Method and apparatus for induction heating of slabs

Abstract

To provide an induction heating method intended for the induction heating of a slab for a grain-oriented electrical steel sheet that prevents a temperature drop on the upper surface of the slab that comes into contact with a support device for preventing the slab from falling over.SOLUTION: While a roll pressed against the top surface of a slab for grain-oriented electrical steel sheets with the short side oriented vertically is being moved in the longitudinal direction, the slab is subjected to induction heating while preventing the slab from falling over.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an induction heating method for preventing a temperature drop of a slab on the upper surface of the slab that comes into contact with a support device for preventing the slab from tipping over, in induction heating of a slab for grain-oriented electrical steel sheet, and an induction heating device used in such a method. [Background technology]

[0002] As is generally known, the excellent magnetic properties of grain-oriented electrical steel sheets are due to the (110) plane on the sheet surface and the (110) plane in the rolling direction. <001> This is achieved by preferentially developing the secondary recrystallized grains in the shaft during final annealing. Therefore, it is important to uniformly disperse and precipitate fine precipitates called inhibitors, such as MnS, MnSe, and AlN, in the steel. The dispersion form of these inhibitors is controlled during the cooling process of hot rolling, after these precipitates are once dissolved during slab heating prior to hot rolling.

[0003] Slab heating for this purpose is usually carried out by placing the slab upright (with the short side facing vertically) in an induction heating furnace and heating it to a high temperature of 1300°C or higher in order to fully dissolve the inhibitor. Here, in the above-mentioned induction heating furnace, a support device (anti-tilt body) is required to be installed on the top surface of the slab to prevent the slab from tipping over, but there was a problem in that the temperature of the supported slab dropped where the support device came into contact with the slab (top surface of the slab).

[0004] In order to prevent such a drop in the temperature of the slab at the location where the support device on the top surface of the slab comes into contact with the slab, various methods have been proposed.

[0005] For example, Patent Document 1 proposes a method of individually driving a plurality of tilt prevention bodies to selectively separate tilt prevention bodies that come into contact with an object to be heated in sequence from the object to be heated.

[0006] Furthermore, Patent Document 2 proposes a method of supporting the upper side of a slab by alternately raising and lowering one or more slab upper surface support devices at a time. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 63-166933 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-273534 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the methods described in Patent Documents 1 and 2 still have the problem that they do not sufficiently prevent the temperature of the slab from dropping at the places where the support devices (tilt prevention bodies) on the top surface of the slab come into contact with the slab.

[0009] In other words, in an induction heating furnace for slabs, support devices, etc. that support the slab on the top surface of the slab are essential to prevent the slab from tipping over, but the temperature at the points where such support devices, etc. come into contact with the slab is lower than at points where they are not in contact.

[0010] Therefore, even if the slab support devices are alternately raised and lowered and replaced at regular intervals, the slab is stationary inside the induction heating furnace, so the support devices will be in contact with the same location on the slab for a certain period of time, and the above-mentioned problem related to temperature drop will not be resolved.

[0011] The present invention has been made to solve these problems, and aims to provide an induction heating method for induction heating slabs for grain-oriented electrical steel sheets, which prevents a drop in the temperature of the slab on the top surface where a support device for preventing the slab from tipping over comes into contact with the slab, and an induction heating device for use in such a method. [Means for solving the problem]

[0012] That is, the gist of the present invention is as follows. 1. A method of induction heating a slab for grain-oriented electromagnetic steel sheets with its short side oriented vertically, by moving a roll pressed against the top surface of the slab in the longitudinal direction while preventing the slab from tipping over.

[0013] 2. The method for induction heating according to 1 above, wherein the roll is a stepped roll in which the diameter is not uniform at least at the center and at the edge.

[0014] 3. The method for induction heating according to 1 or 2 above, wherein the roll is moved periodically.

[0015] 4. The method for induction heating according to any one of the above items 1 to 3, wherein the roll is moved at a speed of 0.1 m / s or more.

[0016] 5. An induction heating device having a furnace wall 4 that can accommodate a slab 1 for grain-oriented electrical steel plate with its short side oriented vertically and is equipped with an induction heating coil 5, a lifting hearth 3 that can be raised and lowered relative to the furnace wall 4, and a slab upper surface roll 2 that can roll along the upper surface of the slab 1 placed on the lifting hearth 3.

