JP2013086132A - Method for controlling cooling of steel sheet and device for manufacturing steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling cooling of a steel sheet which highly accurately predicts a steel sheet temperature and controls the steel sheet temperature after cooling to a prescribed level by a method for calculating specific heat of the steel sheet without predicting a transformation rate.SOLUTION: The method for controlling cooling of a steel sheet comprises controlling a cooling water amount based on a temperature prediction calculation result of a steel sheet and controlling a steel sheet temperature after cooling to a prescribed temperature using a cooling device for jetting cooling water while conveying a high temperature steel sheet heated to a transformation point Ac3 or higher. The predicted temperature of the steel sheet is calculated by using specific heat of the steel sheet derived by analyzing steel sheet temperature actual values before and after cooling measured at an inlet side and an outlet side in the cooling device, and steel sheet temperature actual values measured at one or more spots in the cooling device.

Description

  The present invention is a steel sheet cooling control method for controlling a steel sheet temperature to be a predetermined temperature by cooling with a cooling device that jets cooling water while conveying a heated high-temperature steel sheet, and therefore The present invention relates to a steel plate manufacturing apparatus.

  Taking hot rolling as an example, when cooling with a cooling device that jets cooling water while conveying the hot-rolled hot steel plate, the steel plate temperature after cooling is important to influence the mechanical properties of the steel plate This is one of the major factors. Therefore, in order to manufacture a steel plate having a predetermined mechanical characteristic, it is necessary to accurately control the steel plate temperature after cooling to a predetermined temperature.

  In order to control the steel plate temperature after cooling, it is necessary to set the cooling water amount of the cooling device and the conveyance speed when the steel plate passes through the cooling device before the rolled steel plate enters the cooling device. Therefore, in order to derive this setting condition, the steel sheet temperature prediction model is based on the plate thickness, specific heat, density, conveyance speed, temperature at the start of cooling, cooling water amount of the cooling device, water temperature, and the temperature near the cooling device. The steel plate temperature after cooling is predicted by using it, and the cooling condition setting is adjusted based on the prediction result.

  Here, in order to accurately control the steel plate temperature after cooling to a predetermined temperature, the prediction accuracy of the steel plate temperature prediction model must be high. To that end, in addition to the amount of heat deprived from the steel sheet surface by water cooling (water cooling extraction heat amount), the amount of heat deprived by air cooling (air cooling extraction heat amount), the amount of heat generated during steel phase transformation (transformation heat generation amount) is accurately predicted There is a need to.

  In Patent Document 1, assuming that it is difficult to improve the accuracy of the steel plate temperature prediction model, the steel plate temperature is measured at many points in the steel plate conveyance direction in the cooling device, and the amount of water in the cooling device is based on the measured value. A method of correcting the setting in the middle and controlling the steel plate temperature after cooling with high accuracy is shown.

  Patent Document 2 discloses a technique for increasing the accuracy of steel plate temperature prediction by uniformly converting the amount of heat generated during the progress of steel phase transformation into the specific heat of the steel plate and cooling the front and back surfaces uniformly. .

  Patent Document 3 is also an approach that considers the amount of heat generated during the progress of steel phase transformation by converting it to the specific heat of the steel sheet, but unlike Patent Document 2, the enthalpy of the austenite phase and ferrite phase and the transformation of each phase. The specific heat is calculated using the rate.

JP 2010-23066 A JP 2006-281271 A JP 2006-193759 A

  However, in the method described in Patent Document 1, it is necessary to always provide a large number of temperature measuring means in the cooling device, which increases equipment costs and maintenance costs.

  Although Patent Document 2 shows the existence of a model for calculating the specific heat corresponding to the components of the steel sheet, there is no description about the content of the model for calculating the specific heat, and the temperature of the steel sheet is specifically described using this model. I can't control it.

  The method described in Patent Document 3 is a method that considers dynamic transformation heat generation on the premise of cooling in actual steel sheet production, but this method is based on the assumption that the transformation rate can be accurately predicted. . Here, a method for obtaining the transformation rate by experiment and a method for calculating by a transformation prediction calculation model are shown, but experimenting with many steel types that are actually manufactured involves considerable costs, and transformation prediction calculation Calculation errors are inevitable in the model. In addition, since it is difficult to measure the error, the error cannot be compensated.

