JP2848989B2 - Method of controlling heat input to alloying furnace for hot dip galvanized steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to control of heat input to a heating zone of an alloying furnace in a process of manufacturing a galvannealed steel strip.

[0002]

2. Description of the Related Art In the process of producing a galvannealed steel strip, the steel strip is generally passed through a hot-dip galvanizing bath to deposit a galvanized layer on the steel strip surface, and then to blow gas onto the steel strip surface. Then, the steel strip is passed through an alloying furnace, and the plated layer is formed into an alloy of iron and zinc by diffusion in a heat treatment in the alloying furnace.

[0003] It is important from the viewpoint of quality that the hot-dip galvanized steel strip produced in this way has excellent flaking resistance and powdering properties. In order to obtain a hot-dip galvanized steel strip of preferable quality, the alloying degree (for example, expressed by the content of iron in the plating layer) is controlled by controlling the temperature and the passing speed of the alloying furnace in the manufacturing process. ) Must be controlled to a predetermined state to prevent insufficient alloying or excessive alloying.

[0004] For example, in the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 1-279738, it is disclosed that flaking resistance can be improved by specifying initial heat treatment conditions in an alloying process. Also, Japanese Patent Laid-Open No. 1-2
Japanese Patent No. 52761 discloses that the steel sheet passing speed, zinc adhesion amount,
And the burner amount of the burner according to the deviation between the target plate temperature set based on the Al concentration in the plating bath and the measured plate temperature,
That is, feedback control for adjusting the amount of heat input is disclosed.

[0005]

The degree of alloying of a steel strip is as follows.
Since there is a large correlation with the light reflectance and emissivity of the steel strip surface,
By measuring light reflectivity and emissivity, it is possible to know the degree of alloying of the actual steel strip, and to feed back the results to heat input control to accurately compensate the heat input. Is theoretically possible.

In practice, however, the detection sensitivity of raw burns according to measured values such as light reflectivity is relatively good, whereas the detection sensitivity of overalloys according to measured values such as light reflectivity is considerably low. . Therefore, based on the measured light reflectance and emissivity, raw burns and overalloys are detected, and when raw burns are controlled so that the heat input is increased and in the case of overalloys, the heat input is reduced, the actual heat input is controlled. The amount of heat easily shifts to the overalloy side (excessive heat input) from the optimal heat input, and as a result, the powdering property of the steel strip deteriorates and the product yield decreases.

Accordingly, the present invention controls the heat input of the alloying treatment furnace so that the degree of alloying of the hot-dip galvanized steel strip approaches an optimum state, thereby reducing the yield of the hot-dip galvanized steel strip. The task is to improve it.

[0008]

In order to solve the above-mentioned problems, in a first invention of the present application, a steel strip to which molten zinc is adhered is passed through an alloying furnace, and the steel strip is heated by the alloying furnace. In the step of forming an alloyed layer of iron and zinc in the zone, when controlling the heat input of the alloying furnace, the set value of the heat input,
After determining based on the steel type of the coated steel strip, the coating weight, and the passing speed, at the exit side of the cooling zone of the alloying furnace, the presence or absence of the degree of alloying is identified. The amount of heat input is gradually reduced, and when an insufficient degree of alloying is detected at the position on the exit side of the cooling zone, a compensation heat input sufficient to resolve the insufficient degree of alloying is added to the amount of heat input up to that point. Stop updating calories, lower limit grilling
The cans compensation control is performed.

Further, in the second invention, the temperature of the steel strip, the emissivity of the steel strip,
And measuring at least one of the light reflectance and the degree of alloying at that position, and correcting the set value of the heat input according to the deviation between the detected degree of alloying and its target value.

In the third invention, the light reflectance of the steel strip surface on the heating exit side of the alloying furnace is detected, and the alloying on the heating exit side of the alloying furnace is detected based on the light reflectance. The presence or absence of the degree of insufficiency is identified, and when the insufficiency of the degree of alloying is detected, the heat input is corrected.

[0011]

As described above, when the degree of alloying is detected by measuring the light reflectance or the like, the detection sensitivity of the overalloy side is low, but the detection sensitivity of insufficient alloying is sufficiently high. According to the investigations of the present inventors, the state in which the degree of alloying is optimal is slightly smaller than the state in which regions with high light reflectivity (regions of unburnt burning) appear on the steel strip surface in a dotted manner (called “raw birch”). The degree of alloying is high, and no birth appears. In the present invention, the amount of heat input is automatically adjusted so that the degree of alloying is optimized by performing the lower limit firing sequence compensation control. That is, after the process has stabilized,
By gradually decreasing the heat input, the above-mentioned birth occurs after a while, and when it is detected, the optimum heat input is corrected by adding a predetermined compensation amount based on the heat input at that time and correcting the heat input. The calorific value is obtained. The detection sensitivity of under-alloying is sufficiently high, so by correcting the heat input based on the state where birth (under-alloying) is detected first, that is, the state where the degree of alloying is slightly insufficient. In addition, highly accurate heat input compensation is realized.

When operating conditions such as steel type, coating weight (target value), and sheet passing speed change, the optimal heat input changes accordingly, so that these changes are avoided and the process becomes stable. The lower limit burning sequence compensation control is performed.

