A continuous caster and roller for slabs of metal

Abstract

The invention relates to a continuous caster for steel, comprising a mould, a secondary cooling zone comprising a plurality of support rollers for guiding a metal strand exiting from the base of the mould, and a temperature measurement system which is configured for measuring the temperature in the secondary cooling zone at a plurality of positions along a width of the strand.

Description

[0001] A CONTINUOUS CASTER AND ROLLER FOR SLABS OF METAL

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a continuous caster for casting molten metal, in particular molten steel, to a roller for slabs, blooms, billets or strands of metal, to a method for controlling a continuous caster, and a computer program.

[0004] BACKGROUND TO THE INVENTION

[0005] In continuous casting, in particular of steel, the molten metal is fed from a tundish into an open-base mould. The mould is cooled, for example by internal water-cooling, to solidify the metal directly in contact with the mould wall. This is called the primary cooling process. Thereby, a thin shell of metal next to the mould walls solidifies, and the metal, now called a strand, is extracted from the base of the mould and is guided by rollers which support the walls of the strand against the ferro static pressure of the still-solidifying molten metal within the moving strand. To increase the rate of solidification, the strand is cooled as it passes through a secondary cooling zone, for example by water-cooling of the rollers and / or by directly spraying the strand with water or air-mist. In most continuous casters, the strand exits the mould vertically or nearly vertically, and is gradually curved into a horizontal orientation by the rollers as it travels through the secondary cooling zone. At the end of the secondary cooling zone, the fully solidified strand may be cut to form semi-finished products such as blooms, billets or rolling slabs.

[0006] In continuous casting, the solidification rate of the molten metal needs to be carefully controlled, because it significantly influences the final quality of the cast products. For example, a higher solidification rate on one side of the strand can lead to a deformation of the bloom, billet or slab, so that the final cast product has a curved cross-section. More seriously, if the cooling on one side is insufficient, a breakout of liquid steel may occur, leading to significant down-time of the continuous caster. Breakout occurs when the solidifying shell of the strand ruptures, thereby releasing molten metal throughout the casting facility and installations. For this reason, the mould is often equipped with temperature sensors such as thermocouples or other temperature sensors to monitor the evenness of the temperature along the solidifying shell at the mould wall. Unevenness of temperature may lead to cracking and an open crack may lead to a breakout. The secondary cooling zone, however, cannot be equally well monitored because of the harsh environmental conditions caused amongst others by high temperatures, spray water and steam formation. In the paper by Arnulf Diener and Alfons Drastik, “Heat exchange between strands and guide rollers in the secondary cooling zone of a slab continuous casting machine”, Archiv fur das Eisenhuttenwesen, Volume 53(1982)Nr.1 , p.3-13, doi.org / 10.1002 / srin.198205126, temperature measurements are described in an experimental setup, in which a measuring bolt having several thermocouples was inserted into a radial hole in a guide roller of a continuous caster. By measuring temperatures at different distances from the surface of the guide roller through the several thermocouples in the measuring bolt, it was possible to calculate the flows of heat into and out of the rollers by using mathematical models. However, this was a theoretical study of secondary cooling conditions and only one measuring bolt was inserted into a guide roller.

[0007] Patent document US2007 / 0251663-A1 discloses a caster for continuously casting metal including: a) a mould adapted and configured to mould molten metal into a metal strand; b) a cooling system disposed downstream of the mould adapted and configured to controllably cool and substantially solidify the strand before exiting the caster; and c) a temperature measuring device adapted and configured to detect the surface temperature of the strand, the temperature sensor including: i) a sensor adapted and configured to detect the temperature of the strand; wherein the sensor includes a photon sensor that detects photons emitted from the strand to measure the strand temperature; and ii) a gas purge line operably coupled to the sensor, the gas purge line being adapted and configured to deliver a gas purge to deflect debris from a region of the strand being monitored by the temperature sensor. The caster further comprising an elongate tubular member having a first end disposed proximate the strand and a second end disposed proximate the sensor, the tubular member being adapted and configured to permit passage of photons emitted by the strand from the first end of the tubular member to the sensor.

[0008] Patent document US-6,470,957 discloses a process and a corresponding apparatus with which the actual force and position conditions at the contact surface between roller and strand can be sensed for the production of slabs, blocks or round sections. The known process for casting a continuous metal strand in a continuous casting installation has stand parts lying opposite one another and fitted with bearings in which respectively opposed guide rollers are mounted, and having actuators by which a gap between the respectively opposed rollers can be set infinitely variably, said process comprising the following steps: a) sensing a value of a compressive force occurring in the bearings and feeding said value to a computing unit, and in a preferred embodiment the actual temperature in the bearings in sensed in addition to the compressive force; b) comparing individual measured values of a roller or of a pair of oppositely arranged rollers with respect to a level of said compression force; and c) utilizing at least a relatively highest value measured as a command variable for controlling at least one of the gap, a casting rate, an amount of cooling water, a melt feed, a casting powder feed, and a mould oscillation.

[0009] Patent document US2022 / 0241850-A1 discloses an ingot mould for continuous casting of metals to improve breakout detection, the mould consisting of an assembly of metal plates backed by cooling devices configured to allow cooling of the metal plates by the circulation of a cooling fluid, the ingot mould having a casting axis and including: at least one optical fibre including a plurality of Bragg filters extending in a wall of at least one of said plates and replacing thermocouples used in the prior art, at least one groove formed in a wall of at least one of said plates, in a direction that is not parallel to the casting axis of the ingot mould in at least one portion of the length, the optical fibre extending in the groove, and a tongue of substantially complementary shape to the groove closing the groove over its entire length, the groove and the tongue having a shape suitable for the passage of the optical fibre.

[0010] Patent document W02016 / 072536-A1 discloses a roll checker for measuring the temperature of a roll of a continuous casting machine and monitoring the state of the continuous casting machine without visual inspection, the roll checker comprising: a roll checker body; a sensor unit installed in the roll checker body so as to measure roll gap, roll bending, a roll alignment state, and a roll rotation state; a temperature sensor unit installed in the roll checker body so as to sense the surface temperature of the roll; a camera unit having four cameras installed in upper and lower portions of the roll checker body on both sides thereof; a central processing unit installed inside the roll checker body so as to synchronize and process signals received through the sensor unit, the temperature sensor unit, and the camera unit; a transmission unit installed in the roll checker body so as to transmit the synchronized signal from the central processing unit to an external control unit; and a battery unit for supplying power to the central processing unit.

[0011] There is still a long felt need in the art for an improved continuous casting process to minimize breakouts and improving the surface quality of the continuously cast strand.

[0012] OBJECT OF THE INVENTION

[0013] It is therefore an object of the invention to provide an improved means of monitoring and controlling processes in which strands, blooms, billets or slabs of metal are being processed, in particular a continuous casting process or a combined casting and rolling process. It is a further object of the invention to provide an accurate system and method to determine the condition of support rollers used for supporting or guiding strands of metal during continuous casting.

[0014] DESCRIPTION OF THE INVENTION

[0015] These objects are met or exceeded by a continuous caster according to claim 1 , a roller according to claim 9, a method for controlling a continuous caster according to claim 15 and a computer program according to claim 16. Preferred embodiments are set out in the dependent claims and the description, as well as from the appended drawings.

[0016] According to a first aspect of the invention, a continuous caster for casting molten metal into a semi-finished product in the form of a bloom, billet or slab is provided. The continuous caster comprises a mould, which is configured to be fed with molten metal from a tundish, and which has a primary cooling system in order to solidify a shell of metal close to the mould walls during casting, a secondary cooling zone comprising a plurality of support rollers for guiding a strand exiting from the base of the mould through the secondary cooling zone, wherein the secondary cooling zone comprises a secondary cooling system for cooling the strand, and a temperature measurement system, which is configured for measuring the temperature in the secondary cooling zone at a plurality of positions along a width of the strand, and preferably at a plurality of positions along a length of the strand.

