JP2001137931A - Manufacture of hot-rolled steel sheet excellent in uniformity of crown and shape of steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a hot-rolled steel sheet excellent in the uniformity of the crown and shape by which the variation in the dimension and shape of products is suppressed. SOLUTION: In the manufacturing method of the hot-rolled steel sheet by which the crown and shape of the steel sheet are controlled by heating a rough bar using an induction heating device having plural induction coils which are provided between a roughing mill and a finishing mill, by measuring the temperature of the rough bar 9 between the roughing mill 1 and the induction heating device 2, determining the amount of necessary temperature rise to the target temperature from this measured value of temperature and executing feedforward control to the electric power for each induction coil, the hot-rolled steel sheet excellent in the uniformity of the crown and shape is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating device having a plurality of induction coils provided between a rough rolling mill and a finishing rolling mill to heat a coarse bar to form a crown and a shape of a steel sheet. The present invention relates to a steel sheet crown to be controlled and a method for manufacturing a hot-rolled steel sheet having excellent shape uniformity.

[0002]

2. Description of the Related Art In hot rolling of a thin plate, generally, a slab is rolled to an intermediate thickness by a rough rolling mill, and then rolled to a final product thickness by a finish rolling mill. At that time, the heating temperature of the slab, the rolling conditions of the rough rolling, and the pass schedule, rolling speed and acceleration (acceleration) Rolling) is considered.

In recent years, demands for stricter dimensional accuracy of products, in particular, reduction of variations in the thickness in the longitudinal direction and uniformity of the thickness in the width direction have been strengthened. I have been. (For example, the theory and practice of sheet rolling:
The Iron and Steel Institute of Japan Joint Research Group, Rolling Theory Section, edited by the Iron and Steel Institute of Japan, 1984. Controls are being developed. In this case, in order to increase the response of the roll gap control, hydraulic pressure reduction is introduced to a plurality of stands.

[0004] In order to improve the crown (plate crown) and shape of a rolled plate, remodeling of rolling mills and introduction of devices have been performed in order to correct roll deflection. For example, installing a strong vendor, incorporating a roll cross mill, or using W
R shift and the like are known.

[0005] The bender device is attached to a bearing of a work roll, and applies bending stress to the work roll via the bearing. The high-strength bender device is capable of performing control in accordance with load fluctuations by strengthening the bending stress to provide a margin in the control range, thereby canceling the roll deflection.

The roll cross mill is a technique for adjusting a roll gap (roll interval) by twisting upper and lower work rolls from parallel positions to non-parallel positions. As such rolling mills, there are a pair cross mill that twists a backup roll together with a work roll, and a WR cross mill that twists only a work roll.

[0007] The WR shift is a technique for shifting a work roll in the axial direction to change a profile of a gap between upper and lower rolls. This method includes 4Hi-WR shift for shifting a work roll processed into a predetermined roll profile, and 6Hi in which an intermediate roll (IMR) is provided between a work roll and a backup roll.
A technique such as 6Hi-WR / IMR shift for shifting a work roll or an intermediate roll by using the stand is developed.

Further, an automatic control (ASC control) technique for canceling the roll deflection by performing control according to the load variation using these devices or a device combining them has been studied in the past.

[0009]

However, in order to stabilize and equalize the thickness, crown and shape by installing a strong bender, incorporating a roll cross mill, or introducing a WR shift, mill modification or the like is required. Requires significant capital investment. Furthermore, in order to operate these facilities, complicated control equipment is required, and a large amount of human and material resources are required for technical development such as construction of an advanced automatic control system.

As described above, in order to improve the sheet crown and the sheet shape by remodeling the rolling mill, it is necessary to maintain a control theory and develop sensors and the like as prerequisites for capital investment. However, the responsiveness of the equipment, the control theory and its model are limited, and the problem has not been sufficiently solved. Therefore, there is a problem that it is hard to say that the control of the rolling mill is sufficient especially for the fluctuation of the rolling load caused by the temperature deviation.

