Patent Application
20220355371
The invention relates to an installation for the continuous casting of metals. More particularly, the invention relates to a method for balancing a flow of liquid steel in a casting mold. In another of its aspects, the invention relates to a system for the continuous casting of liquid steel.
An installation for the continuous casting of metals, for example an installation for the continuous casting of steel, generally comprises a casting mold into which a liquid metal is poured from a pouring base or a tundish so that it will solidify in a suitable shape. This may be a bottomless casting mold, in which case the metal cools to form a slab. In order to cool the liquid metal, walls of the casting mold adjoin, or are backed by, cooling devices, for example of the liquid-cooled type. The casting mold and the cooling devices are sized according to the rate of flow of the metal so that the slab, on leaving the casting mold, has a solidified external shell thick enough to trap the still-liquid metal that is at the heart of the slab.
The tundish is equipped with one, or even several, nozzles below the level of steel in the casting mold intended to protect the liquid metal as it flows toward the casting mold. In general, the nozzle is positioned symmetrically with respect to the casting mold so that the flow is as uniform as possible during the continuous casting operations. This is because an unbalanced flow in the casting mold may have negative consequences on the quality of the slab, such as the risks of breakout, heterogeneity in the cast steel, poor distribution of the lubricating powder, etc.
Nevertheless, certain incidents may disturb the balance of the flow of liquid steel from the tundish into the casting mold. For example, one of the openings of the nozzle may become eroded or plugged with alumina, steel may solidify in the nozzle, or debris may become lodged in the nozzle. All of these incidents have the effect of disturbing the symmetry of the flow and therefore potentially of impairing the quality of the slabs produced, or even of damaging the continuous casting installation. To date, there is no solution for detecting such situations, and even less so for remedying them.
It is an object of the invention to allow incidents disturbing the flow of the liquid steel to be detected, and the symmetry of the flow to be reestablished.
To this end, the invention provides a method for balancing a flow of liquid steel in a casting mold, wherein the steel is introduced into the casting mold from a tundish through a protective nozzle opening below the level of steel in the casting mold, comprising the following steps:
Thus, it is possible to determine whether the flow is disturbed by measuring characteristics of the flow and comparing these measurements against a predefined model. The quality of the flow can therefore be evaluated almost instantaneously, and if a disturbance, namely a sufficiently significant discrepancy between the measured characteristics and the model, arises, it is possible to react by adjusting the flow in such a way as to reduce the disturbance. The quality of the slabs produced is thereby significantly improved.
Advantageously, steps a) to c) are repeated continuously during the casting operations.
The method can thus be implemented throughout the period of operation of the continuous casting installation.
Advantageously, the flow characteristics are obtained by an analysis of the thermal characteristics of the steel in the casting mold.
Because casting-mold temperature is easily measurable at a great many positions, this contributes to making the method easy to implement.
Advantageously, the casting mold is of the type consisting of an assembly of metal plates backed by cooling devices which are configured to allow the metal plates to be cooled by the circulation of a cooling fluid, comprising an optical fiber, comprising a plurality of Bragg filters, extending in a wall of at least one of said plates, the optical fiber extending in a direction not parallel to the pouring axis of the casting mold.
Advantageously, the method further comprises the following steps:
The temperature is thus measured using the optical fiber, which is reliable and easy to install in the casting mold. In particular, it is possible to use a casting mold like the one described in Belgian patent application 2018/5193 or in the Belgian patent application filed simultaneously with the present application.
Advantageously, the flow adjustment is performed by effecting a relative movement between the nozzle and the casting mold.
As a preference, the relative movement between the nozzle and the casting mold is effected in a direction parallel to the longitudinal axis of the casting mold.
Advantageously, the nozzle is secured to the tundish and the relative movement between the nozzle and the casting mold is achieved by moving the tundish with respect to the casting mold. For example by effecting a small movement of the tundish car.
According to a variant of the invention, the relative movement between the nozzle and the casting mold is effected by angularly offsetting the nozzle about the longitudinal axis of the casting mold. It is also possible to combine the two movements (linear and angular).
As a variant, in the case where the tundish is provided with a device for replacing the casting nozzle or for regulating the flow of steel by restricting it by means of a plate moved perpendicularly to the direction of flow, it is sufficient to move such a device with respect to the casting mold.
The flow adjustment is thus achieved through an operation that is simple to implement.
The invention also provides a system for the continuous casting of liquid steel from a tundish to a continuous casting mold, comprising:
Advantageously, the adjustment means comprise a tundish car.
The adjustment means are thus formed by simple means.
One embodiment of the invention which is given purely by way of nonlimiting example will now be set out with the support of the attached figures in which:
The installation 2 comprises ladles 4 containing liquid metal that needs to be cooled. Here the ladles 4 are two in number and are carried by a motorized arm 6. This motorized arm 6 is notably able to move the ladles 4 which are brought full into the casting zone by a transport system (for example a traveling train, not depicted) from a filling zone in which the molten metal can be tipped into them, for example a furnace or a converter (not depicted) before they are brought into the position illustrated in
The installation 2 comprises a tundish or pouring basin 8 situated beneath the ladles 4. The latter have a bottom that can be opened to cause the liquid metal to pour out into the tundish 8.
