JP2022537447A - Method and continuous molten steel casting system for balancing the flow of molten steel in a mold - Google Patents

Abstract

A method for balancing the flow of molten steel in a mold, wherein the steel is fed from a distributor into the mold (12) through a protective nozzle opening below the steel surface in the mold, the method comprising: a) in the mold b) comparing the flow characteristics obtained in the previous step with a pre-determined model to determine the adjustment action to be taken to balance the flow; and adjusting. [Selection drawing] Fig. 7

Description

The present invention relates to continuous metal casting equipment. More particularly, the present invention relates to a method for balancing molten steel flow within a mold. According to another aspect, the present invention relates to a continuous casting system for molten steel.

A continuous metal casting facility, such as a continuous steel casting facility, typically includes a mold into which molten metal is poured from a tundish or distributor and allowed to solidify into a desired shape. For example, a bottomless mold is one, where metal is cooled to form a slab. To cool the molten metal, the walls of the mold are provided with cooling devices, such as liquid cooling, beside or behind them. The design of the mold and cooling system is such that when the slab exits the mold, the outer surfaces of the slab have solidified to a thickness sufficient to keep the metal still molten in the center of the slab. It is done in a form that matches the flow rate.

The distributor is equipped with one, and possibly several, nozzles below the steel surface in the mould, to protect the molten metal as it flows towards the mould. Generally, the nozzles are arranged symmetrically with respect to the mold in order to obtain as uniform a flow as possible during the continuous casting operation. In fact, unbalanced flow in the mold can adversely affect slab quality, such as the risk of breakouts, inhomogeneity of the steel after casting, and poor distribution of lubricating powder.

Nonetheless, it is possible that some trouble may disturb the flow balance of the molten steel from the distributor into the mold. For example, one of the holes in the nozzle can be eroded or plugged with alumina, steel can solidify in the nozzle, or even debris can get stuck in the nozzle. Such troubles can disturb 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, let alone measures to deal with them.

SUMMARY OF THE INVENTION An object of the present invention is to detect a trouble in which the flow of molten steel is disturbed and restore the symmetry of the flow.

Therefore, the present invention provides a method for balancing the flow of molten steel in a mold, wherein the steel is fed into the mold from a distributor through a protective nozzle opening below the steel surface in the mold, comprising:
a) obtaining a set of flow signatures in the mold;
b) comparing the flow characteristics obtained in the previous step with the default model to determine the adjustment measures to be taken to balance the flow;
c) adjusting the flow.

Thus, it is possible to determine if the flow is disturbed by measuring the flow characteristics and comparing the measurements to the default model. Thereby the flow quality can be assessed almost instantaneously. And if there is turbulence, ie if there is a large enough gap between the measured features and the model, it can be dealt with by adjusting the flow to mitigate the turbulence. This greatly improves the quality of the slabs produced.

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

In doing so, the method can be implemented throughout the operating period of the continuous casting installation.

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

The temperature of the template can be easily measured at many locations, which helps make the method easy to implement.

Advantageously, the mold is of the type consisting of an assembly of metal plates backed by a cooling device adapted to cool the metal plates by circulation of a cooling fluid, at least one of said metal plates Within the walls of one plate is provided an optical fiber extending in a direction non-parallel to the casting axis of the mold, the optical fiber having a plurality of Bragg filters.

Advantageously, the method further comprises:
- measuring the temperature of at least one wall of the mold with an optical fiber;
- adjusting the flow;

Temperature measurements are thus made by optical fibers, which are reliable and easy to install in the mold. In particular, the template described in Belgian patent application No. 2018/5193 or in the Belgian patent application filed concurrently with this application can be used.

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

Preferably, 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 distributor and relative movement between the nozzle and the mold is effected by moving the distributor with respect to the mold. For example, by slightly moving the distributor holding carriage.

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

As a variant, if the distributor is equipped with a device for changing casting nozzles or a device for adjusting the steel flow rate by means of a throttling action using a plate moving at right angles to the direction of flow, such a device may be incorporated into the mold. It suffices to move the

Adjustment of the flow is thus effected by an easy-to-perform operation.