[0017] The continuous caster of the invention thereby allows to monitor the temperature of the strand, directly or indirectly, during the continuous casting process, preferably in real time. This allows to control the casting process in response to temperature measurements within the secondary cooling zone of a continuous caster, which has so far not been feasible on an industrial scale. In prior art casters, the temperature is measured at the mould, but once the strand exits the mould, no temperature measurements are performed at least up to the caster exit, i.e. where the slabs are cut off. The temperature profile of the strand within the secondary cooling zone is predicted commonly by numerical models. In the prior art, such models could only be validated from time to time and at limited positions, e.g., by disabling one of the water sprays in the secondary cooling zone and replacing it by a thermocouple or pyrometer. However, this has the obvious disadvantage that the cooling system is not intact, and the measurement may in addition be erroneous because of the influence of amongst others steam in the secondary cooling zone. Such temperature measurements would therefore not be suitable to be carried out continuously during a casting process, but merely within an experimental setup, e.g., to test a new metal composition or new casting conditions, in order to build a model of the temperature profile of the strand, which is then used instead of real-time temperature measurements during a casting process.

[0018] The invention, by contrast, provides a system to continuously or continually acquire temperature data at a plurality of positions in a continuous caster, in particular in the secondary cooling zone by measuring the temperature at a plurality of positions along the width of the moving strand. The temperature is preferably measured continuously during the casting process, or continually at a pre-defined sampling rate. The sampling rate at which the temperature is measured during a casting process may for example be in a range of 1 to 200 sec1, preferably in a range of 10 to 60 sec’1.

[0019] Having real-time measurements of the temperature at the strand surface is extremely useful for adapting the cooling on-demand for a particular steel grade or for certain other casting parameters, such as the desired casting speed and mould width, in order to minimize the formation of strand defects. This is particularly important for steel grades that are prone to cracking due to non-optimal cooling or temperature during casting. Therefore, the continuous caster and the related method for controlling the continuous caster can be used to increase productivity. This is because up to now, many steel grades are cast with certain parameters based on historical data and experience in order to avoid defects, but when the temperature is known with increased accuracy during the casting operation, it may be found that a different amount of cooling medium should be used, or the casting speed can be increased. Thereby, not only the costs associated with poor quality are reduced, but also the productivity is increased. Moreover, having optimum cooling strategies allows the caster to optimize the energy and water used, so the invention is also environmentally beneficial.

[0020] By measuring the temperatures along the width of the strand in the secondary cooling zone, it is further is possible to create a temperature map, in particular a two-dimensional (2D) map of the temperature at or close to the strand surface. Such a temperature map may be correlated not only to the overall strand temperature, but can also be used to detect surface defects on the strand, like cracks or depressions. Moreover, such temperature maps may be used to assess the state of the support rollers, in particular with respect to alignment and / or deformation, namely the so-called machine condition. Thereby, the invention allows to detect when a support roller is undesirably deformed or bent or broken at its surface or even in whole. This provides very valuable information, since a roller that is undesirably bent or misaligned, i.e., not sufficiently parallel to the adjacent rollers, imposes forces on the moving strand and causes cracks at the progressing solidification front within the strand. This is because the solidified shell is being pushed by a bent or misaligned roller, causing inhomogeneous solidification of the liquid metal core within the moving strand further down the secondary cooling zone.

[0021] Assessing the machine condition of the rollers, in particular of the support rollers, while the caster is in service may significantly reduce the costs and time required for maintenance. In the state of the art, testing the machine condition is performed with a dedicated device called a roll-gap checker, which is occasionally fed through the secondary cooling zone while the caster is not operational, i.e., not at the in-service temperature. However, some roller deformation may be missed or wrongly measured when comparing it with in-service operations. In addition, this process for testing the machine’s state is time consuming and thus reduces productivity. The invention provides a means of testing the machine condition, in particular of the support rollers, while the continuous caster is in service. Such online measurements will reduce production stops for machine control. Furthermore, replacing the roller(s) only when these are damaged permits a better predictive maintenance and therefore costs savings. The invention thus optionally makes use of the insight that the measured temperature is associated with the condition of the support rollers in terms of deformation, wear and alignment. Thereby, the temperature measurements provide a valuable opportunity to take precautionary actions to control and improve the strand quality, e.g. the surface quality, and to reduce the occurrence of amongst others internal cracking.

[0022] The temperature measurement system is therefore capable of providing at least two types of information: firstly, it provides real-time information on the cooling condition of the moving strand, which can be used to deduce information on the solidifying shell of the strand and to better control the casting process to avoid casting defects. Secondly, it may provide information on the condition of the support rollers themselves, in particular with regard to wear, alignment and deformation.

[0023] Providing the temperature measurement system as part of one or more support rollers has the further advantage that the existing secondary cooling system remains unchanged other than adjusting the continuous casting process in response to the temperature measurements within the secondary cooling zone. Thereby the temperature measurement system forms an integral part of the casting machine. Whereas in some prior art it is suggested to implement temperature measurements using devices positioned in between the support rollers. Any such auxiliary device(s) adversely changes the local cooling conditions and thus influences the quality of the strand, which changes have to be compensated for and provided this compensation is feasible. The continuous caster is configured for casting semi-finished products such as billets, blooms or slabs of metal, preferably of steel. Such casters are usually configured to cast semifinished products continuously with no down-time, except for maintenance of the caster. For casting billets and blooms, the open-base mould has a round or angular horizontal cross section, for example circular, oval, polygonal or rectangular, resulting in a corresponding crosssection of the strand. In such casters, the support rollers will have a contour corresponding to the cross-section of the strand. Thus, for a round strand, the support rollers have a concave outer surface. In continuous slab casters, the mould has an at least approximately rectangular cross-section. The invention is also applicable to continuous casters combining a casting and rolling process. The continuous caster of the invention is preferably a continuous steel caster. The casting speed, i.e., the speed at which the strand exits from the basis of the mould and is transported through the secondary cooling zone, is typically between 0.3 and 10 m / min, preferably between 0.5 and 6 m / min, more preferred between 0.5 and 2 m / min in a continuous slab caster, and between 3 and 6 m / min in a thin slab caster. For billets, the casting speed is typically between 0.5 and 6.0 m / min.

[0024] In an embodiment, the continuous caster is a continuous slab caster for steel having an open-base mould, as known in the art, and having an at least approximately rectangular crosssection, wherein the corners of the rectangular may be rounded. The horizontal cross-section of the mould is preferably formed so that the strand exiting from the base of the mould has an at least approximately rectangular cross-section.

[0025] In continuous casters for casting billets, blooms or slabs, the direction in which the strand travels through the secondary cooling zone is commonly referred to as the casting direction or transport direction, and the respective extension of the strand is the length. The width direction of the strand is perpendicular to the transport direction, and the width indicates in particular the length of a wider side or extension of the strand. The thickness of the strand, in particular in strands with a rectangular cross-section, indicates the length of a narrower side or extension of the strand. The width and thickness directions in particular indicate the width and thickness of the cross-section of the strand.

