TECHNICAL FIELD

The present invention relates to a control instrument and a method to detect the inner geometry of an ingot mould in a continuous casting plant.

The present invention finds advantageous application in a continuous casting plant for the production of steel bars, to which the following discussion will make explicit reference without loss of generality.

PRIOR ART

A continuous casting plant for the production of steel bars comprises a ladle which feeds the molten metal through a vertical solidification path comprising an ingot mould wherein the primary solidification of the steel occurs. The ingot mould is a tubular body consisting of a set of copper plates which are cooled by way of a continuous circulation of cooling water .

The ingot mould has a taper that converges downwards

(namely towards the outlet opening) in a way so that the cross section of the ingot mould gradually decreases from the upper inlet opening to the lower output opening; the taper of the ingot mould is essential to allow the ingot mould to "follow" the reduction of the size of the metal resulting from the temperature reduction. If the taper of the ingot mould is not correct, then it may happen that the inner surface of the ingot mould might lose contact with the semi-solid metal (insufficient taper) resulting in a localized reduction of the cooling capacity (in the absence of contact between the ingot mould and the semisolid metal the transmission of heat greatly decreases) , and then with the formation of undesired heterogeneities in the semisolid metal, or it may happen that the inner surface of the ingot mould might excessively press on the semisolid metal (excessive taper) with the consequent onset of unwanted tensions in the semisolid metal which worsen the quality of the solidification process.

For monitoring the correct taper of the ingot mould it has been proposed to use a control instrument that is applied on the outside of a copper plate that forms the ingot mould and measures the inclination with respect to the vertical direction of the copper plate itself; an example of said control instrument is provided in the patent application WO2012164477A1. However, it has been observed that in some situations unwanted variations of taper of the ingot mould may occur that are not detected by known control instruments of the type described above which measure the inclination with respect to the vertical direction of the copper plates forming the ingot mould. In particular, the known control instruments of the type described above are relatively less reliable when the copper plates are not perfectly flat but have a curved profile .

The patent application DE3642302A1 describes a control instrument to detect the inner geometry of an ingot mould in a continuous casting plant; however, this control instrument is not able to detect, with the neqessary precision, all possible imperfections of the copper plates forming the ingot mould. DESCRIPTION OF THE INVENTION

Purpose of the present invention is to provide a control instrument and a method to detect the inner geometry of an ingot mould in a continuous casting plant, which control instrument and method are free of the drawbacks described above and, in particular, are of easy and economic implementation .

According to the present invention, a control instrument and a method to detect the inner geometry of an ingot mould in a continuous casting plant are provided, as claimed by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying drawings, which illustrate a non- limiting embodiment, wherein: • Figure 1 is a schematic view of a continuous casting plant for the production of steel bars;

• Figure 2 is a schematic perspective view of an upper part of an ingot mould of the system of Figure 1;

• Figure 3 is a schematic side view of the ingot mould of Figure 2 provided with a control instrument which is made in accordance with the present invention and' performs the detection of the inner geometry of the ingot mould;

• Figure 4 is a schematic side view of a measuring head of the control instrument of Figure 3 ;

• ' Figure 5 is a schematic front view of the measuring head of Figure 4 ;

• Figure 6 is a schematic side view of the measuring head of Figure 4 with a centering system acting on the sliding blocks, in evidence;

• Figure 7 is a schematic front view of a different embodiment of the measuring head of Figure 4;

• Figure 8 is a schematic side view of the measuring head of Figure 4 with a track moving system in evidence;

• Figure 9 is a schematic perspective view of the measuring head of Figure 4 coupled to a manual control;

• Figure 10 is a schematic front view of a further embodiment of the measuring head of Figure 4 ; and

• Figure 11 is a schematic side view of the measuring head of Figure 10 with a wheel moving system in evidence.

PREFERRED EMBODEMENTS OF THE INVENTION

In Figure 1, number 1 indicates as a whole a continuous casting plant for the production of steel ingots.

The plant 1 comprises a ladle 2 which feeds the molten steel to an underlying tundish 3 from which the molten steel is fed to a vertical solidification path. The vertical solidification path comprises, at the beginning, a copper ingot mould 4 wherein the primary solidification of the steel occurs; downstream of the copper ingot mould 4 the vertical solidification path continues with water injectors 5. The plant 1 comprises a cutting station 6 of the steel bars provided with extractor rollers 7 and a tilter drum 8 that receives the individual steel bars from the cutting station 6 and feeds the steel bars themselves to an ingot mould 4 (namely to a transport device with rollers) .

