JP2019014953A - Temperature prediction method for steel material - Google Patents

Abstract

To provide a method capable of accurately predicting the temperature of a steel material in a heating furnace.SOLUTION: The temperature prediction method is applied to a steel material which is discharged from a continuous heating furnace having one or a plurality of axial flow burners arranged so that the central axis of the burners is in the conveying direction of the steel material. The temperature prediction method includes: obtaining a reference overall thermal absorption rate of the steel material when the flame length of the axial flow burner is a reference length at each position in the furnace length direction in the heating furnace; correcting the reference overall thermal absorption rate at each position by the flame length ratio with respect to the reference length; acquiring the ambient temperature in the heating furnace by a plurality of temperature sensors provided apart in the furnace length direction in the heating furnace; and predicting the temperature of the steel material at each position in the furnace length direction in the heating furnace based on the corrected overall heat absorption rate and the acquired furnace temperature. It is preferable that the reference length is the maximum flame length of the axial flow burner.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a temperature prediction method for steel materials.

  When a steel material is heated in a continuous heating furnace or the like, the steel material temperature immediately after extraction from the heating furnace is a very important factor in determining the quality of the steel material. If the deviation of the steel material temperature after the extraction from the target temperature is large, desired mechanical characteristics may not be obtained.

  Since the steel material temperature after extraction from the heating furnace is determined by the steel material temperature history in the heating furnace, the operator needs to appropriately control the temperature history of the steel material in the heating furnace in order to ensure product quality.

  In order for the operator to appropriately control the temperature history, it is necessary to accurately predict the temperature of the steel material. On the other hand, from the viewpoint of productivity, it is necessary to suppress the time and cost for temperature prediction. Therefore, the temperature prediction is generally performed using the atmospheric temperature in the heating furnace measured by the temperature measuring devices provided at several places apart in the furnace length direction in the heating furnace. Based on the atmospheric temperature in the heating furnace, the overall heat absorption rate (heat transfer efficiency from the furnace to the steel material) is obtained to predict the temperature of the steel material.

  For this overall heat absorption rate, a value calculated by conducting a steel heating experiment in advance is used as the reference overall heat absorption rate, but if it is used as it is, an error occurs due to a difference in heating conditions of individual steel materials. For this reason, the value corrected from the reference overall heat absorption rate is used as the overall heat absorption rate. As a method for this correction, for example, a method has been proposed in which the temperature of a steel material extracted from a continuous heating furnace is detected and the overall heat absorption rate is corrected according to a deviation from the predicted temperature value of this steel material ( JP-A-58-19435).

  In this conventional correction method, if the heating conditions are the same, the correction is basically performed in a direction that matches the actually measured value. However, when changes occur in the heating conditions, such as when the target extraction temperature changes or when the fuel flow rate changes significantly, this conventional correction method can accurately reflect the effect on the overall heat absorption rate correction. However, there is a limit to the accuracy of temperature prediction.

JP 58-19435 A

  This invention is made | formed based on the above situations, and it aims at provision of the temperature prediction method of the steel materials which can estimate the steel material temperature in a heating furnace accurately.