The tundish 8 comprises an outflow orifice which may be stopped by a stopper rod 10 for controlling the flow of liquid metal. The outflow orifice of the tundish is extended by a protective nozzle 11 (also known as a submerged entry nozzle, SEN) protecting the poured out liquid metal. The nozzle 11 is secured to the tundish 8.
As is more clearly visible in
The installation 2 comprises cooling devices 14 positioned on an external surface of the casting mold 12. These are cooling devices of the liquid-cooled type. To this end they comprise ducts into which a refrigerating fluid, for example water, flows. The refrigerating fluid absorbs the heat of the liquid metal in the casting mold 12 in order to cool and solidify this metal. Here, the metal solidifies in the form of a slab having a solidified external shell 18 enclosing a liquid core 20.
The installation 2 comprises a roller guide 16 downstream of the casting mold 12. The guide 16 guides the slab, an external shell 18 of which has solidified, from the casting mold 12. As is visible in
The casting mold 12 is depicted in greater detail in
In what follows, for the sake of conciseness, the invention will be described in greater detail on the basis of a casting-mold arrangement like the one described in Belgian patent application 2018/5193, namely with an optical fiber housed inside a duct formed in the wall of the casting mold. However, it must be appreciated that, according to another embodiment of the invention, the optical fiber may be housed in a groove formed in the surface of the casting mold and closed by a strip, as described in the Belgian patent application filed simultaneously with the present application.
One of the plates 22 of the casting mold 12 is depicted on a larger scale in
An optical fiber 28 is housed in each of the ducts 24. With reference to
The operation of the optical fiber 28 is illustrated in
λreflected=f(λ0,T)
where λreflected is the wavelength effectively reflected by the filter, f is a known function, T is the temperature of the filter and λ0 is the wavelength reflected by the filter at a predetermined temperature, for example at ambient temperature.
These two properties mean that the optical fiber 28 can be used as a temperature sensor. Initially, Bragg filters 34 having distinct and chosen reflected wavelength values λ0, for example offset from one another by 5 nanometers, are installed in the optical filter 28. A beam of light 35a exhibiting a polychromatic spectrum, for example white light, is then sent into the optical fiber 28 and then the wavelength peaks represented in the spectrum of the reflected beam 35b are determined. For each peak, the measured value λreflected and the theoretical value of the wavelength reflected at ambient temperature λ0 are compared, and the temperature T of the filter in question is calculated using the function f. Alternatively, it is also possible to carry out these steps on the basis of the troughs in the spectrum of the transmitted beam 35c if the configuration of the duct 24 in which the optical fiber 28 is housed permits this.
Thus, installing the optical fiber 28 in one of the plates 22 of the casting mold 12 allows the temperature of this plate, and notably of its wall in contact with the poured metal, to be measured at predetermined positions and to monitor how this evolves over time. In order to obtain a sufficiently high number of measurement points, it is preferable to position at least one optical fiber 28 in two opposing plates 22, or even in each of the four plates 22 of the casting mold 12.
For the purposes of balancing the flow of the liquid steel in the casting mold 12, the installation 2 further comprises:
The operation of these elements will be described in what follows.
At any moment during the flow, measurements of a set of characteristics of the flow in the casting mold 12 are taken. In particular, the emitter-receiver sends light into the optical fiber 28 and the temperature of the wall of the casting mold 12 is measured using the light reflected and/or transmitted by the optical fiber 28. However, more generally, thermal characteristics of the steel present in the casting mold 12 are analyzed.
The processor is then used to compare the measurement of these characteristics against a predefined model. These may, for example, be concerned with measurements of these same characteristics taken previously under normal flow conditions, namely conditions in which the flow is not disturbed.
If the measurement does not deviate from the model by a predetermined amount, the comparison is interpreted as signifying that no disturbance of the flow is occurring. No flow adjustment measure therefore needs to be undertaken. These measurement and comparison steps are preferably repeated continuously throughout the pour.
If the opposite is true, the comparison is interpreted as signifying that at least one disturbance has occurred and that the flow therefore needs to be adjusted. Taking the comparison into consideration, the processor determines the adjustment actions to be taken in order to balance the flow and then emits a control signal to adjustment means that allow adjustment actions to be undertaken.
If the processor detects a measurement that deviates excessively from the model, provision may be made for an alarm signal to be emitted or even for the casting operations to be halted.
The adjustment actions may consist in moving the tundish 8 in a direction parallel to the longitudinal axis of the casting mold 12 using a tundish car 36 of the installation 2. Given that the nozzle 11 is secured to the tundish 8, this movement allows the nozzle 11 to be moved with respect to the casting mold 12. In doing this, symmetry in the flow of the liquid metal is reestablished.
The measurement and comparison steps are then performed again in order to determine whether the moving of the nozzle 11 has had the anticipated effect. Provision may be made for this movement to continue as long as the discrepancy between the measurement and the model remains greater than the predetermined amount. Once this amount becomes smaller than the predetermined amount, the tundish car is deactivated so that the movement of the nozzle 11 is halted. However, the measurement and comparison operations continue to be performed in order to detect any further incident that might arise.
The invention is not restricted to the embodiments described and other embodiments will be clearly apparent to those skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| BE2019/5406 | Jun 2019 | BE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/066604 | 6/16/2020 | WO |
