JP2006224177A - Method for predicting shape of metallic strip, method for judging shape on the basis of predicted shape and method for straightening shape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a predicting method of the shape of a metallic strip by which the shape after cooling to the normal temperature is accurately predicted about the metallic strip after hot rolling and also to provide exact judging method of the shape on the basis of the predicted shape and the straightening method of the shape. <P>SOLUTION: On the basis of the temperature and the shape of the metallic strip 5 which are on-line measured with a thermometer1 and a flatness gage 2 installed on the outlet side of the final stand 6 of a finishing mill or this side of a coiler 10, the shape when the strip is cooled to the normal temperature is predicted by an analytical model taking phase transition into consideration. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a metal band shape prediction method capable of accurately estimating a shape (flatness) after cooling to room temperature in a metal band after hot rolling when rolling a metal band such as a steel band. is there.

  In recent years, metal strips such as steel strips have been demanded by customers to be more flat, and there is an allowable limit for the shape defects of metal strip products such as (a) ear stretch and (b) belly stretch shown in FIG. As quality becomes stricter, quality assurance for shapes has become a very important issue. In FIG. 2, 5 indicates a metal strip.

  In order to control the shape immediately after hot rolling to a specified target accuracy, a rolling mill with good crown and shape controllability such as a 6-fold rolling mill and a cross mill has been developed. Its intermediate roll shift position, cross angle, roll bending Highly accurate shape and crown control was realized by appropriately initializing the amount and further dynamically controlling it.

However, for example, even if the shape of the hot-rolled steel strip is controlled as desired immediately after the finish rolling mill, the shape is usually changed by cooling after the run-out table, and thus there are the following problems. .
(1) When a shape correction process is added in accordance with the shape at the time of shape measurement, if the shape changes after cooling and falls within the reference value, an unnecessary process is added and the cost is increased.
(2) Even if it is within the reference value at the time of shape measurement, if the wave shape increases after cooling and exceeds the reference value, problems such as blockage in the next process and shipment of defective coils occur.

  For example, in Patent Document 1, as a method for controlling the shape of the metal band, a method for correcting the shape by installing a tension leveler upstream of a coiler that winds up the metal band after completion of cooling with a run-out table is disclosed in Patent Document 1. The roll just before the final roll of the tension leveler is a shape detection roll that can measure the distribution of the tension in the metal strip in the width direction, and the push amount setting of the shape detection roll is changed based on the shape information of the metal strip from the shape detection roll. A method for controlling the shape of the metal strip has been proposed.

  In Patent Document 2, as a method of controlling the shape of the metal strip, the surface temperature of the metal strip is measured on the entry side or exit side of the final stage of the finishing mill, and the thermal stress residual stress generated at normal temperature based on the measured temperature distribution. The shape of the metal strip is controlled by applying stress by a finishing mill so that the residual stress does not cause a shape defect.

In [Best Mode for Carrying Out the Invention], the following Non-Patent Document 1 is cited and described here.
JP-A-5-269527 JP 2002-45907 A "Numerical simulation of phase transformation and material behavior" (Corona)

  However, in the metal band shape control method described in Patent Document 1 described above, the information used as a reference for shape control is steepness or elongation strain difference, and temperature distribution in the plate width direction is not considered. If it is cooled to near normal temperature in the rolling process, the temperature distribution in the plate width direction becomes almost uniform.However, since most materials are usually wound at a high temperature to make the material, the temperature distribution in the plate width direction is A temperature deviation is generated in which the end portion is lower than the central portion. Therefore, even if the difference in elongation strain is once eliminated by such a method, since the temperature deviation at this time reaches room temperature, it remains as thermal stress, which does not lead to improvement of the shape.

  Further, in the metal strip shape control method described in Patent Document 2 described above, a shape defect due to thermal stress due to temperature distribution on the entry side or exit side of the final stage of the finishing mill is calculated. It does not consider the generation of permanent strain such as creep strain and plastic strain caused by temperature distribution and phase transformation behavior in the cooling process. Furthermore, in order to accurately evaluate the shape, it is necessary to take into account the winding tension in the coiler and deformation due to the temperature deviation of the coil when the coil is cooled after winding.

  The present invention solves the above-described problems of the prior art and provides a metal band shape prediction method capable of accurately predicting a shape after cooling to room temperature with respect to a metal band after hot rolling. For the purpose. Furthermore, it aims at providing the exact shape determination method and shape correction method based on the prediction shape by this shape prediction method.

