METHOD FOR BALANCING THE FLOW OF MOLTEN STEEL IN A MOLD AND SYSTEM FOR CONTINUOUS CASTING OF MOLTEN STEEL - Patent application

Abstract

A method for balancing the flow of molten steel in a mold, in which steel is fed into the mold (12) from a distributor through protective nozzles that open below the steel surface in the mold, comprises the steps of: a) obtaining a set of flow characteristics in the mold; b) comparing the flow characteristics obtained in the previous step with a predefined model and determining corrective actions to be taken to balance the flows; and c) adjusting the flows.

Description

[Technical field]

[0001] The present invention relates to a continuous casting system for metals. More particularly, the present invention relates to a method for balancing the flow of molten steel in a mold. According to another aspect, the present invention relates to a continuous casting system for molten steel. [Background technology]

[0002] Continuous casting plants for metals, such as steel, typically have a mold into which the molten metal from the tundish is poured to solidify into the desired shape. For example, a bottomless mold is used, where the metal is cooled to form a slab. To cool the molten metal, the walls of the mold are fitted with a cooling device, such as a liquid cooler, next to or behind them. The mold and cooling device are designed to match the flow rate of the metal so that when the slab leaves the mold, its outer surface is solidified to a thickness sufficient to contain the metal still molten in the center of the slab.

[0003] The tundish is equipped with one or sometimes several nozzles below the steel surface in the mold to protect the molten metal as it flows towards the mold. Generally, the nozzles are arranged symmetrically with respect to the mold to ensure as uniform a flow as possible during the continuous casting operation. In fact, uneven flow in the mold can have a negative effect on the quality of the slab, including the risk of breakouts, inhomogeneity of the cast steel, and poor distribution of the lubricant powder.

[0004] However, the equilibrium of the flow of molten steel from the tundish to the mold can be disturbed by some malfunction. For example, one of the nozzle holes can be eroded or blocked with alumina, steel can solidify in the nozzle, or even the nozzle can become clogged with debris. Such malfunctions can disrupt the symmetry of the flow and potentially compromise the quality of the produced slabs, as well as damage the continuous casting equipment. Currently, there is no way to detect such a situation, much less how to deal with it. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to detect a trouble that causes a disturbance in the flow of molten steel and to restore symmetry of the flow. [Means for solving the problem]

[0006] Therefore, the present invention provides a method for balancing the flow of molten steel in a mold, in which the steel is fed from a tundish into the mold through a submerged entry nozzle that opens below the steel surface in the mold, comprising: a) obtaining a set of characteristics of the flow in the mold; b) comparing the flow characteristics obtained in the previous step with a default model and determining the corrective actions to be taken to balance the flows; c) adjusting the flow; The present invention provides a method comprising:

[0007] Thus, by measuring the flow characteristics and comparing the measurements with a predefined model, it is possible to determine whether the flow is disturbed, thereby allowing an almost instantaneous assessment of the quality of the flow, and if disturbances are present, i.e., if there is a large enough discrepancy between the measured characteristics and the model, they can be addressed by adjusting the flow to mitigate the disturbance, thus significantly improving the quality of the produced slabs.

[0008] Advantageously, steps a) to c) are repeated continuously during the casting operation.

[0009] In this way, the method can be carried out throughout the operating life of the continuous casting installation.

[0010] Advantageously, the flow characteristics are obtained by analysis of the thermal characteristics of the steel in the mould.

[0011] The temperature of the mold can be easily measured at numerous locations, which helps make the method easy to implement.

[0012] Advantageously, the mould is of the type consisting of an assembly of metal plates behind a cooling device arranged to cool the metal plates by the circulation of a cooling fluid, and at least one of said metal plates comprises in its wall an optical fibre extending in a direction not parallel to the casting axis of the mould and comprising a number of Bragg filters.

[0013] Advantageously, the method further comprises: - measuring the temperature of at least one wall of the mold by means of optical fibers; - adjusting the flow; Includes.

