JP7396328B2 - Temperature measurement method, temperature measurement device, and manufacturing method for zinc-based hot-dip coated steel sheet - Google Patents

Description

The present invention relates to a temperature measuring method, a temperature measuring device, and a manufacturing method for zinc-based hot-dip coated steel sheets.

In zinc-based hot-dip plating lines in the steel process, control of steel sheet temperature is a very important task in material preparation and plating quality control. Particularly in the alloying process in which the steel sheet is heated after the zinc-based hot-dip plating has been deposited, if the steel sheet temperature is too high, powdering will occur, and if the steel sheet temperature is too low, alloying will be insufficient. For this reason, extremely strict steel sheet temperature control is required in zinc-based hot-dip plating lines.

Here, as a method of heating a steel plate, there is electromagnetic induction heating (hereinafter referred to as IH). Further, as a method of temperature control, there is a method of calculating the temperature of the steel plate immediately after heating by electric heating calculation or simulation using the output of the IH and the conveyance speed of the steel plate. However, with this method, the calculation results of the steel plate temperature may vary due to slight variations in the thickness of the steel plate or the pass line. Therefore, it is important to directly measure the steel plate temperature.

However, since molten zinc plating may adhere to the surface of zinc-based hot-dip coated steel sheets during the alloying process, it is difficult to contact the steel sheets during transportation and measure the temperature of the steel sheets. It is required to measure the steel plate temperature without contact. Therefore, radiation thermometry is generally used to measure the temperature of the steel sheet. The radiation thermometry method is a method of measuring the temperature of a measurement object using infrared rays emitted by the measurement object.

However, when measuring temperature using radiation thermometry, it is important to set the emissivity of the object to be measured. Here, the emissivity is the rate at which an object to be measured emits infrared rays. Unless the correct emissivity is set for each object to be measured, the temperature of the object to be measured cannot be measured accurately. Against this background, emissivity correction methods have been proposed.

Specifically, Patent Document 1 describes a method of calculating the emissivity of each pixel and the emissivity-corrected surface temperature using images taken while changing the environmental radiant temperature in a stepwise manner. . Further, Patent Document 2 describes a method in which a sample is heated to two different temperatures and the emissivity is measured using past temperature data when the temperature becomes stable, and the emissivity is reflected in the surface temperature. Further, Patent Document 3 describes a method of correcting emissivity by dividing the temperature into a plurality of specified temperature ranges set in advance according to the measured temperature.

Japanese Patent Application Publication No. 5-296846 Patent No. 2895587 Japanese Patent Application Publication No. 1-314930

Tetsu to Hagane 79(7), 772-778, 1993 Iron and Steel 86(3), 160-165, 2000

With reference to FIG. 7, changes in the surface shape of a steel plate during the alloying process will be described (see Non-Patent Documents 1 and 2 for details). As shown in FIG. 7(a), the steel plate before heating is composed of two layers: base steel 100 and zinc-based plating 101. When the surface of the steel plate is heated in this state, the outermost surface of the zinc-based plating 101 melts, as shown in FIG. 7(b). As a result, the specular reflectance of the steel plate surface increases, while the diffuse reflectance of the steel plate surface decreases. Next, as shown in FIG. 7(c), alloyed crystals 102 are generated near the interface between the base steel 100 and the zinc-based plating 101, thereby pushing up the surface of the steel sheet and making it finer. As a result, the specular reflectance of the steel plate surface decreases, whereas the diffuse reflectance of the steel plate surface increases. Finally, as shown in FIG. 7(d), alloyed crystals are further formed, and the entire zinc-based plating including the surface is alloyed. This reduces the diffuse reflectance of the steel plate surface. In this way, until the alloyed crystals 102 are generated on the surface of the steel sheet, the emissivity changes due to the formation of fine irregularities on the surface. Therefore, in order to accurately measure the steel plate temperature, it is necessary to correct the emissivity in real time.

