JPH11269627A - Alloying furnace for hot-dip galvanized steel sheet and method for controlling degree of alloying of hot-dip galvanized steel sheet - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To provide an alloying furnace for hot-dip galvanized steel sheet and a hot-dip galvanized steel sheet capable of accurately controlling the degree of alloying of the hot-dip galvanized steel sheet with simple equipment and a control method. Providing a degree control method. SOLUTION: A radiation thermometer having a function of continuously measuring radiant energy from a steel sheet surface in a longitudinal direction of a steel strip from a heating zone of an alloying furnace for hot-dip galvanized steel sheet to a zone in a solitary zone or a zone in a solitary zone. In the galvanizing furnace for hot-dip galvanized steel sheet, and in the galvanizing furnace for hot-dip galvanized steel sheet, the steel sheet temperature and radiant energy were measured using the above-mentioned radiation thermometer, and the obtained measurement results were obtained. A method for controlling the degree of alloying of a hot-dip galvanized steel sheet, comprising detecting an inflection point of the emissivity of the steel sheet surface in the longitudinal direction of the steel sheet in the alloying furnace, and controlling operating conditions of the alloying furnace based on the inflection point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloying furnace for hot-dip galvanized steel sheets and a method of controlling the degree of alloying of hot-dip galvanized steel sheets. The present invention relates to a controllable alloying furnace for a hot-dip galvanized steel sheet and a method for controlling the degree of alloying of the hot-dip galvanized steel sheet.

[0002]

2. Description of the Related Art As a method of controlling the degree of alloying of an alloyed hot-dip galvanized steel sheet, a method of irradiating the steel sheet with X-rays, calculating the degree of alloying from X-ray diffraction intensity, and controlling the degree of alloying is disclosed. (JP-B-56-12314, JP-A-1-1773)
No. 51). In addition, a plurality of radiation thermometers are disposed in a plate temperature holding zone in the galvannealing alloying furnace, and the emissivity of the steel sheet at each position is measured. Alloying position) is a constant position,
A control method for controlling the degree of alloying by manipulating the fuel flow rate and the passing speed of the alloying furnace is disclosed (see Japanese Patent Application Laid-Open No. 7-150328).

However, in the case of the above-mentioned X-ray diffraction method, a measurement error is large unless a measuring device is provided after the steel plate is sufficiently cooled, and the measuring device is considerably post-processed after the soaking process of the alloying furnace. Therefore, there is a problem that the timing of feedback of the obtained information is delayed.
Further, in order to correctly recognize the degree of alloying, information on the amount of plating is required, and a combination of information on X-ray diffraction and information on the amount of plating is required, which complicates the measurement method and the control method. .

On the other hand, in the case of the above-described method of disposing a plurality of radiation thermometers, the change in the emissivity of the steel sheet in the alloying furnace is rapid, as described later. Have difficulty. In addition, when a large number of radiation thermometers are provided in order to accurately control the degree of alloying in response to changes in the amount of Zn deposited, changes in the type of base sheet steel, and changes in the speed at which the steel sheet passes,
There are problems that the equipment cost increases and the control method becomes complicated.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a molten steel capable of accurately controlling the degree of alloying of a hot-dip galvanized steel sheet with simple equipment and a control method. An object of the present invention is to provide an alloying furnace for a galvanized steel sheet and a method for controlling the degree of alloying of a galvanized steel sheet.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have made it possible to move the radiation thermometer itself or to determine whether the optical axis of the radiation thermometer and the steel plate surface can be moved. By making the angle variable, it is possible not only to control the degree of alloying of the hot-dip galvanized steel sheet (hereinafter referred to as the degree of alloying) with simple equipment and a control method,
The present inventors have conceived that accurate control of the degree of alloying can be performed in response to a rapid change in the emissivity of the steel sheet in the alloying furnace, and have led to the present invention.

That is, the first invention is to measure the radiant energy from the steel sheet surface continuously in the longitudinal direction of the steel strip from the heating zone of the galvanizing furnace for hot-dip galvanized steel sheet to the soaking zone or the soaking zone. A galvanizing furnace for hot-dip galvanized steel sheets, comprising a radiation thermometer having a function of performing the function. In the first aspect, it is preferable that the radiation thermometer is a radiation thermometer having a function of continuously measuring radiation energy from a steel sheet surface over 1 m or more in a longitudinal direction of the steel strip.

