JPH0215813A - Method for heating hot sheet bar - Google Patents

Abstract

PURPOSE:To improve the quality of vicinities of length direction ends and the product yield of a sheet bar by installing induction heaters at upper and lower positions of the sheet bar and heating vicinities of the length direction ends of a stopped sheet bar through a high frequency electric source. CONSTITUTION:Upper and lower induction heaters 6 having magnetic poles 62 are installed for a hot sheet bar 3, respectively. The heaters 6 are connected to a high frequency electric source 27 and a driving device 22. At the time of arrival of the top part of the bar 3 at a top part detector 25, a controller 21 detects the arrival and the heaters 6 are separated from each other to avoid generation of cambers of the bar 3. Then, the bar 3 is stopped in a project area of the downstream side magnetic poles 62, an output of the source 27 is controlled, and the heaters 6 are shifted in the width direction of the bar 3. Hence, generation of material defects in vicinities of the length direction ends of the bar 3 is prevented. The quality and yield are improved because a discarding area at ends is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a hot sheet bar heating method for heating the width direction end portion and longitudinal direction end portion of a hot sheet bar being conveyed.

[Conventional technology]

To explain the conventional method of rolling a hot sheet bar in copper strip rolling, in hot rolling, a heated slab with a thickness of 120 to 300 nm is rolled by a rough rolling mill to a thickness of 15 to 60 mm. Rolled into a thick sinitbar,
This is further rolled using a finishing mill until the required product thickness is achieved.

Here, as shown in FIG. 10, the hot sheet bar rolled by the rough rolling mill 1 is transferred to the rolling mill 4 by conveying table rollers 5, and the longitudinal ends (tip, rear) of the sheet bar are edges) are sheared. Next, seat bar 3
The sheet bar 3 is transferred to a high-pressure injection type scaling device 11 having a nozzle 8 for removing surface descaling, and then finished rolled by a finishing mill 2.

During the processing steps from rough rolling to finish rolling, part of the heat held by the hot sheet bar is dissipated into the atmosphere. This amount of heat dissipated increases in proportion to the distance from the end, so there is a difference in the amount of heat dissipated into the atmosphere between the widthwise ends and the center of the hot sheet bar, and the temperature of the hot sheet bar increases. The side edges in the width direction are lower in temperature than the center portion in the width direction. For this reason, there was a problem in that material defects occurred at the side edges, and the quality of the finish-rolled product deteriorated.

Therefore, in order to solve this problem, as shown in FIG. 10, edge heaters 10 are installed to compensate for the temperature drop at both ends of the sheet bar 3, and the edge portions of the hot sheet bar are heated. It has been proposed to compensate for the temperature drop at the edge by increasing the temperature locally (e.g., "Tetsu to Hagane" Vol. 7).
2 (1986) No. 2, pp. 177-178).

As shown in FIG. 10, in this edge heater, a plurality of pairs of upper and lower induction heating coils IOA are connected to a hot sheet bar 3.
It is installed at both edges. Each pair of upper and lower induction heating coils IOA has a mechanism that follows the position corresponding to the edge portion of the hot sheet bar 3 even if the width of the hot sheet bar 3 changes.

Normally, induction heating devices for edge heaters are of the transbar flux type, in which alternating magnetic flux is passed through the plate in the thickness direction, and eddy currents are caused to flow interlinked with the alternating magnetic flux, and these eddy currents are concentrated at the edges. Utilizing this characteristic, only the edge portions are heated intensively and efficiently.

As described above, in the conventional example described above, edge heaters are used to prevent uneven temperature distribution in the width direction of the hot sheet bar 3 between the rough rolling mill 1 and the finishing mill 2. .

[Problem to be solved by the invention]

However, the inventors of the present invention have conducted extensive studies and found that heat dissipation from the seat bar occurs not only at the widthwise ends but also at the longitudinal ends (leading and trailing ends) of the seat bar, resulting in various problems. I found out that

That is, the first problem is that the material at the front and rear ends of the seat bar is defective. The finish rolling temperature is usually Ar, and the operation is carried out to complete rolling at a temperature higher than the transformation point. However, in the above-mentioned conventional sheet bar rolling method, the local temperature drop at the leading and trailing ends of the sheet bar is below the Ar3 point, causing abnormal growth of crystal grains, so-called grain gloss. As a result,
In addition to reducing the workability of the product, it also reduces the cold rolling properties, which are often carried out in succession to hot rolling in recent years.

