WO2020052944A1

WO2020052944A1 - Method for open-loop or closed-loop control of the temperature of a casting strand in a continuous casting machine

Info

Publication number: WO2020052944A1
Application number: PCT/EP2019/072687
Authority: WO
Inventors: Thomas Heimann; Uwe Plociennik
Original assignee: Sms Group Gmbh
Priority date: 2018-09-13
Filing date: 2019-08-26
Publication date: 2020-03-19
Also published as: DE102018215583A1; EP3849729A1; EP3849729B1

Abstract

The invention relates to a method for open-loop or closed-loop control of the temperature of a casting strand (10) in a continuous casting machine (12). Once discharged from a die (14), the casting strand (10) is guided in a conveying direction (F) by a supporting strand guide (16) of the continuous casting machine (12), which has a secondary cooling system, the secondary cooling system being adjusted by an open-loop or closed-loop control unit (18) and the surfaces of the casting strand (10) being cooled in this way. A temperature field is calculated for the casting strand (10) in its conveying direction (F) within the supporting strand guide, and on this basis a position of the sump tip (PS) of the casting strand (10) is determined. A plurality of target temperature curves for the surface of the casting strand (10) are stored in a memory (19) of the open-loop or closed-loop control unit (18) for a material of the casting strand (10) to be cast. For closed-loop control of the temperature of the casting strand (10), a suitable target temperature curve is selected according to or as a function of the position of the sump tip of the casting strand (10).

Description

Process for controlling or regulating the temperature of a casting strand in a continuous casting installation

The invention relates to a method for controlling or regulating the temperature of a casting strand in a continuous casting installation according to the preamble of claim 1 and claim 4, respectively.

When operating continuous casting plants, it corresponds to the state of the art to cool the casting strand after it emerges from the mold in the so-called secondary cooling of a supporting strand guide of the plant until the casting strand has completely solidified. This cooling process plays an important role in the resulting quality of the cast strand and the products made from it. The complete solidification of the casting strand should be achieved within the roller segments of the supporting strand guide, which support the casting strand with the core still liquid.

The operation of the secondary cooling is usually realized with spray or cooling water, the amount of water that is applied to the surfaces of the casting strand being set by specifying target temperature curves. The

Depending on the material of the material to be cast, and e.g. vary depending on certain cooling zones of the supporting strand guide and / or the casting speed. Depending on the material and the selected casting speed, an operator of the continuous casting plant then selects a target temperature curve and thus the

Secondary cooling for applying the spray or cooling water to the surfaces of the cast strand to be cooled. For example, higher (= warmer) target temperature curves can be made at low casting speeds. Conversely, at higher casting speeds, lower (= colder) setpoint temperature curves should generally be used in order to achieve a stronger one

Cooling of the casting strand so that it still solidifies within the supporting strand guide. A setpoint temperature curve determines the setpoints for the surface temperature to be reached, which the strand reaches within the supporting strand guide, for example at the end of individual cooling zones which are part of this supporting strand guide. The spray water quantities of the secondary cooling are regulated so that these target values are achieved.

As already explained above, when operating a continuous caster, it is of great importance that the casting strand solidifies completely within the supporting strand guide and does not run out of this supporting strand guide with its sump tip. To achieve this, an operator usually sets - for safety reasons - set temperature curves that are too low (= cold), which leads to an excessively strong and in any case unnecessary cooling of the casting strand. If, after leaving the supporting strand guide, the casting strand e.g. processed directly in a subsequent hot rolling mill and in preparation for which it passes through a furnace upstream of the hot rolling mill, said excessively strong cooling of the casting strand when leaving the supporting strand guide has the disadvantage that the average temperature of the casting strand at the furnace inlet decreases or is lower. This in turn has to be compensated for by a higher furnace temperature (= greater energy requirement) and by a longer dwell time of the casting strand in the furnace, which can lead to increased scaling on the surfaces of the casting strand.

