DEVICE AND METHOD OF CONTROLLING HEAT EXCHANGE IN A CRYSTALLIZER

Abstract

The invention concerns a device of controlling the heat exchange in a crystallizer (26; 126; 226; 326) in which there are cooling channels (48; 148; 348) and one or more temperature sensors (154, 158, 160; 260; 360) which are arranged at the outlet (148b; 248b) of and/or inside the channels measuring the temperature of a cooling fluid to calculate, for example, the temperature difference ΔT between different values TOUT at the outlet of different channels to identify non-uniformity in the heat exchange during casting. The outlet temperature sensors can be arranged perimetrally on the crystallizer itself or on a separate cover (272; 372a, 372b) that closes a gap (271) between the crystallizer and a relative ingot mould (227). A relative cover with relative kit and relative continuous casting plant and a method for controlling the heat exchange and a use of the device replacing the crystallizers are also described.

Description

TECHNICAL FIELD

This solution concerns a device and a method to monitor the trend and the uniformity, or not, of the heat exchange in a crystallizer and can be used in the continuous casting process of long products such as billets, blooms, beam blanks, or flat products such as conventional slabs or thin slabs.

BACKGROUND OF THE INVENTION

The crystallizer is a known and fundamental component in the continuous casting sector and has the function of giving the shape to the product that is cast inside it, defining by heat exchange the shape and the thickness of the skin of the product itself.

In fact, the liquid steel is poured into the crystallizer and this by being cooled internally by means of a liquid extracts heat from the steel, transferring it to the cooling liquid and causing the progressive formation of the skin which, at the outlet from the crystallizer, must be sufficiently thick to contain the still liquid steel inside without continuous containment.

The crystallizers can have different shapes, suitable for casting flat or long products, they can be composed as a single piece as are typically those for long products or as assemblable pieces as are typically those for flat products. The crystallizers can have different dimensions, starting for example from 110 mm internal width of the crystallizer to 1600 mm and beyond for vertical castings of blooms. In the flat products the crystallizer can have internal widths even greater than 2000 mm, while the thicknesses generally do not exceed 400 mm.

All crystallizers as mentioned, in order to be able to extract heat from the steel and to withstand high operating temperatures, are connected to a closed circuit that cools them by circulating a cooling fluid, which is generally water.

A first generation of crystallizers consisted of tubes with a certain thickness, which were fitted into special chambers called conveyors, so that a gap called also aperture was generated between the outside of the tube and the inside of the conveyor and the whole was fitted into an ingot mould. The cooling fluid, entering from one side, for example from below at room temperature, was then introduced into this conveyor and was extracted warmer on the other side cooling the tubes contained in the conveyor along its path.

An evolution of this concept, which allowed to improve the heat exchange near the liquid steel, by allowing a consequent increase in the casting speed, since the skin was formed more quickly, envisaged to drill longitudinally the thickness of the crystallizer to create through channels, inside which to let the cooling fluid flow.

Furthermore, in order to limit production costs, given that the transversal holes were onerous, the concept evolved into the creation of the cooling channels by externally milling the walls of the crystallizer and their final definition through closure with panels and/or windings, preferably in carbon fibre, such as for example, described in European patent EP 3 013 498B1. This variant of crystallizers allows to have, compared to the version with through channels, lower thicknesses of the walls of the crystallizer.

The evolution of the crystallizers described above has allowed to improve the heat exchange and reduce the production costs of the crystallizer, in particular by switching to the cooling principle with through or externally made channels; the heat exchange at the corners of the crystallizer can be modulated.

Usually, each channel is then fed by a common flow and the fluid flowing through the crystallizer is extracted from a common manifold.

The casting process, however, hides several unknowns while being executed and the skin formation mechanisms happen to give rise to inappropriate conformations: in fact, the support of the skin being formed to the wall of the crystallizer happens to be not optimal, and that hot or cold spots are caused in the crystallizer, which are synonymous with a skin having insufficient thickness or with a detachment thereof from the crystallizer, which therefore no longer exchanges appropriately, with the risk that the uncooled skin melts due to the heat of the internal steel and/or that by solidifying again gives rise to quality defects or still, it exits from the crystallizer having insufficient thickness with the risk of tearing due to the ferrostatic pressure, giving rise to a so-called break-out, i.e. a leakage of liquid steel that causes the interruption of the process, with consequent loss of production, with the possibility of damaging the plant and of risks for the operators' safety.

Therefore, it is essential to know the situation and the evolution of the heat exchange during the continuous casting process, so as to identify any potentially dangerous thermal imbalances in time, before they give rise to potentially harmful phenomena such as skin breakage (so-called break-out) or product quality defects, which require to be identified as early as possible in order to eliminate the causes or at least to mitigate the effect thereof.

In this regard, the state of the art knows systems for measuring the temperature trend in a crystallizer. Exemplarily, patent applications EP 3 668 665 A2 and WO 2020/254688 A1 will be mentioned which describe crystallizers whose walls are provided with channels or grooves that are perpendicular to the casting direction which contain sensors therein to monitor the temperature distribution in the crystallizer. It is a complex and expensive system that also subjects the temperature sensors to high temperatures inside the walls of the crystallizer. Other documents describing systems for monitoring temperature trends in a crystalliser are EP 4 023 359 A1, KR 2001 0017893 A and KR 100 399 233B1 .

DISCLOSURE OF THE INVENTION

The invention aims to overcome the above drawbacks and to propose a device and related method of controlling the heat exchange in a crystallizer that is reliable, but at the same time not very complex. A further object of the invention is to reduce the construction cost of a crystallizer and the cost for managing a relative continuous casting plant, minimizing the risk of accidents during casting and of product quality defects.

Further objects or advantages of the invention will become apparent from the following disclosure.

