Patent Description:
More particularly, the apparatus to control continuous casting allows to detect the surface profile of the liquid metal present in a mold and possibly control the functioning of operating units associated with the mold, namely the electromagnetic brakes.

The present invention also concerns a corresponding method to control continuous casting.

Continuous casting apparatuses are known which generally comprise a mold in which a liquid metal is introduced to be solidified thanks to the interaction of the latter with the cooled walls of the mold.

These continuous casting apparatuses therefore comprise a discharge device, or nozzle, positioned at the entrance end of the mold and which discharges, in the latter, the liquid metal coming from another container, for example a tundish. The nozzle can also be configured to deliver a process gas, for example an inert gas, such as argon, to isolate the liquid metal that is being discharged.

It is also known to distribute powders to cover and protect the liquid metal on the free surface of the liquid metal, also called meniscus.

These powders have the function of preventing the oxidation of the liquid metal and the dispersion of the heat of the liquid metal in the upper part of the mold. Furthermore, the powders are interposed between the walls of the mold and the metal skin that is solidifying, favoring lubrication, facilitating the extraction of the metal product and avoiding adhesion phenomena, also known as "sticking".

It is also known to associate electromagnetic devices with the mold, also known as electromagnetic brakes, provided to control the direction and speed of the recirculation flows present in the liquid metal. The recirculation flows, if controlled, prevent the occurrence of defects of the cast product, such as segregations, inclusions, or internal porosities.

The action of the electromagnetic brakes, however, has to be suitably controlled during the continuous casting at least according to the casting speed, the width of the mold, the depth of the position, that is, immersion, of the nozzle in the mold, the flow rate of the process gasses through the nozzle.

In fact, as a function of the actions that the electromagnetic brakes are able to generate it is possible to obtain different configurations of the flows of the liquid metal.

By way of example only, it is possible to obtain recirculation flows of the liquid metal with a single recirculation, also called "single roll", or double recirculation, also called "double roll".

The single recirculation type is usually unwanted and is normally generated by casting complications that entail problems of quality of the final product. The only recirculation that is generated extends essentially from the inside toward the outside of the mold causing an excessive turbulence of the liquid metal toward the meniscus, in proximity to the nozzle.

The double recirculation type, on the other hand, represents the optimal configuration of the flows inside the mold to obtain a high quality product.

In fact, the double recirculation type generates both a recirculation that extends toward the surface of the liquid metal, and also a recirculation that extends deep into the mold.

To obtain a double recirculation it is necessary to generate a balance between the upper recirculations and the lower recirculations.

In fact, if there are too many upper recirculations compared to lower recirculations, a high vorticity is generated on the surface of the meniscus which can lead to the onset of defects in the cast product such as:.

On the other hand, if there are too many lower recirculations compared to upper recirculations, there is a freezing of the meniscus in proximity to the walls of the mold.

Some known apparatuses and methods to monitor and regulate recirculations are for example described in patent documents <CIT>, <CIT> and <CIT>.

It is a purpose of the present invention to develop an apparatus to control continuous casting which allows to resolve the problems highlighted above, in a more efficient and accurate manner than known apparatuses and methods.

It is also a purpose of the present invention to provide an apparatus to control continuous casting which allows to increase the quality of cast products.

It is also a purpose of the present invention to provide an apparatus to control continuous casting which is simple to make and install, and economical.

It is also a purpose of the invention to perfect a method to control continuous casting which allows to increase the quality of the cast products.

In accordance with the above purposes, an apparatus to control continuous casting, according to the present invention, comprises:.

According to the present claim <NUM> the control apparatus comprises detection means located, at least in a condition of use, above the entrance end of the mold and each configured to detect at least a reciprocal distance with respect to the level of the liquid metal. The control and command unit is also connected to the detection means to acquire the data of each distance from each detection mean, process them in relation to the positioning of the detection means, determining characteristic parameters of the development of the surface profile of the liquid metal, and to command the drive at least of the electromagnetic brake based on the characteristic parameters of the development of the surface profile.

This configuration, in relation to the development of the surface profile of the liquid metal, allows to assess whether the recirculation flows that are established in the mold are particularly effective for obtaining a cast product of high quality.

