Method for controlling a heating furnace, a control device for a heating furnace, and a method for manufacturing hot-rolled steel sheets.

Abstract

A method for controlling heating furnaces in a hot rolling line equipped with multiple heating furnaces, a hot scale breaker, and a rolling mill, wherein, in order to accurately estimate the heating furnace extraction temperature of steel material and appropriately control the heating furnaces, the method involves measuring the temperature of each of the multiple steel material at any point after the exit of the hot scale breaker, obtaining a first estimated temperature using the temperature obtained from the measurement and the operating information of the rolling mill, obtaining a second estimated temperature using the operating information of the heating furnace, obtaining a temperature deviation from the difference between the first estimated temperature and the second estimated temperature, calculating a moving average of the temperature deviation for each group of steel material heated by the same heating furnace among the multiple steel materials, multiplying the moving average by a coefficient of 0 or more and less than 1 to obtain a temperature correction value, and controlling each of the multiple heating furnaces individually based on the corrected estimated temperature obtained by correcting the second estimated temperature using the correction value.

Description

Technical Field

[0001] The present invention relates to a heating furnace control method, a heating furnace control device, and a method for producing a hot-rolled steel sheet, which are used for controlling a heating furnace extraction temperature when a slab is extracted from a heating furnace in a hot rolling line.

Background Art

[0002] In a hot rolling line of an ironworks, after a steel billet called a slab produced by continuous casting equipment is heated in a heating furnace, the slab is rolled to a desired sheet thickness while repeating rolling and cooling to be processed into a hot-rolled steel sheet. Said rolling and cooling are controlled based on the heating furnace extraction temperature when the slab is extracted from the heating furnace. In order to ensure the accuracy of the material quality and rolling dimensions of the hot-rolled steel sheet, it is required to accurately grasp the heating furnace extraction temperature. However, scale is formed on the surface of the slab S extracted from the heating furnace, making it difficult to directly measure the heating furnace extraction temperature with a radiation thermometer. Accordingly, various methods have been used to estimate the heating furnace extraction temperature.

[0003] In relation to this, for example, Patent Document 1 discloses the following method. First, based on the actual temperature (T1) at the outlet side of a rough rolling process, a first heating furnace outlet temperature (Tc1) is calculated using operation data of a roughing mill. Further, a second heating furnace outlet temperature (Tm1) is calculated from the internal conditions of the heating furnace. Then, a variation distribution is obtained using an outlet temperature deviation (ΔT), which is the difference between the second heating furnace outlet temperature (Tm1) and the first heating furnace outlet temperature (Tc1), and this is used for controlling the heating furnace.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] However, the technology described in Patent Document 1 has low calculation accuracy for the furnace exit temperature (Tc1) calculated using the operating data of the roughing mill. Furthermore, after a change in the operating conditions of the roughing mill, the calculated value of the furnace exit temperature (Tc1) calculated using the operating data of the roughing mill changes. For this reason, especially after a change in the operating conditions of the roughing mill, until a certain number of exit temperature deviations (ΔT) have been accumulated for slabs, the variation distribution of the exit temperature deviation (ΔT) calculated based on the low-accuracy furnace exit temperature (Tc1) cannot be used for controlling the furnace.

[0006] The present invention aims to provide a heating furnace control method and heating furnace control device, as well as a method for manufacturing hot-rolled steel sheets, which can accurately estimate the heating furnace extraction temperature when steel material is extracted from the heating furnace in a hot-rolling line and appropriately control the heating furnace. [Means for solving the problem]

[0007] The inventors of this invention conducted intensive research to solve the above problems. They focused on the fact that, in the technology described in Patent Document 1, the calculated value of the furnace exit temperature (Tc1), which is calculated using the operating data of the roughing mill, includes errors caused by the roughing mill temperature model and errors caused by the furnace temperature model. They found that by treating these two types of errors separately, it is possible to accurately estimate the furnace extraction temperature when the steel material is extracted from the furnace.

[0008] This invention was completed as a result of further investigation based on the above-mentioned findings by the inventors, and its gist is as follows.