For example, as described below, on the finishing side, the rolling load fluctuates due to the temperature deviation in the longitudinal direction of the rough bar. The main temperature deviation in the longitudinal direction of the coarse bar is shown in FIG.
As shown in FIG. Temperature drop from the leading end to the tail end of the rough bar at the entrance to the rolling mill (thermal rundown) In the heating furnace, the temperature deviation in the longitudinal direction caused by the temperature drop of the slab support (skid mark) Due to these load fluctuations, The gap between rolls and the deflection of the rolls change, which adversely affects product quality. When the gap between rolls changes, the product plate thickness and plate width change. When the roll deflection changes, the thickness distribution (plate crown) and the shape of the product in the width direction change.

Therefore, at the stage of rolling to an intermediate thickness, a rolled material (coarse bar) is burner-heated in a tunnel furnace. However, although the burner heating device in the tunnel furnace is effective for the thermal rundown in which the coarse bar temperature changes gradually, it is not effective because the temperature control response is low for skid marks in which the temperature changes rapidly. The present invention provides a method for manufacturing a hot-rolled steel sheet having excellent uniformity of a steel sheet crown and a shape, which can solve the above-described problems of the prior art and can suppress fluctuations in product dimensions and shape. The purpose is to do.

[0013]

The above object is achieved by the following invention. A first aspect of the present invention is a hot-rolling apparatus that controls a crown and a shape of a steel sheet by heating a rough bar using an induction heating device having a plurality of induction coils provided between a rough rolling mill and a finishing rolling mill. In the steel sheet manufacturing method, the temperature of the coarse bar is measured between the rough rolling mill and the induction heating device, the required temperature rise amount with respect to the target temperature is determined from the measured temperature value, and the feedforward power is supplied to the power of each induction coil. This is a method for producing a hot-rolled steel sheet excellent in uniformity of a steel sheet crown and a shape characterized by controlling.

According to the present invention, in order to prevent a change in load, which is a cause of a change in a sheet thickness, a crown, and the like, a temperature change in a longitudinal direction of a coarse bar, which is a main cause, is suppressed by an induction heating device before rolling. Here, since induction heating is used as a heating method, the controllability is better and the apparatus is more compact than heating by a burner.

In the control of the induction heating, a control amount based on the measured value of the temperature of the coarse bar is feed-forward controlled to the power of each induction coil. The temperature of the coarse bar is measured between the rough rolling mill and the induction heating device, for example, at the outlet side of the rough rolling mill. From the measured temperature value of the coarse bar, a difference between the coarse bar and the target temperature at that position or a temperature rise required for the target temperature is obtained and used as control information.

Next, the coarse bar being conveyed is tracked, and control information is associated with the position of the coarse bar. When the coarse bar reaches the induction heating device, based on the information for control,
The power of each induction coil is controlled according to the corresponding position of the coarse bar, and feedforward control is performed. in this way,
By applying the feedforward control to the power control of each induction coil, it is possible to cope with a skid mark whose temperature changes rapidly. As a result, the temperature fluctuation in the longitudinal direction of the coarse bar is greatly reduced. In this way, it is possible to manufacture a hot-rolled steel sheet having small variations in the dimensions and crown / shape of the product and excellent in uniformity of the crown / shape.

It is needless to say that the feedforward control of the present invention may be used together with ordinary feedback control. Further, with respect to the rise in the temperature at the front and rear end portions of the rough bar and the rise in the finish outlet temperature due to the acceleration of the finish rolling mill, it is only necessary to cool by a spray between stands to suppress the temperature fluctuation.

According to a second aspect of the present invention, a hot-rolled steel sheet excellent in uniformity of a steel sheet crown and a shape according to the first invention, wherein the target temperature of the coarse bar is controlled to be constant throughout the longitudinal direction. It is a manufacturing method of.

According to the present invention, thermal run-down is prevented by coping with a rapid change in temperature of a skid mark or the like and by keeping the temperature of the rough bar constant.
As a result, there is no need to accelerate the rolling speed,
Can be rolled at a constant speed. By realizing further uniform rolling conditions, uniform dimensions can be achieved.

