EP3441157B1 - Method and apparatus for cintinuous casting of a metallic product - Google Patents

Description

The invention relates to a method for continuously casting a metallic product according to the preamble of claim 1.

During the production of metallic products in a continuous casting plant, the liquid metal is continuously cast in a mold, where a first strand shell is formed. As a rule, the strand emerges from the mold downwards, the strand then being transported along a strand guide and converted into a bending radius in a so-called bending area in order to achieve a deflection of the strand in the horizontal direction. In the case of a circular arc system, the curvature of the strand begins in the mold, with the bending area then being omitted. The strand guide also includes a so-called straightening area in which the strand is then completely deflected in the horizontal direction. In this straightening area, stretching occurs on an upper side (loose side) of the strand, which can lead to cracks or surface cracks.

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

One problem with continuous casting is that, as a result of the curvatures generated there, elongations occur for the strand, particularly in the straightening area of the strand guide, which can lead to cracks in the strand or on its surface. This is in the Fig. 7 illustrates, which shows a simplified side view of a continuous caster. The position of an increased risk of cracking is marked here by way of example.

In order to avoid the problem of an increased risk of cracking explained above, an approach is pursued according to the prior art, 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 in the middle of the strand and for a conventional continuous caster in Fig. 7 shown, with a uniform cooling set along the strand guide over the entire strand width and in Fig. 7 is symbolized by corresponding arrows. Nevertheless, 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 must be completely solidified in its core before the end of the continuous caster, ie for example in front of a pair of scissors. In addition, after exiting the mold, the strand must be cooled sufficiently in order to achieve a sufficiently thick strand shell, because otherwise the strand bulges too much between the support rollers of the strand guide and internal defects would occur as a result.

In general, during continuous casting, the two-dimensional thermal radiation cools the strand down more at its edges than in the center of the strand. This implies the risk of edge cracks. An attempt is made to counteract this effect by reducing the cooling of the strand at its edges. Accordingly, in a conventional continuous caster according to Fig. 8 the amount of spray water in the edge areas of the strand - compared to an area in the middle of the strand - is reduced, which then leads to less cooling in the edge areas and consequently to the generation of higher edge temperatures. Such reduced cooling of the edge areas of the strand takes place in a so-called reduced cooling section, which in the Fig. 8 is identified and in the conveying direction of the strand, especially in front of the straightening area I, and possibly also within the straightening area, lies. Only after the reduced cooling section or straightening area I is the strand cooled again evenly over the entire strand width (also in Fig. 8 marked).

If an undercooling section is provided - as explained above - there is an increase in the surface temperature in the region of the strand near the edge. This can disadvantageously lead to an uneven sump tip across the strand width. Such an uneven sump tip can assume a length difference of, for example, 1.5 m, which in Fig. 9 is illustrated schematically with the route d _sump. Such an uneven sump tip is disadvantageous when performing a soft reduction and leads to the generation of internal cracks in the strand.

Out DE 10 2006 056 683 A1 a method for continuously casting a metallic product having the features according to the preamble of claim 1 is known.

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

The above object is achieved by a method for continuously casting a metallic product with the features specified in claim 1. Advantageous developments of the invention are defined in the dependent claims.

• (i) Bestimmung eines aktuellen Wiedererwärmungsfaktors (WEF_aktuell), unter Verwendung von folgender Beziehung: $$\mathrm{WEF}=\frac{{\mathrm{T}}_1-{\mathrm{T}}_2}{\mathrm{mD}*\mathrm{t}}$$
  
  mit:
  • T₁ = berechnete Temperatur am ersten Messpunkt P₁
  • T₂ = berechnete Temperatur am zweiten Messpunkt P₂
  • mD = mittlere Dicke der Strangschale zwischen P₁ und P₂
  • t = Transportzeit des Stranges (S) zwischen den Messpunkten P₁ und P₂,
• ii) Vergleich des aktuellen Wiedererwärmungsfaktors (WEF_aktuell) mit einem zulässigen maximalen Wiedererwärmungsfaktor (WEF_max), und
• iii) falls (WEF_aktuell) < (WEF_max): Verstärken der Kühlung in den Randbereichen (R) des Stranges (S) innerhalb des Intensivkühlabschnitts (20).