[0014] Thus, the temperature is measured by optical fiber, which is reliable and easy to install in the mould, in particular as described in Belgian patent application no. 2018 / 5193 or in the Belgian patent application filed simultaneously with the present application.

[0015] Advantageously, flow regulation is achieved by inducing relative movement between the nozzle and the mould.

[0016] Preferably, the relative movement between the nozzle and the mold is in a direction parallel to the longitudinal axis of the mold.

[0017] Advantageously, the nozzle is integral with the tundish and relative movement between the nozzle and the mold is achieved by moving the tundish relative to the mold, for example by small movements of a tundish supporting carriage.

[0018] According to a variant of the invention, the relative movement between the nozzle and the mold is performed by angularly offsetting the nozzle according to the longitudinal axis of the mold. It is also possible to combine the two movements (linear and rotational).

[0019] As a variant, if the tundish is equipped with a pouring nozzle changing device or with a device for regulating the steel flow rate by a throttling action using a plate moving perpendicular to the direction of flow, it is sufficient to move such a device relative to the mold.

[0020] Therefore, flow regulation is achieved by an easily implemented manipulation.

[0021] In the present invention, in a molten steel continuous casting system from a tundish to a continuous casting mold, - A tundish, - a mould of the type consisting of an assembly of metal plates behind which is provided a cooling device arranged to cool said metal plates by the circulation of a cooling fluid, and comprising in the wall of at least one of said metal plates an optical fibre extending in a direction not parallel to the casting axis of the mould, said optical fibre comprising a number of Bragg filters; - a submerged nozzle whose lower end opens below the steel surface in the mold when the steel is poured, the nozzle being integral with the tundish; - a transmitter / receiver arranged to transmit light into an optical fiber and receive at least one of reflected light and transmitted light by the optical fiber; - a processor, a) converting data regarding at least one of the reflected light and the transmitted light received by the transmitting / receiving device into information regarding the flow in the mold; b) compare that information with a given model; c) determining the corrective measures to be taken to balance flows; d) Issue a control signal A processor arranged as follows: - adjusting means arranged to receive a control signal and adjust the flow of steel in the mold in response to the control signal; The present invention further provides a system comprising:

[0022] Advantageously, the adjustment means comprises a tundish holding carriage.

[0023] The adjustment means are therefore formed by simple means.

[0024] Embodiments of the invention will now be described, given as non-limiting examples, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0025] [Figure 1] 1 is a general view of a continuous metal casting installation enabling the implementation of a method for balancing the flow of molten steel in a mold according to the invention; [Figure 2a] FIG. 2 is a diagram showing the operation of the equipment of FIG. 1. [Figure 2b] FIG. 2 is a diagram showing the operation of the equipment of FIG. 1. [Diagram 3] FIG. 2 is a cross-sectional view of the mold of the installation of FIG. 1. [Figure 4] FIG. 4 is a perspective view of a plate of the mold of FIG. 3. [Diagram 5] 5 is a longitudinal cross-sectional view of an optical fiber contained in the wall of FIG. 4. [Figure 6] 6 is a diagram illustrating the operation of the optical fiber of FIG. 5. [Figure 7] 2 is an enlarged view of the installation of FIG. 1 illustrating the implementation of a method for balancing the flow of molten steel within a mold. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Figure 1 shows a continuous metal casting plant 2. The plant is of conventional design and most of its components will only be briefly introduced.

[0027] The plant 2 comprises ladles 4 containing the molten metal to be cooled. There are two ladles 4 here, both supported by a mechanical arm 6. This mechanical arm 6 is notably capable of transferring the ladles 4, which have been brought full to the pouring zone by a transfer system (such as an overhead crane, not shown) from a charging zone, such as a furnace or converter (not shown), in which the molten metal can be poured into the ladles 4 before they are brought to the position shown in Figure 1. The mechanical arm 6 is also capable of bringing the emptied ladles 4 to a position where they can be taken up again by the transfer system, from where they are transported to a preparation zone to be reconditioned and then returned to the charging zone.

