Patent Application
20240399434
The present disclosure relates to a strip thickness control device for a hot rolling mill in which a plurality of rolling stands are provided in series and a material-to-be-rolled such as a heated steel plate is successively rolled by these plurality of rolling stands, and more particularly relates to one that is suited for production of an extremely thin hot rolled steel strip having a strip thickness less than or equal to 1.0 mm at a delivery side of a finishing mill.
In general, a hot rolled steel strip is produced by heating a slab which is a material-to-be-rolled to a predetermined temperature in a heating furnace, roughly rolling the heated slab to a thickness of about approximately 30 mm by a roughing mill to obtain a rough bar, rolling the obtained rough bar by a finishing mill in which seven rolling stands, for example, are provided in series to obtain a hot rolled steel strip having a predetermined thickness, cooling this hot rolled steel strip on a run-out table, and then coiling the hot rolled steel strip by a coiler.
As the hot rolled steel strip has a thinner strip thickness, a finishing temperature for a leading end of the hot rolled steel strip decreases more significantly. This raises problems in that as the hot rolled steel strip is thinner, it is more difficult to ensure the finishing temperature for its leading end, and furthermore, it is more difficult to pass the leading end due to a high rolling speed. To solve these problems, a conventional method achieves continuous finishing rolling by connecting a plurality of rough bars to one another and passing the connected ones through a finishing mill at high speed. However, this method requires a bonding device such as a welding device to be installed, which raises equipment cost.
A method disclosed in PTL 1 below compensates for a decrease in temperature of a rough bar by making the thickness of the rough bar less than 20 mm and installing a coil box and an online heating device between a roughing mill and a finishing mill in order to improve dimensional accuracy of a strip profile, a strip shape, a strip width, a strip thickness, and the like. However, the method of PTL 1 mainly focuses on increasing the accuracy of product dimensions, and ensuring of the finishing temperature for the leading end of a steel strip, in particular, remedial measures for the temperature at the entry side of the finishing mill and in particular, product surface properties such as a scale-dependent surface scratch are not considered at all. In addition, when the rough bar has a thickness less than 20 mm, a decrease in temperature in a roughly rolling step increases significantly, and in order to compensate for this decrease in temperature, an extremely high-output online heating device needs to be installed as described above, which raises the equipment cost.
In addition, a method for increasing the thickness of a rough bar can ensure the finishing temperature and is effective in a case in which a product strip thickness is thick, but is difficult to achieve in a case in which the product strip thickness is thin due to constraints in a rolling schedule, such as a force, motive power, and the like of the finishing mill.
In addition, in a method disclosed in PTL 2 below, a rough bar has a thickness ranging from 20 to 30 mm, this rough bar is heated by an online heating device provided at the entry side of a finishing mill such that a finisher entry-side temperature of the rough bar reaches a range of 1000 to 1150° C., and the rough bar heated to this temperature is subjected to finishing rolling. However, the method of PTL 2 also requires the online heating device to be installed, which raises the equipment cost.
As described above, it is difficult to pass the leading end of a material-to-be-rolled due to shape deterioration of the leading end of the material-to-be-rolled caused by a decrease in temperature as well as upper or lower warpage, winding, and the like of the leading end caused by high-speed rolling of the material-to-be-rolled. In order to reduce the decrease in temperature of the leading end, a rolling schedule of increasing the strip thickness at the delivery side of a roughing mill, installation of a heating device at the entry side of the finishing mill so as not to lower the temperature of the material-to-be-rolled, and the like have been proposed in the above-described conventional technologies, but there are restrictions such as the equipment cost and rolling schedule.
An object of the present disclosure, which has been made to solve the problems as described above, is to provide a strip thickness control device for a hot rolling mill in which even in a case of rolling a material-to-be-rolled extremely thinly, the leading end of the material-to-be-rolled can be passed reliably without raising the equipment cost.