As illustrated in Figure 2, the ingot mould 4 is a tubular body of parallelepiped shape and comprises four copper plates 10 which are cooled by a continuous circulation of cooling water. Each copper plate 10 has a specific inclination with respect to the vertical direction and/or a particular profile to give the ingot mould 4 a desired taper that progressively reduces the cross section of the ingot mould 4 from the upper part to the lower part (i.e., from the upper inlet opening which is wider to the lower outlet opening that is narrower) . The function of the taper of the ingot mould 4 is to enable the ingot mould 4 to "follow" the reduction of the steel size due to the temperature reduction (namely the primary solidification). If the taper of the ingot mould is not correct, then it may happen that the inner surface of the ingot mould 4 loses contact with the semisolid steel (insufficient taper), or it may happen that the inner surface of the ingot mould 4 might excessively press on the semisolid metal (excessive taper) .

As illustrated in Figure 3, to detect the inner geometry of the ingot mould 4 (and therefore, among other things, to verify the correct taper of the ingot mould 4) the use of a control instrument 11 is provided. The control instrument 11 comprises a measuring head 12 that is suited to be inserted into the ingot mould 4 to slide along the ingot mould 4 itself; in other words, the measuring head 12 is inserted into an end of the ingot mould 4 to cover the entire ingot mould 4 up to the opposite end. For this purpose, a feeding device 13 is provided (shown schematically in Figures 8 and 11) that is suited to autonomously move the measuring head 12 along the ingot mould 4 (namely from an input end of the ingot mould 4 up to one output end of the ingot mould 4) .

The measuring head 12 has a parallelepiped shape having a lower wall 14 and an upper wall 15 which are parallel and opposite to one another, two lateral walls 16 and 17 which are parallel and opposite to one another, and a front wall 18 and a rear wall 19 which are parallel and opposite to one another. The measuring head 12 comprises sliding blocks 20 which are suited to come into contact with the walls 10 of the ingot mould 4 and project from the lower walls 14, upper wall 15 and lateral walls 16 and 17; in particular, from each wall 14, 15,

16 or 17 of the measuring head 12 a pair of sliding blocks 20 arranged side by side and parallel to one another project

(obviously, according to embodiments perfectly equivalent, from each wall 14, 15, 16 or 17 of the measuring head 12 only one sliding block 20 or three or more sliding blocks 20 could project) .

According to a preferred embodiment shown in Figures 4 , 5 and 6, each sliding block 20 is provided with a series of wheels 21 which are mounted idle and are suited to roll on the corresponding wall 10 of the ingot mould 4. The wheels 21 are generally formed by filled metal cylinders and allow the measuring head 12 to slide into the ingot mould 4 with a very low friction.

A moving system of sliding blocks 20 is provided that always keeps all the sliding blocks 20 in contact with the corresponding walls 10 of the ingot mould 4 and, at the same time, keeps the measuring head 12 in a predetermined and constant transverse position (namely in the cross section) with respect to at least one of the walls 10 of the ingot mould 4.

In the embodiment illustrated in Figures 5 and 6, all the sliding blocks 20 which project from the walls 14, 15, 16 and

17 of the measuring head 12 are mounted in a mobile way so as to slide perpendicular to the corresponding wall 14, 15, 16 or 17 and are pushed outwards, namely outside of the corresponding wall 14, 15, 16 or 17, by respective elastic elements 22 (illustrated schematically and partially in Figure 6); in the embodiment illustrated in Figure 6, the elastic elements 22 are formed by metallic helical springs. According to a preferred, but not binding, embodiment the two sliding blocks 20 which project from the same wall 14, 15, 16 or 17 of the measuring head 12 and are therefore side by side and parallel to one another, are also rigidly constrained to one another so as to move together in an integral manner with respect to the corresponding wall 14, 15, 16 or 17.