[0017] 6. The induction heating device according to 5 above, wherein the slab upper surface side roll 2 is a stepped roll having a non-uniform diameter at least at the center and at the edge. [Effects of the Invention]

[0018] According to the present invention, in induction heating of a slab for grain-oriented electrical steel sheet, a drop in the temperature of the slab can be effectively prevented at the location where the support device on the top surface of the slab comes into contact with the slab. It is also possible to obtain an apparatus having such a support device for the upper surface of the slab. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a diagram showing an induction heating device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view of the induction heating device shown in FIG. [Figure 3] 10A and 10B are diagrams illustrating another induction heating device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view of the induction heating device shown in FIG. [Figure 5] 1 is a graph showing the results (temperature deviation) of an example of the present invention and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing an induction heating device according to an embodiment of the present invention. Fig. 2 is a diagram showing a cross section of the induction heating device shown in Fig. 1. The induction heating device 11 in Figs. 1 and 2 can be applied to induction heating equipment provided on the outlet side of a gas heating furnace in a hot rolling line.

[0021] As shown in FIG. 1, the induction heating device 11 according to the present invention accommodates a slab 1 for grain-oriented electrical steel sheet with its short side oriented vertically and includes a furnace wall 4 equipped with an induction heating coil 5, a lifting hearth 3 that is movable up and down relative to the furnace wall 4, and a slab upper surface roll 2 that is rotatable along the upper surface of the slab 1 placed on the lifting hearth 3 and supports the upper surface of the slab. 3 and 4 denote objects, equipment, devices, etc. that are similar to the above-mentioned slab 1, slab upper surface side roll 2, lifting hearth 3, furnace wall 4, induction heating coil 5, and induction heating device 11, except for the shape of the slab upper surface side roll 2, which will be described later.

[0022] First, a slab for grain-oriented electrical steel sheets, heated in a gas heating furnace with its short sides horizontal, is turned to a right-side up position using a turning device. Next, the now-right-side slab 1 is placed on the lifting hearth 3, and the slab upper surface roll 2 is lowered to support the slab 1 by bringing the slab upper surface roll 2 into contact with the upper surface of the now-right-side slab 1. After that, the lifting hearth 3 and the slab upper surface roll 2 are raised while supporting the now-right-side slab 1, and the now-right-side slab 1 is placed inside the furnace wall 4.

[0023] The slab upper surface roll 2 and the lifting hearth 3 are preferably made of a material that has excellent resistance to compressive deformation and oxidation in high-temperature environments, such as KHR50CM (manufactured by Kubota Corporation) as a high-temperature compressive strength material and UMCo50 (manufactured by Hitachi Metals, Ltd.) as a heat-resistant alloy.

[0024] The slab upper surface roll 2 is a roll that can roll on the upper surface of the slab while supporting the slab, and is preferably a stepped roll in which the diameter is not uniform at least at the center and at the edge, as shown in Figures 3 and 4, in order to prevent the slab 1 from tipping over. Furthermore, it is more preferable that the diameter of the center of the roll is 100 mm or more and 300 mm or less, and the diameter of the roll edge is 300 mm or more and 500 mm or less.

[0025] The slab upper surface side roll 2 is a supporting device for the upper surface of the slab in the present invention. In the present invention, the roll central portion refers to a range of approximately 200 to 250 mm including the center of the roll and covering at least the thickness of the slab 1 to be induction heated. The roll edge portion refers to a range including the ends (leading and trailing ends) of the roll, excluding at least the roll central portion.

[0026] Thereafter, the induction heating coil 5 is energized to perform induction heating until the slab 1 reaches the target temperature, during which time the slab upper surface side roll 2 rotates and moves (rolls) in the longitudinal direction of the slab 1. By this movement, while the slab 1 is being heated, the location where the slab upper surface side roll 2 comes into contact with the slab 1 effectively changes on both the slab 1 side and the roll 2 side.

[0027] Here, it is preferable that the slab upper surface side roll 2 moves periodically, since this makes it possible to further uniformize the temperature distribution.

[0028] Furthermore, from the viewpoint of uniform temperature distribution, the moving speed of the slab upper surface side roll 2 is preferably fast, and is preferably 0.10 m / s or more. On the other hand, if the moving speed is too fast, the risk of the slab 1 tipping over increases. Therefore, the moving speed is preferably 1.00 m / s or less.

[0029] After the slab 1 reaches the target temperature, the movement of the slab upper surface roll 2 is stopped, and the lifting hearth 3 and the slab upper surface roll 2 are simultaneously lowered to extract the slab 1 outside the furnace wall 4. After the slab 1 is transferred to the turning device, the slab upper surface roll 2 is raised to the standby position. After that, the width direction of the slab 1 is returned to a horizontal orientation using the turning device, and the slab is transported to the subsequent rolling line where rolling is carried out.