From WO 2009/071236 A1 it is known to dynamically adapt the target temperature of the casting strand on the basis of data and / or signals, for example possibly changed casting parameters, in the operation of a continuous casting installation. In the technology according to WO 2009/071236 A1, it is provided that the target temperatures are reset to their original values if the casting parameters return to the expected range. Accordingly, the object of the invention is to optimize the energy content of the casting strand at the end or when leaving the supporting strand guide during continuous casting. This object is achieved by a method having the features of claim 1 and by a method having the features of claim 4. Advantageous developments of the invention are defined in the dependent claims. A method according to the present invention is used to control or regulate the temperature of a casting strand in a continuous casting installation. Here, the casting strand after the continuous exit from a mold is guided along a conveying direction by a supporting strand guide of the continuous casting installation, which has at least one segment with a secondary cooling, the secondary cooling being set by a control or regulating unit and thus the surfaces of the casting strand be cooled. A temperature field is calculated for the casting strand along its conveying direction within the supporting strand guide and a position of the bottom tip of the casting strand is determined therefrom. A plurality of target temperature curves for the surface of the cast strand are stored in a memory of the control unit for a material to be cast in the cast strand. With this method, it is of particular importance that in step (i) it is checked whether the position of the bottom tip of the casting strand lies in a predetermined permissible range within the supporting strand guide. Then in a subsequent step (ii), if the position of the sump tip of the casting strand is outside the predetermined permissible range and instead is in a warm-critical area of the supporting strand guide, the cooling capacity is increased by reducing the secondary cooling in the at least one segment of the supporting strand guide to at least the next lower (= colder) target temperature curve is set. Alternatively, in step (ii), if the position of the sump tip is outside the predetermined permissible range and instead in a cold-critical area of the supporting strand guide, the cooling capacity is then reduced by secondary cooling in the at least one segment of the supporting strand guide to at least that next higher (= warmer) target temperature curve is set. According to a further embodiment, the invention provides a method for controlling or regulating the temperature of a casting strand in a continuous casting installation, in which the casting strand, after continuously emerging from a mold, is supported by a supporting strand guide of the continuous casting installation, which has at least one segment with secondary cooling is guided in a conveying direction, wherein the secondary cooling is set by a control or regulating unit and thus the surfaces of the cast strand are cooled. A temperature field is calculated for the casting strand along its conveying direction within the supporting strand guide and a position of the bottom tip of the casting strand is determined therefrom. A plurality of setpoint temperature curves for the surface of the cast strand are stored in a memory of the control unit for a material of the cast strand to be cast. In this embodiment of the method, it is of particular importance that in step (i) it is checked whether the position of the bottom tip of the casting strand lies in a predetermined permissible range within the supporting strand guide. Subsequently, in a step (ii), if the position of the sump tip of the casting strand is in the predetermined permissible range of the supporting strand guide and a target temperature curve set in the area of the at least one segment of the supporting strand guide has not occurred for a predetermined time of preferably at least 5 minutes has changed and the calculated sump lengths for the two next higher (= warmer) setpoint temperature curves are still in the predetermined permissible range of the supporting strand guide, then the cooling capacity is reduced by the secondary cooling in the at least one segment of the supporting strand guide to the next higher (= warmer) target - temperature curve is set. It is also possible here that the predetermined time, which is checked as a condition for a non-change of the set target temperature curve, can also be more than 5 minutes, for example 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, or is either longer than 10 minutes or lies between the values just mentioned.

It goes without saying that the coldest and warmest possible target temperature curve for each material to be cast on a casting strand, depending on the analysis of the Material can be redetermined, and on the basis of this, all further setpoint temperature curves between the coldest and warmest setpoint temperature curve can be determined or defined. Following this, these target temperature curves are then stored in the memory of the control or regulation unit in order to be able to carry out the invention.

It is important for a method according to the present invention that a temperature field is determined, preferably calculated, for the casting strand along its conveying direction within the supporting strand guide, so that the associated temperature is known for each calculated node of the casting strand, namely at a specific point on the Casting strand or the system length, in particular within the supporting strand guide and its cooling segments. An exact position of the bottom of the sump for the casting strand can then be determined. On the basis of this, a method according to the present invention is based on the essential finding that the specific position of the bottom of the casting strand serves as an input variable in order to set or change a specific target temperature curve for the secondary cooling of the supporting strand guide. In other words, the current position of the sump tip of the casting strand and the associated check as to whether this position of the sump tip is either within the predetermined permissible range or where exactly within this range, then lead to an adjustment or change of a selected target temperature curve such that the Energy content of the casting strand at the end of the supporting strand guide is as high as possible. This is equivalent to the fact that the casting strand at the end of the supporting strand guide has a temperature which is as high as possible and thus has a high heat content, and with this high heat content can then be subjected to further processing, for example in a hot rolling mill, and can enter a furnace which precedes the hot rolling mill is. At this point, it is pointed out separately that the “predetermined permissible range”, with respect to which a method according to the invention in step (i) is the checking of the position of the bottom tip of the casting strand provides for the area within the supporting strand guide of the continuous caster in which a position of the sump tip is optimal, namely in connection with the metallurgical length (calculated from the casting level to the last pair of support rollers within the supporting strand guide). In other words, this “predetermined permissible range” is an area of the supporting strand guide in which, on the one hand, the casting strand is just sufficiently cooled and there is therefore no danger that the casting strand with its still liquid sump tip comes out of the supporting strand guide in the The pouring or conveying direction “migrates out” and in which, on the other hand, the casting strand is not cooled too much by selecting a suitable target temperature curve for the secondary cooling, so that the heat content of the casting strand remains as high as possible until it leaves the supporting strand guide. These are expediently

Limits of this “predetermined permissible range” are not rigid or unchangeable, but can be changed either before the program starts or during the casting operation.