[0028] The installation 2 comprises a tundish, or tundish 8, located below the ladle 4. The ladle 4 has a retractable bottom through which molten metal can be poured into the tundish 8.

[0029] The tundish 8 is provided with a sprue which can be closed with a stopper 10 which allows to control the flow of the molten metal. The sprue of the tundish is connected to a submerged entry nozzle 11 (also called submerged casting nozzle, SEN) which allows to protect the molten metal being poured. The submerged entry nozzle 11 is integral with the tundish 8.

[0030] As can be seen best in Figure 2a and enlarged view in Figure 2b, the submerged nozzle 11 opens into the top opening of a mould 12. This is a bottomless mould with a vertical pouring axis. The mould 12 will be described in more detail below.

[0031] The installation 2 comprises a cooling device 14 arranged on the outer surface of the mould 12. This is a liquid cooling device. To this end, the cooling device comprises pipes through which a cooling fluid, such as water, flows. The cooling fluid absorbs heat from the molten metal in the mould 12, thereby cooling it and solidifying it. In this case, the metal solidifies to form a slab with a solidified outer surface 18 encasing a liquid core 20.

[0032] The installation 2 comprises a roller guide 16 downstream of the mould 12. The guide 16 is capable of guiding the slab, whose outer surface 18 has solidified, out of the mould 12. As can be seen in Figure 2a, the slab solidifies gradually as it moves through the guide 16. That is, as it moves away from the mould 12, the volume of the solidified outer surface 18 of the slab increases and the volume of the liquid core 20 of the slab decreases.

[0033] The mould 12 is shown in more detail in Figure 3, which shows four plates 22 (the fourth is not visible due to the position of the cross-section). The plates 22 are made of copper or a copper alloy, a material with a high thermal conductivity, which facilitates heat exchange between the cooling device 14 and the mould 12. The plates 22 are arranged so that the mould 12 has an overall rectangular or square cross-section. However, it is also conceivable to arrange the plates so that the mould has any different shape, whether in cross-section or not, e.g. a funnel-shaped upper part, which is conventionally used in the casting of thin slabs.

[0034] In the following, for simplicity, the invention will be described in more detail on the basis of the mould layout described in Belgian patent application no. 2018 / 5193, i.e. with the optical fibres housed in passages formed in the walls of the mould, although it should be understood that in another embodiment of the invention the optical fibres can also be housed in grooves formed in the surface of the mould and filled by the strip, as described in the Belgian patent application filed concurrently herewith.

[0035] One of the plates 22 of the mold 12 is shown in an enlarged view in FIG. 4. In this view, the vertical direction corresponds to the casting axis. The plate 22 comprises in its wall at least one passage 24 which extends in a direction not parallel to the casting axis of the mold 12. More precisely, the passage 24 has an angle in the range of 75° to 105° to the casting axis. Here, the passages 24 are perpendicular to the casting axis. The number of passages 24 is here four. In the zone of the plate 22 where the passages 24 open, a protective cover 26 is provided to protect the passages 24.

[0036] An optical fiber 28 is housed in each of the passages 24. As shown in Figs. 5 and 6, each optical fiber 28 comprises a cladding 30 and a core 32 surrounded by the cladding 30. The optical fiber 28 comprises a plurality of Bragg filters 34 in its core 32. The optical fiber 28 comprises at least 10 Bragg filters 10 per meter, preferably at least 20 Bragg filters per meter, more preferably at least 30 Bragg filters per meter, and even more preferably at least 40 Bragg filters per meter. In an alternative embodiment, the mold could comprise only one optical fiber. In the following, for ease of explanation, the installation 2 is considered to comprise only one optical fiber.