According to a second aspect of the present invention, there is provided a radiant temperature which is disposed from a heating zone 11 of an alloying furnace for hot-dip galvanized steel sheet to a zone of a soaking zone 12 or a zone of a soaking zone 12, and moves continuously in the longitudinal direction of the strip. This is a galvanizing furnace for hot-dip galvanized steel sheets, comprising: a thermometer 14; and a position detector 17b for the radiation thermometer 14 in the longitudinal direction of the alloying furnace steel strip. The second mentioned above
In the present invention, the radiation thermometer 14 is preferably a radiation thermometer that continuously moves over 1 m or more in the longitudinal direction of the steel strip.

According to a third aspect of the present invention, a hot-dip galvanized steel sheet is arranged in a zone from a heating zone 11 of an alloying furnace to a zone of a soaking zone 12 or a zone of a soaking zone 12, and continuously extends from the steel sheet surface in the longitudinal direction of the strip. A radiation thermometer 30 having a variable angle θ between the optical axis (AX) and the steel sheet surface for measuring radiant energy, and a measurement point detection device 31b for detecting a measurement point on the steel sheet surface of the radiation thermometer 30 It is an alloying furnace for a hot-dip galvanized steel sheet.

In the third aspect of the present invention, the radiation thermometer 30 measures the radiant energy from the surface of the steel sheet continuously over 1 m or more in the longitudinal direction of the steel strip. It is preferable that the radiation thermometer has a variable angle θ with respect to the surface. In the first to third inventions described above, the water-cooled jacket-type cylinder 40 surrounding the optical axis of the radiation thermometer between the steel plate surface and the radiation thermometers 14 and 30 is provided. Is preferred.

A fourth aspect of the present invention is the first to third aspects of the present invention.
In the alloying furnace for hot-dip galvanized steel sheet of the invention, the temperature of the steel sheet and the radiant energy are measured using the above-mentioned radiation thermometer, and the radiation of the steel sheet surface in the steel sheet longitudinal direction in the alloying furnace based on the obtained measurement results Detect the inflection point of the rate,
A method for controlling the degree of alloying of a hot-dip galvanized steel sheet, characterized by controlling operating conditions of an alloying furnace based on the inflection point.

In the fourth aspect of the invention, it is preferable to control the operating conditions of the alloying furnace so that the inflection point is located at a predetermined position. In the fourth aspect, the operating conditions of the alloying furnace are as follows:
The fuel supply amount to the alloying furnace is preferably used.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The feature of the alloyed hot-dip galvanized steel sheet is that the color tone changes significantly due to the degree of alloying of the alloy layer finally formed on the steel sheet surface. For this reason, when the surface of the steel sheet is measured with a radiation thermometer during the alloying process, the radiant energy sharply increases at the alloying completion point regardless of the base material of the galvannealed steel sheet, the coating weight, and the passing speed. .

However, the appropriate setting point in the longitudinal direction of the steel sheet in the alloying furnace at the inflection point of the emissivity, which is the above-mentioned alloying completion point, differs depending on the conditions described above.
In order to accurately recognize the completion point of alloying in the alloying furnace, the present invention makes it possible to continuously move the radiation thermometer itself in the steel strip longitudinal direction, The inflection point of the emissivity is detected by measuring the emissivity of the steel sheet surface at all points continuously in the longitudinal direction of the steel sheet by making the angle between the optical axis and the steel sheet surface variable, and based on the obtained detection results. It is characterized by precisely controlling the degree of alloying.

In the present invention, the radiation thermometer is preferably a radiation thermometer having a function of continuously measuring the radiation energy from the steel sheet surface over 1 m or more in the longitudinal direction of the steel strip. This is to enable continuous passage of various plated products. FIG. 1 is a side view showing an example of a hot-dip galvanizing apparatus according to the present invention and an example of a hot-dip galvanized steel sheet alloying furnace of the present invention.

In FIG. 1, 1 is a steel strip, 2 is a hot dip galvanizing tank, 3 is a sink roll, 4 is molten zinc, 5 is a gas wiping nozzle, 6 is a deflector roll, 10 is an alloying furnace, and 11 is alloying. Furnace heating zone, 12 is alloying furnace soot, 12
W is the side wall of the alloying furnace, 13 is a heating device, 14 is a radiation thermometer, 15 is a rail for moving the radiation thermometer, 16 is a wheel for moving the radiation thermometer, and 17a is a drive for moving the radiation thermometer. Device and drive control device, 17b is a position detection device for the radiation thermometer 14,
18 is a wire winding device for moving the radiation thermometer, 19 is a wire for moving the radiation thermometer, 20 is an emissivity and emissivity inflection point calculation device, 21 is a alloying degree control device, and 22 is a fuel flow control. apparatus, 23 an air flow control device, f ₁ is the traveling direction of the steel strip,
Y is the distance between the starting point P ₁ (: heating zone exit side) and the end point P ₂ (: solitary exit side) where the radiation thermometer 14 can move along the longitudinal direction of the steel strip, and y is the end point from the starting point P _1. any point P ₂ direction indicates the distance to P.