For the implementation of a method according to the invention, it is important that the bottom length of the casting strand is as long as possible in relation to the extent or length of the supporting strand guide and is always within the predetermined permissible range. This takes advantage of the fact that the

The energy content of the casting strand depends directly on the length of the sump tip: the longer the sump tip, the greater the energy content of the casting strand, at least at the end of the supporting strand guide, before the (completely solidified) casting strand then leaves the strand guide. It is of further importance for the invention that the cooling set does not change continuously during operation of the continuous casting installation. In view of this, the setting or selection of a specific target temperature curve for the secondary cooling is not linked to an exact position at which the bottom of the casting strand is currently located, but to an area within which the bottom is located. This area is the “predetermined permissible area” of the supporting strand guide explained above. Depending on whether the sump peak is within this predetermined permissible range, a setpoint temperature curve is then that was defined before the start of the casting process for a specific material, selected such that the sump tip remains within this predetermined permissible range during the casting process, which thus acquires the property of a “target area”. Thus, the cooling for the casting strand in the area of the supporting strand guide is only changed when it is determined that the bottom tip of the casting strand is no longer in a desired interval, ie the predetermined permissible area of the supporting strand guide. This also means that the invention is not based on the fact that the cooling capacity is already changed when the bottom tip of the casting strand already deviates from a precisely defined point.

The aim of the present invention is that the energy content of the casting strand at the end of the supporting strand guide is or becomes as high as possible without the sump length of the casting strand becoming too large. On the one hand, this avoids the risk that the casting strand with its sump tip "runs out" of the last cooling segment of the supporting strand guide, and also achieves the advantage that the highest possible furnace inlet temperature is achieved for the casting strand. It is also pointed out that the “cold-critical” area of the supporting strand guide is the area which, viewed in the direction of conveyance of the casting strand, adjoins the predetermined permissible area upstream. According to its name, the temperature of the casting strand is too low or “too cold” with regard to the length of the supporting strand guide if the (calculated) bottom tip of the casting strand is in this cold-critical area. The “warm-critical” area of the supporting strand guide is the area which, viewed in the direction of conveyance of the casting strand, adjoins the predetermined permissible area downstream. According to its name, the temperature of the casting strand is too high or “too warm” with regard to the length of the supporting strand guide if the (calculated) bottom tip of the casting strand is in the warm-critical area. With regard to the first-mentioned embodiment of the method according to the invention, it is important that if a position of the bottom of the casting strand in the cold-critical area is determined in step (ii), then the cooling capacity of the secondary cooling is reduced by the secondary cooling in the at least one segment the supporting strand guide is set to at least the next higher (= warmer) target temperature curve in order to raise the temperature of the casting strand. As a result, the bottom of the cast strand then returns to the predetermined permissible range. Alternatively, if it is determined in step (ii) that a position of the sump tip of the casting strand is in the warm-critical area, the cooling capacity of the secondary cooling is to be increased by reducing the secondary cooling in the at least one segment of the supporting strand guide to at least the next lower ( = colder) set temperature curve is set and thus the temperature of the cast strand is reduced, so that the bottom of the sump then migrates back into the predetermined permissible range.

In an advantageous development of the invention, the cooling capacity of the secondary cooling is set to a maximum value, i.e. the secondary cooling is set to the coldest possible setpoint temperature curve, if it should be determined in step (ii) that the bottom tip of the casting strand is in a safety area which - seen in the direction of conveyance of the casting strand - is downstream of the warm-critical area. Such maximum cooling prevents the bottom of the casting strand from threatening to run out of the area of the supporting strand guide.

With regard to the second-mentioned embodiment of the method according to the invention, it should be emphasized that it is optimal if the swamp tip is on the right edge of the predetermined permissible range, that is to say shifted from a center of the predetermined permissible range in the direction of the warm-critical range, but in any case is still within the predetermined allowable range. This is achieved in that if the target temperature curve set in the area of the supporting strand guide has been moving for a predetermined time, for example has not changed for at least 10 minutes, then the cooling capacity is reduced by setting the secondary cooling to the next warmer target temperature curve. This setting is made on the condition that the bottom length of both this selected next warmer target temperature curve and the next but one warmer target temperature curve are both still in the predetermined permissible range of the supporting strand guide. For this embodiment, it can be emphasized that the requirement that the cooling set for the casting strand should change as little as possible, as explained above, after a predetermined time (for example 10 minutes), has been deviated from, namely by the overriding goal of a “ high energy content ”for the cast strand when its sump tip is still within the predetermined allowable range. Furthermore, it is pointed out that when switching to a next higher (= warmer) setpoint temperature curve, taking into account the condition that the bottom peak, which is assigned to the next higher (= warmer) setpoint temperature curve, is still within the predetermined permissible range that a constant switching between different target temperature curves, combined with an undesired constant change in the cooling capacity, is effectively prevented and accordingly does not take place.

In all embodiments of a method according to the invention, steps (i) and (ii) are expediently carried out fully automatically by the control or regulating unit. This ensures that the bottom of the casting strand always lies in the predetermined permissible range or returns there. This ensures that on the one hand the casting strand always has the highest possible energy content, especially at the end of the supporting strand guide, and that on the other hand the cooling is automatically increased if the bottom tip of the casting strand should become too long. Since the position or position of the sump tip can move in an interval, namely within the predetermined permissible range, constant process parameters can be poured over a longer period of time. The analysis-dependent calculation of the optimal limit and setpoint temperature curves enables a high energy content to be achieved at the end of the supporting strand guide for each material from which a casting strand is manufactured or cast.

Exemplary embodiments of the invention are described in detail below on the basis of a schematically simplified drawing.