The expression "detection of the surface profile", here and in the following description and claims, is intended to comprise the detection of the shape of the profile of the liquid metal as such and/or the detection of layers normally present above the level of the liquid metal present in the mold, such as layers of protective powders located to protect the liquid metal.

The present invention also concerns a method to control continuous casting which provides to cast a liquid metal by introducing the latter through an entrance end of a mold. During casting, a control and command unit manages the functioning of an electromagnetic brake associated with the mold, to induce recirculation flows in the liquid metal.

According to present claim <NUM> the method comprises the detection of data of at least a reciprocal distance with respect to the level of the liquid metal by means of detection means located, at least in a condition of use, above the entrance end, the processing of the data of at least a distance in relation to the positioning of the detection means, determining characteristic parameters of the development of the surface profile, and the driving at least of the electromagnetic brake based on the characteristic parameters of the development of the surface profile in order to determine predefined recirculation flows of the liquid metal.

According to the present invention, the characteristic parameters comprise the evolution speed of the surface profile and/or the temporal average of the distance calculated on predetermined time intervals and/or the instant deviations from the temporal average for each detection mean.

In some embodiments, the characteristic parameters can comprise the spatial gradient of the surface profile and/or the spatial average of the distances detected in different positions and/or the instant deviations from the spatial average for each detection mean.

These characteristics allow to monitor the development of the surface profile not only on the basis of information localized in space and defined in time, but also evaluating the overall development of the entire shape of the surface profile over time, as a function of the whole cross-section of the mold, providing a more accurate monitoring compared to known apparatuses.

With reference to the attached drawings, an apparatus <NUM> to control continuous casting, according to the present invention, is indicated as a whole with the reference number <NUM>.

The control apparatus <NUM>, according to the present invention, comprises a mold <NUM> provided with an entrance end <NUM> through which the liquid metal <NUM> is introduced to be subsequently solidified.

Preferential, although non-limiting, embodiments of the present invention provide that the mold <NUM> is configured to cast slabs.

In particular, the invention can be applied to all types of continuously castable slabs, for example having thicknesses comprised between <NUM> and <NUM> and widths between <NUM> and <NUM>.

The mold <NUM> is provided with walls <NUM> suitably cooled by means of cooling devices, not shown.

In particular, if the mold <NUM> is of the type for slabs, the walls <NUM> are defined by substantially flat plates located in opposite pairs and wherein a first pair 14a of plates has much bigger surface sizes than the surface sizes of a second pair 14b of plates.

The solidification of the liquid metal <NUM> occurs in the mold <NUM> with the consequent formation of a solidified containing skin <NUM>.

The mold <NUM> extends along a substantially vertical or arched casting axis X.

According to the invention, the control apparatus <NUM> comprises at least one electromagnetic brake <NUM> associated with the mold <NUM> and configured to induce recirculation flows <NUM> in the liquid metal <NUM> (<FIG>).

The electromagnetic brake <NUM> can be attached to the mold <NUM>, for example on the external surface of its walls <NUM>.

According to a possible solution (<FIG>), the control apparatus <NUM> comprises a plurality of electromagnetic brakes <NUM> which are associated on the surfaces which, during use, are external of the first pair 14a of walls of the mold <NUM>.

According to possible embodiments, the control apparatus <NUM> can comprise a plurality of electromagnetic brakes <NUM>, for example at least one per wall <NUM> of the mold <NUM>.

According to a possible solution, the plates of the first pair 14a can each comprise a respective electromagnetic brake <NUM> which extends for the entire width of the plate.

According to variant embodiments, the plates of the first pair 14a can each comprise a plurality of electromagnetic brakes <NUM> located adjacent and in a symmetrical position with respect to the center line of the mold <NUM>.

In particular (<FIG>), it can be provided that for each plate of the first pair 14a there is at least one first electromagnetic brake <NUM>, in this case two, distanced along the casting axis, located on one side with respect to the median axis of the mold <NUM>, and at least one second electromagnetic brake <NUM>, in this case two, distanced along the casting axis X, located on a second side, opposite the first with respect to the median axis of the mold <NUM>. Furthermore, in a central position, that is, aligned with the median axis, for each plate of the first pair 14a another electromagnetic brake <NUM> can be provided interposed between the first and the second electromagnetic brake <NUM>.