  FIG. 2 shows an example of a heating furnace which is an object of the present invention. In this heating furnace, a plurality of pairs of so-called side burners 1a whose craters are opposed to the upper side and / or lower side of the conveying surface 10 of the steel material A in the direction perpendicular to the conveying direction (arrow direction in the figure) of the steel material A, and the center of the crater One or a plurality of axial flow burners 1b having a shaft substantially horizontal and disposed from the heating furnace extraction port in the steel conveying direction toward the heating furnace inlet. Note that “substantially horizontal” means a direction in which the absolute value of the inclination with respect to the horizontal is equal to or less than θ, where θ is the angle at which the flame of the burner contacts the steel with respect to the horizontal. The inventors of the present invention have made extensive studies on the high accuracy of temperature prediction, and as a result, focused on the axial flow burner 1b of the heating furnace. The flame length of this axial flow burner 1b changes according to the target value of the steel material temperature after extraction from the heating furnace, for example. On the other hand, since the position of the temperature measuring device that measures the ambient temperature in the heating furnace does not change, the positional relationship between the tip of the flame length and the temperature measuring device varies depending on the flame length as shown in FIG. In general, the temperature between adjacent thermometers is often calculated by linear interpolation. For example, when the tip of the flame is close to the thermometer on the inlet side of the heating furnace as shown in FIG. The internal temperature tends to shift higher than the furnace temperature calculated by linear interpolation. On the other hand, when the tip of the flame is close to the temperature measuring device on the heating furnace extraction port side as shown in FIG. 4B, the actual furnace temperature is likely to shift in a direction lower than the furnace temperature calculated by linear interpolation. The present inventor knows that the relative relationship between the flame front and the thermometer changes due to the difference in the flame length, and the deviation state between the actual furnace temperature and the furnace temperature calculated by interpolation changes. Got. And this inventor discovered that the prediction of the steel material temperature in a heating furnace could be made highly accurate by reflecting this influence on correction | amendment of a general heat absorption rate, and completed this invention.

  That is, the invention made in order to solve the above-mentioned problem is a temperature prediction of steel materials discharged from a continuous heating furnace including one or a plurality of axial flow burners arranged so that the central axis of the crater is in the steel material conveyance direction. A method for obtaining a reference overall heat absorption rate of a steel material when the flame length of the axial flow burner is a reference length at each position in the furnace length direction in the heating furnace, and the reference overall heat absorption rate A step of correcting the reference overall heat absorption rate at each position acquired in the acquisition step by a flame length ratio with respect to the reference length, and a plurality of thermometers spaced apart in the furnace length direction in the heating furnace A step of acquiring an ambient temperature, a step of predicting the temperature of the steel material at each position in the furnace length direction in the heating furnace based on the overall heat absorption rate after the correction step and the furnace temperature acquired in the temperature acquisition step; Is provided.

  In the steel temperature prediction method, the relative relationship between the flame tip and the thermometer changes due to the difference in flame length, and the overall heat absorption rate accounts for the effect of the difference between the actual furnace temperature and the furnace temperature calculated by interpolation. It is reflected in the correction. Therefore, the temperature prediction method for the steel material has high accuracy.

  The reference length may be the maximum flame length of the axial burner. By setting the reference length as the maximum flame length of the axial flow burner in this way, the correction coefficient used in the correction process changes relatively smoothly, so that adjustment of the correction coefficient is facilitated. Here, the "maximum flame length of the axial flow burner" is the flame length of the axial flow burner when the total amount of combustion of the axial flow burner is maximum (the average flame length when there are multiple axial flow burners). Point to.

  In the temperature prediction step, the furnace temperature at each position calculated by linear interpolation of the furnace temperature acquired in the temperature acquisition step may be used. The temperature prediction method for the steel material absorbs the difference between the actual furnace temperature and the furnace temperature calculated by interpolation by correcting the overall heat absorption rate, so that the furnace temperature at each position calculated by linear interpolation is calculated as the furnace temperature. Even if temperature is used, the temperature prediction accuracy of steel is high. Moreover, since the temperature between adjacent temperature measuring devices is generally calculated by linear interpolation, it is easy to incorporate the temperature prediction method for the steel material into an existing steel temperature prediction system.

  The steel material temperature prediction method of the present invention can accurately predict the steel material temperature in the heating furnace even when the flame length of the axial flow burner is changed.

It is a flowchart which shows the procedure of the temperature prediction method of the steel materials which concern on one Embodiment of this invention. It is a top view explaining arrangement | positioning of the burner in a heating furnace. It is a side view explaining arrangement | positioning of the burner in a heating furnace. It is a figure explaining the in-furnace temperature based on the positional relationship of a flame length and a thermometer, (a) is when the front-end | tip of a flame is near the thermometer on the heating furnace entrance side, (b) is the front-end | tip of a flame It is explanatory drawing when it is close to the temperature measuring device by the side of a heating furnace extraction port. It is a graph which shows the example of correction coefficient K (d, f). It is a graph which shows the standard general heat absorption rate for every zone in an example. It is a graph which shows the correction coefficient for every zone in an Example. It is a graph of the average value of the absolute value of the difference of the predicted temperature in an Example, and a measured value.