[0009] [1] A method for controlling heating furnaces in a hot rolling line comprising: a plurality of heating furnaces for heating steel material; a hot scale breaker for removing scale from the surface of the steel material extracted from the heating furnaces; and a rolling mill for rolling the steel material that has passed through the hot scale breaker, wherein for each of the plurality of steel materials passing through the hot rolling line, the temperature of the steel material is measured at any point on the hot rolling line after the exit of the hot scale breaker; and for each of the steel materials, the heating furnace extraction temperature of the steel material is calculated using the temperature obtained by the measurement and the operating information of the rolling mill for the steel material whose temperature was measured, thereby providing a first prediction A heating furnace control method comprising: obtaining a constant temperature; obtaining a second estimated temperature by calculating the heating furnace extraction temperature of each steel material using the operating information of the heating furnace when the steel material was heated; obtaining a temperature deviation by calculating the difference between the first estimated temperature and the second estimated temperature for the same steel material; calculating a moving average of the temperature deviation for each group of steel materials heated by the same heating furnace among the multiple steel materials; obtaining a temperature correction value by multiplying the moving average by a coefficient of 0 or more and less than 1; and controlling each of the multiple heating furnaces individually based on the corrected estimated temperature obtained by correcting the second estimated temperature using the temperature correction value.

[0010] Here, "calculating the moving average of the temperature deviation for each group of steel materials heated by the same heating furnace" includes cases where the moving average of the temperature deviation is calculated only for groups of steel materials heated by any heating furnace among the "multiple heating furnaces".

[0011] [2] A control device for a heating furnace in a hot rolling line comprising: a plurality of heating furnaces for heating steel material; a hot scale breaker for removing scale from the surface of the steel material extracted from the heating furnace; and a rolling mill for rolling the steel material that has passed through the hot scale breaker, wherein for each of the plurality of steel materials passing through the hot rolling line, the control device includes: a temperature measuring device for measuring the temperature of the steel material at any point on the hot rolling line after the exit of the hot scale breaker; a heating furnace operation information collection unit for collecting operating information of the heating furnace; a rolling operation information collection unit for collecting operating information of the rolling mill; and for each of the steel materials, the control device obtains a first estimated temperature by calculating the heating furnace extraction temperature of the steel material using the temperature measured by the temperature measuring device and the operating information for the steel material whose temperature has been measured, collected by the rolling operation information collection unit. A control device for a heating furnace, comprising: a first estimated temperature acquisition unit; a second estimated temperature acquisition unit that, for each of the steel materials, calculates the heating furnace extraction temperature of the steel material using the operation information collected by the heating furnace operation information acquisition unit when the steel material is heated, thereby acquiring a second estimated temperature; a temperature deviation acquisition unit that, for the same steel material, calculates the difference between the first estimated temperature and the second estimated temperature, thereby acquiring a temperature deviation; a moving average acquisition unit that acquires a moving average of the temperature deviation for each group of steel materials heated by the same heating furnace among multiple heating furnaces; a correction calculation unit that calculates a temperature correction value by multiplying the moving average by a coefficient of 0 or more and less than 1, and corrects the second estimated temperature using the temperature correction value, thereby acquiring a corrected estimated temperature; and a heating furnace control unit that controls each heating furnace based on the corrected estimated temperature.

[0012] Here, "calculating the moving average of the temperature deviation for each group of steel materials heated by the same heating furnace" includes cases where the moving average of the temperature deviation is calculated only for groups of steel materials heated by any heating furnace among the "multiple heating furnaces".

[0013] [3] A method for manufacturing a hot-rolled steel sheet, comprising heating a steel material in a heating furnace controlled by the heating furnace control method described in [1], and hot-rolling the steel material extracted from the heating furnace in a rolling mill. [Effects of the Invention]

