The present invention relates to a surface temperature measuring method, a surface temperature measuring apparatus, a hot-dip zinc plated steel sheet manufacturing method, and a hot-dip zinc plated steel sheet manufacturing equipment.
In a hot-dip galvanizing line (hereinafter, referred to as CGL) in a steel process, temperature control is a very important work in production of materials and quality control of plating. In particular, in the alloying process by heating the steel sheet after zinc adhesion, an excessively high steel sheet temperature causes occurrence of powdering while an excessively low steel sheet temperature causes insufficient alloying. Furthermore, an excessively high steel sheet temperature, in the high-strength material, causes coarsening of the crystal grain size, leading to deterioration of material characteristics. In view of these, CGL is required to achieve very strict temperature control.
Here, examples of a method of heating the steel sheet include electromagnetic induction heating (hereinafter, denoted as IH) and heat transfer by radiant heat. In addition, examples of the method of the temperature control include a method of calculating the temperature of the steel sheet immediately after heating by heat transfer calculation or electromagnetic field simulation based on an output of IH or direct heating, the steel sheet conveyance speed, the sheet size, and the temperature of the molten zinc pod. With this method, however, there would be variations in the calculation result of the steel sheet temperature due to a slight variation in the thickness of the steel sheet and the passline. For this reason, it is also important to directly measure the steel sheet temperature.
Proposed methods of directly measuring the temperature of the steel sheet include methods such as a radiation thermometry and a temperature measurement roll method (refer to Non Patent Literature 1). However, during the manufacture of the hot-dip zinc plated steel sheet, the emissivity of the steel sheet surface greatly fluctuates depending on the progress of alloying, leading to an occurrence of a large measurement error in a radiation thermometer that presets the emissivity as a fixed value. To handle this, several efforts have been made as measures against the problem of emissivity setting necessary for the radiation thermometry.
Specifically, there is an invented thermometer being a multiple reflection radiation thermometer utilizing a rule that the emissivity approaches 1 by multiple reflection of radiation light. In addition, there are other types of thermometers developed, such as a wedge type radiation thermometer (refer to Patent Literature 1) using multiple reflection generated in a gap between a roll and a steel sheet on the assumption that the roll and the steel sheet are isothermal, and a bowl type radiation thermometer (refer to Patent Literature 2) in which a concave member having a high reflectance such as a member with gold plating is brought close to a measurement object.
Furthermore, there is another proposed method in which a reflection characteristic of a measurement object is measured using a law that a sum of an integrating sphere reflectance and an emissivity of the measurement object is 1, and the integrating sphere reflectance is estimated to estimate the emissivity (refer to Patent Literature 3). In addition, there is also a method referred to as a TRACE thermometer that measures the emissivity of the surface of a measurement object under multiple wavelengths or different polarization conditions, and simultaneously estimates the information regarding the change in the surface due to alloying and the temperature by preliminary learning (refer to Non Patent Literature 2).
However, when the surface of the steel sheet has at a high temperature, the steel sheet and the roll cannot be brought into contact with each other in a state where molten zinc adheres to the surface of the steel sheet. Therefore, there is no roll until the subsequent stage of the passline of the steel sheet, and a method such as a temperature measuring roll cannot be used for measuring the temperature of the steel sheet.
On the other hand, the progress of the alloying reaction varies depending on the type and size of the steel sheet and the conveyance conditions. For example, in the case of heating a steel sheet for the purpose of alloying, the target temperature of the steel sheet is about 450° C. to 550° C. In the case of measuring the temperature of the steel sheet using an InGaAs element suitable for radiation thermometry, the emissivity of the surface of the steel sheet changes to the value about 0.2 to 0.7 before and after alloying. This corresponds to a difference of 60° C. or more in terms of temperature, which leads to a failure of accurate measurement of the temperature of the steel sheet.
In addition, among various methods as described above which have been proposed in order to solve the problem of the emissivity fluctuation, the wedge type radiation thermometer is not applicable to the time immediately after heating having temperature measurement needs, similarly to the temperature measuring roll. In addition, the bowl type radiation thermometer also needs to make a lift-off distance of the passline very small. However, fluctuation of the passline cannot be suppressed by the roll after the molten zinc adhesion in the CGL, making it difficult to apply the bowl type radiation thermometer due to the lift-off distance.
