2b

den Drallerzeuger in Seitenansicht;

Figur 2c

Ausgestaltungen der Strömungskanäle im Querschnitt,

Figur 3a

rein schematisch eine Darstellung des numerisch berechneten Einflusses einer Drallströmung einer Schmelze auf die Bewegung nichtmetallischer Einschlüsse in einem zylindrischen Tauchrohr für einen typischen Betriebszustand bei Einschlüssen mit durchschnitt- lich 50 µm Durchmesser und einem spezifischen Gewicht von ca. 3.500 kg/m³;

Figur 3b

in gleicher Darstellung den Einfluß einer Drallströmung auf die Bewegung nichtmetallischer Einschlüsse mit einem durchschnittlichen Durchmesser von 150 µm und einem spezifischen Gewicht von 3.500 kg/m³,

Figur 3c

ein Tauchrohr mit bereichsweise poröser Wandverkleidung und Mittel zur Durchführung von Gas zur Erzeugung eines Gasvorhanges,

Figur 4

Beeinflussung der Strömungsausbildung am Gießspiegel ohne Drallerzeuger (Fig. 4a) und mit Drallerzeuger (Fig. 4b),

Figur 5a,

weitere Ausgestaltungen des Drallerzeugers mit unterschiedlichen

Figur 5b

Stellungen der Drallschaufeln zur Ausbildung von Strömungskanälen,

Show it:

FIG. 1

in section a distributor with bottom-side arranged dip tube and arranged at its inlet region swirl generator,

FIG. 2a

the swirl generator in the section of a sectional plane ∥-∥ in Fig. 2b;

FIG. 2b

the swirl generator in side view;

Figure 2c

Embodiments of the flow channels in cross section,

FIG. 3a

purely schematic representation of the numerically calculated influence of a swirling flow of a melt on the movement of non-metallic inclusions in a cylindrical immersion tube for a typical operating state in inclusions with average Lich 50 microns in diameter and a specific gravity of about 3,500 kg / m ³ ;

FIG. 3b

in the same representation, the influence of a swirling flow on the movement of non-metallic inclusions with an average diameter of 150 μm and a specific weight of 3,500 kg / m ³ ,

Figure 3c

a dip tube with partially porous wall cladding and means for passing gas to produce a gas curtain,

FIG. 4

Influencing the flow formation on the casting mirror without swirl generator (FIG. 4 a) and with swirl generator (FIG. 4 b),

FIG. 5a,

Further embodiments of the swirl generator with different

FIG. 5b

Positions of the swirl vanes for the formation of flow channels,

Fig. 1 shows an embodiment of a device for preventing deposits of non-metallic inclusions of a melt on the immersion tube inner wall 16 of a dip tube 15 during continuous casting with a continuous casting mold. Denoted at 24 is the level of the melt in the manifold 18, with a floating layer of lighter particles thereon, particularly slag and other non-metallic particles. The slag layer serves as a thermal and chemical covering layer against the environment.

The device has a flow control for the melt flow through the dip tube 15, wherein a stuffing rod 5 is used as a control element. There is a swirl generator 4 at this lower region, immediately in front of the inflow opening 23 of the dip tube 15. This swirl generator 4 is formed at the inlet region 23 with a bottom plate 1 and above it with a cover plate 2 preventing a vortex-like vortex in the inflowing melt 22. Between them tangentially oriented flow channels 10 to 10 "', as shown in FIGS 2a, 2b, are arranged tangentially into the inlet region, and variants of the swirl vanes 3 and the flow channels 10 - 10"' formed therefrom are shown in FIGS 5a to 5c. The number of flow channels may vary depending on the spout system. A sufficiently strong swirl flow can already be achieved with a single flow channel. In the practical interpretation, however, the design of multiple channels, which are preferably arranged evenly distributed around the inlet region is recommended.

For the passage of the stuffing bar 5, both the bottom plate 1, and the cover plate 2, each with an opening 6, 7 is formed, as shown in FIG. 1 and Fig. 2a can be seen. From Fig. 2a it can also be seen that the swirl blades 3 have the shape of tapered wedges 14.

In each case two swirl vanes 3, 3 'are provided with against the openings 6, 7 tangentially alignable inner side surfaces 8, 9. These are relative to each other at an angle α of 90 °, each forming a flow channel 10 to 10 "'between a tip 11 of a wedge 14 and the end face 12 of the adjacent wedge 14' is arranged.

An embodiment of the swirl generator 4 provides that the swirl vanes 3 for changing the cross section of the flow channels 10 to 10 '' formed between them about a fixed vertical axis 13 to 13 '' are pivotally adjustable and fixable in the position reached.

The targeted inflow of the dip tube inlet region, forced through the channels, in FIGS. 5a and 5b, for example, represented by the center line along the inflow channel, can be designed to pass laterally as a secant, tangent or the inlet region.

Simple geometrical shapes such as circles, ellipses, rectangles, squares, trapezoids or rhomboids are recommended for the design of the flow channels in cross section, wherein the latter geometric contours can also have fillets (FIG. 2 c). The inflow channels can be made twisted in the center line direction. Along a Anströmkanals the size of the open cross-sectional area can be unchanged, decreasing or increasingly designed.

The swirl generator is industrially preferably designed as a disposable refractory component and fixed in the distributor outlet area at the distributor base. In the simplest case, the design of the swirl generator is provided as a compact single component. But also a design of several exchangeable and joinable refractory single components is conceivable, so that the channel contour and / or leadership is easily changed. By special design measures, the variability of the flow channels can also be provided during operation.

