JPH0565615A - Method for controlling heat input into alloying furnace for hot dip alloying galvanized steel sheet - Google Patents

Abstract

PURPOSE:To eliminate excess/shortage in alloying degree and to improve the alloying yield by compensating heat input quantity into an alloying furnace with the setting value in the position-temp. distribution pattern of a galvanized steel sheet, at the time of applying the alloying treatment to a galvanized layer on the hot dipping galvanized steel sheet with Fe contained in the steel sheet. CONSTITUTION:The cold rolled steel sheet 2 passes through a hot dipping galvanizing bath 1, and after adjusting the Zn sticking rate, the sheet 2 passes through the alloying furnace 4 composed of a heating zone 4a, heat holding zone 4b and cooling zone 4c to apply the Zn-Fe alloying treatment with 6-13% Fe (on the surface of the sheet 2) to the galvanized layer. Joining part in the galvanized steel sheets 2 is detected 22 and inputted to a process computer 14 inputting informations, such as steel kind, sheet passing speed, sheet thickness, sheet width, galvanized stuck thickness. Further, the actual measured values with a thermometer 8 in the heating zone 4a, a thermometer 10 at the outlet side of the heat holding zone 4b and an emissivity meter 9, are inputted to a heat input quantity computing element 13, sheet temp. compensator 16 and emissivity compensator 15, respectively, and these outputs are inputted to feedback into a heat quantity adjustor 11, and by controlling fuel flow rate of a burner in the heating zone 4a, even in the case the kinds, etc., of the steel sheet 2 are changed at the joining part, the alloying treatment in galvanized layer is suitably applied.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In the process of manufacturing hot-dip galvanized steel strip, the steel strip is generally passed through a hot-dip galvanizing bath to deposit a galvanized layer on the surface of the strip, and then a gas is blown onto the surface of the strip. The coating amount is adjusted by attachment, the steel strip is then passed through an alloying treatment furnace, and the plated layer is made of an alloy of iron and zinc by diffusion by heat treatment in the alloying treatment furnace.

It is important in terms of quality that the hot-dip galvanized steel strip produced in this manner has excellent flaking resistance and powdering resistance. In order to obtain a hot-dip galvanized steel strip having a preferable quality, the temperature of the alloying furnace and the strip-passing speed in the manufacturing process are controlled, and the degree of alloying (for example, the content of iron in the plating layer is represented. ) Should be controlled to a predetermined state to prevent insufficient alloying or excessive alloying.

For example, in the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 1-279738, it is shown that the flaking resistance can be improved by specifying the initial heat treatment conditions in the alloying treatment. In addition, JP-A 1-2
Japanese Patent No. 52761 discloses that the steel sheet passing speed, the zinc adhesion amount,
And the burner combustion amount 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]

For example, in the case of performing feedback control in which the temperature of a steel strip is detected by a plate thermometer and the amount of heat input is compensated in accordance with the deviation between the detected value and the plate temperature target value, Since the thermometer must be placed at a position away from the burner, when the temperature of the steel strip changes, there is a time delay until the change is actually detected by the plate thermometer. When the temperature change is large, a heat input amount control error due to the time delay causes a region of insufficient alloying (baking) or overalloying on the steel strip, which lowers the yield. In the actual manufacturing process, a large number of steel materials wound in a coil shape are connected to each other and the galvanized steel strip is alloyed continuously, but at the joint between the coils of the steel strip, the steel type, plate thickness, Since the operating conditions such as strip width, stripping speed, and coating adhesion amount are often changed, the insufficient alloying or overalloying region is caused by the time delay of feedback control every time the region is processed. It occurs on the obi.

By the way, in the hot rolling and cooling process before the plating process, the steel material is liable to cool at its leading end portion and trailing end portion compared to other portions, so that there is a difference in the cooling process depending on the position. As a result, the composition of the steel material after rolling is generally not the same at the coil front and rear ends and at other positions. Therefore, in order to make the composition of the steel material uniform, a cooling method called U-pattern cooling may be adopted. That is, the amount of cooling at the front and rear ends of the coil is reduced, and at other positions, cooling is performed at a normal amount. However, this U-pattern cooled steel material (U
(Referred to as a pattern material), when the zinc plating is heat-treated in the alloying furnace, the front and rear end portions are less likely to be burned than other portions, and the raw burn is likely to occur. In the case of a steel material manufactured by an ordinary cooling method, the difference in burning depending on the position of this kind is not remarkable. Therefore, even in the case of alloying the U pattern material, in the conventional feedback control, due to the delay of the heat input compensation at the leading end portion and the trailing end portion of the steel material, the regions of raw burning and overalloying occur and the yield is increased. The decline of is inevitable.