A first aspect relates to a strip thickness control device for a hot rolling mill in which a plurality of rolling stands are provided in series, and a heated material-to-be-rolled is rolled successively by the plurality of rolling stands. The strip thickness control device comprises a strip thickness meter that is installed at a delivery side of a last one of the rolling stands in a series direction and measures a strip thickness of the material-to-be-rolled; a gap calculating unit that calculates a gap between rolls in each of the rolling stands, the gap being larger than a product target strip thickness of the material-to-be-rolled and corresponding to a passable strip thickness that enables a leading end of the material-to-be-rolled to be passed stably; a gap setting unit that sets the gap calculated by the gap calculating unit for each of the rolling stands; an automatic strip thickness control unit that executes automatic strip thickness control of minimizing a strip thickness deviation between a strip thickness measured value of the strip thickness meter and the passable strip thickness; and a target strip thickness changing unit that changes the passable strip thickness to the product target strip thickness by adding a strip thickness bias to the strip thickness deviation at a predetermined ramp rate after the leading end of the material-to-be-rolled is passed through the last one of the rolling stands.
A second aspect further includes the following characteristics in addition to the first aspect. The target strip thickness changing unit is configured to change the product target strip thickness to the passable strip thickness by adding the strip thickness bias to the strip thickness deviation at the predetermined ramp rate before a tail end of the material-to-be-rolled is passed through a first one of the rolling stands in the series direction.
According to the first aspect, the leading end of the material-to-be-rolled can be passed reliably through the hot rolling mill by setting a gap corresponding to a passable strip thickness even in a case of rolling the material-to-be-rolled extremely thinly. This eliminates the need to install a heating device at an entry side of the hot rolling mill as in the conventional technologies, which can prevent the equipment cost from rising. Furthermore, a portion behind the leading end of the material-to-be-rolled is rolled at an extremely thin product target strip thickness by adding the strip thickness bias to the strip thickness deviation between the strip thickness measured value and the passable strip thickness after the leading end of the material-to-be-rolled is passed through the last one of rolling stands and performing automatic strip thickness control with the strip thickness deviation to which the strip thickness bias has been added. Additionally, since the strip thickness bias is gradually added to the strip thickness deviation, the passable strip thickness is gradually changed to the product target strip thickness. Accordingly, the material-to-be-rolled can be rolled stably and extremely thinly.
According to the second aspect, the product target strip thickness is changed to the passable strip thickness prior to rolling of the tail end of the material-to-be-rolled. In other words, automatic strip thickness control is executed for the tail end of the material-to-be-rolled with the strip thickness deviation between the strip thickness measured value and the passable strip thickness. This can reduce occurrence of tail end winding and tail end squeezing of the material-to-be-rolled.
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that common elements in the respective drawings will be denoted by the same reference numerals, and repeated description will be omitted.
A heating furnace 2, a roughing mill 3, a crop shear 4, a finishing mill 5 as a hot rolling mill, a cooling device 6, and a coiler 7 are installed in the rolling plant 1. In the present embodiment, description will be given using, as an example, a case in which a strip thickness at a delivery side of the finishing mill 5 as the hot rolling mill is controlled to be an extremely thin (for example, less than or equal to 1.0 mm) product target strip thickness.
The heating furnace 2 is configured to heat a slab as the material-to-be-rolled M to a predetermined temperature. The roughing mill 3 has at least one rolling stand and is configured to roll the material-to-be-rolled M heated in the heating furnace 2.
The crop shear 4 is configured to cut a shape defect portion present at a tail end of the material-to-be-rolled M with upper and lower blades based on a shape measured with a shape detector 81 which will be described later.
The finishing mill 5 is a tandem mill including a plurality of rolling stands Fi (1≤i≤N) provided in series in a direction in which the material-to-be-rolled M is conveyed. In the present embodiment, description will be given using, as an example, a case in which seven rolling stands F1 to F7 are provided in series. Each of the rolling stands F1 to F7 includes two upper and lower work rolls 51, two upper and lower backup rolls 52, and a motor 53 for rotating the rolls. The backup roll 52 is provided with a screw-down device 54, and it is configured such that a gap between the upper and lower work rolls 51 can be adjusted by the screw-down device 54.
