EP3441157A1 - Method and apparatus for cintinuous casting of a metallic product - Google Patents

Abstract

The invention relates to processes for continuous casting of a metallic product (11), and to a corresponding continuous casting plant (10). Here, a strand (S) of the metallic product (11) emerges continuously from a mold (12), and is subsequently transported along a strand guide (14) in a conveying direction (F). The strand (S) is deflected in a directional region (I) in the horizontal direction, wherein the edge regions (R) of the strand (S) within a lower cooling section (16) of the strand guide (14) cooled less than compared to a horizontal region (18) of the strand guide (14) which lies in the conveying direction (F) after the straightening region (I). The edge regions (R) of the strand (S) are cooled in an intensive cooling section (20) of the strand guide (14) at least as strong as a central region (M) of the strand (S).

Description

The invention relates to a method for the continuous casting of a metallic product according to the preamble of claim 1, and to a corresponding continuous casting plant according to the preamble of claim 11.

In the production of metallic products in a continuous casting plant, the liquid metal is poured continuously in a mold, where it forms a first strand shell. As a rule, the strand emerges downwards from the mold, wherein the strand is subsequently transported along a strand guide and transferred into a bending radius in a so-called bending region, in order thereby to achieve a deflection of the strand in the direction of the horizontal. In a circular arc, the curvature of the strand already begins in the mold, in which case the bending range is eliminated. The strand guide further includes a so-called straightening region, in which the strand is then completely deflected in the horizontal direction. In this straightening area, strains occur on an upper side (loose side) of the strand, which can lead to cracks or surface cross cracks.

The importance of optimal cooling in the continuous casting of a metallic product after the extrusion of the strand from the mold is well known in the art, for example EP 2 718 042 B1 . WO 2016/012131 A1 or EP 1 937 429 B1 ,

One problem in continuous casting is that for the strand, in particular in the directional region of the strand guide as a result of the curvatures generated there strains occur, which can lead to cracks in the strand or on its surface. This is in the Fig. 7 clarifies that a simplified Side view of a continuous casting plant shows. Herein, the position of increased risk of cracking is exemplified.

In order to avoid the problem of increased risk of cracking explained above, an approach is followed according to which the surface temperature of the strand is kept above the critical ductility temperature of the metal or continuously cast material. This is usually possible on the strand center and for a conventional continuous casting in Fig. 7 shown, wherein along the strand guide a uniform cooling over the entire strand width set and in Fig. 7 symbolized by corresponding arrows. However, this approach is subject to certain restrictions, because the temperature of the strand must not be too high, so that the strand in its core before the end of the continuous casting, ie, for example, before a pair of scissors, must be completely solidified. In addition, the strand after exiting the mold must be sufficiently cooled to achieve a sufficiently thick strand shell, otherwise the strand between the support rollers of the strand guide would bulge too much and thereby internal defects would occur.

In general, the strand during continuous casting by the two-dimensional heat radiation cooled at its edges more than in the middle of the strand. This implies the danger of edge cracks. Lower cooling of the strand at its edges attempts to counteract this effect. Accordingly, in a conventional continuous casting according to Fig. 8 the amount of spray water in the edge regions of the strand - compared to an area in the middle of the strand - reduced, which then leads to less cooling in the edge regions and consequently to the generation of higher edge temperatures. Such a reduced cooling of the edge regions of the strand takes place in a so-called Fig. 8 is indicated and in the conveying direction of the strand in particular in front of the straightening area I, and possibly also within the straightening, is. Only after the short cooling section or the straightening area I is the strand then again cooled evenly over the entire strand width (also in Fig. 8 indicated).

With the provision of a minimum cooling section, as explained above, an increase in the surface temperature occurs in the region of the strand near the edge. This can disadvantageously lead to an uneven sump tip over the strand width. Such a non-uniform sump tip can take a difference in length of, for example, 1.5 m, which is in Fig. 9 is schematically illustrated with the route d _swamp . Such a non-uniform sump tip is disadvantageous when performing a soft reduction and results in generation of internal cracks in the strand.

Accordingly, the object of the invention is to achieve a uniform sump tip over the strand width during the continuous casting of a metallic product, without the edge temperature dropping below the critical temperature determined by the course of the ductility curve.

The above object is achieved by a method for continuous casting of a metallic product having the features specified in claim 1, and by a continuous casting machine having the features defined in claim 11. Advantageous developments of the invention are defined in the dependent claims.