The invention provides a method for continuously casting a metallic product, in which a strand of the metallic product in a continuous casting plant emerges continuously from a mold, in particular vertically downwards, and is then transported along a strand guide in a conveying direction. Here, the strand is deflected in a straightening area in the horizontal direction, the edge areas of the strand being cooled less than in a horizontal area of the strand guide within a reduced cooling section, which is provided at least in the conveying direction in front of the straightening area and preferably also within the straightening area , which in the conveying direction after the straightening area lies. The edge areas of the strand are cooled in an intensive cooling section of the strand guide, which begins immediately after the strand emerges from the mold and is in front of the reduced cooling section in the conveying direction, at least as much as a central area of the strand. Using a first measuring point located within the intensive cooling section and a second measuring point located within the reduced cooling section, the following steps are carried out:

• (i) Determination of a current rewarming factor (WEF _current ), using the following relationship: $$\mathrm{WEF}=\frac{{\mathrm{T}}_1-{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">T</figure-callout>}}_2}{\mathrm{mD}*\mathrm{t}}$$
  
  With:
  • T ₁ = calculated temperature at the first measuring point P ₁
  • T ₂ = calculated temperature at the second measuring point P ₂
  • mD = mean thickness of the strand shell between P ₁ and P ₂
  • t = transport time of the string (S) between measuring points P ₁ and P ₂ ,
• ii) comparison of the current reheating factor (WEF _current ) with an allowable maximum reheating factor (WEF _max ), and
• iii) if (WEF _current ) <(WEF _max ): increase the cooling in the edge areas (R) of the strand (S) within the intensive cooling section (20).

Such a cooling strategy ensures that an essentially uniform sump length is formed, which has a positive effect, for example, when performing a soft reduction.

The method according to the invention can be carried out with a continuous caster which is used to manufacture a metallic product. This continuous caster, which does not belong to the present invention, comprises a mold and a strand guide adjoining the mold, along which a strand emerging 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 a reduced cooling section provided at least in the conveying direction in front of the straightening area, in which the edge areas of the strand are cooled less than in comparison to a horizontal area of the strand guide which lies in the conveying direction after the straightening area. The reduced cooling section can preferably also be provided within the straightening area. Immediately after the strand emerges from the mold, the strand guide has an intensive cooling section located upstream of the reduced cooling section in the conveying direction, in which the edge regions of the strand can be cooled at least as much as a central region of the strand.

In principle, it is known in the field of continuous casting of metallic products that the main reason for the formation of the sump length is 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 influences the strand core, which is still liquid. Taking this into account, the invention is based on the essential knowledge that in the intensive cooling section, the edge areas of the strand are cooled at least as much as its central area, so that this type of cooling is completely on the liquid strand core, and thus on the formation of a desired uniform or uniform swamp tip of the strand affects its width. In other words, by setting a uniform specific amount of spray water across the strand width or by increasing the edge cooling within the Intensive cooling section achieves that the length difference in the sump tip is at least reduced over the strand width. Accordingly, a sump tip that is uniform across the width of the strand is realized for the strand. Overall, the cooling strategy explained above is carried out in any case with compliance with the condition that the temperature does not fall below the minimum temperature determined by the ductility profile along the entire length of the strand guide, and thus also within or along the intensive cooling section.

In an advantageous further development of the invention, the intensive cooling section, in which the edge regions of the strand are cooled at least as much as the central region of the strand, can be provided within a first third of the length of the continuous caster, calculated from the mold exit of the strand. Following the intensive cooling section, the cooling of the edge areas of the strand is then reduced or decreased in the reduced cooling section. This ensures that the temperature of the strand does not fall below the critical temperature determined by the ductility profile, even in its edge areas or zones close to the edge. This applies in particular to the areas of the strand in which additional stresses occur, e.g. in the bending area and / or in the straightening area. In this way, according to the invention, the formation of possible surface cracks in the strand is also avoided in the reduced cooling section of the strand guide.