  The present invention has been made to solve the above-described problems. The initial measurement values of the temperature and shape distribution of the metal strip in the hot state are used to determine the temperature, stress / strain, and phase transformation in the cooling process to room temperature. By performing coupled analysis and analyzing sequentially, the final shape is predicted with high accuracy over the entire length. Furthermore, based on the predicted shape over the entire length of the metal strip according to this shape prediction method, the quality determination and shape correction condition setting are performed.

  The gist of the present invention is as follows.

  [1] The temperature distribution in the plate width direction and the shape distribution in the plate width direction of the metal strip after hot rolling are measured hot, and the metal strip is coiled by an analysis model that takes into account the phase transformation based on the measured values. A method for predicting the shape of a metal strip, which is characterized by predicting the shape after winding to cool to room temperature.

  [2] At the delivery side of the finishing mill, the temperature distribution in the plate width direction and the shape distribution in the plate width direction of the metal strip are measured, and the analysis model includes a heat transfer model, a phase transformation model, and a stress / strain model on the runout table. From the step of analyzing, the step of analyzing the heat transfer model, phase transformation model and stress / strain model in coiler winding, and the step of analyzing the heat transfer model, phase transformation model and stress / strain model in coil cooling The metal band shape prediction method according to the above [1], characterized in that

  [3] The temperature distribution in the plate width direction and the shape distribution in the plate width direction of the metal strip are measured before the coiler, and the analysis model analyzes the heat transfer model, the phase transformation model, and the stress / strain model in the coiler winding. The method for predicting the shape of a metal strip according to the above [1], comprising a step and a step of analyzing a heat transfer model in coil cooling, a phase transformation model, and a stress / strain model.

  [4] The plate width direction temperature distribution and the plate width direction shape distribution of the metal strip are measured over the entire length, and the shape after the metal strip is wound around a coil and cooled to room temperature is predicted over the entire length. [1] The method for predicting the shape of a metal strip according to any one of [3].

  [5] If the predicted shape of the metal band at room temperature obtained by the metal band shape prediction method according to any one of [1] to [4] is within the target shape range, A shape determination method for a metal strip, characterized in that shape correction is omitted and when it is outside the target shape range, whether or not shape correction is necessary is determined so that the shape correction is performed in the next step.

  [6] Based on the predicted shape of the metal band at room temperature obtained by the metal band shape prediction method according to any one of [1] to [4], from the target shape range of the metal band tip and rear end to be discarded in the next step A method for determining the shape of a metal band, comprising determining a length of a defective shape that has been removed.

  [7] Based on the predicted shape of the metal band at room temperature obtained by the metal band shape prediction method according to any one of [1] to [4], the shape correction condition for the next process is set according to the predicted shape. A method for correcting the shape of a metal strip, characterized by:

  According to the present invention, after the metal strip after hot rolling is wound by a coiler through a cooling process on a run-out table, the final shape is predicted over the entire length when cooled to room temperature in a coil state. It becomes possible. Furthermore, based on the predicted shape at normal temperature, it is possible to determine the optimum shape determination and shape correction conditions.

  In other words, by accurately predicting the shape after cooling using the present invention, it is possible to predict the coil where the shape defect occurs after cooling even if the shape defect does not occur after finish rolling or before the coiler. By passing only the coil through the shape correction line by the skin pass or the leveler, it becomes possible to prevent the defectively shaped coil from obstructing the threading plate in the next process and shipping the defectively shaped coil to the customer.

  Furthermore, even if shape defects occur after finish rolling or before the coiler, it is possible to determine that it is not necessary to pass through the shape correction line for coils whose shape defects are eliminated after cooling. At the same time, the processing capability of the shape correction line can be secured.

  Moreover, when shape correction is performed in the next process, by setting the correction condition based on the predicted shape of each position of the coil, effective shape correction is possible, and a flatter coil is obtained.

  Also, if there is a particularly bad shape at the front and rear ends of the coil, but it does not lead to shape correction over the entire length, send information on the length of the shape failure to the next process and cut off only that portion. For example, it is possible to prevent breakage due to poor welding in the pickling line with a minimum cut-off amount, and it is possible to prevent breakage at the welded portion and improve yield.