The second problem mentioned above is roll flaws. In sheet bars made of steel with high deformation resistance, if the above-mentioned material defects occur, the rolls will be plastically deformed when the tip of the sheet bar is bitten by a finishing mill. For this reason, roll flaws may be transferred to the product surface, which may become surface defects and result in defective products. Therefore, it becomes necessary to suddenly replace the rolls, which lowers the operating rate.

In order to prevent the above-mentioned problem, the longitudinal ends of the sheet bar, that is, the front and rear ends must be cut off using a crop shear, but this poses a problem in that the yield of the product decreases.

In order to solve this problem, it is sufficient to heat the longitudinal ends of the seat bar. In this case, if an edge heater installed upstream of the crop shear is used to heat the longitudinal end of the sheet bar before crop cutting, eddy currents will concentrate at the longitudinal end of the sheet bar.
It is conceivable that only the crop portion cut off by the crop shear is heated intensively.

Therefore, it is possible to install an induction heating device on the output side of the crop shear to heat the longitudinal end of the sheet bar after cutting the crop, but the high pressure water from the descaling device is directly applied to the output side of the crop shear. This is an unsuitable environment for installing an induction heating device because it is located in a position where water flows into the pipe.

Therefore, in order to solve these problems, the present invention improves the yield by preventing material defects at the longitudinal ends of the sheet bar, and improves the operating rate by preventing the occurrence of roll defects. Furthermore, it is an object of the present invention to provide a heating method for a hot sheet bar that has good thermal efficiency since no wasteful heat is input from the crop cut-off portion.

[Means to solve the problem]

In order to achieve the above object, the hot sheet bar heating method according to the present invention includes the steps of heating the hot sheet bar by induction heating the widthwise side ends of the hot sheet bar before hot finish rolling. arranged in the longitudinal direction of the hot sheet bar,
An induction heating device having at least two magnetic poles is disposed oppositely above and below the sheet bar, and when the longitudinal end of the sheet bar reaches the projected cross section of the magnetic pole, the conveyance of the sheet bar is controlled. The invention is characterized in that the sheet bar is heated at its longitudinal ends by applying a high frequency power source to the heating coil of the induction heating device.

[Effect]

According to the method for heating a hot sheet bar according to the present invention,
Before finish rolling, not only the edges but also the longitudinal ends of the sheet bar are heated, which can compensate for the temperature drop in this area, preventing abnormal growth of grains, and as a result, reducing the temperature at the longitudinal ends of the sheet bar. No material defects occur. Therefore, compared to the conventional hot sheet bar heating method, it is possible to improve the yield while improving the workability and cold rollability of the product.

Further, as a result of preventing material defects, the roll is not plastically deformed when the tip of the sheet bar made of a steel with high deformation resistance is bitten by the roll, so it is possible to prevent flaws from occurring in the roll.

Further, according to the present invention, since the longitudinal end of the seat bar is stopped within the magnetic pole projection cross section, eddy current concentration does not occur at the end of the seat bar, and as a result, the end of the seat bar is locally There is no heating, and no unnecessary heat is input to the crop cutting section. In other words, the eddy current concentrates between the two magnetic poles arranged in parallel in the longitudinal direction of the hot sheet bar, and the degree of heating is strong, so when heating the tip of the sheet bar, If the rear end of the sheet bar is heated by stopping within the projected cross section of the magnetic pole on the downstream side in the conveyance direction, the rear end of the sheet bar is stopped within the projected cross section of the magnetic pole on the upstream side. Except for the longitudinal ends of the seat bar can be heated. As a result, the thermal efficiency is improved, and even if the sheet bar is cut by the crop shear, the cut portion is sufficiently heated, so that the temperature drop at the longitudinal end portion can be compensated for.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of an apparatus for carrying out the method of the present invention, and FIG. 1 (1) is a perspective view thereof;
2) is its front view. In this embodiment, instead of the edge heater 10 shown in FIG. Two units are installed parallel to each other.

As shown in FIG. 1, this induction heating device 6 has a coil 6
1 and a magnetic pole 62. This induction heating device 6 is configured as a pair of upper and lower parts facing the seat bar 3.

