Continuous casting of long products with a high mass flow

Abstract

The present invention is in the field of continuous casting technology and describes a continuous casting machine, a design method and a method for continuously casting long products with a high mass flow.The continuous casting machine for pouring liquid metal into a strand to produce billets or blooms with a mass throughput of 1.5 to 3.0 t / min is characterized in that the part of the mold in contact with the strand in the area of ​​the bath level has a wall thickness of between 3 and 8% of the smallest distance between two opposite sides of the casting format and the length of a support area is less than 5.5 m and the surface of the strand is cooled by spray cooling in the entire area from 0.6 to 11 m downstream of the bath level to a surface temperature of less than 950 °C and in the entire area from 3 to 7 m downstream of the bath level to a surface temperature of less than 900 °C.

Description

field of technology

[0001] The present invention is in the field of continuous casting technology and describes a continuous casting machine, a method for designing a continuous casting machine, and a method for operating a continuous casting machine. The continuous casting machine is suitable for casting steel into billets or blooms with a square or rectangular cross-section, an aspect ratio of 1:1 to 1:1.5, and a mass throughput of 1.5 to 3.0 t / min.

[0002] The design method is suitable for the design of such a continuous casting machine. The operating method concerns the operation of such a continuous casting machine. State of the art

[0003] If a continuous casting machine is operated in direct conjunction with a rolling mill, for example, this places special demands on the continuous casting machine. Plants for the production of long products in a continuous casting / rolling process are referred to as EBP plants (endless bar production). Cast products in the sense of intermediate products are typically billets, blooms, and pre-sections. A single-strand casting machine is directly connected to a rolling mill to produce a rolled product in a continuous process. In order to economically utilize the technically feasible mass throughputs of the rolling mill, the single-strand casting machine for long products must achieve mass throughputs in the range of 1.5 to 3 t / min. This requires significantly higher casting speeds than can be achieved with typical conventional concepts for such casting machines.

[0004] The production of rolled products in a continuous casting / rolling process offers several advantages. On the one hand, the technology offers the highest yield and the lowest specific CO2 emissions. On the other hand, such a process enables extremely stable and consistent production conditions that are unattainable with conventional, non-combined processes.

[0005] The invention describes a continuous casting machine that achieves the productivity required for operation in a continuous combined casting / rolling process. Even without operation in a continuous combined casting / rolling process, a continuous casting plant with high mass throughput offers economic advantages.

[0006] EP 3 493 929 B1 describes a continuous casting method and a device for continuously casting metal products using a casting arch. The casting of steel into billets or blooms with a polygonal shape is mentioned. WO 2020 / 261311 A1 describes a mold for continuously casting a metal product and a corresponding method. A mold with an octagonal cross-section is mentioned, which is suitable for particularly high casting speeds.

[0007] AT506847B1 describes a process for continuously casting a metal strand in a continuous casting plant. A strand is drawn from a cooled continuous mold, supported in a downstream strand support device, and cooled with a coolant. Thermodynamic changes in the state of the entire strand are taken into account in a mathematical simulation model. In the mathematical simulation model, a three-dimensional heat conduction equation is solved and the cooling of the strand is adjusted. Summary of the invention

[0008] This task is solved by ensuring that the part of the mold in contact with the strand in the area of ​​the bath level has a wall thickness between 3 and 8% of the smallest distance between two opposite sides of the casting format.

[0009] The length of a support area is less than 5.5 m, preferably less than 3 m.

[0010] The surface of the strand is cooled by spray cooling, wherein the spray cooling comprises a plurality of spray nozzles which are arranged in the casting direction along and in a circumferential direction of the strand to be cast.

[0011] Thus, the spray nozzles can apply cooling medium to all sides of the strand to be cast along a single casting direction. The respective spray nozzle positions and cooling medium volume flows largely determine the local distribution of the heat flow dissipated from the strand surface.

[0012] Each spray nozzle is connected to an actuator, which is preferably a valve and / or a pump, wherein a control device and / or regulating device determines a control variable for at least one actuator as a function of at least one casting speed such that a surface temperature of less than 950 °C can be set in an entire range from 0.9 to 11 m, preferably in an entire range from 0.3 m to 14 m downstream of the mold outlet, and a surface temperature of less than 900 °C can be set in an entire range from 3 to 7 m, preferably in an entire range from 2 to 10 m downstream of the mold outlet.