Therefore, according to the present invention, even in the actual operation in which the steel type, the strip running speed, the coating weight, etc. are greatly changed, the steel strip which has undergone a special cooling treatment such as the U pattern material is treated. However, it is an object to constantly control the heat input amount appropriately to prevent the occurrence of underburning and overalloying, and to increase the yield of the hot-dip galvanized steel strip.

[0008]

In order to solve the above-mentioned problems, in the first invention of the present application, a steel strip to which hot-dip zinc has been adhered and which has passed through a hot rolling and cooling process is used in an alloying furnace. Through, in the step of forming an alloyed layer of iron and zinc on the steel strip by heating in the alloying furnace, when controlling the heat input of the alloying furnace, the set value of the heat input is the steel type of the plated steel strip,
In addition to determining based on the amount of plated coating and the strip running speed, the position-temperature distribution pattern of each steel strip in the cooling process before alloying treatment is identified in advance to detect the position of the steel strip to be alloyed. Based on the position-temperature distribution pattern, the set value of the heat input amount is compensated according to the detected position on each steel strip.

Further, in the second invention of the present application, at least one of the temperature, the emissivity, and the light reflectance of the plated steel strip is measured on the heat-retaining side of the alloying furnace to determine the degree of alloying. Is detected, and the set value of the heat input amount is corrected so that the detected degree of alloying approaches the target value.

[0010]

[Operation] The heat input to obtain the optimum degree of alloying in terms of the quality of the steel strip varies depending on the operating conditions such as the steel type of the plated steel strip, the coating adhesion amount, the strip running speed, etc. In this operation, the process computer controlling the operation can be known in advance before the steel strip enters the alloying furnace. In addition, in the cooling step after hot rolling, whether the steel strip subjected to U-pattern cooling or the steel strip subjected to normal cooling is distinguished from the process before the steel strip enters the alloying furnace. The computer can know. Therefore, even if the actual operating conditions are not detected by a sensor or the like, if predetermined calculations are performed based on the operating conditions of each steel strip and the past manufacturing results that are assigned in advance, each steel strip will be processed. Therefore, an appropriate heat input amount can be obtained. Further, in the case of processing a U pattern material, based on the cooling pattern of the U pattern material and past manufacturing results, for example, only when the front end portion and the rear end portion pass through the alloying treatment furnace, a predetermined If the amount of heat input is adjusted by adding the amount of compensation to the amount of heat input, it is possible to avoid the occurrence of regions of underburning and overalloying over the entire length of the steel strip. These controls are so-called feed-forward control, and it is possible to eliminate a phenomenon such as a control delay based on the detection delay during feedback control, so that the operating condition changes at the joint position of the steel strip. However, even if the U-pattern material is alloyed, the yield of burnt and overalloyed regions can be reduced to a minimum and the yield can be reliably increased.

However, when only such feed-forward control is performed, calculated values (set values, etc.) of actual operating conditions (steel type of plated steel strip, coating adhesion amount, and strip running speed). And the fluctuation of the Al (aluminum) concentration in the plating bath may cause a difference between the actually required heat input amount and the calculation result. However, according to the second invention, by detecting at least one of the temperature, the emissivity and the light reflectance of the plated steel strip on the exit side of the heat insulating zone, the degree of alloying at that position is detected, and the detected value is detected. The feedback control is performed so that the value of C approaches the target value, the heat input amount can be compensated more appropriately, and the yield can be further increased.