The electromagnetic brake <NUM> can comprise a plurality of coils, possibly cooled, and suitably electrically powered to generate predetermined recirculation flows <NUM> in the mold <NUM>.

According to the present invention, the control apparatus <NUM> comprises a control and command unit <NUM> connected to the at least one electromagnetic brake <NUM> and configured to manage its functioning.

By way of example only, the control and command unit <NUM> can be configured to control at least one electric parameter of the electric energy supplied to the electromagnetic brakes <NUM>, such as the voltage and/or the electric current. By way of example only, it can be provided that the control and command unit <NUM> is configured to control at least one of either the intensity or frequency of the electric parameter above.

According to the invention, the control apparatus <NUM> comprises detection means <NUM> located, at least in a condition of use, above the entrance end <NUM> of the mold <NUM> and each configured to detect at least a reciprocal distance <NUM> with respect to the level of the liquid metal <NUM>.

The control and command unit <NUM> can be configured to acquire the data of each distance <NUM> from each detection mean <NUM> and process them in relation to the positioning of the detection means <NUM>, determining characteristic parameters of the development of the surface profile <NUM> of the liquid metal <NUM>.

Advantageously, the processing of the distance <NUM> in relation to the positioning of the detection means <NUM> allows to determine the shape of the whole surface profile <NUM> of the liquid metal <NUM> along the whole cross-section of the mold <NUM>, and not only on localized and circumscribed portions as in some known solutions.

Furthermore, the control and command unit <NUM> can process the data of each distance <NUM> determining, as characteristic parameters, the evolution speed of the surface profile and/or the spatial average of the distances <NUM> detected in different positions, and/or the instant deviations therefrom for each detection mean <NUM>.

In some embodiments, other possible characteristic parameters can be the spatial gradient or also higher order derivatives of the surface profile <NUM>, which allow to monitor the extent of the spatial variations in the development of the surface profile <NUM>.

The detection means <NUM> can be configured to detect the reciprocal distance <NUM> at predetermined time instants, for example in relation to specific operating steps of the casting process. According to variant embodiments, the detection means <NUM> can be configured to substantially detect the reciprocal distance <NUM> continuously.

In these embodiments, the control and command unit <NUM> can process the data of each distance <NUM> determining, as characteristic parameters, the temporal average of the distance <NUM> on predetermined time intervals, and the instant deviations from it for each detection mean <NUM>.

In claim <NUM>, possible characteristic parameters can be the evolution speed of the development of the surface profile <NUM>, calculated starting from the time derivatives.

The characteristic parameters associated with instant, temporal and spatial averages and deviations, allow to obtain an accurate determination of the development of the surface profile, since, for example, there is a reduction in the background noise effects linked to the type of sensors used and random errors in the detections due to the formation of bubbles or splashes of liquid metal <NUM>. Furthermore, it is possible to immediately identify possible malfunctions in one or more detection means <NUM>, for example if it/they sends/send data that are significantly and systematically far from the averages.

The control and command unit <NUM> can also determine the action at least on the at least one electromagnetic brake <NUM> on the basis of the characteristic parameters of the development of the surface profile <NUM>, in order to determine predefined recirculation flows <NUM> of the liquid metal <NUM>.

The control and command unit <NUM> can be configured to manage the functioning of the components above and command the drive of at least the electromagnetic brake <NUM>, so as to maintain the development of the surface profile <NUM> uniform.

Advantageously, the characteristic parameters associated with the spatial gradient and the evolution speed of the surface profile <NUM> allow to drive the electromagnetic brake <NUM>, respectively, with suitable drive speed and intensity to efficiently regulate the recirculation flows <NUM>.

This characteristic therefore allows to obtain recirculation flows that are constant and regular in space and time, improving the quality of the cast product.

According to one possible embodiment of the invention, the detection means <NUM> can comprise a plurality of sensors <NUM> located above the surface of the liquid metal <NUM>.

According to possible solutions, each sensor <NUM> is configured to detect a reciprocal distance <NUM> with respect to the level of the liquid metal <NUM>.