[0014] According to the heating furnace control method, heating furnace control device, and hot-rolled steel sheet manufacturing method of the present invention, the heating furnace extraction temperature when the slab is extracted from the heating furnace can be accurately estimated by correcting the second estimated temperature and obtaining a corrected estimated temperature. Then, by controlling the heating furnace and rolling equipment based on the corrected estimated temperature, the material properties and rolling dimensions of the hot-rolled steel sheets produced in the hot-rolling line can be made more precise. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic diagram showing an example of a hot rolling line to which the heating furnace control method, heating furnace control device, and hot-rolled steel sheet manufacturing method of the present invention are applied. [Figure 2] Figure 2 shows an example of a processing flow using the heating furnace control method and heating furnace control device of the present invention. [Figure 3] Figure 3 shows an example of rolling equipment operation information collected by the rolling operation information collection unit of the heating furnace control device of the present invention. [Figure 4] Figure 4 shows an example of the change over time of the temperature deviation acquired by the temperature deviation acquisition unit of the heating furnace control device of the present invention. [Figure 5] Figure 5 shows an example of the relationship between the standard deviation of the difference between the corrected estimated temperature and the first estimated temperature, and the coefficient r. [Figure 6] Figure 6 shows the relationship between the measured temperature of the slab S obtained by a temperature measuring device acquired by the control device of a conventional heating furnace, and the estimated temperature of the slab S at the temperature measurement point calculated based on the first estimated temperature. [Figure 7]FIG. 7 is a diagram showing the relationship between the temperature of slab S measured by a temperature measurement device and the estimated temperature of slab S at a temperature measurement point calculated based on a corrected estimated temperature, which is obtained by an example of the heating furnace control method and heating furnace control device of the present invention. MODE FOR CARRYING OUT THE INVENTION

[0016] Hereinafter, embodiments of the heating furnace control method, the heating furnace control device, and the method for producing a hot-rolled steel sheet according to the present invention will be specifically described with reference to the drawings. <HOT ROLLING LINE> • Overall Configuration The heating furnace control method and heating furnace control device of the present embodiment can be generally applied to a hot rolling line used for hot rolling a slab that is a steel material.

[0017] FIG. 1 schematically shows the overall configuration of the heating furnace control method, the heating furnace control device, and the hot rolling line to which the heating furnace control method and heating furnace control device of the present embodiment are applied.

[0018] As shown in FIG. 1, the hot rolling line 1 includes a plurality of heating furnaces 11a to 11c, a hot scale breaker 12, a sizing press 13, roughing mills 14a and 14b, and a finishing mill (not shown).

[0019] First, a slab S, which is a material to be rolled, is cast by continuous casting equipment (not shown), then carried into the hot rolling line 1, charged into the heating furnaces 11a to 11c and heated. At this time, the slab S is exposed to high-temperature air in the heating furnaces 11a to 11c, and scale is formed on the surface of the slab S. After the slab S heated by the heating furnaces 11a to 11c is extracted from the heating furnaces 11a to 11c, scale on the surface is removed by the hot scale breaker 12. The width of the slab S that has passed through the hot scale breaker 12 is adjusted by the sizing press 13, and then rough-rolled by the roughing mill 14. The slab S that has passed through the roughing mill 14 is finish-rolled to a target sheet thickness by the finishing mill (not shown). · Heating Furnace Each of the plurality of heating furnaces 11a to 11c provided in the hot rolling line 1 is provided with a preheating zone, a heating zone and a soaking zone, which are arranged in this order in the conveying direction of the slab S. The heating zone is equipped with heating equipment for heating the slab S, and the slab S is heated to approximately 1100 to 1200°C. The soaking zone 11c is provided with a device for holding the slab S at a predetermined temperature. The device for holding the slab S at the predetermined temperature has a heating capacity sufficient to compensate for heat dissipated from the furnace body and the like.· Rolling Equipment In the present embodiment, the rolling equipment includes roughing mills 14a, 14b and water cooling devices 15a, 15b associated therewith, as well as a finishing mill (equipment) and a water cooling device (not shown) associated therewith.

[0020] The roughing mills 14a, 14b are constituted by reversible rolling stands that gradually reduce the plate thickness of the slab S while reciprocating the slab S a plurality of times, or non-reversible rolling stands that perform single-pass rolling to reduce the thickness by passing the slab S in one direction. Water cooling devices 15a and 15b for cooling by spraying cooling water onto the slab S are respectively provided on the inlet side of the roughing mills 14a and 14b. <Control apparatus for heating furnace / Control method for heating furnace> Next, the control apparatus for a heating furnace and the control method for a heating furnace according to the present embodiment will be described below. · Overall configuration of control apparatus for heating furnace As shown in FIG. 1, the control apparatus 2 for a heating furnace of the present embodiment includes a temperature measuring device 21, a heating furnace operation information collecting unit 22, a rolling operation information collecting unit 23, a first estimated temperature acquiring unit 24, a second estimated temperature acquiring unit 25, a temperature deviation acquiring unit 26, a moving average acquiring unit 27, a correction calculation unit 28, a heating furnace control unit 29, and a storage device 30. Specifically, the parts other than the temperature measuring device 21 in the control apparatus 2 for a heating furnace are realized by, for example, a computer (not shown) including a memory, an auxiliary storage device such as a hard disk drive or a solid-state drive, a CPU (Central Processing Unit), and the like. The control method for a heating furnace according to the present embodiment is executed by this control apparatus 2 for a heating furnace along the processing flow shown in FIG. 2, as will be described later. • Measurement of slab temperature (Step S1) / Temperature measuring device In the heating furnace control method of this embodiment, first, in step S1 shown in Figure 2, the temperature of each of the multiple slabs S passing through the hot rolling line 1 is measured by the temperature measuring device 21. The temperature of the slabs S is measured at one of the points after the exit of the hot scale breaker 12 on the hot rolling line 1. If the temperature of the slabs S is measured at two or more points after the exit of the hot scale breaker 12 on the hot rolling line 1, the measurement value at the upstreammost point is used.