[0020]

FIG. 1 is a block diagram showing an example of an embodiment of the present invention. The rough rolling mill 1 has five stands, and the figure shows an R5 stand as a final stand. Downstream (left side in the figure) of the R5 stand of the rough rolling mill, an induction heating device (entire rough bar heating device: BH) is installed. Further downstream, a finishing mill 3 is installed. The finishing mill consists of seven stands F1 to F7, between the stands F1 to F6 of the finishing mill, and F1.
A spray for cooling (hereinafter referred to as an inter-stand spray) is provided in front of the stand.

As for the measurement of the temperature of the coarse bar 9, the exit temperature of the rough rolling mill is measured by the thermometer R5T at the exit side of the R5 stand, and the thermometers FIT and B at the entrance and exit sides of the induction heating device BH are measured.
HT measures the inlet and outlet temperatures of the induction heating device, and the finishing thermometer FDT on the outlet side of the finishing mill measures the finishing outlet temperature. Here, as the thermometer R5T on the exit side of the rough rolling mill, measuring the temperature of the lower surface of the rough bar 9 is effective in detecting a skid mark.

The signal of the roughing-out side temperature measured by the thermometer R5T is transmitted to the skid mark removal control means 11. Based on this signal, skid mark removal control means 1
1 calculates the temperature drop of the skid mark portion and outputs the temperature rise amount required for skid mark removal.

The signal of the temperature on the inlet side of the induction heating device measured by the thermometer FIT is transmitted to the BH (induction heating device) outlet side temperature estimating means 12. Based on this, the BH outlet temperature estimating means 12 calculates a relatively long-term temperature change (temperature drop) along the longitudinal direction, that is, a thermal rundown. In addition, the target temperature of the rough bar is set by the BH output side target temperature setting means 13.

These control outputs are used for feedforward control. Here, the position of the coarse bar to be controlled in the longitudinal direction is tracked by the temperature tracking means 14 based on the moving speed of the coarse bar. When the control target position of the coarse bar reaches the induction heating device 2, the output for control described above is transmitted to the BH power sharing control unit 15.

The BH power sharing control means 15 determines the required temperature based on the transmitted control output, that is, the temperature rise required for removing the skid mark, the estimated BH exit temperature, and the BH exit target temperature. Calculate the amount of rise. Based on the calculation result, for each induction coil, induction heating is performed to give a necessary amount of temperature rise to the coarse bar passing through the coil.

It is also effective to provide the temperature tracking means 14 with a tracking function for feedforward control to the inter-stand spray 4 of the finishing mill 3. In this case, for the moving speed of the rolled plate,
Since it changes (increases) depending on the rolling reduction of each stand, that amount is reflected in the calculation. Using this tracking result, the inter-stand spray control means 16 controls the amount of water in the inter-stand spray 4 and the like to control the temperature of the rolled sheet.

The object of the invention can be achieved by the above-described control mainly based on the feedforward control.
Further, more stable control can be performed by combining feedback control as in normal temperature control or cooling control. For example, as for the induction heating device 2, a signal of the induction heating device output temperature measured by the induction heating device output thermometer BHT is feedback-controlled.

The finishing intermediate temperature is measured by the intermediate thermometer F45T (between the stands F4 and F5) of the intermediate stand of the finishing mill, and the finishing temperature is measured by the finishing thermometer FDT. The temperature signals measured by these thermometers F45T and FDT may be feedback-controlled to the spray between stands to control the finishing temperature.

A learning system can be further incorporated in the control system described above. For example, in order to estimate the BH (induction heating device 2) entrance temperature, the actual value of the BH entrance temperature with respect to the R5 (rough rolling mill 1) exit temperature is learned. By this learning, an air-cooled model during the transportation of the rough bar from the rough rolling mill 1 to the induction heating device 2 is obtained.
In order to estimate the BH outlet temperature, the actual value of the BH outlet temperature with respect to the finishing temperature is learned. By this learning, a water-cooled model is obtained from the induction heating device to the exit side of the finishing mill, that is, a spray between stands in finish rolling of the rolled material.

Furthermore, in order to estimate the power consumption of the induction heating device 2, the actual value of the power consumption of the induction heating device 2 with respect to the amount of temperature rise by the induction heating device 2 is learned. Through this learning, a BH efficiency model representing the power efficiency in the induction heating device 2 is obtained.