However, with the methods described in Patent Documents 1 to 3, it is difficult to correct the emissivity in real time. That is, in the method described in Patent Document 1, it is necessary to change the environmental radiation temperature in steps. However, in the alloying process of zinc-based hot-dip coated steel sheets, the steel sheet temperature depends on the amount of heat of IH and the conveyance speed. Therefore, it is difficult to measure the emissivity by changing a single item, and it is necessary to increase the number of items to be changed. Therefore, it is not suitable for correcting temperature measurements during alloying process. On the other hand, in the method described in Patent Document 2, it is necessary to measure a sample at two or more different temperatures in the same field of view. However, it is difficult to place the same sample within the field of view for measuring the steel plate being transported. Furthermore, it is difficult to reproduce the conveyance speed and create conditions where only the temperature of the object to be measured differs. Further, the method described in Patent Document 3 assumes that the emissivity unevenness within the measurement range and the emissivity of the measurement target are known. However, the emissivity of the steel plate during the alloying process changes from moment to moment depending on the progress of alloying as described above, and it is difficult to determine and correct the emissivity in advance.

Note that most of the radiation thermometers used in the steel process are spot type, and are designed to measure the temperature at a single point on a steel plate. However, the temperature of the steel sheet is not uniform in the width direction, and temperature unevenness occurs in the width direction depending on the heating conditions. For this reason, there is a demand for measuring steel plate temperatures over a wide range.

The present invention has been made in view of the above-mentioned problems, and its purpose is to measure the temperature of zinc-based hot-dip coated steel sheets, making it possible to measure the surface temperature of steel sheets in the alloying process over a wide range while correcting emissivity in real time. An object of the present invention is to provide a method and a temperature measuring device. Another object of the present invention is to provide a method for manufacturing a zinc-based hot-dip plated steel sheet that can be manufactured with high yield while accurately controlling the surface temperature of the steel plate.

The method for measuring the temperature of a zinc-based hot-dip coated steel sheet according to the present invention is based on the amount of specularly reflected light when the surface of the zinc-based hot-dipped steel plate is irradiated with light under specular reflection conditions, and the amount of specularly reflected light on the surface of the zinc-based hot-dip coated steel sheet under diffuse reflection conditions. an emissivity calculating step of calculating the emissivity of the surface of the zinc-based hot-dip coated steel sheet based on the amount of diffusely reflected light when irradiated with light; and an imaging step of taking an infrared image of the surface of the zinc-based hot-dip coated steel sheet. , a temperature measuring step of measuring the surface temperature of the zinc-based hot-dipped steel sheet using the emissivity calculated in the emissivity calculating step and the infrared image taken in the imaging step. do.

The method for measuring the temperature of a zinc-based hot-dip coated steel sheet according to the present invention is characterized in that, in the above invention, the temperature measuring step includes a step of measuring a surface temperature distribution in the width direction of the zinc-based hot-dip coated steel sheet.

The method for measuring the temperature of a zinc-based hot-dip coated steel sheet according to the present invention is characterized in that, in the above invention, the emissivity calculation step includes a step of calculating emissivity at a plurality of locations in the width direction of the zinc-based hot-dip coated steel sheet. shall be.

In the method for measuring the temperature of a zinc-based hot-dip coated steel sheet according to the present invention, in the above invention, the emissivity calculation step includes scanning the temperature of the zinc-based hot-dip coated steel sheet by scanning a measuring device along the width direction of the zinc-based hot-dip coated steel sheet. The method is characterized by including the step of calculating emissivity at multiple locations in the width direction of the steel plate.

In the method for measuring the temperature of a zinc-based hot-dip coated steel sheet according to the present invention, in the above-mentioned invention, the temperature measuring step is a step of measuring the surface temperature of the zinc-based hot-dip coated steel sheet using a conveyance speed of the zinc-based hot-dip coated steel sheet. It is characterized by including.

The method for measuring the temperature of a zinc-based hot-dip coated steel sheet according to the present invention is characterized in that, in the above invention, the zinc-based hot-dip coated steel sheet is an alloyed hot-dip galvanized steel sheet.

The temperature measuring device for a zinc-based hot-dip coated steel sheet according to the present invention measures the amount of specularly reflected light when the surface of the zinc-based hot-dipped steel plate is irradiated with light under specular reflection conditions, and the amount of specularly reflected light on the surface of the zinc-based hot-dip coated steel sheet under diffuse reflection conditions. emissivity measuring means for calculating the emissivity of the surface of the zinc-based hot-dip coated steel sheet based on the amount of diffusely reflected light when irradiated with light; and an imaging means for taking an infrared image of the surface of the zinc-based hot-dip coated steel sheet. , temperature measuring means for measuring the surface temperature of the zinc-based hot-dipped steel sheet using the emissivity calculated by the emissivity measuring means and the infrared image taken by the imaging means. do.