In particular, each sensor <NUM> is connected to the control and command unit <NUM> which is configured to acquire the data of each distance <NUM>, process them in relation to the positioning of the sensors <NUM>, and determine the surface profile <NUM>.

In particular, the control and command unit <NUM> can store at least the reciprocal position of each sensor <NUM> with respect to the other sensors, as well as with respect to the upper end <NUM> of the mold <NUM>.

The presence of a plurality of sensors <NUM> distributed above the level of the liquid metal allows to use sensors with a reduced detection field, that is, sensors of small sizes and not very invasive for the upper end <NUM> of the mold <NUM>.

According to possible solutions, the sensors <NUM> can comprise induced current sensors, that is, Eddy Current sensors. The use of this type of sensor allows to have rapid response times. Furthermore, this type of sensor allows to also reuse the latter on other molds and for different applications.

According to possible variant embodiments, the sensors <NUM> can be selected from a group comprising thermal, optical, laser, radar or capacitive sensors.

According to a possible solution of the invention, the sensors <NUM> can be disposed aligned along an axis Y orthogonal to the casting axis X.

In the embodiment in which the mold <NUM> is of the type for slabs, the Y axis is positioned substantially parallel to the pair of walls with bigger sizes.

For example, the plurality of sensors <NUM> can be distributed in a symmetrical manner, on one side and on the other, with respect to the casting axis X, as well as in scattered order.

Furthermore, the sensors <NUM> can be equally distanced from each other to be able to detect the surface profile <NUM> in a uniform manner.

Variations of the embodiments, provide that the plurality of sensors <NUM> is distributed only on one side, that is, only on a part of the surface of the liquid metal <NUM> with respect to the casting axis X.

In these cases, it is assumed that the development of the surface profile <NUM> is symmetrical with respect to the casting axis X. These embodiments can be used on molds <NUM> with small sizes, where the surface profile <NUM> is almost symmetrical along the casting axis X.

In variants of the present invention, the detection means <NUM> can comprise a detector <NUM>, which can be for example a sensor of the type indicated above, configured to detect a distance <NUM> with respect to the liquid metal <NUM>, and a movement device <NUM> configured to move the detector <NUM> above the level of liquid metal <NUM>, that is, above the upper end <NUM>.

According to one possible solution, the movement device <NUM> is configured to move the detector <NUM> along a longitudinal axis Z orthogonal to the casting axis X.

In the embodiment in which the mold <NUM> is of the type for slabs, the longitudinal axis Z is positioned substantially parallel to the pair of walls with bigger sizes.

The movement device <NUM> can be provided with at least a guide element <NUM> on which the detector <NUM> is installed slidable along the longitudinal axis Z.

The guide element <NUM> can be associated with the entrance end <NUM> of the mold <NUM>.

The guide element <NUM> can extend for the entire width of the mold <NUM>.

The detector <NUM> is connected to the control and command unit <NUM> which is configured to receive the distance data <NUM> detected instantly by the detector <NUM> during its movement, in this way performing a scanning of the surface of the liquid metal. The control and command unit <NUM>, by processing this distance data <NUM>, determines the characteristic parameters of the development of the surface profile <NUM>.

In some embodiments of the present invention, the control apparatus <NUM> according to the present invention comprises a nozzle <NUM> configured to discharge the liquid metal <NUM> into the mold.

The nozzle <NUM> is connected to the control and command unit <NUM> which is configured to manage the functioning of the nozzle <NUM>, in relation to the characteristic parameters of the development of the surface profile <NUM> detected.

The nozzle <NUM> is positioned, through the upper end <NUM>, in the mold <NUM>, and is partly immersed in the liquid metal <NUM>.

According to possible solutions, the nozzle <NUM> can be associated with displacement devices <NUM> (<FIG>) configured to move the nozzle <NUM> in a direction parallel to the casting axis X and modify the positioning of the exit end of the nozzle <NUM> in the mold <NUM>.

According to possible solutions, delivery devices <NUM> can also be associated with the nozzle <NUM>, which are configured to deliver in the nozzle <NUM> auxiliary stirring gases of the liquid metal <NUM> in the mold <NUM>.