  Therefore, in view of the above problems, the present invention provides a method for calculating the specific heat of a steel sheet without predicting the transformation rate, thereby increasing the accuracy of the steel sheet temperature prediction and controlling the steel sheet temperature after cooling to a predetermined temperature. It is an object to provide a control method. Moreover, the manufacturing apparatus of the steel plate for that is provided.

  Conventionally, in order to accurately predict the steel plate temperature after cooling, it is necessary to accurately predict the amount of water-cooled heat removal, air-cooled heat removal, and transformation heat generation. On the other hand, as a result of intensive studies, the inventors used the actual steel plate temperature change (measured value), the calculated water-cooled heat removal amount, and the air-cooled heat removal amount without predicting the transformation heat generation amount, and the steel plate temperature. The present invention was completed with the knowledge that the accuracy of the steel plate temperature prediction can be improved by deriving the specific heat of the steel plate so that the calculation result of the prediction model matches the measured value of the steel plate temperature. The present invention will be described below.

  The invention according to claim 1 uses a cooling device that ejects cooling water while conveying a high-temperature steel plate heated to the Ac3 transformation point or higher, and manipulates the amount of cooling water based on the temperature prediction calculation result of the steel plate. A cooling control method for controlling the steel plate temperature after cooling to a predetermined temperature, measured at one or more points in the cooling device and the actual steel plate temperature value before and after cooling measured on the inlet side and outlet side of the cooling device. The steel sheet cooling control method is characterized in that the predicted temperature of the steel plate is calculated using the specific heat of the steel plate derived by analyzing the actual steel plate temperature value.

  The invention according to claim 2 is characterized in that, in the cooling control method for a steel sheet according to claim 1, the value of the specific heat changes according to the temperature of the steel sheet, and the change is expressed by five or more nodes. To do.

  The invention according to claim 3 is the method for cooling control of a steel sheet according to claim 2, wherein the node is calculated so as to minimize the sum of squares of errors between the steel sheet temperature prediction result and the steel sheet temperature actual value. It is characterized by.

  The invention according to claim 4 is a conveying device that conveys a high-temperature steel plate heated to an Ac3 transformation point or higher, a cooling device that jets cooling water to the conveyed steel plate, and an inlet side of the cooling device , At least one thermometer disposed on each of the outlet side and the inner side, the steel plate actual temperature value before and after cooling measured by the thermometers disposed on the inlet side and the outlet side of the cooling device, and the cooling device A steel plate manufacturing apparatus comprising: an arithmetic device that calculates a predicted temperature of a steel plate using a specific heat of the steel plate derived by analyzing a steel plate temperature actual value measured by a thermometer disposed inside.

  The invention according to claim 5 is the steel plate manufacturing apparatus according to claim 4, wherein the specific heat is derived by the arithmetic unit assuming that the value of the specific heat changes according to the temperature of the steel plate, and the change is 5 points or more. It is characterized by being expressed in terms of nodes.

  By this invention, it becomes possible to control the steel plate temperature after cooling to predetermined | prescribed temperature accurately.

It is a figure which shows the manufacturing apparatus of the steel plate which concerns on one embodiment. It is a figure which shows an example of the derived | led-out form of specific heat. It is the figure which showed the derivation | leading-out result of the specific heat of the steel type 1. FIG. It is the figure which showed the derivation | leading-out result of the specific heat of the steel type 2. FIG. It is a figure which shows the manufacturing apparatus of the steel plate at the time of performing steel plate cooling control. It is a figure which shows the specific heat used for the Example and the comparative example.

  The above-mentioned operation and gain of the present invention will be clarified from the following embodiments for carrying out the invention. However, the present invention is not limited to these embodiments.