The cooling device 6 is configured such that the material-to-be-rolled M can be cooled by pouring water on the material-to-be-rolled M from a cooling bank. The cooled material-to-be-rolled M is coiled by the coiler 7. A coiled product is thereby obtained.
Various sensors as measuring instruments are installed at important locations of the rolling plant 1. Examples of important locations of the rolling plant 1 include a delivery side of the heating furnace 2, a delivery side of the roughing mill 3, a delivery side of the finishing mill 5, an entry side of the coiler 7, and the like. The various sensors may also be provided among the rolling stands F1 to F7 of the finishing mill 5. The various sensors include the shape detector 81 that can measure the shape of the material-to-be-rolled M at the delivery side of the roughing mill 3, a pyrometer 82 that measures a surface temperature of the material-to-be-rolled M at an entry side of the finishing mill 5, a pyrometer 83 that measures the surface temperature of the material-to-be-rolled M at the delivery side of the finishing mill 5, a strip thickness meter 84 that measures a strip thickness Ta of the material-to-be-rolled M at the delivery side of the finishing mill 5, and roll force sensors 85 that measure roll forces in the respective rolling stands F1 to F5. The various sensors sequentially measure states of the material-to-be-rolled M and the respective instruments.
The rolling plant 1 is driven (operated) by a control system in which computers are used. The computers include a superordinate computer (host computer) 10 and a process computer 11 connected to each other via a network. An interface screen 12 which is an operation screen and a database 13 are connected to the process computer 11 via a network. Past rolling data is sequentially stored in the database 13. Actual result values of a gap between rollers (which hereinafter may be abbreviated as a “gap”) in each of the rolling stands F1 to F7 are included in the past rolling data. The actual result values of the gap are classified by steel type and a product target strip thickness Tt. In addition, actual result values of a gap at which no trouble in passing the leading end occurs, that is, the leading end of the material-to-be-rolled M is passed stably are stored in the database 23 in association with the strip thickness (corresponding to a “passable strip thickness” which will be described later) at that time.
A strip thickness control device 20 of the present embodiment is configured to control the strip thickness of the material-to-be-rolled M using not only the product target strip thickness Tt but also a passable strip thickness Ts that enables the leading end of the material-to-be-rolled M to be passed stably.
The strip thickness control device 20 includes the above-described strip thickness meter 84, a gap calculating unit 21, a gap setting unit 22, a strip thickness deviation calculating unit 23, an automatic strip thickness control unit 24, and a target strip thickness changing unit 25.
The gap calculating unit 21 is configured to, upon receipt of the product target strip thickness Tt from the superordinate computer 11, calculate the gap between the work rolls 51 of each of the rolling stands F1 to F7, the gap being larger than the product target strip thickness Tt and corresponding to the passable strip thickness Ts that enables the leading end of the material-to-be-rolled M to be passed stably. For example, the gap calculating unit 21 is configured to acquire the passable strip thickness Ts stored in the database 23 in association with the product target strip thickness Tt, and calculate each of the gaps in the respective rolling stands F1 to F7 for achieving the passable strip thickness Ts having been acquired. Note that the gaps in the respective rolling stands F1 to F7 are calculated so as to become smaller in descending order from the first rolling stand F1 to the last rolling stand F7 in the series direction.
The gap setting unit 22 is configured to control each of the screw-down devices 54 in the respective rolling stands F1 to F7 in accordance with the gaps calculated by the gap calculating unit 21, thereby setting the gaps in the respective rolling stands F1 to F7.
The strip thickness deviation calculating unit 23 subtracts the passable strip thickness Ts from the strip thickness measured value (actual strip thickness) Ta measured with the strip thickness meter 84, thereby calculating a strip thickness deviation FBK1 (=Ta−Ts). The automatic strip thickness control unit 24 is configured to control each of the screw-down devices 54 of the respective rolling stands F1 to F7 such that the strip thickness deviation FBK1 calculated by the strip thickness deviation calculating unit 23 becomes the minimum or such that a strip thickness deviation FBK2 obtained by adding a strip thickness bias Tb which will be described later to the strip thickness deviation FBK1 becomes the minimum. The control exerted by the automatic strip thickness control unit 24 corresponds to AGC (Auto Gain Control) control. In addition, the expression that the strip thickness deviation FBK1 or FBK2 becomes the minimum means that the strip thickness deviation FBK1 or FBK2 converges to zero, for example.
