EP1286799B1 - Method and machine for the production of a continuously-cast precursor - Google Patents

Description

The invention relates to a method for producing a continuously cast intermediate product, in particular wide slabs, with a thickness of the precursor D> 100 mm and a width of the precursor B = 2700 mm to 3500 mm at a casting speed v _c <2 m / min in a continuous casting , wherein melt, preferably molten steel, introduced from a reservoir via a submersible nozzle through opposing outlet openings in a mold formed by broad side walls and narrow side walls and continuously in the mold teilerstarrte, a liquid core and a solidified strand shell having precursor continuously withdrawn from the mold and cooled and a continuous casting plant for the production of a continuously cast precursor, see eg EP-0 352 346-A.

When using the Tauchgießverfahrens in continuous casting, it is customary to initiate the melt from a reservoir, usually a tundish, by a coupled to this immersion nozzle in an oscillating mold below a covered with casting powder bath level. This process is easily feasible for small mold cross-sections, but leads, especially in molds with a large width-to-thickness ratio to difficulties in the formation of an optimal mold flow and thus to affect a uniform strand shell growth in the gradual solidification of the melt on the cooled mold wall.

From DE-C 197 24 232 a process for the production of precursors in the form of slabs in a continuous casting plant according to the previously described principle is already known. In this case, the melt is introduced below the bath level by a downwardly in the casting direction and funnel-shaped widening to the narrow side walls of the mold immersion nozzle in the mold. If the dimensioning instructions for the immersion nozzle specified in claim 2 of DE-C 197 24 232 are applied to the widths (B) of the precursor or the mold from 2700 mm to 3500 mm provided according to the invention, immersion pour-out widths (b ) from about 385mm to 2250mm, which are made of refractory materials with the durability required for continuous operation in the High temperature use can not be produced. In addition, such wide immersion spouts increase the known problems with the gap flow between immersion discharge wall and broad side wall of the mold.

From DE-C 196 47 363 a submersible nozzle is known, which is suitable for use in continuous casting of slabs and in which the melt emerges through laterally opposite outlet openings directed to the narrow side walls of the mold below the bath level. An essential feature of this immersion nozzle is its constant outer wall distance to form along the broad side wall strand shell. As a result, this immersion nozzle is suitable for a width-to-thickness ratio of the cast strand or the mold cross-section of a maximum of 8. For larger width-to-thickness ratios, however, this immersion nozzle does not ensure uniform solidification conditions creating mold flow.

In the continuous casting of intermediate products with large widths very high steel throughputs of up to 4 to / min and more are achieved despite usual casting speeds of 1.0 m / min to 1.2 m / min. In practice, it has been shown at these high steel throughputs that the resulting vortex-forming flows in the mold are very unstable. The guiding property of the Kokillenraumes for this flow is worse with increasing distance of the Tauchausguss outlet opening to the narrow side wall. In addition, the exit jet is due to its high local flow velocity in the immersion nozzle, as well as immediately after its exit from the Tauchausguss outlet opening due to the resistance of the melt and the large wall friction along the mold walls braked strongly and because of the negative pressure between the pouring and discharge jet upwards to the casting distracted. Visually, a fluctuating, oscillating bathing motion is observed, which adversely affects product quality.
This unfavorable design of the flow conditions is shown in Fig. 1 with reference to a flow thread. The discharge jet strikes the bath surface in the area between the immersion nozzle and the narrow side wall of the mold, where it is split into two partial beams. This phenomenon leads to uneven melting of the casting powder on the bath surface and to a local impairment of the sliding behavior between Strand and mold wall. When using conventional immersion nozzles for casting wide slabs, it is difficult for the reasons mentioned above to produce a favorable and stable Kokillenströmung.

The object of the invention is therefore to avoid these disadvantages and to provide a method for producing a continuously cast precursor, as well as the necessary continuous casting, whereby even with large casting widths uniform solidification conditions for the strand and uniform melting and distribution conditions are ensured for the casting powder. Furthermore, by means of a defined supply of steel through the immersion nozzle, a stable vortex system is to be created in the mold, which is formed by two large and round upwardly directed vertebrae. Furthermore, it is an object of the invention to allow no strong lateral deflection of the exit jets, in particular to avoid premature impingement of the discharge jet to the bath level.

