Casting mold, control device and continuous casting method of steel

Abstract

The present invention provides a casting mold capable of shortening a temperature detection interval without special processing of a slit groove. A mold (12) is used in the continuous casting of steel, the mold (12) having a plurality of mold copper plates, at least one of the plurality of mold copper plates having an optical fiber temperature sensor (50) embedded in at least two layers of positions that differ in the casting direction in the width direction of the mold copper plates.

Description

Technical Field

[0001] The present invention relates to a casting mold for detecting abnormal phenomena related to longitudinal crack defects and steel leakage (fracture of the solidified shell) generated in the solidified shell in the casting mold with high accuracy during the continuous casting of steel, a control device capable of predicting the longitudinal crack defects and steel leakage with high accuracy, and a continuous casting method for steel. Background Art

[0002] In the continuous casting of steel, the requirements for high productivity and high quality have become more stringent. In particular, from the perspective of stable operation of continuous casting and maintaining and improving the quality of the manufactured slab, it is extremely important to allow the solidified shell in the mold of the continuous casting machine, which is the stage of molten steel solidification, to grow normally. In particular, the outflow of molten steel from the solidified shell (hereinafter referred to as "steel leakage") has become a major problem in the operation and equipment maintenance of continuous casting, and therefore various methods for detecting steel leakage have been proposed in the past.

[0003] As a method for detecting steel leakage, the following methods have been proposed: a method of burying thermocouples in the copper plate of the mold and detecting abnormalities based on temperature information obtained from the thermocouples, and a method of installing a measuring device for pressure measurement in the mold vibration system equipment or the mold and detecting abnormalities based on changes in resistance or friction. Patent document 1 discloses a method of burying armored thermocouples in two layers in the copper plate of the mold and detecting steel leakage based on the temperature measurement results.

[0004] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Publication No. 2012-218039 Summary of the invention

[0005] Problems to be solved by the invention

[0006] However, in the method disclosed in Patent Document 1, armored thermocouples are buried at intervals of 100 to 200 mm in the width direction of the mold copper plate. Therefore, for detecting small-scale steel leaks such as longitudinal crack defects, seepage, and liquid leakage, there is a problem that the buried intervals of the armored thermocouples are wide, and sometimes detection is missed. In order to cope with these problems, it is considered effective to narrow the buried intervals of the armored thermocouples in the width direction to less than 100 mm.

[0007] Here, a conventional mold copper plate provided with a sheathed thermocouple will be described. Figure 1 1 is a schematic diagram showing a conventional mold copper plate 102 with a support plate fixed to the back surface. Figure 1 (a) is the rear view from the support plate side. Figure 1 (b) Yes Figure 1 AA section view of (a).

[0008] A plurality of slit grooves 106 are formed along the casting direction on the back side of the mold copper plate 102. The support plate 104 is fixed to the back side of the mold copper plate 102 by stud bolts 108. By fixing the support plate 104 to the back side of the mold copper plate 102, the slit grooves 106 become cooling water channels for the cooling medium for cooling the mold copper plate 102.

[0009] In order to measure the temperature of the mold during the continuous casting of steel, a plurality of armored thermocouples 110 are embedded in the mold copper plate 102 in the width direction at two different positions in the casting direction of the mold copper plate 102. The armored thermocouples 110 penetrate the support plate 104 and are inserted in a string from the back side of the mold copper plate 102. The armored thermocouples 110 are arranged at positions avoiding the slit grooves 106 in the same manner as the stud bolts 108. Therefore, the armored thermocouples 110 must be arranged near the positions where the stud bolts 108 are provided.

[0010] The stud bolts 108 are arranged at intervals of about 200 mm in the width direction of the mold copper plate 102. Therefore, the armored thermocouples 110 are also arranged at intervals of about 200 mm like the stud bolts 108. In order to arrange the armored thermocouples 110 at intervals of less than 100 mm, a large number of insertion holes are provided in the mold copper plate 102 and the support plate 104, which causes a problem of reduced strength of the support plate 104. In addition, in order to avoid the situation where the insertion hole of the armored thermocouple 110 is connected to the slit groove 106, special processing such as processing the slit groove 106 in a curved shape is required. In addition, there is also a problem that the wiring of the armored thermocouple 110 also needs to be of special specifications. Due to such a problem, there is a problem that the equipment specifications cannot be changed to shorten the temperature detection interval in the width direction.

[0011] The present invention has been made in view of the above problems in the prior art, and an object of the present invention is to provide a casting mold capable of shortening the temperature detection interval without performing special processing on the slit groove, a control device including the casting mold, and a continuous casting method for steel.

[0012] Technical solutions to solve problems

[0013] The technical means for solving the above-mentioned problems are as follows.

[0014] [1] A casting mold used in continuous casting of steel, wherein the casting mold has a plurality of casting copper plates, at least one of the plurality of casting copper plates has an optical fiber temperature sensor, and the optical fiber temperature sensor is buried in at least two different layers in the casting direction along the width direction of the casting copper plates.

[0015] [2] The mold according to [1], wherein the optical fiber temperature sensor is an FBG optical fiber temperature sensor, and a plurality of diffraction gratings are arranged on the optical fiber temperature sensor at intervals of less than 50 mm, and the diffraction gratings of each layer are arranged at the same position in the width direction of the mold copper plate.

[0016] [3] The mold according to [1], wherein the optical fiber temperature sensor is an OFDR optical fiber temperature sensor.

[0017] [4] A casting mold according to any one of [1] to [3], wherein a slit groove is provided on the back side of the casting mold copper plate, and the optical fiber temperature sensor is buried between a position 1 mm away from the molten steel side surface of the casting mold copper plate in the thickness direction and a position 1 mm away from the bottom of the slit groove in the thickness direction.

[0018] [5] A control device comprising: a casting mold as described in any one of [1] to [4]; and a control device for controlling continuous casting of steel using the casting mold, wherein the control device uses the temperature at the same position in the width direction of the casting mold copper plate and at different positions in the casting direction to calculate an indicator representing a sharp drop or a sharp rise in the temperature of the solidified shell.