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

Taking into account the arrangement of the intensive cooling section and the reduced cooling section, namely - viewed in the conveying direction of the strand - one behind the other, 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 stipulation that within the intensive cooling section, the temperature in the edge areas of the strand corresponds to a minimum permissible edge temperature or is always greater than this, the aforementioned reheating factor WEF [° C / (mm * sec )] is calculated, which is determined as follows: $$\mathrm{WEF}=\mathrm{difference}\mathrm{between}\mathrm{the}\mathrm{<figure-callout\; id="1"\; label="temperature\; T"\; filenames="imgf0003.png"\; state="\{\{state\}\}">temperature</figure-callout>}{\mathrm{T}}_{}{\mathrm{}}_1\mathrm{at}\mathrm{one}\mathrm{first}\mathrm{Measuring\; point}{\mathrm{P.}}_1\mathrm{and}\mathrm{the}\mathrm{<figure-callout\; id="2"\; label="temperature\; T"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">temperature</figure-callout>}{\mathrm{T}}_{}{\mathrm{}}_2\mathrm{at}\mathrm{one}\mathrm{second}\mathrm{Measuring\; point}{\mathrm{P.}}_2/\mathrm{middle}\mathrm{thickness}\mathrm{the}\mathrm{Strand\; shell}\mathrm{between}\mathrm{the}\mathrm{Measuring\; points}{\mathrm{P.}}_1\mathrm{and}{\mathrm{P.}}_2/\mathrm{Transport\; time}\mathrm{of}\mathrm{Strand}\mathrm{between}\mathrm{the}\mathrm{Measuring\; points}{\mathrm{P.}}_1\mathrm{and}{\mathrm{P.}}_2.$$

Here are for example:

P1:

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

T1:

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

P2:

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

T2:

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.

A mathematical-physical calculation model is used to calculate the strand temperatures T ₁ and T ₂ and the strand shell thickness at the measuring points P ₁ and P _{2 and the associated sump tip positions.} A reheating factor WEF determined or measured in this way is then compared with a maximum reheating factor WEF _max , which is material-dependent and has been determined or established in advance. As long as the currently measured reheating factor WEF is _currently less than the maximum reheating _{factor WEF max} , the cooling of the edge areas of the strand is increased in at least one cooling zone of the intensive cooling section, e.g. by connecting additional cooling nozzles in the edge area of the strand and / or by increasing the set coolant flow with which the strand in its edge areas is acted upon or cooled. Both of these variants, i.e. the connection of additional cooling nozzles or the increase in the associated amount of coolant (e.g. spray water), always take into account or comply with the following aspects:

• The temperature at the edge of the strand or in the edge areas of the strand is not below the critical temperature specified by the ductility curve;
• The tip of the sump has no or as little as possible a W-shape over the width of the strand; and
• The temperature rise between the last edge nozzle (i.e. at the first measuring point P ₁ within the intensive cooling section) and the first zone without edge nozzles (i.e. at the second measuring point P ₂ within the reduced cooling section) must not be too high, or the maximum permissible reheating factor WEF _max do not exceed.

In addition, it can be provided for the above two variants to increase the cooling in the edge areas of the strand that the current position or position of the sump tip is also checked or taken into account. For this purpose, a calculation of the swamp length over the strand width is carried out. If it is determined on the basis of this calculation that the calculated sump tip difference is too high compared to a predetermined maximum sump tip difference, which represents a permitted upper limit value, then the cooling in the edge areas of the strand is increased according to one of the two variants mentioned. Otherwise, namely in the event that the determined sump tip difference should not be too high, the cooling in the intensive cooling section is not further intensified.

To carry out the method according to the invention, it is advantageous if the intensive cooling section comprises at least one cooling zone with additional cooling nozzles which are assigned to an edge region of the strand and can be switched on to intensify the cooling of the edge regions of the strand.

Fig. 1, Fig. 2

jeweils eine Seitenansicht einer Stranggießanlage, die nicht zur vorliegenden Erfindung gehört, sich jedoch zur Durchführung eines erfindungsgemäßen Verfahrens eignet

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.