Show it:

1 shows a schematically simplified side view of a continuous casting installation with which a method according to the present invention can be carried out,

FIG. 2 shows a diagram for possible target temperature curves that can be selected when carrying out a method according to the invention for the secondary cooling of the continuous casting plant from FIG. 1,

3 shows a basic circuit diagram for a method according to the invention,

4 shows a basic circuit diagram for a method according to the invention according to a further embodiment,

5a, 5b show a flow chart to illustrate a step sequence of a

Method according to the present invention,

Fig. 6 is a diagram for the solidification length, and

Fig. 7 is a diagram for the average temperature at the oven inlet.

Preferred embodiments for a method according to the invention, which is used to control or regulate the temperature of a casting strand 10 in a continuous casting installation 12, are explained below with reference to FIGS. 1 to 7. The same features in the drawing are provided with the same reference numerals. At this point, it is pointed out separately that the drawing is only simplified and in particular is shown without a scale.

1 shows a continuous casting plant 12, with which a method according to the invention can be carried out, is shown in a schematically simplified side view. The Continuous casting plant 12 comprises a mold 14 which has a vertical exit downwards. Liquid metal is poured into the mold 14, a casting strand 10 then emerging from the mold 14 downward. The continuous casting plant 12 comprises a strand guide, along which the casting strand 10 is moved or transported in a conveying direction F. The strand guide can be divided into individual segments, as indicated in the illustration in FIG. 1 by the numbers 1-7.

Here, the segments 1-4 are designed as cooling segments and combined to form a supporting strand guide 16, in which the casting strand 10 is provided from both sides with secondary cooling (not shown), e.g. through spray nozzles, with a cooling medium, in particular in the form of water, and is thus specifically cooled.

The supporting strand guide 16 with the individual cooling segments 1 to 4 is - seen in the conveying direction F of the casting strand 10 - immediately downstream of the mold 14 or arranged downstream thereof. Accordingly, the

Casting strand 10, immediately after it has emerged from the mold 14 downward, then into the downstream supporting strand guide 16.

The continuous caster 12 is constructed as a vertical bending system. This means that the casting strand 10 - as shown and explained in FIG. 1 - first emerges vertically or vertically downward from the mold 14 and only after it has completely solidified when it (= the casting strand 10) leaves the supporting strand guide 16 into which the horizontal is bent. In each of the four cooling segments 1 -4 of the supporting strand guide 16, the amounts of water of the secondary cooling are regulated in such a way that the temperatures at the surfaces of the ends of the cooling segments 1 -4 of the casting strand 10 correspond to the objectives of a target temperature curve set or selected for this purpose. This will be explained separately below. The continuous casting installation 12 further comprises a control or regulating unit 18, which is signaled over a signal path (symbolized in FIG. 1 by a dotted line 20) with the secondary cooling of the cooling segments 1 -4 the supporting strand guide 16 is connected. This signal path can be wired or wireless, for example by a radio path or the like. The control or regulating unit 18 comprises a memory 19, in which a plurality of target temperature curves are stored. The diagram in FIG. 2 shows exemplary setpoint temperature curves i - x, 16 setpoints for the segments 1 - 4 of the supporting strand guide for those to be achieved

Specify surface temperatures of the casting strand 10, namely at the end of each cooling segment 1, 2, 3 or 4. With regard to these temperature curves, it is pointed out that the target temperature curve # i is the “warmest” temperature curve, which is characterized by the Secondary cooling of the supporting strand guide 16, comparatively little cooling water is sprayed onto the surfaces of the casting strand 10, and as a result the (surface) temperature of the casting strand is comparatively high. In contrast, the target temperature curve # x is the “coldest” temperature curve, in which comparatively large amounts of cooling water are sprayed onto the surfaces of the casting strand 10 by the secondary cooling of the supporting strand guide 16, so that the (surface) temperature of the casting strand 10 is cooled more strongly and takes on lower values.

For each new material to be cast in a casting strand 10, the coldest and warmest possible target temperature curve are redetermined depending on the analysis of the material, and on the basis of this, all further target temperature curves between the coldest and warmest target temperature curve are determined, e.g. according to the principle of linear interpolation. Before starting the continuous casting process, many variation calculations are carried out for all possible material groups, strand thicknesses, casting speeds and casting temperatures. For each setpoint temperature curve, an assigned bottom length is calculated on the basis of a regression equation, namely

Bottom length = aO + a1 ^* strand thickness + a2 ^* casting speed + a3 * overheating + a4 * carbon content determined, the coefficients aO, a1, a2, a3, and a4 being stored in the memory 19 of the control and regulating unit 18 for all cooling curves.

The calculation of a current sump length of the casting strand 10 for a currently set target temperature curve takes place only taking into account the current casting parameters, so that a current position of the sump tip for the casting strand 10 can be determined

By means of the control or regulating unit 18, it is also possible to determine a temperature field for the casting strand 10 along its conveying direction F within the supporting strand guide 16, for example by calculation based on the known casting parameters. From the knowledge of the temperatures for the casting strand 10, a conclusion regarding the exact position of the bottom tip of the casting strand 10 can then be obtained, taking into account the solidus temperature of a respective material that is used for the continuous casting of the casting strand 10. To verify the temperatures calculated for the casting strand 10, it is possible to attach suitable (temperature) sensors at certain points along the supporting strand guide, with which the actual temperatures of the casting strand 10 are then determined, in particular on the surfaces thereof, and possibly with the previously calculated ones Values can be compared. In this regard, it goes without saying that the control or regulating unit 18 is also connected to the sensors (not shown) via a signal path in order to receive the measured values of these sensors.