The radiation thermometer 14 is configured so that it can be moved on the rail 15 by a drive device and a drive control device 17a and can be continuously moved within a range of Y = 20 m along the longitudinal direction of the steel strip. . In the hot-dip galvanizing apparatus and the galvanizing furnace for hot-dip galvanized steel sheet shown in FIG. After the amount of plating is adjusted, it is introduced into the alloying furnace 10.

The steel strip 1 introduced into the alloying furnace 10 has a plating layer formed by mutual diffusion of metal between the zinc layer and the steel base.
A steel sheet that is Fe-Zn alloyed and has excellent coating film adhesion and corrosion resistance can be obtained. The emissivity of the steel sheet 1 is measured by detecting the radiant energy emitted from the sheet surface of the steel strip 1 introduced into the alloying furnace 10 by the mobile radiation thermometer 14 disposed in the alloying furnace 10. Is done.

The emissivity is calculated by the following equation (1). ε = ε ₀ · exp {[C (T−T ₀ )] / [λ · T · T ₀ ]} (1) where ε: emissivity, ε ₀ : set emissivity of radiation thermometer ,
C: constant, T: indicated value of radiation thermometer, T ₀ : plate temperature, λ:
It is a measurement wavelength. The radiation thermometer 14 moves back and forth in the direction of f _F and f _B along the steel strip longitudinal direction, that is, in the longitudinal direction of the steel strip, detects radiant energy emitted from the steel strip plate surface, and detects an alloying furnace. The reading value T of the radiation thermometer is continuously obtained with respect to the steel strip plate surfaces at all points in the range of Y = 20 m in the longitudinal direction of the ten steel strips.

Next, from the following relational expression (2) between the position y in the longitudinal direction of the alloying furnace 10 and the obtained indicated value T, the following condition (3) is obtained.
Is determined in the longitudinal direction of the alloying furnace satisfying the following condition. T = f (y)... (2) Position K: dT / dy = α (3) Note that the position K is from the starting point P ₁ (: the heating band exit side) to the ending point P.
_{2 This} is the position where the differential value dT / dy obtained from the change in T corresponding to the change in distance sequentially toward the (equivalent tropical side) reaches α, and the effect of the emissivity fluctuation accompanying the alloying of the steel sheet This is the position where the sheet temperature is measured without receiving the temperature.

The above-mentioned α can be set as appropriate.
The indicated value T of the radiation thermometer at the position K or the indicated value T is, for example, the emissivity of non-alloy plating (ε ₀ = 0.11).
The value corrected in accordance with the above equation (1) is defined as the plate temperature T _0.
The basis of the emissivity epsilon between the position K to the end point P ₂ is calculated continuously in the strip longitudinal direction, in relation to the emissivity epsilon _y at the position y and position y in the longitudinal direction of the alloying furnace The following equation (4) is obtained.

Ε _y = g (y) (4) Next, the position y where the sign of d ² ε _y / dy ² changes, that is, the inflection of the curve of the above relational expression ε _y = g (y) Find the point y ₀ .
On the other hand, an inflection point y _{0b at which} an alloyed hot-dip galvanized steel sheet of optimal quality without plating exfoliation and alloying unevenness is obtained under various operating conditions in which the steel type, the coating weight, and the passing speed are different in advance.
Ask for.

In the control of the degree of alloying, the inflection point y ₀ described above is calculated as needed, and the inflection point y ₀ becomes the optimum inflection point y _{0b under} the operating conditions at that time, for example, by alloying. Adjust the fuel supply to the furnace. That is, the inflection point detected based on the relationship between the operating conditions, such as the previously determined steel type, the amount of plating, and the passing speed, and the inflection point at which a high-quality galvannealed steel sheet is obtained, the inflection point detected is a high-quality Operating conditions are controlled so as to approach the inflection point at which an alloyed hot-dip galvanized steel sheet can be obtained.

