JP7764877B2 - Method and apparatus for induction heating of slabs - Google Patents

Description

The present invention relates to an induction heating method for induction heating slabs for grain-oriented electrical steel sheets that prevents a drop in the temperature of the slab on the top surface that comes into contact with a support device for preventing the slab from tipping over, and an induction heating device used in this method.

As is generally known, the excellent magnetic properties of grain-oriented electrical steel sheets are obtained by preferentially developing secondary recrystallized grains with (110) planes on the sheet surface and <001> axes in the rolling direction 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, and the dispersion form of these inhibitors is controlled during the cooling process during hot rolling, after these precipitates are once dissolved during slab heating prior to hot rolling.

Slab heating for this purpose is usually carried out by heating the slab upright (with the short side facing vertically) in an induction heating furnace 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 that the temperature of the supported slab would drop at the location where the support device came into contact with the slab (top surface of the slab).

Various methods have been proposed to prevent the temperature of the slab from dropping where the support device on the top surface of the slab comes into contact with the slab.

For example, Patent Document 1 proposes a method of individually driving multiple tilt prevention bodies to selectively separate the tilt prevention bodies that come into contact with the object to be heated from the object.

Patent Document 2 also proposes a method of supporting the upper surface of a slab by alternately raising and lowering slab top surface support devices one by one or multiple by one.

Japanese Unexamined Patent Publication No. 166933/1983 Japanese Patent Application Laid-Open No. 2000-273534

However, the methods described in Patent Documents 1 and 2 still have the problem of insufficient prevention of a drop in the temperature of the slab where the support device (tilt prevention device) on the top surface of the slab comes into contact with the slab.

In other words, in induction heating furnaces for slabs, support devices that support the slab on top of the slab are essential to prevent the slab from tipping over, but the temperature in areas where such support devices come into contact with the slab drops compared to areas that are not in contact.

Therefore, even if the slab support devices are alternately raised and lowered at regular intervals, the slab remains stationary inside the induction heating furnace, so the support devices come into contact with the same location on the slab for a certain period of time, and the above-mentioned problem of temperature drop is not resolved.

The present invention was made to solve these problems, and aims to provide an induction heating method for induction heating slabs for grain-oriented electrical steel sheets that prevents a drop in the temperature of the slab on the top surface where a support device, etc., used to prevent the slab from tipping over comes into contact with the slab, and an induction heating device for use in this method.

That is, the gist of the present invention is as follows.
1. A method of induction heating a slab for grain-oriented electrical steel sheets with its short sides 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.

2. The induction heating method described in 1 above, wherein the roll is a stepped roll in which the diameter is not uniform at least at the center and edge portions.

3. The induction heating method described in 1 or 2 above, in which the roll is moved periodically.

4. The induction heating method described in any one of items 1 to 3, wherein the roll moves at a speed of 0.1 m/s or more.

5. An induction heating device that accommodates a slab 1 for grain-oriented electrical steel sheet with its short side oriented vertically and has 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 movable along the top surface of the slab 1 placed on the lifting hearth 3.

6. The induction heating device described in 5 above, wherein the slab upper surface roll 2 is a stepped roll in which the diameter is not uniform at least in the center and edge portions.

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.

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

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 shown 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.

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 provided 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 provided so as to be able to roll along the upper surface of the slab 1 placed on the lifting hearth 3 and that 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.

First, a slab for grain-oriented electrical steel sheets, heated in a gas heating furnace with its short sides horizontal, is turned so that its short sides are in a straight orientation using a turning device. Next, the now-straight 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-straight slab 1. The lifting hearth 3 and slab upper surface roll 2 are then raised while supporting the now-straight slab 1, and the now-straight slab 1 is placed inside the furnace wall 4.

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. Examples include KHR50CM (manufactured by Kubota Corporation) as a high-temperature compressive strength material and UMCo50 (manufactured by Hitachi Metals, Ltd.) as a heat-resistant alloy.