The method for manufacturing a zinc-based hot-dip coated steel sheet according to the present invention includes manufacturing a zinc-based hot-dip coated steel sheet while measuring the surface temperature of the zinc-based hot-dip coated steel sheet using the method for measuring the temperature of a zinc-based hot-dip coated steel sheet according to the present invention. It is characterized by including a manufacturing step.

In the method for manufacturing a zinc-based hot-dip coated steel sheet according to the present invention, in the above invention, the manufacturing step controls the output of an electromagnetic induction heating device that heats the zinc-based hot-dip coated steel sheet based on the surface temperature of the zinc-based hot-dip coated steel sheet. The method is characterized by including the step of:

According to the method and apparatus for measuring the temperature of a zinc-based hot-dip coated steel sheet according to the present invention, it is possible to measure the surface temperature of a steel sheet in the alloying process over a wide range while correcting the emissivity in real time. Further, according to the method for manufacturing a zinc-based hot-dip coated steel sheet according to the present invention, a zinc-based hot-dip coated steel sheet can be manufactured with high yield while accurately controlling the surface temperature of the steel sheet.

FIG. 1 is a schematic diagram showing the configuration of a temperature measuring device for a zinc-based hot-dip coated steel sheet, which is an embodiment of the present invention. FIG. 2 is a diagram for explaining a method of measuring surface temperature using emissivity. FIG. 3 is a schematic diagram showing the configuration of the emissivity measuring device shown in FIG. 1. FIG. 4 is a schematic diagram showing the configuration of an experimental apparatus for determining the relationship between emissivity, specular reflectance, and diffuse reflectance of a steel plate. FIG. 5 is a diagram showing an example of the relationship between emissivity, specular reflectance, and diffuse reflectance of a steel plate. FIG. 6 is a schematic diagram showing an embodiment of the present invention. FIG. 7 is a diagram for explaining changes in the surface shape of a steel plate during the alloying process.

EMBODIMENT OF THE INVENTION Hereinafter, with reference to drawings, the temperature measurement method, temperature measurement apparatus, and manufacturing method of the zinc-based hot-dip galvanized steel sheet which is one Embodiment of this invention are demonstrated.

[Configuration of temperature measuring device]
First, with reference to FIGS. 1 and 2, the configuration of a temperature measuring device for a zinc-based hot-dipped steel sheet, which is an embodiment of the present invention, will be described.

FIG. 1 is a schematic diagram showing the configuration of a temperature measuring device for a zinc-based plated steel sheet, which is an embodiment of the present invention. As shown in FIG. 1, a temperature measuring device 1 for a zinc-based hot-dip coated steel sheet, which is an embodiment of the present invention, measures the surface temperature of a zinc-based hot-dip coated steel sheet (hereinafter abbreviated as steel sheet) S during the alloying process. The device includes an emissivity measurement device 2, a thermography 3, a calculation device 4, and a display device 5 as main components. The emissivity measuring device 2, the thermography 3, and the arithmetic device 4 function as an emissivity measuring means, an imaging means, and a temperature measuring means according to the present invention, respectively.

The emissivity measurement device 2 measures the emissivity of the steel plate S during the alloying process in real time, and outputs an electric signal indicating the measured emissivity to the calculation device 4. In this embodiment, as shown in FIG. 2(a), the emissivity measuring device 2 measures the emissivity at one point in the width direction of the steel plate S being conveyed, and outputs an electrical signal indicating the measured emissivity. Output to the arithmetic device 4. Details of the emissivity measuring device 2 will be described later.

The thermography 3 takes an infrared image of the steel plate S, converts the image signal into a digital signal, and then outputs it to the arithmetic device 4 . Since the temperature of the steel plate S during the alloying process is about 450 to 550° C., it is desirable that the thermography 3 has an element capable of detecting high wavelength signals. According to the thermography 3, it is possible to take infrared images over a wide range of the steel plate surface.