According to the present invention, the change in the surface condition of the steel sheet (color change), which is a characteristic of the alloying reaction, is measured based on the change in the emissivity measured by the radiation thermometer. By continuously measuring the locations and detecting the inflection point of the emissivity, it is possible to accurately grasp at which location in the alloying furnace the alloying is completed. According to the present invention, since the completion point of alloying can be accurately grasped,
The degree of alloying can be accurately controlled even when operating conditions such as the type of steel, the amount of coating, and the passing speed change.

Further, according to the present invention, since only one radiation thermometer is required, it is possible to control the degree of alloying with a simple facility and control method. Next, another preferred embodiment of the alloying furnace and the method for controlling the degree of alloying of the present invention will be described. FIG. 2 is a side view showing another example of the galvanizing furnace for a galvanized steel sheet according to the present invention.

In FIG. 2, 30 is a radiation thermometer, 31a is a driving device and a drive control device for rotating the radiation thermometer, 31b is a measuring point detecting device for detecting a measuring point on the steel plate surface of the radiation thermometer 30, AX is the optical axis of the radiation thermometer 30, f _R is the rotation direction of the radiation thermometer 30, O is the rotation axis of the radiation thermometer 30, θ is the angle between the optical axis AX of the radiation thermometer 30 and the steel plate surface, Other symbols indicate the same contents as in FIG.

The hot-dip galvanized steel sheet alloying furnace of the present invention shown in FIG. 2 is provided with the same hot-dip galvanizing apparatus and auxiliary equipment as those of the hot-dip galvanizing steel sheet shown in FIG. In the alloying furnace shown in FIG. 2, a rotary radiation thermometer 30 is provided in the region of the soaking zone 12 of the alloying furnace, and the optical axis AX of the radiation thermometer 30 is provided.
And the angle between the steel plate and the surface are variable.

As a result, the radiant energy from the steel sheet surface can be continuously measured over 1 m or more in the longitudinal direction of the steel strip. In addition, the measuring point detecting device 31b for detecting the measuring point on the steel sheet surface of the radiation thermometer 30 can know the measuring point of the emissivity in the longitudinal direction of the steel strip of the alloying furnace.

Since the alloying furnace for hot-dip galvanized steel sheet of the present invention shown in FIG. 2 is configured as described above, it is alloyed in the longitudinal direction of the steel strip of the alloying furnace by the same method as in FIG. Can be accurately grasped, and the degree of alloying can be accurately controlled even when the operating conditions such as the type of steel, the coating weight, and the passing speed change. Furthermore, since only one radiation thermometer is required, the degree of alloying can be controlled with simple equipment and a control method.

Next, in the alloying furnace for hot-dip galvanized steel sheet of the present invention, disturbance of the temperature of the surrounding environment of the steel strip is prevented,
An apparatus for accurately measuring radiant energy on a steel sheet surface will be described. FIG. 3 is a partial perspective view showing an example of an arrangement state of a mobile radiation thermometer for achieving the above-described object.

In FIG. 3, reference numeral 40 denotes a cylinder having a water-cooled jacket on the outer peripheral wall, 41 denotes a support for the cylinder 40, 42 denotes a heat-resistant telescopic bellows, f _JF and f _JB denote the moving directions of the cylinder 40, and other symbols: It shows the same contents as in FIG. In the mobile radiation thermometer shown in FIG. 3, a water-cooled jacket-type cylinder 40 surrounding the optical axis of the radiation thermometer between the steel strip 1 and the radiation thermometer 14 is provided.

The radiation thermometer 14 and the cylinder 40 are configured to move in the alloying furnace along the longitudinal direction of the steel strip. In the present invention, by disposing the above-mentioned water-cooled jacket type cylinder 40 in the radiation thermometer, disturbance of the temperature of the surrounding environment of the steel strip is prevented, the radiation energy on the steel sheet surface is accurately measured, and alloying is performed. Can be known more accurately.

In FIG. 3, the case where the water-cooled jacket type cylinder 40 is applied to the radiation thermometer continuously moving in the longitudinal direction of the steel strip shown in FIG. 1 has been described. The water-cooled jacket-type cylinder 40 can be applied to the rotary radiation thermometer shown in FIG. 2 by changing the interlocking system of the radiation thermometer and the device.

[0034]

The present invention will be described more specifically below with reference to examples. (Example 1) A cold-rolled steel sheet having a thickness of 0.7 mm is subjected to alkaline electrolytic degreasing, hydrochloric acid pickling, annealing, and then continuous using a galvanizing apparatus and an alloying furnace shown in FIG. 1 under the following conditions. Alloying treatment hot-dip galvanizing was performed.