As illustrated in Figure 6, the sliding blocks 20 which project from a pair of opposite walls 14 and 15, or 16 and 17 of the measuring head 12 are mechanically constrained to one another so that the sliding blocks 20 themselves always perform equal extension movements as well as equal movements in the opposite direction with respect to the corresponding walls 14 and 15, or 16 and 17 to ensure the centering of the measuring head 12 into the ingot mould 4. In other words, the sliding blocks 20 which project from the lower wall 14 are mechanically constrained to the sliding blocks 20 which project from the upper wall 15 so that the sliding blocks 20 which project from the lower wall 14 always perform equal extension movements as well as equal movements in the opposite direction with respect to the sliding blocks 20 which project from the upper wall 15; in the same way, the sliding blocks 20 which project from the lateral wall 16 are mechanically constrained to the sliding blocks 20 which project from the side wall 17 so that the sliding blocks 20 which project from the lateral wall 16 always perform equal extension movements as well as equal movements in the opposite direction with respect to the sliding blocks 20 which project from the side wall 17. In this way it is always ensured that the measuring head 12 is always centered horizontally and vertically into the ingot mould 4, namely that the longitudinal axis of the measuring head 12 is always coincident with the longitudinal axis of the ingot mould 4.

As illustrated in Figure 6, the two sliding blocks 20 which project from opposite walls 14 and 15, or 16 and 17 of the measuring head 12 are mechanically constrained to one another by at least two racks 23, each of which is integral to a corresponding sliding block 20, extends parallel to the moving direction of the sliding blocks 20, and is arranged so as to face the other rack 23, and by means of a toothed wheel 24 which is mounted idle on a frame 25 of the measuring head 12 and is- arranged between the two racks 23 and simultaneously engages the two racks 23 themselves.

Therefore, in the embodiment illustrated in Figures 5 and 6, the moving system for the sliding blocks 20 keeps the measuring head 12 centered between the four walls 10 of the ingot mould 4.

According to an alternative and perfectly equivalent embodiment illustrated in Figure 7, the moving system for the sliding blocks 20 keeps the measuring head 12 in a predetermined and fixed position with respect to the lower left edge of the ingot mould 4 (namely with respect to the two walls 10 of the ingot mould 4 that form the lower left edge) ; in other words, the moving system for the sliding blocks 20 keeps the measuring head 12 at a predetermined and constant distance with respect to the lower left edge of the ingot mould 4 (namely with respect to the two walls 10 of the ingot mould 4 that form the lower left edge) . In this embodiment shown in Figure 7, the sliding blocks 20 that come into contact with the walls 10 of the ingot mould 4 that form the lower left edge (i.e. the sliding blocks 20 which project from the lower wall 14 and from the lateral wall 16 of the measuring head 12) are mounted in a fixed way on the measuring head 12 so as to establish a predetermined and constant distance between the measuring head 12 and the lower left edge (namely between the measuring head 12 and the two walls 10 of the ingot mould 4 that form the lower left edge) ,· instead, the sliding blocks 20 opposed to the lower left edge (namely the sliding blocks 20 which project from the upper wall 15 and lateral wall 17 of the measuring head 12) are mounted in a mobile way on the measuring head 12 to slide perpendicularly to the corresponding walls 15 and 17 of the measuring head 12 and are pushed towards the outside, namely outside the corresponding walls 15 and 17 of the measuring head 12, by respective elastic elements 22, so as to guarantee that the measuring head 12 is always in contact with all the walls 10 of the ingot mould 4 (namely, to guarantee that the measuring head 12 is always pressed against the lower left edge of the ingot mould 4 while remaining always in contact with the upper right edge of the ingot mould 4) .

According to further, and perfectly equivalent, embodiments not illustrated, it is also possible that the movement system for the sliding blocks 20 is an intermediate solution between the two embodiments described above: for example, the moving system for the sliding blocks 20 could keep the measuring head 12 centered between the upper and lower walls 10 of the ingot mould 4 and, at the same time, could keep the measuring head 12 at a predetermined and fixed distance from the right lateral wall 10 or from the left lateral wall 10 of the ingot mould 4; alternatively, the moving system for the sliding blocks 20 could maintain the measuring head 12 centered between the lateral walls 10 of the ingot mould 4 and, at the same time, could keep the measuring head 12 at a predetermined and fixed distance from the upper wall 10 or from lower wall 10 of the ingot mould 4.