[0019] [6] The control device according to [5], wherein the optical fiber temperature sensor is buried at different positions of i layers (i=2 to 4) in the casting direction, and the control device calculates the M value as the index using any one of the following equations (1) to (3), When i=4, M=|[ΔT1×{t-(L4-L1) / VR(t)}×(ΔT2×{t-(L4-L2) / VR(t)}] a |+|[ΔT2×{t-(L4-L2) / VR(t)}×(ΔT3×{t-(L4-L3) / VR(t)}] b |+|(ΔT3×{t-(L4-L3) / VR(t)}×ΔT4(t)] c |… (1) When i=3, M=|[ΔT1×{t-(L3-L1) / VR(t)}×ΔT2×{t-(L3-L2) / VR(t)}] a |+|[ΔT2×{t-(L3-L2) / VR(t)}×ΔT3(t)] b |… (2) In the case of i=2, M=|[ΔT1×{t-(L2-L1) / VR(t)}×ΔT2(t)]a |… (3) In the above formulas (1) to (3), Li is the distance (m) between the optical fiber temperature sensor of the i-th layer and the meniscus, VR(t) is the casting speed at time t (m / sec), Δt is the time step used in the calculation (sec), a, b, c are the weighting coefficients of the upper and lower layer sensors, ΔTi(t) is the temperature change (°C / sec) and is the value calculated by the following formula (4), ΔTi(t)={Ti ave (t)-Ti(t)} / Δt…(4) In the above formula (4), Ti ave (t) is the average temperature n seconds before time t (°C), and Ti(t) is the temperature of the optical fiber temperature sensor at the i-th layer at time t (°C).

[0020] [7] The control device according to [6], wherein the control device uses the M value to predict the occurrence of at least one of a longitudinal crack defect and a steel leak.

[0021] [8] A method for continuous casting of steel, using the mold described in any one of [1] to [4], wherein an index representing a sharp drop or a sharp rise in the temperature of a solidified shell is calculated using the temperatures at the same position in the width direction of the mold copper plate and at different positions in the casting direction, and the index is used as an operating index.

[0022] [9] The method for continuous casting of steel according to [8], wherein the optical fiber temperature sensor is buried at different i layers (i=2 to 4) in the casting direction, and the M value as the index is calculated using any one of the following equations (1) to (3). When i=4, M=|[ΔT1×{t-(L4-L1) / VR(t)}×(ΔT2×{t-(L4-L2) / VR(t)}] a |+|[ΔT2×{t-(L4-L2) / VR(t)}×(ΔT3×{t-(L4-L3) / VR(t)}] b |+|(ΔT3×{t-(L4-L3) / VR(t)}×ΔT4(t)] c |… (1) When i=3, M=|[ΔT1×{t-(L3-L1) / VR(t)}×ΔT2×{t-(L3-L2) / VR(t)}] a |+|[ΔT2×{t-(L3-L2) / VR(t)}×ΔT3(t)] b |… (2) In the case of i=2, M=|[ΔT1×{t-(L2-L1) / VR(t)}×ΔT2(t)] a |… (3) In the above formulas (1) to (3), Li is the distance (m) between the optical fiber temperature sensor of the i-th layer and the meniscus, VR(t) is the casting speed at time t (m / sec), Δt is the time step used in the calculation (sec), a, b, c are the weighting coefficients of the upper and lower layer sensors, ΔTi(t) is the temperature change (°C / sec) and is the value calculated by the following formula (4), ΔTi(t)={Ti ave (t)-Ti(t)} / Δt…(4) In the above formula (4), Ti ave (t) is the average temperature n seconds before time t (°C), and Ti(t) is the temperature of the optical fiber temperature sensor at the i-th layer at time t (°C).

[0023]

[10] The continuous casting method for steel according to [9], wherein the M value is used to predict at least one of a longitudinal crack defect and a steel leak.

[0024] Effects of the Invention

[0025] By using a mold with an optical fiber temperature sensor embedded therein, the temperature detection interval of the mold can be shortened without special processing of the slit groove. By using this mold to monitor the mold temperature during continuous casting, the abnormal growth of the solidified shell that causes longitudinal crack defects and steel leakage can be predicted with higher accuracy than before. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 1 is a schematic diagram showing a conventional mold copper plate 102 with a support plate fixed to the back surface. Figure 2 The cross-sectional schematic diagram shows an example of a continuous casting facility 10 that includes a casting mold 12 according to the present embodiment and can perform continuous casting of steel. Figure 3 It is a perspective view showing the casting mold 12 according to the present embodiment. Figure 4 Schematic diagram showing a copper plate 40 having long sides of a mold with a support plate fixed to the back surface. Figure 5 1 is a schematic diagram showing a method of embedding the optical fiber temperature sensor 50 in the copper plate 40 on the long side of the mold. Figure 6 It is a schematic diagram showing an example of the structure of the control device 60. Figure 7Schematic diagram showing a copper plate 80 having long sides of a mold with a support plate fixed to the back surface. Figure 8 Schematic diagram showing a copper plate 90 having long sides of a mold with a support plate fixed to the back surface. Fig. 9 Schematic diagram showing a copper plate 94 having long sides of a mold with a support plate fixed to the back surface. Fig.10 This is a graph showing the temporal change in the M value of four adjacent positions in the width direction. DETAILED DESCRIPTION

[0027] Hereinafter, the present invention will be described by way of the embodiments of the present invention. The following embodiments are preferred examples of the present invention, and the present invention is not limited to these embodiments at all.

[0028] Figure 2 1 is a cross-sectional schematic diagram showing an example of a continuous casting device 10 having a mold 12 according to the present embodiment and capable of continuously casting steel. The continuous casting device 10 comprises a mold 12, a tundish 14 disposed above the mold 12, a plurality of cast sheet support rollers 16 arranged below the mold 12, a conveying roller 17, a plurality of secondary cooling belts 26, a cast sheet cutter 30, and a control device 60. Although not shown in the figure, a ladle for accommodating molten steel 18 is disposed above the tundish 14, and the molten steel 18 is injected into the tundish 14 from the bottom of the ladle. An immersion nozzle 20 is disposed at the bottom of the tundish 14, and the molten steel 18 is injected into the mold 12 through the immersion nozzle 20. The molten steel 18 is solidified by removing heat from the inner surface of the mold 12 to form a solidified shell 22. Thus, a cast sheet 28 having an unsolidified layer 24 composed of the molten steel 18 inside and having the solidified shell 22 as an outer shell is formed.