[0021] The temperature measuring device 21 consists of a radiation thermometer and is installed at one of the points on the hot rolling line 1 after the exit of the hot scale breaker 12. Scale is formed on the surface of the slab S extracted from the heating furnaces 11a to 11c, making it difficult to directly measure the temperature of the slab S with a radiation thermometer. Therefore, the temperature of the slab S from which the scale has been removed by the hot scale breaker 12 is measured by the temperature measuring device 21 installed at one of the points after the exit of the hot scale breaker 12.

[0022] In this embodiment, the temperature of the slab S is measured by the temperature measuring device 21 during the rough rolling process, using the results of a rough-out side thermometer commonly used in hot rolling lines. Specifically, as shown in Figure 1, the temperature measuring device 21, consisting of the rough-out side thermometer, is installed at the exit of the downstream rough rolling mill 14b of the rough rolling mills 14a and 14b on the hot rolling line 1, and measures the temperature of the slab S at this point. The temperature information of each slab S measured by the temperature measuring device 21 is stored in a database stored in the storage device 30.

[0023] When installing a temperature measuring device 21 for measuring the temperature of the slab S in a hot rolling line, it is necessary to place the temperature measuring device 21 in a location that can avoid disturbances that affect temperature measurement, such as water and steam. However, depending on the position of the descaler between the rolling stands and the distance between the roughing mills 14a and 14b, it may be difficult to place the temperature measuring device 21 in a location that can avoid disturbances. In contrast, in this embodiment, a roughing-side thermometer, which is commonly used in hot rolling lines, is used as the temperature measuring device 21 for measuring the temperature of the slab S, and this roughing-side thermometer is installed in a location that can avoid disturbances such as water and steam. Then, using the temperature of the slab S measured by the temperature measuring device 21 consisting of the roughing-side thermometer, a first estimated temperature, which will be described later, can be calculated, and using this first estimated temperature, the furnace extraction temperature when the slab S is extracted from the heating furnace can be estimated.

[0024] The temperature of the slab S measured by the temperature measuring device 21 may be performed at any point on the hot rolling line 1 after the exit of the hot scale breaker 12, as long as the surface of the slab S is not covered with scale and temperature measurement by a radiation thermometer is not possible. For example, the temperature of the slab S measured by the temperature measuring device 21 may be performed in the finish rolling process instead of the rough rolling process. However, the further downstream the measurement point of the slab S by the temperature measuring device 21 is, the greater the amount of calculation required for the first estimated temperature described later, and the lower the calculation accuracy. For this reason, it is preferable to measure the temperature of the slab S by the temperature measuring device 21 at a point as far upstream as possible on the hot rolling line 1 after the exit of the hot scale breaker 12. • Acquisition of the first estimated temperature (Step S2) / First estimated temperature acquisition unit Next, in step S2 shown in Figure 2, the first estimated temperature acquisition unit 24 acquires the first estimated temperature for each of the multiple slabs S passing through the hot rolling line 1.

[0025] Specifically, the first estimated temperature acquisition unit 24 calculates the furnace extraction temperature of the slab S using the measured temperature of the slab S obtained from the temperature measuring device 21 and the operating information of the rolling equipment for the slab S whose measured temperature was measured. This calculation result is acquired as the first estimated temperature and stored in the database stored in the storage device 30. The calculation of the first estimated temperature is performed using a rough rolling mill temperature model based on the heat conduction equation, using the sheet passing time in the rough rolling mills 14a and 14b, the rolling load and input / output thickness setting values, the water cooling conditions in the water cooling devices 15a and 15b, etc.