This object is achieved according to the invention by a method, which is characterized in that the melt leaves the immersion nozzle with directed to the narrow side walls of the mold movement impulse and for a certain width-thickness ratio of the precursor, depending on the ratio of the speed of the melt in the core cross-section of the immersion nozzle (v _k ) to the casting speed (v _c ), design values for the width (b) of the dip tube and the height (h) of the lateral outlet opening of the immersion nozzle are chosen so that a uniform strand shell formation in the casting direction and circumferential direction along the broad side walls and Narrow sidewalls of the mold set.

und $$\frac{b}{h}=1,9-2,0$$

genügt und eine die Geschwindigkeit der Schmelze im Kernquerschnitt des Tauchausgusses (v_k) zur Gießgeschwindigkeit (v_c) in Beziehung setzende Verhältniszahl ψ nach der Bedingung $\mathrm{\psi }=0,1\cdot {\left(\frac{B}{D}\right)}^{-0,7}$

bestimmt wird.Optimal conditions for strand shell formation are established when the immersion nozzle in relation to the mold conditions $$\frac{H}{B}=\frac{9}{5}\psi +\frac{1}{5}\frac{D}{B}$$

and $$\frac{b}{H}=1.9-2.0$$

and satisfies a relationship of the speed of the melt in the core cross-section of the immersion nozzle (v _k ) to the casting speed (v _c ) relative ratio ψ according to the condition $\mathrm{\psi }=0.1\cdot {\left(\frac{B}{D}\right)}^{-0.7}$

is determined.

They mean: B = width of the precursor (mm)
D = thickness of the precursor (mm)
b = width of immersion nozzle (mm)
h = height of the lateral outlet opening of the immersion nozzle (mm)
ψ = ratio (dimensionless)

For the selected width-thickness ratios, ψ values of 0.011 to 0.015 result from the above condition. These values express that for optimal flow conditions low flow velocities are necessary in the immersion nozzle, which are achieved according to the invention by means of large core and outlet cross sections at the immersion nozzle. By reducing the flow velocity strong lateral deflections of the discharge jet are avoided, which are caused by the negative pressure between the exit jet and the casting mirror.

By these measures, it is possible to form a stable vortex system with large and substantially circular upwardly rotating vortices, as shown schematically in Fig. 2 for the left of the submersible nozzle half of Kokillenraumes using a flow line. The vortex diameter corresponds to about half the strand width. The necessary beam exit angle of about 40 to 45 ° is achieved by the large height (h) of the lateral outlet opening of the immersion nozzle. This reduces the phenomenon known in the case of a strong flow deflection in the immersion nozzle (small exit angle) in such a way that the outlet jet is already directed to the casting level after a short running distance. Due to the large height (h) of the lateral outlet opening, there is a flow that is not subject to any or only slight rotation.

The measures according to the invention further ensure that a system with large pronounced vertebrae can build up. For this purpose, the exit jet leaving the immersion nozzle must not be slowed down too much between the two broad sides of the casting. The braking effect on the discharge jet is determined by wall friction, which results from the contact of the moving discharge jet with the strand shell. Since the braking frictional force increases approximately with the square of the flow velocity, the exit velocity is kept low according to the invention.

vorzugsweise ein Breiten-Dicken-Verhältnis $\frac{B}{D}$

von etwa 20, aufweist.An advantageous application for the method is given when the precursor has a width-to-thickness ratio $\frac{B}{D}=15-25.$

preferably a width-to-thickness ratio $\frac{B}{D}$

of about 20.

Preferably, in the proposed precursor cross sections, the casting speed v _{c is set} to a value between 0.5 m / min and 1.5 m / min.

und $$\frac{b}{h}=1,9-2,0$$

erfüllt sind und eine die Geschwindigkeit der Schmelze im Kernquerschnitt des Tauchausgusses (v_k) zur Gießgeschwindigkeit (v_c) in Beziehung setzende Verhältniszahl ψ nach der Bedingung $\psi =0,1\cdot {\left(\frac{B}{D}\right)}^{-0,7}$

bestimmt ist.A continuous casting plant according to the invention for producing a continuous cast product, in particular wide slabs, with a thickness of the precursor D> 100 mm and a width of the precursor B = 2700 mm to 3500 mm at a casting speed of v _c <2 m / min, consisting of a formed by broad side walls and narrow side walls mold, wherein the inner dimensions of the mold at the level of the lateral outlet openings of the immersion nozzle substantially the dimensions of the precursor correspond to an input side projecting into the mold immersion nozzle with opposite outlet openings and a reservoir for the melt, and arranged on the output side of the mold Devices for stripping, guiding and cooling of the partially solidified in the mold, a liquid core and a solidified strand shell having precursor is characterized in that the immersion nozzle opposite each other, in the Betriebsstellun g to the narrow side walls of the mold towards oriented outlet openings, and the width (b) of the immersion nozzle and the height (h) of the lateral outlet opening of the immersion nozzle in relation to a certain width-thickness ratio of the precursor or the mold are set so that the conditions $$\frac{H}{B}=\frac{9}{5}\psi +\frac{1}{5}\frac{D}{B}$$

and $$\frac{b}{H}=1.9-2.0$$

are met and a speed of the melt in the core cross-section of the immersion nozzle (v _k ) to the casting speed (v _c ) in relation ratio ψ after the condition $\psi =0.1\cdot {\left(\frac{B}{D}\right)}^{-0.7}$

is determined.