In the present invention, in a molten steel continuous casting system from a distributor to a continuous casting mold,
- a distributor;
- a mold of the type consisting of an assembly of metal plates behind which a cooling device is arranged so as to be able to cool the metal plates by circulation of a cooling fluid, the walls of at least one of said metal plates a mold comprising an optical fiber extending therein in a direction non-parallel to the casting axis of the mold, the optical fiber comprising a plurality of Bragg filters;
- protective nozzles whose lower end opens below the steel surface in the mold when the steel is poured, and which nozzles are integral with the distributor;
- a transmitting/receiving device arranged to emit light onto an optical fiber and to receive at least one of reflected light and transmitted light by the optical fiber;
- a processor,
a) converting data about at least one of reflected light and transmitted light received at the transceiver into information about flow in the mold;
b) comparing the information to a pre-defined model;
c) determine the adjustment measures to be taken to balance flows;
d) a processor arranged to issue control signals;
- adjusting means arranged to receive a control signal and adjust the flow of steel in the mold in response to the control signal;

Advantageously, the adjustment means comprise a distributor holding carriage.

The adjustment means are thus formed by simple means.

Embodiments of the invention, taken as non-limiting examples, will now be described with reference to the accompanying drawings.

1 is a general view of a continuous metal casting installation allowing implementation of the method for balancing the flow of molten steel in the 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. Figure 4 is a perspective view of a plate of the mold of Figure 3; 5 is a longitudinal cross-sectional view of an optical fiber included in the wall of FIG. 4; FIG. 6 is a diagram for explaining the operation of the optical fiber of FIG. 5; FIG. 2 is an enlarged view of the installation of FIG. 1 showing the implementation of the method for balancing the flow of molten steel in the mold; FIG.

FIG. 1 shows a continuous metal casting facility 2 . This equipment has a conventional configuration, and most of its components are only briefly introduced.

The installation 2 comprises a ladle 4 containing molten metal to be cooled. There are two ladles 4 here, both supported by mechanical arms 6 . This mechanical arm 6 is inter alia filled from a filling zone, such as a furnace or a converter (not shown), in which molten metal can be poured into the ladle 4 before conveying the ladle 4 to the position shown in FIG. , the ladle 4 brought to the casting zone by a transfer system (such as an overhead crane not shown) can be moved. The mechanical arm 6 can also bring the ladle 4 after it has been emptied to a position where it can be picked up again by the transfer system, from which the ladle 4 is transported to the preparation zone and after being reconditioned. , is returned to the filling zone.

The installation 2 comprises a distributor located below the ladle 4 , namely a distributor 8 . The ladle 4 has a retractable bottom that allows the molten metal to flow into the distributor 8 .

The distributor 8 comprises a sprue that can be closed with a stopper 10 that can control the flow of molten metal. The sprue of the distributor leads to a protective nozzle 11 (also called immersion casting nozzle, SEN), which can protect the molten metal being poured. A protective nozzle 11 is integral with the distributor 8 .

The protective nozzle 11 opens into the upper opening of the mold 12, as best seen in FIG. 2a and the enlarged view of FIG. 2b. This is a bottomless mold with a vertical casting axis. The mold 12 will be described in greater detail below.

The installation 2 comprises a cooling device 14 arranged on the outer surface of the mold 12 . This is a liquid cooling device. Therefore, the cooling device comprises a conduit through which a cooling fluid, such as water, flows. The cooling fluid cools and solidifies the molten metal by absorbing heat from the molten metal within the mold 12 . In this case, the metal solidifies to form a slab having an outer surface 18 that solidifies around the liquid core 20 .

The installation 2 comprises a roller guide 16 downstream of the mold 12 . The guides 16 can guide the slab with the solidified outer surface 18 out of the mold 12 . As can be seen in FIG. 2a, the slab gradually solidifies as it travels through the guide 16. FIG. That is, the volume of the solidified slab outer surface 18 increases and the volume of the liquid core 20 of the slab decreases with distance from the mold 12 .

The mold 12 is shown in more detail in FIG. In the drawing, there are four plates 22 (the fourth plate is not visible due to the positional relationship in the sectional view). Plate 22 is made of copper or a copper alloy, a material that has a high thermal conductivity, thereby facilitating heat exchange between cooling device 14 and mold 12 . Plates 22 are arranged such that mold 12 has a generally rectangular or square cross-section. However, it is also conceivable to arrange the plates so that the mold has some different shape, whether in cross section or not. For example, the funnel-shaped top is conventionally used in casting thin slabs.