According to a study by the present inventors, in controlling the alloying of hot-dip galvanized zinc coating having an iron content of 6 to 13% in the plating alloy, the surface of the plating layer is required to improve the flaking resistance and the like. In order to control the formation of 制 御 phase etc. in the part, and to perform alloying through the preservation zone next to the heating zone for uniform alloying control, the heating zone is based on the specifications such as steel type, threading speed, coating weight etc. It has been found that it is effective to calculate and control the heat input. Therefore, a relatively appropriate heat input can be obtained by determining the set value of the heat input based on the steel type of the plated steel strip, the amount of plating applied, and the passing speed.

However, when only such feedforward control is performed, the calculated values (set values, etc.) of the actual operating conditions (the steel type of the coated steel strip, the coating weight, and the passing speed) are used. And a change in the concentration of Al (aluminum) in the plating bath causes a difference between the actually required preferable heat input and the calculation result, and easily causes overburning and overalloying.

[0015] In the second invention, at least one of the steel strip temperature, the emissivity of the steel strip, and the light reflectance is measured on the exit side of the preserving zone of the alloying furnace, and the alloy at that position is measured. The set value of heat input is corrected so as to eliminate the deviation according to the deviation between the detected alloying degree and its target value. Feedback between the target value of heat input and the actually required heat input caused by the deviation between the set value of the sheet passing speed and the actual value and the fluctuation of the aluminum concentration in the plating bath. Can be compensated by:
On the exit side of the preserving zone of the alloying furnace, the degree of alloying can be detected relatively accurately, so that the heat input can be compensated with high accuracy.

[0016] In the third invention, the light reflectance of the steel strip surface on the heating outlet side of the alloying furnace is detected,
Based on the light reflectance, the presence or absence of the degree of alloying is identified.If the degree of alloying is insufficient, the set value of the heat input is corrected. Is corrected, and the yield of the hot-dip galvanized steel strip can be increased. It is difficult to detect the degree of alloying with high accuracy at the heating orifice side position of the alloying furnace, but it is easy to detect raw burning by reflectance,
By detecting it earlier at the heating-side exit position than at the preserving-outside position and quickly compensating the heat input, it is possible to minimize the area where hot-burn occurs and to increase the yield.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of a main part of a manufacturing process of a galvannealed steel strip. This will be described with reference to FIG. The steel strip 2 is transported in the direction of the arrow in the figure, and after the molten zinc is deposited on the surface thereof through the molten zinc bath 1, the amount of the deposited molten zinc is adjusted by blowing gas when passing through the nozzle 3. Then, it enters the alloying treatment furnace 4. The inside of the alloying furnace 4 is divided into a heating zone 4a, a tropical zone 4b, and a cooling zone 4c. The steel strip 2 entering the alloying furnace 4 is rapidly heated to 470 ° C. or higher in the heating zone 4a. It is heated to the plate temperature, subsequently maintained at a constant temperature in the preservation zone 4b and subjected to an alloying treatment, and then cooled in the cooling zone 4c to have an iron content of 6-1.
A zinc-iron alloy plating layer of about 3% is formed near the surface. The steel strip 2 exiting the alloying furnace 4 is conveyed to the next step through a roll 20.

In this embodiment, heat is supplied to the heating zone 4a of the alloying furnace by burning gas, and the heating zone 4a is controlled by controlling the flow rate of the supplied fuel gas.
The amount of heat input a is controlled. This control is performed by the calorie controller 1
1 is performed by adjusting the opening of a flow control valve (not shown). The calorie adjuster 11 is supplied with a calorie set value (target value: heat input) output from the heat input calculator 13 and a compensation amount from a feedback compensation control system described later.

A furnace thermometer 8 is installed in the heating zone 4a, and a reflectometer 21 for detecting the light reflectance of the surface of the steel strip is installed on the exit side of the heating zone 4a (during protection). On the exit side,
A sheet thermometer 10 for measuring the sheet temperature of the steel strip 2 and an emissivity meter 9 for measuring the emissivity of the surface of the steel strip 2 are arranged. The furnace temperature detected by the furnace thermometer 8 is input to the heat input calculator 13, the light reflectance detected by the reflectometer 21 is input to the raw burn compensator 22, and the plate temperature Tx measured by the plate thermometer 10 is determined by the plate temperature. The emissivity εx input to the temperature compensator 16 and measured by the emissivity meter 9 is input to the emissivity compensator 15. The emissivity meter 9 uses a conventionally known method as a principle of measuring the emissivity.
In the vicinity of the roll 20 on the exit side of the alloying furnace 4, an illuminating device 5 and an ITV camera 6 are used to measure the degree of alloying of the steel strip 2a that has been alloyed. Are directed toward the steel strip on the roll 20.