[0012]

EXAMPLE FIG. 1 shows the structure of the main part of the manufacturing process of hot-dip galvanized steel strip. This will be described with reference to FIG. After passing through a hot rolling step and a cooling step (not shown), the steel strip 2 is guided to this alloy plating step, conveyed in the direction of the arrow in the figure, and passes through the molten zinc bath 1 to deposit molten zinc on its surface. After passing through the nozzle 3, the amount of molten zinc deposited is adjusted by spraying gas, and then the alloying treatment furnace 4 is entered. Inside the alloying treatment furnace 4, there are a heating zone 4a and a heat retaining zone 4
The steel strip 2 which has been divided into the cooling zone 4c and the cooling zone 4c and which has entered the alloying treatment furnace 4 is first rapidly heated to a plate temperature of 470 ° C. or higher in the heating zone 4a, and then to a constant temperature in the heat retaining zone 4b. The alloy is subjected to an alloying treatment while being kept at a temperature, and then cooled in the cooling zone 4c to form a zinc-iron alloy plating layer having an iron content of about 6 to 13% near its surface. The steel strip 2 exiting the alloying treatment furnace 4 is conveyed to the next step through the roll 20.

The steel materials produced by rolling and wound in the form of coils are joined to each other at their ends so that the ends of the coils are joined together so that they can be continuously plated. A hole (not shown) is formed in the joint portion of the steel strip 2 (coil-to-coil joint portion: Pn) to detect its position. The seam detector 22 optically detects the hole to determine the position of each seam of the steel strip 2.
It can be detected before entering the plating process. The position information detected by the seam detector 22 is input to the process computer (pro computer) 14. In addition, information on various manufacturing conditions such as the steel type (including normal material / U-pattern material) of each coil forming the steel strip 2, the strip running speed, the strip thickness, the strip width, and the plating deposition amount is also provided. The coil is determined (or measured) before entering this plating step and input to the process computer 14.

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

A furnace thermometer 8 is installed inside the heating zone 4a, and a plate thermometer 10 for measuring the sheet temperature of the steel strip 2 and an emissivity of the surface of the steel strip 2 are provided on the outlet side of the heat retaining zone 4b. An emissometer 9 for measurement is arranged. The furnace temperature measured by the furnace thermometer 8 is input to the heat input calculator 13, and the plate temperature T measured by the plate thermometer 10 is input.
x is input to the plate temperature compensator 16, and the emissivity εx measured by the emissometer 9 is input to the emissivity compensator 15. The emissometer 9 uses a conventionally known method as a principle of measuring the emissivity.

The flow rate of the gas discharged from the nozzle 3 is controlled by the plating amount controller 12. The coating amount controller 12 controls the flow rate of the gas supplied to the nozzle 3 in accordance with the input coating amount (set value). The process computer (pro computer) 14 controls the entire manufacturing process of the hot-dip galvanized steel strip, and outputs the set value of the coating amount to the coating amount controller 12,
To the heat input amount calculator 13, the information on the amount of plating adhered, the steel type, the plate passing speed, the plate width and the plate thickness is output, and the target value calculator 1
For No. 8, information about the amount of plated coating, steel type, and strip running speed is output. The heat input amount calculator 13 calculates the heat input amount Q, that is, the heat amount set value, based on the input furnace temperature and the information of the amount of adhered plating, the steel type, the plate passing speed, the plate width, and the plate thickness as follows.
It is calculated by the formula and the result is applied to the heat quantity controller 11.

[0017]

[Equation 1] Q = a0 + a1 × furnace temperature + a2 × plated coating amount × passing speed × [1 + k1 (plate width−plate width standard value) + k2 (plate thickness−plate thickness standard value) + a3 × steel grade constant where a0 to a3, k1, k2: constants (1) Further, in this embodiment, the heat input calculator 13 is actually shown in FIG. 4 in order to give special compensation to the heat input to the U pattern material. Perform the indicated process. FIG. 5 shows an example of the relationship between each position on the steel strip 2, the time when the steel strip 2 passes through the heating zone 4a, and the heat input amount Q. The operation of the heat input calculator 13 will be described with reference to FIGS. 4 and 5.

In step 51, it is determined whether the seam detector 22 has detected the seam position Pn of the steel strip 2. When the seam position Pn is detected, the routine proceeds to step 52,
Otherwise, go to step 56.

In step 52, the detected seam position, that is, the position of the tip of the next coil is detected based on the distance from the position of the seam detector 22 to the heating zone 4a and the strip running speed of the steel strip 2. The time tn to arrive at is calculated and obtained.