In a first aspect of the invention, the object is achieved by a device of controlling the heat exchange in a crystallizer comprising:

• • (a) a crystallization unit in turn comprising
    • (a-1) a crystallizer for continuous casting comprising
      • (a-1.1) a tubular body with at least one wall which defines a longitudinal through cavity; and
      • (a-1.2) a plurality of preferably longitudinal first cooling channels, wherein one end of said first cooling channels serves as their inlet and the other end serves as outlet; and
  • (b) one or a plurality of first temperature sensors
    • which is/are positioned at the outlet of said first cooling channels to measure the relative outlet temperature Tour of said cooling fluid that during use of the crystallizer runs through said first cooling channels and/or
    • which is/are positioned inside said first cooling channels along their longitudinal extension, preferably at N different heights to measure one or more respective temperatures T_N corresponding to the different heights of said cooling fluid that during use of the crystallizer runs through said first cooling channels,
      wherein in the case of the presence of only one temperature sensor said only one temperature sensor is a multi-point sensor.

By the term “cooling channel(s)” is meant both channels passing through said at least one wall and grooves obtained in at least a part of an external surface of said at least one wall and covered with a respective covering.

By the term “through channel” is meant a channel that is perforated in the wall of the crystallizer and closed along its longitudinal extension by the wall itself with openings only in the end parts. The “grooves” instead represent the recesses applied to an external surface of the wall of the crystallizer, which are open outwards along their longitudinal extension. Covering this longitudinal opening results in a closed channel on the longitudinal sides with openings only at the ends thereof, thus at the inlet and at the outlet of the channel.

The term tubular refers to tubes, hence hollow elongated bodies, with sections having various geometries: circular, rectangular, polygonal, H-shaped etc. The list is not exhaustive.

The preferred extension of the cooling channels is the longitudinal one that follows the course of the casting and therefore of the solidification and of the connected cooling of the metal in transit through the crystallizer. Extensions that are not parallel to the casting direction, such as transverse or oblique extensions, are also conceivable.

By the definition of “at the outlet of the channel” not only positions directly corresponding to the actual outlet of the cooling channel, but also positions inside the end section thereof, or external positions, can be identified in which the distance between a temperature measurement sensor with respect to the actual outlet is preferably less than 10 cm, more preferably less than 4 cm, even more preferably less than 2 cm.

In the case of a crystallizer provided with grooves, the outlet position may be located in an end zone of the groove that is not closed by a respective covering. In the case of temperatures measured at the outlet of the channel, and therefore in the outlet zone, mention can be made of a temperature value T_OUT.

The positioning of the first sensor(s) at the outlet of the cooling channels of the crystallizer, makes the system much less complex than state-of-the-art crystallizers, which provide dedicated systems or channels for cooling the crystallizer and for measuring the thermal situation in the crystallizer. In addition, the temperature sensor, being directly affected by the flow of the cooling fluid, is exposed to lower temperatures with respect to sensors inserted in channels made in the thickness of the wall of the crystallizer, as envisaged by the state of the art, for example in EP 4 023 359 A1, which are adapted to measure the temperature of copper in contact with steel and not that of the cooling fluid like in the present invention.

The comparison between the measurements of the outlet temperature T_OUT, and therefore the mere presence of temperature sensors at the outlet of the cooling channels, already provides information on the thermal differences between said channels, indicating irregularities of the heat exchange in the crystallizer. This implies that, preferably, the device according to the invention may comprise a control unit configured to receive T_OUT values and calculate differences between them. The comparison with the input temperature is not strictly necessary in order to have sufficient information on the temperature trend in the crystalliser having measured the temperature at the outlet of the channels, thus at the same height at the terminal part of the crystalliser.

For any occurrence of thermal non-uniformity or irregularity to be identified, use will therefore be made of the characteristic of the most advanced crystallizers of the state of the art described above of being provided with separate cooling channels, monitoring and subsequently comparing the thermal delta ΔT that is generated between the flows of the cooling fluid of the different cooling channels, for example, as will be described below, at the same height, or even within the individual cooling channels.

The periodic or even better continuous monitoring of this thermal delta ΔT will allow to identify any peaks or drops of local heat exchange in the temperature trend of the monitored channels in time, thus allowing to understand which zones of the crystallizer are most at risk and take the appropriate measures in time. This monitoring is the object of a further aspect of the invention and is illustrated below.

In a preferred embodiment of the invention, the heat exchange control device according to the invention further comprises

• • (c) at least one second temperature sensor positioned upstream of said first cooling channels to measure the inlet temperature T_IN of a cooling fluid that during use of the crystallizer runs through said first cooling channels.

The at least one second temperature sensor may be located outside the crystallizer or in the inlet zone of the cooling channels of the crystallizer.

The term “at the inlet” is to be understood, mutatis mutandis, like the term “at the outlet” defined above.

The readings of the inlet temperature (which is probably a temperature common to all cooling channels) and of the outlet temperatures of at least one of the cooling channels, or preferably some of them, more preferably all of them, once they are compared, help understand the intensity of the cooling that occurred in the crystallizer. The inlet temperature is usually in a range between 10° C. and 50° C., preferably in a range between 20° C. and 40° C. (room temperature).

A comparison with the inlet temperature is also possible without measuring it with a temperature sensor, as the device according to the invention may comprise a system for setting it to a desired value.

In one embodiment of the invention, the crystallization unit further comprises a source of a cooling fluid, in particular a cooling system or circuit that is connected to said first cooling channels to feed them through their inlets with a cooling fluid.

Obviously, the device according to the invention may comprise a control unit which receives the various measured temperature data and calculates the desired temperature differences, but also conceivable is a reading of the temperature values indicated by the sensors by an operator and an evaluation of the individual values in mind.