FIG. 1 is a diagram illustrating one embodiment, and is a diagram schematically showing a steel plate manufacturing apparatus 100 that includes a cooling device 20 and is used for data acquisition.
The steel plate manufacturing apparatus 100 includes a transport device 2 that transports a steel plate 1 that is an object of cooling control, and a cooling device 20 is provided in the middle of a line that transports the steel plate 1.

The cooling device 20 is a device that cools the steel plate 1 by ejecting cooling water from above and below the steel plate 1 that passes through the cooling device 20. Specifically, a total of n cooling headers 3 are arranged in the conveying direction of the steel plate 1, and each cooling header is provided with a water amount adjusting valve and a water meter that measures the amount of cooling water ejected to the steel plate 1.
A known device can be applied as such a cooling device 20.

  Furthermore, the steel plate manufacturing apparatus 100 includes a speedometer 7, a plate thickness gauge 8, and a cooling device entry-side thermometer 4 on the upstream side in the transport direction from the cooling device 20, and thereby, when entering the cooling device 20. The speed, plate thickness, and entry temperature of the steel plate 1 are measured.

  Further, the steel plate manufacturing apparatus 100 includes two cooling device thermometers 6 in the cooling device 20 and a cooling device outlet thermometer 5 on the cooling device outlet side. The cooling device outlet temperature is measured. Furthermore, when the steel plate 1 passes through the cooling device 20, the amount of water ejected from each header is also measured by the water meter provided in the cooling device 20.

In addition to the above, the steel plate manufacturing apparatus 100 is provided with an arithmetic device 10 and a data storage device 11.
The arithmetic unit 10 includes a cooling device inlet side thermometer 4, a cooling device outlet side thermometer 5, a cooling device thermometer 6, a speed meter 7, a plate thickness meter 8, and a water meter of the cooling device 20 (hereinafter referred to as these). When collectively describing, it may be described as “each measuring device.”) Is a device that obtains each measured value from, calculates based on this, and outputs the result. The specific calculation will be described in detail later. The calculation includes calculation for predicting the steel plate temperature based on the temperature prediction model, and calculation of specific heat performed in the calculation.

  Although the specific form of such an arithmetic unit 10 is not specifically limited, What is called a computer apparatus can be mentioned. That is, the arithmetic unit 10 includes a receiving unit that receives each measurement value described above, a storage unit that stores a program that is a basis for the calculation, a central operator (CPU) that performs a calculation based on the program, a work area of the CPU, A RAM that functions as a temporary data storage unit and an output unit that outputs a calculation result are provided.

  The storage device 11 is a device that sends data to be stored, such as measurement value data acquired by the arithmetic device 10 and calculation results of the arithmetic device 10, from the arithmetic device 10, and stores the data.

  By performing the cooling control of the steel plate with the steel plate manufacturing apparatus 100 as described above, the steel plate temperature after cooling can be accurately controlled to a predetermined temperature. Hereinafter, the steel sheet cooling control method will be described more specifically.

  When the steel plate 1 moves on the conveying device 2 and the tip of the steel plate 1 reaches each measuring device, the arithmetic device 10 collects measurement values from each measuring device at intervals of the predetermined length of the steel plate 1. The sampling is continued until the tail end of the steel plate 1 reaches the cooling device outlet thermometer 5. Then, various calculations are performed based on the collected measurement data, and the results are stored in the storage device 11.

  Here, in various calculations, the steel plate 1 is an aggregate of cut plates obtained by cutting the steel plate 1 with a predetermined length, and each cut plate is considered to pass through the measurement region of each measuring device. This facilitates the prediction of the steel sheet temperature, which will be described later, and treats one steel sheet as a plurality of cut plates cut into a predetermined length, so that a plurality of predicted values can be obtained from one steel sheet. .

  Next, prediction calculation of the steel sheet temperature performed by the arithmetic device 10 for cooling control of the steel sheet will be described. This prediction calculation is performed by the following steel plate temperature prediction model.

  As described above, in the cooling device 10, n cooling headers are arranged in the conveyance direction of the steel plate 1, but this one region is called a cooling zone, and the steel plate temperature prediction model indicates the temperature drop amount for each zone. The steel plate temperature after cooling is estimated by calculating.