[0029] In the gap between the adjacent slab support rollers 16 in the casting direction, a plurality of secondary cooling zones 26 provided with spray nozzles (not shown) are provided along the casting direction from just below the mold 12. The slab 28 is cooled while being drawn by the cooling water sprayed from the spray nozzles of the secondary cooling zones 26. The slab 28 is conveyed by the slab support rollers 16, and while passing through the plurality of secondary cooling zones 26, the solidified shell 22 is appropriately cooled to promote the solidification of the unsolidified layer 24, and the solidification of the slab 28 is completed.

[0030] A plurality of conveying rollers 17 are provided on the downstream side in the casting direction for continuously conveying the cast piece 28. A cast piece cutter 30 is arranged above the conveying rollers 17 for cutting the cast piece 28. The cast piece 28 after solidification is cut into a predetermined length by the cast piece cutter 30, thereby manufacturing a slab 29.

[0031] Figure 3 1 is a perspective view showing the casting mold 12 according to the present embodiment. Figure 3 As shown, the mold 12 is composed of a plurality of mold copper plates. In this embodiment, the plurality of mold copper plates are, for example, a pair of mold long side copper plates 40 and a pair of mold short side copper plates 42.

[0032] Figure 4 Schematic diagram showing a copper plate 40 having long sides of a mold with a support plate fixed to the back surface. Figure 4 (a) is the rear view from the support plate side. Figure 4 (b) Yes Figure 4 (a) BB section view. It should be noted that Figure 4 In, with Figure 1 The same structures of the mold copper plate 102 are denoted by the same reference numerals, and the description thereof will be omitted.

[0033] An FBG optical fiber temperature sensor 50 is embedded in the copper plate 40 on the long side of the mold. Figure 4 In (a), since the optical fiber temperature sensor 50 is embedded in the copper plate 40 on the long side of the mold, it should be indicated by a dotted line, but in order to clearly indicate the installation position of the optical fiber temperature sensor 50, it is indicated by a solid line. Figure 7 (a) Figure 8 (a) and Fig. 9 The same is true for (a). An FBG (Fiber Bragg Grating) optical fiber temperature sensor is a temperature sensor that detects temperature by providing a diffraction grating that diffracts a specific wavelength in an optical fiber and utilizing the Bragg diffraction phenomenon in the diffraction grating.

[0034] like Figure 4 As shown in (a) and (b), a plurality of slit grooves 106 are formed along the casting direction on the back of the long side copper plate 40 of the mold. The support plate 44 is fixed to the back of the long side copper plate 40 of the mold by stud bolts 108. In the long side copper plate 40 of the mold, optical fiber temperature sensors 50 are embedded in four different layers in the casting direction.

[0035] The four-layer optical fiber temperature sensor 50 is preferably arranged in the range of 50 to 600 mm below the meniscus (liquid surface position) of the long side copper plate 40 of the mold. In the long side copper plate 40 of the mold involved in this embodiment, the optical fiber temperature sensor 50 of the first layer is buried at a position of 50 mm below the meniscus, and the optical fiber temperature sensor 50 of the second layer is buried at a position of 150 mm below the meniscus. In addition, the optical fiber temperature sensor 50 of the third layer is buried at a position of 250 mm below the meniscus, and the optical fiber temperature sensor 50 of the fourth layer is buried at a position of 350 mm below the meniscus. Diffraction gratings 52 are arranged at intervals of less than 50 mm in the optical fiber temperature sensors 50 of the first to fourth layers. The optical fiber temperature sensors 50 of the first to fourth layers are buried in a manner so that the positions of the diffraction gratings 52 in the width direction are aligned in each layer, so that the positions of the diffraction gratings 52 in the width direction of each layer are the same.

[0036] In the FBG optical fiber temperature sensor 50, the temperature of the position where the diffraction grating 52 is provided is detected. Figure 4 In the mold long-side copper plate 40 shown, the mold temperature reflecting the temperature of the solidified shell 22 can be detected at four different positions in the casting direction and at intervals of 50 mm or less in the width direction.

[0037] Figure 5 1 is a schematic diagram showing a method of embedding the optical fiber temperature sensor 50 in the copper plate 40 on the long side of the mold. Figure 5 (a) is a perspective view showing the mold long-side copper plate 40 after hole processing. Figure 5 (b) is a perspective view showing the optical fiber temperature sensor 50 . Figure 5 (c) is a perspective view showing a double tube 58 including the optical fiber temperature sensor 50 and the copper tube 56 .

[0038] like Figure 5 As shown in (a), four holes 48 are horizontally formed in the mold long side copper plate 40 by electrical discharge machining from one side to the other side of the mold long side copper plate 40. The optical fiber temperature sensor 50 is inserted into the hole 48 to be embedded in the mold long side copper plate 40. Figure 5 The diameter of the optical fiber temperature sensor 50 shown in (b) is about 1 mm. Therefore, when the optical fiber temperature sensor 50 is inserted into the mold long side copper plate 40 and buried, the hole 48 with a diameter of about 1 mm corresponding to the diameter of the optical fiber temperature sensor 50 needs to cover the entire length of the mold long side copper plate 40 in the width direction.

[0039] However, it is difficult to discharge-machine a hole 48 having a diameter of about 1 mm over the width direction length of the mold long side copper plate 40, that is, 2500 mm. Furthermore, it is also difficult to insert the flexible optical fiber temperature sensor 50 into the hole 48 having a length of 2500 mm.

[0040] Therefore, if Figure 5 As shown in (c), it is preferable to use a double tube 58 formed by inserting the optical fiber temperature sensor 50 into a copper tube 56 having a diameter of 3 to 5 mm. Figure 5 In the double tube 58 shown in (c), the diameter of the hole 48 for the discharge machining of the mold long side copper plate 40 becomes 3 to 5 mm, so the discharge machining of the mold long side copper plate 40 becomes easy. In addition, in order to bury the optical fiber type temperature sensor 50, the rigid double tube 58 is inserted into the mold long side copper plate 40, so the embedding workability of the optical fiber type temperature sensor 50 in the mold long side copper plate 40 is also improved.

