Slab heating equipment and continuous casting equipment

Abstract

To provide a slab heater allowed to efficiently heat up an upper corner of a slab while preventing a magnetic flux from going into a roll, and a continuous casting installation.SOLUTION: A slab heater, in a continuous casting installation having a plurality of rolls provided in a transport direction to carry slabs successively while restraining them, comprises a heating coil provided in a manner to face a side-face portion of the slab and a magnetism shielding member provided between the rolls and the heating coil in a thickness direction of the slab.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a slab heating device and continuous casting equipment for heating a slab that is continuously transported by a plurality of rolls. [Background technology]

[0002] In a continuous casting facility where molten metal (molten steel) is cooled in a mold and a slab is produced by a casting process, the slab is first cooled and drawn vertically by a plurality of roll pairs arranged along the direction of slab transport. After that, the slab is gradually curved in an upper straightening band while changing the drawing direction, and then straightened to a straight shape in a lower straightening band before being drawn horizontally.

[0003] When a slab is straightened in the lower straightening zone, tensile stress is generated in the upper corners of the slab, and if the slab has low ductility, cracks will occur in the upper corners. Generally, the ductility of steel depends on the temperature of the steel. In particular, it is known that when the temperature of the steel is 750 to 900°C, the ductility of the steel decreases and embrittlement progresses.

[0004] When a slab is cast in a continuous casting facility, the upper corners cool faster than other parts of the slab. The temperature of the upper corners reaches 750 to 900°C (hereinafter referred to as the "ductility reduction temperature"), at which the ductility of the slab decreases, when the slab passes through the lower straightening zone. This temperature reduction in the slab's ductility and the tensile stress generated by straightening the slab to a horizontally oriented straight shape cause cracks to form in the upper corners of the slab.

[0005] To prevent cracks from occurring in the upper corners of a slab, a technique has been proposed in which a coil for heating the upper corners of the slab is disposed upstream of the lower straightening band. That is, this technique involves heating the upper corners of the slab by induction heating using a coil before the slab reaches the lower straightening band, thereby maintaining the temperature at the upper corners above the ductility reduction temperature, at which the ductility of the slab decreases.

[0006] As an example of such a technique, Patent Document 1 discloses a technique in which coils made of conductors are arranged on the upper surface of a cast slab so as to form a predetermined group of straight lines, and the upper corners are heated by induction heating the cast slab, thereby suppressing cracks in the upper corners.

[0007] Patent Document 2 discloses a technology in which an iron core is provided to cover the upper corner portion of a cast slab, and induction heating is performed on the cast slab using a coil wound around the iron core to heat the upper corner portion, thereby suppressing cracks in the upper corner portion. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-218062 [Patent Document 2] Patent Publication No. 2021-87963 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the techniques disclosed in Patent Documents 1 and 2 employ a configuration in which only induction heating coils for heating the slab are arranged between multiple rolls arranged along the slab's transport direction. Because the distance (pitch) between the multiple rolls arranged along the slab's transport direction is short, it is difficult for the induction heating coils arranged between the multiple rolls to have a length sufficient to sufficiently heat the slab. Therefore, in a configuration in which induction heating coils are arranged between multiple rolls, it is difficult to sufficiently heat the slab, and the effect of preventing cracks at the upper corners of the slab cannot be fully achieved.

[0010] Furthermore, when induction heating coils are placed at the same positions as rolls along the slab's transport direction, the magnetic flux generated by the induction heating coil penetrates both the slab and the rolls. This causes the temperatures of both the slab and the rolls to rise, leading to thermal deformation of the rolls and fatigue damage due to the thermal cycle, shortening the service life of the rolls. Furthermore, sparks may occur between the rolls and the slab through the penetration of the magnetic flux, resulting in defects in the slab and the rolls. Patent Documents 1 and 2 do not disclose or suggest any solutions to these problems, and therefore, in preventing cracks in the upper corners of the slab, the penetration of magnetic flux into the rolls due to heating of the upper corners of the slab becomes a problem.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a slab heating device and continuous casting equipment that can prevent magnetic flux from penetrating into the rolls and enable efficient heating of the upper corner portions of the slab. [Means for solving the problem]