In a further embodiment of the invention, the heat exchange control device further comprises

• • (d) a control unit configured to
    • (d-1) receive the measurement signals of the outlet temperature T_OUT of the respective cooling channels and/or to receive the measurement signals of the temperature(s) T_N at different heights in the crystallizer from said first sensors;
    • (d-2) optionally, in case of presence of said at least one second temperature sensor, receive measurement signals of the temperature T_IN from said sensors;
    • (d-3) calculate temperature differences ΔT among received temperature values; and
    • (d-4) process commands to control casting parameters of a continuous casting plant comprising said crystallizer on the basis of the calculated values ΔT.

The differences between the temperatures measured at the outlet T_OUT between different channels, such as for example adjacent channels or opposite channels, indicate different temperatures of the cooling fluid inside the channels, therefore they also indicate differences between the heat exchanges that take place between the crystallizer and the steel. The person skilled in the art identifies with his general knowledge the differences ΔT to be analysed in order to have information on the heat exchange in the crystallizer.

Preferably, in case of presence of sensors arranged at different heights in the cooling channel it is possible to calculate different values of ΔT between the various measurement points within the respective cooling channels by providing a more detailed mapping of the distribution of the temperatures in height and of the position and extension of the cooling non-uniformity in the crystallizer. The more sensors are provided, inside one or more channels and/or at the outlet of one or more channels, the more the correction of the cooling or of the casting itself can be targeted.

Further useful information can be obtained by calculating temperature differences between values of T_N or T_OUT and T_IN.

To reduce the cost in constructive and economic terms, the number of sensors can be reduced. In a preferred embodiment of the invention, the crystallizer is divided in its cross-section into sectors and it is envisaged for each sector to comprise a certain number of said first cooling channels. For each sector, a number of first temperature sensors that is lower than the number of cooling channels is then provided. It is possible for the number of sensors to be equal to zero in some sectors, for example by providing alternating sectors with and without sensor(s). The presence of a plurality of first temperature sensors positioned at the outlet of said first cooling channels and/or positioned within said first cooling channels therefore does not mean that every outlet of a channel or every interior of a channel is equipped with a temperature sensor.

For example, it is possible to divide the perimeter of the crystallizer into quadrants and provide each of them with at least one outlet sensor and to compare the quadrants between them, the measurement will consequently be less precise, but the investment in terms of installed instrumentation and maintenance/replacement will be lower.

As set out at several points in the description, it is also clear that there might also be multiple sensors per channel without departing from the scope of protection of the present invention.

The temperature sensors used can be of various kind. In one embodiment of the invention, the temperature sensor of a plurality of sensors is a one-point sensor that is single-point, preferably selected from thermocouples and heat resistors. The one-point sensors or transducers allow to acquire their signals over time, thus allowing monitoring the thermal trend of the casting.

The acquisition frequency can be for example 1 Hz, but nothing prohibits increasing or decreasing it according to need, this applies to all forms of implementation.

In order to increase the reliability of the temperature detection system, limiting the number of cables to be managed, it is possible to think of adopting multi-point measurement systems, such as for example optical fibres. In this regard, in another preferred embodiment of the invention, said temperature sensors are multi-point sensors, preferably a Bragg grating optical fibre. An optical fibre with several measurement points allows temperature mapping along the cooling channel or also in one or more annular arrangements or along the perimeter, which will be illustrated later. In the zone at the outlet from the channel, these fibres also always allow a value T_OUT to be measured.

Two sub-variants are therefore conceivable within this embodiment of the invention: in the first one the optical fibre is inserted longitudinally in the channels (at least some) of the crystallizer, in the second one the optical fibre is in a horizontal position that can also assume an arrangement along the perimeter of the crystallizer. Horizontal arrangements that do not affect the entire perimeter of the end part of the crystallizer are also imaginable, for example in crystallizers for flat products in which sensors could be provided only in some of the plates forming the crystallizer.

Optical fibres generally contain, at equivalent distances, a plurality of reflection (measurement) points, which when subjected to thermal variation undergo a deformation modifying the extent of their dimension and therefore their capacity for reflection. As a function of these variations it is possible to understand the value of the temperature that was detected by the reflection point. The use and the operation of Bragg fibres are well known to the skilled person and need not be described in more detail.

In an advantageous embodiment of the invention, a multi-point temperature sensor is inserted in the longitudinal direction, and thus parallel to the casting direction, in at least one of said first cooling channels. In this case the measurement point at the end of the cooling channel provides a temperature value T_OUT. The insertion of a vertical fibre in the cooling channels can be combined with the presence of sensors in front of the outlet of the channels, in this case the value T_OUT would correspond to the value of the sensor placed in front of the outlet of the channels.

It is also possible, for example, to make additional channels for the installation of the optical fibres in the thickness of the crystallizer, inside the cooling channels and once they are inserted to cement them with some paste that allows a slight deformation thereof, such as for example a silicone-based paste.

By measuring the temperature with different fibres passing through the cooling channels of a crystallizer, it is possible to compare the thermal distributions along all the walls of the same as a function of the solidification progression, by comparing the reading of several channels it is possible to establish if there are zones with hot or cold spots and intervene.

With regard to the number and to the positioning of the temperature sensors, it is therefore possible to divide the control device according to the invention into several variants.

In a first variant, for example, it is possible to insert first temperature sensors or transducers with a single measurement point at the outlet from a cooling channel. By applying multiple sensors, i.e. multi-channel transducers it is possible to compare these values of ΔT and check if there are relevant differences, indications of some dysfunction in the crystallizer.

By assuming exemplarily to have a crystallizer with 52 channels, 52 sensors or transducers in fluid output will be required for at least a complete reading. However, nothing prevents inserting multiple sensors even at the inlet, even if this increases the installation costs.

Another arrangement is the longitudinal, or vertical, one (parallel to the casting direction) already described inside one or more cooling channels.