[0013] Typically, several spray nozzles are connected to a control element. Each of these spray nozzles forms a zone. Different zones can be supplied with different cooling medium volume flows via the control elements. This allows the spatial distribution of the heat flow dissipated from the strand surface to be influenced.

[0014] The high mass throughput through the continuous casting machine results in a high heat flow in the mold. In order to keep the temperature of the mold as low as possible, especially the wall in contact with the liquid steel, a thin wall thickness is required. The heat flow from the solidifying strand via the mold wall to the cooling water thus leads to a wall temperature on the strand side that is within the permissible range for the mold material, typically a copper alloy. After the strand leaves the mold, the still thin and fragile solidified strand shell must be supported by a corset of strand guide rollers that is as dense as possible. The area from the meniscus to the end of this corset, comprising the mold and the support rollers arranged at a short distance from one another, is referred to as the support zone. The design of the support zone involves considerable technical effort.This applies to the manufacture of the continuous casting machine, as well as its operation and maintenance. From this perspective, the shortest possible support length is advantageous.

[0015] To achieve the high mass throughputs described, appropriate cooling of the strand is required. The design of the spray cooling system includes the arrangement of the spray nozzles in the continuous casting machine, the type of spray nozzles, as well as the pressures and volume flows of the cooling media supplied to the nozzles, preferably water and air. The first cooling section, or section I, is located in the mold. Here, heat transfer takes place via thermal conduction. In the second cooling section, or section II, which extends over a support area below the mold, a high heat flux density must be maintained. This is achieved by a correspondingly high strand-related water density of typically 100 to 500 liters / m². The surface temperature is brought below the described limits and initially maintained there. This ensures sufficient rigidity of the strand shell.The first and second cooling sections are referred to as the support zone, as the strand requires support here due to the still thin strand shell. Subsequently, in the third cooling section, or Section III, a controlled reheating of the strand surface takes place. This is achieved by an appropriate water application density of typically 10 to 100 liters / m². In the fourth cooling section, or Section IV, the strand is no longer exposed to water. The limited reheating in the fourth cooling section limits thermal stresses in the strand.

[0016] In a preferred embodiment, the casting format has four chamfers, each of 10 to 27% of the length of a side.

[0017] The shape of the cross-section of the strand, i.e. the casting cross-section, has a significant influence on the possible mass throughput through the continuous casting machine for a given length of the support area.

[0018] On the one hand, the cross-sectional area of ​​the strand should be maximized for a given width and height. This requirement would result in a rectangle.

[0019] On the other hand, mechanical stresses in the strand shell due to the hydrostatic pressure in the liquid core of the strand should be reduced as much as possible. This requirement would result in a circle.

[0020] The solution is a rectangle with chamfers, i.e. a rectangle whose corners are trimmed by straight lines.

[0021] To numerically specify the chamfers, the distances by which the respective intersection points are removed from the corners of the underlying rectangle are related to the side lengths of this rectangle.

[0022] A further advantage over a rectangular casting format results from the fewer acute angles of consecutive straight sections along the edge of a strand cross-section. This results in less "overcooling" of the edges, thus achieving a more uniform surface temperature of the strand and reducing the susceptibility to cracking in the edge area.

[0023] A further development of this approach leads to higher-order polygons with, for example, ten or twelve sides.

[0024] In a further preferred embodiment, the spray nozzles are supplied with a water pressure of 10 to 30 bar, preferably 12 to 20 bar.

[0025] To achieve the intensive cooling of the strand surface in the first and second cooling sections with correspondingly high cooling water flows for spray cooling, high water pressure is required. The level of water pressure influences the heat transfer coefficient, which determines the heat transfer from the strand to the cooling water due to convection. In particular, the Leidenfrost temperature, i.e., the surface temperature below which a significantly increased heat transfer coefficient occurs, can be influenced by the water pressure or spray density.

[0026] In a further preferred embodiment, the continuous casting machine is directly connected to a rolling mill.

[0027] In a further preferred embodiment, the strand is supported in a support area below the mold by strand guide rollers on all sides of the strand. The distances between the axes of the immediately adjacent strand guide rollers in the casting direction are between 100 and 500 mm, preferably between 125 and 400 mm, with these roller spacings increasing successively in the casting direction.

[0028] After the strand leaves the mold, the still thin and fragile strand shell must be supported by a tightly packed corset of strand guide rollers. In this part of the support area below the mold, a close spacing of the strand guide rollers adjacent in the casting direction is important. The greater the spacing of the strand guide rollers, the greater the bulging of the strand shell due to its thinness, its softness, and the hydrostatic pressure in the liquid core of the strand. As the thickness of the strand shell increases and the temperature of the strand shell decreases, the permissible spacing of the strand guide rollers increases.