[0012] [1] A slab heating device in a continuous casting facility in which a plurality of rolls that continuously transport a slab while restraining the slab are arranged along the transport direction of the slab, the slab heating device having a heating coil arranged to face the side portion of the slab, and a magnetic shielding member arranged between the roll and the heating coil in the thickness direction of the slab. [2] The slab heating device according to [1], wherein the heating coil is a circuit that connects and circles two long side portions of the coil extending in the transport direction and two short side portions of the coil extending in the thickness direction of the slab in the same plane. [3] The slab heating device according to [2], wherein the magnetic shielding member has a relative magnetic permeability of 1000 or more at the frequency of the alternating current supplied from the power supply unit to the heating coil. [4] The casting heating device according to [3], wherein the magnetic shielding member is a plate-shaped member and the plate-shaped member is arranged so as to be perpendicular to the shortest line segment connecting the central axis of the roll and the long side portion of the heating coil. [5] The slab heating device described in [4], wherein the magnetic shielding members include an upper magnetic shielding member that is arranged perpendicular to the shortest line segment connecting the center axis of the upper roll of the rolls and the upper coil long side portion of the coil long side portion of the heating coil, and a lower magnetic shielding member that is arranged perpendicular to the shortest line segment connecting the center axis of the lower roll of the rolls and the lower coil long side portion of the coil long side portion of the heating coil. [6] A slab heating device according to [5], wherein the length of the magnetic shielding member along the width direction of the slab perpendicular to the conveying direction is equal to or greater than the coil diameter of the heating coil at the long side portion of the coil. [7] The slab heating device according to [3], wherein the magnetic shielding member has an arc shape or a cylindrical shape that conforms to the peripheral surface of the roll. [8] The slab heating device according to [5], wherein the length of the magnetic shielding member along the conveying direction is 0.7R or more where R is the diameter of the roll. [9] The slab heating device according to any one of [1] to [8], further comprising a carriage for adjusting the positions of the heating coil and the magnetic shielding member relative to the side surface of the slab in the width direction of the slab.

[10] A continuous casting facility, in which the slab heating device according to any one of [1] to [8] is provided in a lower straightening zone.

[11] A continuous casting facility having a plurality of rolls arranged along the direction of transport of the slab, which constrain and continuously transport the slab, and which has a circuit that connects and rotates two long side portions of a coil extending in the direction of transport and two short side portions of a coil extending in the thickness direction of the slab on the same plane, and which has a slab heating device having a heating coil arranged so that the circuit faces the side portion of the slab, and the material of the rolls includes a non-magnetic material. [Effects of the Invention]

[0013] According to the present invention, it is possible to prevent the magnetic flux from penetrating into the rolls and to efficiently heat the upper corners of the slab. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic side view of an example of continuous casting equipment. [Figure 2] FIG. 2 is a perspective schematic view showing the configuration of a roll, a slab, and a slab heating device. [Figure 3] FIG. 2 is a schematic side view showing the configuration of a slab heating device. [Figure 4] FIG. 2 is a schematic front view showing the configuration of a magnetic shielding member. [Figure 5] FIG. 10 is a diagram showing the distribution of magnetic flux when a slab heating device without a magnetic shielding member is used. [Figure 6] FIG. 10 is a diagram showing the distribution of magnetic flux when a slab heating device having a magnetic shielding member is used. [Figure 7] FIG. 10 is a schematic side view showing the configuration of a magnetic shielding member in a slab heating device according to a second embodiment. [Figure 8] FIG. 10 is a schematic side view showing the configuration of a magnetic shielding member in a slab heating device according to a third embodiment. [Figure 9] FIG. 10 is a schematic side view showing the configuration of a magnetic shielding member in a slab heating device according to a fourth embodiment. [Figure 10] FIG. 10 is a schematic front view showing the configuration of a slab heating device according to a fifth embodiment. [Figure 11] FIG. 10 is a diagram showing the results of the temperature history of the slab and roll when no magnetic shielding member is used. [Figure 12] FIG. 10 is a diagram showing the results of the temperature history of the slab and roll when a magnetic shielding member is used. [Figure 13] FIG. 10 is a diagram showing the results of the temperature history of the slab and roll when a roll containing a non-magnetic material is used. [Figure 14] FIG. 10 is a diagram showing the results of the temperature history of the slab and roll when magnetic shielding members divided in the conveying direction are used. [Figure 15] FIG. 10 is a diagram showing the results of the temperature history of the slab and roll when a magnetic shielding member having an arc shape is used. DETAILED DESCRIPTION OF THE INVENTION

[0015] First Embodiment A first embodiment of the present invention will be described in detail below. FIG. 1 shows a schematic side view of an example of continuous casting equipment 10. The continuous casting equipment 10 has a tundish 1, a mold 2, rolls 3, and a slab heating device 7. The tundish 1 has an immersion nozzle 1a. The rolls 3 are arranged from the upstream side to the downstream side in the transport direction D of the slab S. The rolls 3 sandwich the slab S between multiple pairs of rolls 3 at each position in the transport direction D of the slab S and transport the slab S along the transport direction D. That is, the continuous casting equipment 10 has multiple rolls 3 arranged along the transport direction D of the slab S that constrain and continuously transport the slab S.

[0016] As shown in FIG. 1, a tundish 1 stores molten steel T before casting. An immersion nozzle 1a pours the molten steel T into a mold 2 from the bottom of the tundish 1. After being cooled in the mold 2, the molten steel T is transported along a vertical transport direction E by a plurality of rolls 3 and cooled in a cooling zone 4 to become a slab S having a thickness of 200 to 300 mm and a width of 1 to 2 m. The slab S is then transported along a curved transport direction F by the rolls 3 and curved in an upper straightening zone 5. The slab S is then transported along a horizontal transport direction G by the rolls 3 and straightened to a straight shape in a lower straightening zone 6.

