JPH01321010A - Method for heating hot sheet bar - Google Patents

Abstract

PURPOSE:To prevent generation of material defects in ends in the length direction of a sheet bar by stopping transfer of the bar or reducing a transfer speed of the bar in a heating zone and shifting an induction furnace in the width direction of the bar. CONSTITUTION:At the time when the top of a sheet bar 3 arrives at a top end detector 25, the detector 25 outputs a theoretical value signal showing arrival of the top of the bar 3 to a controller 21. Then, a temp. sensor 26 starts temp. detection to detect a temp. of the top of the bar 3 and sends the detection signal to a controller 21. Next, the controller 21 calculates a difference between the measured top end temp. of the bar 3 and a target temp. and controls outputs of a high frequency power source 27 based on a detected speed value of the bar 3 detected by a speed detector 24. An induction heat oil is shifted with an approach limit distance of the coil kept. As the result, the top of the bar 3 over the entire area in the width direction is heated by the induction heating coil and temp. drop in the top end is compensated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for heating a hot sheet bar, and particularly to a hot sheet produced by heating the widthwise ends of the hot sheet bar. Concerning a method of heating a bar.

[Prior Art] To explain the conventional method of rolling a hot sheet bar in steel strip rolling, generally speaking, in hot rolling, a heated slab with a thickness of 120 to 300 cm is rolled by a rough rolling mill. The sheet bar is rolled into a sheet bar having a thickness of 15 to 60 mm, and then further rolled to the required product thickness using a finishing mill.

Here, as shown in FIG. 6, the hot sheet bar rolled by the rough rolling mill I is transferred to the crop shear 4 by conveying table rollers 5, and the tip of the sheet bar is sheared. Next, the sheet bar 3 is transferred to a high-pressure injection type scaling device 11 having a nozzle 8 for removing surface scale, and then the sheet bar 3 is 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 as it approaches the heat dissipation surface (i.e., front and back surfaces and side surfaces), so there is a difference in the amount of heat dissipated into the atmosphere between the widthwise side edges and the center of the hot sheet bar. The temperature of the hot sheet bar is lower at the end portions in the width direction than at 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. 6, edge heaters 6 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 (for example, see Tetsu to Hagane, No. 2, 1986, pp. 177-178).

In this edge heater, as shown in FIG. 6, a plurality of pairs of upper and lower induction heating coils IOA are installed at both edge portions of the hot sheet bar 3. 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.

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, as a result of intensive studies by the inventors of the present invention, heat dissipation from the seat bar occurs not only at the side ends in the width direction but also at the longitudinal ends (tip and rear ends) of the seat bar, and as a result, various problems arise. I found out what was happening.

That is, the first problem is that the material at the front and rear ends of the seat bar is defective. In finish rolling, usually Ar3
Operations are conducted to complete rolling at or above the transformation point.

However, in the conventional sheet bar rolling method described above, the local temperature drop at the leading and trailing ends of the sheet bar becomes below the Ar point, causing abnormal growth of crystal grains, so-called grain gloss.

As a result, the workability of the product decreases, as well as the cold rollability, which is often performed in succession to hot rolling in recent years.

The second problem mentioned above is roll flaws. In a sheet bar made of a steel with high deformation resistance, when the above-mentioned material defects occur, the roll is plastically deformed when the tip of the sheet bar is bitten by the finishing roll. 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, it is necessary to cut off the longitudinal ends of the sheet bar, that is, the front and rear ends, but this poses a problem in that the yield of the product decreases.

The inventors of the present invention have therefore discovered that the above-mentioned problem can be solved by heating not only the edge portions of the sheet bar but also the ends in the longitudinal direction (the leading edge and the trailing edge).

However, if you try to heat the entire length of the long edge of the sheet bar, it is necessary to stop conveying the sheet bar or significantly reduce the conveyance speed in order to heat it sufficiently, which reduces productivity. I discovered a new challenge.

Therefore, in order to solve such problems, the present invention can sufficiently heat the longitudinal ends of the seat bar without reducing productivity, and as a result, prevents material defects at the longitudinal ends of the seat bar. The object of the present invention is to provide a hot sheet bar heating method that improves the yield, prevents the occurrence of roll defects, and improves the operating rate.