It is further provided that the dip tube is at least partially equipped with porous wall panels 26, which are associated with means 17 for supplying gas, preferably inert gas, such that gas through the wall panels 16 in the rotating melt stream of the dip tube 15 in the form of a "Gas curtain" is initiated and the deposition of non-metallic particles is additionally prevented at the dip tube inner wall.

Such a gas curtain is shown in FIG. 3c. Therein, the same components are designated by the same reference numerals. The dip tube 15 is internally lined with a wall portion 26 of porous material, behind which an air gap 20 is arranged in the form of a slot which is connected to the connection channel 17 to means for supplying gas. The reference numeral 19 and the corresponding arrows, a gas curtain is indicated purely schematically.

In accordance with the law of centrifugal force, Figures 3a and 3b show the numerically calculated influence of a swirling flow of the melt on the movement of non-metallic inclusions in a cylindrical dip tube for a typical operating condition. Inclusions with a particle diameter dp of 150 microns and a weight of Pρ = 3500 kg / m ³ move within the specific heavier melt significantly away from the dip tube inner wall to Center down. For inclusions with a particle diameter dp of 50 μm, this effect is slightly lower. In any case, it is expected that the centripetal force will have a positive effect in reducing particle deposition on the dip tube inner wall 16.

Fig. 4a compared to Fig. 4b shows the use of a swirl flow in the dip tube to equalize the melt velocity in the mold and in particular on the mold level. The measurement results for the flow at the casting level in the stationary operating state in the water model without, Fig. 4a, and with, Fig. 4b, swirl flow in the dip tube prove that can be significantly reduce the time-dependent speed fluctuations using the twist in their amplitude. This speaks for a stabilization of the flow in the mold associated with a significant improvement of the near-surface flow conditions in the mold. This can be expected to improve product quality or increase productivity while maintaining product quality.

In order to avoid buildup of the immersion tube inner wall, a relatively high inert gas volume flow has hitherto often been added to the immersion tube in practice. This has the disadvantage that it leads to unwanted gas inclusions in the solidified product, whereas in swirling flow through the addition of only a small amount of inert gas through the porous dip tube wall cladding 26 is sufficient to further reduce the tendency to buildup much more. Both model experiments and simulation calculations lead to the conclusion that the generation of a "gas curtain" during operation is of considerable advantage. It is expected that particle inclusions will be effectively transported away from the wall to the center of the melt flow.

List of reference numbers

1

baseplate

2

cover plate

3

swirl blade

4

swirl generator

5

plug rod

6

opening

7

opening

8th

side surface

9

side surface

10

channel

11

Top of the wedge

12

end face

13

vertical axis

14

wedge

15

dip tube

16

Dip tube inner wall

17

Gas supply / connection duct

18

distributor

19

gas curtain

20

Slot / air gap

22

inflowing melt

23

Inlet opening dip tube

24

Mirror of the melt

25

scum

26

wall covering

Claims (12)

1. Device for introducing a melt from a distributor (18) by way of an immersion pipe (15) into a continuous casting mould, comprising a throughflow regulation for the melt in the distributor (18) by means of a plug rod (5), wherein a swirl generator (4) is arranged in the inlet region (23) of the immersion pipe (15), characterised in that the swirl generator (4) is formed by a base plate (1) and a cover plate (2), between which one or more flow channels (10 - 10"') opening into the inlet region are formed.
2. Device according to claim 1, characterised in that not only the base plate (1) but also the cover plate (2) are each constructed with a respective opening (6, 7) for passage of the plug rod (5).
3. Device according to claim 1 or 2, characterised in that the flow channels (10 - 10"') are so arranged in their flow direction that they are incident on the immersion pipe inlet region as secants or tangents or laterally pass the inlet region.
4. Device according to one or more of claims 1 to 3, characterised in that the flow channels (10 - 10"') can have in flow cross-section a circular, elliptical, rectangular, square, trapezium-shaped or rhomboidal form, which in a given case can be executed with radiusings.
5. Device according to one or more of claims 1 to 4, characterised in that the flow channels (10 - 10"') are formed along their alignment to be unchanging, decreasing or tapering in the size of the open cross-sectional area.
6. Device according to one or more of claims 1 to 4, characterised in that the flow channels (10 -10"') are formed along their alignment to be twisted.
7. Device according to one or more of claims 1 to 4, characterised in that the flow channels (10 - 10"') in the swirl generator (4) are formed to be identical or different in their geometry.
8. Device according to one or more of claims 1 to 4, characterised in that the flow channels (10 - 10"') are arranged to be non-uniformly distributed or uniformly distributed around the inlet region.
9. Device according to one or more of claims 1 to 8, characterised in that the geometry of the flow channels (10 - 10''') is variable during operation.
10. Device according to one or more of claims 1 to 9, characterised in that the swirl generator (4) is constructed as a compact refractory single component or consists of several exchangeable and/or connectible refractory individual components.
11. Device according to one or more of claims 1 to 10, characterised in that the swirl generator (4) comprises swirl vanes (3) and that the swirl vanes (3) are pivotably adjustable about a respective stationary vertical axis (13 - 13"') for changing the cross-section, which is formed therebetween, of the flow channels (10 - 10"') and are fixable in the position reached.
12. Device according to one or more of claims 1 to 11, characterised in that the immersion pipe (15) is equipped at least in areas at the wall region (16) with porous wall linings (26), which are connected with means (17) for the feed of gas, preferably inert gas, in such a manner that gas is introduced through the wall linings (26) into the rotating melt flow of the immersion pipe (15) in the form of a 'gas curtain'.

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