(Hot-dip galvanizing conditions :) Plating bath composition: Al: 0.14 wt%, Fe: 0.04 wt%, Pb: 0.00
8 wt%, balance: Zn bath temperature; 460 ° C Entry plate temperature; 480 ° C Immersion time: 1 sec Plating weight: 50 g / m ² (Alloying condition :) Alloying furnace heating zone temperature; Operating condition 1: 800 ° C, Operating condition 2: 900 ° C, operating condition 3: 1000 ° C, soaking temperature of alloying furnace; operating condition 1: 500 ° C, operating condition 2: 520 ° C, operating condition 3: 540 ° C Passing speed; 100 mpm (constant) In the example, in each of the operating conditions 1 to 3 in which the fuel supply amount to the above-mentioned alloying furnace heating zone was changed, FIG.
The emissivity was continuously measured in the longitudinal direction of the steel strip by the continuous movement type radiation thermometer 14 shown in FIG. 1, and the quality of the obtained galvannealed steel sheet was evaluated.

FIG. 4 shows the measurement results of the obtained emissivity together with the plating quality. The plated steel sheet of the operating condition 1 suffered peeling of plating, and the plated steel sheet of the operating condition 3 caused uneven alloying, whereas the plated steel sheet of the operating condition 2 did not have these defects and had good plating quality. . That is, it is shown that the inflection point of the emissivity needs to be set at the position of y _0b shown in FIG.

Example 2 In the alloying furnace of the present invention shown in FIG. 1, the coating weight was set to 50 g / m ² , and the above-described present invention was carried out under the condition that the passing speed in the alloying furnace was changed. The degree of alloying of the hot-dip galvanized steel sheet was controlled based on the method of controlling the degree of alloying and the results of Example 1 described above.

That is, in the alloying furnace 10, the radiation thermometer 14 is continuously moved by 20 m in the longitudinal direction of the steel strip and in the conveying direction of the steel strip, and the change of the emissivity is indicated by the radiation thermometer at the position K at a predetermined value. the value T as a sheet temperature, determined from the equation (1), the following formula is a relation between the emissivity epsilon _y at the position y and position y alloying furnace longitudinal direction (4), the curve of the relation The inflection point y ₀ was determined.

Ε_y= G (y) (4) Next, the inflection point y₀Is the inflection point based on the result of Example 1.
Position y_0bIf it is on the exit side of the alloying furnace,
Increase the fuel supply to the tropics, and conversely, the inflection point y ₀Is located
y_0bIf it is closer to the inlet of the alloying furnace, lower the fuel supply
Down, inflection point y ₀Is the position y_0bIt will be almost equal to
Controlled.

As a result, the average length of defective alloying per coil was 0.83 m, and it was found that the degree of alloying of the galvannealed steel sheet could be appropriately controlled by the present invention. . (Comparative Example) The following test was conducted in order to compare the present invention with the fixed arrangement method of a plurality of radiation thermometers, which is a conventional technique.

That is, in the alloying furnace shown in FIG.
Operating under the same operating condition 1, operating condition 2, and operating condition 3 as in Example 1 under the conditions of coating weight: 50 g / m ² , passing speed: 100 mpm (constant), From the heating zone to the solitary zone, the radiation thermometer 14 was moved to position A at 5 m intervals.
The emissivity was measured by B, C, D, E, and F, and the quality of the obtained galvannealed steel sheet was evaluated.

As a result, in the case of the operating condition 2, the plating quality is good. In this case, the relational expression (the five straight lines) between the position y in the longitudinal direction of the alloying furnace and the emissivity ε at the position y shown in FIG. Is obtained. Then, set the coating weight to 50 g / m ^2, under conditions of varying sheet passage speed in the alloying furnace, the heating zone - soaking alloying furnace,
Move the radiation thermometer 14 to position A, B, C, D,
E, the emissivity was measured with F, in the resulting 5 similar relation (composed relationship by a plurality of straight lines), as in FIG. 5, the emissivity is epsilon _k position is located The amount of fuel supplied to the alloying furnace heating zone was controlled so as to be y _k .

As a result, the average length of defective alloying per coil was 1.38 m. From the results of Example 1, Example 2, and Comparative Example described above, according to the present invention, the method of controlling the degree of alloying by a plurality of radiation thermometer fixed arrangement methods is different from that of the alloyed hot-dip galvanized steel sheet. It has been found that the length of the defective portion can be reduced by half.