In this embodiment, with respect to the U pattern material, the heat input amount in the range from the front end to the length x and the range from the rear end to the length x are different from those in the other regions. The amount of heat input is compensated for. Therefore, in the next step 53, the time te2 at which the position before the joint position Pn by x reaches the heating zone 4a is calculated based on tn, x and the strip passing speed. Similarly, in step 54,
The time te1 at which the position behind the joint position Pn by x reaches the heating zone 4a is calculated based on tn, x and the strip passing speed.

In step 55, each calculated time t
In n, te1 and te2, a timer is set to execute a predetermined process described later. Then, at time te2, the process proceeds from step 56 to 57, at time tn, the process proceeds from step 59 to 60, and at time te1, the process proceeds from step 63 to 64.

At time tn, that is, when the seam position Pn of the steel strip 2 reaches the position of the heating zone 4a of the alloying furnace, the calculation of the equation (1) is carried out in step 60, and then the alloying is carried out. The heat input Q to the coil (steel strip 2) to be processed is obtained. Further, in the next step 61, the steel type of the next coil is checked to identify whether it is a U pattern material or not. U pattern
If it is a material, step 62 is executed. In step 62, the compensation amount ΔQ (constant) is added to the heat input amount (heat amount setting value) Q calculated in step 60.

At time te1, that is, the position advanced from the joint position Pn of the steel strip 2 by the length x is the heating zone 4 of the alloying furnace.
When the position "a" is reached, the steel grade of the coil is checked in step 64 to identify whether or not it is a U pattern material. If it is a U pattern material, step 65 is executed. In step 65, the compensation amount ΔQ is subtracted from the heat input amount (heat amount setting value) Q up to that point.

At time te2, that is, when the position before the joint position Pn (rear end) of the steel strip 2 by the length x reaches the position of the heating zone 4a of the alloying furnace, the steel type of the coil is selected in step 57. Check to identify if it is U-pattern material. If it is a U pattern material, step 5
Execute 8. In step 58, the compensation amount ΔQ is added to the heat input amount (heat amount set value) Q up to that point.

That is, when the ordinary material is processed, the heat input amount Q is updated only at the joint position Pn of the steel strip 2, and when the U pattern material is processed, the heat input amount Q at the joint position Pn of the steel strip 2.
Is calculated, but at the front end (range of length x from the front end) and the rear end (range of length x from the rear end) of the coil,
The heat input amount calculated by the equation is corrected to a value obtained by adding the compensation amount ΔQ, and the heat input amount calculated by the equation (1) is set as it is for the other regions.

In the case of the U pattern material, due to the difference in temperature distribution in the rolling / cooling process, the leading end and the trailing end are less likely to be burned in the alloying furnace 4 than other portions, and raw burning is likely to occur. By setting a large amount of heat input to the front end portion and the rear end portion in advance, it is possible to prevent the occurrence of raw burn.
Since this compensation is feedforward compensation according to the position of the steel strip, there is no delay in compensation control.

In this embodiment, the U-pattern material is compensated so that the heat input amount at the leading end and the trailing end is larger than that at the other portions. On the contrary, depending on the distribution method, it may be better to compensate the heat input amount at the front end portion and the rear end portion so as to be smaller than the other portions. Further, although the leading end and the trailing end are tracked by the timer, they may be tracked by the pulse count of the pulse generator attached to the roll 20, for example.

The description will be continued with reference to FIG. 1 again. The target value calculator 18 generates a plate temperature target value and an emissivity target value based on the 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 and is used for feedback control. These target values are calculated by the following formula.

[0029]

[Equation 2] T0 = b0 + b1 x coating amount + b2 x strip speed + b3 x steel type constant ... (2) ε0 = c0 + c1 x plating amount + c2 x strip speed + c3 x steel type constant (3) where b0 to b3, c0 to c3: constants The heat input amount calculated by the heat input amount calculator 13 is based on the process conditions (furnace temperature, plating deposition amount, strip passing speed, strip width, strip thickness,
Due to the deviation 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 deviation from the optimum heat input amount. In order to compensate for such a control error, in this embodiment, on the outgoing 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.