The target strip thickness changing unit 25 has a ramp 251, a timer 252, a bias amount 253 input to the ramp 251 by a trigger by the timer 252, and a ramp rate 254 to be input to the ramp 251. The bias amount 253, that is, a difference between the passable strip thickness Ts and the product target strip thickness Tt can be set in accordance with the steel type of the material-to-be-rolled M, and can be set at 300 μm, for example. The target strip thickness changing unit 25 can output (change) the strip thickness bias Tb to be added to the strip thickness deviation FBK1 at a predetermined ramp rate. The strip thickness deviation FBK2 obtained by adding the strip thickness bias Tb is plus, and the automatic strip thickness control unit 24 performs the AGC control so as to cause the strip thickness deviation FBK2 to converge to zero. Therefore, the gaps in the respective rolling stands F1 to F7 are changed gradually to a tightening direction.
Herein, the timer 252 brings a trigger signal to SET after a predetermined time duration TD1 elapses from a time (F7_In) at which the leading end of the material-to-be-rolled M is passed through the last rolling stand F7. Accordingly, the strip thickness bias Tb to be output from the target strip thickness changing unit 25 gradually increases at a predetermined ramp rate. When the AGC control is performed with the strip thickness deviation FBK2 to which this strip thickness bias Tb is added, the gaps in the respective rolling stands F1 to F7 are changed gradually in the tightening direction. As a result, the strip thickness behind the leading end of the material-to-be-rolled M is changed gradually from the passable strip thickness Ts to the product target strip thickness Tt.
In addition, the timer 252 brings the trigger signal to RESET after the tail end of the material-to-be-rolled M is cut with the crop shear 4. Accordingly, the strip thickness bias Tb to be output from the target strip thickness changing unit 25 gradually decreases at a predetermined ramp rate. When the AGC control is performed with the strip thickness deviation FBK2 to which this strip thickness bias Tb is added, the gaps in the respective rolling stands F1 to F7 are changed gradually in a loosening direction. As a result, the strip thickness of the tail end of the material-to-be-rolled M is changed gradually from the product target strip thickness Tt to the passable strip thickness Ts.
A specific structure of the strip pressure control device 20 is not limited, but may be the following as an example.
At least part of the processing circuit may be at least one piece of dedicated hardware 20a. In this case, a single circuit, a composite circuit, a programmed processor, a parallel-programmed processor, ASIC, FPGA, or a combination of them, for example, fall under the processing circuit.
The processing circuit may include at least one processor 20b and at least one memory 20c. In this case, each function of the process computer 11 is achieved by software, firmware, or a combination of software and firmware. The software and firmware are written as a program, and are stored in the memory 20c. The processor 20b reads out and executes the program stored in the memory 20c, thereby achieving the function of each unit.
The processor 20b is also called a CPU (Central Processing Unit), a central processor, a processing device, an arithmetic device, a microprocessor, a microcomputer, or DSP. A non-volatile or volatile semiconductor memory or the like, such as RAM, ROM, flash memory, EPROM, or EEPROM, for example, falls under the memory 20c. Note that it can also be configured such that the memory 20c also serves as the database 13.
In this manner, the processing circuit can achieve each function of the strip pressure control device 20 by means of hardware, software, firmware, or a combination of them.