[0026] The secondary cooling zone comprises a plurality of support rollers, preferably on two opposing sides of the strand, or on four sides of the strand, wherein the axial direction of the support rollers extends at least approximately perpendicular to the casting direction. The support rollers support and keep the strand in shape, as only a relative thin shell is solidified at the point where the strand exits from the base of the mould. The liquid centre of the strand solidifies progressively while it travels through the secondary cooling zone, where it is actively cooled. The secondary cooling system may comprise one or both of a direct and an indirect cooling system. The direct cooling system is a spray system for spraying a cooling medium, in particular water, directly onto the strand surface through a series of water or air mist sprays positioned in-between the rolls. The indirect cooling system includes an internal cooling system within the rollers. Such internally cooled rollers have ducts for a cooling medium pumped through the rollers, in particular along the axial direction of the rollers. For example, a cooling medium duct may be at the centre of the roller running along its axis. When heat is extracted from the strand only through the internally-cooled support rollers, with no direct spray system onto the strand surface, this is termed in the art as “dry-casting”.

[0027] The support rollers may be arranged in segments or groups, each comprising between 4 and 10, preferably between 6 and 8 rollers. The support rollers in one segment may be arranged in a single cycle of the internal cooling medium, so that the flow rate of internal cooling medium is controlled for all rollers of the segment together. The nozzles for the spray cooling disposed between the rollers of each segment may also be arranged in a single cycle. The control system of the caster may allow to control the amount of heat extraction by adjusting the amount of cooling medium used for each cycle or for each segment of rollers separately.

[0028] The support rollers may comprise both driven rollers, also referred to as guide rollers, and non-driven rollers, also referred to as loose rollers. Both driven and non-driven rollers may be internally cooled, in particular being water-cooled.

[0029] The temperature measurement system of the invention is configured for measuring the temperature in the secondary cooling zone at a plurality of positions along the width direction of the strand. The positions may be distributed along a direction perpendicular to the transport direction, for example along an axial direction of a roller. The positions at which the temperature is measured are preferably at or close to the strand surface. The temperature measurement system preferably allows to determine the temperature of the strand surface at a plurality of positions along its width, either by measuring the temperature of the strand surface directly or by measuring the temperature of one or several support rollers which are in direct contact with the strand surface. The temperature measurement system may comprise temperature sensors at a plurality of positions along a width of the strand, in particular at 3 to 500, preferably 5 to 200, more preferred 10 to 80 positions distributed along the strand width. Thereby, a temperature profile of the strand along its width can be obtained, which provides detailed information on the cooling condition of the strand. The positions are preferably spaced at equal distances from one another. Since during casting, the strand is moving in the transport direction past the temperature measurement system, it will over time acquire temperature measurements along the transport direction, i.e. along length of the strand. Thereby, a 2D temperature map can be obtained. Nevertheless, in some embodiments the temperature measurement system is configured for measuring the temperature also at a plurality of positions along a length direction of the strand. Thereby, a temperature profile over the width and length of the strand can be acquired at very high temporal resolution.

[0030] The temperature measurements may be taken at a distance from 0 to 200 mm from the strand surface, preferably at a distance from 0.5 mm to 20 mm, more preferred 1 mm to 10 mm from the strand surface. In an embodiment, the temperature measurement system is configured for measuring the temperature on one or on both sides of the strand, in particular the long sides extending along the width direction of the strand.

[0031] According to an embodiment the temperature measurement system comprises a roller, in particular a support roller, which is adapted to be placed in direct contact with the strand in the secondary cooling zone during continuous casting, and wherein the roller is provided with a plurality of temperature sensors distributed along the axial extension of the roller. There may be 3 to 500, preferably 5 to 200, more preferred 10 to 80 temperature sensors distributed along the axial extension of the roller. By distributing temperature sensors over the complete axial direction of the roller, it is possible to determine the width of the strand, since the temperature beyond the strand width drops significantly. In an embodiment, the temperature sensors are also distributed around the circumference of the roller.

[0032] In the following, a roller, in particular a support roller, equipped with temperature or other sensors is also referred to as “instrumented roller”.

[0033] By providing temperature sensors in or on a roller which is in contact with the strand surface, useful information may be gathered about the temperature of the strand surface, preferably information related to a temperature profile along its width and optionally along its length, wherein the length direction is the transport direction of the strand, and information on the condition of the roller itself, in particular with respect to alignment, wear and deformation.

[0034] In an embodiment, the roller is a support roller, preferably an undriven roller. In another embodiment, the roller is a driven roller. It may be internally cooled, in particular water-cooled, or it may not be internally cooled. In an embodiment, temperature sensors are provided in one or more support roller(s) of the secondary cooling zone.

[0035] By measuring the temperatures at several positions along the axial extension of a support roller, it is possible to assess the state of the support roller, in particular with respect to alignment and / or deformation, namely the so-called machine condition. This may be done by analysing a temperature map of the strand surface. Thereby, it is possible to detect when a support roller is undesirably deformed or bent or broken.

[0036] The temperature sensors are preferably embedded into the support roller. Thereby, they are protected from the harsh conditions within the secondary cooling zone, allowing more accurate measurements as well as a longer lifespan of the temperature sensors. They may for example be embedded into the roller at a distance of between 0.5 to 20 mm, preferably 1 to 10 mm from the outer surface of the rollers. The sensors may be embedded in a notch in the roller surface, whereby the notch may have an extension along the axial direction of the roller. Instead of a notch, the sensors may be embedded in a channel, which is not open to the roller outer surface, extending at least in part along an axial direction of the roller. The channel may run along an axis of the roller, it may also run at a distance of 0.5 to 20 mm, preferably 1 to 10 mm below the roller outer surface. The notches or channels are machined, e.g. drilled into a roller. A cylinder-shaped sheath may in addition be placed around the roller in order to protect the sensors. In another embodiment, the roller is manufactured by placing sensors on the outer surface of a roller, and placing a cylinder-shaped sheath around the roller and the sensors. The sensors are thereby protected from wear and breaking by the sheath.

[0037] The temperature sensors may be arranged or positioned in one or more lines, which follow such notch(es) or channel(s). The temperature sensors are in particular arranged along one or several lines which extend in the axial direction of the roller in case of a rectangular slab, bloom or billet. In case of a round billet, the rollers are not cylindrical, so the lines run axially and in addition follow the outer contour of the roller. The lines may be formed by optical fibres e.g. for Fibre Bragg Gratings or electrical cables for connecting thermocouples, depending on the type of temperature sensors used. In case the temperature sensors are thermocouples, the lines may also be formed by a thin-film temperature sensor as disclosed by Z. Liu et al. “A thin- fllm temperature sensor based on a flexible electrode and substrate”, Nature Microsystems & Nanoengineering (2021)7:42, doi.org / 10.1038 / s41378-021-00271-0, and incorporated herein by reference. The temperature sensors may be disposed at about equal distances along the line(s). The temperature sensors may further be arranged at about equal distances along the axial direction of the roller, wherein “about” herein means within + / - 15%, preferably within + / - 10%.

[0038] According to an embodiment, the line(s) may extend only in the axial direction, so that the temperature sensors are arranged in one or several lines running on or parallel to the roller axis. In case of round billets, the lines additionally follow the concave contour of the roller. According to an embodiment, the temperature sensors are arranged on a plurality of parallel lines which are distributed around the circumference of the roller, preferably 2 to 12 lines, more preferably 4 to 8 lines.

[0039] According to another embodiment, the temperature sensors are arranged in lines which extend in both the axial and the circumferential direction of the roller, in particular having a spiral shape. The temperature sensors may be distributed in one or several lines, e.g., 2 to 4 spirals, running around the roller circumference.

[0040] According to a further embodiment, the temperature sensors are arranged in a plurality of rings running close to or at the roller surface and having the roller axis at its centres. The rings may be at least approximately equally spaced along the axial direction of the roller, and can be formed by notches or channels housing the temperature sensors.