[Means to solve the problem]

In order to achieve the above object, the method for heating a hot sheet bar according to the present invention includes rough rolling a slab transferred to a hot rough rolling mill into a sheet bar, and finish rolling the sheet bar in a finishing rolling mill. In the hot sheet bar heating method of heating the widthwise end portion of the sheet bar, a plurality of heating devices movable in the width direction of the sheet bar are arranged so as to face each other in the width direction of the sheet bar. When the longitudinal end of the sheet bar is conveyed to the heating area of the induction heating device, the conveyance of the sheet bar is stopped or the conveyance speed is reduced, and the induction heating device is moved to the approach limit. The present invention is characterized in that by moving the seat bar in the width direction while maintaining a distance, the entire longitudinal end portion of the seat bar is heated.

[Effect]

According to the hot sheet bar rolling method according to the present invention,
Before finish rolling, not only the widthwise ends but also the longitudinal ends of the sheet bar are heated, and the temperature drop in this area can be compensated for, thereby preventing abnormal growth of grains, and as a result,
Material defects do not occur at the longitudinal ends of the seat bar. Therefore, compared to the conventional hot sheet bar rolling method, it is possible to improve the workability and cold rollability of the product while improving the walking speed.

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.

Furthermore, according to the method for heating a hot seat bar according to the present invention, since the plurality of heating devices are moved while maintaining the approach limit distance 51], the entire longitudinal end portion of the seat bar is heated with the shortest moving distance. can do. Therefore, the time required to stop the general feeding of the sheet bar or to reduce the conveyance speed is minimized, so that productivity can be improved.

〔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 the apparatus for carrying out the method of the present invention, in which instead of the edge heater 10 shown in FIG. An induction heating device 6 is provided that heats both the directional ends (front end and rear end). This induction heating device 6 is composed of a pair of upper and lower induction heating coils 30A and 30B, as shown in the side view of FIG. As shown in the figure, two sets 6A are arranged parallel to each other in the width direction of the seat bar 3.

6B is provided. The output of these induction heating coils can be controlled separately, and the movement position of the seat bar 3 in the width direction can be adjusted.

Next, FIG. 2 shows a block diagram of the above-mentioned FIG. 1. Note that the same parts as in FIG. 1 are designated by the same reference numerals, and the explanation thereof will be omitted. FIG. 2 is a side view of the rolling equipment, and to explain its configuration, a high frequency power source 27 is connected to each of the induction heating coils of the induction heating device 6. Further, a coil drive circuit 22 is connected to the induction heating coil for synchronously moving the induction heating device 6 in the width direction of the seat bar 3. These, coil drive circuit 2
2 and a 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. A speed detector 24 is provided. These measuring rolls 23 and speed detector 2
4 is 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 induction heating device used in this embodiment has a pair of upper and lower induction heating coils 30A, 30, as shown in the side view of FIG.
The upper induction heating coil 30B is fixed to the tip of the upper support arm 31A. Furthermore, a lower induction heating coil 30B is fixed to the tip of the lower support arm 31B. This pair of upper and lower support arms 31A, 31B are
It is fixed to the left end of the support stand 38 of the truck 32 so as to be swingable about the support part 39 . An opening/closing cylinder 35 is fixed to the right side of the upper support arm 31A, and an opening/closing cylinder 36 is similarly fixed to the right end of the lower support arm 31B. 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, 36
is the conveyance roller 50 bearing.

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

31B is an induction heating coil 30A provided at the left end;
The length is sufficient to move 30B to the center of the seat bar 3. This induction heating device can be moved on the rail 33 at right angles to the conveyance direction of the sheet bar 3. That is, when moving the induction heating coils 30A and 30B to the widthwise center of the seat bar 3, by running the induction heating coils 30A and 30B toward the seat bar on the rail 33, these induction heating coils are moved to the widthwise center of the seat bar. It is possible to move towards. Note that if the seat bar 3 is warped, the induction heating coil may be destroyed, so by driving the opening/closing cylinders 35 and 36, the supporting arms 31A, 3
1'B can swing around a support shaft 39.

Next, the operation of the embodiment shown in FIG. 2 will be explained based on FIG. 4. FIG. 4 shows an embodiment of the method for heating a hot sheet bar according to the present invention.