vorzugsweise ein Breiten-Dicken-Verhältnis $\frac{B}{D}$

von etwa 20, aufweist.A continuous casting plant of this type is particularly suitable when the precursor has a width-to-thickness ratio $\frac{B}{D}=15-25.$

preferably a width-to-thickness ratio $\frac{B}{D}$

of about 20.

To achieve an optimal beam exit angle of the inner bottom of the immersion nozzle is formed from the immersion nozzle center to the outlet opening in the casting direction inclined. Particularly favorable conditions arise when the inclination of the inner bottom of the immersion nozzle 10 ° to 20 °, preferably about 15 °.

Thus, the tendency to form a swirl-free exit jet is significantly enhanced. At the immersion nozzle only two, substantially rectangular-shaped outlet openings are arranged.

Fig. 1

schematische Darstellung der Kokillenströmung bei Verwendung eines Tauchausgusses in der Kokille einer Stranggießanlage nach dem Stand der Technik,

Fig. 2

schematische Darstellung der Kokillenströmung bei Verwendung eines Tauchausgusses in der Kokille einer Stranggießanlage gemäß der Erfindung

Fig. 3a

Teil eines Längsschnitt durch den erfindungsgemäßen Tauchausguss,

Fig. 3b

schematischer Grundriss mit Kokille und Tauchausguss entlang der Schnittlinie A - A durch den Tauchausguss in Fig. 3a.

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

Fig. 1

schematic representation of the Kokillenströmung using a Tauchausgusses in the mold of a continuous casting machine according to the prior art,

Fig. 2

schematic representation of Kokillenströmung when using a Tauchausgusses in the mold of a continuous casting plant according to the invention

Fig. 3a

Part of a longitudinal section through the immersion nozzle according to the invention,

Fig. 3b

schematic plan view with mold and immersion nozzle along the section line A - A through the immersion nozzle in Fig. 3a.

Steel strand continuous casting plants for the production of wide slabs are well known, described in the literature and consist essentially of an intermediate vessel for receiving the molten steel, from which the melt is transferred via a submersible nozzle in an oscillating mold. From the mold a teilerstarrter cast steel strand is discharged vertically down and cooled in a subsequent strand guide and deflected in a horizontal direction. Subsequently, the solidified cast strand is cut with a flame cutting machine in slabs, which are then fed to a further treatment.

The molding of the cast strand takes place in an oscillating continuous casting mold 1, which, as shown schematically in Fig. 3b, of opposite broad side walls 2, 3 and between these clamped arranged narrow side walls 4, 5 is formed, wherein the narrow side walls 4, 5 for setting different strand widths (B) are displaceable transversely to the casting direction. The inner surfaces of these walls form a format-defining space for the formation of a semi-solid cast strand, which is discharged as precursor from the mold.

The invention is limited to a process for producing a precursor having a width B of 2700 to 3500 mm and a thickness D> 100 mm and to a continuous casting plant with a mold having these cross-sectional dimensions. In the mold itself, the cast strand undergoes no significant deformation.

The melt to be cast is introduced into the continuous casting mold 1 from a reservoir, not shown, but notoriously known in such casting plants via a dip nozzle 6 below the formed by the melt in the mold bath mirror 7 by lateral, directed to the narrow side walls 4, 5 outlet openings 8 , The melt flows through the immersion nozzle 6 in the vertical direction, which corresponds to the casting direction in the mold at the speed v _k and is in the range the closed inner bottom 9 of the immersion nozzle 6 is deflected to the lateral outlet openings 8 and exits through this into the mold space. The inner bottom 9 is formed starting from its center to the outlet opening 8 in the casting direction inclined. This inclination and the height (h) of the lateral outlet opening 8 determine the direction (the angle) of the exiting melt and thus influence the flow formation. The immersion nozzle thickness (d) is essentially determined by the thickness of the precursor (D). The width (B) and the thickness (D) of the precursor are determined by the production specifications. It follows that the width (b) of the immersion nozzle, the height (h) of the lateral outlet opening of the immersion nozzle and the dimensionless number ψ, which essentially the ratio of casting speed v _c and the velocity v _{k of} the liquid steel in the immersion nozzle (Core cross-section) describes, are freely selectable.