Meanwhile, the method of estimating the emissivity by estimating the integrating sphere reflectance has been used in an application example in other cold rolled steel sheet processes. However, the diffusibility of the surface of the steel sheet is very high in the alloying process, lowering the estimation accuracy of the integrating sphere reflectance and the emissivity. Furthermore, the TRACE thermometer, which is not based on a physical model, is susceptible to unexpected disturbance and phenomenon, and thus has a limited practicability.
Under these circumstances, there has been a high demand for a technique capable of accurately measuring the temperature of a steel sheet in a hot-dip galvanizing line regardless of a fluctuation in emissivity of the surface of the hot-dip zinc plated steel sheet during the manufacture of the hot-dip zinc plated steel sheet.
The present invention has been made in view of the above problems and aims to provide a surface temperature measuring method and a surface temperature measuring apparatus capable of accurately measuring a surface temperature of a measurement object regardless of a fluctuation in emissivity of the surface of the measurement object. The present invention also aims to provide a hot-dip zinc plated steel sheet manufacturing method and a manufacturing equipment capable of manufacturing a hot-dip zinc plated steel sheet with high yield by accurately measuring a steel sheet temperature in a hot-dip galvanizing line regardless of an alloying process.
To solve the problem and achieve the object, a surface temperature measuring method according to the present invention includes: a first imaging step of acquiring a radiation light amount of a surface of a measurement object; a second imaging step of irradiating the surface of the measurement object with light under a specular reflection condition, and acquiring a specular reflection light amount; a third imaging step of irradiating the surface of the measurement object with light under a diffuse reflection condition, and acquiring a diffuse reflection light amount; an emissivity calculating step of calculating an emissivity of the surface of the measurement object by using a model indicating a relationship between an emissivity and a specular reflectance, and a relationship between the emissivity and a diffuse reflectance of the surface of the measurement object, the specular reflection light amount acquired in the second imaging step, and the diffuse reflection light amount acquired in the third imaging step; and a temperature measurement step of calculating a surface temperature of the measurement object using the radiation light amount acquired in the first imaging step and the emissivity calculated in the emissivity calculating step.
Moreover, in the surface temperature measuring method according to the present invention, the emissivity calculating step is executed in a case where a specular reflection light amount acquired in the second imaging step is a predetermined value or more, and a fixed value is used as the emissivity in the temperature measurement step in a case where the specular reflection light acquired in the second imaging step is less than a predetermined value.
Moreover, in the surface temperature measuring method according to the present invention, each of the second imaging step and the third imaging step includes a step of correcting the specular reflection light amount and the diffuse reflection light amount by subtracting the radiation light amount acquired in the first imaging step.
Moreover, in the surface temperature measuring method according to the present invention, the first imaging step, the second imaging step, and the third imaging step include a step of receiving light using a light receiving element having a plurality of visual fields to which acquisition ranges of the radiation light amount, the specular reflection light amount, and the diffuse reflection light amount are assigned in a conveyance direction of the measurement object.
Moreover, in the surface temperature measuring method according to the present invention, the measurement object is a hot-dip zinc plated steel sheet.
Moreover, a surface temperature measuring apparatus according to the present invention includes: a first imaging unit configured to acquire a radiation light amount of a surface of a measurement object; a second imaging unit configured to irradiate the surface of the measurement object with light under a specular reflection condition, and to acquire a specular reflection light amount; a third imaging unit configured to irradiate the surface of the measurement object with light under a diffuse reflection condition, and to acquire a diffuse reflection light amount; an emissivity calculating unit configured to calculate an emissivity of the surface of the measurement object by using a model indicating a relationship between an emissivity and a specular reflectance, and a relationship between the emissivity and a diffuse reflectance of the surface of the measurement object, the specular reflection light amount acquired by the second imaging unit, and the diffuse reflection light amount acquired by the third imaging unit; and a temperature measurement unit configured to calculate a surface temperature of the measurement object using the radiation light amount acquired by the first imaging unit and the emissivity calculated by the emissivity calculating unit.