This magnetic pole is further movable in parallel to the width direction of the seat bar 3, as shown in the front view of FIG. 1(2). The magnetic flux penetrates the sheet bar 3 in the thickness direction, and an eddy current is generated in the sheet bar 3. Furthermore,
The induction heating device 6 can adjust the movement position of the seat bar 3 in the width direction.

FIG. 2 is a plan view showing a state in which eddy currents are generated on the surface of the seat bar 3 due to induction heating.

In this way, eddy currents are generated around the magnetic poles 62, and the density of eddy currents is highest between the magnetic poles 62. Normally, the density of eddy currents is concentrated at the end of the sheet bar, but In the invention, since the end portion is stopped within the projected cross section of the magnetic pole on the downstream side in the conveyance direction, eddy currents do not concentrate on the end portion.Therefore, as shown in the plan view of the sheet bar 3 in FIG. By moving the induction heating device 6 in the width direction of the seat bar 3 as shown in FIG. 3 (70), that is, as shown in FIG. 2, the leading edge in the conveying direction of the sheet bar 3 is stopped within the projected cross section of the magnetic pole 62 on the conveying direction side, that is, on the downstream side, and the sheet bar 3 is guided as shown in FIG. 1 (2). By moving the heating device in the width direction of the sheet bar 3, it is possible to heat the tip of the sheet bar 3 (70), except for the part (71) that is cut by the crop shear, as shown in FIG. .

For this reason, the part that would normally be cut with a crop shear (the third
With the exception of FIG. 71), the tip of the sheet bar 3 can be heated, so the thermal efficiency is improved accordingly.

Note that after the end of the sheet bar 3 is heated, the first
If the induction heating device 6 shown in FIG. 1 is moved to the side edge of the sheet par 3 and the sheet bar is continuously conveyed, the heating of the sheet bar edge portion can be continued accordingly. In this case, the induction heating device 6 is 9 usually 1. It is similar to that used for edge heaters, and can also be used as an edge heater, reducing equipment costs.

Next, a block diagram of the apparatus according to the embodiment of the present invention explained in FIG. 1 above will be described with reference to FIG. 4.

FIG. 4 is a side view of the rolling equipment, and to explain its configuration, the induction heating device 6 is connected to a high frequency power source 27 for applying a high frequency power source. Furthermore, a drive device 22 for moving the induction heating device 6 in the width direction of the seat bar 3 is connected to the induction heating device 6 . These drive device 22 and high frequency power source 27 are connected to the controller 21.

On the upstream side of the induction heating device 6, a tip detector 25 for detecting passage of the tip of the seat bar 3 and a temperature sensor 26 for detecting the temperature of the seat bar 3 are provided. 26 is connected to the controller 21 mentioned above.

Furthermore, a measuring roll 23 for measuring the amount of movement of the sheet bar 3 is connected to one of the transport rollers 5, and a measuring roll 23 for measuring the movement speed of the sheet bar 3 is connected to one of the transport rollers 5. Pulse generator 2 that generates pulses of
4 is provided.

These measuring rolls 23 and speed detector 24 are connected to the controller 21.

The controller 21 is configured by a microcomputer, for example, and has an interface (not shown).
A target temperature value to be raised by the induction heating device 6 can be set by connecting a temperature setting circuit (not shown).

The overall configuration of the induction heating device used in this example will be explained using the side view of FIG. 5. The induction heating devices 6 shown in FIG. 1 are arranged in an upper and lower pair (6A, 6B) facing the seat bar 3, and the upper induction heating device 6A is fixed to the tip of the upper support arm 31A. Furthermore, a lower induction heating device 6B is fixed to the tip of the lower support arm 31B. This pair of upper and lower support arms 31A, 31B
is swingably fixed to the left end of the support base 38 of the trolley 32. An opening/closing cylinder 35 is fixed to the right side of the upper support arm 31A, and the lower support arm 3
Similarly, an opening/closing cylinder 36 is fixed to the right end of 1B. 33 is a rail formed perpendicular to the rolling line, and 34 is a wheel for moving the cart 32 along the rail. In addition, 40 is a bearing of the conveyance roller 5.

Support arm 31A of the induction heating device shown in FIG.