In another embodiment of the invention, the heat exchange control device comprises a plurality of single-point sensors or in a particularly advantageous way at least one multi-point sensor which are/is positioned in a perimetral manner around the end part of said crystallizer and at the outlet of said first cooling channels so that it is/they are affected by the flow of a cooling fluid at the outlet of said first cooling channels. An arrangement along or around the perimeter of the crystallizer, particularly simple to make with an optical fibre, allows to collect the values T_OUT of a plurality of channels at the same time and is a configuration with easy construction. A particularly simple construction provides that, advantageously, the crystallizer further comprises in the end part, and therefore in the outlet zone of said first cooling channels, a cavity along the perimeter which houses said plurality of single-point sensors or said at least one multi-point sensor. The perimetral cavity can be located on the side wall of the crystallizer or on the edge thereof. The perimetral cavity is preferably groove-shaped in order to be able to accommodate the sensor(s), and can be suitably covered, but could also be a through channel communicating with said first cooling channels.

Advantageously, the system can be integrated with sensors that detect the temperature of the cooling fluid at the inlet T_IN to the crystallizer in order to be able to determine temperature differences with respect to the value of T_IN.

A particularly advantageous embodiment of the invention concerns a horizontal arrangement of the sensor(s), that is of the relative temperature measurement points wherein the sensors are located around the perimeter of the crystallizer but detached therefrom. Such an embodiment provides that the crystallization unit further comprises

• • (a-2) an ingot mould into which said crystallizer is inserted; and
  • (a-3) a first cover, preferably disc-shaped, with a central opening adapted to close the gap between said crystallizer and said ingot mould, wherein said opening is complementary to the outlet of said crystallizer and wherein said first cover comprises
    • (a-3.1) a plurality of second channels arranged radially around said opening which in the closed state of the gap with said first cover are the continuation of said first cooling channels; and
    • (a-3.2) a cavity, preferably annular and extending around said central opening, which is in communication with said second channels and houses said one or plurality of first temperature sensors, in particular a multi-point sensor.

The cavity can also be a complex of multiple single cavities to contain individual temperature sensors.

For further cooling the crystallizer it is advantageous to fill the ingot mould with a cooling fluid by introducing the water into the channels of the crystallizer directly inserted in the ingot mould. Advantageously, the distances of the single-point sensors or of the measurement points of the multi-point sensor substantially correspond to the distance of the second channels in the cover. The perimetral arrangement of the sensors around the opening of the crystallizer can therefore be made with a perimetral cavity directly on the crystallizer and/or on a separate element, i.e. on a closing element, i.e. on a cover, in a relative perimetral or annular cavity. The horizontal arrangement in a cover can, in other words, be described as a transverse arrangement. i.e. perpendicular to the casting direction.

The type of “vertical” measurement of the temperature, i.e. along the cooling channels, seen above, shows a precise, but very complex system, which certainly offers a lot of data, but which entails an aggravation in terms of the number of sensors to be installed (with relative encumbrances and costs). Furthermore, making and blocking the sensors in the channels are also not easy and are expensive due to the further processing in order to house the fibres, in particular in small-sized tubular crystallizers.

The use in particular of the sensors with multiple measurement points, in particular of optical fibres, and their horizontal positioning, specifically also perimetral one, allows the realization of an apparatus for measuring the temperature of the cooling fluid that allows to achieve a good result in terms of data acquisition, but which at the same time allows to make the installation process easier and economically sustainable.

As seen above, by horizontal installation of the fibres is meant their positioning near the holes at the outlet from the cooling channels, advantageously paying attention to positioning the sensors or the reflection points of the optical fibre in front of said channel so that they are hit by the flow of warmer water exiting the crystallizer over time. The term “perimetral” indicates an arrangement around or along the perimeter of the crystallizer.

The signals detected by the reflection points can thus be acquired to monitor the thermal variations of the individual channels, in particular cases also starting from the common inlet temperature in the various cooling channels.

A preferred embodiment of the invention solves the problem of fixing the sensor, in particular an optical fibre, in the first cover, avoiding the application of fixing means, such as glue, silicone paste or clamps: it is envisaged that said first cover comprises a plurality of second channels in the form of grooves and a cavity, preferably annular, in the form of a groove that are as defined above and that said crystallization unit further comprises

• • (a-4) a second cover
    • (a-4.1) preferably disc-shaped, having a central opening adapted to close the gap between said crystallizer and said ingot mould, wherein said opening is complementary to the outlet of said crystallizer, and being
    • (a-4.2) compatible with said first cover in such a way as to enclose between said first and said second cover said one or plurality of temperature sensors and to close said second grooves.

Advantageously, said second cover comprises a plurality of third grooves arranged radially around said opening and a cavity, preferably annular and extending around said central opening. The arrangement of said second and third grooves and preferably of said cavity is specular among the covers in such a way that in the closed state of the gap with said first and second covers second and third grooves form closed channels as do the corresponding cavities, as well. In particular, it is therefore advantageous to use a component for closing a cooling channel, adapted to be at least partly coupled with one end of the crystallizer, which is generally grooved, in which a special space is also made, such as an annular cavity, for the installation of the optical fibre. This closing component can also be made, as illustrated above, as two or more bodies adapted to couple with each other enclosing one or more fibres between them. In addition to the annular cavity, other forms of cavity are also conceivable to house the sensor(s).

This configuration is particularly advantageous, because the fibre is blocked between closing components (covers), leaving only small sections thereof visible, which being hit by the flow of the cooling fluid, do not undergo dangerous vibrations that can disrupt the reading and lead over time to an early wear of the fibre.

In the case of optical fibres inserted into the first cooling channels, a cover with through channels or grooves that let the fibres coming out of the crystallizer pass can help block the fibres further.