In FIG. 2, 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 (for example, composed of an infrared sensor), the detector 25 detects infrared rays from the tip of the seat bar 3, thereby indicating that the tip of the seat bar 3 has reached the bottom of the detector 25. A signal of value (1) is output to the controller 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 controls the induction heating coils 30A, 30B is moved in the direction of separation.

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 coil 6 in advance in the storage device of the controller 21, it is possible to detect when the tip of the sheet bar 3 reaches the induction heating coil 6. I can do it.

When the tip of the sheet bar 3 reaches the induction heating coil 6,
The controller 21 outputs a signal to a moving device for the seat bar 3 (not shown) to stop the tip of the seat bar 3 between the induction heating coils 3OA and 30B.

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 a target temperature (preset in the controller with a setting device), and further 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). The output of the high frequency power source 27 is controlled based on the speed detection value of the seat bar 3 detected at 24. At this time, as shown in FIG. 4(A), the seat bar 3
Induction heating coils 6A and 6B that were present at both ends in the width direction of
As shown in FIG. 4(B), the induction heating coil 6A is brought close to the induction heating coil 6B up to its approach limit distance. What determines the approach limit position? The induction heating coil has various structures attached to it, and these structures protrude in the width direction of the seat bar. When approached, the maximum distance at which the two do not come into contact is the approach limit distance.

Next, as shown in FIG. 4(C), the induction heating coil 6A
and 6B together toward the drawing table while maintaining the approach limit distance, and further move the induction heating coil 6B toward the left side of the drawing, as shown in FIG. 4(D).
Return to the position shown in FIG. 4(A). As a result, since the entire widthwise region of the tip of the seat bar 3 is heated by the induction heating coil, it is possible to compensate for the temperature drop at the tip.

The induction heating coil generates induced power 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. Furthermore, in the case where induction heating is performed with the seat bar 3 running instead of stopping the seat bar 3 and performing induction heating as in this embodiment, a large-capacity induction heating device is required.

As shown in FIG. 4(D), the induction heating coils 6A and 6B that have moved to the edge portions of the seat bar 3 continue to heat the edge portions after heating the tip portions of the seat bar 3. That is, after moving the induction heating coils 6A and 6B to the respective edge portions of the sheet bar 3 as shown in FIG. 4 (CD), the sheet bar is restarted to heat the edges of the sheet bar 3 continuously.

According to the method of heating the seat bar shown in FIG. 4 above, since both induction heating coils 6A and '6B are moved while maintaining the approach limit position, the entire longitudinal end of the seat bar is covered in the shortest distance. Can be heated. Therefore, the time required for stopping conveyance of the sheet bar is minimized, and productivity can be improved.

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 sheet bar 3, but this is done by setting the length of the sheet bar 3 on the control roller 21 in advance, and using the measuring roll 23 to detect the rear end of the sheet bar 3. This is easy because the amount of movement is constantly monitored.

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

A pinch roller can be provided upstream of the induction heating coil shown in FIG. 2 to correct the warpage of the tip of the sheet bar 3. Seat bar 3 by pinch roller
By correcting the warpage and flattening the tips, the gap between the upper induction heating coil and the lower induction heating coil in the induction heating device 6 and the sheet bar 3 through which they pass can be set small. 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. 5 is a graph showing the amount of temperature drop at the longitudinal end of a sheet bar at 1050° C. that has been 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 only the edge portion of the sheet bar is heated.
5 is a graph when both the edge portion and the front and rear end portions of the sheet bar are heated by the method shown in FIG. 4 based on the apparatus shown in the figure. In addition, in FIG. 5, 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 35 mm,
The thickness of the product finished rolled by the finish rolling mill is 2 mm.

Normally, if the temperature drop at the longitudinal end of the sheet bar exceeds 30°C, there will usually be grain gloss (material defects) in that area. The material defect area at the tip of the bar is 5m (
Product equivalent length (the same applies hereinafter)). Further, as shown in FIG. 5(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 seat bar as shown in FIG. ), the material defects at the rear end of the seat bar are reduced to within a range of 1 m. Therefore, by heating the longitudinal end of the seat bar by 40"C, a general low carbon material of 1000 m in the longitudinal direction can be reduced. In the conventional example in which the longitudinal end of the seat bar is not heated, 5 m is cut off at the leading end and 2 m is cut off at the rear end. The length is reduced to 2 m, and the amount of cut off at the rear end is reduced to 1 m. The resulting product is 100
Since the cut-off amount is reduced by 3 m at the leading end and 1 m at the rear end per 0 m, the yield is improved by 0.4%, leading to a significant cost reduction.