31B is formed to be larger than the seat bar width in order to move the induction heating device 6A6B provided at the left end to the other end of the seat bar 3 in the width direction. The induction heating device shown in FIG. 5 can be moved on the rail 33 at right angles to the direction in which the sheet bar 3 is conveyed. That is,
The induction heating device 6A extends to the widthwise center of the seat bar 3.
When moving the induction heating device 6B, it is possible to move these induction heating devices across the width direction of the seat bar by running on the rail 33 at a distance greater than the width of the seat bar. Note that if the seat bar 3 is warped, there is a risk of destroying the induction heating device, so by driving the opening/closing cylinders 35 and 36, the support arm 31A
, 31B can swing around the support shaft 39.

Next, the operation of the embodiment shown in FIG. 4 will be explained.

In FIG. 4, the sheet bar 3 is conveyed toward the right side of the drawing, and the tip of the sheet bar 3 is detected by the tip detector 2.
5 (consisting of an infrared sensor, for example), the detector 25 detects the infrared rays of the sheet bar 3 and sends a signal of logical value "1" indicating that the tip of the sheet bar 3 has arrived to the controller. Output to 21.

Next, the temperature sensor 26 starts temperature detection, detects the temperature at the tip of the seat bar 3, and sends this detected signal to the controller 21. Note that as the temperature sensor, for example, an infrared thermometer can be used. When the controller 21 detects the tip of the sheet bar 3 based on a signal from the detector 25, the controller 21 starts the induction heating device so that the upper and lower pairs of induction heating coils are not damaged due to the warping of the tip of the hot sheet bar 3. 6A and 6B are moved in a direction away from each other.

The controller 21 can detect the amount of movement of the sheet bar 3 based on the signal from the measuring roll 23. Therefore, by storing the distance from the tip detector 25 to the induction heating device 6 in advance in the storage device of the controller 21, the time when the tip of the seat bar 3 reaches the induction heating device 6 can be detected. be able to.

As shown in FIG. 1 (1), when the leading edge of the seat bar 3 reaches the projected cross section of the downstream magnetic pole 62 of the induction heating device 6, the controller 21 sends a signal to a moving device for the seat bar 3 (not shown). The tip of the seat bar 3 is stopped within the projected cross section of the magnetic pole 62 on the downstream side.

Next, the controller 21 calculates the difference between the temperature at the tip of the seat bar 3 measured by the temperature sensor 26 and the target temperature (preset in the controller with a setting device), and this difference becomes zero. In addition, the thickness of the seat bar and
The output of the frequency accumulating power source 27 is controlled based on the detected speed value of the seat bar 3 detected by the detector 24.

At this time, the induction heating device 6 is moved across the width direction of the seat bar 3, as shown in FIG. 1(2).

As a result, as shown in FIG. 3, the tip portion 70 of the seat bar 3 excluding the portion 71 cut by the crop shear is heated over the entire width direction. Therefore, it is possible to compensate for the temperature drop at the tip of the seat bar.

In the above embodiment, the seat bar 3 is stopped within the projected cross section of the downstream magnetic pole;
A case where the vehicle decelerates extremely within the projected cross section of 2 is also included in the concept of stopping.

The induction heating coil generates an induced current in the sheet bar 3 to heat it. The capacity of the induction heating coil can be made smaller as the expected amount of warpage (tolerance) of the tip of the seat bar 3 is smaller. It is necessary to use an induction heating coil.

In the above embodiment, the induction heating device 6 is used for edge heating and for heating the leading and trailing ends, but a separate edge heater may be provided.

The induction heating device 6 and edge heater 10 heat the seat bar 3 by generating an induced current therein.

Note that the capacity of the heating coil in the induction heating device 6 and the edge heater IO can be made smaller as the expected amount of warpage (tolerance M) of the tip of the seat bar 3 is smaller. In this case, it is necessary to use a large-capacity induction heating coil.

Next, the rear end of the seat bar 3 is heated in the same manner as the front end. At this time, it is necessary to detect the rear end of the seat bar 3, but this is done after the tip detector 25 no longer detects the infrared rays of the seat bar and the logical value becomes "O". Sheet bar 3 with measuring roll 23"
This can be easily done by measuring the amount of movement. Regarding the stopping position of the rear end of the seat bar, when the rear end of the seat bar reaches the projected cross section of the induction heating coil 61 on the upstream side, conveyance of the seat bar 3 is stopped and heating is performed.

Note that after the hot sheet bar 3 passes through the induction heating coil, the edge portion is heated by narrowing the induction heating coil, so that the heating efficiency is significantly increased.