In the following, for the sake of simplicity, the invention will be based on the mold layout described in Belgian Patent Application No. 2018/5193, i.e. with optical fibers contained in channels formed in the walls of the mold. will be described in more detail. However, in another embodiment of the present invention, as described in the Belgian patent application filed concurrently with this application, optical fibers are placed in grooves formed in the surface of the mold and filled by strips. It must also be understood that it can be accommodated.

One of the plates 22 of mold 12 is shown in enlarged view in FIG. In this figure, the vertical direction corresponds to the casting axis. Plate 22 includes at least one passageway 24 in its wall extending in a direction non-parallel to the casting axis of mold 12 . More specifically, passageway 24 has an angle in the range of 75° to 105° with respect to the casting axis. Here the passages 24 are perpendicular to the casting axis. The number of passages 24 is four here. A protective cover 26 is provided to protect the passageway 24 in the zone of the plate 22 where the passageway 24 opens.

An optical fiber 28 is housed in each of the passageways 24 . 5 and 6, each optical fiber 28 comprises a cladding 30 and a core 32 surrounded by the cladding 30. As shown in FIG. Optical fiber 28 includes a plurality of Bragg filters 34 within 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, even more preferably. has at least 40 Bragg filters per meter. Alternatively, the mold could contain only one optical fiber. In the following, for ease of explanation, installation 2 will be considered as comprising only one optical fiber.

The operation of the optical fiber 28 is shown in FIG. Bragg filter 34 is a filter capable of reflecting light in a wavelength band centered at a predetermined value, called the reflection wavelength, which is adjustable by the filter manufacturer. This predetermined value is also a function of, among other things, the temperature at which the filters are placed, the relationship of which can be written for each filter as:
λ _reflection = f(λ ₀ ,T)
where λ _reflection 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, eg ambient temperature.

These two properties allow the optical fiber 28 to be used as a temperature sensor. First, the Bragg filters 34 are placed in the optical fiber 28 with different reflected wavelength values .lambda..sub.0, chosen by, for example, ₅ nanometers. Subsequently, a light beam of polychromatic spectrum 35a, for example white light, is launched into the optical fiber 28 and then the wavelength peaks appearing in the spectrum 35b of the reflected beam are 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 the function f. Alternatively, if the configuration of the path 24 in which the optical fiber 28 is accommodated permits, these steps can be performed based on the spectral valleys of the transmitted beam 35c.

Thus, by placing an optical fiber 28 in one of the plates 22 of the mold 12, the temperature of that plate, particularly the temperature of the wall of that plate in contact with the metal being cast, can be measured at a given location and Changes over time can be traced. In order to obtain a sufficient number of measurement points, 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 mold 12. FIG.

The equipment 2 is for the purpose of balancing the flow of molten steel in the mold 12,
- a transceiver arranged to emit light onto the optical fiber 28 and to receive at least one of reflected light and transmitted light by the optical fiber 28;
- a processor,
a) converting data about at least one of reflected light and transmitted light received at the transceiver into information about flow in the mold;
b) comparing the information to a pre-defined model;
c) determine the adjustment measures to be taken to balance flows;
d) a processor arranged to issue control signals to the coordination system;
- a system arranged to regulate the flow of steel in the mold 12 in response to control signals issued by the processor;

The operation of these elements is described below.

At any time during flow, a set of flow characteristics within the mold 12 is measured. Among other things, the transceiver transmits light into the optical fiber 28 and the temperature of the walls of the mold 12 is measured by at least one of the light reflected and transmitted by the optical fiber 28 . More generally, however, the thermal characteristics of the steel within mold 12 are analyzed.

A processor is then used to compare the measurements of those features to a predefined model. A default model can be, for example, a measurement of the same feature previously performed under normal conditions of flow, ie, without disturbances in the flow.

If the measurement does not deviate from the model by a predetermined distance, the comparison is interpreted as indicating that no flow disturbance has occurred. Therefore, no flow control measures need to be taken. Preferably, the series of measuring and comparing steps are repeated continuously throughout the flow.

In the opposite case, the comparison results are taken to indicate that at least some disturbance is occurring and therefore the flow needs to be adjusted. The processor considers the results of the comparison and determines the adjustment action to be taken to balance the flows and issues a control signal to the adjustment means enabling the implementation of the adjustment action.

When the processor detects measurements that deviate significantly from the model, an alarm signal may be issued and the casting operation may be halted.