The mode of operation of methods according to the invention is explained below. In this explanation, the individual method steps, which are shown in the corresponding flowchart according to FIGS. 5a and 5b, are also given in parentheses. First, before a first casting start, the associated regression coefficients for the above-mentioned regression equation are stored in the memory 19, so that - based on a currently set target temperature curve - the position of a sump peak of neighboring target temperature curves (“neighboring curves”) in the warmer area (ie with a lower cooling capacity in the area of the supporting strand guide 16) (step S1 of FIG. 5a).

Then, before the first casting of a new material, the coldest and warmest possible target temperature curves are determined anew depending on the analysis of the material. As already explained, all further setpoint temperature curves (for example ten such curves i to x, cf. FIG. 2) are then determined according to the principle of linear interpolation, this also being based on empirical values for crack avoidance (= step S2 of FIG. 5a) . More or less than ten target temperature curves can also be determined.

The length of the supporting strand guide 16 is divided into different areas, namely in a predetermined permissible area B, a cold-critical area K, a warm-critical area W, and a safety area S. The cold-critical area is seen in the conveying direction F of the casting strand 10 K upstream of the predetermined permissible range B, the warm-critical range W and the safety range S, in this order, each being downstream of the predetermined permissible range B. These four areas are illustrated in FIG. 3 on the basis of a circuit diagram, which will be explained below. The limits of these areas are preferably determined before the start of the continuous casting process, and can also be changed or adapted during the casting operation. In this context, it should be pointed out that the areas B, W and S of the areas K, B, W and S, or at least the predetermined permissible area B, may or lie in the last cooling segment 4 of the supporting strand guide 16 should). The boundaries between the areas K, B, W and S can preferably also lie between the cooling segments. In the operation of the continuous casting plant 12 or when carrying out a method according to the present invention, the aim of selecting or setting a suitable target temperature curve for the secondary cooling of the supporting strand guide 16 is that a position of the bottom tip of the casting strand 10, in FIG “PS” denotes, is always within the predetermined permissible range B. In the representation of FIG. 3, the position of the sump tip PS is approximately in the middle within the area B.

After the casting process has been started, in each calculation step, e.g. every 5 seconds, for the currently set target temperature curve, the amount of spray water in the area of the supporting strand guide 16 varies so that at the ends of the cooling zones of the supporting strand guide 16 the surface temperatures of the casting strand 10 match the values of the currently set target temperature. This is illustrated in the diagram of FIG. 2 and corresponds to step S3 in FIG. 5a.

In a step (i) of a method according to the invention, it is first checked whether the position of the sump tip PS is within the predetermined permissible range B. 5a, this corresponds to a sequence of steps S4, S6, S8 and S10.

According to one embodiment of a method according to the invention, in a step (ii), if the position of the sump tip PS is in the cold-critical region K, the cooling capacity for the secondary cooling of the supporting strand guide 16 is reduced by the secondary cooling being at least the next higher (= warmer) Set temperature curve is set (steps S4 + S5 of Fig. 5a). This is symbolized in FIG. 3 for the temperature curves which are indicated in the area K by the arrow pointing obliquely upward to the right. If necessary, depending on the position or position of the sump tip PS within the area K, the setpoint temperature curve can also be changed directly from the currently set curve to the set temperature curve which is higher (= warmer) than the next. As a result of the lower cooling capacity set in this way The position of the swamp tip PS then “migrates” in the conveying direction F back into the predetermined permissible range B.

Alternatively, in step (ii), if the position of the sump tip PS is in the warm-critical area W, the cooling capacity for the secondary cooling of the supporting strand guide 16 is increased by setting the secondary cooling to at least the next lower (= colder) target temperature curve (= Steps S6 + S7 of Fig. 5a). This is symbolized in FIG. 3 for the temperature curves, which are indicated in the area W, by the arrow pointing obliquely to the bottom left, depending on the location or position of the swamp tip PS (PS = "Point of Solidification") within the Area W, the setpoint temperature curve can also be changed directly from the currently set curve to the set temperature curve below (= colder). As a result of the larger cooling capacity set in this way, the position of the sump tip PS then also “moves” back to the predetermined permissible range B against the conveying direction F.

If it should be determined in step (ii) that the position of the sump tip PS is already in the safety area S, the secondary cooling of the supporting strand guide 16 (in this case in the cooling segment 4) is immediately - for safety reasons - to the lowest (= coldest) target temperature curve # x (see Fig. 2) set (=

Steps S8 + S9 of Fig. 5a), so that in any case it is avoided that the sump tip comes out of the supporting strand guide 16.