[0041] The hole 48 is preferably provided between a position 1 mm from the molten steel side surface of the copper plate 40 on the long side of the mold in the thickness direction to a position 1 mm from the bottom of the slit groove 106 in the thickness direction. Thus, the influence of the molten steel side surface of the copper plate 40 on the long side of the mold, the cooling water temperature, and the surface condition of the slit groove that change due to wear, etc. can be reduced. The hole 48 is more preferably provided between a position 5 mm from the molten steel side surface in the thickness direction to a position 5 mm from the bottom of the slit groove 106 in the thickness direction. Thus, the influence of the molten steel side surface of the copper plate 40 on the long side of the mold, the cooling water temperature, and the surface condition of the slit groove 106 that change due to wear, etc. can be further reduced.

[0042] In this way, in the copper plate 40 of the long side of the mold, the optical fiber temperature sensor 50 can be buried in the copper plate 40 of the long side of the mold without providing a through hole in the support plate 44. In addition, since the hole 48 for burying the optical fiber temperature sensor 50 is provided at a position that is not connected to the slit groove 106, it is not necessary to process the slit groove 106 in a curve. Therefore, the mold 12 involved in the present embodiment having the copper plate 40 of the long side of the mold becomes a mold that can shorten the temperature detection interval in the width direction of the mold without performing special processing on the slit groove 106. In addition, since the optical fiber temperature sensor 50 can be buried in the copper plate 40 of the long side of the mold without providing a through hole in the support plate 44, it is also possible to suppress the reduction in the strength of the support plate 44.

[0043] Refer again Figure 4. The demodulator 54 is connected to the end of the optical fiber temperature sensor 50. The demodulator 54 allows light to enter the optical fiber temperature sensor 50, and analyzes the reflected light from each diffraction grating 52 to create temperature data. The demodulator 54 outputs the created temperature data to the control device 60 together with the identification information indicating the position of the diffraction grating 52 in the long-side copper plate 40 of the mold. The so-called identification information indicating the position of the diffraction grating 52 is, for example, information including the order and number of layers in the width direction from the reference position. For example, for the 20th diffraction grating from the right end (reference position) of the optical fiber temperature sensor set on the fourth layer, 20-4 becomes the information indicating the position of the diffraction grating 52.

[0044] Figure 6 1 is a schematic diagram showing an example of the structure of the control device 60. The control device 60 is, for example, a general-purpose computer such as a workstation or a personal computer. The control device 60 including the casting mold 12 serves as a control device for controlling continuous casting.

[0045] The control device 60 has a control unit 62, an input unit 64, an output unit 66, and a storage unit 68. The control unit 62 is, for example, a CPU, and by executing a program read from the storage unit 68, the control unit 62 functions as a temperature data acquisition unit 70 and a calculation unit 72. The storage unit 68 is, for example, an updateable flash memory, a hard disk built in or connected via a data communication terminal, a memory card, and other information recording media and their read-write devices. The storage unit 68 stores programs for the control unit 62 to perform various functions, data used by the programs, and the like. The input unit 64 is, for example, a keyboard, a touch panel integrally provided with a display, and the like. The output unit 66 is, for example, an LCD or CRT display, and the like.

[0046] Next, the processing performed by the temperature data acquisition unit 70 and the calculation unit 72 will be described. The temperature data acquisition unit 70 acquires temperature data and information indicating the position of the diffraction grating 52 from the demodulator 54 at a sampling time of, for example, 0.5 to 1.0 seconds. In high-speed casting with a casting speed of 3.0 m / min, the cast piece 28 is pulled out from the mold 12 at 50 mm / sec. Therefore, by acquiring temperature data every 0.5 to 1.0 seconds, the mold temperature reflecting the temperature of the solidified shell 22 can be detected at a pitch of 50 mm or less. The temperature data acquisition unit 70 outputs the acquired temperature data and information indicating the position of the diffraction grating 52 to the calculation unit 72.

[0047] When the calculation unit 72 obtains temperature data for more than 10 seconds from the temperature data acquisition unit 70, the calculation unit 72 reads the following formula (1) and the like from the storage unit 68. The calculation unit 72 calculates the M value using the temperature data detected from the four diffraction gratings 52 having the same position in the width direction and different positions in the casting direction and the following formula (1). The calculation unit 72 calculates the M value for each position in the width direction of the copper plate 40 on the long side of the mold.

[0048] M=|[ΔT1×{t-(L4-L1) / VR(t)}×(ΔT2×{t-(L4-L2) / VR(t)}] a |+|[ΔT2×{t-(L4-L2) / VR(t)}×(ΔT3×{t-(L4-L3) / VR(t)}] b |+|(ΔT3×{t-(L4-L3) / VR(t)}×ΔT4(t)] c |… (1) In the above formula (1), Li is the distance (m) between the optical fiber temperature sensor of the i-th layer and the curved liquid surface, VR (t) is the casting speed at time t (m / sec), Δt is the time step used in the calculation (sec), a, b, c are the weighting coefficients of the upper and lower layer sensors, and ΔTi (t) is the temperature change (°C / sec) and is the value calculated by the following formula (4).

[0049] ΔTi(t)={Ti ave (t)-Ti(t)} / Δt…(4) In the above formula (4), Ti ave (t) is the average temperature n seconds before time t (°C), and Ti(t) is the temperature of the optical fiber temperature sensor at the i-th layer at time t (°C).

[0050] It should be noted that the time step Δt used in the calculation is preferably 0.5 to 1.0 seconds, which is the same as the sampling time, and the time n used for the calculation of the average temperature is preferably 5 to 10 seconds. In addition, the weighting coefficients a, b, and c are coefficients determined based on experience. For example, the temperature sensor of the top layer is prone to misdetection due to the influence of the liquid level fluctuation of the molten steel, so it is preferred to set the weighting coefficient a to a value smaller than the other weighting coefficients b and c. On the other hand, the bottom layer is likely to have a temperature difference due to longitudinal cracks and the bite of foreign matter, so it is preferred to set the weighting coefficient c to a value larger than the weighting coefficients a and b.

[0051] The M value calculated according to the above formula (1) becomes an indicator indicating a sharp drop or a sharp rise in the temperature of the solidified shell 22. When abnormal growth of the solidified shell 22 occurs, which causes longitudinal crack defects and steel leakage, the temperature of the solidified shell 22 drops or rises sharply, and the temperature change becomes larger, so the M value becomes larger. Therefore, if the M value at the beginning of abnormal growth of the solidified shell 22 is predetermined as a threshold, the occurrence of longitudinal crack defects and steel leakage can be predicted by judging whether the calculated M value exceeds the threshold. In this way, by using the M value, the occurrence of longitudinal crack defects and steel leakage can be predicted, so the M value becomes an operating indicator for suppressing the occurrence of longitudinal crack defects and steel leakage and stably implementing continuous casting of steel.