[0026] The first estimated temperature acquisition unit 24 uses the rolling equipment operation information collected by the rolling operation information collection unit 23 in calculating the first estimated temperature. The rolling operation information collection unit 23 collects operating information of the rolling equipment located upstream of the temperature measuring device 21 in the hot rolling line 1. In this embodiment, the rolling operation information collection unit 23 collects operating information of the roughing mills 14a and 14b and their associated water cooling devices 15a and 15b.

[0027] Figure 3 shows an example of rolling equipment operation information collected by the rolling operation information collection unit of the heating furnace control device in this embodiment. In this embodiment, as shown in Figure 3, the rolling operation information collection unit 23 collects information for each of the multiple slabs S passing through the hot rolling line 1, such as the passing time in the roughing mills 14a and 14b, the rolling load and input / output thickness setting values, and the water cooling conditions in the water cooling devices 15a and 15b. • Acquisition of the second estimated temperature (Step S3) / Second estimated temperature acquisition unit Next, in step S3 shown in Figure 2, the second estimated temperature acquisition unit 25 calculates the furnace extraction temperature of the slab S using the operating information of the furnaces 11a, 11b, or 11c when the slab S whose measured temperature was measured was heated. This calculation result is acquired as the second estimated temperature and stored in the database stored in the storage device 30. The calculation of the second estimated temperature is performed using a furnace temperature model based on the heat conduction equation. The operating information of the furnaces 11a to 11c used in this calculation includes the temperature of the slab S when it is charged into the furnace, the specific heat of the slab S, the time the slab S is in each region of the furnace (preheating zone, heating zone, uniform zone), and the upper and lower furnace temperatures, etc.

[0028] The second estimated temperature acquisition unit 25 uses the operation information of the heating furnaces 11a to 11c collected by the heating furnace operation information collection unit 22 in calculating the second estimated temperature. The heating furnace operation information collection unit 22 collects operation information of the heating furnaces 11a to 11c. Specifically, it collects the temperature of the slab S when it is charged into the heating furnaces 11a to 11c, the specific heat of the slab S, the time the slab S is in the furnace in each region of the heating furnaces 11a to 11c (preheating zone, heating zone, uniform zone), and the upper and lower furnace temperatures, etc. The time the slab is in the furnace can be calculated based on the length of each region of the heating furnaces 11a to 11c (preheating zone, heating zone, uniform zone) and the transport speed of the slab S. The upper and lower furnace temperatures of the heating furnaces 11a to 11c are the temperatures of the upper and lower furnace walls of the heating furnaces 11a to 11c, and can be those measured by thermometers (not shown) provided in the heating furnaces 11a to 11c. • Acquisition of temperature deviation (Step S4) / Temperature deviation acquisition unit Next, in step S4 shown in Figure 2, the temperature deviation acquisition unit 26 calculates the difference between the first estimated temperature and the second estimated temperature. This calculation result is then acquired as a temperature deviation and stored in the database stored in the storage device 30. • Calculation of moving average of temperature deviation (Step S6) / Moving average calculation unit Next, in step S5 shown in Figure 2, it is determined whether the number of slabs S from which the measured temperature, first estimated temperature, second estimated temperature, and temperature deviation were obtained in steps S1 to S4 is N or greater for each group of slabs heated by the same heating furnace among heating furnaces 11a to 11c. The number of slabs S N used in the determination in step S5 is set to a number sufficient to adequately reflect the trend of the change in temperature deviation over time when obtaining the moving average of the temperature deviation described later. For example, by setting the number of slabs S extracted during the time required to change the furnace temperature setting of the heating furnace (approximately 20 minutes) as N, the trend can be adequately reflected.

[0029] If the result of the determination in step S5 is No, return to step S1 and continue accumulating the measured temperature, first estimated temperature, second estimated temperature, and temperature deviation. If the result of the determination in step S5 is Yes, proceed to step S6.