Moreover, in the surface temperature measuring apparatus according to the present invention, the measurement object is a hot-dip zinc plated steel sheet.
Moreover, a hot-dip zinc plated steel sheet manufacturing method according to the present invention includes manufacturing steps of manufacturing a hot-dip zinc plated steel sheet, the manufacturing steps of manufacturing the hot-dip zinc plated steel sheet includes: a temperature measurement step of measuring a surface temperature of the hot-dip zinc plated steel sheet by the surface temperature measuring method according to the present invention; and a step of controlling manufacturing conditions in the manufacturing steps by using the surface temperature measured in the temperature measurement step.
Moreover, a hot-dip zinc plated steel sheet manufacturing equipment according to the present invention includes: the surface temperature measuring apparatus according to the present invention; and an equipment that manufactures a hot-dip zinc plated steel sheet based on a surface temperature of a hot-dip zinc plated steel sheet measured by the surface temperature measuring apparatus.
According to the surface temperature measuring method and the surface temperature measuring apparatus of the present invention, the surface temperature of the measurement object can be accurately measured regardless of the fluctuation in the emissivity of the surface of the measurement object. In addition, according to the hot-dip zinc plated steel sheet manufacture method and manufacturing equipment according to the present invention, it is possible to accurately measure the temperature of a steel sheet in a hot-dip galvanizing line regardless of an alloying process, enabling manufacture of a hot-dip zinc plated steel sheet with high yield.
The radiation thermometry is a method of calculating the surface temperature of a measurement object using a measured radiation amount and a preset emissivity by using a rule that the radiation amount of the measurement object is theoretically determined by the temperature and the emissivity. Here, the emissivity of the measurement object changes within a range of 0 to 1 depending on the state and shape of the surface of the measurement object. Therefore, in order to accurately measure the surface temperature of the measurement object, the emissivity of the measurement object needs to be set to a correct value. Accordingly, many commonly used radiation thermometers preliminarily measure the emissivity of the measurement object or use a known emissivity for the measurement object to preset the emissivity as a fixed value. Under this condition, the radiation light amount is measured, and the surface temperature of the measurement object is obtained from a standard curve. Examples of the method of measuring the emissivity described herein include a method in which a black body paint having a known emissivity is applied to measure a radiation light amount ratio with respect to a measurement target site, and a method in which a surface temperature value obtained by another measuring method such as a thermocouple is theoretically converted into a radiation amount for comparison.
On the other hand, in a general radiation thermometer that presets an emissivity as a fixed value, an actual emissivity greatly deviating from the set emissivity would produce a large measurement error. In particular, on the exit side of the alloying process by IH heating after the zinc pod, the steel sheet surface can take a variety of states, including a state where the surface of the steel sheet is close to a mirror surface far from being alloyed and a state where the alloying progresses to be close to a rough surface. Therefore, presetting the emissivity as a fixed value will inevitably lead to occurrence of a large deviation from the actual emissivity. In addition, the progress of the degree of alloying greatly changes depending on components and manufacturing conditions, making it difficult to predict the surface state and the emissivity in advance. To handle this situation and accurately perform the radiation temperature measurement, the inventors have studied techniques of correctly estimating the emissivity in real time with respect to the fluctuating surface property of the measurement object and converting the radiance into the temperature with the estimated emissivity. Here, a method of estimating the emissivity focuses on the Kirchhoff's law in which the sum of the emissivity and the integrating sphere reflectance is 1. Patent Literature 3 describes a method of calculating an integrating sphere reflectance based on reflection distribution information, although it is difficult to accurately measure a parameter of a spread of a specular reflection component that greatly contributes to accuracy, leading to failure of acquisition of sufficient accuracy. Still, the reflection characteristic of the measurement object has a close physical relationship with the emissivity, and thus, is considered to be an important clue in estimating the emissivity even for a surface that changes in the course of alloying the hot-dip zinc plated steel sheet.