That is, as shown in FIG. 2, the plate temperature and the emissivity of the steel strip have a correlation with the degree of alloying, respectively,
The greater their value, the greater the degree of alloying. However, these relationships are non-linear and change depending on the process conditions such as steel type, strip running speed, and coating weight. Further, the emissivity rapidly increases as the alloying progresses, and when the desired alloying degree is exceeded, the rate of change with respect to changes in the alloying degree decreases. Further, the plate temperature and the emissivity are not uniform in the entire width direction of the steel strip. Therefore, in order to eliminate the insufficient alloying, it is necessary to measure the plate temperature and the emissivity over the entire width of the steel strip. It is conceivable that there are various management methods for the plate temperature data group Tx and the emissivity data group εx measured over the entire width, but in this embodiment, the average value Td in the width direction of the plate temperature data group is calculated. The representative value is used for the plate temperature compensation control, and the minimum value εd in the width direction of the emissivity data group is used as the representative value for the emissivity compensation control. Such control is effective for detecting insufficient alloying.

The plate temperature compensator 16 forming a part of the feedback compensation control system calculates the compensation amount Ct according to the deviation between the plate temperature target value T0 and the plate temperature detection value (width direction average value) Td. And output to the maximum value selector 17. The emissivity compensator 15 forming a part of the feedback compensation control system calculates the compensation amount Cε according to the deviation between the emissivity target value ε0 and the emissivity detection value (minimum value in the width direction) εd. Obtained and output to the maximum value selector 17. Maximum value selector 17
Compares two input compensation amounts Ct and Cε,
The larger value of the two is selected, the selected compensation amount is added to the heat amount set value (heat input target value) generated in the feedforward control system via the switch SW, and the heat amount adjuster 11 is selected. Apply.

An example of the operation of the feedback compensation control system is shown in FIG.
Shown in. Referring to FIG. 3, since the plate temperature compensation amount Ct is larger than the emissivity compensation amount Cε at the beginning, the plate temperature compensation amount Ct is output as the heat input amount compensation amount, and the plate temperature target value T0
The amount of heat input is corrected so that the deviation between the plate temperature detection value Td (which is also the target value of the degree of alloying) and the plate temperature detection value Td approaches 0. The emissivity compensation amount Cε gradually increases, which is the plate temperature compensation amount Ct.
Is exceeded, that is, the detected emissivity value εd is equal to the target value ε0.
Below (which is also the target value for 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 emissivity detection 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,
Both 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. As a result, the occurrence of insufficient alloying is reliably prevented regardless of whether the estimation is made from the factors of the plate temperature and the emissivity. If the smaller of the two compensation amounts Ct and Cε corresponds to the correct alloying degree, the control deviates from the target value in the direction of promoting the alloying degree. Compared to the case of insufficient liquefaction, there are fewer quality problems and the quality of operation is safe.

The heat input calculator 13 calculates the heat set value based on the information output from the process computer 14 as described above, but additionally controls the opening and closing of the switch SW. That is, normally, the switch SW is closed and the feedback compensation is turned on. However, the process conditions (steel type, plating adhesion amount, etc.) output by the process computer 14 are determined depending on the timing at which the seam position of the steel strip passes. ) Is changed, the switch SW is temporarily opened to turn off the feedback compensation control.

In the above embodiment, the emissivity of the steel strip is used as one means for estimating the degree of alloying of the steel strip. However, theoretically, instead of the emissivity, a parameter similar to that is used. It is possible to use the light reflectance of the surface of the steel strip. In the case of light reflectance, its value is large when the degree of alloying is low, and it is small when the degree of alloying is high. However, it is practical to use the emissivity because it is difficult to detect the light reflectance of the steel strip on the outflow side of the tropical zone in the actual operation.

Further, the calculation formulas for obtaining the plate temperature target value T0 and the emissivity target value ε0 are not limited to the above formulas (2) and (3), and for example, the following formula in which the item of strip speed is omitted You may ask by.

[0037]

[Equation 3] T0 = b0 + b1 x coating weight + b2 x steel grade constant (4) ε0 = c0 + c1 x plating weight + c2 x steel grade constant (5) In addition, only the lower limit control of alloying is implemented Alternatively, the plate temperature target value T0 and the emissivity target value ε0 may be constants.

Further, as the equation for estimating the heat input,
For example, the following equations may be used instead of the equation (1).