In addition, even when a sheet bar made of a steel with high deformation resistance with the leading and trailing ends of the sheet bar heated to 40°C as described above was bitten by a finishing roll 60 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 10 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. .

As can be seen from this specific example, the heating area at the longitudinal end of the seat bar only needs to heat a width of about 200 mm at the tip, and a width of about 100 s+m at the rear end. It turns out that you just need to heat it up. However, this does not preclude heating a wider area.

As explained above, according to this embodiment, material defects at the longitudinal ends of the sheet bar are prevented, and as a result, the yield can be improved and the rolls can be prevented from being scratched.

In this example, one induction heating device was used for heating the longitudinal ends of the sheet bar and for edge heating, but these functions were separated and used for edge heating. The device and the heating device for longitudinal end heating can be provided separately.

Further, in this embodiment, the heating device is installed before the crop shear, but the heating device is not limited to this, and it can also be installed after the crop shear.

Furthermore, the number of induction heating devices installed is not limited to that of this embodiment, and more than one heating device can be installed.

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

In addition, in this example, when heating the tip of the sheet bar,
Although conveyance of the sheet bar is stopped, it is also possible to heat the longitudinal ends of the sheet bar while reducing the conveyance speed of the sheet bar.

Furthermore, in this example, both the leading and trailing ends of the sheet bar are heated, but from the standpoint of preventing roll defects and improving yield to some extent, only the leading end of the sheet bar is heated. It is also possible to heat and not heat the rear end.

Furthermore, although induction heating has been described in this embodiment, the present invention is not limited to this, and the same objective can be achieved using other heating means.

〔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 greatly reduced, and as a result, the stop is improved. In addition, in sheet bars made of steel with high deformation resistance, the occurrence of roll flaws can be prevented, and as a result, sudden roll replacement can be avoided, and the operating rate can be improved.

Further, according to the present invention, it is possible to heat the entire length of the sheet bar while minimizing the moving distance of the heating device in the width direction of the sheet bar, so that the time required to stop conveying the sheet bar or decelerate the conveyance speed is minimized. Productivity improves.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an apparatus for carrying out the hot sheet bar heating method according to the present invention, FIG. 2 is a block diagram of FIG. 1, and FIG. 3 is a block diagram of an induction heating device. FIG. 4 is a side view showing the configuration, FIG. 4 is a front view showing a method of moving an induction heating coil according to an embodiment of the method of the present invention, and FIG. 5 is a relationship between sheet bar conversion length or product conversion length and temperature drop amount. FIG. 6 is a side view showing the configuration of a conventional hot sheet bar rolling apparatus. In the figure, ■ is a hot rough rolling mill, 2 is a finishing rolling machine, 3 is a sheet bar, 5 is a conveyance roller, 6 is an induction heating device, IO is an edge heater, 21 is a controller, 22 is a coil drive circuit, 23 is a Measuring roll, 24 is speed detector,
25 is a tip detector, 26 is a temperature sensor, and 27 is a high frequency power source, 30A. 30B shows an induction heating coil. Figure 1 (G) (b)! Dan Figure 5

Claims (1)

[Claims] (1) A hot sheet bar that heats the widthwise ends of the sheet bar before rough rolling the slab transferred to a hot rough rolling mill and finishing rolling the sheet bar in a finishing mill. In the heating method, a plurality of heating devices movable in the width direction of the sheet bar are arranged in the width direction of the sheet bar so as to face each other, and the heating area of the induction heating device is located in the longitudinal direction of the sheet bar. When the end portion is conveyed, by stopping the conveyance of the sheet bar or reducing the conveyance speed, and moving the induction heating device in the width direction of the sheet bar while maintaining the approach limit distance, A method for heating a hot sheet bar, the method comprising heating the entire length of the sheet bar in the longitudinal direction.