Therefore, the inventors of the present invention have focused on the fact that reflection characteristics are typically expressed by the sum of specular reflection and diffuse reflection, and have studied the relationship between the emissivity and two types of reflection characteristics, namely, specular reflection and diffuse reflection, in the surface state in the alloying process of the hot-dip zinc plated steel sheet. As a result, as will be described below, the present inventors have found that the surface state in the alloying process includes two processes: step S1 in which the specularity gradually decreases from a state in which the specularity is very high by hot-dip zinc plating and the diffusibility is increased to almost a perfect diffusion surface; and step S2 in which the diffuse reflectance gradually decreases from a state in which the surface is the perfect diffusion surface. In addition, it has been found that the emissivity does not fluctuate in step S1, and the emissivity increases as the diffuse reflectance decreases according to Kirchhoff's law in step S2 in which almost no specular reflection component exists. In these steps, it is difficult to follow the alloying process with either one of only the specular reflection component or only the diffuse reflection component. The progress of alloying and the emissivity can be correctly estimated by combining both reflection components. As a result of intensive studies based on these findings, the inventors of the present invention have conceived a technical idea that a surface temperature of a hot-dip zinc plated steel sheet can be accurately measured by a method in which a surface image of the hot-dip zinc plated steel sheet is captured under specular reflection conditions and diffuse reflection conditions in a hot-dip galvanizing line, and an emissivity is calculated in real time from a preliminarily modeled relationship between the emissivity and the specular reflectance, and between the emissivity and the diffuse reflectance.
Specifically, when measuring the surface temperature of the hot-dip zinc plated steel sheet using the present invention, the first step will be a calibration of the radiation thermometer and preliminary modeling of the relationship between the emissivity and the specular reflectance, and the relationship between the emissivity and the diffuse reflectance. Here, as the radiation thermometer, since the target surface temperature of the hot-dip zinc plated steel sheet is about 450° C. to 550° C., it is preferable to use an InGaAs element, and preferable to make the wavelength sensitivity as narrow as possible using a long pass filter, a short pass filter, or a band pass filter. Among various methods for calibrating the radiation thermometer, and the method described in Non Patent Literature 3 may be applied as an example. The radiation thermometer described herein is an optical sensor such as an area sensor, a line sensor, or a single element sensor, and has a function as a radiation thermometer by being graduated at each temperature of the black body condition.
The relationship between the emissivity and the specular reflectance, and the relationship between the emissivity and the diffuse reflectance can be modeled by measuring the specular reflection light amount, the diffuse reflection light amount, and the radiation light amount when the hot-dip zinc plated steel sheet is actually heated by an experimental apparatus as illustrated in
When the relationship between the emissivity and the specular reflectance, and the relationship between the emissivity and the diffuse reflectance is modeled using the experimental apparatus illustrated in
Next, operations are performed to install a radiation thermometer 4, a specular reflection light source 5 that irradiates the surface of the hot-dip zinc plated steel sheet S with light under a specular reflection condition, and a diffuse reflection light source 6 that irradiates the surface of the hot-dip zinc plated steel sheet S with light under a diffuse reflection condition. Although the radiation thermometer 4 cannot be installed in front of the hot-dip zinc plated steel sheet S in order to match the light projection angle and the light reception angle of the specular reflection light source 5, it is still desirable to install the radiation thermometer 4 so as to be perpendicular to the surface of the hot-dip zinc plated steel sheet S as much as possible within an installable range. The diffuse reflection condition is desirably set to an angle different from the specular reflection condition by 45° or more. In addition, it is preferable that turning on/off of the specular reflection light source 5 and the diffuse reflection light source 6 can be switched by a power source, a shutter, or the like.
The hot-dip zinc plated steel sheet in the present specification is not particularly limited as long as zinc is contained in the plating layer. Examples of the hot-dip zinc plated steel sheet include a hot-dip galvanized steel sheet (GI), a hot-dip galvannealed steel sheet (GA) obtained by alloying a hot-dip galvanized steel sheet, a Zn—Al—Mg plated steel sheet (for example, Zn-6 mass % Al-3 mass % Mg alloy plated steel sheet and Zn-11 mass % Al-3 mass % Mg alloy plated steel sheet), and a Zn—Al plated steel sheet (for example, Zn-5 mass % Al-alloy plated steel sheet and Zn-55 mass % Al-alloy plated steel sheet).