FIG. 4 shows the configuration of the reflectometer 21. This will be described with reference to FIG. The laser light output from the laser diode 51 is divided into a longitudinal vibration mirror 52 and a lateral vibration mirror 53.
, And is incident on the surface of the steel strip 2, and the reflected light is incident on the light receiver 54. The vertical vibration mirror 52 and the horizontal vibration mirror 53 are driven to swing in the vertical and horizontal directions, respectively, and thereby constantly scan the incident position of the laser beam on the steel strip in the vertical and horizontal directions. That is, even if the incident position of the laser beam is fixed and the reflected light from the specular reflection point on the surface of the steel strip is positioned so as to be incident on the light receiver 54, the steel strip 2 can be positioned.
The reflected light incident on the photodetector 54 may deviate from the specular reflection point due to the vertical and horizontal vibrations. Therefore, by scanning the surface of the laser light, the reflection from the specular reflection point must be made within the scanning range. There is an opportunity for light to enter the light receiver 54. That is, the peak value of the incident light intensity corresponds to the intensity of the reflected light from the specular reflection point. The light reception level signal detected by the light receiver 54 passes through the preamplifier 55,
The signal is converted into a digital value by a converter 56, and a peak detector 57
Holds the peak value within the scanning range, and outputs the peak value as a light reflectance signal.

The description will be continued with reference to FIG. The flow rate of the gas emitted from the nozzle 3 is controlled by the plating amount controller 12. The plating amount controller 12 controls the flow rate of the gas to be supplied to the nozzle 3 in accordance with the input plating amount (set value). The process computer (pro computer) 14 manages the entire manufacturing process of the hot-dip galvannealed steel strip, outputs a set value of the amount of plating to the plating amount controller 12, and outputs the heat input. The arithmetic unit 13 outputs information on the coating amount, the steel type, the passing speed, the plate width and the plate thickness, and the target value calculating unit 18 outputs the plating amount, the steel type, and the passing speed. Output information. The heat input calculator 13 calculates the heat input Q, that is, the heat value set value in the following (1) based on the input furnace temperature and the information of the coating adhesion amount, the steel type, the sheet passing speed, the sheet width and the sheet thickness. The calculation is performed according to an equation, and the result is applied to the calorie controller 11.

[0022]

[Formula 1] Q = a0 + a1 × furnace temperature + a2 × amount of plating × sheet passing speed × [1 + k1 (plate width−plate width standard value) + k2 (plate thickness−plate thickness standard value)] + a3 × steel type constant where a0 ~ a3, k1, k2: constants (1) The target value calculator 18 generates a plate temperature target value and an emissivity target value based on information output by the process computer 14. The plate temperature target value T0 is applied to the plate temperature compensator 16, the emissivity target value ε0 is applied to the emissivity compensator 15,
Both are used for feedback control. These target values are calculated by the following equations.

[0023]

## EQU2 ## T0 = b0 + b1.times.plated amount + b2.times.plate speed + b3.times.steel type constant .. (2) .epsilon.0 = c0 + c1.times.plated amount + c2.times.plate speed + c3.times.steel type constant .. (3) where b0 ~ b3, c0 to c3: constants The heat input calculated by the heat input calculator 13 is based on the process conditions (furnace temperature, coating weight, plating speed, sheet width, sheet thickness,
Due to the difference between the set value of the steel type constant) and the actual value, and the fluctuation of the aluminum concentration in the molten zinc bath 1, there is a slight difference from the optimum heat input. In order to compensate for such a control error, in this embodiment, at the exit side of the tropical zone 4b,
The degree of alloying of the steel strip 2 is measured, and feedback compensation control is performed based on the measured value. In addition, in order to quickly compensate for sudden burning that occurs suddenly, at the exit side of the heating zone 4a, the reflectometer 21 detects insufficient alloying from the light reflectance of the steel strip surface, that is, when the burning is detected, and the burning is detected. , Feedback control is performed so that the raw burn compensator 22 compensates for the amount of heat input.

That is, as shown in FIG. 2, the sheet temperature and emissivity of the steel strip have a correlation with the degree of alloying, respectively.
The higher these values, the greater the degree of alloying. However, these relations are non-linear, and change depending on the process conditions such as the type of steel, the passing speed, and the amount of plating. Further, the emissivity increases rapidly as the alloying proceeds, and after the desired degree of alloying, the rate of change with respect to the change in the degree of alloying decreases. Furthermore, the plate temperature and the emissivity are not uniform over the entire width of the steel strip. Therefore, in order to eliminate insufficient alloying, it is necessary to measure the sheet temperature and the emissivity over the entire width of the steel strip. Various methods of managing the plate temperature data group Tx and the emissivity data group εx measured over the entire width can be considered, but in this embodiment, the average value Td of the plate temperature data group in the width direction is calculated. The representative value is used for the plate temperature compensation control, and the minimum value .epsilon.d in the width direction of the emissivity data group is used for the emissivity compensation control as the representative value. Such a control is effective in detecting insufficient alloying.

The plate temperature compensator 16, which forms a part of the feedback compensation control system, calculates a compensation amount Ct according to the deviation between the target plate temperature value T0 and the detected plate temperature value (average value in the width direction) Td. And outputs it to the maximum value selector 17. The emissivity compensator 15, which forms a part of the feedback compensation control system, calculates a compensation amount Cε according to a deviation between the emissivity target value ε0 and the emissivity detection value (minimum value in the width direction) εd. It is obtained and output to the maximum value selector 17. Maximum value selector 17
Compares two input compensation amounts Ct and Cε,
The larger of the two values is selected, and the selected compensation amount is added to the heat amount set value (heat input target value) generated by the feedforward control system via the switch SW1. Apply.