[0017] In the upper straightening band 5, the temperature of the slab S is about 1000°C at the center in the width direction and about 900°C at the upper corners. On the other hand, in the lower straightening band 6, the temperature of the slab S drops to about 750°C at the upper corners. That is, the temperature of the slab S reaches the ductility reduction temperature in the lower straightening band 6. For this reason, when the slab S that has reached the ductility reduction temperature in the lower straightening band 6 is straightened into a straight shape, cracks occur due to the tensile stress generated at the upper corners of the slab S.

[0018] Therefore, in the present invention, as shown in Fig. 1, a slab heating device 7 is provided in the lower straightening band 6. Specifically, the slab heating device 7 is provided from a position on the upstream side of the lower straightening band 6 to a position on the downstream side of the lower straightening band 6. Then, for the slab S straightened to a straight shape in the lower straightening band 6, the temperature of the upper corners is compensated so as not to reach the ductility reduction temperature.

[0019] Next, the configuration of the slab heating device 7 will be described with reference to FIG. 2. FIG. 2 is a perspective schematic diagram showing the configuration of the rolls 3, the slab S, and the slab heating device 7. As shown in FIG. 2, the slab heating device 7 is provided between a pair of rolls 3 (an upper roll 3a and a lower roll 3b) near the side portion B of the slab S. The slab heating device 7 has a heating coil 7a and a magnetic shielding member 7h. The heating coil 7a generates magnetism around it based on an alternating current supplied from a power source, and heats the surrounding structure (an upper corner portion C of the slab S) by induction heating.

[0020] Here, the detailed configuration of the slab heating device 7 will be described with reference to FIG. 3. FIG. 3 is a side view showing the configuration of the slab heating device 7. As shown in FIG. 3, the heating coil 7a of the slab heating device 7 has a coil long side portion 7b and a coil short side portion 7e. The coil long side portion 7b has an upper coil long side portion 7c and a lower coil long side portion 7d. In other words, the coil long side portion 7b has two coil long side portions extending in the transport direction D of the slab S. Furthermore, the coil short side portion 7e has an upstream coil short side portion 7f and a downstream coil short side portion 7g. In other words, the coil short side portion 7e has two coil short side portions extending in the thickness direction H of the slab S.

[0021] That is, the heating coil 7a is a circuit that connects and circles two long side portions of the coil extending in the slab transport direction D and two short side portions of the coil extending in the slab thickness direction H on the same plane, and is arranged so that the circuit faces the side portion B of the slab S.

[0022] The length of the coil long side portions 7b (upper coil long side portion 7c and lower coil long side portion 7d) is preferably 1500 mm or more. This is because, in order to prevent the temperature at the upper corner portions C of the slab S from decreasing to the ductility decreasing temperature throughout the entire lower straightening zone 6 (see FIG. 1), a preheat zone of 500 mm or more in length is provided upstream of the lower straightening zone 6, and a heat retention zone of 1000 mm or more in length is required throughout the entire lower straightening zone 6.

[0023] Regarding the heating coil 7a, if it is difficult to sufficiently heat the upper corner portion C using a single circuit formed by a single coil, multiple circuits based on multiple coils may be created and the multiple circuits may be arranged in sequence along the transport direction D of the slab S, thereby dividing the heating area of ​​the upper corner portion C into multiple areas for heating. In this case, the length of the coil long sides 7b (upper coil long sides 7c and lower coil long sides 7d) of the multiple divided heating coils 7a is preferably 500 mm or more. This is because if the coil long sides 7b are shorter than the coil short sides 7e, induced currents will cancel out between the coil short sides 7e of adjacent coils, reducing the effectiveness of heating the upper corner portion C.

[0024] The length of the coil short sides 7e (upstream coil short sides 7f and downstream coil short sides 7g) is preferably 125 mm or more and less than the thickness L of the slab S. This is because if the length of the coil short sides 7e is less than 125 mm, the induced currents will cancel out between the coil long sides 7b of adjacent coils, reducing the heating effect of the slab S. In addition, if the length of the coil short sides 7e is greater than or equal to the thickness L of the slab S, the coil long sides 7b will interfere with the rolls 3.

[0025] The effect of the present invention is small even if there is a difference of about 10 mm between the distance between the upper coil long side portion 7c and the side portion B of the slab S and the distance between the lower coil long side portion 7d and the side portion B of the slab S. Furthermore, the configuration of the coil short side portion 7e (upstream coil short side portion 7f and downstream coil short side portion 7g) is not limited as long as it connects the coil long side portion 7b (upper coil long side portion 7c and lower coil long side portion 7d) as a circuit.

[0026] The heating coil 7a may be wound one or more times as long as it is configured as a circuit in which the long side 7b and the short side 7e of the coil are connected by a conductor connected to a power supply. The heating coil 7a may be made of a conductor such as copper. The conductor constituting the heating coil 7a may be a hollow member, and cooling water may be circulated through the hollow space to cool the conductor. The diameter of the conductor constituting the heating coil 7a is preferably 3 mm or more. Increasing the diameter of the conductor reduces the resistance of the heating coil 7a and prevents melting due to heat generation by the heating coil 7a.