[0052] It should be noted that the threshold value of the M value is preferably grouped according to the type of steel, the type of mold slag and the sampling time of continuous casting, and is empirically determined according to the group based on past performance data. In addition, the threshold value of the M value can be predetermined and stored in the storage unit 68, or can be input by the operator via the input unit 64.

[0053] The operation unit 72 determines whether the calculated M value exceeds the threshold value. When it is determined that the calculated M value exceeds the threshold value of the M value, the operation unit 72 predicts the occurrence of a longitudinal crack defect or steel leakage, and, for example, causes the output unit 66 to display a warning display indicating that there is a risk of the occurrence of a longitudinal crack defect or steel leakage. Thus, the operator can predict the occurrence of a longitudinal crack defect or steel leakage in advance, and thus can take countermeasures. For example, when the occurrence of steel leakage is predicted, the molten steel 18 can be prevented from leaking from the lower end of the mold 12 by reducing the casting speed.

[0054] On the other hand, when it is determined that the calculated M value is below the threshold, the operation unit 72 does not predict the occurrence of longitudinal crack defects and steel leakage, and waits for the calculation process of the next M value. The operation unit 72 calculates the M value at intervals of Δt (0.5 to 1.0 seconds) and repeatedly performs the above-mentioned process. It should be noted that the M value is not limited to the prediction of the occurrence of longitudinal crack defects and steel leakage, but can also be used to evaluate whether the combination of continuous casting steel type and crystallizer powder is appropriate. Therefore, the M value can also be used as an indicator of quality management and batch management of crystallizer powder.

[0055] As described above, by using the casting mold in which the optical fiber temperature sensor is embedded according to the present embodiment, the temperature detection interval in the width direction of the casting mold can be shortened without performing special processing of the slit groove. Furthermore, by using the temperature data obtained from the casting mold and the M value calculated by the above (1) as an operation index, the occurrence of longitudinal crack defects and steel leakage can be predicted with higher accuracy than before, thereby contributing to the realization of stable continuous casting of steel.

[0056] It should be noted that the embodiments of the present invention are not limited to the above-mentioned embodiments, and various modifications can be made. Figure 4 1 shows an example in which the mold 12 is composed of a mold long side copper plate 40 and a mold short side copper plate 42, but the mold 12 is not limited thereto. The mold 12 may also be composed of four mold copper plates of equal width. Figure 4 2 shows an example in which the optical fiber temperature sensor 50 is embedded in the mold long side copper plate 40, but the optical fiber temperature sensor 50 may also be embedded in the mold short side copper plate 42. The optical fiber temperature sensor 50 only needs to be provided in at least one of the plurality of mold copper plates constituting the mold 12.

[0057] exist Figure 4, an example of providing a slit groove 106 on the back of the copper plate 40 on the long side of the mold is shown, but the invention is not limited thereto, and holes for passing the cooling medium may be provided on the back of the copper plate 40 on the long side of the mold instead of the slit groove 106. In the case where holes are provided on the back of the copper plate 40 on the long side of the mold, the support plate 44 may not be fixed on the back of the copper plate 40 on the long side of the mold.

[0058] exist Figure 4 The example of setting the optical fiber temperature sensor 50 at four different positions in the casting direction is shown in the figure, but it is not limited to this. The optical fiber temperature sensor 50 only needs to be set at at least two different positions in the casting direction. In the case where the optical fiber temperature sensor 50 is set at three different positions in the casting direction, the M value can be calculated by the following formula (2). Moreover, in the case where the optical fiber temperature sensor 50 is set at two different positions in the casting direction, the M value can be calculated by the following formula (3).

[0059] M=|[ΔT1×{t-(L3-L1) / VR(t)}×ΔT2×{t-(L3-L2) / VR(t)}] a |+|[ΔT2×{t-(L3-L2) / VR(t)}×ΔT3(t)] b |… (2) M=|[ΔT1×{t-(L2-L1) / VR(t)}×ΔT2(t)] a |… (3) In the above formulas (2) and (3), Li is the distance (m) between the optical fiber temperature sensor of the i-th layer and the curved liquid surface, VR(t) is the casting speed at time t (m / sec), Δt is the time step used in the calculation (sec), a and b are weighting coefficients of the upper and lower layer sensors, and ΔTi(t) is the temperature change (°C / sec) and is the value calculated by the following formula (4).

[0060] ΔTi(t)={Ti ave (t)-Ti(t)} / Δt…(4) In the above formula (4), Ti ave (t) is the average temperature n seconds before time t (°C), and Ti(t) is the temperature of the optical fiber temperature sensor at the i-th layer at time t (°C). It should be noted that Δt and n can use the same values ​​as in formula (1), and the weighting coefficients a and b can be determined empirically in the same way as in formula (1).

[0061] In addition, Figure 4 , 6In the above description, the demodulator 54 and the control device 60 are described as different devices, but the demodulator 54 and the control device 60 may be constituted by the same device. In addition, in the above embodiment, an example in which the control device 60 calculates the M value is described, but the present invention is not limited to this, and the operator may calculate the M value using the above formula (1) and the temperature data output from the demodulator 54.

[0062] In addition, in the above-mentioned embodiment, the M value is calculated by using the temperature detected by the optical fiber temperature sensor 50 embedded in the copper plate 40 of the long side of the mold, but it is not limited to this. Since a sharp temperature rise and temperature drop occur near the two ends of the copper plate 40 of the long side of the mold in the width direction, the temperature detected from the two ends of the copper plate 40 of the long side of the mold to the predetermined position (about 20 mm) may not be used for the calculation of the M value. In this way, it is possible to suppress erroneous detection.

[0063] Figure 7 Schematic diagram showing a copper plate 80 having long sides of a mold with a support plate fixed to the back surface. Figure 7 (a) is the rear view from the support plate side. Figure 7 (b) Yes Figure 7 (a) CC cross-sectional view. Figure 7 , another example of a copper plate with a long side of a mold in which an FBG optical fiber temperature sensor is embedded is described. Figure 7 In the copper plate 80 of the long side of the mold shown in FIG. Figure 4 The same structures of the copper plate 40 on the long side of the mold shown are denoted by the same reference numerals and their description is omitted.