[0030] In step S6, the moving average acquisition unit 27 calculates the moving average of the temperature deviation, which is the difference between the first estimated temperature and the second estimated temperature, for N slabs S for each group of slabs heated by the same heating furnace among the heating furnaces 11a to 11c. When calculating the moving average of the temperature deviation for each group of slabs heated by the same heating furnace, the number N of slabs S to be calculated should be sufficient to adequately reflect the trend of the temperature deviation over time. For example, it is preferable that N be 10 or more. Note that the calculation of the moving average of the temperature deviation in step S6 may be performed only for groups of steel materials heated by any heating furnace among the multiple heating furnaces 11a to 11c.

[0031] Figure 4 shows an example of the change over time of the temperature deviation calculated by the temperature deviation acquisition unit 26 of the heating furnace control device 2 of this embodiment.

[0032] The first estimated temperature calculated by the roughing mill temperature model and the second estimated temperature calculated by the furnace temperature model each contain errors due to factors that cannot be modeled. Therefore, the temperature deviation, which is the difference between the first estimated temperature and the second estimated temperature, includes errors caused by the roughing mill temperature model and errors caused by the furnace temperature model. The errors caused by the furnace temperature model are specific to each of the multiple furnaces 11a to 11c and change with a relatively long period for each furnace (horizontal arrows in Figure 4). In addition, the errors caused by the roughing mill temperature model change with a shorter period than the errors caused by the furnace temperature model, depending on the steel type (specification) of the slab S being rolled (vertical arrows in Figure 4).

[0033] Therefore, in this embodiment, the moving average of the temperature deviation, which is the difference between the first estimated temperature and the second estimated temperature, is calculated for each group of slabs heated by the same heating furnace among the heating furnaces 11a to 11c. In this way, the temperature deviation to be used for the moving average calculation does not include errors caused by the heating furnace temperature model, but only errors caused by the roughing mill temperature model. • Correction calculation unit / acquisition of temperature correction value and corrected estimated temperature (steps S7, S8) Next, in step S7 shown in Figure 2, the correction calculation unit 28 calculates a temperature correction value for each heating furnace 11a to 11c by multiplying the moving average calculated by the moving average acquisition unit 27 by a predetermined coefficient r that is between 0 and 1. That is, the temperature correction value is as shown in equation (2) below.

[0034]

number

[0035] In this way, a temperature correction value can be obtained to correct for the error in the second estimated temperature for each of the multiple heating furnaces 11a to 11c, which is caused by the heating furnace temperature model unique to each of the heating furnaces.

[0036] Furthermore, as the temperature correction value, if M is the moving average calculated for N slabs S out of a plurality of slabs S, and M' is the moving average calculated for N' slabs S out of a plurality of slabs S (where N > N'), then the following equation (1) r × M + (1 - r) × M' …(1) It is preferable to use the value obtained by this method.

[0037] As described above, the temperature deviation, which is the difference between the first estimated temperature and the second estimated temperature, includes errors that change with relatively long periods and errors that change with relatively short periods. Therefore, in equation (1) above, the moving average of the temperature deviation is calculated for N' slabs (less than N) and used in the calculation of the temperature correction value. For example, when N is 10, it is preferable to set N' to about 5. It is preferable to set the lower limit of N to 7, the upper limit of N to 13, the lower limit of N' to 3, and the upper limit of N' to 6.

[0038] The correction calculation unit 28 corrects the second estimated temperature using the temperature correction value obtained as described above. Specifically, it adds the temperature correction value to the second estimated temperature to obtain a corrected estimated temperature for each of the heating furnaces 11a to 11c. This corrected estimated temperature allows for accurate estimation of the slab extraction temperature for each of the heating furnaces 11a to 11c.

[0039] Figure 5 shows an example of the relationship between the standard deviation of the difference between the corrected estimated temperature and the first estimated temperature, and the coefficient r.