[0027] The heating coil 7a may be connected to a power supply that supplies alternating current. The output of the power supply that supplies alternating current to the heating coil 7a is preferably 300 to 1000 kW. The alternating current supplied to the heating coil 7a preferably has a current (effective value) of 10 to 30 kA. This is because if the output and current (effective value) of the power supply are low, the upper corners C of the slab S cannot be sufficiently heated, and if the output and current (effective value) of the power supply are high, the upper corners C may be melted.

[0028] The alternating current supplied to the heating coil 7a preferably has a frequency of 1 to 10 kHz. If the frequency is less than 1 kHz, the entire side surface portion B of the slab S is heated, but it becomes difficult to heat the upper corner portion C to a temperature exceeding the ductility reduction temperature. If the frequency exceeds 10 kHz, only the very outer surface layer of the upper corner portion C is heated locally, making it difficult to heat the entire upper corner portion C uniformly.

[0029] The magnetic shielding member 7h is provided between the roll 3 and the heating coil 7a in the thickness direction H of the slab S. The magnetic shielding member 7h includes an upper magnetic shielding member 7i and a lower magnetic shielding member 7j. It is preferable that the magnetic shielding member 7h has a relative permeability of 1000 or more at the frequency of the alternating current supplied from the power supply to the heating coil 7a and a thickness of 1 mm or more and 10 mm or less.

[0030] Relative permeability is a parameter that indicates the degree of magnetic permeability when a material is placed in a magnetic field; the higher the value, the less magnetic permeability the material has. Therefore, if the relative permeability of the magnetic shielding member 7h is low, it is necessary to increase the thickness of the magnetic shielding member 7h to prevent the magnetic field generated in the heating coil 7a from penetrating the roll 3. However, in this case, as the thickness of the magnetic shielding member 7h increases, the distance between the coil long side 7b (upper coil long side 7c and lower coil long side 7d) of the heating coil 7a and the upper corner C of the slab S increases, making it difficult to efficiently heat the upper corner C.

[0031] On the other hand, if the relative permeability of the magnetic shielding member 7h is increased to reduce the thickness of the magnetic shielding member 7h, it is possible to prevent the magnetic field generated in the heating coil 7a from penetrating into the roll 3, but it is difficult to ensure the strength of the member.

[0032] Therefore, the magnetic shielding member 7h has a thickness of 1 mm to 10 mm, which allows for prevention of deformation due to the effects of heating, and by providing a relative permeability of 1000 or more based on this thickness, it is possible to prevent the magnetic field generated in the heating coil 7a from penetrating (magnetic flux leakage) into the roll 3. Examples of materials for the magnetic shielding member 7h include iron-based materials, ferrite, amorphous, permalloy, and sendust, but the material is not limited as long as it prevents magnetic field penetration. The magnetic shielding member 7h may be configured as a hollow member, and cooling water for cooling the magnetic shielding member 7h may be circulated through the hollow space.

[0033] The magnetic shielding member 7h is a plate-like member and is provided so as to be perpendicular to the shortest line segment N connecting the central axis P of the roll 3 and the coil long side portion 7b. Specifically, in this embodiment, the magnetic shielding member 7h includes an upper magnetic shielding member 7i provided so as to be perpendicular to the shortest line segment N connecting the central axis P of the upper roll 3a of the roll 3 and the upper coil long side portion 7c of the coil long side portion 7b, and a lower magnetic shielding member 7j provided so as to be perpendicular to the shortest line segment N connecting the central axis P of the lower roll 3b of the roll 3 and the lower coil long side portion 7d of the coil long side portion 7b.

[0034] By arranging the magnetic shielding member 7h, which is a plate-shaped member, so that it is perpendicular to the shortest line segment N between the center axis P of the roll 3 and the coil long side portion 7b (upper coil long side portion 7c and lower coil long side portion 7d), it is possible to more efficiently prevent the magnetic field emitted from the upper coil long side portion 7c and lower coil long side portion 7d of the heating coil 7a from penetrating into the roll 3 (upper roll 3a and lower roll 3b).

[0035] Next, the configuration of the magnetic shielding member 7h in the slab heating device 7 will be described with reference to Fig. 4. Fig. 4 is a schematic front view showing the configuration of the magnetic shielding member 7h in the slab heating device 7. That is, Fig. 4 shows a schematic front view of the slab heating device 7 viewed in the conveying direction D of the slab S.

[0036] 4, the length of the magnetic shielding member 7h in the width direction W of the slab S, which is perpendicular to the conveying direction D, is preferably equal to or greater than the coil diameter U of the heating coil 7a at the coil long side portions 7b (upper coil long side portion 7c and lower coil long side portion 7d).From the viewpoint of suppressing heating of the rolls 3, the length of the magnetic shielding member 7h in the width direction W of the slab S is more preferably equal to or greater than 50 mm.