[0029] In a further preferred embodiment, the strand is supported in the support area below the mold by strand guide rollers on all sides and chamfers of the strand.

[0030] The larger the chamfers, the greater the bulging of the strand's side surfaces in the chamfer area, and thus the deformation of the strand shell there. To limit this deformation, strand guide rollers are used, which also support these surfaces.

[0031] In a further preferred embodiment, the corners on the cast product are rounded with a radius between 2 and 30 mm, preferably between 6 and 15 mm.

[0032] Stress concentrations can occur in the corners of the cast product, leading to the formation of cracks, especially edge cracks. This leads to quality problems and requires complex post-processing of the cast product.

[0033] This problem is solved by introducing radii at the corners of the strand cross-section. These radii reduce stress peaks and thus lower maximum stresses, resulting in fewer cracks in the cast product.

[0034] In a further preferred embodiment, the sides and / or bevels of the casting format are concave, i.e. curved on the inside, wherein the indentation, i.e. the maximum normal distance from the respectively assumed straight contour, corresponds to 0.25 - 5%, preferably 0.5 - 2.5% of the length of the latter.

[0035] These indentations, also known as "negative bulging," act as pre-deformation. The hydrostatic pressure in the liquid core of the strand causes the side surfaces to bulge outward. By superimposing these effects, largely flat or less bulging outer surfaces of the strand are achieved.

[0036] In a further preferred embodiment, the sides and / or bevels of the casting format are convex, i.e. curved on the outside, wherein the bulge, i.e. the maximum standard distance from the respectively straight-line assumed contour, corresponds to at least 1% of the length of the latter.

[0037] In a further preferred embodiment, the sides and / or chamfers of the casting format are initially straight from the top edge of the mold to the mold outlet and assume a concave shape as they extend toward the mold outlet. There, they are thus curved inward, with the indentation, i.e., the maximum standard distance from the respectively assumed straight contour of the side or chamfer in the area of ​​the mold outlet, corresponding to 0.25-5%, preferably 0.5-2.5%, of the length of this assumed straight contour.

[0038] The state of the art already demonstrates an adaptation of the mold cross-section to shrinkage caused by strand cooling in the form of conical or "tapered" molds. According to one embodiment, an indentation of the mold walls that increases in the casting direction is described. This indentation counteracts the lifting of the strand shell from the mold wall caused by shrinkage of the casting format and can even lead to overcompensation for thermal shrinkage. This avoids or reduces the size of areas where reduced contact pressure or even lifting occurs between the mold wall and the strand. This ensures good heat transfer between the mold wall and the strand shell, especially away from the edges. In the area of ​​the already colder edges, the contact pressure and thus the heat transfer are reduced by the convex shape of the indentation.This promotes uniform shell growth and reduces friction in the mold. This prevents high pull-out forces and the associated high tensile stresses in the strand shell, which could cause it to crack, while simultaneously promoting uniform and rapid strand shell growth through improved heat transfer. This enables high casting speeds with a reduced risk of breakouts.

[0039] In a further preferred embodiment, the length of the mold, seen in the casting direction, is between 0.9 and 1.3 m. It has been found that this range of values ​​represents a good compromise between a sufficiently thick shell due to a residence time of the strand in the mold and the lowest possible strand friction in the mold.

[0040] Reducing the length of the mold also reduces the contact area between the mold wall and the strand surface. This also reduces the forces resulting from friction. However, due to the short residence time of each strand section in the mold, only a very thin strand shell can form, increasing the risk of shell breakouts.

[0041] Although this risk can be counteracted by extending the mold, this comes at the expense of increased friction.

[0042] In a further preferred embodiment, the mold performs an oscillation movement in the vertical direction with an oscillation frequency between 3 and 6.6 Hz, preferably between 3.3 and 5.5 Hz.

[0043] The oscillation movement creates a defined relative movement between the strand shell and the mold wall, thus preventing the strand shell from sticking to the mold wall.

[0044] In a further preferred embodiment, a drive / straightening unit is included which comprises three or more driven rollers.