FIG. 3 shows an example of the operation of the feedback compensation control system.
Shown in Referring to FIG. 3, since the plate temperature compensation amount Ct is larger than the emissivity compensation amount Cε at first, the plate temperature compensation amount Ct is output as the heat input amount compensation amount, and the plate temperature target value T0 is set.
The amount of heat input is corrected so that the deviation between the plate temperature detection value Td (which is also a target value of the degree of alloying) and the plate temperature detection value Td approaches zero. The emissivity compensation amount Cε gradually increases, and this is the plate temperature compensation amount Ct.
Is exceeded, that is, the emissivity detection value εd is equal to its target value ε0
If it falls below (which is also a target value of the degree of alloying), the emissivity compensation amount Cε is output as the heat input amount compensation amount, and the heat input amount is corrected so that the detected emissivity value εd approaches the target value ε0.

That is, by selecting the larger one of the two compensation amounts Ct and Cε as the compensation amount of the heat input amount,
The plate temperature and the emissivity can be controlled so as not to fall below their set values, that is, the set values of the degree of alloying. Accordingly, the occurrence of insufficient alloying can be reliably prevented regardless of whether the estimation is made from any of the plate temperature and the emissivity. If the smaller of the two compensation amounts Ct and Cε is a value corresponding to the correct degree of alloying, the control will deviate from its target value in a direction to promote the degree of alloying. There are fewer quality problems compared to the case where the production is insufficient, and the operation is safe in terms of quality.

The heat input calculator 13 calculates the heat setting value based on the information output from the process computer 14 as described above, but also controls the switches SW1 and SW2 to open and close. That is, normally, the switches SW1 and SW2 are closed and the feedback compensation is turned on. However, the process conditions (steel type, plating adhesion) output from the process computer 14 may be changed depending on the timing at which the joint position of the steel strip passes. When the amount is changed, the switches SW1 and SW2 are temporarily opened to turn off the feedback compensation control.

As shown in FIG. 5, like the emissivity, the light reflectance has a great correlation with the degree of alloying. Therefore, it is possible to estimate the degree of alloying at the heating band side from the light reflectance detected by the reflectometer 21. However,
Since the accurate degree of alloying cannot be detected at the heating band side, the detected light reflectance is used for control for quickly compensating for sudden burning, etc.

In the raw burn compensator 22, in this embodiment, the reference compensation amount is a constant, and the compensation amount is determined based on the constant and the compensation rate of each region shown in FIG. FIG.
Referring to FIG. 5, the detected light reflectance R and its change rate ΔR
The two-dimensional space represented by is 3 of region 1, region 2 and region 3.
It is divided into areas. Also, the boundary between regions is not clear, and the range (hatched portion)
Linear interpolation is performed using the functions FN, FP, FL and FS. In this example, the compensation rate of the area 1 is set to 100%, the compensation rate of the area 2 is set to 70%, and the compensation rate of the area 3 is set to 0%.

For example, when the light reflectance R is large (FL = 1) and the change rate ΔR is positive (FP = 1), 40 Nm ³ / hour is output from the raw burn compensator 22 as a compensation amount, and the light reflectance R Is large (FL = 1) and the rate of change ΔR is negative (FN = 1), 28 Nm ³ / hour is used as the compensation amount for the raw burn compensator 22.
And when the light reflectance R is small (FS = 1),
The compensation amount becomes zero.

In this embodiment, the control cycle of the raw burn compensator 22, that is, the update cycle of the compensation amount output by the raw burn compensator 22, is such that the steel strip 2 extends from the entrance of the heating zone 4a to the detection position of the reflectometer 21. It is set to be longer than the time required to pass through the space.

In this embodiment, the reference compensation amount in the raw burn compensator 22 is a constant, but this is a function that varies depending on, for example, the passing speed output from the process computer 14, the type of steel, the amount of plating, and the like. May be changed so as to be obtained by a mathematical expression or a table lookup.

An illuminating device 5 disposed on the exit side of the alloying furnace 4 irradiates the steel strip 2 with ordinary visible light, and an ITV camera 6 captures an image of the visible light. That is, since there is a correlation as shown in FIG. 5 between the light reflectance of the steel strip 2a and the degree of alloying, in this embodiment, the output of the alloying furnace is determined based on the light reflectance of the surface of the steel strip 2a. The degree of alloying on the side is detected. In practice, this measurement detects the presence or absence of births in which the burnt area appears dotted.

FIG. 8 (a) shows the intensity distribution of the received light for three samples Sa (high), Sb (medium) and Sc (low: close to raw burn) having different degrees of alloying. It can be seen that the light receiving intensity increases as the degree of formation approaches the raw burn.

In this embodiment, the steel strip 2a wound around the roll 20 is to be imaged. However, since the steel strip at the position to be imaged has a curved surface, the steel strip 2a at the position on the roll 20 is to be imaged. The difference greatly changes the incident angle and the reflection angle of the illumination light. That is, on the image captured by the ITV camera 6, the area of the specular reflection point in the image is narrow, and the boundary between the specular reflection point and other positions clearly appears.