[0037] In addition, in order to avoid contact due to meandering of the slab S during transport and to promote heating of the slab S, the magnetic shielding member 7h may be spaced from the slab S in the width direction W by the distance equal to the distance between the long side portion 7b of the coil and the side portion B of the slab S (hereinafter referred to as "distance CS"). Furthermore, in order to avoid contact with the long side portion 7b of the coil due to meandering of the slab S, the distance CS is preferably 25 mm or more. If the distance CS is too large, the heating effect of the slab S decreases. Additionally, since an increase in the current (effective value) of the alternating current intended to improve heating efficiency may induce melting of the coil, the distance CS is preferably less than 50 mm.

[0038] The distance between the long side 7b of the heating coil 7a and the roll 3 (hereinafter referred to as "distance CR") is preferably 1 mm or more from the viewpoint of providing a magnetic shielding member 7h. Furthermore, if the distance between the long side 7b of the coil and the roll 3 is too large, the distance between the long side 7b of the coil and the upper corner C also increases, reducing the heating efficiency of the upper corner C. In addition, an increase in the current (effective value) of the alternating current intended to improve heating efficiency may also induce melting of the coil. For this reason, the distance CR is preferably less than 30 mm.

[0039] Next, the effects of the above-described configuration will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a diagram showing the distribution of magnetic flux when a slab heating device 7 without a magnetic shielding member 7h is used. Fig. 6 is a diagram showing the distribution of magnetic flux when a slab heating device 7 with a magnetic shielding member 7h is used.

[0040] As shown in FIG. 5, when an AC current is supplied to the heating coil 7a in a slab heating device 7 that does not have a magnetic shielding member 7h, magnetic flux M is generated and penetrates the rolls 3. On the other hand, when an AC current is supplied to the heating coil 7a in a slab heating device 7 that has a magnetic shielding member 7h, magnetic flux M is generated and drawn into the magnetic shielding member 7h as shown in FIG. 6. The magnetic flux M drawn into the magnetic shielding member 7h is directed parallel to the surface of the magnetic shielding member 7h that extends in the width direction W of the slab S, preventing it from penetrating the rolls 3. Furthermore, the magnetic flux M directed parallel to the surface of the magnetic shielding member 7h efficiently penetrates the upper corners C of the side surfaces B of the slab S while maintaining its direction. Therefore, the magnetic shielding member 7h enables efficient heating of the upper corners C of the slab S and prevents magnetic flux from penetrating the rolls 3.

[0041] 3, the magnetic shielding member 7h has been described as including an upper magnetic shielding member 7i and a lower magnetic shielding member 7j, but the magnetic shielding member 7h may be configured to include only the upper magnetic shielding member 7i without providing the lower magnetic shielding member 7j. In this case, providing at least the upper magnetic shielding member 7i enables efficient heating of the upper corner portion C of the slab S and prevents magnetism from penetrating into the upper roll 3a.

[0042] Furthermore, in addition to using the magnetic shielding member 7h, the roll 3 may also contain a non-magnetic material. By including a non-magnetic material in the roll 3 material, it is possible to more effectively prevent magnetism from penetrating the roll 3 than when only the magnetic shielding member 7h is used. This provides an excellent effect in preventing heating of the roll 3 and damage to the roll 3. Examples of materials that make the roll 3 non-magnetic include ceramic materials and austenitic stainless steel.

[0043] Second Embodiment Next, a second embodiment of the present invention will be described. Fig. 7 schematically shows the configuration of a magnetic shielding member 72b in a slab heating device 72 of the second embodiment. Fig. 7 shows an example of a configuration in which the magnetic shielding member 72b is divided in the conveying direction D of the slab S. The second embodiment has the same configuration as the first embodiment, except for the configuration in which the magnetic shielding member 72b is divided.

[0044] As shown in FIG. 7 , by dividing the magnetic shielding members 72b in the conveying direction D of the slab S and arranging the magnetic shielding members 72b only between the rolls 3 and the heating coil 72a (including the coil long side portions 72c and 72d), it is possible to prevent magnetic fields from penetrating the rolls 3 and simplify the configuration of the magnetic shielding members 72b. Furthermore, by not providing the magnetic shielding members 72b in the same positions in the conveying direction D as positions where the rolls 3 are not disposed, it is possible to allow the magnetic flux generated from the heating coil 72a to act on the upper corner portions C of the slab S. As a result, it is possible to efficiently heat the upper corner portions C. From the viewpoint of preventing magnetic fields from penetrating the rolls 3, it is preferable that the length of the magnetic shielding members 72b in the conveying direction D be 0.7R or more, where R is the roll diameter of the rolls 3.

[0045] Third Embodiment Next, a third embodiment of the present invention will be described. Fig. 8 schematically shows the configuration of a magnetic shielding member 73b in a slab heating device 73 of the third embodiment. Fig. 8 shows an example of a configuration in which the length of the magnetic shielding member 73b in the width direction W of the slab S is approximately the same as the coil diameter of the heating coil 73a. The third embodiment has the same configuration as the first embodiment, except for the configuration in which the length of the magnetic shielding member 73b in the width direction W of the slab S is approximately the same as the coil diameter of the heating coil 73a.