Furthermore, the hot-dip zinc plated layer may contain, as a small amount of dissimilar metal elements or impurities, one or more of nickel, cobalt, manganese, iron, molybdenum, tungsten, titanium, chromium, aluminum, magnesium, lead, antimony, tin, copper, and silicon. The hot-dip zinc plated layer may be formed by using two or more hot-dip zin plated layers of the same type or different types among the hot-dip zinc plated layers described above.
Next, a model indicating the relationship between the emissivity and the diffuse reflectance, and the relationship between the emissivity and the specular reflectance is generated using the above-described experimental apparatus. Specifically, the following steps (a) to (e) are repeatedly executed while gradually heating the hot-dip zinc plated steel sheet S.
Note that it is preferable to set the heating rate so that substantially the same surface state of the hot-dip zinc plated steel sheet S can be imaged in the processes (a) to (c) in consideration of the exposure time and the measurement time. With this operation, for example, within the range of the heating temperature of the hot-dip zinc plated steel sheet S as illustrated in
With this model, the emissivity of the hot-dip zinc plated steel sheet can be accurately estimated by measuring the specular reflectance and the diffuse reflectance of the surface of the hot-dip zinc plated steel sheet. This makes it possible to perform accurate calculation of the surface temperature of the hot-dip zinc plated steel sheet by using the radiation light amount and the emissivity regardless of the fluctuation in the emissivity of the surface of the hot-dip zinc plated steel sheet during the production of the hot-dip zinc plated steel sheet. In addition, by manufacturing a hot-dip zinc plated steel sheet based on the calculated surface temperature, the hot-dip zinc plated steel sheet can be manufactured with good yield.
The specular reflectance and the diffuse reflectance of the hot-dip zinc plated steel sheet can be obtained by measuring relative values with respect to the specular reflectance and the diffuse reflectance of a sample piece having a reflectance as a normal reference being close to 1. Examples of the sample piece can be a gold mirror and an aluminum mirror for acquisition of the specular reflectance, and can be barium sulfate for acquisition of the diffuse reflectance. Alternatively, the modeling can be performed using a reflection light amount with reference to the light amount of the light source. In this case, a light source with a constant irradiation light amount can be applied to an imaging system with a constant sensitivity, and the obtained luminance value can be directly used as a model. In addition, although the shutter is used in the modeling procedure described above, it is not always necessary to use the shutter as long as it is possible to acquire the specular reflection image, the diffuse reflection image, and the self-emitted light image in the same surface state. Alternatively, instead of using a shutter, it is allowable to prepare a plurality of samples in states of different degrees of alloying, measure the specular reflectance and the diffuse reflectance, and further heat the sample to such an extent that the surface state does not change to obtain the emissivity to achieve modeling.
When the temperature measuring method according to an embodiment of the present invention is applied to the actual line, the radiation light amount, the amount of specular reflection light, and the diffuse reflection light amount are acquired from the hot-dip zinc plated steel sheet of the actual line. At this time, the emissivity is calculated using the model from the acquired specular reflection light amount and diffuse reflection amount. The emissivity can be calculated by various methods. For example, when the number of points of the model obtained in an experiment is N, the specular reflection light amount is rs, the diffuse reflection light amount is rd, and the emissivity is e, the model can be expressed as a three-dimensional vector ((rsn,rdn,en) (n=1, . . . , N). When the number of points of the actual operation model is insufficient, it is allowable to increase the points by interpolation. When en is uniquely determined by first determining rsn and rdn, e may be approximated and used as a function of rs and rd, such as e=f(rs,rd).
Here, assuming that the specular reflection light amount obtained by actual measurement is Rs and the diffuse reflection light amount is Rd, the coordinate position (degree of alloying) and the emissivity on the model at the time of measurement can be estimated by distance minimization as in the following Formula (1). Note that weights may be applied to the specular reflection light amount and the diffuse reflection light amount as necessary. Naturally, a similar result can be obtained even when the norm of the distance is changed.