The invention provides a method for continuous casting of a metallic product in which a strand of the metallic product emerges continuously from a mold, in particular vertically downwards, in a continuous casting plant and is subsequently transported along a strand guide in a conveying direction. Here, the strand is deflected in a directional region in the horizontal direction, wherein the edge regions of the strand within a Minderkühlabschnitts which is provided at least in the conveying direction before the straightening region and preferably also within the straightening region, reduced be cooled as compared to a horizontal region of the strand guide, which lies in the conveying direction after the straightening area. The edge regions of the strand are cooled at least as strongly as a central region of the strand in an intensive cooling section of the strand guide, which starts immediately after the strand emerges from the mold and lies in the conveying direction before the minor cooling section. By such a cooling strategy is achieved that a substantially uniform sump length is formed, which has a positive effect, for example, when performing a Softreduktion.

The invention also provides a continuous casting plant which serves to produce a metallic product. This continuous casting plant comprises a mold, and a strand guide adjoining the mold, along which a strand issuing from the mold, in particular vertically downwards, can be transported in a conveying direction. The strand guide has a straightening area, through which the strand can be deflected in the horizontal direction. Furthermore, the strand guide has an at least in the conveying direction in front of the straightening area provided on the cooling section, in which the edge regions of the strand are cooled less than compared to a horizontal region of the strand guide, which lies in the conveying direction after the straightening. Preferably, the minimum cooling section can also be provided within the straightening area. Immediately after the strand has emerged from the mold, the strand guide has an intensive cooling section lying in the conveying direction in front of the minor cooling section, in which the edge regions of the strand can be cooled at least as strongly as a central region of the strand.

Basically, it is known in the field of continuous casting of metallic products that is responsible for the formation of the swamp length mainly the cooling of the strand directly after its exit from the mold. Here, the strand shell is still very thin, so that the cooling effect also affects the still liquid strand core. Taking this into account, the invention is thus based on the essential knowledge that in the Intensive cooling section, the edge regions of the strand are cooled at least as strong as the central region, so that this type of cooling completely affects the liquid strand core, and thus the formation of a desired uniform or uniform Sumpfspitze the strand across its width. In other words, by setting a uniform specific amount of spray water over the strand width or by increasing the edge cooling within the intensive cooling section, the length difference in the sump tip over the strand width is at least reduced. Accordingly, over the strand width uniform bottom tip is realized for the strand. Overall, the above-described cooling strategy takes place in any case while maintaining the condition that the minimum temperature determined by the ductility curve is not undershot along the entire length of the strand guide, and thus also within or along the intensive cooling section.

In an advantageous embodiment of the invention, the intensive cooling section, in which the edge regions of the strand are cooled at least as strong as the central region of the strand, be provided within a first third of the length of the continuous casting, calculated from the Kokillenaustritt the strand. Subsequent to the intensive cooling section, the cooling of the edge regions of the strand is then reduced or reduced in the minor cooling section. This ensures that the temperature of the strand does not fall below the critical temperature determined by the ductility curve even in its edge regions or near-edge zones. This is especially true for those areas of the strand where additional stresses occur, e.g. in the bending area and / or in the straightening area. As a result, according to the invention, the formation of possible surface cracks in the strand is avoided even in the minor cooling section of the strand guide.

In an advantageous embodiment of the invention, the edge regions of the strand are cooled more than within the intensive cooling section of the strand guide the central area of the strand. This can be conveniently achieved in that the specific amounts of water in the edge control loops are higher than the amounts of water, which is applied to the central region of the strand. This leads to the advantage that in the region of the intensive cooling section of the strand guide, a difference in length in the sump tip of the strand over its width is further reduced in order to achieve a (possibly) uniform sump tip.