As shown in FIG. 9, the range of the image picked up by the ITV camera 6 includes a specular reflection point, but in this embodiment, a position shifted from the specular reflection point Pc (for example, P
1, P2) is set as a region of interest, and the received light intensity is detected at a position that is not a regular reflection point. That is, FIG. 10 shows an example of the entire image. As shown in FIG. 10, a position slightly shifted from the specular reflection point in the image is set as the attention area.

As shown in FIG. 1, the monochrome image signal (composite video signal) output from the ITV camera 6 is
The image is input to the image processing device 23, and the presence or absence of a raw burn is determined, and the result is applied to the lower limit burn compensator 24. FIG. 7 shows the configuration of the image processing device 23.

A description will be given with reference to FIG. ITV camera 6
Are output to the frame memory 37. The frame memory 37 stores an image area vertically 25
6. The luminance signal level (light receiving intensity) of each of the divided pixel areas is converted into a digital quantity of 64 gradations (hereinafter, referred to as luminance information), and the luminance information is converted into each pixel position. Is written to the memory address associated with. In the following description, the vertical pixel position of the luminance information is represented by y.
, And the pixel position in the horizontal direction is represented by x. The edge detector 39 reads one line of luminance information from the frame memory 7 and detects the edge positions at both ends of the steel strip. Specifically, each position (x) at which the luminance information d (x) at each pixel position obtained by the edge enhancement calculation takes the maximum value and the minimum value
, And the left edge and the right edge are detected by adding a correction in consideration of the safety factor to those x.

[0040]

## EQU3 ## d (x) = p (x) + 2p (x + 1) -2p (x + 2) -p (x + 3) (4) p (x): luminance of pixel at position x Information level p (x + 1): luminance information level of pixel at position x + 1 p (x + 2): luminance information level of pixel at position x + 2 p (x + 3): luminance information level of pixel at position x + 3 Masking processing unit 40 masks the luminance information at each pixel position other than the range of interest and excludes the information from the processing target. This attention range includes four points (x1, y1), (x2, y
1) A rectangular area (including a boundary) having vertices at (x2, y2) and (x1, y2), and horizontal positions x1 and x2 of this area are left edges output from the edge detection unit 39. And the right edge position, and the vertical positions y1 and y2 are predetermined fixed positions. In fact, |
y1−y2 | = 3, and the number of pixels in the vertical direction in the range of interest is set to 4. The vertical range of the range of interest is shown in FIG.
0 corresponds to the attention area.

The background level detecting section 41 calculates a reference luminance by referring to luminance information of a background area (a part such as a roll: see FIG. 10) other than the steel strip on the image. This reference luminance is not affected by the steel type, the passing speed, the steel strip temperature, and the like. In this embodiment, since the brightness of the illumination changes according to the position x in the horizontal direction, the reference luminance R (x) at the position x is converted into a linear function R (x) = A + Bx in consideration of the change. And the coefficients A and B are obtained by the following least squares approximation formula.

[0042]

(Equation 4)

In this example, it is assumed that the number n of reference points (predetermined points in the background area) is 10, and that 10 reference point luminances p
The reference luminance R (x) is obtained based on (xi, yi).

The ratio calculation unit 42 calculates the relationship between each luminance information within the range of interest output from the masking processing unit 10 and the reference luminance R (x) output from the background level detection unit 41 based on the following equation. Calculate the ratio q1 (x, y).

[0045]

## EQU5 ## q1 (x, y) = p (x, y) / R (x) (6) The level of the luminance information in the steel strip region is not limited to the light reflectance of the surface of the steel strip but also to the level of extraneous light. Intensity fluctuation, power supply voltage fluctuation of illumination light source,
It may also change due to the temporal change of the characteristics of the lighting device and the light receiving sensor. Therefore, by estimating the degree of alloying based on the ratio of the intensity of the reflected light from the steel strip to the intensity of the reflected light from the background area other than the steel strip, fluctuations in factors other than the actual light reflectivity are reduced. It can be prevented from affecting the measurement of the degree.

In other words, a coefficient K that summarizes changes in the intensity of extraneous light, fluctuations in the power supply voltage of the illumination light source, changes in the characteristics of the illuminating device and the light-receiving sensor over time, etc. is determined, and the reflectance and luminance information level of the target point on the steel strip Are respectively ε and B, and the reflectance and luminance information level of the reference point (background) are εr and B, respectively.
Assuming that B = K · ε and Br = K · εr hold, the luminance information level ratio B / Br is ε / εr, which does not include K, and is therefore other than the light reflectance of the steel strip surface. Are not affected by fluctuation factors.

In the noise removing section 43, the luminance ratio q1 (x, y) of each pixel position output from the ratio calculating section 42
, And the maximum value q2 (x) of each of the four pixels in the vertical direction is first extracted by the following equation (6). In other words, since the portion where the burn has occurred becomes bright, this is a process for sensitively detecting it. In the edge detection unit 39, the detection operation may be unstable, and sometimes the detection edge may be off the steel strip surface. In such a case, the brightness of the edge part becomes extremely high, which causes a malfunction. In order to remove this kind of abnormal luminance information and noise, the noise elimination unit 43 extracts the smaller one of the luminance ratios of two pixels adjacent in the horizontal direction according to the following equation (4). Therefore, 1
If only the pixels are particularly bright, it is considered noise and is ignored.