The adjustment measure may consist of moving the distributor 8 in a direction parallel to the longitudinal axis of the mold 12 using the distributor holding carriage 36 of the installation 2 . Since the protective nozzle 11 is integral with the distributor 8 , this movement allows movement of the protective nozzle 11 relative to the mold 12 . By doing so, the symmetry of the molten metal flow is restored.

Then, the measurement step and the comparison step are performed again to determine whether the movement of the protective nozzle 11 has produced the expected effect. As long as the difference between the measurement result and the model exceeds a predetermined distance, the movement can be continued further. When the distance becomes less than the predetermined distance, the distributor holding cart is stopped to stop the movement of the protective nozzle 11. - 特許庁However, measurement and comparison work continues so that possible new troubles can be detected.

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

2 Equipment (metal continuous casting equipment)
4 Ladle 6 Mechanical Arm 8 Distributor 10 Stopper 11 Protective Nozzle 12 Mold 14 Cooling Device 16 Guide 18 Solidified Outer Surface 20 Liquid Core 22 Plate 24 Channel 26 Protective Cover 28 Optical Fiber 30 Cladding 32 Core 34 Bragg Filter 35a Polychromatic spectrum 35b Reflected beam spectrum 36c Transmitted beam spectrum 36 Distributor holding carriage

Claims (12)

A method for balancing the flow of molten steel in a mold (12), said mold (12) from a distributor (8) through a protective nozzle (11) opening below the steel surface in said mold (12). In the way the steel is fed into
a) obtaining a set of characteristics of said flow within said mold (12);
b) comparing the flow characteristics obtained in the previous step with a predefined model to determine adjustment measures to be taken to balance the flow;
c) adjusting said flow. 2. The method of claim 1, wherein steps a)-c) are repeated continuously during the casting operation. 3. A method according to claim 1 or 2, wherein said characteristics of said flow are obtained by analysis of the thermal characteristics of said steel in said mold (12). of the type in which said mold (12) consists of an assembly of said metal plates (22) behind which is provided a cooling device (14) adapted to cool said metal plates (22) by circulation of a cooling fluid. and a plurality of Bragg filters ( A method according to any one of the preceding claims, comprising an optical fiber (28) comprising 34). - measuring the temperature of at least one wall of said mold (12) by means of said optical fiber (28);
- adjusting said flow. A method according to any one of the preceding claims, wherein said adjustment of said flow is effected by inducing a relative movement between said protective nozzle (11) and said mold (12). 7. Method according to claim 6, wherein the relative movement between the protective nozzle (11) and the mold (12) takes place in a direction parallel to the longitudinal axis of the mold (12). 7. The method according to claim 6, wherein the relative movement between the protective nozzle (11) and the mold (12) is effected by angularly offsetting the protective nozzle according to the longitudinal axis of the mold (12). the method of. Said relative movement between said protective nozzle (11) and said mold (12) causes the nozzle to follow the longitudinal axis of said mold (12) also in a direction parallel to the longitudinal axis of said mold (12). 7. The method of claim 6, also performed by shifting the angle of . The protective nozzle (11) is integral with the distributor (8), and the relative movement between the protective nozzle (11) and the mold (12) causes the distributor (8) to A method according to any one of claims 5 to 9, effected by moving relative to said template (12). In the molten steel continuous casting system from the distributor to the continuous casting mold,
- a distributor (8);
- a mold (12) of the type consisting of an assembly of said metal plates (22) behind which is provided a cooling device (14) adapted to cool said metal plates (22) by circulation of a cooling fluid; an optical fiber (28) extending in a wall of at least one of said metal plates (22) in a direction non-parallel to the casting axis of said mold (12), comprising a plurality of Bragg filters (34); a mold (12) comprising an optical fiber (28) comprising
- a protective nozzle (11), integral with said distributor (8), whose lower end opens below the steel surface in said mold (12) when casting steel;
- a transceiver arranged to emit light into said optical fiber (28) and to receive at least one of reflected light and transmitted light by said optical fiber (28);
- a processor,
a) converting data about at least one of said reflected light and transmitted light received at said transceiver device into information about flow in said mold (12);
b) comparing the information to a pre-defined model;
c) determining the adjustment actions to be taken to balance said flows;
d) a processor arranged to issue control signals;
- adjusting means (36) arranged to receive said control signal and to adjust said flow of said steel in said mold (12) in response to said control signal. 12. The system of claim 11, wherein said adjustment means (36) comprises a distributor holding carriage.

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