Taking into account the arrangement of the intensive cooling section and the minor cooling section, namely - consecutively seen in the conveying direction of the strand, it is important for the present invention that a temperature rise for the strand between these two cooling sections does not become too high. For this purpose, according to the invention, and preferably in compliance with the proviso that within the intensive cooling section, the temperature in the edge regions of the strand corresponds to a minimum allowable edge temperature or is always greater than this, a so-called rewarming factor WEF [° C / (mm * sec )], which is determined as follows: $$\mathrm{WEF}={\mathrm{Difference\; between\; the\; <figure-callout\; id="1"\; label="temperature\; T"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">temperature\; T</figure-callout>}}_1{\mathrm{at\; a\; first\; <figure-callout\; id="1"\; label="measuring\; point\; P"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">measuring\; point\; P</figure-callout>}}_1{\mathrm{and\; the\; <figure-callout\; id="2"\; label="temperature\; T"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">temperature\; T</figure-callout>}}_2{\mathrm{at\; a\; second\; <figure-callout\; id="2"\; label="measuring\; point\; P"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">measuring\; point\; P</figure-callout>}}_2/{\mathrm{average\; thickness\; of\; the\; strand\; shell\; at\; the\; <figure-callout\; id="1"\; label="measuring\; points\; P"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">measuring\; points\; P</figure-callout>}}_1{\mathrm{and\; <figure-callout\; id="2"\; label="P"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">P</figure-callout>}}_2/{\mathrm{Transport\; time\; of\; the\; strand\; between\; the\; <figure-callout\; id="1"\; label="measuring\; points\; P"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">measuring\; points\; P</figure-callout>}}_1{\mathrm{and\; <figure-callout\; id="2"\; label="P"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{,}$$

P₁:

Ende der letzten Kühlzone des Intensivkühlabschnitts, jedenfalls zumindest ein Messpunkt innerhalb des Intensivkühlabschnitts,

T₁:

mittlere Strangschalentemperatur an dem ersten Messpunkt P₁,

P₂:

Ende der ersten Kühlzone des Minderkühlabschnitts, jedenfalls zumindest ein Messpunkt innerhalb des Minderkühlabschnitts, und

T₂:

mittlere Strangschalentemperatur an dem zweiten Messpunkt P₂.

Here are, for example:

P ₁ :

End of the last cooling zone of the intensive cooling section, in any case at least one measuring point within the intensive cooling section,

T ₁ :

average strand shell temperature at the first measuring point P ₁ ,

P ₂ :

End of the first cooling zone of the lower cooling section, in any case at least one measuring point within the lower cooling section, and

T ₂ :

mean strand shell temperature at the second measuring point P ₂ .

• Die Temperatur an der Strangkante bzw. in den Randbereichen des Stranges liegt nicht unter der durch den Duktilitätsverlauf vorgegebenen kritischen Temperatur;
• Die Sumpfspitze besitzt keine oder eine möglichst gering ausgeprägte W - Form über der Strangbreite; und
• Der Temperaturanstieg zwischen der letzten Kantendüse (d.h. an dem ersten Messpunkt P₁ innerhalb des Intensivkühlabschnitts) und der ersten Zone ohne Kantendüsen (d.h. an dem zweiten Messpunkt P₂ innerhalb des Minderkühlabschnitts) darf nicht zu hoch sein, bzw. den zulässigen maximalen Wiedererwärmungsfaktor WEF_max nicht überschreiten.

To calculate the strand temperatures T ₁ and T ₂ and the strand shell thicknesses at the measurement points P ₁ and P ₂ and the associated sump tip positions, a mathematical-physical calculation model is used. A rewarming factor WEF determined or measured in this way is then compared with a maximum rewarming factor WEF _max , which is material-dependent and has been determined in advance. As long as the currently measured rewarming factor WEF is _currently smaller than the maximum rewarming factor WEF _max , the cooling of the edge regions of the strand is reinforced in at least one cooling zone of the intensive cooling section, eg by adding additional cooling nozzles in the edge region of the strand and / or by increasing the set coolant flow with which the strand is acted upon or cooled in its edge regions. Both of these variants, ie the connection of additional cooling nozzles or the increase of the associated amount of coolant (eg spray water), always takes place in compliance with or compliance with the following aspects:

• The temperature at the edge of the strand or in the edge regions of the strand is not below the critical temperature given by the course of the ductility;
• The sump tip has no or as little as possible W - shape over the strand width; and
• The temperature increase between the last edge nozzle (ie at the first measuring point P ₁ within the intensive cooling section) and the first zone without edge nozzles (ie at the second measuring point P ₂ within the minor cooling section) must not be too high, or the maximum permissible rewarming factor WEF _max do not exceed.

In addition, it can be provided for the above two variants for enhancing the cooling in the edge regions of the strand, that the respective current position or position of the sump tip is checked or taken into account. For this a calculation of the sump length profile over the strand width is made. If it is determined on the basis of this calculation that the computed sump tip difference is too high in comparison to a predetermined maximum sump tip difference, which represents an allowed upper limit, then the cooling in the edge regions of the strand is amplified according to one of the two variants mentioned. Otherwise, namely, in the event that the detected sump tip difference should not be too high, the cooling in the intensive cooling section is not further enhanced.