[0064] The optical fiber temperature sensor 82 having approximately half the length of the optical fiber temperature sensor 50 is inserted from the left and right sides of the mold long side copper plate 80 and embedded in the mold long side copper plate 80. Figure 4 The optical fiber temperature sensor 82 having half the length of the optical fiber temperature sensor 50 shown is embedded in the copper plate 80 on the long side of the mold symmetrically with respect to the center line in the width direction. As a result, the length of the discharge machining of the hole 48 is shortened, and the insertion amount of the optical fiber temperature sensor 82 during embedding is also reduced, so the discharge machining performance and embedding workability are improved. In addition, since the number of diffraction gratings 52 analyzed by the demodulator 54 is reduced, even a demodulator 54 with a small number of diffraction gratings 52 that can be analyzed can be used, and the versatility is improved.

[0065] Figure 8 Schematic diagram showing a copper plate 90 having long sides of a mold with a support plate fixed to the back surface. Figure 8 (a) is the rear view from the support plate side. Figure 8 (b) Yes Figure 8 (a) DD cross-sectional view. Figure 8 , the long side copper plate 90 of the mold in which the OFDR optical fiber temperature sensor is embedded is described. Figure 8 In the long side copper plate 90 of the mold shown, Figure 4 The same structures of the copper plate 40 on the long side of the mold shown are denoted by the same reference numerals and their description is omitted.

[0066] The OFDR (Optical Frequency Domain Reflectometry) method is a method of using backscattered light based on Rayleigh scattering, performing Fourier transform on the intensity distribution of backscattered light from a specific range to obtain a change in frequency, and then obtaining the temperature based on the change in frequency. Therefore, the OFDR optical fiber temperature sensor 92 can detect the temperature in a specific range without providing a diffraction grating in the optical fiber, so the entire length of the optical fiber functions as a temperature sensor.

[0067] On the other hand, the measurement distance of the FBG method is several kilometers, while the measurement distance of the OFDR method is tens of meters. The OFDR method has the disadvantage of having a shorter measurement distance than the FBG method. However, the width direction dimension of the copper plate 90 of the long side of the mold is only about 3 meters even if it is long, so as long as the measurement distance is tens of meters, the temperature range of the width direction of the copper plate 90 of the long side of the mold can be fully covered. Therefore, as the optical fiber temperature sensor, it is preferable to use the optical fiber temperature sensor 92 of the OFDR method.

[0068] like Figure 8 As shown, the OFDR optical fiber temperature sensor 92 can also be embedded in the mold long side copper plate 90 in the same manner as the FBG optical fiber temperature sensor. Figure 5 As shown in (c), the optical fiber temperature sensor 92 of the OFDR method can also be made into a double tube by inserting the optical fiber temperature sensor 92 into a copper tube 56 with a diameter of 3 to 5 mm, and inserting the double tube into the mold long-side copper plate 90 to bury the optical fiber temperature sensor 92.

[0069] Fig. 9 Schematic diagram showing a copper plate 94 having long sides of a mold with a support plate fixed to the back surface. Fig. 9 (a) is the rear view from the support plate side. Fig. 9 (b) Yes Fig. 9 (a) EE cross-sectional view. Fig. 9 , another example of a copper plate with a long side of a mold in which an OFDR optical fiber temperature sensor is embedded is described. Fig. 9 In the copper plate 94 of the long side of the mold shown, Figure 4 The same structures of the copper plate 40 on the long side of the mold shown are denoted by the same reference numerals and their description is omitted.

[0070] In the copper plate 94 on the long side of the mold, an optical fiber temperature sensor 96 having a length four times that of the optical fiber temperature sensor 92 of the OFDR method is bent and buried at four different positions in the casting direction. Although the optical fiber temperature sensor of the OFDR method has a short measurement distance, its measurement distance is several tens of meters. Therefore, by Fig. 9 By embedding the OFDR optical fiber temperature sensor 92 as shown, the temperature of four layers of the copper plates 94 on the long sides of the mold can be measured by one optical fiber temperature sensor.

[0071] Example

[0072] Next, an example of continuous casting of steel using a mold having a copper plate on the long side of the mold in which an optical fiber temperature sensor is embedded is described. The type of steel for continuous casting is medium carbon steel, and the basicity of the mold protection slag used is 1.6 to 1.8, and the viscosity is 0.4 poise. The thickness of the cast slab is 220 to 260 mm, and the width of the slab is 800 to 1900 mm. The mold length is 820 mm, and the casting speed VR is set to a maximum of 3.0 m / min to implement continuous casting.

[0073] In the embodiment, FBG-type optical fiber temperature sensors and OFDR-type optical fiber temperature sensors are prepared in which the interval of the diffraction grating is changed to 50mm, 100mm and 200mm. These optical fiber temperature sensors are buried in four different positions in the casting direction of the long side copper plate of the mold along the entire length in the width direction, and the long side copper plate of the mold is produced in which the interval of the temperature sensors is changed to four levels of continuous (OFDR method), 50mm, 100mm and 200mm. Invention Examples 1 and 2 are invention examples in which the interval of the temperature sensors is set to be continuous and 50mm, and the optical fiber temperature sensors are buried in four different positions in the casting direction. Among the four different positions in the casting direction, the first layer is 50mm below the meniscus, the second layer is 150mm below the meniscus, the third layer is 250mm below the meniscus, and the fourth layer is 350mm below the meniscus. Comparative Examples 1 and 2 are comparative examples in which conventional armored thermocouples are assumed and the intervals of the diffraction gratings are set to 100 mm and 200 mm, and the diffraction gratings are buried at four different positions in the casting direction, similarly to Inventive Examples 1 and 2.

[0074] During the continuous casting process, the temperature data output from the demodulator is collected, and the M value is calculated for each position in the width direction. Then, the calculated M value is compared with a predetermined threshold value, and the position in the width direction is recorded when the M value exceeds the threshold value. After that, the longitudinal cracks, restraint marks, or foreign matter bites are confirmed on the cast slab by visual inspection, and the correspondence between the position in the width direction where the calculated M value exceeds the threshold value and the position in the width direction where the longitudinal cracks, restraint marks, or foreign matter bites are confirmed on the slab is investigated, thereby calculating the detection rate of longitudinal cracks, restraint marks, and foreign matter bites. The results are shown in Table 1 below.