[0041] Distributing the sensors along the axial extension of the roller allows to measure the temperature over the whole width of the strand. If there is a single line of temperature sensors extending in the axial direction, a measurement may be taken once for each turn of the roller, which results in a relatively large spacing along the transport direction of the strand, e.g., resulting in only 2 to 10 measurements at the slab surface per minute, or one measurement every 0.3 to 1.2 meter along the strand length depending on the diameter of the roller. Therefore, it is advantageous to distribute the temperature sensors also along the circumference of the roller, in particular in a spiral arrangement. Thereby, the temperature is measured on or close to the strand surface in a close measurement on the side of the strand where the roller is situated. By placing such a roller on either side of the strand, temperature maps may be obtained from opposite sides of the strand at a so-far unprecedented high temporal and spatial resolution. For example, the spatial resolution may be one sample per 1 to 1000 cm2, and preferably 10 to 100 cm2, of strand surface.

[0042] By providing two or more temperature sensors on a support roller, which are spaced from one another in the radial direction in the roller, i.e. towards the inside of the roller, it is further possible to calculate the heat transfer from the temperature difference and spacing between the sensors. In an embodiment, two lines of temperature sensors are provided on a support roller, at two different depths (radial distances) from the roller surface, for example one line at a depth of 1 to 3 mm, the other at a depth of 4 to 6 mm.

[0043] According to an embodiment, the temperature sensors are fibre Bragg gratings, wherein in particular a plurality of fibre Bragg gratings (FBG) are disposed on a single optical fibre. In this embodiment, the roller is provided with one or more optical fibres, each having up to several hundreds FBGs. A fibre Bragg grating is a part of an optical fibre, in which a periodic refractive index variation is written in the core. The modulation of the refractive index causes an FBG to act like a mirror that reflects certain wave lengths and transmits others. The wave length that an FBG reflects depends on the spacing between the high index and low index regions within the fibre. The distance between two high-index regions within the fibre is called the period of the FBG. Since the spacing of the high-index regions will change when the optical fibre compresses or extends along its length, FBGs may be used as sensors for strain, temperature and pressure sensing. They have the advantage that the measurement is performed none- electricaily and that the measurement signal is transported on optical fibre, which resists the high temperatures and humidity within the secondary cooling zone. Moreover, several FBGs can be integrated within one optical fibre, in particular distributed along its length, allowing the measuring of the temperature at a plurality of positions distributed along the axial direction of the roller. For example, there may be 2 to 500, preferably 10 to 100 FBGs, arranged on one optical fibre running along a roller, either axially or spirally, e.g., within a notch or channel close to the roller outer surface. The optical fibre may comprise a core with a high refractive index, in which the FBGs are inscribed, surrounded by a cladding with a higher refractive index that confines the light within the core. The FBGs can be configured to measure temperature. According to an embodiment, there may also may FBGs configured to measure the state of compression or extension of the optical fibre, in order to thereby measure a state of deformation of the roller.

[0044] In other embodiments, the temperature sensors may be thermocouples. The thermocouples may be connected with electrical cables running within notches or channels along the roller. For example, thin-film thermocouples may be used wherein a number of thermocouples may be fitted into a notch or channel. Other types of temperature sensors may also be used, in particular other types of sensors which are integrated into optical fibres.

[0045] According to an embodiment, the temperature measurement system comprises a plurality of support rollers, which are each provided with a plurality of temperature sensors in the manner described herein or in the claims, e.g., with FBGs arranged on one or more optical fibres. In an embodiment, there may be two instrumented rollers, in particular support rollers, on either side of the strand. According to another embodiment, each segment of support rollers includes at least one support roller provided with temperature sensors. For example, the driven rollers may instrumented rollers. By providing several support rollers with temperature sensors, it is possible to obtain a higher resolution temperature map of the strand surface. In addition, the temperature measurements made by the sensors on a support roller provide valuable information on the machine state of that roller, in particular with respect to alignment, wear and deformation. It may also provide information on the neighbouring rollers to the one provided with temperature sensors. Therefore, it is advantageous to provide several support rollers with temperature sensors in order to deduce better information on the machine state. In an embodiment, more than 20% up to 100%, preferably more than 40% up to 100%, and most preferred more than 60% and up to 100%, of the support rollers in the secondary cooling system are instrumented rollers.

[0046] According to an preferred embodiment, at least one or more of the support roller(s) further comprise each at least one deformation sensor. Thereby, it is possible to determine the force related to the interaction of the support roller(s) and the strand. This allows to detect defects in the strands, such as cracks that may arise due to deformations in the support rollers. The deformation sensors may provide measurements on the deformation of the at least one support roller continuously or at a pre-determined sampling rate during the continuous casting process. It is thus possible to measure a deformation of the support roller in real-time (online). The measurements can be used to monitor the state and integrity of the support roller or the segment of the support roller on which the deformation sensor is provided, while the continuous caster is in service, and thereby provides valuable information about the maintenance requirements and thus about the machine condition. The at least one deformation sensor may be an FBG. There may be additional optical fibres dedicated to measuring the deformation, in addition to the temperature sensors. In another embodiment, both FBGs for measuring the temperature, and FBGs for measuring the deformation, are integrated in one or several optical fibres running along the axial direction of the roller, e.g., in notches or channels. The optical fibres may run spirally around the roller, or in parallel to its axis. In an embodiment, all undriven rollers in the secondary cooling section are provided with temperature sensors, and all driven support rollers are provided with deformation sensors.

[0047] In other embodiments, the deformation sensor(s) are formed by resistance sensor(s). For example, the sensors may be as disclosed by Z. Liu et al. “A thin-film temperature sensor based on a flexible electrode and substrate”, Nature Microsystems & Nanoengineering (2021)7:42, doi.org / 10.1038 / s41378-021-00271-0, and incorporated herein by reference.

[0048] According to an embodiment, the temperature measurement system further comprises a thermal imaging camera (TIC) configured for imaging a section of the strand and / or at least one of the support rollers. Thermal imaging is an additional way of capturing a temperature map of the strand surface, on one or both sides thereof. Preferably, the TIC is arranged at a distance from the strand surface sufficient to capture a thermal image of at least a substantial part (>50%) of the strand width. Thereby, high resolution temperature measurements may be taken directly from the strand surface. The TIC is preferably configured to take thermal images at a pre-determined sampling rate of 10 to 1000 sec1, so that very high-resolution temperature maps may be obtained. In addition or alternatively, the TIC can be configured to take a thermal image of one or several of the support rollers. It may therefore capture the temperature at a point of the support roller where it is not directly in contact with the strand, but e.g. on the opposite side. Preferably, a thermal imaging camera is present in addition to one or more instrumented rollers.

[0049] According to an embodiment, the continuous caster further comprises a control unit for controlling the continuous caster configured for adjusting at least one casting parameter of the continuous caster in response to the measured temperatures in the secondary cooling zone at a plurality of positions along a width of the strand. The control unit may be a computing device, such as a central processing unit. It may be connected to user input / output devices such as a screen, mouse, keyboard, etc. The control unit may be embodied in a computer, laptop, mobile device, etc. Prior art control systems use models to make a prognosis of the cooling in the secondary cooling zone, since no real-time temperature measurements exist in the prior art for secondary cooling zones. By contrast, the invention provides real-time temperature measurements in between the primary cooling zone at the mould and the caster exit, where the slabs are cut off. Thereby, for example an optimal cooling strategy may be used at any time during casting, in order to have a product, in particular a cast slab, with reduced amounts of defects. Thereby, cracks arising during solidification and cooling due to uneven or none-optimal cooling can be avoided. The casting parameters adjusted in response to the measured temperatures comprise one or more of a cooling parameter of the secondary cooling system, a cooling parameter of the primary cooling system, and an exiting speed of the strand from the mould (casting speed) and mould width. The cooling parameters of the secondary cooling system comprise the amount of cooling medium sprayed per unit of time in total or in each segment of the support rollers in the secondary cooling zone. It may also comprise the rate at which cooling medium is flowing through the internally cooled support rollers. Cooling parameters of the primary cooling system may include the amount of cooling medium sprayed onto the mould.