In an advantageous embodiment of the invention, the intensive cooling section comprises at least one cooling zone with additional cooling nozzles, which are associated with an edge region of the strand and can be switched on to reinforce the cooling of the edge regions of the strand.

• Fig. 1, Fig. 2 jeweils eine Seitenansicht einer erfindungsgemäßen Stranggießanlage,
• Fig. 3 eine Darstellung des Sumpfspitzenverlaufen (A) sowie des Temperaturverlaufes nach dem Intensivkühlbereich (B) und des Temperaturverlaufes nach dem Minderkühlabschnitt (C),
• Fig. 4, Fig. 5 jeweils Ablaufdiagramme zur Optimierung einer Kühlung innerhalb des Intensivkühlabschnitts der Stranggießanlage von Fig. 1, und
• Fig. 6 eine Draufsicht auf Kühlzonen innerhalb des Intensivkühlabschnitts einer Stranggießanlage von Fig. 1.

Hereinafter, preferred embodiments of the invention with reference to a schematically simplified drawing are described in detail. Show it:

• Fig. 1 . Fig. 2 each a side view of a continuous casting plant according to the invention,
• Fig. 3 a representation of the Sumpfspitzenverläufe (A) and the temperature profile after the intensive cooling area (B) and the temperature profile after the Minor cooling section (C),
• Fig. 4 . Fig. 5 each flowchart for optimizing cooling within the intensive cooling section of the continuous casting of Fig. 1 , and
• Fig. 6 a plan view of cooling zones within the intensive cooling section of a continuous casting of Fig. 1 ,

In Fig. 1 is a continuous casting 10 according to the invention shown in principle simplified in a side view. The continuous caster 10 is used to produce a metallic product 11, and for this purpose comprises a mold 12 and an adjoining strand guide 14, along which one of the mold 12 preferably downwardly emerging strand S of the metallic product 11 is transported in a conveying direction F. Below the mold 12, and on both sides of the strand S, a plurality of support rollers 2 are arranged, wherein spray water 4 is sprayed onto the strand S, for the purpose of cooling the bar S. At the point where in Fig. 1 the strand S is marked with the reference line "5", the strand still has a liquid sump. The sump tip of the strand S is indicated by the reference numeral "6". Downstream of this, the strand S is completely solidified, eg at the in Fig. 1 with the reference line "11d" marked position. Downstream thereof, a water cooling is also provided along the strand guide 14, which is marked with the reference line "8".

The strand guide 14 of the continuous caster 10 comprises a straightening region I, by means of which the strand S is completely deflected in the horizontal direction. Furthermore, the strand guide 14 comprises a bending region II, through which the strand S, after it has emerged from the mold 12, is deflected in the direction of the horizontal. The straightening area I and the bending area II are shown in FIG Fig. 1 each simplified symbolized by dashed rectangles.

The conveying direction in which the strand S is transported along the strand guide 14 of the continuous casting plant 10 is shown in FIG Fig. 1 denoted by "F". The strand guide 14 comprises a minimum cooling section 16 which, viewed in the conveying direction F of the strand S, lies upstream or in front of a horizontal region 18 of the strand guide 14. The minor cooling section 16 can be designed such that it detects the straightening region I at least partially or completely. The minimum cooling section 16 of the strand guide 14 is characterized in that the cooling zones provided therein are designed such that the edge regions of the strand S are cooled in a reduced manner compared to the horizontal region 18 of the strand guide 14.

An essential feature of the continuous caster 10 is that the strand guide 14 has an intensive cooling section 20, which begins immediately after the emergence of the strand S from the mold 12 and - as in Fig. 1 illustrated - in the conveying direction F seen before the minor cooling section 16 is located. The intensive cooling section 20 is formed with at least one cooling zone provided therein such that the edge regions of the strand S are cooled at least as strongly as a central region of the strand S.

Fig. 2 shows the continuous caster 10 of Fig. 1 again in a simplified side view. Herein, the longitudinal extensions of the lower cooling section 16 and the intensive cooling section 20 along the strand guide 14 of the continuous casting installation 10 are illustrated. In detail, the length of the intensive cooling section 20 is denoted by "L ₂₀ ", wherein this length may amount to about one third of the length L _{10 of} the continuous caster 10. For this case, the intensive cooling section 20 is provided within a first third of the length L _{10 of} the continuous caster 10, starting from the exit of the strand S from the mold 12. A length of the minor cooling section 16 is shown in FIG Fig. 2 denoted by "L ₁₆ ". Furthermore, by the Fig. 2 illustrates that the intensive cooling section 20 - seen in the conveying direction F of the strand S - is provided in front of the lower cooling section 16 and upstream thereof, wherein the intensive cooling section 20 begins immediately after Kokillenaustritt or a Gießspiegelnahen area.