[0048]

[Formula 6] q2 (x) = maxY [q1 (x, y)] y1 ≦ y ≦ y2 (7) q (x) = min [q2 (x), q2 (x + 1)] (8) maxY []: maximum value in the y direction of [] min []: minimum value of [] In the alloying degree calculation unit 44, the luminance ratio (that is, the received light intensity ratio) q output by the noise removal unit 43. (x) is input, and the degree of alloying G is calculated based on the following equations (9) to (11). Further, the correlation between the light reflectance and the degree of alloying as shown in FIG. 5 greatly changes depending on the type of steel strip (including the surface properties), and therefore, a process computer (procomputer) 14 for managing the operating state. The steel type information M (including surface properties etc.) of the current steel strip output from the
Steel type constant C registered in advance in the constant memory 45
1 () and C2 () are searched and input using the steel type information M and used for calculating the degree of alloying.

[0049]

G1 = maxX [q (x)] x1 ≦ x ≦ x2 (9) If G1 ≦ C1 (M), G = 0 (10) If G1> C1 (M), G = C2 (M) · (G 1 −C 1 (M)) (11) maxX []: maximum value of [] in the x direction The alloying degree G calculated by the alloying degree calculating unit 44 is displayed on the display device 47. It is displayed as a numerical value indicating that.

In this embodiment, the presence or absence of a sharp increase in the luminance ratio q (x) is determined at each pixel position in order to further detect a raw burn. For this purpose, the smoothing processing section 48 smoothes the temporal change of the luminance ratio q (x) to generate a smoothed luminance ratio (smoothed received light intensity ratio), which is used as a reference level.

Actually, the luminance ratio G1 (output of the expression (5)) of the point of interest is calculated by a first-order IIR modified digital low-pass filter expressed by the following expression (12) or (13). By processing, a smoothed luminance ratio (or a smoothed received light intensity ratio) Ga is obtained.

[0052]

## EQU8 ## Ga = Af Ga1 + (1-Af) G1 G1 ≦ Ga1 (12) Ga = Ar Ga1 + (1-Ar) G1 G1> Ga1 (13) Af, Ar: Filter constant (Af <Ar) Ga1: Ga at previous calculation In this example, the constant that determines the filter time constant is Af <
Because of Ar, as shown in FIG. 12, the change in the smoothed received light intensity ratio Ga is such that the change in the rise is gentle (the time constant is large) and the change in the fall is relatively fast (the time constant is small). . If the time constants of the rise and fall are equal, if the burned portion appears periodically and repeatedly, the level of the smoothed light receiving intensity ratio may increase and the burn may not be partially detected. By reducing the falling time constant, it is possible to reliably detect each of the repeatedly burned portions.

The raw burn determination unit 49 includes an alloying degree calculation unit 4
4, the light receiving intensity ratio (instantaneous value) G1 of the target point and the smoothed light receiving intensity ratio Ga output by the smoothing processing unit 48 are input, and the difference Gr between the two is equal to or greater than a predetermined threshold gr. Is activated for a predetermined time Tr, the burn-in warning is turned on, and if the time in which Gr is equal to or less than the threshold value gf continues for a predetermined time Tf, the burn-in warning is turned off (Gr = G1).
-Ga). When the hot burn alarm is on, a predetermined alarm is displayed on the display device 47. When the burned portion appears periodically and repeatedly, as shown in FIG. 12, the burn is repeatedly detected. In this example, the signal processing device 7
Is repeated every 0.3 seconds to execute the measurement of the degree of alloying and the raw burn detection processing.

The lower limit burning compensator 24 shown in FIG. 1 performs control with reference to the degree of alloying G output from the image processing section 23. FIG. 13 shows the contents of the processing of the lower limit burning compensator 24
FIG. 14 shows an example of a change in the amount of heat input. FIG. 14
1 is based on the signal detected by the reflectometer 10 in FIG. 1, and “Birch detection” is based on the degree of alloying G output from the image processing unit 23 in FIG. In each case, the vertical axis indicates the degree of deficiency of the degree of alloying. The contents of the processing of the lower limit burning compensator 24 will be described with reference to the drawings.

In step 61, the contents of the register Qs holding the heat input correction amount for initialization are cleared. The content of Qs is constantly output from the lower limit burning compensator 24, and is added to the input of the calorie controller 11 via the switch SW2.

At step 62, the process waits until the position of the coil joint of the steel strip 2 is detected with reference to the information output from the process computer 14. The steel strip 2 is configured as one steel strip by joining a large number of coils to one another in order to continuously treat a steel material wound in a coil shape in advance.
Accordingly, the type of steel, plate thickness, plate width, and the like often change at the joint of the coil, and the heat input to the alloying furnace 4 changes accordingly. When there is such a rapid change in the heat input, the process is not stabilized, so it is better to prohibit the feedback control. Therefore, in this embodiment, in the range of the front end 50m and the rear end 50m of each coil, the feedback control including the lower limit firing sequence described later is prohibited.

In step 63, the time t0 at which the position of the tip of each coil reaches the entry side of the alloying furnace 4 is calculated.
The process computer 14 is configured to be able to detect the position of the tip of each coil at various positions in the manufacturing equipment, and to detect the position of the tip of each coil considerably upstream from the entry side of the alloying furnace 4. Therefore, when the process computer 14 detects the coil tip (the joint of the steel strip) at a predetermined position, based on the time, the distance from the detection position to the alloying treatment furnace entrance side, and the steel strip transport speed, Time t0 is calculated.