[0050] The control unit may be configured to perform data analysis steps on the measured temperatures, i.e., the acquired temperature data. For example, when FBGs are used on a support roller as described herein, the diameter of the roller, the position of each FBG in the axial and circumferential direction of the roller, as well as the casting speed and thus the rate of rotation of the roller may be taken into account in order to reconstruct a two-dimensional temperature map of the section of the strand which is in contact with the roller. It is possible to reconstruct such a two-dimensional map from on single optical fibre having a plurality of FBGs thereon. The control unit may also take into account that the temperature at each temperature sensor will vary periodically as the roller rotates, with the highest temperature reached at the point of contact with the strand. The periodical variation may roughly have a sawtooth shape.

[0051] According to an embodiment, the control unit is configured for reconstructing a two- dimensional temperature map of at least a part of the strand in its width direction. This may in particular be a side or part of the strand from which temperature measurements are taken, in particular by means of a roller in contact with the part of the strand. Such a two-dimensional temperature map may already be obtained from the temperature measurements for one roller provided with temperature sensors distributed along its axial direction. The more temperature sensors are arranged on the roller, the better the spatial resolution of the temperature map. In particular, when temperature is measured at a sufficiently high spatial resolution on the part of the strand, e.g., by providing a roller with one or several optical fibres having a large number, e.g., 20 to 500 FBGs thereon, the temperature map may be used to detect surface defects, like cracks or depressions. For example, a crack may become visible by an abrupt temperature change on the 2D temperature map. This information is highly valuable, as not only can the casting conditions immediately be adjusted, e.g., by reducing the casting speed, but also the surface defect can be identified and localized in the cast slab and the affected section can be discarded.

[0052] According to an embodiment, the control unit is configured to determine the condition of at least one of the support rollers of the secondary cooling system, in particular a state of alignment and / or of deformation of the at least one support roller and thereby provides valuable information about the maintenance requirements of the support roller and thus about the machine condition. Preferably, the support roller is an instrumented roller. In particular, if a two- dimensional temperature map of a part of the strand which is in contact with the support roller is reconstructed, it is possible to assess the condition of the roller. This is because a deformed, bent, broken or misaligned roller will not exert a uniform force on the strand along its length (axial extension). Rather, where the support roller is deformed, it will alternatively be pressed stronger into the solidifying strand, and a half rotation later will have turned away from the strand, up to not being in contact with it anymore. At those positions and time points where the roller presses into the strand, the measured temperature will be higher than at those positions and time points when it is turned away from the strand. This will result in an alternating pattern, herein referred to as “chess pattern”, on the 2D temperature map, which provides information both on the type of deformation from an analysis of the distribution of the chess pattern, as well as on its severity, namely through the amount of the temperature variation between the parts of high temperature any low temperature in the pattern. When the support rollers are not perfectly aligned, this may result in adjacent rollers having different temperature profiles, since one of the rollers may be exposed to more force on the strand than another. If the support roller from which the temperature measurements are taken is skewed, in particular one side is disposed further towards the strand than the other side, the temperature pattern acquired from the support roller will also be skewed, having higher temperatures on one side than on the other. This information on the machine's state of the support rollers is extremely valuable, since it allows to timely replace the support rollers when necessary. Thereby, an optimal slab quality may always be obtained, and in addition the costs for predictive maintenance are reduced.

[0053] According to another aspect, the invention is directed to a roller, preferably a support roller, adapted to be placed in contact with a strand, billet, bloom or slab of metal, wherein the roller is provided with a plurality of temperature sensors distributed along the axial extension of the roller, and preferably around the circumference of the roller. Thus, the roller is an instrumented roller. The roller is in particular configured for guiding, transporting or supporting semi-finished steel products in any industrial process for processing steel, in which the temperature of the steel is important. Preferably the roller is a support roller for a continuous caster, in particular may be adapted to be placed in contact with the strand in a secondary cooling zone of the continuous caster. In another embodiment, the roller is a table roller of a run-out table of a rolling mill of a thin slab caster. The run-out table is the table on which a slab is guided before and after passing through a rolling mill, which may be a hot-rolling or coldrolling mill. In either of these processes, the temperature of the slab is closely monitored, since it is relevant for the outcome of the rolling procedure. Such table rollers are adapted to be placed in contact with a metal slab during hot- or cold-rolling.. In such process, preferably the temperature sensors are arranged close to the surface of the roller in view of the higher rotational speed of the rollers during the process, and the resulting lower contact time between the roller and the slab.

[0054] According to a further embodiment the roller, preferably a support roller, further comprises at least one deformation sensor. Thereby, it is possible to determine the force related to the interaction of the support roller and the strand. This allows to detect defects in the strands, such as cracks that may arise due to deformations in the support rollers. The deformation sensors may provide measurements on the deformation of the support roller. The measurements can be used to monitor the state and integrity of the support roller or a segment of the support roller on which the deformation sensor is provided, while the continuous caster is in service, and thereby provides valuable information about the maintenance requirements and thus about the machine condition. The at least one deformation sensor may be an FBG.

[0055] All features and advantages mentioned with respect to the continuous caster also apply to the roller and vice versa. In particular the temperature sensors are preferably a plurality of fibre Bragg gratings exposed on at least one optical fibre. The roller is preferably equipped with one or several optical fibres running along the axial direction, possibly also in the circumferential direction resulting in a spiral configuration. There may be one or more such optical fibres. Other types of sensors may also be used.

[0056] According to an embodiment, the temperature sensors are embedded in the roller, in particular in a channel running below the outer surface of the roller. Thereby, the temperature sensors are protected from the harsh environment in the secondary cooling zone. However, since the roller is arranged in a position where it has direct contact with the strand or slab, the temperature measurement is still sufficiently accurate. The channel is for example a duct completely embedded in the roller, or alternatively a notch which is open towards the roller outer surface. The notch or channel may run parallel to the axial direction, or it may have a spiral configuration.

[0057] According to an embodiment the roller comprises a converter box disposed at the head of the roller and configured to rotate together with the roller, wherein the converter box comprises a media converter converting the optical signal from at least one optical fibre into an electrical or electromagnetic signal. This embodiment is preferably combined with embodiments where the temperature sensors are FBGs disposed on at least one optical fibre. Since the optical fibres cannot be twisted, the optical signal is preferably converted on the roller itself into another type of signal, in particular into an electromagnetic signal which can be transmitted wirelessly. Therefore, the converter box may be disposed at one axial end of the roller. The required energy for transmitting the signal may be derived from a Peltier generator. The wireless signal is preferably transmitted using a low range protocol, such as WIFI or. In an alternative embodiment, the optical fibre, in particular glass fibre, is guided to the head of the roller exactly at its rotational axis and must be aligned with a stationary optical fibre which directly abuts the end of the rotating optical fibre on the roller. Thereby, optical signals may also be transferred.