The slab upper surface roll 2 is a roll that can roll on the upper surface of the slab while supporting the slab. To prevent the slab 1 from tipping over, it is desirable that it be a stepped roll with a non-uniform diameter at least at the center and edge portions, as shown in Figures 3 and 4. Furthermore, it is even more desirable for such a roll to have a diameter of 100 mm or more and 300 mm or less at the center and a diameter of 300 mm or more and 500 mm or less at the edge portions.

The slab upper surface side roll 2 is a support device for the upper surface of the slab in the present invention.
In the present invention, the central part of the roll refers to a range of about 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 edge part of the roll refers to a range including the ends (leading and trailing ends) of the roll, excluding at least the central part of the roll.

Then, current is passed through the induction heating coil 5 to perform induction heating until the slab 1 reaches the target temperature. During this time, the slab upper surface roll 2 rotates and moves (rolls) in the longitudinal direction of the slab 1. By moving in this manner, the location where the slab upper surface roll 2 comes into contact with the slab 1 effectively changes on both the slab 1 side and the roll 2 side while the slab 1 is being heated.

Here, it is preferable that the slab upper surface roll 2 moves periodically, as this allows for a more uniform temperature distribution.

Furthermore, from the viewpoint of uniform temperature distribution, it is preferable that the movement speed of the slab upper surface roll 2 is fast, preferably 0.10 m/s or more. On the other hand, if this movement speed is too fast, the risk of the slab 1 tipping over increases. Therefore, this speed is preferably 1.00 m/s or less.

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 lowered simultaneously to extract the slab 1 outside the furnace wall 4. The slab 1 is then transferred to the turning device, and the slab upper surface roll 2 is then raised to its standby position. The turning device is then used to return the width of the slab 1 to a horizontal orientation, and the slab is then transported to the subsequent rolling line where rolling is carried out.

Note that the embodiments of the present invention are not limited to heating slabs for grain-oriented electrical steel sheets, but can be applied to heating any metal sheet other than steel sheets, as long as it is a metal sheet that can be heated by an induction heating device.

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

An embodiment of the present invention will now be described.
Inventive Example 1 used the 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, the induction heating device according to the embodiment of the present invention shown in Figures 3 and 4. In each example, a steel slab measuring 1000 mm wide x 230 mm thick x 10000 mm long was heated until the temperature of 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.

The roll movement speed of the slab top surface support device used in Example 1 of the present invention was 0.05 m/s, and it moved intermittently, moving for 1 second and then stopping for 1 second.

The roll movement speed of the slab top surface support device used in Example 2 of the present invention was 0.05 m/s, and it moved intermittently, moving for 1 second and then stopping for 1 second.

The roll movement speed of the slab top surface support device used in Example 3 of the present invention was 0.05 m/s, and it repeatedly and periodically moved from one end of the slab top surface to the other.

The roll movement speed of the slab top surface support device used in Example 4 of the present invention was 0.10 m/s, and it repeatedly and periodically moved from one end of the slab top surface to the other.

In contrast, in 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.

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 Example 1 of the present invention.

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 measuring the temperature distribution over the entire upper surface of the heated steel slab using a thermography camera (GF309 manufactured by FLIR) and calculating the temperature deviation (the difference between the maximum and minimum temperatures).

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.

REFERENCE SIGNS LIST 1 Slab for grain-oriented electrical steel sheet 2 Slab upper surface roll 3 Elevating hearth 4 Furnace wall 5 Induction heating coil 11 Induction heating device

Claims (7)

A method of induction heating a slab for grain-oriented electrical steel sheets with its short sides 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. The induction heating method according to claim 1, wherein the roll is a stepped roll in which the diameter is not uniform at least at the center and edge portions. The induction heating method according to claim 1 or 2, wherein the roll is moved periodically. The induction heating method according to claim 1 or 2, wherein the roll is moved at a speed of 0.1 m/s or more. The induction heating method according to claim 3, wherein the periodic movement is at a speed of 0.1 m/s or greater. An induction heating device that accommodates a slab 1 for grain-oriented electrical steel sheet with its short side oriented vertically and has a furnace wall 4 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 top surface of the slab 1 placed on the lifting hearth 3. The induction heating device described in claim 6, wherein the slab upper surface roll 2 is a stepped roll whose diameter is not uniform at least at the center and edge portions.