Due to the aforementioned intensive cooling of the edge regions of the strand S in the intensive cooling section 20, which also influences the still liquid strand core because of the still very thin strand shell, it is achieved according to the invention that the difference in length in the sump tip is advantageously reduced in comparison to the prior art , This is in the presentation of Fig. 3 with the curve "A" showing a course of the sump tip 6 over the strand width. Here, the length difference d is the _swamp , which is a measure of the unevenness of the swamp tip, for example only about 150 mm. Thus, by means of the invention, a substantially uniform or uniform sump tip over the strand width is achieved without the edge temperature dropping below the critical temperature determined by the ductility profile. In any case, the realized by the present invention length difference d _sump is substantially smaller than in the prior art, the as initially on the basis of Fig. 9 explained may be 1.5 m.

How out Fig. 3 Further, the temperature profile after the intensive cooling section (B) is not constant over the strand width. In the edge area, the temperature is lower than in the center of the strand. Due to the reduced cooling of the edge region in the subsequent so-called. Minderkühlabschnitt the temperature difference largely compensates and the temperature profile after the minimum cooling section (C) over the strand width is substantially constant.

In operation of the continuous casting 10 according to the invention or in carrying out a corresponding method for continuous casting of a metallic product 11 is between the intensive cooling section 20, in which the edge regions of the strand S subjected to increased edge cooling, and the Minor cooling section 16, in which a reduced coolant for the edge regions of the strand S is provided, a temperature rise. It is important for the invention that such a temperature rise is not too high. An excessive and too rapid rise of the already solidified material of the strand S can otherwise lead to internal cracks.

The maintenance of a not too high temperature increase between the intensive cooling section 20 and the minimum cooling section 16 is ensured according to the invention by the formation of a reheating factor WEF [° C / (mm * sec)]. Such a reheating factor WEF is determined by the quotient of the difference between a temperature T ₁ at a first measuring point P ₁ and a temperature T ₂ at a second measuring point P ₂ , the average thickness of the strand shell at the measuring points P ₁ and P ₂ , and Transport time of the strand S between the measuring points P ₁ and P ₂ . Accordingly, the unit for reheating factor WEF is determined to be [° C / (mm * sec)]. In this regard, it is understood that the first measuring point P _{1 is arranged} in a cooling zone within the intensive cooling section 20, the second measuring point P _{2 being arranged} in a cooling zone within the minor cooling section 16. For example, the first measuring point P _{1 is located} at the end of the last cooling zone of the intensive cooling section 20 (with reinforced edge cooling), the second measuring point P _{2 being} located at the end of the first cooling zone of the minor cooling section 16 (with reduced edge cooling). The temperatures T ₁ and T ₂ are the average strand shell temperatures at the measuring points P ₁ and P ₂ . To calculate the strand temperatures T ₁ , T ₂ , the sump tip positions and the strand shell thicknesses, a mathematical-physical calculation model is used.

A position of the first and second measuring points along the strand guide 14 is shown in FIG Fig. 1 simplified with the designations "P ₁ " and "P ₂ " indicated.

Using the measurement points P ₁ and P ₂ explained above, when performing a method according to the present invention, a current reheat factor is first determined or calculated, namely using the following relationship: $$\mathrm{WEF}={\mathrm{Difference\; between\; a\; <figure-callout\; id="1"\; label="temperature\; T"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">temperature\; T</figure-callout>}}_{\mathrm{1}}{\mathrm{at\; the\; first\; <figure-callout\; id="1"\; label="measuring\; point\; P"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">measuring\; point\; P</figure-callout>}}_{\mathrm{1}}{\mathrm{and\; a\; <figure-callout\; id="2"\; label="temperature\; T"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">temperature\; T</figure-callout>}}_{\mathrm{2}}{\mathrm{at\; the\; second\; <figure-callout\; id="2"\; label="measuring\; point\; P"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">measuring\; point\; P</figure-callout>}}_{\mathrm{2}}/{\mathrm{average\; thickness\; of\; the\; strand\; shell\; at\; the\; measuring\; <figure-callout\; id="1"\; label="points\; P"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">points\; P</figure-callout>}}_{\mathrm{1}}{\mathrm{and\; <figure-callout\; id="2"\; label="P"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{2}}/\mathrm{Transport\; time\; of\; the\; strand}\left(\mathrm{S}\right){\mathrm{between\; the\; measuring\; <figure-callout\; id="1"\; label="points\; P"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">points\; P</figure-callout>}}_{\mathrm{1}}{\mathrm{and\; <figure-callout\; id="2"\; label="P"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{2}}\mathrm{,}$$