The calculation device 4 calculates the surface temperature of the steel plate S using the emissivity of the steel plate S output from the emissivity measurement device 2 and the infrared image of the steel plate S taken by the thermography 3. For example, when the conveyance speed of the steel plate S is 60 mpm, the calculation device 4 calculates the surface temperature of the steel plate S every time the steel plate S advances by 1 m. Furthermore, when the emissivity measuring device 2 measures the emissivity at one point in the width direction of the steel plate S as shown in FIG. The surface temperature is calculated using the emissivity, and for points An' whose emissivity is not measured, the surface temperature is calculated using the emissivity of the point An at the same position in the width direction. Thereby, the surface temperature distribution in the width direction of the steel plate S can be measured using the emissivity measured in real time. Then, the calculation device 4 visually displays information regarding the calculated surface temperature of the steel plate S on a display device 5 such as a liquid crystal display.

Note that depending on the location where the surface temperature is measured, there is a distance between the emissivity measurement device 2 and the thermography 3, so a temperature difference may occur due to the difference in distance when the surface temperature is calculated using the immediate output. . Therefore, it is desirable to correct the calculated position of the surface temperature according to the conveyance speed of the steel plate S. Specifically, the distance L between the emissivity measurement device 2 and the thermography 3 is set in advance, and the calculation device 4 calculates the distance L and the conveyance speed LS of the steel plate S using the following formula (1). Calculate the correction time t from . Then, the calculation device 4 calculates the surface temperature of the steel plate S from the infrared image using the emissivity according to the correction time t. However, since many other correction methods using the transport speed of the steel plate S and the distance between the devices have been proposed, any method may be used as long as it determines the calculated position correctly.

Furthermore, in the configuration shown in FIG. 1, the thermograph 3 is installed on the downstream side of the emissivity measuring device 2 in the conveying direction of the steel plate S. Even when the thermography 3 is installed on the upstream side of the emissivity measuring device 2 in the conveyance direction of the steel plate S, the surface temperature of the steel plate S can be measured in the same manner. Further, the number of emissivity measuring devices 2 may be increased. As shown in FIG. 2(b), when two emissivity measuring devices 2 (emissivity measuring devices A and B) are installed in the width direction of the steel plate S, the emissivity at two points is measured. At this time, it is determined in advance which emissivity measurement device 2 to use the measurement results within the measurement width of the thermography 3. For example, for the right-hand side from the center of the steel plate, use the emissivity measured by the emissivity measuring device 2 installed on the right side, and for the left-hand side, use the emissivity measured by the emissivity measuring device 2 installed on the left side. . Furthermore, if necessary, the emissivity measuring device may scan in the width direction. In that case, the emissivity is changed depending on the measurement position of the emissivity measuring device. As an example, as shown in FIG. 2C, the emissivity measuring device 2 measures data at five points in the width direction, and uses the emissivity at the same position in the width direction as the emissivity at other points than the measurement points.

[Configuration of emissivity measuring device]
Next, the configuration of the emissivity measuring device 2 will be described in detail with reference to FIGS. 3 and 4.

FIG. 3 is a schematic diagram showing the configuration of the emissivity measuring device 2 shown in FIG. 1. As shown in FIG. 3, the emissivity measuring device 2 includes a specular reflection light source 21, a diffuse reflection light source 22, a radiation thermometer 23, and an arithmetic unit 24.

The specular reflection light source 21 irradiates the surface of the steel plate S with illumination light L1 under specular reflection conditions. The diffuse reflection light source 22 irradiates the surface of the steel plate S with illumination light L2 under diffuse reflection conditions. Note that it is desirable that the diffuse reflection condition be set at an angle that differs from the specular reflection condition by 45° or more. Further, it is preferable that the light source 21 for specular reflection and the light source 22 for diffuse reflection be switched on/off using a power source, the shutter 25, or the like.

The radiation thermometer 23 takes a surface image of the steel plate S and outputs an image signal to the calculation device 24. Note that the radiation thermometer 23 cannot be installed perpendicular to the surface of the steel plate S in order to match the projection angle of the specular reflection light source 21 and the reception angle of the radiation thermometer 23; It is desirable to install it perpendicularly to the surface of the steel plate S as much as possible within the installation range.