In the above-described rolling plant 1, the material-to-be-rolled M is raised in temperature in the heating furnace 2, and then extracted onto a roller table (not shown) on a rolling line. The material-to-be-rolled M in this stage is a steel piece, for example. When arrived at the roughing mill 3, the material-to-be-rolled M is repeatedly rolled while the rolling direction is changed. The material-to-be-rolled M in this stage is a bar having a thickness of approximately several tens millimeters, for example. The shape of the material-to-be-rolled M is measured with the shape detector 81 at the delivery side of the roughing mill 3, and based on a measurement result, a shape defect portion at the tail end of the material-to-be-rolled M is cut with the crop shear 4. The material-to-be-rolled M is rolled while being successively engaged with the rolling stands F1 to F7 of the finishing mill 5 to be controlled to the product target strip thickness Tt as desired.
Next, a method for controlling the strip thickness through use of the strip thickness control device 20 of the above-described finishing mill 5 will be described.
When the product target strip thickness Tt is input to the process computer 12 from the superordinate computer 11 before a routine shown in
When the routine shown in
Since F7_In is OFF before time t1, the strip thickness bias Tb to be output from the target strip thickness changing unit 25 is zero (that is, the strip thickness bias Tb to be added to the strip thickness deviation FBK1 is zero). In this case, the automatic strip thickness control unit 24 subjects each of the screw-down devices 54 of the respective rolling stands F1 to F7 to the AGC control such that the strip thickness deviation FBK1 becomes the minimum (for example, zero) (step S2). Accordingly, the gaps in the respective rolling stands F1 to F7 are controlled to be wide in order to reliably pass the leading end of the material-to-be-rolled M.
Herein, when F7_In becomes ON at time t1 after a predetermined time duration elapses from the time at which the leading end of the material-to-be-rolled M is detected with the shape detector 81, the process transitions to step S3.
In step S3, it is discriminated whether or not the time duration TD1 has elapsed. The time duration TD1 corresponds to a time delay. In a case where the time duration TD1 has not elapsed, the trigger signal from the timer 252 is OFF, so that the strip thickness bias Tb to be output from the target strip thickness changing unit 25 is zero (that is, the strip thickness bias Tb to be added to the strip thickness deviation FBK1 is zero). Also in this case, the automatic strip thickness control unit 24 subjects each of the screw-down devices 54 of the respective rolling stands F1 to F7 to the AGC control such that the strip thickness deviation FBK1 becomes the minimum (for example, zero) (step S4). Also in step S4, the gaps in the respective rolling stands F1 to F7 are controlled to be wide in order to reliably pass the leading end of the material-to-be-rolled M. Thereafter, the process returns to step S3.
When the trigger signal from the timer 252 becomes SET at time t2 at which the time duration TD1 elapses from time t1, it is determined that passing of the leading end of the material-to-be-rolled M has finished, and the strip thickness bias Tb is output from the target strip thickness changing unit 25. The strip thickness bias Tb having been output is added to the strip thickness deviation FBK1, so that the strip thickness deviation FBK2 is obtained. Herein, in a case where a bias amount of the strip thickness bias Tb is 300 μm, for example, the strip thickness bias Tb to be output from the target strip thickness changing unit 25 increases at a predetermined ramp rate in a time duration from time t2 to time t3. When the strip thickness bias Tb reaches 300 μm, FBK2=Ta−Ts+300 μm holds. The automatic strip thickness control unit 24 subjects each of the screw-down devices 54 of the respective rolling stands F1 to F7 to the AGC control such that the plus strip thickness deviation FBK2 to which the strip thickness bias Tb has been added becomes the minimum (for example, zero) (step S5). In the time duration from time t2 to time t3, the gaps in the respective rolling stands F1 to F7 are controlled to be gradually smaller by the AGC control (the gaps are gradually controlled in the tightening direction). This enables a strip thickness of a portion behind the leading end of the material-to-be-rolled M to be the product target strip thickness Tt which is extremely thin.
Herein, when the tail end of the material-to-be-rolled M becomes extremely thin, tail end winding and tail end squeezing of the material-to-be-rolled M are likely to occur. As a result, the tail end of the material-to-be-rolled M is likely to get entangled with the work rolls 51 of each of the rolling stands F1 to F7, which may increase the number of replacements of the work rolls 51.