[0037] The operation of the optical fiber 28 is shown in Figure 6. The Bragg filter 34 is a filter capable of reflecting light in a wavelength band centered on a given value, called the reflection wavelength, which can be adjusted by the filter manufacturer. This given value is also a function, among other things, of the temperature at which the filter is placed, and the relationship can be written for each filter as follows: λ 反射 =f(λ0,T) Here, λ 反射 is the wavelength effectively reflected by the filter, f is a known function, T is the temperature of the filter, and λ 0 is the wavelength reflected by the filter at a given temperature, e.g., ambient temperature.

[0038] These two properties make it possible to use the optical fiber 28 as a temperature sensor. First, a Bragg filter 34 is arranged in the optical fiber 28, each having a different reflected wavelength value λ0, chosen, for example, 5 nanometers apart. Then, a light beam of polychromatic spectrum 35a, for example white light, is sent into the optical fiber 28 and the wavelength peaks appearing in the spectrum 35b of the reflected beam are determined. For each peak, the measured value λ 反射with the theoretical reflected wavelength λ0 at ambient temperature, and calculate the temperature T of the filter in question by function f. Alternatively, if the configuration of the passage 24 in which the optical fiber 28 is housed allows, these steps can be performed based on the spectral valley of the transmitted beam 35c.

[0039] Thus, by placing an optical fiber 28 on one of the plates 22 of the mould 12, it is possible to measure the temperature of that plate, and in particular the temperature of its walls in contact with the cast metal, at defined locations and to follow its changes over time. In order to obtain a sufficient number of measurement locations, it is preferable to place at least one optical fiber 28 in two opposing plates 22, preferably in each of the four plates 22 of the mould 12.

[0040] The equipment 2 has the following features for the purpose of balancing the flow of molten steel in the mold 12: a transmitter / receiver arranged to transmit light into the optical fiber 28 and to receive at least one of the reflected light and the transmitted light by the optical fiber 28; - a processor, a) converting data regarding at least one of the reflected light and the transmitted light received by the transmitting / receiving device into information regarding the flow in the mold; b) compare that information with a given model; c) determining the corrective measures to be taken to balance flows; d) Issue control signals to the regulation system A processor arranged as follows: - a system arranged to regulate the flow of steel in the mould 12 in response to a control signal issued by the processor; It further comprises:

[0041] The operation of these elements is described below.

[0042] At all times during flow, a set of measurements are taken of the characteristics of the flow within the mold 12. In particular, the transmitter / receiver transmits light to the optical fiber 28, which measures the temperature of the walls of the mold 12 by reflecting and / or transmitting light through the optical fiber 28. More generally, however, the thermal characteristics of the steel within the mold 12 are analyzed.

[0043] A processor is then used to compare the measurements of those features to pre-defined models, which can be, for example, previous measurements of the same features under normal flow conditions, i.e., when there are no disturbances to the flow.

[0044] If the measurements do not deviate from the model by a predetermined distance, the comparison is interpreted as indicating that no flow disturbances are occurring, and therefore no action needs to be taken to adjust the flow. Preferably, the sequence of measurement and comparison steps is repeated continuously throughout the flow.

[0045] In the opposite case, the comparison result is interpreted as an indication that at least some disturbance has occurred and that the flows therefore need to be adjusted. Taking into account the comparison result, the processor determines the corrective measures to be taken to balance the flows and issues control signals to the regulating means enabling the corrective measures to be carried out.

[0046] When the processor detects measurements that deviate significantly from the model, an alarm signal can be issued and even the casting operation can be stopped.

[0047] The corrective action may consist in moving the tundish 8 in a direction parallel to the longitudinal axis of the mould 12 by means of the tundish-holding carriage 36 of the installation 2. As the submerged entry nozzle 11 is integral with the tundish 8, this movement allows movement of the submerged entry nozzle 11 relative to the mould 12, thereby restoring symmetry of the flow of the molten metal.