[0058] According to another embodiment, the roller may comprise a stationary shaft and a rotatable shell surrounding the shaft, wherein the temperature sensors are disposed in a fixed position with respect to the stationary shaft, in particular embedded in the stationary shaft. The rotatable shell is for example mounted on the shaft by means of ball bearings. The space between the stationary shaft and the rotatable shell may contain a lubricant. Alternatively, no bearings are present but only a lubricant between the stationary shaft and the rotatable shell. In this embodiment, the temperature sensors are disposed in the space between the shaft and the shell, or alternatively they are embedded in the shaft. The temperature sensors may be disposed on notches or channels running along the axis or below the surface of the stationary shaft. Since the temperature sensors in this embodiment may be arranged in a stationary fashion, this facilitates the transmission of the optical signals from the roller to the control unit. In this case, an optical fibre may run from the roller to a converter, wherein the converter is mounted in a stationary fashion. The signal runs wirelessly or via cables from the converter to the control unit. In an alternative embodiment, the temperature sensors may be arranged on the rotatable shell.

[0059] According to a further aspect, the invention is directed to a method for controlling a continuous caster as described herein and claimed. The method comprises the steps of receiving either continually or continuously temperature measurements from the temperature measurement system and preferably also about the deformation via one or more deformation sensors; adjusting at least one casting parameter of the continuous caster in response to the temperature measurements; and / or determining the condition of at least one of the support rollers of the secondary cooling system, in particular a state of alignment and / or a state of deformation of the at least one support roller, from temperature measurements and optionally also from the deformation measurements. All features and advantages described with respect to the continuous caster and the roller also apply to the inventive method and vice versa. In particular, the method may be carried out by a control unit of a continuous caster as described herein and claimed. In particular, the method may also include further process steps of analysing the temperature measurements and deformation measurements, for example reconstructing a 2D temperature map therefrom, and process steps of analysing such 2D temperature maps.

[0060] According to a further aspect, the invention is directed to a computer program comprising program code, which, when executed by the control unit of a continuous caster, will cause the control unit to perform the method described herein or claimed. The computer program may be embodied as a computer program product. All features and advantages described with respect to the continuous caster, the roller, and the method also apply to the computer program and computer program product and vice versa. The invention is also directed to a non-transient digital storage medium on which the computer program or computer program product is stored. The storage medium may be an optical, magnetic or solid state storage medium such as an SD-card, SSD-card, hard disc, CD-ROM, etc. The computer program may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.

[0061] SHORT DESCRIPTION OF THE DRAWINGS

[0062] The invention shall now be described by means of embodiments with reference to the attached drawings. In the drawings:

[0063] Fig. 1 shows a schematic cross-section through a continuous slab caster according to an embodiment of the invention;

[0064] Fig. 2 shows schematic perspective view of six different embodiments of support rollers provided with a plurality of temperature sensors;

[0065] Fig. 3 shows a schematic view of a fibre Bragg grating and the radiated and reflected light spectrum;

[0066] Fig. 4 shows a cross-section of a segment of rollers in the secondary cooling system according to an embodiment of the invention;

[0067] Fig. 5 shows a cross-section through a support roller according to an embodiment of the invention;

[0068] Fig. 6 shows a cross-section of a roller according to a further embodiment of the invention;

[0069] Fig. 7 shows a plan view of two support rollers (left) and of the corresponding 2D temperature map (right);

[0070] Fig. 8 shows a plan view of a deformed support roller in two different positions (right), and the corresponding temperature map (left); and

[0071] Fig. 9 shows a schematic cross-section (top) and a schematic perspective view (bottom) of asupport roller according to a further embodiment of the invention.

[0072] DETAILED DESCRIPTION OF THE DRAWINGS

[0073] The same or corresponding features are designated with the same reference signs throughout the drawings and claims.

[0074] Fig. 1 shows a schematic cross-section of a continuous slab caster 1 according to an embodiment of the invention. In the continuous slab caster, molten metal 8, in particular steel, is kept in a ladle 7 from which it is transferred into a tundish 6. From the tundish 6, the liquid metal is fed through a submerged entry nozzle 3 into the mould 2. The flow of molten steel may be controlled by a valve or stopper 5. The molten steel forms a liquid pool 12 having a meniscus level 4 in the mould 2. The mould 2 can be cooled by internal cooling, so that the steel solidifies at the mould walls and forms a solidified shell 16. This part of the cooling system is called the primary cooling system 11. The solidified shell 16 is withdrawn from the base of the mould by means of motor-driven guide rollers 15 located below the mould. Besides the motor-driven guide rollers, the strand 10 comprising the solidified shell 16 and a liquid core 17 is supported by a number of closely-spaced loose rollers 14. Support rollers 14 and 15 may be internally cooled by a cooling medium. Further, water spray nozzles 18 are usually interspaced between the support rollers 14,15, to further cool the strand 10 during the ongoing solidification process while moving the strand into the casting direction. This part of the continuous slab caster is called the secondary cooling zone 22. The support rollers 14 and 15 further bend the strand 10 into a horizontal path and then straighten it flat before the now fully solidified strand may be cut off to form a semi-finished product in the form of a rolling slab 20 for example by means of a torch cut-off 25. The operation of the continuous slab caster 1 is controlled by a control unit 28. The control unit 28 controls amongst others the flow of molten metal 8 from the tundish 6 through the submerged entry nozzle 3 into the mould 2, as well as the speed at which the motor-driven guide rollers 15 extract the strand 10 from the mould 2 (commonly also referred to as the casting speed). Moreover, the control unit 28 may also be configured to control the cooling rate, in particular the flow rate of the cooling medium, such as water, delivered by the nozzles 9 in the primary cooling system 11 and the nozzles 18 in the secondary cooling zone 22.

[0075] According to an embodiment of the invention, a temperature measurement system 30 is installed in the secondary cooling zone 22, configured for measuring the temperature at a plurality of positions along a width of the strand, which may in particular be the direction perpendicular to the paper in Fig.1. Preferably, the temperature measurement system 30 comprises at least one support roller adapted to be placed in contact with the strand 10 and having a plurality of temperature sensors 30b. Such a roller may be an additional roller 24, which is present in addition to the support rollers 14,15 of the secondary cooling zone and preferably having a smaller diameter than the support rollers 14,15 and placed in between two regular support rollers. Since this additional roller 24 has got a smaller diameter, it may suffice to provide said roller with only one or two lines of temperature sensors along its length, since sufficient measurements will be taken along the casting direction L of the strand 10. Instead of or in addition to such additional roller 24, one a more preferred basis one or several of the support rollers 14,15 which are required for supporting and guiding the strand 10 in the secondary cooling zone, may be provided with temperature sensors. For example, one or several of rsupport oilers 14 may have one or several (for example two to eight, for example three as shown in Fig. 1) lines of temperature sensors 30b arranged along the axial extension of the roller, which is generally along the width direction of the strand 10 and perpendicular to the casting direction L of the strand 10. Optionally, the temperature measurement system can in addition include one or more thermal imaging cameras (TIC) 30a arranged on one or both sides of the strand. Such a TIC 30a may take a thermal image of a section of the secondary cooling zone, and may in particular register the temperature of the support rollers 14,15. This gives valuable information on the state of solidification of the strand 10 or of the machine condition of the support rollers 14,15. The temperature measurements made by the temperature measurement system 30a, 30b are transmitted to the control unit 28, e.g., by a wireless transmission such as WIFI, and used by the control unit 28 to better control the casting process and to monitor the condition of the support rollers. The control unit 28 may perform a computer program stored on digital storage medium 29, in this case a CD-ROM. According to preferred embodiments, the temperature measurement system does not comprise a thermal imaging camera 30a, but instead thereof or in addition thereto one or more support rollers 14,15 provided with temperature sensors 30b.

[0076] Fig. 2 shows schematically several embodiments of a support roller 14a to 14f with different arrangements of temperature sensors. The roller 14 can be undriven or driven.