A second aspect of the invention concerns a cover for closing a gap between an ingot mould and a crystallizer inserted therein wherein the cover, preferably disc-shaped, has a central opening, wherein said opening is complementary to the outlet of said crystallizer and wherein said cover comprises

• • (i) a plurality of channels arranged radially around said opening which in the closed state of the gap with said cover are alignable with cooling channels present in the crystallizer; and
  • (ii) a cavity, preferably annular, and extending around said central opening, preferably connecting said radial channels, which is adapted to house one or a plurality of temperature sensors, in particular a multi-point sensor, in particular a Bragg grating optical fibre; and optionally
  • (iii) one ore a plurality of temperature sensors, in particular a multi-point sensor, in particular a Bragg grating optical fibre inserted in said cavity.

The channels can be through channels or grooves hollowed out into the surface of the cover. As an alternative to the annular cavity, there may be cavities with other shapes adapted to accommodate sensors in the zone of the channels/grooves.

As mentioned at the beginning of this description, the crystallizer is placed inside an ingot mould, being able to be provided with a conveyor, so as to be able to connect cooling delivery and return; while the crystallizer is consumable and is replaced once a certain number of castings are reached, the ingot mould (and any conveyor) can be recovered, therefore it is optimal to install the fibre in components that are part of the latter, or in separate components, so as to be able to use them on several crystallizers. Having in a preferred embodiment of the invention provided for the installation of the sensors on the closing element (cover), it will be easy to replace a crystallizer without having to replace or discard the sensors, as well. As the cover can be easily produced, it is also economically convenient to produce a cover with integrated temperature measurement system (e.g. with 3D printing).

Crystallizers can have various lengths and sections (circular, square, rectangular, polygonal, such as for example octagonal, H-shaped or combinations thereof and others) to produce various forms of cast products having round, square, rectangular, octagonal profiles, joined rounded frames, H-Shapes or more. The invention is independent of the forms of the crystallizers or of the cast products.

A heat exchange measurement system integrated in the cover of the ingot mould is easily adaptable to different crystallizers.

The invention provides in a further aspect a cover kit comprising

• • (i) a plurality of covers according to the invention compatible between them so as to close the gap between the crystallizer and the ingot mould and enclose a temperature sensor between them; and/or
  • (ii) a plurality of covers according to the invention each having a different shape and/or dimensions making them compatible with various types of crystallizers.

A further aspect of the invention concerns a continuous casting plant comprising a heat exchange control device according to the invention.

The concept of the invention can be applied to crystallizers for flat products generally having a substantially rectangular outlet shape, or for long products having more varied profiles as listed above in exemplary form.

Another aspect of the invention concerns a method for controlling the heat exchange in a crystallizer comprising the following steps:

• • (I) providing a crystallizer with preferably longitudinal cooling channels applied in at least one wall of said crystallizer;
  • (II) introducing a cooling fluid into said cooling channels such that the flow of the cooling fluid is preferably parallel to the casting direction, wherein said cooling fluid has for all channels preferably a common inlet temperature T_IN, and performing a casting through said crystallizer;
  • (III) measuring for a plurality of said cooling channels the temperature of the cooling fluid at the outlet (T_OUT) and/or measuring, for at least one of said cooling channels, but preferably for a plurality of them, the temperature of the cooling fluid along the cooling channel (T_N);
  • (IV) optionally measuring or determining the temperature T_IN at the inlet to said cooling channels;
  • (V) calculating, preferably for all channels provided with a temperature sensor, the temperature difference ΔT
    • (V-1) between at least two outlet temperatures T_OUT of two different cooling channels; and/or
    • (V-2) between two temperatures measured at different heights of a cooling channel or between two temperatures measured in different cooling channels at the same height; and optionally
    • (V-3) between the inlet temperature T_IN and the outlet temperature T_OUT of a cooling channel; and/or
    • (V-4) between the inlet temperature T_IN and a temperature T_N along a cooling channel;
  • (VI) identifying irregularities of the value ΔT; and
  • (VII) correcting the casting parameters, e.g. casting speed or lubrication, based on the irregularities determined in step (VI).

Measurements and calculations preferably take place as a function of time. If the control of heat exchange is limited to monitoring temperatures and their differences, step (VII) can be omitted; if the control extends to the management of continuous casting, step (VII) is also performed. As already mentioned above, other temperature differences can be imagined which can be calculated from data T_OUT, T_N and optionally T_IN of various channels useful for determining irregularities of the value ΔT and that can be identified by the expert. In particular, more or less prolonged increases or decreases of the “normal” value indicate respectively insufficient or excessive cooling in certain zones of the crystallizer. As an alternative to the method with the calculations according to (V-1), (V-2) a method using only the calculations according to (V-3) and/or (V-4) is conceivable.

The method advantageously is implemented with the heat exchange control device according to the invention.

A last aspect of the invention relates to a use of a heat exchange control device in a crystallizer with cover, that is closure element according to the invention in a continuous casting process with measurement of the heat exchange in the crystallizer wherein:

• • (α) the worn crystallizer is replaced with a new crystallizer; or
  • (β) the crystallizer is replaced with a crystallizer with another shape and/or other dimensions and consequently the first cover is replaced with a new cover adapted in the shape thereof and/or in the dimensions thereof to the new crystallizer and to the respective gap created between the new crystallizer and the ingot mould.

Step (α) is possible with the maintenance of the heat exchange control system without having to discard it or provide for it in the new crystallizer.

The term “another shape” comprises geometric shapes (dimensions, section), but also the number and the configuration of the cooling channels.

The features and advantages described for one aspect of the invention may be transferred mutatis mutandis to the other aspects of the invention.

The industrial applicability is obvious from the moment in which it is possible to solve the technical problems illustrated initially and to provide a device and a method of controlling the heat exchange in a crystallizer that is reliable, not very complex, economical, in some embodiments thermally less stressful for the sensor(s) employed and that in some cases increases the flexibility when the measurement system is detached from the crystallizer itself and it is easier to change the type of crystallizer inside the ingot mould. The invention has therefore achieved the objects initially described.