In step 64, the time t1 until the tip of the coil (the range from the tip to 50m) passes through the alloying furnace 4 is determined based on the time t0, the length (50m), and the steel strip transport speed. calculate.

At step 65, until time t1 is reached.
That is, after the change in the heat input by the feedforward control system (heat input calculator 13), the process waits until the process is stabilized. At time t1, the process proceeds to the next lower limit baking sequence.

In step 66, a predetermined small value ΔQs is subtracted from the content of the register Qs holding the heat input correction amount, and the result is used as the content of Qs. That is, each time step 66 is executed, the actual heat input is reduced by ΔQs.

In step 67, referring to the degree of alloying G output by the image processing unit 23, it is checked whether or not any births (insufficient degree of alloying) have been detected. When no birth is detected, the process proceeds to step 69, and when birth is detected, the process proceeds to step 68.

In step 68, a predetermined value ΔQo is added to the previous contents of the register Qs holding the heat input correction amount, and the result is stored in Qs. ΔQo is the amount of change in the amount of heat input required to reduce the amount of heat input and to reduce the amount of heat generated to the optimum degree of alloying when burrs begin to appear on the steel strip surface. In the embodiment, a constant is adopted as the change amount.

In step 69, it is checked whether or not one waiting time which determines a cycle for executing step 66 in the lower limit burning sequence has elapsed. If the waiting time has not elapsed, the process proceeds to step 70, and if the waiting time has elapsed, the process proceeds to step 66 again. This waiting time is a value obtained by further adding a predetermined dead time to a time constant of two to three times the time from when the heat input is changed to when the change appears in the alloying degree G.

In step 70, it is checked whether or not the operating conditions have been changed by referring to the information output from the process computer 14. If there is a change in operating conditions, the heat input is corrected by the feedforward control,
Stop the lower bake sequence to stabilize the process.

That is, as shown in FIG. 14, the lower limit firing sequence is started when a certain time has passed after the coil seam has passed and the process is stabilized, and the heat input is reduced by a predetermined amount (ΔQs) at regular intervals. , If a birthplace is detected,
A predetermined amount (ΔQo) is added to the heat input at that time, and this
End Kens. Birch can be detected with very high sensitivity by measuring the light reflectance using the ITV camera 6 (the sensitivity is higher than that of the burn-in detection shown in FIG. 14). The degree of alloying is almost constant and accurate, and the heat input corresponding to the optimum degree of alloying can be obtained by obtaining the heat input by adding the predetermined amount ΔQo based on the heat input in that state.

The switch SW2 is opened for a predetermined time after the heat input calculator 13 changes the heat input and for a predetermined time after the raw burn compensator 22 detects the raw burn, and the lower limit burn compensator is opened. The compensation amount Qs output by 24 becomes invalid.

Further, in the above embodiment, the light reflectance of visible light is measured by the ITV camera 6. However, as is apparent from FIG. 5, the light reflectance is similarly measured by using the emissivity instead of the light reflectance. Both can be detected. Further, as the equation for estimating the amount of heat input in the heat input calculator 13, for example, the following equations may be used instead of the equation (1).

[0068]

## EQU9 ## Q = a0 + a1 × (coating amount × plate speed) + a2 × steel type constant ・ ・ (14) Q = a0 + a1 × plated amount + a2 × plate speed + a3 × steel type constant ・ ・ (15) Q = a0 + a1 × furnace temperature + a2 × plating adhesion amount + a3 × plate passing speed + a4 × plate width + a5 × plate thickness + a6 × steel type constant ··· (16) In the above embodiment, the absolute value of the heat input Q is determined. Actually, the calculation of heat input is repeatedly executed at a constant cycle, so the deviation of the heat input is repeatedly calculated, and the control contents are added so that the obtained heat input deviation is added to the previous heat input. May be changed. In that case, the heat input amount deviation may be calculated using any of the following formulas. Here, one operation cycle (Δ
The change of the variable during t) is denoted by Δ.

[0069]

## EQU10 ## ΔQ = a0 + a1 × Δfurnace temperature + a2 × Δheat input correction value + a3 × Δsteel type constant (17) Δheat input correction value = Δ [plating adhesion amount × passing speed × ｛1 + k1 (plate width −Sheet width standard value) + k2 (Sheet thickness−Sheet thickness standard value)｝] · (18) ΔQ = a0 + a1 × Δ (Plating adhesion amount × Pulling speed) + a2 × ΔSteel type constant ・ ・ ・ (19) ΔQ = a0 + a1 × ΔCoating amount + a2 × ΔPassing speed + a3 × ΔSteel type constant (20) ΔQ = a0 + a1 × Δ Furnace temperature + a2 × ΔPlating amount + a3 × ΔPlating speed + a4 × ΔSheet width + a5 × Δ Plate thickness + a6 x Δ steel grade constant (21)

[0070]