[0046] As shown in FIG. 8, by making the length of the magnetic shielding member 73b in the width direction W of the slab S approximately the same as the coil diameter of the heating coil 73a, it is possible to prevent magnetism from penetrating into the roll 3 and also to simplify the configuration of the magnetic shielding member 73b.

[0047] <Fourth embodiment> Next, a fourth embodiment of the present invention will be described. FIG. 9 schematically shows the configuration of magnetic shielding members 74c and 74d in a slab heating device 74 of the fourth embodiment. FIG. 9(a) shows an example of a configuration in which the magnetic shielding member 74c has an arc shape along the circumferential surface K of the roll 3. FIG. 9(b) shows an example of a configuration in which the magnetic shielding member 74d has a cylindrical shape along the circumferential surface K of the roll 3. The fourth embodiment has the same configuration as the first embodiment, except for the configuration in which the magnetic shielding members 74c and 74d have an arc shape or a cylindrical shape. Note that the heating coil 74a in FIG. 9(a) includes a coil long side portion 74e and a coil long side portion 74f. The heating coil 74b in FIG. 9(b) includes a coil long side portion 74g and a coil long side portion 74h.

[0048] 9 , by forming the magnetic shielding members 74c and 74d in an arc-shaped or cylindrical shape along the circumferential surface K of the roll 3 in the conveying direction D of the slab S, it is possible to more reliably prevent magnetic fields from penetrating the roll 3, while positioning the magnetic shielding members 74c and 74d in proximity to the upper corners C of the slab S. With this configuration, magnetic flux concentrated in the magnetic shielding members 74c and 74d can be concentrated at the upper corners C, thereby efficiently heating the upper corners C. From the viewpoint of preventing magnetic fields from penetrating the rolls 3, when the magnetic shielding members 74c are configured in an arc-shaped shape, it is preferable that the chord length of the arc be 0.7R or more, where R is the roll diameter of the roll 3.

[0049] Fifth Embodiment Next, a fifth embodiment of the present invention will be described. Fig. 10 schematically shows the configuration of a slab heating apparatus 75 according to the fifth embodiment. Fig. 10 shows an example of a configuration in which the slab heating apparatus 75 is provided with a carriage 75e and a distance measuring device 75f. The fifth embodiment has the same configuration as the first embodiment, except for the configuration in which the slab heating apparatus 75 is provided with the carriage 75e and the distance measuring device 75f.

[0050] As shown in Figure 10, the slab heating device 75 includes a heating coil 75a, a magnetic shielding member 75b, a conductive rod 75c, a power supply unit 75d, a carriage 75e, a distance measurement device 75f, and a drive unit 75g. The power supply unit 75d supplies AC current to the conductive rod 75c. The conductive rod 75c supplies the AC current supplied from the power supply unit 75d to the heating coil 75a. The heating coil 75a heats an upper corner C of the slab S with the AC current supplied via the conductive rod 75c.

[0051] The distance measuring device 75f may be a laser distance meter. The distance measuring device 75f may measure the distance between the heating coil 75a and the magnetic shielding member 75b and the side surface B of the slab S. The carriage 75e may be controlled to adjust the distance between the heating coil 75a and the magnetic shielding member 75b and the side surface B of the slab S based on the distance measurement value measured by the distance measuring device 75f.

[0052] Furthermore, the distance measuring device 75f may measure the distance between the upper roll 3a and the lower roll 3b. The driving unit 75g may be controlled to adjust the distance between the upper heating coil 75a and the magnetic shielding member 75b and the lower heating coil 75a and the magnetic shielding member 75b, based on the distance measurement value measured by the distance measuring device 75f.

[0053] That is, in this embodiment, the positions of the heating coil 75a and the magnetic shielding member 75b relative to the side surface B of the slab S may be adjusted by the carriage 75e in the width direction W of the slab S. Furthermore, since the distance between the upper heating coil 75a and the magnetic shielding member 75b and the lower heating coil 75a and the magnetic shielding member 75b can be adjusted, the upper corner portion C can be reliably heated regardless of the size of the slab S.

[0054] Sixth Embodiment Next, a sixth embodiment of the present invention will be described. In the sixth embodiment, instead of using a magnetic shielding member, the material of the roll 3 may be a non-magnetic material. The sixth embodiment has the same configuration as the first embodiment, except that the magnetic shielding member is not used and the material of the roll 3 is a non-magnetic material.

[0055] By using a non-magnetic material for the roll 3, it is possible to more effectively prevent the intrusion of magnetism than when only a magnetic shielding member is used. This prevents the roll 3 from heating up, and is highly effective in preventing damage to the roll 3. Examples of materials that can be used to make the roll 3 non-magnetic include ceramic materials and austenitic stainless steel.