As illustrated in Figure 4, the measuring head 12 supports a distance sensor 26 (typically a laser distance measuring device) which detects the inner surface of the ingot mould 4, namely measures the distance between the longitudinal axis of the measuring head 12 and the inner surface of the ingot mould 4. The distance sensor 26 is mounted in a rotating way on the front wall 18 (alternatively may be mounted in a rotating way on the rear wall 19) of the measuring head 12 to rotate about a longitudinal rotation axis 27 (coincident with the longitudinal axis of the measuring head 12) . An actuator device 28 is provided (e.g. an electric stepper motor) to rotate the distance sensor 26 around the longitudinal rotation axis 27; in the embodiment illustrated in the attached figures, the actuator device 28 is arranged in front position (namely in correspondence of the front wall 18 of the measuring head 12) , but according to alternative and completely equivalent embodiments the actuator device 28 could be arranged into the measuring head 12 in a central position, or the actuator device 28 could be arranged in the rear position (namely in correspondence of the rear wall 19 of the measuring head 12), possibly projecting cantilevered from rear wall 19 of the measuring head 12.. Furthermore, an angular position sensor 29 is provided (for example an angular encoder) to detect the angular position of the distance sensor 26 around the longitudinal rotation axis 27; in the embodiment illustrated in the attached figures, the angular position sensor 29 is arranged in front position (namely in correspondence of the front wall 18 of the measuring head 12) , but according to alternative and completely equivalent embodiments the angular position sensor 29 could be arranged into the measuring head 12 in a central position, or the angular position sensor 29 could be arranged in a rear position (namely in correspondence of the rear wall 19 of the measuring head 12) .

As illustrated in Figure 5, the feeding device 13 moves the measuring head 12 along the ingot mould 4 and comprises a pair of motor-driven tracks 30 opposite to one another, each of which project from a lateral wall 16 or 17 of the measuring head 12. According to a different embodiment not illustrated, the feeding device 13 may comprise a pair of motor-driven tracks 30 opposite to one another each of which projects from the lower wall 14 or from the upper wall 15 of the measuring head 12; according to a further embodiment not illustrated, the feeding device 13 could comprise a single motor-driven track 30 which projects from a lateral wall 16 or 17, or a lower wall 14, or an upper wall 15 of the measuring head 12. Normally, the tracks 30 are made of rubber material to present high friction. According to a preferred embodiment shown in Figure 7, each track 30 is mounted in a mobile way to slide perpendicularly to the corresponding lateral wall 16 or 17 and is pushed outwards, namely outside of the corresponding lateral wall 16 or 17, by at least one respective elastic element 31; in the embodiment illustrated in Figure 8, the two elastic elements 31 are formed by metallic helical springs. In the embodiment illustrated in Figure 8, each track 30 is wound around two end pulleys 32 that are mounted idle and are connected to the frame 25 of the measuring head 12 to slide perpendicularly to the corresponding lateral wall 16 or 17 under the thrust of corresponding elastic elements 31. In addition, each track 30 is wound around a central motorized pulley 33 which imparts movement to the track 30 itself; the central pulley 33 is mechanically connected to an actuator device 34 (preferably an electric stepper motor) provided with an angular position sensor 35 (for example, an angular encoder) which determines the angular position of the central pulley 33 and thus, indirectly, the position of the track 30. According to a possible embodiment, a single common actuator device 34 actuates both tracks 30; alternatively, each track 30 has its own actuator device 34 separate and independent from the actuator device 34 of the other track 30. By way of a routine processing of the signal provided by the position sensors 35 it is possible to accurately reconstruct the movement of the tracks 30, and therefore the axial position (longitudinal) of the measuring head 12 along the ingot mould 4. According to a different (and perfectly equivalent) embodiment not illustrated, the position sensor 35 which determines the axial position (longitudinal) of the measuring head 12 along the ingot mould 4 is separate and independent from the feeding device 13 and is preferably coupled to a wheel 21 of a sliding block 20.

According to the embodiment shown in Figure 9, the control instrument 11 comprises an interface box 36 provided with a handle 38 which may be firmly grasped by an operator; the interface box 36 is mechanically connected to the measuring head 12 by means of a connection element 37 which is arranged on the opposite side of the handle 38. Preferably, the connection element 37 is mechanically connected in a detachable way to both the measuring head 12, and the interface box 36.