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

  The temperature prediction method of the steel material is a temperature prediction method of a steel material that is discharged from a continuous heating furnace including one or a plurality of axial flow burners that are arranged so that the central axis of the crater is in the conveyance direction of the steel material. As shown in FIG. 1, the steel material temperature prediction method mainly includes an initial condition setting step S1, a reference overall heat absorption rate acquisition step S2, a correction step S3, a temperature acquisition step S4, and a temperature prediction step S5. Prepare.

  The temperature prediction method for the steel material can be applied to a known heating furnace including an axial flow burner. Specifically, for example, as shown in FIGS. 2 and 3, a plurality of craters face the upper side and / or the lower side of the conveying surface 10 of the steel material A in the direction perpendicular to the conveying direction (arrow direction in the drawing) of the steel material A. A heating furnace comprising a pair of side burners 1a and one or a plurality of axial flow burners 1b disposed with a central axis of the crater substantially horizontal and from the heating furnace extraction port in the conveying direction of the steel material A toward the heating furnace inlet Is used. In addition, the conveyance surface 10 is a surface which conveys the steel material A by a walking beam.

  2 and 3, two pairs of side burners 1a and four pairs of axial flow burners 1b are disposed on the downstream side in the conveyance direction above and below the conveyance surface 10, but the side burners 1a and the axial flow burners are disposed. The number and position of 1b are not limited to this. In addition, the heating furnace may have a configuration in which the configuration shown in FIGS. 2 and 3 is used as one heating zone and a plurality of heating zones are used. In addition, the space | interval of the conveyance direction of several pairs of burners can be designed suitably.

  The shape of the steel material A targeted by the temperature prediction method of the steel material is not particularly limited, and the temperature prediction method of the steel material can be applied to a wire, a steel bar, a steel plate, and the like. Moreover, the heating furnace used with the temperature prediction method of the said steel material can be used in combination with another heating furnace. In addition, the final heating temperature of the steel material A is 900 degreeC or more and 1300 degrees C or less, for example.

  As shown in FIG. 3, the heating furnace includes a plurality of temperature measuring devices 2 that are spaced apart in the furnace length direction in the heating furnace. As the temperature sensor 2, for example, a known thermocouple can be used.

  In FIG. 3, three pairs of thermometers 2 are provided above and below the conveyance surface 10, but the position and number are not limited as long as the atmospheric temperature distribution in the heating furnace can be acquired. However, in consideration of the installation cost of the thermometer 2 and maintainability, it is preferable that the temperature is 2 to 8 pairs.

<Initial condition setting process>
In the initial condition setting step S1, the heating condition of the steel material A is mainly set. Specifically, the type of the steel material A, the initial heating temperature, the in-furnace time, the heating furnace temperature, and the like are set.

<Standard overall heat absorption rate acquisition process>
In the reference overall heat absorption rate acquisition step S2, the reference overall heat absorption rate of the steel A when the flame length of the axial flow burner 1b is the reference length is obtained at each position in the furnace length direction in the heating furnace.

  The reference overall heat absorption rate can be obtained by, for example, actually measuring the temperature when the steel material A is actually heated at a predetermined combustion amount in a heating furnace and calculating from this measured value.

Here, the overall heat absorption rate φ _CG (d) at the conveyance direction position d in the heating furnace is a coefficient in the relationship of the following formula (1).

In the above formula (1), q [W / m ² ] is the heat flux to the steel material, σ [W / m ² / K ⁴ ] is the Stefan-Boltzmann constant, T _f [K] is the furnace temperature, and T _s [K ] Is the steel surface temperature.