  The present inventors have made various studies on the mechanism of shape deterioration and the measures for flattening the shape. The principle of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a shape prediction system used in an embodiment of the present invention, and a plate surface temperature realized by a scanning thermometer or the like for measuring a plate width direction temperature distribution of a plate surface of a metal strip 5. The measurement means 1, the shape measurement means 2 for calculating the shape distribution in the plate width direction of the metal strip 5 by a laser distance meter or the like on the downstream side of the measurement means 1, and the measurement results of both the measurement means 1 and 2 are An arithmetic processing control device 3 such as a microcomputer that performs a predetermined calculation by being introduced, and a display device 4 such as a CRT that displays each information such as the calculation result of the arithmetic processing control device 3 on the screen. Yes. The metal strip 5 to be measured is rolled in a hot rolling line, and both the measuring means 1 and 2 are the temperature in the width direction of the metal strip in the warm state after the finish rolling mill or before the coiler. For example, the distribution and the shape distribution in the plate width direction are measured in a non-contact manner.

  The arithmetic processing control device 3 uses the plate surface temperature profile measured by the plate surface temperature measuring unit 1 and the shape distribution measured by the shape measuring unit 2 as initial values, and the cooling conditions, plate passing conditions, winding conditions, etc. that follow the measurement. Shape calculation means to estimate the shape of the metal strip after cooling to room temperature by coupling and solving heat transfer analysis to obtain temperature distribution, viscoelastic plastic analysis to obtain stress / strain state, and phase transformation analysis Is provided.

  An outline of the shape prediction method based on the shape prediction system having such a configuration will be described below.

  FIG. 3 shows an example of a metal strip production line used for carrying out the present invention, and is a schematic diagram showing each step after finish rolling in a hot rolling line for producing a hot-rolled steel strip. As shown in FIG. 3, after the metal strip 5 exiting the finishing mill final stand 6 passes through the cooling zone 7 and is wound around the drum 9 in the coiler 10 to become the coil 8, it reaches the room temperature in the coil yard 11. To be cooled.

  In this embodiment, the plate width direction temperature distribution and the plate width direction shape distribution of the metal strip 5 measured online by the thermometer 1 and the shape meter 2 installed on the exit side of the finishing mill final stand 6 or in front of the coiler 10. Based on the above, a shape is predicted when cooled to room temperature by an analysis model considering phase transformation.

  The analysis procedure in the shape prediction method according to this embodiment is shown in the flowchart of FIG.

  First, material conditions (metal strip dimensions, yield function, mechanical properties, thermophysical values, parameters indicating phase transformation behavior, etc.), plate feed conditions (plate speed, plate tension, etc.), cooling conditions (heat transfer) Coefficient, cooling medium temperature, cooling zone length, etc.) and winding conditions (winding tension, drum diameter, etc.). Thereafter, based on the plate width direction temperature distribution and the plate width direction shape distribution measured by the thermometer 1 and the shape meter 2 installed on the exit side of the finishing mill final stand 6, the run-out table provided with the cooling zone 7. Analyzing the heat transfer model, phase transformation model and stress / strain model in the coil, analyzing the heat transfer model, phase transformation model and stress / strain model in the coiler winding in the coiler 10, the coil yard 11 and the like The step of analyzing the heat transfer model, the phase transformation model, and the stress / strain model in the coil cooling is executed, and the final shape at normal temperature is output.

  The outline of each model on the flowchart is shown below.

  The temperature distribution of the plate cross section is calculated by solving the following heat conduction equation (1) and boundary condition equation (2). As the heat transfer model, for example, by using an explicit method differential model obtained by discretizing Equation (1) and Equation (2), calculation in a short time that can withstand online use is possible.

  As a phase transformation model, it is desirable to introduce a phase transformation analysis method considering temperature history in order to perform highly accurate analysis. For example, it can be realized by a technique using the TTT diagram described in Chapter 5 of Non-Patent Document 1. Since the material constants used in the heat transfer model and the phase transformation model depend on the temperature and the transformation rate, it is necessary to solve the two models in combination.

  The stress / strain analysis model requires different models for the state of the plate on the run-out table, the coil state during winding by the coiler, and the coil state after winding (after extraction). In order to perform accurate shape prediction analysis, it is necessary to use a model that takes into account heat shrinkage, volume expansion associated with phase transformation, creep deformation, and plastic deformation. The outline of these models will be described below.