[0040] In the calculation of the temperature correction value described above, it is preferable to set the value of the coefficient r so as to minimize the difference between the corrected estimated temperature and the first estimated temperature. The coefficient r determines the distribution between the long-term trend (moving average of temperature deviations for N slabs) and the short-term trend (moving average of temperature deviations for N' slabs) of the change in temperature deviation over time. If the correction is performed based only on the long-term trend, it is not possible to reduce the error in the estimated temperature caused by short-term factors. Conversely, if the correction is performed based only on the short-term trend, it is not possible to reduce the error in the estimated temperature caused by the heating furnace having a long-term trend. Therefore, the value of the coefficient r is set so that the long-term trend and the short-term trend are combined in a way that provides the best accuracy in the estimated temperature. It is preferable that the lower limit of r be 0.4 and the upper limit of r be 0.6. In the example shown in Figure 5, it is preferable to set the value of the coefficient r to 0.5. • Furnace control (step S9) / Furnace control unit Then, in step S9 shown in Figure 2, the furnace control unit 29 controls each of the furnaces 11a to 11c individually based on the corrected estimated temperature acquired for each furnace as described above. This allows for appropriate combustion settings for the furnaces. <Manufacturing method for hot-rolled steel sheets> The method for manufacturing hot-rolled steel sheets in this embodiment is achieved by heating a slab S in heating furnaces 11a to 11c controlled by the heating furnace control method described above, and then hot-rolling the slab S extracted from the heating furnaces 11a to 11c using the rolling equipment described above. [Examples]

[0041] The heating furnace control method of the present invention and the conventional heating furnace control method were applied to a hot rolling line, and 8,000 slabs were hot-rolled in each of the following examples: Invention Example 1, Invention Example 2, and Conventional Example. The effects of the present invention were verified by comparing the estimated slab extraction temperatures. This will be explained below.

[0042] The hot rolling line used in this verification was the same as that shown in Figure 1, with three heating furnaces and two roughing mills, each equipped with a water cooling system. A temperature measuring device was installed at the outlet of the downstream of the two roughing mills to measure the temperature of the slab S. Ten slabs were extracted per hour from each of the three heating furnaces.

[0043] In this verification, first, the heating furnace control method of the present invention and the conventional heating furnace control method were applied to each group of slabs heated by the same heating furnace among the three heating furnaces. A moving average of the temperature deviation, which is the difference between the first estimated temperature and the second estimated temperature, was calculated, and a corrected estimated temperature was obtained by correcting the second estimated temperature. This is referred to as the "Example of Invention".

[0044] Here, based on the corrected estimated temperature, the estimated temperature of slab S at the temperature measurement point can be calculated using the operating information of the rolling equipment (roughing mill and its associated water cooling system). The difference between the estimated temperature of slab S at the temperature measurement point and the temperature measured by the temperature measurement device roughly corresponds to the difference between the first estimated temperature and the second estimated temperature. Therefore, in this verification, instead of the difference between the first estimated temperature and the second estimated temperature, the difference between the estimated temperature of slab S at the temperature measurement point and the temperature measured by the temperature measurement device is used.

[0045] Figure 5 shows the relationship between the standard deviation of the difference between the estimated temperature of slab S at temperature measurement points calculated based on the corrected estimated temperature obtained during the hot rolling of the first 2000 slabs out of 8000 slabs in the inventive example, and the measured temperature of slab S by the temperature measuring device, and the coefficient r. As shown in Figure 5, in the inventive example, the above difference is minimized when the value of the coefficient r is 0.5. Therefore, the value of the coefficient r used in the calculation of the temperature correction value was also set to 0.5 during the hot rolling of the remaining 6000 slabs out of 8000 slabs.

[0046] Furthermore, for comparison purposes, without distinguishing between the three heating furnaces, the moving average of the temperature deviation (the difference between the first estimated temperature and the second estimated temperature) was calculated for the entire slab heated by the three furnaces to obtain the second estimated temperature. This will be referred to as the "conventional example."

[0047] In the example of the invention, when calculating the moving average of the temperature deviation for each group of slabs heated by the same heating furnace, the number of slabs S to be calculated, N, was set to 10.

[0048] Figure 6 shows the relationship between the measured temperature of the slab S obtained by the temperature measuring device in the conventional example and the estimated temperature of the slab S at the temperature measurement point calculated based on the first estimated temperature. Figure 7 shows the relationship between the measured temperature of the slab S obtained by the temperature measuring device in the inventive example and the estimated temperature of the slab S at the temperature measurement point calculated based on the corrected estimated temperature.

[0049] Furthermore, the relationship between the furnace extraction temperature when slab S is extracted from the furnace and the first estimated temperature is understood to be close to the relationship shown in Figure 6. Similarly, the relationship between the furnace extraction temperature when slab S is extracted from the furnace and the corrected estimated temperature is understood to be close to the relationship shown in Figure 7.