[0075] [Table 1]

[0076] As shown in Table 1, in Invention Example 1 and Invention Example 2, in which the interval between the temperature sensors is set to 50 mm or less, the longitudinal cracks and foreign matter bites of the slab can be detected at a detection rate of more than 90%. Moreover, the restraint marks can be detected at a detection rate of 100%. On the other hand, in Comparative Examples 1 and 2, in which the interval between the temperature sensors is set to 100 mm or more, the detection rate of longitudinal crack defects is less than 50%, and the detection rate of restraint marks and foreign matter bites related to steel leakage is also less than 60-65%. Based on this result, it is confirmed that in Comparative Examples 1 and 2, in which the interval between the temperature sensors is set to 100 mm or more, more defects are omitted.

[0077] Fig.10 This is a graph showing the time-dependent change in the M value at four positions adjacent in the width direction in a copper plate on the long side of a mold in which an FBG-type optical fiber temperature sensor with a diffraction grating interval of 50 mm is embedded. Fig.10 In (a) to (d), the vertical axis is the M value (-), and the horizontal axis is the time (sec). Fig.10 As shown in (b) and (c), the M values ​​of width positions 5 and 6 exceed the threshold value 60 at the 28-second position. On the other hand, the M values ​​of width positions 4 and 7 are 10 or less at the 28-second position.

[0078] After the casting, the slab was checked and depressions of about 40 mm in diameter and 8 mm in depth were found at the positions corresponding to width positions 5 and 6. It is presumed that this is because the thickness of the solidified shell is insufficient due to the bite of foreign matter such as mold powder, which increases the temperature change of the solidified shell and the M value. When such depressions become larger, it will cause steel leakage, so it is confirmed that management based on the M value is effective for abnormality detection related to steel leakage.

[0079] In addition, Fig.10 In (b) and (c), the M value exceeds the threshold. Fig.10In (a) and (d), the M value does not exceed the threshold value, so it can be seen that the range affected by the temperature change of the solidified shell caused by the bite of foreign matter is greater than 50 mm and less than 100 mm in the width direction. Therefore, as shown in Table 1, it is believed that when the interval between the temperature sensors is 100 mm or more, the number of defects missed increases.

[0080] Description of symbols 10 Continuous casting equipment 12. Casting 14 Tundish 16 Casting Slab Support Roller 17 Conveyor roller 18 Molten Steel 20 Dipping nozzle 22 Solidification Shell 24 Unsolidified layer 26 Secondary cooling zone 28 Casting 29 Slab 30 Slab cutting machine 40 Moulded long side copper plate 42 Moulded short side copper plate 44 Support plate 48 holes 50 Fiber Optic Temperature Sensor 52 Diffraction grating 54 Demodulator 56 Copper tube 58 Double Pipe 60 Control device 62 Control Department 64 Input section 66 Output 68 Storage 70 Temperature data acquisition unit 72 Operation unit 80 Moulded long side copper plate 82 Fiber Optic Temperature Sensor 90 Moulded long side copper plate 92 Fiber Optic Temperature Sensor 94 Moulded long side copper plate 96 Fiber Optic Temperature Sensor 100 Continuous casting equipment 102 molded copper plate 104 Support plate 106 Slit slot 108 Stud Bolt 110 Armored thermocouple.

Claims

1. A casting mold for use in continuous casting of steel, wherein: The casting mold has a plurality of casting copper plates. At least one of the plurality of mold copper plates has an optical fiber temperature sensor, and the optical fiber temperature sensor is embedded in positions of at least two layers different in the casting direction along the width direction of the mold copper plate.

2. The casting mold according to claim 1, wherein The optical fiber temperature sensor is an FBG optical fiber temperature sensor. The optical fiber temperature sensor is provided with a plurality of diffraction gratings at intervals of 50 mm or less, and the diffraction gratings of each layer are provided at the same position in the width direction of the mold copper plate.

3. The casting mold according to claim 1, wherein The optical fiber temperature sensor is an OFDR optical fiber temperature sensor.

4. The casting mold according to any one of claims 1 to 3, wherein A slit groove is provided on the back of the mold copper plate. The optical fiber temperature sensor is buried between a position 1 mm away from the molten steel side surface of the mold copper plate in the thickness direction and a position 1 mm away from the groove bottom of the slit groove in the thickness direction.

5. A control device comprising: a casting mold according to any one of claims 1 to 3; and a control device for controlling continuous casting of steel using the casting mold, wherein: The control device calculates an index indicating a sharp drop or a sharp rise in the temperature of the solidified shell using the temperatures at the same position in the width direction of the mold copper plate and at different positions in the casting direction.

6. A control device comprising: the casting mold according to claim 4; and a control device for controlling continuous casting of steel using the casting mold, wherein: The control device calculates an index indicating a sharp drop or a sharp rise in the temperature of the solidified shell using the temperatures at the same position in the width direction of the mold copper plate and at different positions in the casting direction.

7. The control device according to claim 5, wherein: The optical fiber temperature sensor is buried at different i layers in the casting direction, where i=2-4. The control device calculates the M value as the index using any one of the following equations (1) to (3). When i=4, M=|[ΔT1×{t-(L4-L1) / VR(t)}×(ΔT2×{t-(L4-L2) / VR(t)}] a |+|[ΔT2×{t-(L4-L2) / VR(t)}×(ΔT3×{t-(L4-L3) / VR(t)}] b |+|(ΔT3×{t-(L4-L3) / VR(t)}×ΔT4(t)] c |…(1) When i=3, M=|[ΔT1×{t-(L3-L1) / VR(t)}×ΔT2×{t-(L3-L2) / VR(t)}] a |+|[ΔT2×{t-(L3-L2) / VR(t)}×ΔT3(t)] b |…(2) In the case of i=2, M=|[ΔT1×{t-(L2-L1) / VR(t)}×ΔT2(t)] a |…(3) In the above formulas (1) to (3), Li is the distance (m) between the optical fiber temperature sensor of the i-th layer and the meniscus, VR(t) is the casting speed at time t (m / sec), Δt is the time step used in the calculation (sec), a, b, c are the weighting coefficients of the upper and lower layer sensors, ΔTi(t) is the temperature change (°C / sec) and is the value calculated by the following formula (4), ΔTi(t)={Ti ave (t)-Ti(t)} / Δt…(4) In the above formula (4), Ti ave (t) is the average temperature n seconds before time t (°C), and Ti(t) is the temperature of the optical fiber temperature sensor at the i-th layer at time t (°C).