[0045] By having multiple driven rollers, the forces required to drive the strand can be distributed. This reduces localized forces and the associated deformation of the soft and sensitive strand shell. This improves the quality of a metallurgical product. Experience has shown that the specified minimum number of driven rollers ensures smooth and jerk-free strand withdrawal. Strand jerking can lead to mold level fluctuations. These occur particularly at high casting speeds and increase the risk of breakouts.

[0046] In a further preferred embodiment, the mold is straight, i.e. designed in such a way that the strand in the mold does not experience any curvature.

[0047] Since in this case all sides of the mold are designed very similarly and without significant curvature, a similar heat transfer occurs between all sides of the mold and the strand surface. This leads to uniform and thus advantageous growth of the strand shell.

[0048] A further advantage is that the mold oscillation can be linear. This leads to a simpler design of the continuous casting machine. Experience has shown that straight molds have a positive effect on the friction between the mold and the strand surface.

[0049] In a further preferred embodiment, the mold is bent, i.e. designed in such a way that the strand undergoes a curvature in the mold.

[0050] Due to the curved design, the already bent strand leaves the mold and can pass through the arch of a continuous casting machine without first passing through a bending zone.

[0051] With this design, no bending of the strand in the strand guide is required. This also prevents any associated deformation of the strand shell or mechanical stresses in the strand shell.

[0052] In a further preferred embodiment, strand guide rollers are arranged on all sides of the casting format between the end of the support area and before the start of the driving / straightening unit, as seen in the casting direction, wherein the length sections of the areas not guided by these strand guide rollers, as seen in the casting direction, are between 1.5 and 3 m.

[0053] The support and guidance of the strand on all sides of the casting format also prevents the strand from "running out," i.e., breaking away from the strand guide area. Causes of this breakaway tendency could be temperature differences on the strand surface or uneven application of forces from the driving / straightening unit to the strand.

[0054] Furthermore, the task is solved by a design method that includes a calculation model for calculating the thickness of a strand shell as well as mechanical stresses in the strand shell. The result of the calculation model depends on the casting format and a calculated hydrostatic pressure in the liquid core of the strand. The thickness of the strand shell itself depends on several variables. For example, these include spray cooling, including spray nozzles and cooling medium volume flows / pressures, as well as the temperature of the steel flowing into the mold.

[0055] The yield stress of the steel of the strand shell depends on the chemical composition of the steel and the temperature of the steel and can be found in the literature.

[0056] The design is such that the ratio of a maximum calculated tensile stress in the strand shell of the solidifying strand to a yield stress in the solidified shell is less than one, preferably less than 0.5, particularly preferably less than 0.2. If this ratio were greater than one, severe deformation of the strand shell would occur, leading to subsequent tearing.

[0057] Furthermore, the object is achieved by a method for operating a continuous casting machine, wherein the temperature distribution in the strand and on its surface during operation is calculated using a mathematical model. The temperature of the strand surface is controlled by controlling the cooling water flow from spray nozzles such that, after the end of the secondary cooling, the strand surface is reheated by less than 200 K. This reheating is preferably between 50 K and 150 K, particularly preferably 100 K.

[0058] The mathematical model can determine temperature profiles on the surface and inside the strand from input variables such as operating parameters and design data of a spray cooling system. The spray cooling system includes spray nozzles, characterized by their nozzle characteristics, spray patterns, and spray nozzle positions. The operating parameters include cooling medium flow rates and cooling medium pressures. Using iterative calculation steps, the operating parameters can be optimized to achieve the desired temperature profiles on the strand surface.

[0059] A key point here is that the calculation of the local heat transfer coefficients required to determine the convective heat transfer from the train to the cooling water depends on the cooling water pressure and the local cooling water flow density. In particular, the calculation of the Leidenfrost temperature, i.e., the temperature below which the local heat transfer coefficient increases sharply, plays a crucial role.

[0060] In a preferred embodiment, the temperature distribution inside the strand and on its surface during operation is calculated using a mathematical model, and a locally averaged temperature of a cross-section of the strand is determined. Furthermore, a minimum and maximum temperature of this cross-section are determined.