When the standard overall heat absorption rate is obtained from the actual measured value of the steel surface temperature, the temperature can be measured by a thermocouple embedded in the steel material A, for example. Using the obtained steel material temperature, furnace temperature, heat input, and the like, the overall heat absorption rate φ _CG is calculated from the equation (1), and set as the reference overall heat absorption rate.

  The reference length of the flame length when obtaining the reference overall heat absorption rate of the steel material A is preferably the maximum flame length of the axial flow burner 1b. By setting the reference length as the maximum flame length of the axial flow burner 1b, the correction coefficient K (d, f) described later changes relatively smoothly, so that the adjustment of the correction coefficient K (d, f) is facilitated. .

<Correction process>
In the correction step S3, a reference overall heat absorption rate phi _CG of each position acquired by the reference overall heat absorption rate obtaining process S2 is corrected by the flame length ratio with respect to the reference length.

  The present inventor has learned that the relative relationship between the flame front and the thermometer 2 changes due to the difference in the flame length, and the deviation state between the actual furnace temperature and the furnace temperature calculated by interpolation changes. ing. And this inventor has discovered that the steel material temperature in a heating furnace can be accurately estimated by reflecting this influence on correction | amendment of a general heat absorption rate.

Reference overall heat absorption rate phi _CG correction can be performed by the following equation (2).

In the formula ^{_{(2), φ CG BASE (}} d) is a reference overall heat absorption rate obtained by the reference overall heat absorption rate obtaining step S2. K (d, f) is a correction coefficient, and f represents a flame length ratio with respect to the reference length.

  The correction coefficient K (d, f) is acquired in advance. For example, as shown in FIG. 5, the correction coefficient K (d, f) is obtained by actually measuring the temperature when the steel material A is actually heated at a predetermined combustion amount in a heating furnace using the flame length ratio f as a parameter. It can be obtained by calculation. Or it is also possible to calculate from numerical analysis and performance data when the flame length ratio f is changed.

  The influence of the flame length of the axial flow burner 1b is limited to the downstream side of the position where the influence occurs when the flame length is set to the maximum flame length (hereinafter also simply referred to as “flame influence limit position”). The correction coefficient K (d, f) may be calculated only for the heating furnace extraction port side from the flame influence limit position. The correction coefficient K (d, f) is 1 for the heating furnace inlet side of the flame influence limit position.

  Since the correction coefficient K (d, f) is prepared, for example, by actual measurement as described above, it may be prepared as discrete numerical data using the transport direction position d and the flame length f as parameters. In such a case, in order to obtain the correction coefficient K (d, f) at an arbitrary conveyance direction position d and flame length f, for example, interpolation from nearby numerical data can be used.

<Temperature acquisition process>
In temperature acquisition process S4, the atmospheric temperature (furnace temperature _Tf ) in a heating furnace is acquired with the temperature measuring device 2 provided in multiple numbers spaced apart in the furnace length direction in a heating furnace.

  In FIG. 1, the temperature acquisition step S4 is performed after the correction step S3. However, these steps may be performed in reverse order or simultaneously.

<Temperature prediction process>
In the temperature prediction step S5, the steel material at each position d in the furnace length direction in the heating furnace based on the overall heat absorption rate φ _CG ^NEW (d) after the correction step S3 and the furnace temperature T _f acquired in the temperature acquisition step S4. Predict the temperature of A.

  As a method for predicting temperature, the temperature from the surface to the inside of the steel material A at the conveyance direction position d using the well-known two-dimensional heat conduction equation, with the conditions set in the above equation (1) and the initial condition setting step S1 as boundary conditions. Find the distribution. The two-dimensional heat conduction equation is represented by the following formula (3).

In the above formula (3), ρ [g / m ³ ] is the density of the steel material, c [J / g / K] is the specific heat of the steel material, T [K] is the temperature [K] of the steel material, and δt is the minute time [s. ], [Delta] x, [delta] y are micro sections [m], [lambda] x, [lambda] y [W / m / K] are the thermal conductivities in the x direction or y direction.