  The model on the run-out table can be analyzed in a short time by, for example, the slit model shown in FIG. FIG. 5A is a diagram in the case where the temperature of the plate end portion is larger than that of the center portion on the run-out table. When the strip end is formed into a strip shape due to a difference in thermal contraction, the end portion becomes less elongated. FIG. 5 (b) shows a uniform elongation of FIG. 5 (a), and FIG. 6 shows a schematic diagram of the difference in elongation and the stress acting on the plate at this time. A plastic deformation occurs in a portion where a very large elongation occurs. Further, it is assumed that, in the case of a thin plate, the portion where the elongation is large and the plate is left is buckled and no stress is generated. Deformation can be analyzed by obtaining an elongation such that the sum of the stress distributions in FIG.

  For the analysis in coil winding and the analysis in coil cooling, a model in which cylinders as shown in FIG. 7 are stacked is considered.

  Winding by a coiler is expressed by fitting a cylinder in which circumferential stress equal to winding tension acts on the outermost periphery in the model of FIG. The distribution in the width direction of the coiler tension at this time is obtained by correcting the shape after winding until the shape after fitting the cylinders converges according to the flowchart shown in FIG.

  The flowchart of the coil cooling analysis when the cylindrical model is used is as shown in FIG. The contact condition equation in the flowchart is an equation that gives a contact force such that the displacements of the contact surfaces are equal, considering the two cylinders shown in FIG. It consists of a crown term. Unlike the case where the coil is analyzed as an integral object, the cylindrical model obtains the contact force between each plate of the coil and considers the contact / non-contact between the plates, enabling accurate stress / strain analysis. Yes.

  By analyzing to the normal temperature using the heat transfer model, phase transformation model, and stress / strain model, permanent deformation can be obtained as the sum of thermal shrinkage (including volume expansion accompanying phase transformation), creep deformation and plastic deformation. I want. The final shape is evaluated by the width direction elongation strain difference obtained from the width direction distribution of permanent deformation.

  When the final shape is predicted using the plate width direction temperature distribution and the plate width direction shape distribution measured by the thermometer 1 and the shape meter 2 installed in front of the coiler 10 as initial values, The step of analyzing the heat transfer model, phase transformation model and stress / strain model is omitted, the step of analyzing the heat transfer model, phase transformation model and stress / strain model in coiler winding, and the heat transfer in coil cooling The step of analyzing the model, the phase transformation model and the stress / strain model is executed, and the final shape at room temperature is output. However, it is assumed that the transformation rate at the measurement position is known.

  And the final shape after cooling can be accurately predicted over the entire length of the coil by applying the shape prediction method as described above to the entire length of the metal strip (the entire length of the coil). Furthermore, an accurate shape determination method and shape correction method can be implemented based on the predicted shape over the entire length of the coil.

  As the shape determination method, for example, based on whether the maximum value or average value of the predicted shape over the entire length of the coil is within the target shape range, if it is within the target shape range, by a skin pass or leveler for the cooled metal band It is possible to omit the shape correction and determine whether or not the shape correction is necessary so that the shape correction is performed when the shape correction is out of the target shape range.

  Also, as another shape determination method, based on whether the maximum value or average value in the predetermined length of the leading edge, the trailing edge, or the leading and trailing edges is within the target shape range, the shape deviating from the target shape range at the front and rear ends If there is a defective portion, it is possible to discard only the shape defective portion at the front and rear ends by sending information on the length of the defective shape portion to the next process.

  Furthermore, as the shape correction method, effective shape correction can be performed by setting the correction condition based on the predicted shape of each position of the coil by sending information on the predicted shape over the entire length to the correction process.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The shape prediction method of the present invention is shown in comparison with a conventional shape prediction method (a method for predicting a shape in consideration of only the temperature distribution on the finishing mill exit side) based on a specific example.

  FIG. 11 shows a comparison between the shape (steepness) predicted by the conventional shape prediction method and the actual measurement value. In contrast, FIG. 12 shows a comparison between the shape (steepness) predicted by the shape prediction method of the present invention and the actual measurement value. Here, the determination of the quality of the shape is that the target shape (target steepness) is 1%, and the shape having a maximum steepness over the entire coil length of more than 1% is regarded as a defective shape (NG).

  As shown in FIG. 11, the conventional shape prediction method does not have sufficient prediction accuracy. For this reason, even if the coil has a poor shape in the prediction, it is within the target steepness when actually measured after cooling. Coils that do not require correction will be transported to the correction line, or conversely, despite the prediction that the shape is good, a shape defect actually occurs after cooling, Troubles in the next process and complaints from customers will occur, and sufficient effects cannot be achieved.