In this case, step S1 and step S2 can be separated as clearly different physical phenomena. Accordingly, it is allowable to first select whether the surface state of the hot-dip zinc plated steel sheet is classified into step S1 or step S2, and then calculate the coordinate position on the model in each process. For example, a simplest method would be setting a threshold for the specular reflectance, and classifying the state to step S1 when the specular reflectance is the threshold or more, and classifying the state into step S2 when the specular reflectance is the threshold or less. In step S1, since the emissivity hardly fluctuates, the emissivity can be set to a fixed value (about 0.2), and in step S2, the coordinate position on the model and the emissivity can be estimated from the value of the diffuse reflection light amount. Many methods of determining the optimum coordinate position on the model have been proposed in addition to this method, and thus, any method may be used as long as the coordinate position on the model can be correctly obtained.
In the example illustrated in
Since there is no conveying roll for several tens of meters at the subsequent stage of the molten zinc pot of CGL, the passline is not stable. There is also a technique of stabilizing a passline using an electromagnet (refer to Patent Literature 3). However, the technique basically intends to suppress flutter at an installation position of an air knife for uniformizing the adhesion amount of molten zinc. Therefore, the position and inclination of the passline fluctuate immediately after alloying heating, which is a timing to be a temperature measurement target. Therefore, it is preferable to optimize installation conditions and irradiation light of the specular reflection light source 5 and the diffuse reflection light source 6. Hereinafter, an example of installation conditions of the specular reflection light source 5 and the diffuse reflection light source 6 will be described on the premise of the arrangement illustrated in
Now, a longitudinal direction of the hot-dip zinc plated steel sheet S is defined as a y-axis direction, a width direction of the hot-dip zinc plated steel sheet S is defined as a c-axis direction, the amount of fluctuation of the passline position of the hot-dip zinc plated steel sheet S from a reference position is defined as ±Δd, the amount of angular fluctuation of the surface of the hot-dip zinc plated steel sheet S from a reference angle in an x-axis direction is defined as ±Δθx, and the amount of angular fluctuation from a reference angle in the y-axis direction is defined as ±Δθy.
First, installation conditions of the specular reflection light source 5 will be described with reference to
Next, installation conditions of the diffuse reflection light source 6 will be described with reference to
Moreover, the diffuse reflection light source needs to be applied to an optical system under a condition of a low reflectance such as a diffuse reflection condition, and at the same time, needs to ensure a sufficiently high reflection light amount with respect to self-emitted light, which requires irradiation of light with very high intensity. However, using an excessively high-intensity infrared light source, for example, a halogen light source, would allow the light source itself to heat the hot-dip zinc plated steel sheet, leading to a possibility of a change in the surface temperature of the hot-dip zinc plated steel sheet. Therefore, based on the concept of radiation heat transfer, the condition illustrated in the following formula (2) is to be preferably satisfied. Here, an allowable temperature change amount is ΔT(° C.), an output of the diffuse reflection light source is P(W), an absorptivity (emissivity) of the hot-dip zinc plated steel sheet in an irradiation region of the diffuse reflection light source is εh, an irradiation area of the diffuse reflection light source on the hot-dip zinc plated steel sheet is α(mm2), a thickness of the hot-dip zinc plated steel sheet is t (mm), a specific gravity of iron is ρ(g/mm3), a specific heat of iron is c (J/g), an irradiation region of the diffuse reflection light source in the longitudinal direction of the hot-dip zinc plated steel sheet is l (m), and the conveyance line speed of the hot-dip zinc plated steel sheet is v (m/s).
For example, when the allowable temperature change amount ΔT(° C.) is 1(° C.), the output P(W) of the halogen light source is 100 (W), the absorptivity (emissivity) Eh of the hot-dip zinc plated steel sheet in the irradiation region of the halogen light source is 0.8, the irradiation area α(mm2) of the halogen light source on the hot-dip zinc plated steel sheet is 10000 (mm2), the thickness t (mm) of the hot-dip zinc plated steel sheet is 1 (mm), the specific gravity ρ (g/mm3) of iron is 0.78 (g/mm3), the specific heat c (J/g) of iron is 0.435 (J/g), the irradiation region l (m) of the halogen light source in the longitudinal direction of the hot-dip zinc plated steel sheet is 100 (m), and the conveyance line speed v (m/s) of the hot-dip zinc plated steel sheet is 0.5 (m/s), the result is such that the temperature rise of the irradiation site is 0.471(° C.), the temperature being lower than the allowable temperature change amount 1(° C.). Consequently, it is preferable to use a halogen light source having an output P of 100 (W) under these conditions.
