JP7621287B2 - METHOD FOR BALANCING THE FLOW OF MOLTEN STEEL IN A MOLD AND SYSTEM FOR CONTINUOUS CASTING OF MOLTEN STEEL - Patent application - Google Patents

Description

The present invention relates to a continuous metal casting installation. 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.

Continuous metal casting plants, such as steel casting plants, 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 one in which the metal is cooled to form a slab. To cool the molten metal, the walls of the mold are fitted with a cooling system, such as a liquid cooler, next to or behind them. The mold and cooling system 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.

The tundish is fitted with one or sometimes several nozzles, located 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 adverse effects on slab quality, including the risk of breakouts, inhomogeneity of the cast steel, and poor distribution of the lubricant powder.

Nevertheless, some malfunction can disrupt the equilibrium of the flow of molten steel from the tundish into the mold. For example, one of the nozzle holes may become eroded or blocked with alumina, steel may solidify in the nozzle, or the nozzle may become clogged with debris. Such malfunctions can disrupt the symmetry of the flow and potentially compromise the quality of the slabs produced, as well as damage the continuous casting equipment. Currently, there is no way to detect such situations, much less how to deal with them.

The purpose of this invention is to detect troubles that cause disturbances in the flow of molten steel and restore symmetry to the flow.

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) acquiring a set of characteristics of the flow in the mold;
b) comparing the flow characteristics obtained in the previous step with a predefined model and determining the corrective actions to be taken to balance the flows;
and c) adjusting the flow.

In this way, 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.

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

This allows the method to be carried out throughout the operating life of the continuous casting equipment.

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

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

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

Advantageously, the method further comprises:
- measuring the temperature of at least one wall of the mould by means of optical fibres;
- adjusting the flow.

Thus, the temperature measurement is performed by optical fiber, which is reliable and easy to install in the mould. In particular, the moulds described in Belgian patent application No. 2018/5193 or the Belgian patent application filed simultaneously with the present application can be used.

Advantageously, flow regulation is achieved by inducing relative movement between the nozzle and the mold.

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

Advantageously, the nozzle is integral with the tundish and the relative movement between the nozzle and the mould is achieved by moving the tundish relative to the mould, for example by slightly moving a tundish-holding carriage.

According to a variant of the invention, the relative movement between the nozzle and the mold is achieved by shifting the angle of the nozzle according to the longitudinal axis of the mold. It is also possible to combine the two movements (linear and rotational).

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

Therefore, flow adjustments are made through easy-to-perform operations.

In the present invention, in a molten steel continuous casting system from a tundish to a continuous casting mold,
- A tundish and
a mould of the type consisting of an assembly of metal plates behind which is provided a cooling device arranged to cool the metal plates by the circulation of a cooling fluid, at least one of said metal plates being provided in its wall with 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 mould when the steel is poured, the nozzle being integral with the tundish;
a transmitter/receiver arranged to transmit light into an optical fiber and to receive at least one of the reflected light and the transmitted light by the optical fiber;
a processor comprising:
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) comparing that information to a predefined model;
c) determining the corrective measures to be taken to balance flows;
d) a processor arranged to issue control signals;
- adjusting means arranged to receive a control signal and to adjust the flow of steel in the mould in response to said control signal.

Advantageously, the adjustment means comprises a tundish holding carriage.

The adjustment means is therefore formed by simple means.

Now, non-limiting examples of embodiments of the present invention will be described with reference to the accompanying drawings.

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; FIG. 2 is a diagram showing the operation of the equipment of FIG. 1; FIG. 2 is a diagram showing the operation of the equipment of FIG. 1; FIG. 2 is a cross-sectional view of the mold of the installation of FIG. 1; FIG. 4 is a perspective view of a plate of the mold of FIG. 3 . 5 is a longitudinal cross-sectional view of an optical fiber contained in the wall of FIG. 4; 6A to 6C are diagrams illustrating the operation of the optical fiber of FIG. 5 . 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.

Figure 1 shows a continuous metal casting line 2. This line has a conventional configuration, and most of its components will only be introduced briefly.

The installation 2 comprises a ladle 4 containing the molten metal to be cooled. Here, there are two ladles 4, both supported by a mechanical arm 6. This mechanical arm 6 is capable, among other things, of moving the ladle 4, which has been brought full to the pouring zone by a transport system (such as an overhead crane, not shown) from a charging zone, such as a furnace or converter (not shown), where the molten metal can be poured into the ladle 4, before it is brought to the position shown in FIG. 1. The mechanical arm 6 is also capable of bringing the ladle 4, once empty, to a position where it can be taken up again by the transport system, from where it is transported to a preparation zone, where it is reconditioned, and then returned to the charging zone.

The installation 2 comprises a tundish, i.e. tundish 8, located below the ladle 4. The ladle 4 has an openable bottom through which molten metal can be poured into the tundish 8.

The tundish 8 has a sprue that can be closed with a stopper 10 that can control the flow of the molten metal. The sprue of the tundish leads to a submerged entry nozzle 11 (also called a submerged casting nozzle, SEN) that can protect the molten metal being poured. The submerged entry nozzle 11 is integral with the tundish 8.