[0077] Support roller 14a illustrates an embodiment with several optical fibres arranged at or close to the support roller surface, running parallel to each other in axial direction. For example, four to twelve optical fibres may be distributed around the circumferential direction <p, preferably at about equal distances, three of which are illustrated in roller 14a. The optical fibres 33 can be disposed in notches, so that these will not be directly in contact with the strand. Spaced along each optical fibre 33 are several fibre Bragg gratings (FBGs) 32. Each FBG 32 acts as a temperature sensor so that the roller is provided with a close-spaced mesh of temperature sensors 32 adapted for measuring the temperature on a side of the strand at high spatial resolution. For example, the temperature sensors may be arranged on the surface roller at distances between 5 mm and 100 mm in both axial direction z and circumferential direction (p. According to an embodiment, not every sensor arranged on the optical fibres 33 is a temperature sensor 32. For example, every other optical fibre can be provided with deformations sensors 34 instead. Alternatively, every other FBG may be adapted to measure elongation rather than temperature. Thereby, it is also possible to measure the deformation of the support roller 14a providing important information on the state of wear of said support roller 14a.

[0078] Support roller 14b is also provided with an optical fibre 35, but it is running spirally around the roller circumference. As in support roller 14a, temperature sensors 32 and / or deformation sensors 34 are spaced along the length of the optical fibre 35. The advantage of the spiral arrangement is that the sensors may be distributed over both axial and circumferential section, while still requiring only a single optical fibre.

[0079] With two spiralling optical fibres 35a, 35b, a better spatial coverage of the roller surface is achieved, as illustrated by support roller 14c.

[0080] Instead of FBGs, thermocouples can also be used as temperature sensors, as illustrated in support rollers 14d, 14e and 14f. In roller 14d, the thermocouples 36 are arranged in several lines 38 which are axially aligned and spaced over the circumference of the roller. In an embodiment, the thermocouples are inserted into notches running along the lines 38. Alternatively, channels may run below the outer surface of the roller, in which the thermocouples are positioned. In support roller 14e, a line 39 of thermocouples 36 is arranged in a spiral configuration around the roller surface, thus requiring only a single line. To achieve a better spatial coverage of the roller surface, a double-loop 39a, 39b may also be arranged, as illustrated in support roller 14f. Support rollers 14c and 14f use a closed-loop and a doublespiral, which is advantageous in particular in terms of spatial resolution.

[0081] Fig. 3 illustrates a fibre Bragg grating 32 on an optical fibre 33. An optical fibre 33 usually includes a core 41 surrounded by a cladding layer 40 made of a material having a different refractive index, such that light will travel along the core 41. The FBG 32 itself has structure having a length of for example 0.3 to 5 mm and comprising several regions having different refractive indices layered in sequence. By this periodic modulation of the refractive index, the FBG is tuned to selectively reflect a certain temperature f0. This is illustrated in the two graphs below, wherein the upper graph shows the frequency spectrum of light with which the FBG is irradiated. The graph below shows the spectrum of light which is reflected by the FBG. This frequency, called Bragg-frequency f0, will vary with the temperature because of the thermal optical effect on the refractive index. A further contribution may be the thermal expansion, which changes the dimensions of the Bragg grating 32. The advantage of FBGs is that they are multiplexed, i.e. hundreds of FBGs may be enclosed in a single optical fibre 33. In addition, each of the fibre Bragg gratings may measure not just the temperature, but for example also the elongation, so that the optical fibre 33 with FBGs can also be used as a sensor for the deformation of a support roller 14,15. Each FBG may operate at a different frequency f0of the light spectrum, so that e.g., 10 to 500, preferably 50 to 100 FBGs can be arranged on one optical fibre 33 and may be irradiated by a single light source. In an embodiment, the refractive signal received by an optical sensor is converted into an electromagnetic signal.

[0082] Fig. 4 illustrates schematically a cross-section through two segments of support rollers 14,15 in the secondary cooling zone according to an embodiment of the invention, one segment arranged on either side of the strand 10. Each segment may be controlled as one unit. In the embodiment shown, each segment has one driven roller 15 and several loose rollers (in this case 5 loose rollers 14). The spray nozzles 18 for cooling the strand are arranged between the support rollers 14,15. The amount of cooling medium can be controlled for each segment individually.

[0083] The temperature sensors, e.g., FBGs or thermocouples, may be arranged as follows: Preferably, rollers with temperature sensors are present on opposite sides of the strand 10, for example in pairs of rollers on either side of the strand. For example, the two support rollers 14 at the lower end may be equipped with temperature sensors. In addition, the two driven rollers 15 may optionally be equipped with deformation sensors. Alternatively, both pairs of rollers may be provided with both temperature sensors and deformation sensors, possibly on the same optical fibres. In a further embodiment, temperature sensors are present on each roller in these two segments 44. Fig. 4 also illustrates how a thermal imaging camera 30a may be arranged to take a thermal image of a part of the secondary cooling zone 22. The TIC 30a has a field-of-view 31 which is arranged to capture the temperature on three rollers of a segment 44. Since the TIC 30a will measure the temperature at the roller side facing away from the strand 10, the measured temperature will not be exactly the temperature of the strand surface, but will still be sufficiently accurate to use for controlling the casting process and provide information on the machine condition, in particular a state of deformation or damage of the rollers.

[0084] Fig. 5 shows a cross-section through a support roller 14g and illustrates a position of the temperature sensors 30b. This embodiment shows a support roller 14g with water cooling, wherein the cooling medium is conducted through a central cooling duct 48. In other embodiments of rollers, several cooling ducts 48 may be arranged further radially outwards and distributed over the circumference of the roller. To accommodate the temperature sensors 30b, support roller 14g has channels 46 running below the outer surface of the roller, in which TCs or FBGs may be positioned. The channels 46 may have an axial orientation or they may also be spiralling along the roller. The channels 46 may for example be disposed between 1 mm and 5 mm below the outer surface of the support roller 14g. In an alternative embodiment, the optical fibres may be disposed in notches 47, which have a similar size and orientation as the channel 46, but which are open to the strand surface.

[0085] Fig. 6 illustrates a further embodiment of a support roller 14h, having a stationary shaft 50 and a rotatable shell 51 , which is ring-shaped in cross-section. An advantage of this roller configuration is that in use, the shaft 50 remains stationary, and may thus be arranged to hold the temperature measurement system, thereby simplifying the transmission of the temperature measurement system to a control unit 28 (not shown). A cooling duct 48 may also be arranged in the shaft 50. For example, TCs or FBGs may be disposed in axial or spiral notches 52 which are machined into the outer surface of the shaft 50. Thereby, the temperature sensors 30b are essentially arranged at or embedded in the outer surface of the shaft 50 or in the space between the shaft 50 and the outer shell 51 .

[0086] Fig. 7 illustrates 2D temperature maps 56 which are reconstructed from the temperature measurements of the temperature sensors 30b on support roller 14,15. The temperature map 56 may maximally have a width z corresponding to the axial length of the support roller 14, more precisely the length z along which temperature sensors 30b are distributed. The casting direction is indicated as L. Thus, the 2D temperature maps 56 may be updated continually or continuously in the casting direction L as the continuous casting process proceeds and the strand is transported along the rollers.