[0044]

According to the present invention, the degree of alloying of a hot-dip galvanized steel sheet can be accurately controlled with simple equipment and a control method. It became possible to reduce the length of the part by half.

[Brief description of the drawings]

FIG. 1 is a side view showing an example of a hot-dip galvanizing apparatus according to the present invention and an example of a hot-dip galvanized steel sheet alloying furnace of the present invention.

FIG. 2 is a side view showing an example of an alloying furnace for a hot-dip galvanized steel sheet according to the present invention.

FIG. 3 is a partial perspective view showing an example of an arrangement state of a radiation thermometer according to the present invention.

FIG. 4 is a graph showing a relationship between a position y in an alloying furnace longitudinal direction and an emissivity ε according to the present invention.

FIG. 5 is a graph showing the relationship between the position y in the longitudinal direction of the alloying furnace and the emissivity ε.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel strip 2 Hot-dip galvanizing tank 3 Sink roll 4 Hot-dip zinc 5 Gas wiping nozzle 6 Deflector roll 10 Alloying furnace 11 Heating zone of alloying furnace 12 Uniform tropicalization of alloying furnace 12W Alloying furnace uniform tropical side wall 13 Heating device 14, 30 Radiation thermometer 15 Rail for moving the radiation thermometer 16 Wheel for moving the radiation thermometer 17a Drive and drive control device for moving the radiation thermometer 17b Position detection device for the radiation thermometer 18 For moving the radiation thermometer Wire winding device 19 Wire for moving the radiation thermometer 20 Emissivity and emissivity inflection point computing device 21 Alloying degree control device 22 Fuel flow control device 23 Air flow control device 31a Drive device for rotating the radiation thermometer and Drive controller 31b Measurement point detector for detecting the measurement point on the surface of the steel plate of the radiation thermometer 40 Cylinder with a water-cooled jacket on the outer peripheral wall 41 Support for the cylinder 42 Heat-resistant telescopic bellows AX Radiation thermometer The optical axis of f ₁ The traveling direction of the steel strip f _JF , the moving direction of the f _JB cylinder f _R The rotation direction of the radiation thermometer O The rotation axis of the radiation thermometer Y The starting point where the radiation thermometer can move along the steel strip longitudinal direction Distance between P ₁ and end point P ₂ y Distance from start point P ₁ to any point P in the direction of end point P ₂ θ Angle between optical axis AX of radiation thermometer and steel plate surface

Claims (6)

[Claims] 1. A radiant temperature having a function of continuously measuring radiant energy from the surface of a steel sheet in a longitudinal direction of a steel strip from a heating zone of an alloying furnace for hot-dip galvanized steel sheet to a zone in a solitary zone or a zone in a solitary zone. A galvanizing furnace for hot dip galvanized steel sheets, characterized by having a gauge installed. 2. A heating zone of a galvanizing furnace for galvanized steel sheet.
A radiation thermometer (14) that is disposed in the region of (11) to the isotropy (12) or the isotropy (12), and moves continuously in the steel strip longitudinal direction, and the radiation thermometer (14). An alloying furnace for hot-dip galvanized steel sheets, comprising a position detecting device (17b) in the longitudinal direction of the steel strip. 3. A heating zone of a galvanizing furnace for galvanized steel sheet.
The optical axis (AX) and the steel plate are installed in the region from (11) to the isotropy (12) or the isotropy (12) to measure the radiant energy from the steel plate surface continuously in the longitudinal direction of the steel strip. Melting characterized by having a radiation thermometer (30) with a variable angle θ with respect to the surface, and a measurement point detection device (31b) for detecting a measurement point on the steel sheet surface of the radiation thermometer (30). An alloying furnace for galvanized steel sheets. 4. The galvanizing furnace for hot-dip galvanized steel sheet according to any one of claims 1 to 3, wherein the temperature of the steel sheet and the radiant energy are measured using the radiation thermometer, and the obtained measurement result is obtained. Detecting the inflection point of the emissivity of the steel sheet surface in the longitudinal direction of the steel sheet in the alloying furnace, and controlling the operating conditions of the alloying furnace based on the inflection point; Degree control method. 5. The control of the degree of alloying of a galvanized steel sheet according to claim 4, wherein the operating conditions of the alloying furnace are controlled so that the inflection point is at a predetermined position. Method. 6. The method for controlling the degree of alloying of a hot-dip galvanized steel sheet according to claim 4, wherein the operating condition of the alloying furnace is a fuel supply amount to the alloying furnace.