The overall heat absorption rate φ _CG ^NEW (d) is preferably obtained for each part of the steel material A. For example, when the steel material A is heated in the heating furnace shown in FIGS. 2 and 3, the reference overall heat absorption rate φ _CG ^BASE (d) and the correction coefficient K (d, f) are separately obtained for the upper surface, the lower surface, and the side surface of the steel material A. It is preferable to do.

Since the temperature measuring device 2 is provided separately in the heating furnace with respect to the furnace temperature _{Tf at} the conveyance direction position d, the atmospheric temperature _Tf that can be actually measured is limited. In the temperature prediction step S5, the in-furnace temperature _{Tf at} the conveyance direction position d that cannot be actually measured is also used. For this reason, the in-furnace temperature _{Tf at} the conveyance direction position d that cannot be measured is obtained by interpolation.

The interpolation method is not particularly limited, but the furnace temperature _Tf at each position d calculated by linear interpolation of the furnace temperature acquired in the temperature acquisition step S4 may be used. The steel temperature prediction method absorbs the error between the actual furnace temperature and the furnace temperature calculated by linear interpolation by correcting the overall heat absorption rate, so the furnace temperature at each position calculated by linear interpolation as the furnace temperature is absorbed. Even if the internal temperature is used, the temperature prediction accuracy of the steel material A is high. Moreover, since the temperature between adjacent temperature measuring devices is generally calculated by linear interpolation, it is easy to incorporate the temperature prediction method for the steel material into an existing steel temperature prediction system.

In addition, the furnace temperature _Tf between the heating furnace charging inlet and the temperature measuring device 2 located closest to the heating furnace charging side is represented by the temperature of the temperature measuring device 2 positioned closest to the heating furnace charging side. The in-furnace temperature _Tf between the temperature measuring device 2 located closest to the heating furnace extraction side and the heating furnace extraction port may be represented by the temperature of the temperature measuring device 2 located closest to the heating furnace extraction side.

For example, a difference method can be used as a method of solving the differential equation of the above formula (3). In the difference method, the heating furnace is divided into equal length zones in the furnace length direction, and the differential equation is converted into a difference equation with the transport direction position d _i at the center position of each zone Z _i as a representative value. The predicted temperature of the steel material A is calculated every time. The number n of zone divisions is preferably 50 or more and 100 or less from the viewpoint of prediction accuracy and calculation efficiency.

  When the deviation between the predicted temperature of the steel material A to be discharged obtained in the temperature prediction step S5 and the target value is large, for example, the flame length of the axial flow burner 1b is adjusted. In this way, when the flame length of the axial flow burner 1b is adjusted, the correction step S3, the temperature acquisition step S4, and the temperature prediction step S5 are performed again. Then, the adjustment and the re-execution of the correction step S3, the temperature acquisition step S4, and the temperature prediction step S5 are repeated until the deviation between the predicted temperature of the steel material A and the target value is equal to or less than the desired difference.

<Advantages>
In the steel temperature prediction method, the relative relationship between the flame front and the thermometer 2 changes due to the difference in flame length, and the overall heat absorption reflects the effect of the difference between the actual furnace temperature and the furnace temperature calculated by interpolation. Reflect in rate correction. Therefore, the temperature prediction method for the steel material has high accuracy.

[Other Embodiments]
The method for predicting the temperature of the steel material of the present invention is not limited to the above embodiment. For example, the temperature prediction method for the steel material may include steps other than those described above as necessary.

In the above embodiment, the reference overall heat absorption rate φ _CG ^BASE (d) and the correction coefficient K (d, f) are defined by values at an arbitrary conveyance direction position d, but the temperature prediction step S5 is performed using a difference method. In this case, it may be defined for each zone.

  In the said embodiment, although demonstrated using the heating furnace provided with a side burner and an axial-flow burner, another structure may be sufficient as long as a heating furnace is provided with an axial-flow burner. For example, a heating furnace composed only of an axial flow burner is also intended by the present invention.

  EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, this invention is not interpreted limitedly based on description of this Example.