The objects and advantages will be further highlighted in the disclosure of preferred examples of embodiments of the invention given by way of non-limiting example only.

Variant and further features of the invention are the subject matter of the dependent claims. The description of the preferred embodiment examples of the device, of the cover, of the kit, of the method, of the plant and of the use of the device according to the invention is given by way of example and not by way of limitation with reference to the attached drawings. In particular, unless otherwise specified, the number, shape, size and materials of the system and of the individual components may vary, and equivalent elements may be applied without deviating from the inventive concept.

DESCRIPTION OF PREFERRED EMBODIMENT EXAMPLES

FIG. 1 represents a principle diagram of the heat exchange control in a crystallizer for long products according to the invention.

FIG. 2 represents a principle diagram of the heat exchange control in a crystallizer for flat products according to the invention.

FIG. 3 represents an embodiment of a crystallization unit according to the invention with crystallizer and cover not mounted for the horizontal arrangement of temperature sensors.

FIG. 4 takes up FIG. 3 with the cover mounted.

FIG. 5 illustrates in enlarged form the cover of FIGS. 3 and 4 provided with an optical fibre.

FIG. 6 represents the trend of a value AT as a function of the time under various aspects where AT is understood as the difference between various values of TOUT.

FIG. 7 represents the thermal trend in a crystallizer comprising vertical optical fibres.

FIG. 8 illustrates in schematic form an embodiment of the positioning and fixing of an optical fibre in the end part of a crystallizer.

The principle of measurement of the temperature in the crystallizer and of the regulation of the casting system is illustrated in FIGS. 1 and 2 which are distinguished by the type of crystallizer, a crystallizer for long products in FIG. 1 and for flat products in FIG. 2. For purely illustrative purposes in the crystallizers various possible positions are indicated for the temperature sensors, not necessarily present simultaneously.

In FIG. 1, the crystallizer 126, cylindrical in the example, is provided with a series of grooves 148 extending in the longitudinal direction thereof, i.e. parallel to the casting direction, which are closed by a covering 149 defining cooling channels, their ends are open and form, respectively, inlet 148a and outlet 148b zones of the channels. The arrow 150 symbolizes the inlet of cooling water (at a common temperature T_IN in all channels). The water passes through the channels 148 along the crystallizer 126 and cools the cast product (not represented) inside the crystallizer and by means of the heat exchange warms up, then exiting the channels (arrow 152). In the figure various configurations have been inserted for the temperature sensors: an optical fibre 154 with various measurement points 156; a single one-point sensor 158 at the outlet of the channel and a circular or circumferential optical fibre 160 inserted in a perimetral groove arranged in such a way that the relative measurement points 162 come into contact with the outlets of the channels in front of each channel. Temperature data 164 (T_OUT and/or T_N) measured by the sensors 154, 156; 158; 160, 162 are transmitted to an automation unit 166 which calculates the temperature differences ΔT between various temperature values T_OUTand/or T_N and optionally with respect to T_IN and identifies any non-uniformity. From these results the automation unit processes the commands to adjust 168 the casting parameters of the continuous casting unit 110.

FIG. 2 corresponds in the essential parts to FIG. 1. A crystallizer 26 fed through the nozzle 22 with a liquid metal 20 can be noted. The crystallizer 26 serves to produce flat products and is made up of long walls 25 and narrow walls 27. In the walls 25, 27 vertical through channels 48 are made, at least one of which exemplarily contains an optical fibre 54 with a plurality of measurement points 56. A through channel 61 perpendicular to the vertical channels 48 which is provided with an optical fibre 60 with an exemplary measurement point 62 can also be noted. The channels are crossed by a flow (50, 52) of cooling fluid. Temperature data taken from the sensors 54, 60 are transmitted 64 to the automation unit 66 which calculates from values ΔT commands to adjust 68 the casting parameters of the continuous casting unit 10 comprising the crystallizer 26.

FIG. 3 and FIG. 4 represent, respectively in a not mounted view (FIG. 3) and in a mounted view (FIG. 4) of the cover an embodiment of a crystallization unit according to the invention with an ingot mould 227, a crystallizer 226 and a cover 272 for the horizontal arrangement of temperature sensors. The crystallization unit can be noted in a bottom view which is composed of an ingot mould 227 in which the actual crystallizer 226 is inserted, in which the outlet zones of the channels 248b can be noted. To close the interspace 271 between the crystallizer 226 and the ingot mould 227, the cover 272 with a series of grooves 247 is provided which are the continuation of the end parts 248b of the grooves of the crystallizer 226. An annular cavity 261 surrounds the opening 273 of the cover 272 which is complementary to the outlet of the crystallizer 226. The annular cavity 261 connects all the grooves 247 that are arranged transversely. i.e. horizontally with respect to the longitudinal extension of the crystallizer 226. FIG. 5 illustrates in enlarged form the cover of FIGS. 3 and 4 with respect to which nothing is added besides the presence of an optical fibre 260 inserted in the annular cavity 261.

It is understood that the system for analysing the cooling fluid temperature with optical fibres illustrated in FIGS. 3 to 5 for a crystallizer for long products can of course also be applied to crystallizers for flat products, such as for example a plate crystallizer for slabs, according to the principles described herein, thus with the aid of a cover associated with the cooling channels.