The calculation device 24 calculates the emissivity of the steel plate S using the surface image of the steel plate output from the radiation thermometer 23, and outputs an electric signal indicating the calculated emissivity to the calculation device 4. Specifically, in calculating the emissivity, first, the relationship between the emissivity, specular reflectance, and diffuse reflectance of the steel plate S is modeled in advance. The relationship between the emissivity, specular reflectance, and diffuse reflectance of the steel plate S can be modeled by measuring the amount of specularly reflected light and the amount of diffusely reflected light when the steel plate S is actually heated using an experimental device such as the one shown in Fig. 4, for example. can be converted into The configuration of the experimental apparatus shown in FIG. 4 and the modeling procedure will be described below.

When modeling the relationship between the emissivity, specular reflectance, and diffuse reflectance of the steel plate S using the experimental apparatus shown in FIG. 4, first, a thermocouple 31 is welded to the surface of the steel plate S before alloying. Furthermore, a black body spray 32 is applied to a part of the surface of the steel plate S. Next, the steel plate S is placed on a heater 33 that can uniformly heat the entire steel plate S. The heating method for the steel plate S may be heat transfer, IH heating, or electrical heating as long as the steel plate S can be heated uniformly, but if the thermocouple 31 is welded, temperature measurement may be affected during IH heating or electrical heating. It is necessary to devise measures to prevent this from occurring.

Next, a model showing the relationship between the emissivity, diffuse reflectance, and specular reflectance of the steel plate S is generated. Specifically, the following steps (a) to (e) are repeatedly performed while gradually heating the steel plate S. The acquired data is recorded in the logger 34.

(a) The amount of emitted light from the steel plate S is calculated by taking a surface image of the steel plate S with the specular reflection light source 21 and the diffuse reflection light source 22 turned off or the shutter closed.
(b) By lighting only the specular reflection light source 21 or opening the shutter to capture a surface image of the steel plate S, the sum of the specularly reflected light amount and the emitted light amount of the steel plate S is obtained.
(c) By lighting only the light source 22 for diffuse reflection or opening the shutter to capture a surface image of the steel plate S, the sum of the amount of diffusely reflected light and the amount of emitted light of the steel plate S is obtained.
(d) Calculate the specularly reflected light amount and diffusely reflected light amount of the steel plate S by subtracting the light amount obtained in step (a) from the respective light amounts obtained in steps (b) and (c). At this time, if the exposure time differs each time the surface image is captured, correction is performed taking into account the difference in light amount due to the difference in exposure time.
(e) Compare the surface temperature measured by the thermocouple 31 with the surface temperature measured by the calibrated radiation thermometer 23, or compare the emissivity component if the radiation thermometer 23 is a line sensor or an area sensor. The emissivity of the steel plate S is calculated by comparing it with the emissivity of the area where the black body spray 32 is applied. Then, the amount of specularly reflected light and the amount of diffusely reflected light of the steel plate S calculated in step (d) are associated with the emissivity of the steel plate S calculated in step (e).

Note that it is preferable to set the heating rate so that approximately the same surface state of the steel plate S can be imaged in steps (a) to (c), taking into account the exposure time and measurement time. As a result, a model showing the relationship between the emissivity, specular reflectance, and diffuse reflectance of the surface of the steel plate S within the heating temperature range of the steel plate S, as shown in FIGS. 5(a) and 5(b), for example, can be created. can be created.

Figures 5(a) and (b) show the relationship between the emissivity, specular reflectance (specular reflection brightness value), and diffuse reflectance (diffuse reflection brightness value) of the steel plate S obtained by the above modeling procedure, respectively. An example is shown below. As shown in FIGS. 5(a) and 5(b), the surface state of the steel plate S is such that the specularity gradually decreases as it is heated and the diffusivity increases to an almost completely diffused surface in step S1, and the step S1 in which the diffusivity increases to an almost completely diffused surface. It can be seen that the process is comprised of two processes: step S2, in which the diffuse reflectance gradually decreases from the state where it has become. According to this model, it can be seen that the emissivity of the steel plate S can be estimated with high accuracy by measuring the specular reflectance and diffuse reflectance of the surface of the steel plate S.