A pinch roller can be provided upstream of the induction heating device shown in FIG. 1 to correct the warpage of the tip of the sheet bar 3. By correcting the warpage and flattening the tip of the sheet bar 3 by the pinch roller, the upper induction heating device 6A and the lower induction heating device 6B of the induction heating device 6 set a small gap with the sheet bar 3 passing through. be able to. Therefore, the capacity of these heating coils can be significantly reduced to reduce equipment costs. Further, there is no need to make the heating coil a movable type that moves vertically toward the seat bar 3.

Next, specific examples will be described. FIG. 6 is a graph showing the amount of temperature drop at the longitudinal end of a sheet bar at 1050° C. that was rough rolled in a hot rough rolling mill.

The graphs in Figures 5(A) and (C) show the amount of temperature drop at the tip of the seat bar, and the graphs in Figure 5(B) show the amount of temperature drop at the tip of the seat bar.
) and (D) are graphs showing the amount of temperature drop at the rear end of the seat bar. Furthermore, FIGS. 5(A) and (B)
) is the case where only the edge portion of the sheet bar is heated, and the graphs (C) and (D) are the case where the first
4 is a graph when both the edge portion and the leading and trailing end portions of the sheet bar are heated based on the apparatus shown in FIGS. At this time, the output of the induction heating device was 1150 W, and the induction heating device was moved at a speed of 350+u/s in the width direction of the sheet bar. In addition, in FIG. 6, FET indicates the temperature on the inlet side of the finishing rolling mill, and FDT indicates the temperature on the exiting side of the finishing rolling mill.

The sheet bar thickness used in this example was 40 mm, the plate width was 1000 mm, and the thickness of the product finish rolled by the finish rolling mill was 2 fl.

Normally, when the temperature drop at the longitudinal end of the sheet bar exceeds 30°C, material defects due to grain gloss usually occur in that part. Therefore, as shown in Figure 6(A), the material defect area at the tip of the seat bar is 5 m (
Product equivalent length (the same applies hereinafter)). Further, as shown in FIG. 6(B), the material defective portion at the rear end of the seat bar extends to 2 m. On the other hand, when the temperature is increased by 40°C at the tip of the sheet bar as shown in FIG. 6(C), the number of defective materials decreases to within 2 m from the tip. Further, as shown in FIG. 6(D), the defective material portion at the rear end of the seat bar is reduced to within a range of 1 m. Therefore, by raising the temperature of the longitudinal end of the sheet bar by 40°C, in the case of a general low carbon material with a length of 1000 m in the longitudinal direction, in a conventional example in which the longitudinal end of the sheet bar is not heated, in a crop shear, the tip end of the sheet bar is heated. 5m and 2m at the rear end were cut off, but by heating the front and rear end of the sheet bar, the truncated part at the front end was a defective part that was cut by a conventional crop shear.2
m, and the amount of truncation at the rear end is similarly 1 m.
decreases to As a result, per 1000 m of seat bar, the amount of cut-off at the leading end is reduced by 3 m, and the amount of cut-off is reduced by 1 m at the rear end, resulting in a 0.4% improvement in walking distance and a significant cost reduction. Connect.

Further, even when a sheet bar made of a steel with high deformation resistance and having the leading and trailing ends of the sheet bar heated to 40° C. was bitten into a finishing roll 100 times, no flaws were generated in the roll. On the other hand, when a sheet bar made of a steel with high deformation resistance was bitten into a finishing roll 20 times based on a conventional example in which the leading and trailing ends were not heated, it was confirmed that flaws occurred in the roll. Ta.

As can be seen from this specific example, the heating area at the longitudinal end of the sheet bar is approximately 200 f at the tip.
It can be seen that it is sufficient to heat a width of a little more than i (sheet bar equivalent length), and a width of about 100 n or more (sheet bar equivalent length) at the rear end. However, this does not preclude heating a wider area.

As explained above, according to this embodiment, 1. Material defects at the longitudinal ends of the sheet bar are prevented, and as a result, the yield is improved and the rolls are prevented from being scratched. Furthermore, the tip end of the sheet bar can be sufficiently heated without heating the portion cut off by the crop shear, improving thermal efficiency.