[0048] Then, the measurement and comparison steps are carried out again to determine whether the movement of the SEN 11 has had the expected effect. As long as the difference between the measurement result and the model is greater than a predetermined distance, the movement can be continued. When the distance falls below the predetermined distance, the tundish holding car is stopped and the movement of the SEN 11 is halted. However, the measurement and comparison operations are continued so that any new problems that may occur can be detected.

[0049] The invention is not limited to the described embodiment, and other embodiments will occur to those skilled in the art. [Explanation of symbols]

[0050] 2. Equipment (metal continuous casting equipment) 4 Ladle 6 Mechanical Arm 8 Tundish 10 Stopper 11 Submerged nozzle 12 Mold 14 Cooling device 16 Guide 18 Solidified outer surface 20 Liquid core 22 Plate 24 Aisle 26 Protective cover 28 Optical Fiber 30 Clad 32 cores 34 Bragg Filter 35a Multicolor Spectrum 35b Spectrum of reflected beam 36c Spectrum of transmitted beam 36 Tundish holding cart

Claims

1. A method for restoring symmetry of flow of molten steel in a mold (12), in which steel is fed from a tundish (8) into the mold (12) through a submerged entry nozzle (11) opening below the steel surface in the mold (12), comprising: said mould (12) being of the type consisting of an assembly of metal plates (22) behind which is provided a cooling device (14) arranged to cool said metal plates (22) by the circulation of a cooling fluid, the assembly being an assembly of a pair of opposing small plates and a pair of opposing wide metal plates, comprising in the wall of at least one of said wide metal plates (22) an optical fibre (28) extending in a direction not parallel to the casting axis of said mould (12), said optical fibre (28) being provided with a number of Bragg filters (34); a) obtaining the temperature of at least one wall of said mold (12) at all times during flow; b) comparing the temperature of at least one wall of said mould (12) obtained in the previous step with a predefined model and determining the corrective measures to be taken to restore symmetry of said flow; c) adjusting the symmetry of the flows by inducing a relative movement between the submerged nozzle (11) and the mould (12) in a direction parallel to the longitudinal axis of the mould (12); The method includes:

2. The method of claim 1 , wherein steps a) through c) are repeated continuously during a casting operation.

3. 2. The method according to claim 1, wherein the relative movement between the submerged nozzle (11) and the mould (12) is performed both in a direction parallel to the longitudinal axis of the mould (12) and by offsetting the angle of the nozzle according to the longitudinal axis of the mould (12).

4. 2. The method according to claim 1, wherein the submerged entry nozzle (11) is integral with the tundish (8) and the relative movement between the submerged entry nozzle (11) and the mold (12) is achieved by moving the tundish (8) relative to the mold (12).

5. In the continuous casting system of molten steel from the tundish to the continuous casting mold, said tundish (8), a mould (12) of the type consisting of an assembly of metal plates (22) behind which is provided a cooling device (14) adapted to cool said metal plates (22) by the circulation of a cooling fluid, the assembly being an assembly of a pair of opposing small plates and a pair of opposing wide metal plates, the mould (12) comprising an optical fibre (28) extending in the wall of at least one of said wide metal plates (22) in a direction not parallel to the casting axis of said mould (12), said optical fibre (28) being provided with a number of Bragg filters (34); - an immersion nozzle (11) whose lower end opens below the steel surface in the mold (12) when the steel is poured, the immersion nozzle (11) being integral with the tundish (8); a transmitter / receiver arranged to transmit light into said optical fiber (28) and to receive at least one of the reflected and transmitted light by said optical fiber (28); a processor comprising: a) converting data received by the transmitting / receiving device relating to at least one of the reflected light and the transmitted light into information comprising a temperature of at least one broad wall of the mold (12); b) comparing that information to a predefined model; c) determining the corrective measures to be taken to restore flow symmetry; d) Issue a control signal A processor arranged as follows: - adjusting means (36) arranged to receive said control signal and to adjust the symmetry of the flow of said steel in said mould (12) in response to said control signal; A system comprising:

6. The system of claim 5, wherein the adjustment means (36) comprises a tundish support carriage.

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