If it is determined by a corresponding query that the sump tip SP of the casting strand 10 is within the predetermined permissible range (= step S10 of FIG. 5a), the position of the sump tip PS within the predetermined permissible range B becomes according to a further embodiment of a method according to the invention optimized. Border areas are defined along the supporting strand guide 16, namely a first border area G1 between areas B and K, and a second border area G2 between areas B and W. These two border areas G1 and G2 are each completely within the predetermined permissible area B, and make part of it from, for example, 20% each. The optimization just mentioned within the permissible range B now works as follows:

In a step ii of this method, the target temperature curve is set to a next higher (= warmer) temperature curve. For this purpose, it is first checked whether the bottom tip PS of the casting strand is neither in the first boundary region G1 nor in the second boundary region G2 (= step S1 1 of FIG. 5b). If this is not the case, then the setpoint temperature curve is switched to the next higher temperature curve for the case or if the conditions exist that the position of the sump tip PS is not only within the predetermined permissible range B, but that on the one hand there is a set setpoint temperature curve for the casting strand 10 within a predetermined time of, for example Has not changed for 10 minutes (= step S12 of FIG. 5b) and, on the other hand, the calculated swamp lengths for the two next higher (= warmer) target temperature curves are also still within the predetermined range B (= step S13 of FIG. 5b). In this regard, it is emphasized that in step S13 of FIG. 5b, the determination of the sump length (and thus the position of the associated sump tip) for these two next higher neighboring target temperature curves is based both on the quantities stored in the memory 19 at the beginning of the continuous casting process and on the quantities Regression equations can be calculated. On the basis of this, the sump lengths of these two adjacent curves can be approximately determined from the regression equations. If the above-mentioned conditions are met, the cooling capacity of the secondary cooling in the region of the supporting strand guide 16 is then reduced by switching to the next higher (= warmer) target temperature curve (= step S14 of FIG. 5b).

At this point, it is emphasized separately that the use of the quantities stored in the memory 19 at the beginning of the continuous casting process and the said regression equation (s) in order to determine the bottom length of the two adjacent next higher target temperature curves in the last-mentioned embodiment is based on the fact that these neighboring curves have other target temperature curves and thus have a cooling different from the current casting process. Alternatively, the sump positions of the adjacent curves can also be determined using a further computing module, in which case the current casting parameters in combination with the cooling changed by the other target temperature curves are included in the calculation or are taken into account accordingly.

With the last-explained embodiments of a method according to the invention it is achieved that the position of the sump tip PS is shifted within the predetermined permissible range B - as shown in FIG. 3 - in the direction of the right edge or in the direction of the warm-critical area W. Said predetermined time can also deviate from said 10 minutes, and e.g. either take a value of> 5 minutes, have a value between 5 and 10 minutes, or 1 1 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes amount, or assume values of> 20 minutes.

The above-described switching is to be explained using a numerical example: Curve # v (cf. FIG. 2) is currently set for the setpoint temperature curve of the secondary cooling, the sump tip being located, for example, in the center within the predetermined permissible range B (cf. FIG. 3 ). If, based on this, the set temperature curve set for the casting strand 10 does not change for a period of, for example, 10 minutes, it is possible to switch to the next higher (= warmer) curve # iv, provided that both the position of the sump tip PS of this target temperature curve iv as well as the next but one target temperature curve iii are both still within area B. After another 10 minutes, for example, a next check is carried out in accordance with step (ii) of this method as to whether it is then possible to switch to the target temperature curve # iii. In addition to the numerical example mentioned above, it is pointed out that it is not possible at all casting speeds to select the warmest target temperature curve from the plurality of possible target temperature curves, which are shown, for example, in FIG. 2. This is due to the fact that the cooling of the casting strand in the area of the supporting strand guide should always be sufficiently high or intensive that the strand shell between the support rollers in the individual segments of the supporting strand guide does not bulge. In other words, the cooling of the casting strand, in particular in the first (inlet) segments of the supporting strand guide 16, must not be set too low, because otherwise the casting strand would undesirably bulge between the support rollers due to the strand shell being too thin. For example, at a selected casting speed, the target temperature curve # 3 (see FIG. 2) can be set as a minimum, but at a higher casting speed the target temperature curve # 5 (see FIG. 2) - as the minimum possible (= warmest possible) temperature curve - is to be set.

4 shows a circuit diagram according to a further embodiment of a method according to the invention. If it should now be recognized in step ii that the position of the sump tip PS of the casting strand 10 should lie in one of these boundary regions G1, G2 (fulfillment of the “YES” condition, in step S1 1 of FIG. 5b), the cooling capacity becomes Secondary cooling suitably changed (ie reduced if the position of the sump tip PS is in the first border area G1; and increased if the position of the sump tip PS is in the second border area G2), namely on the condition that an additional query should be made to determine that the position of the swamp tip (or the swamp length) “wanders” at a relatively high or significant speed and moves either in the direction of the cold-critical area K or in the direction of the warm-critical area W. This means that a change in the position of the sump tip over time is taken into account if this is relatively high, so that the cooling capacity can then be suitably changed as a function thereof. By changing the cooling capacity in this way, the bottom of the cast strand is achieved according to the invention 10 does not even get into the critical areas K or W when their position in one of the border areas G1 or G2 is recognized. This achieves the goal that if the bottom length of the sump of the casting strand 10 is in the first limit region G1 and “migrates” relatively quickly in the direction of the cold-critical region K, then a switch to a next higher (= warmer) setpoint temperature curve takes place soon enough, in order to avoid excessive switching or cooling, which may otherwise be necessary if the bottom of the sump had already entered the cold-critical area K. This applies mutatis mutandis in the case of an increasing or increasing sump length if the bottom tip of the casting strand 10 lies in the second border area G2 and moves relatively quickly in the direction of the warm-critical area W: in this case, the next lower (= colder) area is used early enough Setpoint temperature curve switched to thereby cool the casting strand 10 more intensely. The above-mentioned relationship of switching the cooling capacity as a function of a change in the length of the sump is explained using two examples:

If the position of the sump tip of the casting strand 10 is in the first limit area G1 of the predetermined permissible area B (= fulfillment of the “YES” condition in step S1 1 of FIG. 5b) and it is recognized that the position of the sump tip is significant is reduced or moves in the direction of the cold-critical area K, for example at a speed which corresponds to at least a change in the total sump length of the casting strand 10 of at least 1% (= steps S15 and S16 of FIG. 5b), then immediately the next higher (= warmer) target temperature curve switched (= step S17 of Fig. 5b) and thereby reduces the cooling capacity. In this way it can be prevented that, with the cooling capacity remaining the same, the bottom of the sump actually runs into the cold-critical area K due to the decreasing length of the sump, which would disadvantageously (and unnecessarily) reduce the energy content of the casting strand 10. Otherwise, ie in the event that the sump tip PS is in the first limit area G1, its position (ie the sump length of the casting strand 10) only changes changes slightly, namely with a value of <1% of the total sump length of the casting strand 10, the method after step S15 or S16 can also go directly to step S12 (see FIG. 5b). In contrast: If the position of the sump tip of the casting strand 10 is in the second limit area G2 of the predetermined permissible range B and it is recognized that the sump length increases significantly or the position of the sump tip PS moves in the direction of the warm-critical area W (= steps S15 and S18 from FIG. 5b), for example at a speed that corresponds to a change in the total sump length of the casting strand 10 of at least 1%, then the system immediately switches to the next lower (= colder) setpoint temperature curve (= step S19 from FIG. 5b) ) and thereby increases the cooling capacity. In this way, it can be prevented that, with the cooling capacity remaining the same, the sump tip would either run into the safety area S or even run out of the last segment 4 of the supporting strand guide 16 by further increasing the sump length. Otherwise, ie in the event that the position of the sump tip PS changes only slightly within the second limit range G2, namely with a value of <1% of the total sump length of the casting strand 10, the method can then proceed from step S18 to step S12 ( see Fig. 5b) go.

In connection with a switching of the target temperature curves mentioned above, namely to a next warmer temperature curve (= step S14 or step S17 of FIG. 5b) or to a next colder temperature curve (= step S19), it is pointed out that the process then then takes place Step S3 of Fig. 5a goes back.

With regard to the two examples mentioned above for taking into account the temporal change in the bottom position, it has been pointed out that this change can correspond to at least 1% of the change in the total bottom length of the casting strand 10. As an alternative to this, the "speed" at which the sump tip moves its position (either in the direction of the cold-critical area K or changed in the direction of the warm-critical area W), also a change in the total swamp length by 1, 1%, 1, 2%, 1, 3%, 1, 4%, 1, 5%, 1, 6%, 1, 7%, 1, 8%, 1, 9%, 2.0%, 2.1%, 2.2%, 2.3%, 2, 4%, 2, 5%, 2, 6%, 2, 7%, 2, 8%, 2.9%, 3.0%, or assume values that are either greater than 3.0% or between the above values.

The diagrams in FIGS. 6 and 7 illustrate the advantages of the invention over the conventional operation of a continuous casting installation. 6 illustrates the solidification length of the casting strand 10, and FIG. 7 illustrates the average temperature of the casting strand 10 at the inlet of a furnace (not shown) after the casting strand 10 has left the supporting strand guide 16, as a function of time, respectively. Here, the graphs according to the thick solid line are each achieved with a method according to the invention, the graphs according to the dotted lines in each case using a method or a method

Operation of a continuous caster according to the prior art. Fig. 6 illustrates that longer solidification lengths can be achieved with a method according to the present invention, synonymous with larger sump lengths and thus a higher energy content of the casting strand at the end of the supporting strand guide 16. Fig. 7 illustrates that with the invention a higher average temperature at Oven inlet is reached, which is on average above a desired target temperature.