Hereinafter, results of application of this control method will be described. (1) Skid Compensation Control by Induction Heating (Application Example 1) FIG. 2 shows a result of applying skid compensation according to the present invention to a hot rolling line.

The finishing inlet temperature is the result of measuring the temperature in the longitudinal direction of the rough bar before and after heating by the induction heating device. In the figure, the rough bar temperature before induction heating (before BH heating) indicated by a thin curve is lower in the temperature of the skid portion. It can be seen that the induction heating control of the present invention eliminates the temperature drop in the skid portion as shown by the thick curve in the figure. In this manner, in the drawing, the portion indicated by the BH heat amount is heated by the induction heating control, and the high temperature portion of the rolling top is cooled by the spray between stands to reduce the temperature fluctuation of the rolled material.

Further, a thermal run-down phenomenon in which the temperature on the finishing side gradually decreases during finish rolling has occurred.
This is compensated for by accelerated rolling in a finishing mill. As a result, by combining the AGC and ASC controls, the finish exit plate thickness and the plate crown are almost constant.

(2) Finishing-side Temperature Constant Control by Induction Heating (Application Example 2) In the above-mentioned application example 1, the finishing-side temperature is gradually decreased (with thermal rundown). With respect to the side temperature, thermal rundown was compensated for in addition to skid compensation, and control was performed to keep the temperature constant. The result is shown in FIG.

As shown in the figure, the finishing inlet temperature is almost constant. The rolling load was constant for both F1 and F7. In this example, since the finish-side temperature is constant, the rolling speed is constant. As a result, the rolling load is also uniform over the entire length, and it is possible to produce a steel sheet having a uniform thickness at the finishing outlet and a uniform overall length of the sheet crown and shape without complicated automatic control.

[0036]

According to the present invention, in controlling induction heating,
By performing feedforward control of the control amount based on the measured temperature value of the coarse bar to the power of each induction coil, it is possible to quickly deal with skid marks whose temperature changes rapidly.

Furthermore, by setting the temperature of the rough bar to a constant temperature, thermal rundown is prevented, and by rolling at a constant speed, the dimensions of the rolled material can be further homogenized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of an embodiment of the present invention.

FIG. 2 is a diagram showing an example (skid compensation) of a result of applying the present invention to a hot rolling line.

FIG. 3 is a diagram showing an example of a result of applying the present invention to a hot rolling line (finish-inlet-side temperature constant control).

FIG. 4 is a diagram showing a main temperature deviation in a coarse bar longitudinal direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rough rolling mill 2 Induction heating device 3 Finishing rolling mill 4 Spray between stands 9 Coarse bar 11 Skid mark removal control means 12 Outlet temperature estimating means 13 Outlet target temperature setting means 14 Temperature tracking means 15 Electric power sharing control means 16 Between stands Spray control means

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) B21B 45/00 B21B 37/00 BBM H05B 6/06 311 116D 6/10 381 117Z (72) Inventor Hiroshi Sekine Chiyoda, Tokyo 1-2-1 Marunouchi-ku, Nihon Kokan Co., Ltd. (72) Inventor Seiji Nakano 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Toru Minote Chiyoda-ku, Tokyo 1-2-2 Marunouchi Nihon Kokan Co., Ltd. F-term (reference) 3K059 AB26 AB28 AC09 AC33 AD05 AD08 BD04 CD06 4E024 AA03 BB07 BB09 EE01

Claims (2)

[Claims] 1. A hot-rolled steel sheet for controlling a crown and a shape of a steel sheet by heating a rough bar using an induction heating device having a plurality of induction coils provided between a rough rolling mill and a finishing rolling mill. In the manufacturing method, the temperature of the coarse bar is measured between the rough rolling mill and the induction heating device, the required temperature rise relative to the target temperature is determined from the measured temperature, and the feedforward control is performed on the power of each induction coil. A method for producing a hot-rolled steel sheet having excellent uniformity in crown and shape of the steel sheet. 2. The method according to claim 1, wherein the target temperature of the coarse bar is controlled to be a constant temperature over the entire longitudinal direction.