[0050] As shown in Figure 6, in the conventional example, the RMSE (root mean square error) of the temperature deviation, which is the difference between the temperature measured by the temperature measuring device for the slab S and the estimated temperature of the slab S at the temperature measurement point calculated based on the first estimated temperature, was 10.6°C. In contrast, as shown in Figure 7, in the inventive example, the RMSE of the temperature deviation, which is the difference between the temperature measured by the temperature measuring device for the slab S and the estimated temperature of the slab S at the temperature measurement point calculated based on the corrected estimated temperature, was 9.3°C. It was confirmed that the estimation accuracy of the slab extraction temperature was improved by (10.6-9.3) / 10.6×100 = 12.3% compared to the comparative example. [Explanation of Symbols]

[0051] 1. Hot rolling line 2. Control device for the heating furnace 11a~11c Heating furnace 12 Hot Scale Breaker 13. Sizing press machine 14a, 14b Rough rolling mill 15a, 15b Water cooling device 21 Temperature measuring device 22. Furnace Operation Information Collection Department 23. Rolling Mill Operation Information Collection Department 24 1st estimated temperature acquisition section 25 Second estimated temperature acquisition section 26 Temperature deviation acquisition section 27 Moving average acquisition part 28 Correction calculation section 29 Heating Furnace Control Unit 30 Storage device S slab (steel material)

Claims

1. A method for controlling heating furnaces in a hot rolling line comprising: multiple heating furnaces for heating steel material; a hot scale breaker for removing scale from the surface of the steel material extracted from the heating furnaces; and a rolling mill for rolling the steel material that has passed through the hot scale breaker, For each of the multiple steel materials passing through the hot rolling line, the temperature of the steel material is measured at any point on the hot rolling line after the exit of the hot scale breaker. For each of the aforementioned steel materials, the first estimated temperature is obtained by calculating the furnace extraction temperature of the steel material using the temperature obtained by the measurement and the operating information of the rolling equipment for the steel material whose temperature was measured. For each of the aforementioned steel materials, a second estimated temperature is obtained by calculating the furnace extraction temperature of the steel material using the operating information of the heating furnace when the steel material is heated. For the same steel material, the temperature deviation is obtained by calculating the difference between the first estimated temperature and the second estimated temperature. For each group of steel materials heated in the same heating furnace among the multiple steel materials, the moving average of the temperature deviation is calculated. The moving average is multiplied by a coefficient between 0 and 1 to obtain a temperature correction value. A heating furnace control method comprising controlling each of the multiple heating furnaces individually based on a corrected estimated temperature obtained by correcting the second estimated temperature using the temperature correction value.

2. A control device for a heating furnace in a hot rolling line comprising: multiple heating furnaces for heating steel material; a hot scale breaker for removing scale from the surface of the steel material extracted from the heating furnaces; and a rolling mill for rolling the steel material that has passed through the hot scale breaker, For each of the multiple steel materials passing through the hot rolling line, a temperature measuring device is provided to measure the temperature of the steel material at any point on the hot rolling line after the exit of the hot scale breaker, A heating furnace operation information collection unit collects operational information of the aforementioned heating furnace, A rolling operation information collection unit collects operational information of the aforementioned rolling equipment, A first estimated temperature acquisition unit obtains a first estimated temperature by calculating the furnace extraction temperature of each of the steel materials using the temperature measured by the temperature measuring device and the operation information for the steel material whose temperature was measured, which is collected by the rolling operation information acquisition unit. For each of the aforementioned steel materials, a second estimated temperature acquisition unit obtains a second estimated temperature by calculating the furnace extraction temperature of the steel material using the operation information collected by the furnace operation information acquisition unit when the steel material is heated, A temperature deviation acquisition unit obtains a temperature deviation by calculating the difference between the first estimated temperature and the second estimated temperature for the same steel material. A moving average acquisition unit acquires a moving average of the temperature deviation for each group of steel materials heated by the same heating furnace among multiple heating furnaces, among the multiple steel materials. A correction calculation unit calculates a temperature correction value by multiplying the moving average by a coefficient between 0 and 1, and corrects the second estimated temperature using the temperature correction value to obtain a corrected estimated temperature. A control device for a heating furnace, comprising: a heating furnace control unit that controls each heating furnace based on the corrected estimated temperature.

3. A method for manufacturing a hot-rolled steel sheet, comprising heating a steel material in a heating furnace controlled by the heating furnace control method described in claim 1, and hot-rolling the steel material extracted from the heating furnace using the rolling equipment.

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