The value ψ in connection with the immersion nozzle geometry determines the melt velocity in the immersion nozzle outlet cross-section and is thus decisive for the quality of the mold flow. When casting medium-thick and wide slabs (width-to-thickness ratio of about 20), Tauch values of 0.006 to 0.008 are achieved with conventional immersion nozzles. Investigations have shown that G values of 0.011 to 0.015 must be achieved for casting over-wide cast strands with the same width-thickness ratio. For lower speeds in the immersion nozzle are necessary, which are achieved by large core and outlet cross-sections.

$\mathrm{\psi }=0,006-0,008$

$\mathrm{\psi }=0,011-0,015$

$\frac{D}{B}=0.0628$

$\frac{h}{B}=0,023-0,026$

$\frac{h}{B}=0,032-0,040$

$\frac{B}{D}=16$

$\mathrm{h}=58-67\mathrm{\hspace{0.17em}}\mathrm{mm}$

$\mathrm{h}=81-99\mathrm{\hspace{0.17em}}\mathrm{mm}$

$\mathrm{B}=3000\mathrm{\hspace{0.17em}}\mathrm{mm}$

$\mathrm{\psi }=0,006-0,008$

$\mathrm{\psi }=0,011-0,015$

$\frac{D}{B}=0.052$

$\frac{h}{B}=0,021-0,025$

$\frac{h}{B}=0,030-0,037$

$\frac{B}{D}=20$

$\mathrm{h}=63-75\mathrm{\hspace{0.17em}}\mathrm{mm}$

$\mathrm{h}=91-112\mathrm{\hspace{0.17em}}\mathrm{mm}$

Table 1 below illustrates these ratios for an exemplarily selected precursor thickness D = 157 mm with precursor widths of B = 2500 mm and B = 3000 mm. The immersion nozzles according to the invention are characterized by the greater height h of the lateral outlet openings 8. Table 1 konventionellerTauchausguss erfindungsgemäßertauchausguss $\mathrm{B}=2500\mathrm{}\mathrm{mm}$

$\mathrm{\psi }=0.006-0.008$

$\mathrm{\psi }=0.011-0.015$

$\frac{D}{B}=0.0628$

$\frac{H}{B}=0.023-0.026$

$\frac{H}{B}=0.032-0.040$

$\frac{B}{D}=16$

$\mathrm{H}=58-67\mathrm{}\mathrm{mm}$

$\mathrm{H}=81-99\mathrm{}\mathrm{mm}$

$\mathrm{B}=3000\mathrm{}\mathrm{mm}$

$\mathrm{\psi }=0.006-0.008$

$\mathrm{\psi }=0.011-0.015$

$\frac{D}{B}=0052$

$\frac{H}{B}=0.021-0.025$

$\frac{H}{B}=0.030-0.037$

$\frac{B}{D}=20$

$\mathrm{H}=63-75\mathrm{}\mathrm{mm}$

$\mathrm{H}=91-112\mathrm{}\mathrm{mm}$

Fig. 1 shows a schematic representation of the formation of Kokillenströmung based on a flow thread when using a conventional immersion nozzle, wherein the exit jet in the area between immersion nozzle 6 and mold narrow side wall 4 meets the bath surface and is divided there into two partial beams. In contrast, FIG. 2 shows the flow pattern with a diving nozzle according to the invention, in which the flow is divided into two partial streams only in the area of the narrow side wall 4 and forms two approximately circular vortices.

Claims (10)

1. A process for producing a continuously cast primary product, in particular broad slabs, having a thickness of the primary product D>100 mm and a width of the primary product B = 2700 mm to 3500 mm at a casting rate v_c<2 m/min in a continuous-casting plant, in which molten material, preferably molten steel, from a reservoir is introduced via a submerged nozzle through opposite outlet openings into a permanent mold, which is formed by wide side walls and narrow side walls, and the primary product, which has partially solidified in the permanent mold and has a liquid core and a solidified strand shell, is continuously withdrawn from the permanent mold and cooled, characterized in that the molten material leaves the submerged nozzle with a momentum which is directed toward the narrow side walls of the permanent mold, and for a defined width:thickness ratio of the primary product, as a function of the ratio of the velocity of the molten material in the core cross section of the submerged nozzle (v_k) to the casting rate (v_c), design values for the width (b) of the submerged nozzle and the height (h) of the lateral outlet opening of the submerged nozzle are selected in such a way that a uniform strand shell is formed in the casting direction and peripheral direction along the wide side walls and narrow side walls of the permanent mold.
2. The process as claimed in claim 1, characterized in that the submerged nozzle in relation to the permanent mold satisfies the following conditions $$\frac{\mathrm{h}}{\mathrm{B}}=\frac{9}{5}\mathrm{\psi }+\frac{1}{5}\frac{\mathrm{D}}{\mathrm{B}}$$