Preferred embodiments of the invention are described in detail below with reference to a schematically simplified drawing. Show it:

Fig. 1, Fig. 2

each a side view of a continuous caster which does not belong to the present invention, but is suitable for carrying out a method according to the invention

Fig. 3 a

Representation of the sump peak curve (A) as well as the temperature curve after the intensive cooling area (B) and the temperature curve after the reduced cooling section (C),

Fig. 4, Fig. 5

flow charts for optimizing cooling within the intensive cooling section of the continuous caster from FIG Fig. 1 , and

Fig. 6 a

Top view of cooling zones within the intensive cooling section of a continuous caster from Fig. 1 .

In Fig. 1 a continuous caster 10 is shown in a basically simplified manner in a side view. The continuous casting plant 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 a strand S of the metallic product 11, which preferably emerges downward from the mold 12, 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, with spray water 4 being applied or sprayed onto the strand S for the purpose of cooling the bar S. At the point where in Fig. 1 If 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 with the reference number "6". Downstream of this, the strand S is completely solidified, for example at the in Fig 1 position marked with reference line "11d". Downstream of this, a water cooling system is also provided along the strand guide 14, which is identified by the reference line “8”.

The strand guide 14 of the continuous caster 10 comprises a straightening area I through 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. 1 each symbolized in a simplified manner by dashed rectangles.

The conveying direction in which the strand S is transported along the strand guide 14 of the continuous caster 10 is shown in FIG Fig. 1 labeled "F". The strand guide 14 comprises a reduced cooling section 16 which - as seen 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 undercooling section 16 can be designed in such a way that it at least partially or completely covers the directional area I. The undercooling section 16 of the strand guide 14 is characterized in that the cooling zones provided therein are designed in such a way that the edge regions of the strand S are cooled to a lesser extent than in comparison 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 strand S has emerged from the mold 12 and - as in FIG Fig. 1 illustrates - is seen in the conveying direction F in front of the lower cooling section 16. The intensive cooling section 20 is designed with at least one cooling zone provided therein in such a way that the edge regions of the strand S are cooled at least as much as a central region of the strand S.

Fig. 2 FIG. 10 shows the continuous caster 10 of FIG Fig. 1 again in a simplified side view. This illustrates the length extensions of the reduced cooling section 16 and the intensive cooling section 20 along the strand guide 14 of the continuous casting installation 10. In detail, the length of the intensive cooling section 20 is designated by “L ₂₀ ”, this length being approximately one third of the length L _{10 of} the continuous casting installation 10. For this case, the intensive cooling section 20 is provided within a first third of the length L _{10 of} the continuous casting installation 10, starting from the exit of the strand S from the mold 12. A length of the undercooling section 16 is shown in FIG Fig. 2 labeled "L ₁₆ ". Furthermore, the Fig. 2 illustrates that the intensive cooling section 20 - viewed in the conveying direction F of the strand S - is provided in front of the reduced cooling section 16 or upstream thereof, the intensive cooling section 20 beginning immediately after the mold exit or an area near the mold level.

Due to the above-mentioned intensive cooling of the edge areas 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 here, the method according to the invention ensures that the length difference in the sump tip compared to the prior art is advantageously reduced. This is in the representation of Fig. 3 illustrated with the curve "A", which shows a course of the sump tip 6 over the strand width. Here, the difference in length d _sump , which is a measure of the unevenness of the sump tip, is only about 150 mm, for example. Thus, by means of the method according to the invention, a substantially uniform or uniform sump tip is achieved across the strand width without the edge temperature falling below the critical temperature determined by the ductility profile. In any case, the difference in length d _sump realized by means of the method according to the invention is significantly smaller than according to the prior art, which, as described above, based on FIG Fig. 9 explained can be 1.5 m.

How out Fig. 3 It can also be seen that the temperature profile after the intensive cooling section (B) is not constant over the strand width. The temperature is lower in the edge area than in the middle of the strand. Due to the reduced cooling of the edge area in the subsequent so-called reduced cooling section, the temperature difference is largely equalized and the temperature profile after the reduced cooling section (C) over the strand width is essentially constant.