Auxiliary gases can comprise inert gases, such as argon.

According to possible solutions, at least one, or both, of either the displacement devices <NUM> or the delivery devices <NUM> can be connected to the control and command unit <NUM> which is configured to determine a movement of the displacement devices <NUM> and/or the drive of the delivery devices <NUM> in relation to the characteristic parameters of the development of the surface profile <NUM> detected and to determine a control of the fluid-dynamic flows of the liquid metal <NUM> in the mold <NUM>.

According to some embodiments of the invention, the control and command unit <NUM> is configured to manage the functioning at least of the electromagnetic brake <NUM>, and possibly of the displacement devices <NUM> and the delivery devices <NUM>, so as to obtain desired recirculation flows <NUM> such as to allow to obtain a high quality cast product.

Specifically, it is provided that the control and command unit <NUM>, as a function of the development of the surface profile <NUM> detected, allows to generate double recirculation flows of the liquid metal <NUM>, as shown in <FIG>.

In particular, this flow configuration allows to generate a first recirculation 17a which develops from the discharge end of the nozzle <NUM> toward the surface of the liquid metal <NUM>, and a second recirculation 17b which develops from the discharge end of the nozzle <NUM> toward the inside of the mold <NUM>.

The first recirculation 17a allows to avoid a stagnation of the liquid metal <NUM> in the upper part of the mold, which determines the so-called freezing of the meniscus, that is, an unwanted cooling of the portion of liquid metal <NUM> present on the surface.

By means of the detection of the surface profile <NUM> with the detection means <NUM>, it is possible to determine the modes, that is, the development, of the recirculation flows <NUM> that are established inside the mold <NUM>. The surface profile <NUM>, that is, the shape of the meniscus, is closely connected to the speed of the flow of the liquid metal <NUM> in the first recirculation 17a. The amplitude of the waves and their positioning, that is, the type of development of the surface profile <NUM>, allow to reliably determine the energy, the speed, and therefore the flow rate of the first recirculation 17a.

Based on the flow rate of the first recirculation 17a, the control unit <NUM> is able to act on the functioning of the electromagnetic brakes <NUM>, in order to optimize the motion of the recirculation flows <NUM> contained in the liquid metal <NUM>.

In particular, it is possible to obtain the correct flow distribution between the first recirculation 17a and the second recirculation 17b in any operating casting condition.

It is clear that modifications and/or additions of parts may be made to the apparatus <NUM> as described heretofore, without departing from the field and scope as defined by the claims of the present invention.

For example, in one possible solution, the detection means <NUM> can be able to detect, in addition to the development of the surface profile, also the level of the meniscus of the mold <NUM>.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of control apparatus <NUM>, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claim 1:
Apparatus to control continuous casting, comprising a mold (<NUM>) provided with at least one entrance end (<NUM>) through which liquid metal (<NUM>) is introduced, at least one electromagnetic brake (<NUM>) associated with the mold (<NUM>) and configured to induce in said liquid metal (<NUM>) recirculation flows (<NUM>), and a control and command unit (<NUM>) connected at least to said electromagnetic brake (<NUM>) and configured to manage the functioning thereof, the apparatus comprising detection means (<NUM>) located, at least in a condition of use, above the entrance end (<NUM>) and each configured to detect at least a reciprocal distance (<NUM>) with respect to the level of said liquid metal (<NUM>), wherein said control and command unit (<NUM>) is also connected to said detection means (<NUM>) to acquire the data of each distance (<NUM>) from each detection mean (<NUM>), process them in relation to the positioning of said detection means (<NUM>), determining characteristic parameters of the development of the surface profile (<NUM>) of said liquid metal (<NUM>), and command the drive at least of said electromagnetic brake (<NUM>) based on said characteristic parameters of the development of said surface profile (<NUM>) in order to determine predefined recirculation flows (<NUM>) of the liquid metal (<NUM>) characterized in that said control and command unit (<NUM>) is configured to process the data of each distance (<NUM>) determining, as characteristic parameters, the evolution speed of the surface profile (<NUM>) and/or the temporal average of each said distance (<NUM>) on predetermined time intervals and/or the instant deviations from the temporal average for each detection mean (<NUM>).