8. The control device according to claim 6, wherein: The optical fiber temperature sensor is buried at different i layers in the casting direction, where i=2-4. The control device calculates the M value as the index using any one of the following equations (1) to (3). When i=4, M=|[ΔT1×{t-(L4-L1) / VR(t)}×(ΔT2×{t-(L4-L2) / VR(t)}] a |+|[ΔT2×{t-(L4-L2) / VR(t)}×(ΔT3×{t-(L4-L3) / VR(t)}] b |+|(ΔT3×{t-(L4-L3) / VR(t)}×ΔT4(t)] c |…(1) When i=3, M=|[ΔT1×{t-(L3-L1) / VR(t)}×ΔT2×{t-(L3-L2) / VR(t)}] a |+|[ΔT2×{t-(L3-L2) / VR(t)}×ΔT3(t)] b |…(2) In the case of i=2, M=|[ΔT1×{t-(L2-L1) / VR(t)}×ΔT2(t)] a |…(3) In the above formulas (1) to (3), Li is the distance (m) between the optical fiber temperature sensor of the i-th layer and the meniscus, VR(t) is the casting speed at time t (m / sec), Δt is the time step used in the calculation (sec), a, b, c are the weighting coefficients of the upper and lower layer sensors, ΔTi(t) is the temperature change (°C / sec) and is the value calculated by the following formula (4), ΔTi(t)={Ti ave (t)-Ti(t)} / Δt…(4) In the above formula (4), Ti ave (t) is the average temperature n seconds before time t (°C), and Ti(t) is the temperature of the optical fiber temperature sensor at the i-th layer at time t (°C).

9. The control device according to claim 7, wherein: The control device predicts the occurrence of at least one of a longitudinal crack defect and a breakout using the M value.

10. The control device according to claim 8, wherein: The control device predicts the occurrence of at least one of a longitudinal crack defect and a breakout using the M value.

11. A method for continuous casting of steel, using the casting mold according to any one of claims 1 to 3, wherein: An index showing a sharp drop or a sharp rise in the temperature of the solidified shell is calculated using the temperatures at the same position in the width direction of the mold copper plate and at different positions in the casting direction, and the index is used as an operation index.

12. A method for continuous casting of steel, using the casting mold according to claim 4, wherein: An index showing a sharp drop or a sharp rise in the temperature of the solidified shell is calculated using the temperatures at the same position in the width direction of the mold copper plate and at different positions in the casting direction, and the index is used as an operation index.

13. The method for continuous casting of steel according to claim 11, wherein: The optical fiber temperature sensor is buried at different i layers in the casting direction, where i=2-4. The M value as the index is calculated using any one of the following equations (1) to (3): When i=4, M=|[ΔT1×{t-(L4-L1) / VR(t)}×(ΔT2×{t-(L4-L2) / VR(t)}] a |+|[ΔT2×{t-(L4-L2) / VR(t)}×(ΔT3×{t-(L4-L3) / VR(t)}] b |+|(ΔT3×{t-(L4-L3) / VR(t)}×ΔT4(t)] c |…(1) When i=3, M=|[ΔT1×{t-(L3-L1) / VR(t)}×ΔT2×{t-(L3-L2) / VR(t)}] a |+|[ΔT2×{t-(L3-L2) / VR(t)}×ΔT3(t)] b |…(2) In the case of i=2, M=|[ΔT1×{t-(L2-L1) / VR(t)}×ΔT2(t)] a |…(3) In the above formulas (1) to (3), Li is the distance (m) between the optical fiber temperature sensor of the i-th layer and the meniscus, VR(t) is the casting speed at time t (m / sec), Δt is the time step used in the calculation (sec), a, b, c are the weighting coefficients of the upper and lower layer sensors, ΔTi(t) is the temperature change (°C / sec) and is the value calculated by the following formula (4), ΔTi(t)={Ti ave (t)-Ti(t)} / Δt…(4) In the above formula (4), Ti ave (t) is the average temperature n seconds before time t (°C), and Ti(t) is the temperature of the optical fiber temperature sensor at the i-th layer at time t (°C).

14. The method for continuous casting of steel according to claim 12, wherein: The optical fiber temperature sensor is buried at different i layers in the casting direction, where i=2-4. The M value as the index is calculated using any one of the following equations (1) to (3): When i=4, M=|[ΔT1×{t-(L4-L1) / VR(t)}×(ΔT2×{t-(L4-L2) / VR(t)}] a |+|[ΔT2×{t-(L4-L2) / VR(t)}×(ΔT3×{t-(L4-L3) / VR(t)}] b |+|(ΔT3×{t-(L4-L3) / VR(t)}×ΔT4(t)] c |…(1) When i=3, M=|[ΔT1×{t-(L3-L1) / VR(t)}×ΔT2×{t-(L3-L2) / VR(t)}] a |+|[ΔT2×{t-(L3-L2) / VR(t)}×ΔT3(t)] b |…(2) In the case of i=2, M=|[ΔT1×{t-(L2-L1) / VR(t)}×ΔT2(t)] a |…(3) In the above formulas (1) to (3), Li is the distance (m) between the optical fiber temperature sensor of the i-th layer and the meniscus, VR(t) is the casting speed at time t (m / sec), Δt is the time step used in the calculation (sec), a, b, c are the weighting coefficients of the upper and lower layer sensors, ΔTi(t) is the temperature change (°C / sec) and is the value calculated by the following formula (4), ΔTi(t)={Ti ave (t)-Ti(t)} / Δt…(4) In the above formula (4), Ti ave (t) is the average temperature n seconds before time t (°C), and Ti(t) is the temperature of the optical fiber temperature sensor at the i-th layer at time t (°C).

15. The method for continuous casting of steel according to claim 13, wherein: The M value is used for prediction of at least one of a longitudinal crack defect and a breakout.

16. The method for continuous casting of steel according to claim 14, wherein: The M value is used for prediction of at least one of a longitudinal crack defect and a breakout.

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