During operation of the continuous casting plant 10 or when carrying out a method according to the invention for the continuous casting of a metallic product 11, there is between the intensive cooling section 20, in which the edge areas of the strand S are subjected to increased edge cooling, and the reduced cooling section 16, in which a reduced application of coolant for the Edge areas of the strand S is provided, a temperature rise. It is important here for the invention that such a temperature rise does not become too high. An excessively strong and rapid rise in the already solidified material of the strand S can otherwise lead to internal cracks.

Compliance with a not too high temperature rise between the intensive cooling section 20 and the reduced cooling section 16 is ensured in the method 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 , to the mean thickness of the strand shell between the measuring points P ₁ and P ₂ , and to Transport time of the strand S between the measuring points P ₁ and P ₂ . Accordingly, the unit for the rewarming factor WEF is determined as [° C / (mm * sec)]. In this regard, it goes without saying 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 reduced 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 increased edge cooling), the second measuring point P _{2 being} located at the end of the first cooling zone of the reduced cooling section 16 (with reduced edge cooling). The temperatures T ₁ and T ₂ are the mean strand shell temperatures at the measuring points P ₁ and P ₂ . A mathematical-physical calculation model is used to calculate the strand temperatures T ₁ , T _{2, the sump tip positions and the strand shell thicknesses.}

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 carrying out a method according to the present invention, a current reheating factor is first determined or calculated, namely using the following relationship: $$\mathrm{WEF}=\mathrm{difference}\mathrm{between}\mathrm{one}\mathrm{<figure-callout\; id="1"\; label="temperature\; T"\; filenames="imgf0003.png"\; state="\{\{state\}\}">temperature</figure-callout>}{\mathrm{T}}_{}{\mathrm{}}_1\mathrm{at\; the}\mathrm{first}\mathrm{Measuring\; point}{\mathrm{P.}}_1\mathrm{and}\mathrm{one}\mathrm{<figure-callout\; id="2"\; label="temperature\; T"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">temperature</figure-callout>}{\mathrm{T}}_{}{\mathrm{}}_2\mathrm{at\; the}\mathrm{second}\mathrm{Measuring\; point}{\mathrm{P.}}_2/\mathrm{middle}\mathrm{thickness}\mathrm{the}\mathrm{Strand\; shell}\mathrm{at}\mathrm{the}\mathrm{Measuring\; points}{\mathrm{P.}}_1\mathrm{and}{\mathrm{P.}}_2/\mathrm{Transport\; time}\mathrm{of}\mathrm{Strand}\left(\mathrm{S.}\right)\mathrm{between}\mathrm{the}\mathrm{Measuring\; points}{\mathrm{P.}}_1\mathrm{and}{\mathrm{P.}}_2.$$

Following this, the current reheating factor with WEF _{current is} compared with a maximum permissible reheating factor WEF _max , which is material-dependent and is defined in advance. Depending on the comparison between WEF _actual and WEF _max , the cooling of the edge areas of the strand S within the intensive cooling section 20 can then be increased, which is explained in detail below with reference to the flowcharts:
The flowchart of Fig. 4 illustrates an optimization of the amount of coolant, preferably in the form of spray water, 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, including the edge temperatures of the strand S, ie the temperature of the strand S in its edge areas. A check is then made as to whether the edge temperature thus calculated is greater than a minimum permissible edge temperature T _{EdgeTarget in front of the straightening area I or within the straightening area I.} If this is not the case, the cooling in the intensive cooling section 20 is not increased, so that no further minimization of the sump tip difference is possible. This takes place on the basis that the edge temperature should not fall below the critical temperature determined by the ductility profile, referred to above as T _EdgeTarget . If, on the other hand, the calculated edge temperature should be greater than the minimum permissible edge temperature T _{KanteZiel, the strand shell temperatures T 1} and T ₂ at the measuring points P ₁ and P ₂ , as well as the mean strand shell thickness between these measuring points, are calculated using the mathematical-physical calculation model the transport time of the strand S between the measuring points P ₁ and P _{2 is also} determined. Taking into account the values thus calculated or determined, the current reheating factor WEF is then _currently determined using the above equation.