[0087] In order to reconstruct a temperature map 56, the distribution of the individual temperature sensor 30b on the surface of support roller 14,15 should be known. For example, the temperature sensors may be arranged at a spacing of 1 to 5 cm in the axial direction and at a spacing of 1 to 20 cm around the circumference of the support roller 14. From the individual measurements and knowledge of the spatial distribution of this temperature sensor 30b, the control unit 28, or another computing device, may reconstruct the 2D temperature map 56. This may be performed in real-time during the casting operation such that an up-to-date temperature map 56 is available at any time, and can also be analysed for defects in the rollers and / or possible defects in the strand, wherein at least the defects in the strand may be alleviated by adjusting the casting parameters. The upper part of Fig. 7 illustrates the casting of a relatively narrow strand 10a, which accordingly results in a narrow 2D temperature map 56. The width of the map 56, Wi, corresponds to the width of the strand 10a, which may therefore also be measured by the temperature measurement system. The lower part of Fig. 7 shows the temperature map 56 which is achieved when casting a strand 10b having a larger width W2.

[0088] The temperature maps 56 will usually also indicate lower temperatures towards the ends of the support roller 14 and higher temperatures at its centre. If the temperature map 56 is relatively smooth, as illustrated in the Fig. 7, this indicates good machine condition of support roller 14.

[0089] Fig. 8 illustrates how the temperature map 56 may be affected by deformation of the roller carrying the temperature sensors 30b. In this case, support roller 14i is bent in the middle, which means that during the continuous casting process, support roller 14i will alternately press into the strand at the centre (illustrated at the bottom) or press into the strand at the outer edges in z-direction (illustrated in the top part). At those positions were the support roller 14i is pressed into the strand 10, a higher temperature will be measured compared to those positions along the width direction z, where the support roller 14i is bent away from the strand 10. Thus, alternately the highest temperatures will be measured either in the centre of the strand or at the outer edges in the z direction, resulting in a “chess- pattern” on the temperature map 56. By analysing the pattern of the temperature map 56, it is thus feasible to deduce the type and severity of the deformation of support roller 14i. This analysis can be performed by the control unit 28 or another computing device, and can be used to trigger a replacement or maintenance of support roller 14i, if and when required. Similar useful information may be gained from deformation sensors. If the temperature sensors 30b are arranged not on the deformed support roller 14i, but on a neighbouring support roller 14, a similar temperature pattern may also be detected, since the strand 10 would be deformed accordingly and will thus also press into a non-deformed roller in different ways along the length of the roller. Thus, similar information may be obtained also for the neighbouring roller of the one carrying the temperature sensors.

[0090] Fig. 9 illustrates how the temperature measurements made by optical fibres 33 can be transmitted to a control unit. The Fig. 9 illustrates a support roller 14k which is rotatable around ball bearings 62. The optical fibres 33 are led over the length of support roller 14, through the part on the ball bearings 62, towards a so-called interrogator box 66. For example, four fibres 33 having sixteen FBGs per fibre may be used. The interrogator box 60 comprises a media converter 64 converting the optical signal into an electromagnetic signal. This electromagnetic signal may be transferred via a wireless signal 66, e.g., a low range signal, towards a receiver 27, which may be connected with the control unit 28 (not shown in Fig. 9). The interrogator box 60 is arranged to rotate together with the support roller 14.

[0091] The above-discussion is intended to be merely illustrative of the present system and method and should not be construed as limiting the appended claims to any particular embodiment or group of embodiments. ln the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article “an” or “a” does not exclude a plurality.

[0092] Any reference signs in the claims should not be construed as limiting the scope of the appended claims.

Claims

CLAIMS1. A continuous caster (1) for casting molten metal, in particular molten steel (8), into a semi-finished product (20) in the form of a bloom, billet or slab, the continuous caster (1) comprising: a mould (2), which is configured to be fed with molten metal (8) from a tundish (6) and has a primary cooling system (11) in order to solidify a shell (16) of solid metal close to the mould walls during casting; a secondary cooling zone (22) comprising a plurality of support rollers (14,15) for guiding a strand (10) exiting from the base of the mould (2) through the secondary cooling zone (22), wherein the secondary cooling zone (22) comprises a secondary cooling system (18) for cooling the strand (10); and a temperature measurement system (30a, 30b) which is configured for measuring the temperature in the secondary cooling zone (22) at a plurality of positions along a width of the strand (10), and preferably at a plurality of positions along a length of the strand (10).

2. The continuous caster (1) of claim 1 , wherein the temperature measurement system (30a, 30b) comprises a roller (14,24,15), in particular a support roller, which is adapted to be placed in contact with the strand (10) in the secondary cooling zone (22) during casting, wherein the roller (14,24,15) is provided with a plurality of temperature sensors (32,36) distributed along the axial extension (z) of the roller (14,15).

3. The continuous caster (1) of claim 1 or 2, wherein the temperature measurement system (30a, 30b) comprises (30) a plurality of support rollers (14,15), each provided with a plurality of temperature sensors (32,36) distributed along the axial extension (z) of the roller.

4. The continuous caster (1) of any one of the preceding claims, wherein at least one of the support rollers (14,15) comprises at least one deformation sensor (34).

5. The continuous caster (1) of any one of the preceding claims, wherein the temperature measurement system (30a, 30b) further comprises a thermal imaging camera (30a)configured for imaging a section of the strand (10) and / or at least one of the support rollers (14,15).

6. The continuous caster (1) of any one of the preceding claims, further comprising a control unit (28) for controlling the continuous caster (1), wherein the control unit (28) is configured for adjusting at least one casting parameter of the continuous caster (1) in response to the temperatures measured by the temperature measurement system (30a, 30b).

7. The continuous caster (1) of claim 6, wherein the control (28) unit for is configured for determining the condition of at least one of the support rollers (14,15) of the secondary cooling system (22), in particular a state of alignment and / or deformation of the at least one support roller (14,15).

8. The continuous caster (1) of any one of the preceding claims 6 or 7, wherein the control unit for (28) is configured for reconstructing a two-dimensional temperature map (56) of at least a part of the strand (10).

9. Roller (14,15) for supporting a semi-finished product (20) or strand (10) of metal, in particular of steel, in a secondary cooling zone (22) of a continuous caster (1) according to any one of claims 1 to 8, wherein the roller (14) is provided with a plurality of temperature sensors (32,36) distributed along the axial extension (z) of the roller, and preferably in addition around the circumference (<p) of the roller (14).

10. Roller (14,15) according to claim 9, wherein the temperature sensors are embedded in the roller, in particular in a channel (46) running below the outer surface of the roller (14).

11. Roller (14,15) according to any one of claims 9 or 10, wherein the temperature sensors are a plurality of fibre Bragg gratings (32) disposed on at least one optical fibre (33).

12. Roller (14,15) according to claim 11, wherein the roller comprises a converter box (60) disposed at the head of the roller and configured to rotate together with the roller,wherein the converter box (60) comprises a media converter (64) for converting the optical signal from the at least one optical fibre (33) into a wireless signal (66).

13. Roller (14,15) according to any one of claims 9 to 12, wherein the roller comprises a stationary shaft (50) and a rotatable shell (51) surrounding the shaft, wherein the temperature sensors (32,36) are disposed in a fixed position (52) with respect to the stationary shaft, in particular embedded in the stationary shaft (50).

14. Roller (14,15) according to any one of claims 9 to 13, wherein the roller further comprises at least one deformation sensor (34).

15. A method for controlling a continuous caster (1) according to any one of claims 1 to 8, the method comprising the steps of(a) receiving either continuously or continually temperature measurements from the temperature measurement system (30a, 30b);(b1) adjusting at least one casting parameter of the continuous caster (1) in response to the temperature measurements; and / or(b2) determining the condition of at least one of the support rollers (14,15) of the secondary cooling system, in particular a state of alignment and / or a state of deformation of the at least one support roller (14,15), based on the temperature measurements.

16. Computer program comprising program code, which, when executed by the control unit (28) of a continuous caster (1), will cause the control unit (28) to perform the method of claim 15.

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