[0061] This cross-section is located in the area where the strand enters a rolling mill stand. The measured temperatures are used for the rolling process. Short description of the drawings

[0062] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of an embodiment, which is explained in more detail in conjunction with the drawings. Fig. 1 a sectional view of a continuous casting machine comprising a strand, a mold, a support area, spray nozzles, a drive / straightening unit, driven rollers and strand guide rollers, Fig. 2 a representation of a surface temperature profile of a strand along a casting direction, Fig. 3 a representation of the cross-section of a cast product with a cross-section based on a rectangular cross-section with four chamfers, Fig. 4 a representation of the cross-section of a cast product with rounded corners and Fig. 5 an exaggerated representation of a concave shape of the sides and bevels of a casting format, Fig. 6 a representation of the cross-section of a cast product with four first chamfers and four further chamfers, Fig. 7 a representation of another cross-section of a cast product with four first chamfers and four further chamfers. Description of the embodiments

[0063] Fig. 1 shows an embodiment of the invention in the form of a sectional view of a continuous casting machine, comprising a strand 1, a mold 2, a support area 4, spray nozzles 6, a drive / straightening unit 7 with driven rollers 8 and strand guide rollers 10. In the support area, the strand guide rollers, in addition to their function of guiding the strand, also take on the task of supporting the strand cross-section. The strand 1 extends from the bath level 3 in the casting direction 5 by strand guide rollers 10 through the continuous casting machine until it leaves the drive / straightening unit. The strand 1 forms a strand shell 11 which, starting from the outer surfaces, grows continuously as it passes through the continuous casting machine until a complete solidification point is reached. The cross-sectional area of ​​the liquid core 12 decreases continuously until it disappears completely at the complete solidification point.During the solidification process, the strand is cooled, thus dissipating heat into the environment. The spray nozzles 6 play a key role in this, enabling significant heat transfer via convection. The spray nozzles thus represent an important control variable for influencing the surface temperature of the strand.

[0064] Fig. 2 shows a representation of the surface temperature profile of strand 1 along casting direction 5. The graph begins in the area of ​​the meniscus below which the strand shell begins to form. In section I, i.e. the mold, there is initially particularly strong cooling of the strand surface within the mold. This is made possible by a still very thin strand shell and very effective cooling within the mold. In section II, i.e. in the support area below the mold, the strong cooling of the strand surface is initially continued by spray cooling and then the low temperature level achieved is kept below a certain limit temperature. In section III, the strand continues to be cooled by spray cooling, but there is already a moderate increase in the surface temperature of the strand.In section IV, there is no spray cooling, resulting in a more pronounced temperature rise and thus reheating of the strand surface. The amount of reheating is significant. The support area extends over sections I and II, while the spray cooling area extends over sections II and III.

[0065] Fig. 3 shows a representation of the cross section of a cast product with a cross section based on a rectangular cross section and 4 chamfers.

[0066] Fig. 4 shows a representation of the cross-section of a cast product with rounded corners, which reduces stress concentrations and thus susceptibility to cracking in the area of ​​the edges of the strand.

[0067] Fig. 5 Shows an exaggerated representation of the concave shape of the sides and chamfers of the casting format. This shape can be advantageous, for example, in the area of ​​the mold outlet. The sides and chamfers can initially be straight in the area of ​​the mold's upper edge. The transition is made in such a way that the mold wall exerts as even a pressure as possible on the wall of the casting format during its journey through the mold, thus improving heat transfer from the cast product to the mold.

[0068] Fig. 6 shows a representation of a cross-section of a cast product based on a rectangular cross-section with initially four first chamfers 20 and four further chamfers 21.

[0069] Fig. 7shows a representation of a cross-section of a cast product based on a rectangular cross-section with initially four first chamfers 20 and four further chamfers 21, such that a decagon results for the casting format.

[0070] Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention. List of reference symbols

[0071] 1 Strand 2 Mould 2a Mould outlet 3 Bath level 4 Support area 5 Casting direction or z-direction 6 Spray nozzles 7 Drive / straightening unit 8 Driven rollers 9 Length of the support area 10 Strand guide rollers 11 Strand shell 12 Liquid core 20 First chamfers 21 Further chamfers

Claims

1. Continuous casting machine for casting a liquid metal, preferably steel, into a strand to produce billets or blooms with a cross-section based on a square or rectangular cross-section with an aspect ratio of 1 to 1 to 1 to 1.5 and a mass throughput of 1.5 - 3.0 t / min, comprising a spray cooling system (6) with an arrangement of spray nozzles characterized by thatthe part of a mold (2) in contact with the strand (1) to be cast has a wall thickness of between 3% and 8% of the smallest distance between two opposite sides of a casting format in the area of ​​a bath level (3), and the length of a support area (9) is less than 5.5 m, preferably less than 3 m, and the surface of the strand to be cast is cooled by spray cooling, wherein the spray cooling comprises a plurality of spray nozzles arranged in the casting direction along and in a circumferential direction of the strand to be cast, wherein each spray nozzle is connected to an actuator, which is preferably a valve and / or a pump, wherein a control device and / or regulating device determines a control variable for at least one actuator as a function of at least one casting speed in such a way that thatin an entire range of 0.9 to 11 m, preferably in an entire range of 0.3 to 14 m downstream of the mold outlet (2a), a surface temperature of less than 950 °C can be set, and in an entire range of 3 to 7 m, preferably in an entire range of 2 to 10 m downstream of the mold outlet, a surface temperature of less than 900 °C can be set.