Following this, the current reheating factor WEF is then compared to a _currently permissible maximum reheating factor WEF _max, the depends on the material and is determined in advance. Depending on the comparison between WEF _actual and WEF _max , the cooling of the edge regions of the strand S within the intensive cooling section 20 can then be intensified, which is explained in detail below with reference to the flow diagrams:
The flowchart of Fig. 4 illustrates an optimization of the amount of coolant, preferably in the form of spray, with which the strand S is cooled in its edge regions. With the aid of a mathematical-physical calculation model, all relevant temperatures of the strand S are calculated, in this case, inter alia, the edge temperatures of the strand S, ie the temperature of the strand S in its edge regions. Then it is checked whether, before the straightening range I or within the straightening range I, the edge temperature thus calculated is greater than a minimum allowable edge temperature T _{edge target} . If this is not the case, the cooling in the intensive cooling section 20 is not amplified, so that no further minimization of the sump tip difference is possible. This is because of the proviso that the edge temperature should not fall below the critical temperature determined by the ductility _curve, referred to above as T _{edge target} . If, on the other hand, the calculated edge temperature should be greater than the minimum permissible edge temperature T _{edge target} , the strand _{shell temperatures} T ₁ and T ₂ at the measurement points P ₁ and P ₂ and the average strand shell thickness between these measurement points are calculated using the mathematical-physical calculation model also determines the transport time of the strand S between the measuring points P ₁ and P ₂ . Taking into account the values thus calculated or determined, the actual reheating factor WEF is then _actually determined on the basis of the above equation.

In a next step, the value of the current rewarming factor WEF is _currently compared with a permissible maximum rewarming factor WEF _max . If WEF is _currently greater than WEF _max , this is an indication that the temperature rise between the intensive cooling section 20 and the minimum cooling section 16 is already too large, so that the cooling in the intensive cooling section 20 is not amplified, or the amount of coolant used in this section is not increased. However, if the condition WEF _actual <WEF _max should be fulfilled, in a next step the sump length course over the strand width is calculated on the basis of a mathematical-physical calculation model. As a result, if it should turn out that the calculated sump peak difference is too high when compared with a predetermined maximum sump peak difference representing a permitted upper limit value, cooling in the intensive cooling section 20 can be appropriately enhanced by increasing the associated amount of refrigerant in At least one cooling zone of the intensive cooling section 20, preferably in all cooling zones of the intensive cooling section 20. In contrast, the cooling performance in the intensive cooling section 20 remains unchanged, if the calculated sump point difference for the strand S is not too high.

The flowchart according to Fig. 4 illustrates that the above-described sequence of steps is formed in the form of a control loop. Such a control circuit preferably detects all the cooling nozzles of the cooling zones, which are arranged within the intensive cooling section 20 in the edge regions of the strand S.

The flowchart of Fig. 5 illustrates a scheme for optimizing the nozzle assembly or the use of cooling nozzles in the edge regions of the strand S. As a starting point for the flowchart of Fig. 5 serves a mode of operation of the continuous casting 10, in which the edge regions or the edges of the strand S are not overspent. Then, using a mathematical-physical calculation model, the edge temperature of the strand S within the intensive cooling section 20 is calculated, followed by a query as to whether the calculated edge temperature is greater than a minimum edge temperature T _{edge target} before the directional region I or within the directional region _I. From this step, the flowchart corresponds to FIG. 5 essentially the logic of the flowchart of Fig. 4 so that reference may be made to avoid it.

The flowchart of Fig. 5 differs from the flowchart according to Fig. 4 solely in that, if the calculated sump tip difference should be classified as too high, then in at least one cooling zone of the intensive cooling section 20 additional cooling nozzles in the edge regions of the strand S are switched on. In this way, the cooling in the edge regions of the strand S is suitably reinforced.