  For the cooling zone in which cooling water is jetted from the cooling header and cooled by water, the water cooling part temperature drop ΔTw is calculated using the water cooling part temperature drop prediction formula of equation (1).

Here, i is a subscript indicating a cooling zone, α _L is a heat transfer coefficient (kcal / m ² h ° C.) of a water-cooled portion, ρ is a density (kg / m ³ ) of a steel plate, h is a plate thickness (m), T represents the steel sheet temperature (° C.), _TL represents the cooling water temperature (° C.), and t represents the passage time (h) of the cooling zone i. The following expressions are also the same.

  Further, c means specific heat (kcal / kg ° C.), and calculation of the specific heat c will be described in detail later. The same applies to the specific heat c used in the following formula (4).

In equation (1), α _Li is obtained from equation (2), and t is obtained from equation (3).

In Equations (2) and (3), a and b are constants, W is the cooling water density (m ³ / m ² · h), L is the cooling zone length (m), and V is the steel sheet passing through the cooling zone. Speed (m / h). The same applies to the following expressions.

  On the other hand, for the zone where the cooling water is not jetted, the air cooling part temperature drop ΔTa is calculated using the air cooling part temperature drop prediction formula (4).

Here, T _A is the temperature (° C.), σ is the Stefan-Boltzmann constant, ε is the emissivity (−), and α _A is the convective heat transfer coefficient (kcal / m ² h ° C.) of the air-cooled part.

Such calculation method, the temperature T _S measured by the cooling device inlet temperature meter 4 can predict the temperature T _E after cooling to a base point. In addition, the predicted temperatures T _M1 and T _M2 for the two thermometers 6 in the cooling device are also predicted temperature values of the cooling zone in the middle of the cooling device, and can be obtained simply by changing the number of zones. The equation for obtaining T _E is represented by Equation (5), the equation for _obtaining T _M1 is represented by Equation (6), and the equation for _obtaining T _M2 is represented by Equation (7).

  Here, n is the total number of cooling zones, and m1 and m2 are the cooling zone numbers where the thermometer 6 in the cooling device is installed.

  Next, a method for deriving the specific heat c will be described. The specific heat used in the steel sheet temperature prediction calculation in the present embodiment is such that the specific heat value changes corresponding to the steel plate temperature, the specific heat value increases in a certain temperature range during the transformation heat generation, and the low temperature side of the rising part, and On the high temperature side of the rising part, the change in specific heat value is small and almost constant.

  The figure explaining the form of the specific heat derived | led-out in FIG. 2 was shown. As can be seen from FIG. 2, specific heat values that change in accordance with the steel plate temperature are set as five nodes (nodes A to E), and linearly interpolated values are used between the nodes. The positions of the five nodes are derived by a method described later, but the positions of the nodes are subject to the following restrictions. In the following description, “temperature direction” means the horizontal axis direction in FIG. 2, and “specific heat direction” means the vertical axis direction in FIG.

  The specific heat before transformation exotherm is the value of the austenite phase, and the node E is fixed at both temperature and specific heat. The node D is movable only in the temperature direction, but the movement in the temperature direction is higher than the node B. The specific heat after transformation heat generation is the value of the ferrite phase, and the node A is a fixed value for both temperature and specific heat. The node B is movable on the line segment X-Y, but the temperature direction is lower than the node D. The node C can move in both the temperature direction and the specific heat direction, but the movement in the temperature direction is between the node B and the node D.

  Here, the description has been given of the case where there are five nodes A to E. However, in order to more accurately express the specific heat of the austenite phase and the ferrite phase, the number of fixed nodes may be further increased and the number of nodes may be more than five. Further, in order to take into account the transformation heat generation phenomenon in which the temperature range and the heat generation amount vary depending on the components and cooling conditions of the steel plate, at least three movable nodes are necessary. However, if there are too many, it becomes difficult to set the constraint condition of each node, so it is desirable that there are at most four movable nodes.

  Therefore, the specific heat c determined by the relationship between the temperature and the specific heat in consideration of such nodes is applied to the expressions (1) and (4).