FIG. 6 represents the trend of a value ΔT as a function of time under various aspects where ΔT is understood as the difference between absolute values of T_OUT for various channels. The values ΔT are the result of statistical calculations for all individual channels measured in a crystallizer according to the invention. The graph of FIG. 6 represents as a function of time the absolute value of the temperature difference in ° C. between various values of T_OUT and under various aspects: ΔT_AV shows the mean value, ΔT_MED the median value, ΔT_MAX the maximum value, ΔT_MIN the minimum value and ΔT_TOT the overall value of the primary cooling. By measuring only the values T_OUT and with various statistical calculations and by the comparison with statistical values it is possible to identify any malfunctions within the crystallizer. By monitoring the temperature of the cooling fluid at some or preferably all of the outlet channels of the crystallizer, it is possible to check if there are abnormal thermal trends and also to identify the location (the respective channel) of the malfunction. By comparing them then with the temperature of the inflow, it is also possible to determine how much temperature has been removed over time. The trend over time of the maximum delta ΔT_MAX indicates a degree higher than the average ΔT_AV and a thermal peak can be noted (indicated by the arrow) which may be an indicator of a temporary lowering of the heat exchange (for example due to a momentary detachment of the skin from the wall).

The operator or an algorithm, by noticing this, can choose to adapt the casting parameters to solve the emergency. In this case apparently the casting speed has also been increased by the thermal peak as the thermal delta decreases and therefore the heat exchange is more uniform through the channels; therefore the skin is thinner and therefore it should adhere better to the walls by exchanging heat more uniformly. However, the increase in casting speed has probably also caused the skin to detach temporarily.

FIG. 7 represents the thermal trend in a crystallizer comprising vertical optical fibres. What is represented is a detail of a vertical section in the direction of the trend of the casting. As can be noted from the example of thermal distribution (simulation) in the crystallizer, by measuring the temperature with different fibres passing through the cooling channels in the walls 340 of a crystallizer, it is possible to compare the thermal distributions along the walls 340 of the same as a function of the solidification progression. By comparing the reading of several channels it is possible to establish if there are zones with hot or cold spots and intervene. The entry or inlet temperature T_IN (dark band at the top) is the same for all channels. A decrease in temperature is visible from top down (T↓) starting from the meniscus zone m with the warmer temperature T₁ with the progress of the solidification (lightening of the bands) and the lowering of the temperature through T₂ and T_N-1, T_N to the temperature T_OUT at the outlet of the respective channel. The number N=1 of T_N corresponds for channels having a longitudinal course to the height closest to the inlet of the crystallizer, while higher values represent in succession temperature detection points closer to the outlet of the crystallizer. A rectangle angle of the crystallizer (image (a) on the left) shows a cooling behaviour different from a blunt angle (image (b) on the right). The “noses” of the bands correspond to zones that do not coincide with the cooling channels (not visible but present in the walls 340) that are cooled with a slight delay compared to zones that are directly at the back of the cooling channels.

In FIG. 8 is illustrated an exemplary embodiment of the positioning and of the fixing of an optical fibre 360 with a plurality of measurement points 362 in the end portion of a crystallizer 326. A series of cooling channels 348 affect in their outlet zone the optical fibre 360 arranged along the perimeter of the crystallizer 326. One possibility for fixing the optical fibre 360 is the application of respective hooks 380 directly on the crystallizer 326. An alternative preferred fixing instead provides for keeping the fibre 360 in a position enclosed between a pair of covers 372a and 372b seen in section with respective grooves 361.

Claims

1. A device of controlling a heat exchange in a crystallizer comprising: wherein in the case of the presence of only one temperature sensor said only one temperature sensor is a multi-point.

(a) a crystallization unit comprising

(a-1) a crystallizer for continuous casting comprising (a-11) a tubular body comprising at least one wall which defines a longitudinal casting through cavity, and (a-1.2) a plurality of first cooling channels, wherein an end of said first cooling channels serves as an inlet of the corresponding first cooling channels and another end serves as an outlet; and

(b) one or a plurality of first temperature sensors which is/are positioned at the outlet of said first cooling channels to measure a relative outlet temperature TOUT of a cooling fluid that during use of the crystallizer runs through said first cooling channels, and/or which is/are positioned inside said first cooling channels along a longitudinal extension of the first cooling channels,

2. The device of controlling a heat exchange in a crystallizer according to claim 1, wherein the device of controlling the beat exchange in a crystallizer further comprises

(c) at least one second temperature sensor positioned upstream of said first cooling channels to measure an inlet temperature TIN of the cooling fluid that during use of the crystallizer runs through said first cooling channels.

3. The device for controlling a heat exchange in a crystallizer according to claim 1, wherein said crystallization unit further comprises a source of the cooling fluid, in particular a cooling system or circuit that is connected to said first cooling channels to feed the first cooling channels through the inlets of the first cooling channels with the cooling fluid.

4. The device for controlling a heat exchange in a crystallizer according to claim 1, wherein the device of controlling the heat exchange in a crystallizer further comprises

(d) a control unit configured to (d-1) receive measurement signals of the outlet temperature TOUT of the respective cooling channels and/or to receive measurement signals of the temperature(s) TN at different heights in the crystallizer from said first temperature sensors; (d-2) optionally, in case of presence of at least one second temperature sensor positioned upstream of said first cooling channels to measure an inlet temperature TIN of the cooling fluid that during use of the crystallizer runs through said first cooling channels, receive measurement signals of the temperature TIN from said at least one second temperature sensors; (d-3) calculate temperature differences ΔT among received temperature values; and (d-4) process commands to control casting parameters of a continuous casting plant comprising said crystallizer on the basis of the calculated ΔT.

5. The device for controlling a heat exchange in a crystallizer according to claim 1, wherein said first temperature sensors are multiple-point sensors.

6. The device for controlling a heat exchange in a crystallizer according to claim 1, wherein the device for controlling the heat exchange in a crystallizer comprises as first temperature sensors a plurality of first single-point sensors or at least one first multiple-point sensor which are/is positioned in a perimetral manner around the end portion of said crystallizer and at the outlet of said first cooling channels so that the at least one first multiple point is the plurality of first single-point sensors are affected by the flow of cooling fluid at the outlet from said first cooling channels.