In a next step, the value of the current reheating factor WEF is _currently compared with a maximum permissible reheating factor WEF _max . If WEF should _{currently be} greater than WEF _max , this is an indication that the temperature rise between the intensive cooling section 20 and the reduced cooling section 16 is already too great, so that the cooling in the intensive cooling section 20 or that in this section is not increased the amount of coolant used is not increased. If, however, the condition WEF _currently <WEF _max should be met, the next step is to calculate the swamp length over the strand width using a mathematical-physical calculation model. If, in this context, a comparison with a predetermined maximum sump peak difference, which represents a permitted upper limit value, should show that the calculated sump peak difference is too high, the cooling can be carried out as a result are suitably increased in the intensive cooling section 20, namely by increasing the associated amount of coolant 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 capacity in the intensive cooling section 20 remains unchanged if the calculated sump tip difference for the strand S is not represents too high.

The flow chart according to Fig. 4 illustrates that the sequence of steps explained above is designed in the form of a control loop. Such a control circuit preferably records all 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 arrangement or the use of cooling nozzles in the edge areas of the strand S. As a starting point for the flow chart of FIG Fig. 5 an operating mode of the continuous casting plant 10 is used in which the edge regions or the edges of the strand S are not overmolded. 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 permissible edge temperature T _{KanteZiel before the straightening area I or within the straightening area I.} From this step the flow chart corresponds to Fig. 5 essentially the logic of the flowchart of Fig. 4 so that reference may be made to it in order to avoid it.

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

Fig. 6 FIG. 11 shows a schematically simplified plan view of cooling zones within the intensive cooling section 20 and the reduced cooling section 16. The additional cooling nozzles, which are produced according to the flow chart of FIG Fig. 5 can be switched on to increase the cooling of the edge areas of the strand S are in Fig. 6 labeled "22". In addition, the edge regions of the strand S, in which these connectable cooling nozzles 22 are arranged, are shown in FIG Fig. 6 denoted by "R", with a central region of the strand S denoted by "M".

In the same way as with Fig. 4 goes for the flow chart of Fig. 5 that the associated step sequence is designed as a control loop. Thus, when the cooling is intensified in the edge regions R of the strand S, it is always ensured that possible process changes are recognized in good time. Accordingly, the temperature rise between the intensive cooling section 20 and the reduced cooling section 16 remains moderate if the condition WEF _currently <WEF _{max is} met, while at the same time the temperature at the strand edge or in the edge areas of the strand S does not fall below the critical temperature T specified by the ductility curve _EdgeTarget falls.

The flowcharts of Fig. 4 and Fig. 5 and the determination of the current reheating factor WEF _current carried out here relate, for example, to the first and second measuring points P ₁ , P ₂ , which are shown in FIG Fig. 6 are also indicated symbolically by arrows. This means that these measuring points are provided in individual cooling zones of the intensive cooling gate 20 or the reduced cooling section 16. Taking this into account, the determination of the current _{rewarming factor WEF currently} enables an assessment of the temperature rise between the intensive cooling section 20 and the reduced cooling section 16. In this context, it is finally pointed out that the measuring points P ₁ and P _{2 are} also at points other than those shown in FIG Fig. 1 and Fig. 6 indicated can be provided. Furthermore, a plurality of first measuring points P ₁ or of second measuring points P _{2 are also} possible, each of which are provided within the intensive cooling section 20 or within the reduced cooling section 16.

List of reference symbols

2

Support roller

4th

Coolant, e.g. splash water

5

Liquid swamp (of strand S)

6th

Swamp tip

7th

Rigid part of the S range

8th

Water cooling

10

Continuous caster

11

Metallic product

12th

Mold

14th

Strand guide

16

Reduced cooling section (of strand guide 14)

18th

Horizontal area (of strand guide 14)

20th

Intensive cooling section (of strand guide 14)

22nd

Additional (switchable) cooling nozzle (s)

F.

Direction of conveyance (of line S)

I.