2 and 3 for a steel material having a thickness (dimension in the direction perpendicular to the conveyance surface) 155 mm, width (dimension in the conveyance direction) 155 mm, and a certain length (dimension in the conveyance direction and the direction perpendicular to the conveyance surface). The heating furnace was used to heat the axial flow burner 1b with the maximum flame length. Under this condition, the temperature of the steel material being heated was measured at three points of 25 mm (A), 77.5 mm (B), and 130 mm (C) from the upper surface. From the measured temperature described above, the overall heat absorption rate φ _CG ^BASE (d) of the upper surface and the lower surface in the central part in the steel material length direction was calculated for each zone as the reference overall heat absorption rate. The calculation results are shown in FIG. The number of zone divisions was 70.

  The correction coefficient K (d, f) when the flame length ratio was 0.9, 0.7, and 0.5 was calculated by temperature measurement. The calculation conditions are the same as the calculation conditions for the overall heat absorption rate. The calculation results are shown in FIG.

As an example, the correction step S3, the temperature acquisition step S4, and the temperature prediction step S5 of the temperature prediction method for the steel material are performed using the overall heat absorption rate φ _CG ^BASE (d) and the correction coefficient K (d, f) described above. Then, the temperature of the steel material discharged from the heating furnace was predicted and compared with the actual measurement value. Specifically, for flame length ratios of 0.9, 0.7, and 0.5, the absolute value of the difference between the predicted temperature and the actually measured value was obtained, and the average value was calculated. Table 1 shows the number of samples under each condition.

  In addition, as a comparative example, comparison was made between a predicted temperature obtained by executing only a conventional steel material temperature prediction method in which the correction step S3 is not performed, that is, the temperature acquisition step S4 and the temperature prediction step S5, and an actual measurement value.

The graph of the average value of the absolute value of the difference between the predicted temperature and the actual measurement value of the example and the comparative example is shown in FIG. From the graph of FIG. 8, a flame length ratio of 0.9 close to the condition of the acquired overall heat absorption rate φ _CG ^BASE (d) is not recognized, but the flame length ratio is 0.7, 0.5. As the general heat absorption rate φ _CG ^BASE (d) is acquired, the error increases in the comparative example, whereas the error decreases in the embodiment. From this, it can be seen that the temperature prediction method of the steel material using the correction coefficient K (d, f) is higher in accuracy than the conventional temperature prediction method not using the correction coefficient K (d, f).

  Since the steel material temperature prediction method can accurately predict the steel material temperature in the heating furnace even when the flame length of the axial flow burner is changed, it can be suitably applied to the production of various steel materials involving a heating process.

DESCRIPTION OF SYMBOLS 1a Side burner 1b Axial flow burner 2 Thermometer 10 Conveying surface A Steel material S1 Initial condition setting process S2 Reference | standard overall heat absorption rate acquisition process S3 Correction process S4 Temperature acquisition process S5 Temperature prediction process

Claims (3)

A method for predicting the temperature of a steel material discharged from a continuous heating furnace provided with one or a plurality of axial flow burners arranged so that the central axis of the crater is in the conveying direction of the steel material,
Obtaining a reference overall heat absorption rate of the steel when the flame length of the axial flow burner is the reference length at each position in the furnace length direction in the heating furnace;
Correcting the reference overall heat absorption rate of each position acquired in the reference overall heat absorption rate acquisition step by the flame length ratio with respect to the reference length;
Acquiring the atmospheric temperature in the heating furnace with a plurality of temperature measuring devices provided apart in the furnace length direction in the heating furnace;
A method for predicting the temperature of the steel material at each position in the furnace length direction in the heating furnace based on the overall heat absorption rate after the correction step and the furnace temperature acquired in the temperature acquisition step.   The method for predicting a temperature of a steel material according to claim 1, wherein the reference length is a maximum flame length of an axial flow burner.   The steel material temperature prediction method according to claim 1 or 2, wherein in the temperature prediction step, the furnace temperature at each position calculated by linear interpolation of the furnace temperature acquired in the temperature acquisition step is used.

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