Fig. 6 shows a schematically simplified plan view of cooling zones within the intensive cooling section 20 and the lower cooling section 16. The additional cooling nozzles, which according to the flowchart of Fig. 5 can be switched to strengthen the cooling of the edge regions of the strand S are in Fig. 6 denoted by "22". In addition, the edge regions of the strand S, in which these switchable cooling nozzles 22 are arranged, in Fig. 6 denoted by "R", wherein a central portion of the strand S is denoted by "M".

In the same way as in Fig. 4 is understood for the flowchart of Fig. 5 in that the associated sequence of steps is designed as a control loop. Thus, with a strengthening of the cooling in the edge regions R of the strand S is always ensured that possible process changes are detected in a timely manner. Accordingly, the temperature rise between the intensive cooling section 20 and the minor cooling section 16 remains moderate when the condition WEF _actual <WEF _{max is} met, at the same time the temperature at the strand edge or in the edge regions of the strand S is not below the predetermined by the ductility curve critical temperature T _{Edge target} falls.

The flowcharts of Fig. 4 and Fig. 5 and the determination of the current reheat factor WEF _currently carried out in this case relate, for example, to the first and second measuring points P ₁ , P ₂ , which in the Fig. 6 also symbolically indicated by arrows. This means that these measuring points are provided in individual cooling zones of the intensive cooling section 20 or the minimum cooling section 16. In view of this, the determination of the current reheating factor WEF _currently enables an evaluation of the temperature rise between the intensive cooling section 20 and the minor cooling section 16. In this connection, it is finally pointed out that the measuring points P ₁ and P _{2 are} also at different locations than in the illustration of FIG Fig. 1 and Fig. 6 can be provided indicated. Furthermore, a plurality of first measuring points P ₁ or of second measuring points P _{2 are also} possible, which are respectively provided within the intensive cooling section 20 and within the minimum cooling section 16.

LIST OF REFERENCE NUMBERS

2

Support roller (s)

4

Coolant, e.g. splash

5

Liquid swamp (Strand S)

6

crater tip

7

Steady part of the S S

8th

water cooling

10

continuous casting plant

11

Metallic product

12

mold

14

strand guide

16

Minor cooling section (strand guide 14)

18

Horizontal area (strand guide 14)

20

Intensive cooling section (the strand guide 14)

22

Additional (switchable) cooling nozzle (s)

F

Conveying direction (strand S)

I

Straightening range (strand guide 14)

II

Bending area (strand guide 14)

L ₁₀

Length of the continuous casting plant 10

L ₁₆

Length of the minimum cooling section 16

L ₂₀

Length of the intensive cooling section 20

M

Middle section (strand S)

P ₁

First measuring point (within the intensive cooling section 20)

P ₂

Second measuring point (within the lower cooling section 16)

R

Edge region (s) of the strand S

S

Strand (of the metallic product 11)

T ₁

Temperature at the first measuring point P ₁

T ₂

Temperature at the second measuring point P ₂

WEF _current

Current reheat factor

WEF _max

Permissible maximum reheating factor

Claims (15)

Method for continuous casting of a metallic product (11), wherein in a continuous casting plant (10) a strand (S) of the metallic product (11) emerges continuously from a mold (12), in particular vertically downwards, and then along a strand guide (14) a conveying direction (F) is transported, wherein the strand (S) in a directional region (I) is deflected in the horizontal direction, wherein the edge regions (R) of the strand (S) within a Minderkühlabschnitts (16) of the strand guide (14), which is provided at least in the conveying direction (F) in front of the straightening region (I) and preferably also within the straightening region (I) are cooled less than compared to a horizontal region (18) of the strand guide (14) in the conveying direction (F) after Straightening range (I),
characterized,
in that the edge regions (R) of the strand (S) begin in an intensive cooling section (20) of the strand guide (14) which starts immediately after the strand (S) leaves the mold (12) and in the conveying direction (F) in front of the minor cooling section (FIG. 16), be cooled at least as strong as a central region (M) of the strand (S). A method according to claim 1, characterized in that the intensive cooling section (20) within a first third of the length of the continuous casting plant (10) starting from the outlet of the strand (S) from the mold (12) is provided. A method according to claim 1 or 2, characterized in that within the intensive cooling section (20), the edge regions (R) of the Stranges (S) are cooled more than the central region (M) of the strand (S). A method according to claim 3, characterized in that within the intensive cooling section (20), the specific amounts of water in the edge control loops are higher than the amounts of water which are discharged to the central region (M) of the strand (S). Method according to one of the preceding claims, characterized in that the following steps are carried out using a first measuring point (P ₁ ) located within the intensive cooling section (20) and a second measuring point (P ₂ ) lying within the minimum cooling section: (i) determining a current reheat factor (WEF _actual ) using the relationship: $$\mathrm{WEF}={\mathrm{Difference\; between\; a\; temperature\; T}}_{\mathrm{1}}{\mathrm{at\; the\; first\; measuring\; point\; P}}_{\mathrm{1}}{\mathrm{and\; a\; temperature\; T}}_{\mathrm{2}}{\mathrm{at\; the\; second\; measuring\; point\; P}}_{\mathrm{2}}/{\mathrm{average\; thickness\; of\; the\; strand\; shell\; at\; the\; measuring\; points\; P}}_{\mathrm{1}}{\mathrm{and\; P}}_{\mathrm{2}}/\mathrm{Transport\; time\; of\; the\; strand}\left(\mathrm{S}\right){\mathrm{at\; the\; measuring\; points\; P}}_{\mathrm{1}}{\mathrm{and\; P}}_{\mathrm{2}}.$$