Furthermore, the present embodiment performs imaging on the moving hot-dip zinc plated steel sheet by switching the radiation light amount, the specular reflection light amount, and the diffuse reflection light amount, at mutually different timings. In this case, it is most preferable that the imaging be completed three times in total, that is, once for measuring the radiation light amount, once for measuring the specular reflection light amount, and once for measuring the diffuse reflection light amount, within a range that can be regarded as the same surface property. That is, the present embodiment assumes that alloying progress is the same when estimating the emissivity from the specular reflection luminance and the diffuse reflection luminance, and therefore, when the specular reflection light amount measurement and the diffuse reflection light amount measurement are performed with different surface properties, it would be difficult to estimate the emissivity by the model. In addition, when the surface property at the time of measuring the radiation light amount is different from the property at estimation of the emissivity, the actual emissivity and the estimated emissivity would be different. However, when the distribution of the degree of alloying unevenness of the hot-dip zinc plated steel sheet changes in a narrow range, and the surface properties of the portions are not the same due to the relationship among the responsiveness of the mechanical shutter, the exposure time, and the conveyance speed of the hot-dip zinc plated steel sheet, it is preferable to perform correction using filtering in the spatial direction or the temporal direction. Specifically, by performing filtering using a mean value, a maximum value, a minimum value, a median, and a percentile of a radiation light amount, a specular reflection light amount, a diffuse reflection light amount, an emissivity, and a surface temperature within a certain imaging range or in a certain period in the past, it is possible to reduce the influence of the degree of alloying unevenness.
Incidentally, when the filtering processing is used, there is a possibility that a delay occurs due to the processing. In this case, the surface temperature can be measured with less delay by using a configuration of the temperature measuring apparatus of modifications described below.
[First Modification]
[Second Modification]
The embodiments to which the invention made by the present inventors is applied have been described as above. Note that the present invention is not limited by the description and drawings constituting a part of the disclosure of the present invention according to the present embodiments. For example, in the present embodiment, a hot-dip zinc plated steel sheet is set as a measurement object. However, the measurement object is not limited to the hot-dip zinc plated steel sheet, and the present invention can be generally applied to substances in which the emissivity can be uniquely determined from specular reflection light and diffuse reflection light. In this manner, other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.
In addition, the present invention may be applied to a temperature measurement step included in a method of manufacturing a hot-dip zinc plated steel sheet, and the temperature of the hot-dip zinc plated steel sheet may be measured in a known or existing step of manufacturing a hot-dip zinc plated steel sheet. That is, the method of manufacturing a hot-dip zinc plated steel sheet includes: a temperature measurement step of measuring a surface temperature of a hot-dip zinc plated steel sheet by the hot-dip zinc plated steel sheet temperature measuring method according to the present invention; and a step of controlling manufacturing conditions of the hot-dip zinc plated steel sheet based on the measured surface temperature of the hot-dip zinc plated steel sheet.
In this case, it is preferable to provide, in the middle of a known, unknown, or existing production step, a temperature measurement step of measuring the temperature of the hot-dip zinc plated steel sheet in the middle of production using the temperature measuring method according to the present invention. In particular, in the hot-dip zinc plated steel sheet, it is preferable to measure the temperature of the steel sheet having an unknown emissivity fluctuating in accordance with the degree of alloying of plating. When the feedback control is used, the temperature measurement step uses the temperature measured in the temperature measurement step to control a condition of one or a plurality of processes before the temperature measurement step among the processes included in the manufacturing step. When the control is used in the case of measuring the temperature of the steel sheet to which zinc is attached or not attached during conveyance, it is most favorable because the effect of the present invention can be utilized to the maximum.