[0056] Although the configurations of the first to sixth embodiments have been described above, the present invention can also combine the configurations of the respective embodiments as long as the effects of preventing the magnetic flux M from entering the rolls 3 and enabling efficient heating of the upper corner portions C of the slab S are achieved. For example, the magnetic shielding members 74c may be configured to have an arc shape along the circumferential surface K of the rolls 3 in the conveying direction D (see FIG. 9(a)), and the length of the magnetic shielding members 7h in the width direction W may be set to be equal to or greater than the coil diameter U of the heating coil 7a (see FIG. 4), and further the rolls 3 may be made of a material containing a non-magnetic material. [Example]

[0057] Next, the results of implementing the slab heating device and continuous casting equipment according to the present invention in a process for casting a slab S will be described. The comparative example and invention example 1 described below are implementation results focusing on the configuration of the first embodiment. Inventive example 2 is an implementation result focusing on the configuration of the sixth embodiment. Inventive example 3 is an implementation result focusing on the configuration of the second embodiment. Inventive example 4 is an implementation result focusing on the configuration of the fourth embodiment.

[0058] In the examples, the cross-sectional size of the slab S was a width of 1200 mm and a thickness of 300 mm, and plain carbon steel was used as the material for the slab S. In the casting process, the initial temperature of the corners of the slab S was 750°C, and the conveying speed of the slab S in the conveying direction D was 0.9 m / min. The length of the long side of the heating coil was 1500 mm, and the length of the short side of the coil was 250 mm. The magnetic shielding member had a relative permeability of 1000 and a thickness of 1 mm. The alternating current supplied to the heating coil had a frequency of 10 kHz and a current (effective value) of 10 kA.

[0059] As a comparative example, FIG. 11 shows the results of the temperature history from the heating start point of the slab S and the roll 3 when the magnetic shielding member 7h was not used. FIG. 11(a) is a perspective schematic diagram showing the configuration of the slab S, the roll 3, and the heating coil 7a. FIG. 11(b) is a front schematic diagram showing the configuration of the slab S, the roll 3, and the coil long side portion 7b in the width direction W. FIG. 11(c) is a diagram showing the results of the temperature history of the upper corner portion (X) of the slab S and a position (Y) on the roll 3 near the coil long side portion 7b. The roll 3 in the comparative example was a normal roll without including a non-magnetic material.

[0060] As shown in Figure 11(c), the upper corner (X) of the slab S was heated to a temperature of only about 900°C, which was the ductility-reducing temperature, when it passed through the lower straightening zone, causing cracks at the upper corner (X). Furthermore, the heated temperature at a position (Y) near the coil long side 7b on the roll 3 also reached about 850°C, causing damage due to thermal deformation. Furthermore, a spark occurred between the coil long side 7b and the roll 3, damaging the slab S.

[0061] FIG. 12 shows the results of the temperature history from the heating start point of the slab S and the roll 3 when a magnetic shielding member 7h was used as Example 1. FIG. 12(a) is a perspective schematic diagram showing the configuration of the slab S, the roll 3, the magnetic shielding member 7h, and the heating coil 7a. FIG. 12(b) is a front schematic diagram showing the configuration of the slab S, the roll 3, the magnetic shielding member 7h, and the coil long side portion 7b in the width direction W. FIG. 12(c) is a diagram showing the results of the temperature history of the upper corner portion (X) of the slab S and a position (Y) on the roll 3 near the coil long side portion 7b. The roll 3 in Example 1 was a normal roll without including a non-magnetic material.

[0062] As shown in Figure 12(c), the upper corners (X) of the slab S were heated to a temperature of about 1000°C, exceeding the ductility reduction temperature, when the slab passed through the lower straightening zone, so no cracks occurred at the upper corners (X). In addition, the heated temperature at the position (Y) near the coil long side 7b on the roll 3 was only about 200°C, preventing damage due to thermal deformation.

[0063] In Example 2, instead of using the magnetic shielding member 7h, a roll 8 made of a non-magnetic austenitic stainless steel (SUS304) was used. The results of the temperature history of the slab S and the roll 8 from the heating start point in this case are shown in FIG. 13. FIG. 13(a) is a perspective schematic diagram showing the configuration of the slab S, the roll 8, and the heating coil 7a. FIG. 13(b) is a front schematic diagram showing the configuration of the slab S, the roll 8, and the coil long side 7b in the width direction W. FIG. 13(c) is a diagram showing the results of the temperature history of the upper corner (X) of the slab S and the position (Y) of the roll 8 near the coil long side 7b.

[0064] As shown in Figure 13(c), the upper corners (X) of the slab S were heated to a temperature of about 1000°C, exceeding the ductility reduction temperature, when the slab passed through the lower straightening zone, so no cracks occurred at the upper corners (X). In addition, the heated temperature at the position (Y) near the coil long side 7b on the roll 8 was only about 140°C, preventing damage due to thermal deformation.

[0065] In Example 3, a magnetic shielding member 72b divided in the conveying direction D of the slab S was used. FIG. 14 shows the temperature history of the slab S and the roll 3 from the heating start point. FIG. 14(a) is a perspective schematic diagram showing the configuration of the slab S, roll 3, magnetic shielding member 72b, and heating coil 72a. FIG. 14(b) is a front schematic diagram showing the configuration of the slab S, roll 3, magnetic shielding member 72b, and coil long side portion 72c and coil long side portion 72d in the width direction W. FIG. 14(c) is a diagram showing the temperature history of the upper corner portion (X) of the slab S and a position (Y) on the roll 3 near the coil long side portion 72c. The roll 3 in Example 3 was a normal roll without a non-magnetic material.