[0039]

[Equation 4] Q = a0 + a1 x (coating adhesion amount x plate passing speed) + a2 x steel type constant ・ ・ (6) Q = a0 + a1 × plating adhesion amount + a2 × plate passing speed + a3 × steel type constant ・ ・ (7) Q = a0 + a1 × furnace temperature + a2 × coating amount + a3 × plate passing speed + a4 × plate width + a5 × plate thickness + a6 × steel type constant (8) In the above embodiment, the absolute value of the heat input Q is calculated. Actually, since the calculation of the heat input amount is repeatedly executed at a constant cycle, the deviation of the heat input amount is repeatedly calculated, and the control content is added so that the obtained heat input amount deviation amount is added to the heat input amount up to that point. May be changed. In that case, the heat input deviation may be calculated using one of the following formulas. Note that here, one calculation cycle (Δ
The change of the variable during t) is indicated by Δ.

[0040]

[Formula 5] ΔQ = a0 + a1 x Δ furnace temperature + a2 x Δ heat input correction value + a3 x Δ steel grade constant ... (9) Δ heat input correction value = Δ [plating adhesion amount x strip speed x {1 + k1 (plate width -Plate width standard value) + k2 (Plate thickness-Plate thickness standard value)}] ... (10) ΔQ = a0 + a1 x Δ (plating adhesion amount x stripping speed) + a2 x Δ Steel grade constant ... (11) ΔQ = a0 + a1 × Δ plating deposit + a2 × Δ strip speed + a3 × Δ steel grade constant (12) ΔQ = a0 + a1 × Δ furnace temperature + a2 × Δ plating deposit + a3 × Δ strip speed + a4 × Δ strip width + a5 × Δ Plate thickness + a6 × Δ steel type constant (13) The constants and compensation amounts in the above-mentioned calculation formulas are preset based on past manufacturing results so that optimum results can be obtained.

[0041]

As described above, according to the present invention, the position-temperature distribution pattern of the steel strip in the cooling step is suitable for the special position such as the U-pattern material in advance. Perform compensation automatically (steps 58, 62,
65), even in the case of this kind of special steel strip, it is possible to prevent the occurrence of raw burning over the entire length and to improve the yield.

Further, in the second invention of the present application, even if the actual alloying degree deviates from the target value, the alloying degree is controlled by the feedback compensation control based on the detected alloying degree. Since the amount of heat input is automatically compensated so that is corrected in a preferable direction, the yield can be further improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a manufacturing process of a hot-dip galvanized steel strip.

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

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

FIG. 4 is a flowchart showing the operation of the heat input calculator 13.
It is

FIG. 5 is a timing chart showing an example of changes in the position and time of the steel strip and the heat input amount.

[Explanation of symbols]

1: Molten zinc bath 2: Steel strip 3:
Nozzle 4: Alloying treatment furnace 4a: Heating zone 4
b: tropical zone 4c: cooling zone 8: furnace thermometer 9:
Emissivity meter 10: Plate thermometer 11: Heat quantity controller 12: Plating amount controller 1
3: Heat input calculator 14: Processor 15: Emissivity compensator 1
6: Plate temperature compensator 17: Maximum value selector 18: Target value calculator 2
0: Roll 22: Seam detector SW: Switch

Continuation of the front page (72) Inventor Isao Nakamura 1-1-1 Edamitsu, Hachimanto-ku, Kitakyushu City Nippon Steel Co., Ltd.

Claims (2)

[Claims] 1. A steel strip having molten zinc adhered thereto is passed through a hot rolling and cooling step, and is passed through an alloying furnace, and an alloyed layer of iron and zinc is formed on the steel strip by heating in the alloying furnace. In controlling the heat input amount of the alloying furnace in the process, the set value of the heat input amount is set as follows:
And, the position of each steel strip in the cooling step after hot rolling-the temperature distribution pattern is identified in advance, and the position of the steel strip to be alloyed is detected, and the position is determined based on the strip speed. An alloying furnace heat input control method for a hot-dip galvanized steel strip, which compensates the set value of the heat input amount according to the detected position on each steel strip based on the temperature distribution pattern. 2. The alloying degree is detected by measuring at least one of the temperature, the emissivity, and the light reflectance of the plated steel strip on the heat retaining side of the alloying furnace, and the detected alloying degree is The alloying furnace heat input control method for a hot-dip galvanized steel strip according to claim 1, wherein the set value of the heat input amount is corrected so as to approach the target value.