2. Continuous casting machine according to claim 1, wherein a casting format of the strand has four chamfers of 5 to 30% each, preferably 10 to 27% each of a length of one side.

3. Continuous casting machine according to claim 2, wherein the support of the strand in the support area below the mold is provided by strand guide rollers on all sides and chamfers of the strand.

4. Continuous casting machine according to claim 1, wherein the corners on the strand are rounded with a radius between 2 and 30 mm, preferably between 6 and 15 mm.

5. Continuous casting machine according to claim 1, wherein the sides and / or bevels of the casting format are concave, i.e. curved inwards, wherein the indentation, i.e. the maximum normal distance from the respectively assumed straight contour, corresponds to 0.25 - 5%, preferably 0.5 - 2.5% of the length of the latter.

6. Continuous casting machine according to claim 1, wherein the sides and / or bevels of the casting format from a mold upper edge to a mold outlet at the mold upper edge are initially straight (or convex) and assume a concave (or flat) shape towards the mold outlet, i.e. are curved inwards (or flat), wherein the bulge, i.e. the maximum standard distance from the respectively assumed straight contour of the side or bevel in the region of the mold outlet corresponds to 0.25 - 5%, preferably 0.5 - 2.5% of the length of this assumed straight contour.

7. Continuous casting machine according to claim 1, comprising a drive / straightening unit (7) comprising at least three driven rollers (8).

8. Continuous casting machine according to claim 1, wherein the mold is straight, i.e. designed in such a way that the strand in the mold does not experience any curvature.

9. Continuous casting machine according to claim 1, wherein the mold is curved, i.e. designed in such a way that the strand undergoes a curvature in the mold.

10. Continuous casting machine according to one of the preceding claims, wherein strand guide rollers are arranged on all sides of the casting format between the end of the support area and before the start of the driving / straightening unit, viewed in the casting direction, wherein the length sections of the areas not guided by these strand guide rollers, viewed in the casting direction, are between 1.5 and 3 m.

11. Continuous casting machine according to claim 2, wherein the casting format of the strand has four further chamfers of 5 to 30% each, preferably 10 to 27% each of a length of one side.

12. Continuous casting machine according to claim 2, wherein the casting format of the strand has four further chamfers of 5 to 50% of a length of one side each, such that the casting format results in a decagon.

13. Continuous casting machine according to claim 1, characterized by that the continuous casting machine is directly connected to a rolling mill and the temperature distribution inside a strand and on its surface during operation is calculated by a mathematical model, and a locally averaged temperature of a cross-section of the strand is determined, as well as a minimum and maximum temperature of this cross-section, and these temperatures are made available to a rolling process downstream of the continuous casting machine.

14. Method for designing a continuous casting machine for casting steel into a strand with a predetermined casting format, preferably for producing billets or blooms, characterized by thata calculation model is created for calculating a thickness of a strand shell (11) and a liquid core (12), as well as mechanical stresses in the strand shell as a function of at least the casting format, a calculated hydrostatic pressure in the liquid core, a spray cooling, comprising cooling medium volume flows, a chemical composition and a temperature of the steel flowing into the mold, and plant parameters, comprising roller spacings and cooling medium volume flows, are designed such that the ratio of a maximum tensile stress in the strand shell of the solidifying strand, calculated by means of the calculation model, to a predetermined yield stress in the strand shell is less than one, preferably less than 0.5, particularly preferably less than 0.

3.

15. Method for operating a continuous casting machine for casting steel into a strand with a predetermined casting format, preferably for producing billets or blooms, characterized by that the temperature distribution in the strand and on its surface is calculated during operation by a mathematical model, and the temperature of the surface of the strand is controlled / regulated by controlling cooling water quantities from spray nozzles in such a way that after the end of secondary cooling, the strand surface is reheated by less than 200 K, preferably less than 150 K.

Images