[0066] As shown in Figure 14(c), the heating temperature of the slab S at the upper corners (X) could be increased at an earlier stage than in a configuration in which the magnetic shielding members were provided without being divided across the conveyance direction D (see Example 1). As a result, the slab S passed through the lower straightening zone at a temperature above the ductility reduction temperature, and no cracks were generated at the upper corners (X). Furthermore, the temperature at the positions (Y) near the coil long side portions 72c on the rolls 3 could be maintained at approximately the same level as in a configuration in which the magnetic shielding members were provided without being divided across the conveyance direction D (see Example 1), and damage due to thermal deformation could be prevented.

[0067] In Example 4, a magnetic shielding member 74c having an arc shape along the circumferential surface of the roll 3 was used in the conveying direction D of the slab S. FIG. 15 shows the temperature history of the slab S and the roll 3 from the heating start point. FIG. 15(a) is a perspective schematic diagram showing the configuration of the slab S, the roll 3, the magnetic shielding member 74c, and the heating coil 74a. FIG. 15(b) is a front schematic diagram showing the configuration of the slab S, the roll 3, the magnetic shielding member 74c, and the coil long side portion 74e and the coil long side portion 74f in the width direction W. FIG. 15(c) shows the temperature history of the upper corner portion (X) of the slab S and the position (Y) of the roll 3 near the coil long side portion 74e. The roll 3 in Example 4 was a normal roll without a non-magnetic material.

[0068] As shown in Figure 15(c), at the upper corners (X) of the slab S, the heating temperature of the slab S could be increased at an earlier stage than in a configuration in which the magnetic shielding members were provided without being divided across the conveyance direction D (see Example 1). As a result, the slab S passed through the lower straightening zone at a temperature above the ductility reduction temperature, and no cracks were generated at the upper corners (X). Furthermore, at the positions (Y) near the coil long side portions 74e on the rolls 3, the temperature could be maintained at approximately the same level as in a configuration in which the magnetic shielding members were provided without being divided across the conveyance direction D (see Example 1), and damage due to thermal deformation could be prevented. [Explanation of symbols]

[0069] 1 tundish 2. Mold 3, 8 rolls 3a Upper roll 3b Lower Roll 4 Cooling Zone 5 Upper orthodontic belt 6 Lower Correction Belt 7 Slab heating device 7a Heating coil 7b Long side of coil 7c Upper coil long side 7d Long side of lower coil 7e Short side of coil 7f Short side of upstream coil 7g Short side of downstream coil 7h Magnetic shielding material 7i Upper magnetic shielding member 7j Lower magnetic shielding member B Side part C Upper corner D Conveying direction E Vertical conveyance direction F Curved conveying direction G Horizontal transport direction H thickness direction M magnetic flux S slab T Molten steel W width direction

Claims

1. A slab heating device in a continuous casting facility in which a plurality of rolls that continuously convey a slab while restraining the slab are provided along a conveying direction of the slab, a heating coil provided to face a side surface of the slab; a magnetic shielding member provided between the roll and the heating coil in the thickness direction of the slab, the heating coil is a circuit that connects two long side portions of the coil extending in the transport direction and two short side portions of the coil extending in the thickness direction of the slab in the same plane, and is wound around the circuit, a magnetic shielding member having a relative magnetic permeability of 1000 or more at a frequency of an alternating current supplied from a power supply unit to the heating coil, and having an arc-shaped or cylindrical shape that follows the circumferential surface of the roll;

2. 2. The slab heating device according to claim 1, wherein the magnetic shielding member is a plate-shaped member, and the plate-shaped member is arranged so as to be perpendicular to the shortest line segment connecting the central axis of the roll and the long side portion of the heating coil.

3. 3. The slab heating device according to claim 2, wherein the magnetic shielding members include an upper magnetic shielding member that is provided so as to be perpendicular to the shortest line segment connecting a central axis of an upper roll of the rolls and an upper coil long side portion of the coil long side portion of the heating coil, and a lower magnetic shielding member that is provided so as to be perpendicular to the shortest line segment connecting a central axis of a lower roll of the rolls and a lower coil long side portion of the coil long side portion of the heating coil.

4. 4. The slab heating device according to claim 3, wherein the length of the magnetic shielding member along the width direction of the slab perpendicular to the conveying direction is equal to or greater than the coil diameter of the heating coil at the coil long side portion.

5. The slab heating device according to claim 3 , wherein the length of the magnetic shielding member along the conveying direction is equal to or greater than 0.7R where R is the diameter of the roll.

6. The slab heating device according to any one of claims 1 to 5, further comprising a carriage that adjusts the positions of the heating coil and the magnetic shielding member relative to the side surface of the slab in the width direction of the slab.

7. A continuous casting facility, comprising a slab heating device according to any one of claims 1 to 5, provided in a lower straightening zone.

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