Specific examples of methods for estimating the emissivity of the steel plate S include the following methods. First, it is determined whether the surface condition of the steel sheet S is classified into step S1 or step S2, and then the coordinates on the model (characteristic curves shown in FIGS. 5(a) and 5(b)) within each process are determined. Calculate the position. For example, the simplest method is to set a threshold value for the specular reflectance, and if the specular reflectance is greater than or equal to the threshold value, the process is classified into step S1, and if it is less than the threshold value, the process is classified into step S2. Then, in the process of step S1, the emissivity is set to a fixed value (approximately 0.2) because it hardly changes, and in the process of step S2, the coordinate position on the model is determined from the value of the amount of diffusely reflected light. Estimate emissivity. In addition, many methods have been proposed for determining the optimal coordinate position on the model, and any method may be used as long as the coordinate position of the alloying process can be determined correctly. Similarly, on an actual manufacturing line, emissivity can be estimated in real time by continuously measuring the specular reflectance (specular reflection brightness value) and diffuse reflectance (diffuse reflection brightness value).

As is clear from the above description, according to the temperature measuring device for a zinc-based hot-dip coated steel sheet, which is an embodiment of the present invention, the specular reflection when the surface of the zinc-based hot-dip coated steel sheet is irradiated with light under specular reflection conditions. The emissivity of the surface of the zinc-based hot-dipped steel sheet is calculated based on the amount of light and the amount of diffusely reflected light when the surface of the zinc-based hot-dipped steel sheet is irradiated with light under diffuse reflection conditions, and the infrared rays of the surface of the zinc-based hot-dipped steel sheet are calculated. An image is taken, and the surface temperature of the zinc-based hot-dip plated steel sheet is measured using emissivity and an infrared image. This makes it possible to measure the surface temperature of a zinc-based hot-dipped steel sheet in the alloying process over a wide range while correcting the emissivity in real time. In addition, by manufacturing zinc-based hot-dip coated steel sheets while measuring the surface temperature of the zinc-based hot-dip-coated steel sheets using this temperature measurement method, it is possible to manufacture zinc-based hot-dip coated steel sheets with high yield while accurately controlling the steel plate temperature. be able to. Note that it is desirable to control the output (IH output) of the electromagnetic induction heating device that heats the zinc-based hot-dip-coated steel sheet based on the surface temperature of the zinc-based hot-dip-coated steel sheet. Specifically, a model showing the relationship between the alloying temperature and IH output of zinc-based hot-dip galvanized steel sheets is created and set in advance, and the electromagnetic induction heating device is heated according to the IH output of the model corresponding to the measured alloying temperature. It is good to control. Thereby, zinc-based hot-dip galvanized steel sheets can be manufactured with higher yield.

FIG. 6 shows an embodiment of the present invention. In this example, an emissivity measuring device 2 and a thermograph 3 were installed on the outlet side of an alloying furnace of a zinc-based hot-dip plating line. The emissivity measuring device 2 was installed so as to measure the emissivity at one point in the center of the steel plate S in the width direction. The thermograph 3 was installed at a location approximately 3 m downstream from the emissivity measurement device 2 in the conveyance direction of the steel plate S. The temperature of the steel plate to be measured is approximately 400 to 600°C. Therefore, the measurement wavelength of thermography 3 was set in the range of 1 to 1.5 μm. Moreover, the measurement range was about 1000 mm in width x about 1500 mm in length. As the emissivity measuring device 2, a device based on the configuration shown in FIG. 3 was used. When the surface temperature of the steel plate S was measured with the emissivity as a fixed value, the surface temperature of the steel plate S could not be accurately measured because the emissivity of the steel plate S changed during transportation. On the other hand, by measuring the surface temperature of the steel plate S while correcting the emissivity in real time as in the present invention, the surface temperature of the steel plate S could be measured with high accuracy.

Although embodiments to which the invention made by the present inventors is applied have been described above, the present invention is not limited to the description and drawings that form part of the disclosure of the present invention according to the present embodiments. That is, all other embodiments, examples, operational techniques, etc. made by those skilled in the art based on this embodiment are included in the scope of the present invention.