Next, a method for deriving a node of specific heat c will be described. The values in the temperature direction of the movable nodes B, C, and D shown in FIG. 2 are T _XB , T _XC , and T _XD , respectively, and the value in the specific heat direction of the movable node C is C _XC . As described above, the steel plate temperature prediction value is calculated as j pieces of T _M1 , T _M2 , and T _E cut by a predetermined length from one steel plate, and this is calculated as 3 × j prediction values T _CAL. The measured values at the two cooling device thermometers 6 and the measured values at the cooling device outlet side thermometer 5 corresponding to this are similarly 3 × j _TACTs .
Thus, T _CAL can be regarded as a function with respect to the positions of the nodes B, C, and D, and in order to improve the prediction accuracy, the sum of squares of errors between T _CAL and T _ACT shown in Equation (8) is used. What is necessary is just to obtain T _XB , T _XC , T _XD , and C _XC that are minimized. For example, the calculation may be performed using an optimization method such as a least square method, or an optimization method other than this may be used.

  Next, an example in which two steel types are applied to the derivation of specific heat described so far will be shown. Table 1 shows the additive elements of Steel Type 1 and Steel Type 2.

The result of steel type 1 is shown in FIG. FIG. 3 (a) shows the result of the derivation of the specific heat. FIG. 3 (b) shows the measured value measured at the cooling device inlet side thermometer, the two-point cooling device thermometer, the cooling device outlet temperature, and the derived specific heat. It is a predicted value corresponding to the two thermometers in the cooling device and the cooling device outlet side thermometer calculated using the measured value of the cooling device inlet side thermometer as a base point.
Similarly, the results for steel type 2 are shown in FIGS. 4 (a) and 4 (b).

  Thus, if the steel plate temperature prediction is performed using the specific heat derived for each steel type, good temperature prediction accuracy can be obtained. Since the derived specific heat is calculated so as to match the actual steel plate temperature measurement value, applying this specific heat to the steel plate temperature prediction model causes some calculation errors in the water-cooled heat extraction amount and air-cooled heat extraction amount. Even if it exists, the steel plate temperature after cooling can be accurately predicted.

  Although the present invention derives the transformation heat value from the temperature measurement value of the steel sheet, the specific heat nodal point cannot be accurately derived without the temperature measurement value during the transformation heat generation. Therefore, the thermometer installation position in the cooling device needs to be able to measure the temperature during the transformation heat generation. Therefore, although one thermometer is installed in the cooling device, two or more thermometers are installed in order to cope with various steel types that undergo phase transformation in different temperature ranges. It is desirable. In addition, the thermometer in the cooling device is necessary only for deriving a specific heat node, and is not necessarily provided permanently.

Above-described formula (1) to (5), and wherein the Mochiiraru specific heat by finding as described above, it is possible to calculate the temperature of the steel strip T _E after cooling to be predicted. Here, in the formulas (1) to (5), it is desirable to make error factors other than the derived specific heat c as small as possible. Specifically, by appropriately adjusting the constants a and b for obtaining the temperature drop amount of the water cooling part, the emissivity ε for obtaining the temperature drop amount of the air cooling part, and the convective heat transfer coefficient α _A of the air cooling part. is there. These values show cooling data under conditions where the transformation heat generation does not occur during cooling and the specific heat c value is a known austenitic stainless steel plate, or the cooling start temperature is low so that the phase transformation is completed before cooling. It is desirable to use and adjust.

  So far, the derivation of the specific heat and the temperature prediction using the specific heat have been described. Next, a method for controlling the steel plate temperature to a predetermined temperature using the specific heat and temperature prediction derived will be described. FIG. 5 shows a diagram for this purpose. In addition, the same code | symbol is attached | subjected about the part which is common in FIG. 1, and description is abbreviate | omitted.