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

The equipment 2 includes a cooling device 14 arranged on the outer surface of the mold 12. This is a liquid cooling device. Therefore, the cooling device includes a pipeline through which a cooling fluid, such as water, flows. The cooling fluid absorbs heat from the molten metal in the mold 12, thereby cooling and solidifying the molten metal. In this case, the metal solidifies to form a slab having a solidified outer surface 18 encasing the liquid core 20.

The installation 2 includes a roller guide 16 downstream of the mold 12. The guide 16 is capable of guiding the slab, whose outer surface 18 has solidified, out of the mold 12. As can be seen in FIG. 2a, the slab gradually solidifies as it moves through the guide 16; that is, the volume of the solidified outer surface 18 of the slab increases and the volume of the liquid core 20 of the slab decreases as it moves away from the mold 12.

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 good 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.

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. However, 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 with the present application.

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.

An optical fiber 28 is housed in each of the passages 24. As shown in Figs. 5 and 6, each optical fiber 28 has a cladding 30 and a core 32 surrounded by the cladding 30. The optical fiber 28 has a plurality of Bragg filters 34 in its core 32. The optical fiber 28 has 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 may include only one optical fiber. In the following, for ease of explanation, the installation 2 is considered to include only one optical fiber.

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 band of wavelengths centered on a predetermined value, called the reflection wavelength, which can be adjusted by the filter manufacturer. This predetermined 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 _reflection = f(λ ₀ , T)
where _λreflect 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.

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 reflection wavelength value λ _0, chosen, for example, 5 nanometers apart. A light beam of polychromatic spectrum 35a, for example white light, is then sent into the optical fiber 28, and the wavelength peaks appearing in the spectrum 35b of the reflected beam are then determined. For each peak, the measured λ _reflection is compared with the theoretical value λ ₀ of the reflection wavelength at ambient temperature, and the temperature T of the filter in question is calculated by means of the function f. Alternatively, if the configuration of the passage 24 in which the optical fiber 28 is located allows, these steps can also be carried out on the basis of the spectral valleys of the transmitted beam 35c.

Thus, by placing an optical fiber 28 on one of the plates 22 of the mold 12, the temperature of that plate, and in particular the temperature of the wall of that plate in contact with the cast metal, can be measured at a given location and its changes over time can be followed. 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, and preferably in each of the four plates 22 of the mold 12.

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 and transmitted light by the optical fiber 28;
a processor comprising:
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) comparing that information to a predefined model;
c) determining the corrective measures to be taken to balance flows;
d) a processor arranged to issue control signals to a regulation system;
a system arranged to regulate the flow of steel within the mould 12 in response to control signals issued by the processor.

The behavior of these elements is explained below.

At all times during flow, a set of measurements are taken of the flow characteristics within the mold 12. In particular, the transmitter/receiver transmits light to the optical fiber 28, and the temperature of the walls of the mold 12 is measured by the light reflected and/or transmitted by the optical fiber 28. However, more commonly, the thermal characteristics of the steel within the mold 12 are analyzed.

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

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 flow adjustment measures need to be taken. Preferably, the series of measurement and comparison steps are repeated continuously throughout the flow.

In the opposite case, the comparison result is interpreted as an indication that at least some disturbance has occurred and that the flow therefore needs to be adjusted. The processor takes into account the comparison result and determines the corrective action to be taken to balance the flows and issues control signals to the adjustment means enabling the implementation of the corrective action.

If the processor detects that the measurements deviate significantly from the model, an alarm signal can be issued and the casting operation can be stopped.

The adjustment measure may consist of moving the tundish 8 in a direction parallel to the longitudinal axis of the mold 12 using 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 mold 12, thereby restoring symmetry of the molten metal flow.

Then, the measurement and comparison steps are carried out again to determine whether the movement of the submerged nozzle 11 has had the expected effect. As long as the gap between the measurement result and the model exceeds a predetermined distance, the movement can be continued. When the distance falls below the predetermined distance, the tundish holding cart is stopped and the movement of the submerged nozzle 11 is halted. However, the measurement and comparison work is continued so that any new problems that may occur can be detected.

The present invention is not limited to the described embodiments, and other embodiments will be apparent to those skilled in the art.

2. Equipment (metal continuous casting equipment)
4 ladle 6 mechanical arm 8 tundish 10 stopper 11 submerged nozzle 12 mould 14 cooling device 16 guide 18 solidified outer surface 20 liquid core 22 plate 24 passage 26 protective cover 28 optical fibre 30 cladding 32 core 34 Bragg filter 35a polychromatic spectrum 35b spectrum of reflected beam 36c spectrum of transmitted beam 36 tundish holding carriage

Claims (6)

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;
and 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 of claim 1, wherein steps a)-c) are repeated continuously during the casting operation. The method according to claim 1, wherein the relative movement between the submerged nozzle (11) and the mold (12) is performed both in a direction parallel to the longitudinal axis of the mold (12) and by shifting the angle of the nozzle according to the longitudinal axis of the mold (12). The method according to claim 1, wherein the submerged nozzle (11) is integral with the tundish (8) and the relative movement between the submerged nozzle (11) and the mold (12) is achieved by moving the tundish (8) relative to the mold (12). 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) a processor arranged to issue control signals; and
- adjusting means (36) arranged to receive said control signal and to adjust the symmetry of said flow of said steel in said mould (12) in response to said control signal. The system of claim 5, wherein the adjustment means (36) comprises a tundish support carriage.

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