   

   
   and $$\frac{\mathrm{b}}{\mathrm{h}}=1.9-2.0$$

   

   
   and a numerical ratio ψ, which sets the relationship of the velocity of the molten material in the core cross section of the submerged nozzle (v_k) to the casting rate (v_c), is determined according to the following condition $\mathrm{\psi }=0.1{\left(\frac{\mathrm{B}}{\mathrm{D}}\right)}^{-0.7}$

   

   
   in which: B = width of the primary product (mm)
   D = thickness of the primary product (mm)
   b = width of the submerged nozzle (mm)
   h = height of the lateral outlet opening of the submerged nozzle (mm)
   ψ = numerical ratio (no dimensions).
3. The process as claimed in claim 1 or 2, characterized in that the primary product has a width:thickness ratio $\frac{\mathrm{B}}{\mathrm{D}}=15-25$

   
4. The process as claimed in claim 1 or 2, characterized in that the primary product has a width:thickness ratio $\frac{\mathrm{B}}{\mathrm{D}}$

   

   of approximately 20.
5. The process as claimed in one of claims 1 to 4, characterized in that the casting rate v_c is set to between 0.5 m/min and 1.5 m/min.
6. A continuous-casting plant for producing a continuously cast primary product, in particular broad slaps, having a thickness of the primary product D>100 mm and a width of the primary product B = 2700 mm to 3500 mm at a casting rate of v_c<2 m/min, comprising a permanent mold (1), wherein the internal dimensions of the permanent mold at the level of the lateral outlet openings of the submerged nozzle substantially correspond to the dimensions of the primary product, which is formed by wide side walls (2, 3) and narrow side walls (4, 5), a submerged nozzle (6) which projects into the permanent mold on the entry side through opposite outlet openings (8) and a reservoir for the molten material, and also devices which are arranged on the exit side of the permanent mold for withdrawing, guiding and cooling the primary product, which has partially solidified in the permanent mold and has a liquid core and a solidified strand shell, characterized in that the submerged nozzle includes outlet openings (8) which lie opposite one another and in the operating position are directed toward the narrow side walls (4, 5) of the permanent mold, and the width (b) of the submerged nozzle and the height (h) of the lateral outlet opening of the submerged nozzle are fixed in relation to a defined width:thickness ratio of the primary product or the permanent mold in such a way that the following conditions $$\frac{\mathrm{h}}{\mathrm{B}}=\frac{9}{5}\mathrm{\psi }+\frac{1}{5}\frac{\mathrm{D}}{\mathrm{B}}$$

   

   
   and $$\frac{\mathrm{b}}{\mathrm{h}}=1.9-2.0$$

   

   
   are fulfilled and a numerical ratio ψ which sets the relationship between the velocity of the molten material in the core cross section of the submerged nozzle (v_k) to the casting rate (v_c) is determined according to the following condition $\mathrm{\psi }=0.1{\left(\frac{\mathrm{B}}{\mathrm{D}}\right)}^{-0.7}$

   

   
   in which: B = width of the primary product or of the permanent mold (mm)
   D = thickness of the primary product or of the permanent mold (mm)
   b = width of the submerged nozzle (mm)
   h = height of the lateral outlet opening of the submerged nozzle (mm)
   ψ = numerical ratio (no dimensions).
7. The continuous-casting plant as claimed in claim 6, characterized in that the primary product or the permanent mold has a width:thickness ratio $\frac{\mathrm{B}}{\mathrm{D}}=15-25.$

   
8. The continuous-casting plant as claimed in claim 6, characterized in that the primary product or the permanent mold has a width:thickness ratio $\frac{\mathrm{B}}{\mathrm{D}}$

   

   of approximately 20.
9. The continuous-casting plant as claimed in one of claims 6 to 8, characterized in that the inner base (9) of the submerged nozzle is designed to be inclined from the center of the submerged nozzle toward the outlet opening (8) in the casting direction.
10. The continuous-casting plant as claimed in claim 9, characterized in that the inclination of the inner base (9) of the submerged nozzle is from 10° to 20°, preferably approximately 15°.

Images