[0030] The embodiment of the present invention is not limited to the example of heating a slab for a grain-oriented electrical steel sheet, but can be applied to heating any metal sheet other than a steel sheet, as long as it is a metal sheet that can be heated by an induction heating device.

[0031] In the induction heating method and induction heating device according to the present invention, any items not described in this specification can be performed using conventional methods and known equipment. [Example]

[0032] An embodiment of the present invention will now be described. Inventive Example 1 used an induction heating device according to the embodiment of the present invention shown in Figures 1 and 2, and in Inventive Examples 2, 3, and 4, induction heating devices according to the embodiment of the present invention shown in Figures 3 and 4 were used. In each case, a steel slab measuring 1000 mm wide x 230 mm thick x 10000 mm long was heated until the center of the slab width reached 1420°C. The central part of the slab width means the surface of the slab with a diameter of 2 mm, centered at a position where the slab width is 500 mm and the length is 5000 mm.

[0033] The roll of the slab upper surface supporting device used in Inventive Example 1 moved at a speed of 0.05 m / s, and moved intermittently, repeating a 1 second movement followed by a 1 second pause.

[0034] The roll of the slab upper surface supporting device used in Inventive Example 2 moved at a speed of 0.05 m / s, and moved intermittently, repeating a 1 second movement followed by a 1 second pause.

[0035] The roll of the slab upper surface supporting device used in Inventive Example 3 moved at a speed of 0.05 m / s, and was periodically moved repeatedly from one end of the slab upper surface to the other.

[0036] The roll of the slab upper surface supporting device used in Inventive Example 4 moved at a speed of 0.10 m / s, and repeatedly and periodically moved from one end of the slab upper surface to the other.

[0037] In contrast, as Comparative Example 1, a steel slab was heated using the induction heating device described in Patent Document 1, with the other conditions being the same as those in Example 1 of the present invention.

[0038] In Comparative Example 2, a steel slab was heated using the induction heating device described in Patent Document 2, with the other conditions being the same as those in Inventive Example 1.

[0039] Then, the temperature deviation on the top surface of the steel slab after heating was investigated for each case (Inventive Examples 1 to 4, Comparative Examples 1 and 2). The results for the Inventive Examples and Comparative Examples are shown in FIG. The temperature deviation was investigated by using a thermography camera (GF309 manufactured by FLIR) to measure the temperature distribution over the entire top surface of the steel slab after heating, and calculating the temperature deviation (the difference between the maximum and minimum temperatures).

[0040] As shown in FIG. 5, it can be seen that in all of the invention examples 1 to 4, the temperature deviation is smaller than in the comparative examples 1 and 2. This confirms the effectiveness of the present invention. It is also clear that the temperature deviation is further reduced by satisfying the preferred requirements of the present invention. [Explanation of symbols]

[0041] 1. Grain-oriented electrical steel slabs 2 Slab top side roll 3 Elevating hearth 4 Furnace wall 5 induction heating coil 11 Induction heating device

Claims

1. A method for induction heating a slab for grain-oriented electromagnetic steel sheets, with the short side oriented vertically, by moving a roll pressed against the upper surface of the slab in the longitudinal direction while preventing the slab from tipping over.

2. 2. The method for performing induction heating according to claim 1, wherein the roll is a stepped roll having a non-uniform diameter at least at the center and at the edge.

3. 3. The method for induction heating according to claim 1, wherein the rolls are moved periodically.

4. 3. The method for induction heating according to claim 1, wherein the roll is moved at a speed of 0.1 m / s or more.

5. 4. The method for performing induction heating according to claim 3, wherein the periodic movement is performed at a speed of 0.1 m / s or greater.

6. An induction heating device comprising: a furnace wall 4 that accommodates a slab 1 for grain-oriented electrical steel sheet with its short side oriented vertically and is equipped with an induction heating coil 5; a lifting hearth 3 that is arranged so as to be able to rise and fall relative to the furnace wall 4; and a slab upper surface side roll 2 that is arranged so as to be able to roll along the upper surface of the slab 1 placed on the lifting hearth 3.

7. 7. The induction heating device according to claim 6, wherein the slab upper surface side roll (2) is a stepped roll having a non-uniform diameter at least at the center and at the edge portions.

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