Finally, it should be pointed out that, for the supporting strand guide, deviating from the representation in FIGS. 1 and 2, more or less than four cooling segments are also possible, and that for the number of setpoint temperature curves, deviating from the representation in FIG. 2, can also be more or less than ten. Reference list

10 cast strand

12 continuous caster

14 mold

16 supporting strand guide (the continuous caster 12)

1, 2, 3, 4 cooling segment (s) of the strand guide 16

18 control unit

19 memory (of the control unit 18)

20 signal path

B predetermined permissible range (within the supporting

Strand guide 16)

G1 first limit range

G2 second border area

K cold critical area (within the supporting strand guide 16) F conveying direction (for the casting strand 10)

PSP position of the solidification point (of the casting strand 10)

s security area

PS position of the sump tip (of the casting strand 10)

w warm critical area (within the supporting strand guide 16)

Claims

1. A method for controlling or regulating the temperature of a casting strand (10) in a continuous casting plant (12), the casting strand (10) after the continuous exit from a mold (14) by a supporting strand guide (16) of the continuous casting plant (12), which has at least one segment (1, 2, 3, 4) with secondary cooling, is guided along a conveying direction (F), the secondary cooling being set by a control or regulating unit (18) and thus the surfaces of the casting strand (10) are cooled, a temperature field being calculated for the casting strand along its conveying direction (F) within the supporting strand guide, and a position of the bottom tip (PS) of the casting strand (10) is determined therefrom, in a memory (19) of the control or regulating unit ( 18) for a casting strand material to be cast

(10) a plurality of target temperature curves (i - x) for the surface of the casting strand (10) are stored,

marked by:

(i) checking whether the position of the sump tip (PS) of the casting strand (10) is within a predetermined permissible range (B) within the supporting strand guide (16), and

(11) if the position of the sump tip (PS) of the casting strand (10) lies outside the predetermined permissible range and instead lies in a warm-critical region (W) of the supporting strand guide (16): increase the cooling capacity by the secondary cooling in the at least one segment (3) the supporting strand guide (16) is set to at least the next lower (= colder) target temperature curve; or:

If the position of the sump tip lies outside the predetermined permissible range (B) and instead lies in a cold-critical range (K) of the supporting strand guide (16): Reduction of the cooling capacity by the secondary cooling in the at least one Segment (3) of the supporting strand guide (16) is set to at least the next higher (= warmer) target temperature curve.

2. The method according to claim 1, characterized in that by means of the control or regulating unit (18) for all target temperature curves, which are stored in the memory (19) for the material to be cast, the resulting associated positions of the sump tip within the supporting strand guide (16) are calculated, in step (ii) the secondary cooling of the supporting strand guide (16) is set to the target temperature curve, the bottom of which is in the center of the predetermined permissible range (B).

3. The method according to claim 1 or 2, characterized in that if it should be determined in step (ii) that the bottom tip of the casting strand (10) is in a safety area of the warm-critical area, then the secondary cooling in the at least one segment of the supporting Strand guide (16) is immediately set to the lowest (= coldest) target temperature curve.

4. A method for controlling or regulating the temperature of a casting strand (10) in a continuous casting plant (12), the casting strand (10) after the continuous exit from a mold (14) by a supporting strand guide (16) of the continuous casting plant (12), which has at least one segment (1, 2, 3, 4) with secondary cooling, is guided along a conveying direction (F), the secondary cooling being set by a control or regulating unit (18) and thus the surfaces of the casting strand (10) be cooled, a temperature field being calculated for the casting strand along its conveying direction (F) within the supporting strand guide (16) and a position of the sump tip (PS) of the casting strand (10) being determined therefrom, wherein in a memory (19) the controller or Control unit (18) for a material to be cast Casting strand (10) a plurality of target temperature curves (ix) for the upper surface of the casting strand (10) are stored,

marked by:

(ii) if the position of the sump tip (PS) of the casting strand (10) is in the predetermined permissible range (B) of the supporting strand guide (16) and a set temperature curve has been set in the area of the at least one segment of the supporting strand guide (16) Has not changed the predetermined time of preferably at least 5 minutes and the calculated sump lengths for the two next higher (= warmer) target temperature curves are still in the predetermined permissible range (B) of the supporting strand guide (16): Reduction of the cooling capacity by the secondary cooling in the at least a segment (2) of the supporting strand guide (16) is set to the next higher (= warmer) target temperature curve.

5. The method according to claim 4, characterized in that if the position of the sump tip (PS) of the casting strand (10) is in the direction of the cold critical

Range (K) moves, then the cooling capacity is reduced by setting the secondary cooling in the at least one segment (2) of the supporting strand guide (16) to the next higher (= warmer) target temperature curve.

6. The method according to claim 5, characterized in that the cooling capacity is reduced by switching to the next higher (= warmer) target temperature curve if the bottom tip (SP) of the casting strand (10) in a first limit range (G1) of the predetermined permissible range ( B) is adjacent to the cold-critical area (K) and in the direction of the cold-critical area

Area (K) moves at a speed which corresponds to a change of at least 1% of the total sump length of the casting strand (10).

7. The method according to claim 4, characterized in that if the position of the sump tip (PS) of the casting strand (10) moves in the direction of the warm-critical area (W), then the cooling capacity is increased by the secondary cooling in the at least one segment (2) the supportive

Strand guide (16) is set to the next lower (= colder) target temperature curve.

8. The method according to claim 7, characterized in that the cooling capacity is increased by switching to the next lower (= colder) target temperature curve if the bottom tip (SP) of the casting strand (10) in a second limit range (G2) of the predetermined permissible range ( B) is adjacent to the warm-critical area (W) and moves in the direction of the warm-critical area (W) at a speed which corresponds to a change of at least 1% of the total sump length of the casting strand (10).

9. The method according to any one of the preceding claims, characterized in that steps (i) and (ii) are carried out fully automatically by the control or regulating unit (18).