In the above embodiment, as shown in FIG. 1, a pair of upper and lower induction heating devices are disposed so as to be movable across the width direction of the seat bar 3, but the arrangement is not limited thereto. It is also possible to arrange two pairs of induction heating devices 6 in parallel to the edge portion of the seat bar 3 in the width direction. At this time, the induction heating device 6 shown in FIG. 7 is configured to be movable across the width direction of the seat bar 3, similar to the induction heating device R6 shown in FIG.

Further, as shown in the front view of FIG. 8, induction heating devices 6 having magnetic poles 62 equal to the width of the seat bar 3 can be arranged above and below the seat bar 3 as a pair.

Furthermore, as shown in the side view of FIG. 9, induction heating devices 6 having four magnetic poles can be arranged in pairs above and below the seat bar 3. At this time, the sheet bar 3 is stopped so that the leading edge of the sheet bar 3 is within the projected cross section (80) of the magnetic pole on the downstream side of the sheet bar 3 in the conveying direction. be.

In the above embodiment, the arrival of the tip of the seat bar is detected by an infrared sensor, but the present invention is not limited to this, and other optical sensors can also be used.

Further, in the above embodiment, the rear end of the seat bar is detected based on a distance tracking method using a microcomputer, but the rear end of the seat bar can be detected using another optical sensor.

Furthermore, in this embodiment, both the tip and rear ends of the sheet bar are heated, but the distance from the heating device to the finishing mill is short, and when the rear end reaches the heating device, the tip of the sheet bar is heated. If the sheet bar is caught in the finishing mill, it is not possible to stop the sheet bar, so from the standpoint of preventing roll flaws and improving the yield to some extent, the sheet bar is It is also possible to heat only the leading end and not the rear end.

〔Effect of the invention〕

As explained above, according to the method for heating a hot sheet bar according to the present invention, not only the edges of the hot sheet bar but also the longitudinal ends are heated, so that the grain gloss at the longitudinal ends is reduced. As a result, the occurrence of material defects in such portions can be avoided. Therefore, the area where the front and rear ends of the seat bar are cut off is significantly reduced, and as a result, walking performance is improved. In addition, sheet bars made of steel with high deformation resistance can prevent the occurrence of roll flaws, and as a result, it is possible to avoid sudden roll replacements and improve operating efficiency.

Furthermore, according to the present invention, the longitudinal end portions of the sheet bar can be sufficiently heated without heating the portions to be cut by the cutter, thereby improving thermal efficiency.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of an induction heating device, in which (1) is a perspective view, (2) is a front view, and FIG. FIG. 3 is a plan view showing the heating state of the seat bar, FIG. 4 is a block diagram for carrying out the heating method according to the present invention, and FIG. 5 is a side view showing the overall configuration of the induction heating device.
Figure 6 is a graph showing the relationship between sheet bar conversion length or product conversion length and temperature drop, Figures 7, 8, and 9.
The figures show other embodiments of the arrangement of the induction heating device, in which FIG. 7 is a front view, FIG. 8 is a plan view thereof, FIG. 9 is a side view thereof, and FIG. 10 is a conventional heating device. FIG. 3 is a side view of the rolling equipment. In the figure, 1 is a hot rough rolling mill, 2 is a finishing mill, 3 is a hot sheet bar, 5 is a conveyance roller, 6 is an induction heating device, 10 is an edge heater, 21 is a controller, 22 is a drive device, 23 .23° is a measuring roll, 24 is a speed detector, 25 is a tip detector, 26 is a temperature sensor, 27 is a high frequency power source, 61 is a heating coil, and 62 is a magnetic pole. 1st figure broom 2nd degree 3rd figure 6th figure (A) +8) (C) (D) Jitno V-η year old page and (mrn + sheet 8-勺(ward length (mml !S!, quality) Page length (m) Pear convex grinding ILza (m) 7th = Figure 8 Figure 9, /'q Figure 10

Claims (1)

[Claims] (1) In a method for heating a hot sheet bar by induction heating a widthwise side end of the hot sheet bar before hot finish rolling, at least two magnetic poles arranged in the longitudinal direction of the hot sheet bar are provided. An induction heating device having an induction heating device is disposed oppositely above and below the sheet bar, and when the longitudinalmost end of the sheet bar reaches the projected cross section of the magnetic pole, the conveyance of the sheet bar is stopped and the induction heating device is disposed to face the sheet bar. 1. A method for heating a hot sheet bar, comprising heating a longitudinal end of the sheet bar by applying a high frequency power source to a heating coil of a heating device.