Straightening area (of strand guide 14)

II

Bending area (of strand guide 14)

L10

Length of the continuous caster 10

L16

Length of the undercooling section 16

L20

Length of the intensive cooling section 20

M.

Central area (of strand S)

P1

First measuring point (within the intensive cooling section 20)

P2

Second measuring point (within the reduced cooling section 16)

R.

Edge area (s) of the strand S

S.

Strand (of metallic product 11)

T1

Temperature at the first measuring point P ₁

T2

Temperature at the second measuring point P ₂

WEFaktuell

Current rewarming factor

WEFmax

Allowable maximum rewarming factor

Claims (9)

1. Method for continuous casting of a metallic product (11) in which in a continuous casting plant (10) a strip (S) of the metallic product (11) continuously issues from a mould (12), in particular perpendicularly downwardly, and is subsequently transported along a strip guide (14) in a conveying direction (F), wherein the strip (S) is deflected in a straightening region (I) into the horizontal direction, wherein the edge regions (R) of the strip (S) within a lesser cooling section (16) of the strip guide (14), which is provided at least in conveying direction (F) in front of the straightening region (I) and preferably also within the straightening region (I), is cooled less by comparison with a horizontal region (18) of the strip guide (14) in conveying direction (F) after the straightening region (I),
   wherein the edge regions (R) of the strip (S) in an intensive cooling section (20) of the strip guide (14), which begins directly after exit of the strip (S) from the mould (12) and in conveying direction (F) lies in front of the lesser cooling section (16), are cooled at least just as strongly as a middle region (M) of the strip (S),
   characterised in that
   the following steps are performed with use of a first measuring point (P₁) lying within the intensive cooling section (20) and a second measuring point (P₂) lying within the lesser cooling section;

   (i) determining a current reheating factor (WEF_current) with use of the following equation: $$\mathit{WEF}=\frac{T_1-T_2}{\mathit{mD}\ast t}$$

   

   wherein

   T₁ = calculated temperature at the first measuring point P₁

   T₂ = calculated temperature at the second measuring point P₂

   mD = mean thickness of the strip skin between P₁ and P₂

   t = transport time of the strip (S) between the measuring points P₁ and P₂,

   (ii) comparison of the current reheating factor (WEF_current) with a permissible maximum reheating factor (WEF_max) and

   (iii) if (WEF_current) < (WEF_max): strengthening the cooling in the edge regions (R) of the strip (S) within the intensive cooling section (20).
2. Method according to claim 1, characterised by a repetition of steps (i) to (iii), wherein according to step (iii) the cooling is strengthened in the edge regions (R) of the strip (S) as long as the condition WEF_current < WEF_max is fulfilled.
3. Method according to claim 1 or 2, characterised in that for strengthening of the cooling in accordance with step (iii) further additional cooling nozzles in the edge regions (R) of the strip (S) are switched on in at least one cooling zone of the intensive cooling section (20).
4. Method according to any one of the preceding claims, characterised in that for strengthening of the cooling according to step (iii) the coolant quantity applied to the strip (S) is increased in at least one cooling zone of the intensive cooling section (20).
5. Method according to any one of the preceding claims, characterised in that the steps (i) to (iii) are carried out if ahead of the straightening region (I) or within the straightening region (I) the temperature in the edge regions (R) of the strip (S) is greater than a minimum permissible edge temperature (T_{edge target}).
6. Method according to any one of the preceding claims, characterised in that a plot of end of liquid phase over strip width is calculated, wherein the step (iii) is carried out under the further condition that the calculated difference of end of liquid phase is greater than a predetermined maximum difference of end of liquid phase.
7. Method according to any one of the preceding claims, characterised in that the intensive cooling section (20) is provided within a first third of the length of the continuous casting plant (10) beginning from the exit of the strip (S) from the mould (12).
8. Method according to any one of the preceding claims, characterised in that within the intensive cooling section (20) the edge regions (R) of the strip (S) are cooled more strongly than the middle region (M) of the strip (S).
9. Method according to claim 8, characterised in that within the intensive cooling section (20) the specific water quantities in the edge regulating circuits are higher than the water quantities which are applied to the middle region (M) of the strip (S).

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