1 Temperature measuring device for zinc-based hot-dip coated steel sheet 2 Emissivity measuring device 3 Thermography 4 Arithmetic device 5 Display device 21 Light source for specular reflection 22 Light source for diffuse reflection 23 Radiation thermometer 24 Arithmetic device 25 Shutter 31 Thermocouple 32 Black body spray 33 Heater 34 Logger 100 Substrate 101 Zinc plating 102 Alloyed crystal L1, L2 Illumination light S Steel plate

Claims (9)

The amount of zinc based on the amount of specularly reflected light when the surface of the zinc-based hot-dip coated steel sheet is irradiated with light under specular reflection conditions and the amount of diffusely reflected light when the surface of the zinc-based hot-dipped steel sheet is irradiated with light under diffuse reflection conditions. an emissivity calculation step of calculating the emissivity of the surface of the hot-dip galvanized steel sheet;
an imaging step of taking an infrared image of the surface of the zinc-based hot-dip coated steel sheet;
a temperature measuring step of measuring the surface temperature of the zinc-based hot-dip plated steel sheet using the emissivity calculated in the emissivity calculating step and the infrared image taken in the imaging step,
In the emissivity calculation step, when the specular reflectance is above a threshold value, the emissivity is set to a fixed value, and when the specular reflectance is below the threshold value, the relationship between the emissivity, the diffuse reflectance, and the specular reflectance is calculated. A method for measuring the temperature of a zinc-based hot-dip coated steel sheet , characterized in that emissivity is estimated using a model shown in FIG . 2. The method for measuring temperature of a zinc-based hot-dip coated steel sheet according to claim 1, wherein the temperature measuring step includes a step of measuring a surface temperature distribution in the width direction of the zinc-based hot-dip coated steel sheet. 3. The temperature measuring method for a zinc-based hot-dip coated steel sheet according to claim 2, wherein the emissivity calculation step includes a step of calculating emissivity at a plurality of locations in the width direction of the zinc-based hot-dip coated steel sheet. The emissivity calculation step includes a step of calculating emissivity at a plurality of locations in the width direction of the zinc-based hot-dip coated steel sheet by scanning a measuring device along the width direction of the zinc-based hot-dip coated steel sheet. The method for measuring the temperature of a zinc-based hot-dipped steel sheet according to claim 3. Any one of claims 1 to 4, wherein the temperature measuring step includes a step of measuring the surface temperature of the zinc-based hot-dip coated steel sheet using a conveyance speed of the zinc-based hot-dip coated steel sheet. A method for measuring the temperature of a zinc-based hot-dip coated steel sheet as described in . The method for measuring the temperature of a zinc-based hot-dip coated steel sheet according to any one of claims 1 to 5, wherein the zinc-based hot-dip coated steel sheet is an alloyed hot-dip galvanized steel plate. The amount of zinc based on the amount of specularly reflected light when the surface of the zinc-based hot-dip coated steel sheet is irradiated with light under specular reflection conditions and the amount of diffusely reflected light when the surface of the zinc-based hot-dipped steel sheet is irradiated with light under diffuse reflection conditions. emissivity measuring means for calculating the emissivity of the surface of the hot-dip galvanized steel sheet;
an imaging means for taking an infrared image of the surface of the zinc-based hot-dipped steel sheet;
temperature measuring means for measuring the surface temperature of the zinc-based hot-dipped steel sheet using the emissivity calculated by the emissivity measuring means and the infrared image taken by the imaging means;
Equipped with
The emissivity measuring means fixes the emissivity when the specular reflectance is above the threshold value, and determines the relationship between the emissivity, the diffuse reflectance, and the specular reflectance when the specular reflectance is below the threshold value. 1. A temperature measuring device for a zinc-based hot-dip coated steel sheet , characterized in that the emissivity is estimated using a model shown in FIG . A manufacturing step of manufacturing a zinc-based hot-dip coated steel sheet while measuring the surface temperature of the zinc-based hot-dip coated steel plate using the method for measuring the temperature of a zinc-based hot-dip coated steel plate according to any one of claims 1 to 6. A method for producing a zinc-based hot-dip galvanized steel sheet. The zinc-based hot-dipped steel sheet according to claim 8, wherein the manufacturing step includes a step of controlling the output of an electromagnetic induction heating device that heats the zinc-based hot-dipped steel sheet based on the surface temperature of the zinc-based hot-dipped steel sheet. Method of manufacturing plated steel sheets.

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