The present embodiment therefore executes the following control. In other words, it is discriminated whether or not CS_TCut is ON, that is, whether or not the shape defect portion at the tail end of the material-to-be-rolled M has been cut with the crop shear 4 (step S6). In a case where CS_TCut is OFF, the process returns to step S5 described above.
When CS_TCut becomes ON at time t4, that is, when cutting with the crop shear 4 is performed, the process transitions to step S7. In step S7, it is discriminated whether or not a time duration TD2 has elapsed. The time duration TD2 corresponds to a time delay. The time duration TD2 is set such that the tail end of the material-to-be-rolled M is not passed through the first rolling stand F1 after cutting with the crop shear 4. The time duration TD2 is usually different from the time duration TD1. Until the time duration TD2 elapses, the AGC control is executed continuously with the product target strip thickness Tt at which Tb=300 μm, similarly to step S5 described above (step S8).
When a trigger from the timer 252 becomes RESET at time t5 at which the time duration TD2 elapses from time t4, the strip thickness bias Tb to be output from the target strip thickness changing unit 25 gradually decreases from 300 μm to 0 μm at a predetermined ramp rate, the automatic strip thickness control unit 24 subjects each of the screw-down devices 54 of the respective rolling stands F1 to F7 to the AGC control such that the strip thickness deviation FBK2 becomes the minimum (for example, zero) (step S8). Accordingly, each of the gaps in the respective rolling stands F1 to F7 is changed gradually to be wider by each AGC control in a time duration from time t5 to time t6. As a result, the strip thickness of the tail end of the material-to-be-rolled M is changed gradually from the product target strip thickness Tt to the passable strip thickness Ts. Then, occurrence of tail end winding and tail end squeezing of the material-to-be-rolled M can be reduced. Accordingly, the tail end of the material-to-be-rolled M is less likely to get entangled with the work rolls 51 of each of the rolling stands F1 to F7, which can reduce an increase in the number of replacements of the work rolls 51.
As described above, according to the present embodiment, the leading end of the material-to-be-rolled M can be passed reliably through the finishing mill 5 by setting the gaps in the respective rolling stands F1 to F7 at gaps corresponding to the passable strip thickness Ts even in the case of rolling the material-to-be-rolled M to the product target strip thickness Tt which is extremely thin. This eliminates the need to install a heating device at the entry side of the finishing mill 5 as in the background technologies, which can prevent the equipment cost from rising. Furthermore, by executing the AGC control with the strip thickness deviation FBK2 obtained by gradually adding the strip thickness bias Tb to the strip thickness deviation FBK1 after reliably passing the leading end of the material-to-be-rolled M, the gaps in the respective rolling stands F1 to F7 are changed gradually to a gap corresponding to the product target strip thickness Tt. Accordingly, in conjunction with not abruptly changing the gaps in the respective rolling stands F1 to F7, the material-to-be-rolled M can be rolled stably and extremely thinly.
Although an embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, but can be variously modified and implemented within a range not departing from the spirit of the present invention. In a case where numbers such as the number, quantity, amount, and range of each element are referred to in the aforementioned embodiment, this invention is not limited to the referred numbers unless particularly demonstrated or obviously specified to those numbers in principle. In addition, the structure and the like described in the aforementioned embodiment are not necessarily essential for this invention unless particularly demonstrated or obviously specified to them in principle.
5 . . . Finishing mill (hot rolling mill), 20 . . . Strip thickness control device, 21 . . . Gap calculating unit, 22 . . . Gap setting unit, 23 . . . Strip thickness deviation calculating unit, 24 . . . Automatic strip thickness control unit, 25 . . . Target strip thickness changing unit, 84 . . . Strip thickness meter, F1-F7 . . . Rolling stands, F1 . . . First rolling stand, F7 . . . Last rolling stand, FBK1, FBK2 . . . Strip thickness deviation, M . . . Material-to-be-rolled, Ta . . . Strip thickness measured value, Tb . . . Strip thickness bias, Ts . . . Passable strip thickness, Tt . . . Product target strip thickness
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/031680 | 8/23/2022 | WO |