7. The device for controlling a heat exchange in a crystallizer according to claim 6, wherein the crystallizer further comprises in an end part and therefore in an outlet zone of said first cooling channels a perimetral cavity which houses said plurality of single-point sensors or said at least one multiple-point sensor.

8. The device for controlling a heat exchange in a crystallizer according to claim 6, wherein said plurality of single point sensors or said multi-point sensor are/is positioned either directly at a physical outlet of the respective first cooling channel or externally at an end section of the respective first cooling channel, wherein a distance between the temperature sensor with respect to the physical outlet is less than 10 cm.

9. The device for controlling a heat exchange in a crystallizer according to claim 7, wherein the crystallization unit further comprises

(a-2) an ingot mould into which said crystallizer is inserted; and

(a-3) a first cover with a central opening adapted to close a gap between said crystallizer and said ingot mould, wherein said opening is complementary to an outlet of said crystallizer and wherein said first cover comprises (a-3.1) a plurality of second channels radially arranged around said opening which in the closed state of the gap with said first cover are a continuation of said first cooling channels; and (a-3.2) a cavity, which is in communication with said second channels and houses said one or plurality of first temperature sensors.

10. The device for controlling a heat exchange in a crystallizer according to claim 9, wherein said first cover comprises the plurality of second channels in the form of grooves and the cavity in the form of a groove and in that said crystallization unit further comprises

(a-4) a second cover (a-4.1) having a central opening adapted to close the gap between said crystallizer and said ingot mould, wherein said central opening is complementary to the outlet of said crystallizer, and being (a-4.2) compatible with said first cover in such a way as to enclose between said first and said second cover said one or plurality of temperature sensors and to close said second channels in the form of grooves.

11. The device for controlling a heat exchange in a crystallizer according to claim 1, wherein a multiple-point first temperature sensor is inserted, in at least one of said first cooling channels.

12. A cover for closing a gap between an ingot mould and a crystallizer inserted in the ingot mould wherein the cover has a central opening, wherein said central opening is complementary to an outlet of said crystallizer and wherein said cover comprises

(i) a plurality of channels arranged radially around said central opening which in the closed state of the gap with said cover are alignable with cooling channels present in the crystallizer; and

(ii) a cavity, connecting said radial channels, which is adapted to house one or a plurality of temperature sensors; and optionally

(iii) one or a plurality of temperature sensors, inserted in said cavity.

13. A method for controlling a heat exchange in a crystallizer comprising the following steps:

(I) providing a crystallizer with cooling channels applied in at least one wall of said crystallizer;

(II) introducing a cooling fluid into said cooling channels, and performing a casting through said crystallizer;

(III) measuring, for a plurality of said cooling channels an outlet temperature TOUT of the cooling fluid at an outlet of the cooling channels and/or measuring, for at least one of said cooling channels a temperature of the cooling fluid along the cooling channel (TN);

(IV) optionally measuring or determining a temperature TIN at an inlet to said cooling channels;

(V) calculating, a temperature difference ΔT temperature difference AT (V-1) between at least two outlet temperatures TOUT of two different cooling channels; and/or (V-2) between two temperatures measured at different heights of a cooling channel or between two temperatures measured in different cooling channels at the same height; and optionally (V-3) between the inlet temperature TIN and the outlet temperature TOUT of a cooling channel; and/or (V-4) between the inlet temperature TIN and a temperature TN along a cooling channel;

(VI) identifying irregularities of the temperature difference ΔT; and

(VII) correcting casting parameters based on the irregularities determined in step (VI).

14. The method for controlling a heat exchange in a crystallizer according to claim 13 wherein in a continuous casting process with measurement of the heat exchange in the crystallizer the crystallizer forms part of a crystallization unit that comprises

(a-2) an ingot mould into which said crystallizer is inserted; and

(a.3) a first cover, with a central opening adapted to close a gap between said crystallizer and said ingot mould, wherein said opening is complementary to an outlet of said crystallizer and wherein said first cover comprises (a-3.1) a plurality of second channels radially arranged around said opening which in the closed state the gap with said first cover are a continuation of said first cooling channels; and (a-3.2) a cavity, which is in communication with said second channels and houses said one or plurality of first temperature sensors; wherein:

(α) the worn crystallizer is replaced with a new crystallizer; or

(β) the crystallizer is replaced with a crystallizer with another shape and/or other dimensions and consequently the first cover is replaced with a new cover adapted in the shape thereof and/or in the dimensions thereof to the new crystallizer and to the respective gap created between the new crystallizer and the ingot mould.

15. A cover kit comprising

(i) a plurality of covers according to claim 12 compatible between them for closing a gap between a crystallizer and an ingot mould (227) and enclosing a temperature sensor (260; 360, 362) between them; and/or

(ii) a plurality of said covers each having a different shape and/or dimensions making them compatible with various types of crystallizers.

16. A continuous casting plant comprising a heat exchange control device according to claim 1.

17. The device of controlling a heat exchange in a crystallizer according to claim 1, wherein one or a plurality of first temperature sensors which is/are positioned inside said first cooling channels along a longitudinal extension of the first cooling channels is/are positioned at N different heights to measure one or more respective temperatures TN corresponding to the different heights of said cooling fluid that during use of the crystallizer runs through said first cooling channels.

18. The device of controlling a heat exchange in a crystallizer according to claim 5, wherein said multiple-point sensors are a Bragg grating optical fibre.

19. The device of controlling a heat exchange in a crystallizer according to claim 9, wherein said cavity is annular and extending around said central opening.

20. The method for controlling a heat exchange in a crystallizer according to claim 13, wherein in step (III) the outlet temperature TOUT of the cooling fluid is measured for a plurality of the cooling channels along the cooling channel (TN) and wherein in step (V) for all cooling channels provided with a temperature sensor the temperature difference ΔT is calculated.