  On the other hand, as shown in FIG. 12, the shape prediction method of the present invention can predict the shape after cooling to room temperature with very high accuracy. It can be conveyed to the shape correction line.

  As is clear from the above results, the present invention proves that the shape after cooling can be estimated with higher accuracy by analyzing the transition of temperature, stress / strain, and phase transformation in combination. It was.

  As a result, the ratio of adding unnecessary shape correction steps can be deleted from 15% to 0%, and the delivery time was shortened. In addition, it was possible to eliminate the hindrance in the next process and complaints from customers due to shape defects exceeding the target value developed after cooling.

It is a block diagram which shows the structure of embodiment of this invention. It is a schematic diagram which shows the shape of a metal strip, (a) Ear extension figure, (b) Belly extension figure. It is the schematic which shows each process of cooling in a runout table-coiler-coil yard. It is a flowchart which shows the analysis procedure in the shape prediction method of this invention. It is a schematic diagram of a stress / strain analysis model in the run-out table, (a) a diagram showing an elongation difference at each position in the width direction, and (b) a diagram when the elongations are aligned. It is a schematic diagram which shows the relationship between the elongation at the time of analyzing with a slit model, and stress, (a) The figure showing the stress with respect to each deformation | transformation, (b) The figure showing the deformation | transformation of the board corresponding to FIG.5 (b). It is a schematic diagram of the coil which laminated | stacked the cylinder. It is a flowchart which calculates | requires the tension distribution at the time of coiler winding. It is a figure showing the contact conditions between cylindrical coils. It is a flowchart which calculates | requires the contact force which acts between cylindrical coils. It is a comparison figure of the shape (steepness) after cooling estimated by the conventional method, and an actual measurement value. It is a comparison figure with the shape (steepness) after cooling estimated by the invention, and the measured value.

Explanation of symbols

1 ... Plate surface temperature measuring means (thermometer)
2. Shape measuring means (shape meter)
3 ... Arithmetic processing control device 4 ... Display device 5 ... Metal strip 6 ... Final stand 7 of finishing mill ... Cooling zone 8 ... Coil 9 ... Drum 10 ... Coiler 11 ... Coil yard

Claims (7)

  The metal strip after hot rolling is measured for the temperature distribution in the plate width direction and the shape distribution in the plate width direction, and based on the measured values, the metal strip is wound into a coil by an analysis model that takes into account the phase transformation. A method for predicting the shape of a metal strip, wherein the shape after cooling to room temperature is predicted.   Step of measuring the temperature distribution in the plate width direction and the shape distribution in the plate width direction at the delivery side of the finishing mill and analyzing the heat transfer model, phase transformation model and stress / strain model in the run-out table. And a step of analyzing the heat transfer model, phase transformation model and stress / strain model in coiler winding, and a step of analyzing the heat transfer model, phase transformation model and stress / strain model in coil cooling. The metal band shape prediction method according to claim 1, wherein the metal band shape is predicted.   Measuring the sheet width direction temperature distribution and the sheet width direction shape distribution of the metal strip before the coiler, and the analysis model analyzing a heat transfer model, a phase transformation model and a stress / strain model in the coiler winding; The method for predicting the shape of a metal strip according to claim 1, comprising a step of analyzing a heat transfer model in coil cooling, a phase transformation model, and a stress / strain model.   The plate width direction temperature distribution and the plate width direction shape distribution of the metal strip are measured over the entire length, and the shape after the metal strip is wound around a coil and cooled to room temperature is predicted over the entire length. The shape prediction method of the metal strip in any one of 3.   If the predicted shape of the metal band at room temperature obtained by the metal band shape prediction method according to any one of claims 1 to 4 is within a target shape range, shape correction for the cooled metal band is omitted, A shape determination method for a metal strip, characterized by determining whether or not shape correction is necessary so that the shape correction is performed in the next step when the shape is out of a target shape range.   The shape defect portion length deviated from the target shape range of the rear end of the metal band to be discarded in the next step based on the predicted shape of the metal band at room temperature obtained by the metal band shape prediction method according to any one of claims 1 to 4. A method for determining the shape of a metal band, characterized in that   The shape correction condition of the next process is set according to the predicted shape based on the predicted shape of the metal band at room temperature obtained by the metal band shape prediction method according to any one of claims 1 to 4. Metal band shape correction method.

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