More specifically, the step may be provided immediately after the heating apparatus that promotes alloying, which is after zinc adhesion to the surface of the steel sheet, and feedback control may be used for the output of the heating apparatus so as to obtain a temperature on the heating apparatus exit side with an appropriate degree of alloying. Furthermore, control may be performed to obtain an appropriate degree of alloying by performing a feedback of output to an actuator that controls a factor having an influence on the likelihood of alloying, such as a dew point in the preceding process. In particular, it is most preferable to provide the step in the middle of a hot-dip galvanizing line for applying hot-dip zinc plating to a steel sheet.
Furthermore, when alloying is performed in an induction heating furnace (also referred to as an IH heating furnace as abbreviation), it is most preferable to measure the temperature immediately after the exit side of the IH heating furnace, which is the highest point of the temperature in the alloying process after plating, in the hot-dip galvanizing line. When the maximum temperature in the alloying process is too low, the alloying does not sufficiently progress, and when the maximum temperature is too high, the crystal grains of the structure become coarse and adversely affect the material, having a possibility of excessive progress of alloying. Therefore, temperature control is very important. By controlling the output of the IH heating furnace so that the temperature immediately after the IH exit side is within a predetermined control range using the present apparatus, it is possible to manufacture a hot-dip zinc plated steel sheet having a target material and a target degree of alloying.
From the above reason, the present invention is most effective for the production of the hot-dip galvannealed steel sheet (GA) among hot-dip zinc plated steel sheets.
In addition, the present invention may be applied as a temperature measuring apparatus constituting a manufacturing equipment for a hot-dip zinc plated steel sheet. In addition, a hot-dip zinc plated steel sheet may be manufactured using the manufacturing equipment on the basis of the surface temperature of the hot-dip zinc plated steel sheet measured by the temperature measuring apparatus according to the present invention. In this case, the manufacturing equipment for manufacturing the hot-dip zinc plated steel sheet may be any of known, unknown, and existing facilities. In addition, the manufacturing equipment for manufacturing the hot-dip zinc plated steel sheet includes a hot-dip zinc plating equipment for applying hot-dip zinc plating to the steel sheet. The temperature measuring apparatus according to the present invention is preferably provided in the conveyance equipment. Furthermore, it is most preferable that the transfer roller is provided between two conveyance rollers provided in the hot-dip zinc plating equipment. The present invention is most effective in manufacturing the hot-dip galvannealed steel sheet (GA) among hot-dip zinc plated steel sheets.
Furthermore, the present invention may be applied to a steel sheet quality control method, and the quality control of the steel sheet may be performed by measuring the temperature of the steel sheet. Specifically, in the present invention, the temperature of the steel sheet is measured in the temperature measurement step, and the quality control of the steel sheet can be performed based on the measurement result obtained in the temperature measurement step. A subsequent quality control step determines whether the manufactured steel sheet satisfies a predetermined standard based on the measurement result obtained in the temperature measurement step to achieve quality control of the steel material. According to such a method for quality control of a steel sheet, a high-quality steel sheet can be provided. The present invention is most effective in manufacturing the hot-dip galvannealed steel sheet (GA) among hot-dip zinc plated steel sheets.
In the present example, the surface temperature of the actual CGL induction-heating furnace exit side hot-dip zinc plated steel sheet was measured by the configuration illustrated in
Since the conditions such as the size and the conveyance speed of the hot-dip zinc plated steel sheet are constant, it is expected that there is a physical correlation between the degree of alloying and the surface temperature. However, as illustrated in
According to the present invention, it is possible to provide the surface temperature measuring method and the surface temperature measuring apparatus capable of accurately measuring the surface temperature of a measurement object regardless of fluctuations in the emissivity of the surface of the measurement object. Regarding another aim of the present invention, it is possible to provide a hot-dip zinc plated steel sheet manufacturing method and a manufacturing equipment capable of manufacturing a hot-dip zinc plated steel sheet with high yield by accurately measuring a steel sheet temperature in a hot-dip galvanizing line regardless of an alloying process.
Number | Date | Country | Kind |
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2020-179302 | Oct 2020 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2021/031087 | 8/25/2021 | WO |