According to a possible embodiment, the measuring head 12 could be moved axially along the ingot mould 4 not only using the feeding device 13 (namely by way of an independent and fully automated motion) , but also by the operator who acts upon the handle 38 of the interface box 36.

In order to make the use of the control instrument 11 more practical, the connection element 37, is connected to the interface box 36 in a flexible manner, namely so as to allow a relative movement between the connection element 37 and the interface box 36. Furthermore, the connection element 37 can be made of metallic material, and then may be rigid (non- deformable) , or alternatively the connection element 37 can be made of elastically deformable plastic material to be flexible and therefore be able to deform (also forming angles greater than 90°) during the use (in substance, in this case the connection element 37 is a flexible cable) . Obviously there may be two (or more) connection elements 37 to be used as an alternative according to the needs: a metal connection element 37 and thus rigid (non-deformable) , and another connection element 37 made of deformable plastic material and therefore deformable .

Finally, as illustrated in Figures 3 and 8, the control instrument 11 comprises a processing unit 39 (typically a computer possibly of the tablet type) which is connected in wireless mode with the measuring head 12 (typically in radiofrequency according to the Bluetooth data transmission standard) for receiving from the measuring head 12 readings performed by the distance sensors 26, 29 and by the positions sensor 35.

According to a preferred embodiment, the interface box 36 comprises a radio frequency communication device, which is connected, by way of wiring housed in the connection element 37 with the measuring head 12 (and in particular with the distance sensors 26 and 29 and position sensor 35 carried by the measuring head 12) and communicates- in radio frequency with the processing unit 39. In addition, according to a preferred embodiment, the interface box 36 supports a screen that allows to view the operation status of the control instrument 11 and allows to view and control in real time the progress of the measurements actuated by the measuring head 12 (namely by the distance sensors 26 and 29 and position sensor 35 carried by the measuring head 12) . Finally, according to a preferred embodiment, the interface box 36 supports a keyboard through which an operator can control the operation of the control instrument 11 and can decide which information display on the screen; the keyboard can be physical (namely provided with physical buttons arranged around the screen) and/or virtual (namely provided with virtual buttons displayed on the screen being of the "touch" type) .

In the embodiment illustrated in Figures 4-5 and 7-8, the feeding device 13 which moves the measuring head 12 along the ingot mould 4 comprises a pair of motor-driven tracks 30 opposite to one another. In the alternative, and perfectly equivalent, embodiment illustrated in Figures 10 and 11, the motor-driven tracks 30 are replaced by a motor-driven wheel 40 which projects from the lower wall 14 of the measuring head 12 (obviously, the motor-driven wheel 40 could project from another wall 15, 16 or 17 of the measuring head 12, or two motor-driven wheels 40 could be provided which project from two opposite walls 14, 15, 16, 17 of the measuring head 12) .

Normally, the annular surface of the wheel 40 is covered by a layer of rubbery material to present a high friction. As is already the case for the tracks 30, the wheel 40 receives motion from the actuator device 34, typically by means of a common drive belt. As is already the case for the tracks 30, the wheel 40 is mounted in a mobile way to slide perpendicularly to the corresponding lower wall 14 and is pushed outwards, namely outside of the lower wall 14, by at least one respective elastic element 31.

In the embodiment illustrated in the attached figures, the actuator device 28 of the position sensor 26 and the actuator device 34 of the feeding device 13 are separated and independent; according to one alternative and simplified embodiment not illustrated a single common actuator device is provided that provides motion to both the distance sensor 26, and to the feeding device 13. In other words, instead of having two distinct actuator devices 28 and 34 a single common actuator device that moves the distance sensor 26 and the feeding device 13 is provided. In this simplified embodiment, when the measuring head 12 is manually fed by way of the interface box 36, the effectors (namely the tracks 30 or the wheels 40) of the feeding device 13 are moved towards the inside of the measuring head 12 so as to not touch the walls 10 of the ingot mould 4 (namely the effectors of the feeding device 13 continue to move without touching the walls 10 of the ingot mould 4, and therefore without allowing any displacement to the measuring head 12) .