The steel plate manufacturing apparatus 200 has a cooling device 20, a total of n cooling headers 3 are arranged in the conveying direction of the steel plate, a water amount adjusting valve is installed in each cooling header, and the cooling device controller 12 instructs It is the structure which can eject the amount of water which was made to the steel plate.
When the steel plate 1 enters the cooling device 20, the speed, plate thickness, and temperature are measured by the speedometer 7, the plate thickness meter 8, and the cooling device entry side thermometer 4. In addition to this measurement information, the specific heat of the corresponding steel type from the density of the steel plate 1, the initial cooling water amount of the cooling device 20, the water temperature, the air temperature in the vicinity of the cooling device, and the specific heat corresponding to various steel types stored in the data storage device 11. Is selected, and the steel plate temperature after cooling is predicted using Equations (1) to (5).

  Then, the water density of the cooling device 20 is calculated such that the predicted steel plate temperature value matches the target value, and the cooling steel plate temperature is controlled to the target value by instructing the water amount setting so that the water density setting is realized. can do.

  In the above description, a hot-rolled steel sheet is targeted, but the present invention is not limited to this, and can be applied to other processes such as continuous annealing.

As an example, for the five steel types shown in Table 2, cooling control of the steel sheet was performed using the specific heat derived as described above under the conditions described in Table 2. As a comparative example, cooling control using specific heat described in Document 1 below was also performed.
(Reference 1) Cooling technology in steel manufacturing process, cooling technology research subcommittee report,
August 1988 Japan Iron and Steel Association

  Table 2 shows the target ratio (%) of the cooling stop temperature ± 20 ° C., and the derived specific heat and the specific heat described in Reference 1 of the comparative example are shown in FIG. The specific heat used in the comparative examples was 0.06% C carbon steel for steel types A, B and C, and 0.23% C carbon steel for steel types D and E.

  The target values shown in Table 2 are determined for steel types A to E with a target value for the cooling stop temperature, which is the steel plate temperature after cooling, and with a probability of ± 20 ° C. of this target value. It is evaluated whether it can be controlled. As can be seen from Table 2, it was confirmed that the example controlled to the target value with higher probability than the comparative example.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Conveying means 3 Cooling header 4 Cooling device entrance side thermometer 5 Cooling device exit side thermometer 6 Cooling device thermometer 7 Steel plate speed measuring device 8 Steel plate thickness measuring device 10 Arithmetic device 11 Data storage device 12 Cooling device control Controller 20 Cooling device 100 Steel plate manufacturing device 200 Steel plate manufacturing device

Claims (5)

Using a cooling device that ejects cooling water while conveying a high-temperature steel plate heated to the Ac3 transformation point or higher, the amount of cooling water is manipulated based on the temperature prediction calculation result of the steel plate, and the steel plate temperature after cooling is set to a predetermined temperature. A cooling control method for controlling
The specific heat of the steel sheet derived by analyzing and analyzing the steel sheet temperature actual value before and after cooling measured at the inlet side and the outlet side of the cooling apparatus and the steel sheet temperature actual value measured at one or more points in the cooling apparatus. A method for controlling the cooling of a steel sheet, comprising calculating a predicted temperature of the steel sheet.   The steel sheet cooling control method according to claim 1, wherein the specific heat value changes according to the temperature of the steel sheet, and the change is expressed by five or more nodes.   The steel sheet cooling control method according to claim 2, wherein the node is calculated so as to minimize a sum of squares of errors between the steel plate temperature prediction result and the steel plate temperature actual value. A transport device for transporting a high-temperature steel sheet heated to an Ac3 transformation point or higher;
A cooling device for ejecting cooling water to the conveyed steel plate;
At least one thermometer disposed on each of the inlet side, the outlet side, and the inner side of the cooling device;
Analyzing the actual steel plate temperature measured before and after cooling measured with the thermometers arranged on the inlet side and the outlet side of the cooling device, and the actual steel plate temperature measured with the thermometer arranged inside the cooling device And a computing device that computes the predicted temperature of the steel sheet using the specific heat of the steel sheet derived as described above.   The derivation of the specific heat in the arithmetic device is calculated by expressing the change with five or more nodes, assuming that the value of the specific heat changes according to the temperature of the steel sheet. Steel plate manufacturing equipment.

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