(ii) Comparison of the current reheating factor (WEF _actual ) with a maximum permissible rewarming factor (WEF _max ), and (iii) if (WEF _actual ) <(WEF _max ): boosting the cooling in the edge regions (R) of the strand (S) within the intensive cooling section (20). A method according to claim 5, characterized by a repetition of steps (i) to (iii), wherein according to step (iii) the cooling in the edge regions (R) of the strand (S) is amplified, as long as the condition WEF _actual <WEF _max is. A method according to claim 5 or 6, characterized in that when reinforcing the cooling according to step (iii) in at least one cooling zone of the intensive cooling section (20) further additional cooling nozzles in the edge regions (R) of the strand (S) are switched on. Method according to one of claims 5 to 7, characterized in that the reinforcing of the cooling according to step (iii) in at least one cooling zone of the intensive cooling section (20) on the strand (S) discharged coolant amount is increased. Method according to one of claims 5 to 8, characterized in that the steps (i) to (iii) are carried out, if before the straightening region (I) or within the straightening region (I) the temperature in the edge regions (R) of the strand ( S) is greater than a minimum permissible edge temperature (T _{edge target} ). Method according to one of claims 5 to 9, characterized in that a sump peak over the strand width is calculated, wherein the step (iii) is performed under the further condition that the calculated sump peak difference is greater than a predetermined maximum Sumpspitzendifferenz. Continuous casting plant (10) for producing a metallic product (11), comprising a mold (12), and a strand guide (14) adjoining the mold (12), along which a strand (S) emerging from the mold (12), in particular vertically downwards, can be transported in a conveying direction (F), wherein the strand guide (14) has a straightening region (14) I), by which the strand (S) can be deflected in the horizontal direction, wherein the strand guide (14) at least in the conveying direction (F) in front of the straightening region (I) and preferably also within the straightening region (I) provided at least cooling section (16 ), in which the edge regions (R) of the strand (S) can be cooled to a reduced extent compared to a horizontal region (18) of the strand guide (14) in the conveying direction (F) after the directional region (I), characterized,
that the strand guide (14) immediately after the exit of the strand (S) from the mold (12) comprises in the conveying direction (F) prior to reducing cooling section (16) lying intensive cooling section (20) in which the edge regions (R) of the strand ( S) are at least as strong coolable as a central region (M) of the strand (S). Continuous casting plant (10) according to claim 11, characterized in that the intensive cooling section (20) within a first third of the length of the continuous casting plant (10) starting from the outlet of the strand (S) from the mold (12) is formed. Continuous casting plant (10) according to claim 11 or 12, characterized in that within the intensive cooling section (20) at least one cooling zone is formed such that thus the edge regions (R) of the strand are more coolable than the central region (M) of the strand (S ). Continuous casting plant (10) according to claim 13, characterized in that within the intensive cooling section (20) at least one cooling zone is formed such that thus the specific amounts of water in the Edge control loops are higher than the amounts of water that can be discharged to the central region (M) of the strand (S). Continuous casting plant (10) according to claim 13, characterized in that within the intensive cooling section (20) at least one cooling zone with additional cooling nozzles (22) is provided which is associated with an edge region (R) of the strand (S) and for strengthening the cooling of the edge regions ( R) of the strand (S) are switchable.

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