Preferably, both the measuring head 12 and the processing unit 39 are provided with their own rechargeable electric batteries in order to be completely autonomous during use.

The following describes the operation of the control instrument 11.

As previously mentioned, initially the measuring head 12 is inserted into the ingot mould 4, and by way of the feeding device 13 or by the handle 38 of the interface box 36, is advanced (preferably at a constant speed) along the entire ingot mould 4 from one end to the other. While the measuring head 12 advances along the ingot mould 4, the actuator device 28 rotates (preferably at a constant speed) the distance sensor 26 around the longitudinal rotation axis 27 so that the distance sensor 26 "scans" cyclically by 360° the entire inner surface of the ingot mould 4 arranged around the distance sensor 26. In this way,_ the reading of the distance sensor 26 occurs along a circumference, whose pitch depends both on the rotation speed of the distance sensor 26 around the longitudinal rotation axis 27, and on the feeding speed of the measuring head 12 along the ingot mould 4. Obviously, for special needs, it is also possible that the distance sensor 26 is made to rotate by 360° around the longitudinal rotation axis 27 keeping still the measuring head 12 with respect to the ingot mould 4 (in this case the reading of the distance sensor 26 occurs along a circumference), or it is possible that the position sensor 26 is not made to rotate while the measuring head 12 advances along the ingot mould 4 (in this case the reading of the distance sensor 26 occurs along a straight line) .

The processing unit 39 receives the readings of the distance sensors 26 and 29 and of the position sensors 35 and therefore determines in real time the inner geometry of the ingot mould 4.

According to a preferred embodiment, the control instrument 11 comprises a transportable metal case, which is internally provided with shaped compartments which are suited to receive and house respectively the measuring head 12, the interface box 36 and the connection element 37 (or two or more connection elements 37 that differ to one another in size and shape and in rigid or flexible conformation) . The metal case may also have a compartment for also housing the processing unit 39 (normally formed by a computer possibly of a tablet type) provided with a software dedicated to the control instrument 11, but it may also be used for other purposes. The function of the case is both to allow to easily carry/send the control instrument 11 and to guarantee adequate mechanical protection to the control instrument 11 during transport (or shipment) .

The control instrument 11 described above has numerous advantages. In the first place, the control instrument 11 described above is easy and intuitive to use, even by a non-expert user; in other words, the above mentioned control instrument 11 can be effectively used even after simply reading the instruction manual provided with the control instrument 11 itself without the need of special training. In fact, once the measuring head 12 is inserted into the ingot mould 4, the control device 11, proceeds to carry out the measurement completely autonomously without requiring any external intervention by the operator.

The control instrument 11 described above allows to carry out the measurement in fully automatic way and then allows to make objective findings (namely completely free from the subjectivity of the operator) ensuring high reliability and repeatability of the finding of the inner geometry of the ingot mould 4.

The control instrument 11 described above allows to detect quickly and with extreme precision the inner geometry of the ingot mould 4. Basically, the control instrument 11 described above provides the operator, in real time, with information on the inner geometry of the ingot mould 4; this information is displayed in real time on a screen of the processing unit 39 (that is lightweight and easy to move as powered by batteries) . Obviously, the information about the inner geometry of the ingot mould 4 is stored in non-volatile memory of the processing unit 39 and thus can be further certified and processed at any time.

Thanks to the use of the control instrument 11 described above the time to verify the inner geometry of the ingot mould 4 can be significantly reduced.

The control instrument can also be used directly in the continuous casting plant 1 and does not require disassembly of the ingot mould 4; it can, in fact, be placed into the ingot mould 4 in a vertical position (namely, in the natural placement position of the ingot mould 4 in the continuous casting plant 1) and effectively carry out its measuring functions (with both automatic and manual motion) . The measuring instrument 11 is therefore able to perform its functions in an ingot mould 4 arranged both horizontally and vertically.

Using the control instrument 11 described above before and after a certain ^" period of productive activity, it is possible to determine the wear rate of the ingot mould 4, and then it is possible to optimize the operational life of the ingot mould 4 without incurring in serious damage of the product (caused by an excessive use of the ingot mould 4), or in an incomplete use of the ingot mould 4 (related to a premature - and unprofitable - replacement) .

Additionally, the control instrument 11 described above is of simple and economical implementation.