As described above, according to the present invention, it is determined whether or not the degree of alloying is insufficient at the cooling outlet side of the alloying furnace.
After the process has stabilized, the heat input is gradually reduced,
Since the heat is intentionally generated and the heat input is corrected based on the state where it first appeared, this feedback control allows the heat input to be adjusted so that the degree of alloying of the steel strip is optimized. Can be modified to

Further, in the second invention of the present application, at least one of the steel strip temperature, the emissivity of the steel strip, and the light reflectance is measured on the exit side of the preserving zone of the alloying furnace, and its position is measured. The set value of heat input is corrected so as to eliminate the deviation according to the deviation between the detected degree of alloying and its target value.
The difference between the target value of heat input and the actually required heat input caused by the difference between the set value of the coating weight and the passing speed and the actual value, and the fluctuation of the aluminum concentration in the plating bath is calculated. It can be compensated by feedback control. On the exit side of the preserving zone of the alloying furnace, the degree of alloying can be detected relatively accurately, so that the heat input can be compensated with high accuracy. It is difficult to detect the degree of alloying with high accuracy at the heating outlet side of the alloying furnace, but if sudden burning occurs suddenly, it should be detected at the heating outlet side. Detect faster than position,
By quickly compensating the amount of heat input, the area where underburning occurs can be minimized, and the yield can be increased.

Further, in the third invention of the present application, if the degree of alloying is already insufficient on the heating and unwinding side, the set value of the heat input is corrected early. Can be minimized, and the yield of hot-dip galvanized steel strip can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a manufacturing process of a galvannealed steel strip.

FIG. 2 is a graph showing the correlation between the plate temperature and the degree of alloying and between the emissivity and the degree of alloying.

FIG. 3 is a timing chart showing an operation example of a feedback compensation control system.

FIG. 4 is a block diagram illustrating a configuration of a reflectometer 21.

FIG. 5 is a graph showing the correlation between light reflectance and emissivity and the degree of alloying.

FIG. 6 is a graph showing a relationship between a region division according to R and ΔR in the raw burn compensator 22 and a compensation rate.

FIG. 7 is a block diagram illustrating a configuration of an image processing unit 23.

FIG. 8 is a graph showing an intensity distribution of reflected light.

FIG. 9 is a front view showing the positional relationship between the lighting device and the ITV camera.

FIG. 10 is a front view illustrating an example of an image captured by an ITV camera.

FIG. 11 is a waveform diagram showing one scanning line segment of an image signal.

FIG. 12 is a timing chart showing an example of the operation of the raw burn determining unit 19;

FIG. 13 is a flowchart showing processing of the lower limit burning compensator 24;

FIG. 14 is a timing chart showing an example of a change in the amount of heat input due to a lower limit firing sequence.

[Explanation of symbols]

1: molten zinc bath 2: steel strip 3: nozzle 4: alloying furnace 4a: heating zone 4b:
Preservation 4c: Cooling zone 5: Lighting device 6: I
TV camera 8: Furnace thermometer 9: Emissivity meter 10: Plate thermometer 11: Calorimeter 12:
Plating weight controller 13: Heat input calculator 14: Procon 15:
Emissivity compensator 16: Plate temperature compensator 17: Maximum value selector 18:
Target value calculator 20: Roll 21: Reflectometer 22:
Raw burn compensator 23: Image processing unit 24: Lower limit burn compensator SW1, SW2: Switch

Continuing on the front page (72) Isao Nakamura, Inventor 1-1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu-shi Inside Nippon Steel Corporation Technology Development Headquarters Equipment Technology Center (56) References JP-A-3-188255 ( JP, A) JP-A-3-100155 (JP, A) JP-A-3-100154 (JP, A) JP-A-2-93056 (JP, A) JP-A-1-177351 (JP, A) JP 58-210159 (JP, A) JP-A-52-95542 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 2/00-2/40

Claims (3)

(57) [Claims] 1. A step of passing a steel strip to which molten zinc is adhered through an alloying furnace and forming an alloyed layer of iron and zinc on the steel strip by heating in the alloying furnace. When controlling the heat input, the set value of the heat input should be changed according to the steel type of the coated steel strip, the coating weight,
In addition to determining the degree of alloying shortage at the cooling exit side of the alloying furnace, and then determining the degree of alloying deficiency, and gradually reducing the heat input after the process condition has stabilized, When a shortage of the degree of alloying is detected at the position, a compensation heat input sufficient to eliminate the shortage of the degree of alloying is added to the amount of heat input up to that point, and thereafter, updating of the heat input is stopped. A method for controlling the heat input to the alloying furnace of a galvannealed steel strip, which performs cans compensation control. 2. At the exit side of the preserving zone of the alloying furnace, at least one of the steel strip temperature, the emissivity of the steel strip, and the light reflectivity is measured to detect the degree of alloying at that position and to detect the degree of alloying. The method for controlling heat input to an alloying furnace of a galvannealed steel strip according to claim 1, wherein the set value of the heat input is corrected according to a deviation between the degree of alloying and a target value thereof. 3. Detecting the light reflectance of the surface of the steel strip on the heating outlet side of the alloying furnace, and identifying whether or not the degree of alloying is insufficient on the heating outlet side of the alloying furnace based on the light reflectance.
2. The method for controlling heat input to an alloying furnace of a galvannealed steel strip according to claim 1, wherein when the degree of alloying is insufficient, the heat input is corrected.