JP5167895B2 - Method for producing hot-dip steel strip - Google Patents

Description

  The present invention relates to a method of manufacturing a hot-dip galvanized steel strip in which a long strip of steel strip is continuously plated with a molten metal such as hot dip zinc.

FIG. 5 shows an example of a conventional continuous galvanizing equipment. It is shown by a longitudinal sectional view. In FIG. 5, 22 is a plating pot, 26 is a sink roll, 24 is a hot dip zinc plating bath stored in the plating pot 22, 32 is a gas wiping device for controlling the amount of plating, 12 is a steel strip, and F is The conveyance direction of the steel strip 12 in a continuous hot dip galvanizing equipment is shown.
In the continuous hot dip galvanizing equipment, the steel strip 12 is continuously infiltrated into the plating bath 24, the direction is changed by the sink roll 26 in the plating bath 24, and the galvanizing is continuously performed by pulling upward from the plating bath 24. To produce hot dip galvanized steel strip. Moreover, in the hot dip galvanizing equipment, in general, the normal hot dip galvanized steel sheet (GI) as it is plated is the same as the galvannealed steel sheet (GA) that is heat-alloyed after galvanization. Manufactured by switching processing appropriately on the line.

Among these, alloyed hot-dip galvanized steel sheets are widely used mainly as automotive steel sheets because they have excellent corrosion resistance, weldability and workability, but especially when used as exterior steel sheets. Demands for quality are becoming stricter, such as high definition after painting. Under such circumstances, in the hot dip galvanizing pot, Fe and Zn eluted from the steel strip react to form bottom dross containing FeZn ₇ as a main component and deposit on the bottom of the plating pot.

  Such bottom dross may be wound up by the plating solution that is an accompanying flow of the steel strip that is conveyed around the sink roll in the plating bath and may adhere to the steel strip. In this case, when the manufactured plated steel sheet is pressed, surface defects such as so-called press bumps occur, and not only the sharpness is impaired, but also the attached dross damages the mold. The bottom dross that can be a cause of such a defect is increased in the production amount of an alloyed hot-dip galvanized steel sheet having a low Al content in the plating bath. For this reason, the GA type hot dip galvanized steel sheet is more susceptible to surface defects due to bottom dross than the GI hot dip galvanized steel sheet.

For example, Patent Document 1 discloses a technique aimed at solving the above problems. In this method of continuous plating of molten zinc described in Patent Document 1, a steel strip is continuously penetrated into a plating bath in which molten metal is stored, and after turning around a sink roll in the plating bath, the direction is changed, and the plating bath When continuously plating by pulling up further, during continuous plating and / or when continuous plating is stopped, the bath temperature at different locations of the plating bath is measured, and the temperature in the plating bath is determined based on the measurement result. The difference (difference between the maximum temperature and the minimum temperature) is reduced to 5 ° C. or less, preferably 3 ° C. or less, more preferably 2 ° C. or less. Further, as means for reducing the temperature difference in the plating bath, for example, it is described that a screw type plating bath stirring device, a plating pot bottom heating device, and a plating pot side wall heating device are used in appropriate combination. .
JP 2001-107208 A

From the description of Patent Document 1, it is clear that the generation of bottom dross can be effectively suppressed if the difference between the maximum temperature and the minimum temperature in the entire plating bath can be reduced, but in the plating bath performed by the inventors of the present application. According to the heat flow analysis and experiment for molten zinc, the temperature difference of the entire plating bath is sufficiently reduced in a short time just by controlling the amount of heat generated from the plating pot bottom heating device or the plating pot side wall heating device. In addition, when the temperature difference of the entire plating bath is attempted to be sufficiently reduced in a short time by the plating bath stirring device, the stirring force of the plating bath stirring device becomes excessive, and the stirring force As a result, it was found that the bottom dross may be diffused in the plating bath and the surface defects of the plated steel sheet due to the bottom dross may be increased.
An object of the present invention is to provide a method for producing a hot-dip galvanized steel strip that can effectively reduce the surface defects of the hot-dip metal-plated steel plate caused by bottom dross generated in the plating bath in consideration of the above facts.

In the method for manufacturing a hot-dip plated steel strip according to claim 1 of the present invention, the steel strip cooled by the cooling zone after being annealed by the annealing furnace is continuously infiltrated into the plating bath storing the molten metal. A hot-dip plated steel strip manufacturing method in which the steel strip is continuously pulled by being pulled upward from the plating bath, and the temperature of the steel strip entering the plating bath is set to a temperature of the steel strip. The width and thickness, the conveying speed of the steel strip in the plating bath, the temperature of the flow region of the molten metal formed by the contact flow and convection phenomenon flowing in contact with the steel strip surface in the plating bath, and the temperature of the flow region and the temperature Control is performed according to a temperature difference from the temperature of the stagnation region adjacent to the flow region.
In addition, the method for manufacturing a hot-dip galvanized steel strip according to claim 2 of the present invention is the method for manufacturing a hot-dip galvanized steel strip according to claim 1, wherein the temperature difference between the temperature of the flow region and the temperature of the stagnation region is 5 ° C. The infiltration plate temperature is controlled so as to be maintained below.

  According to the manufacturing method of the hot dip galvanized steel strip according to the present invention described above, the surface defects of the hot dip galvanized steel sheet due to the bottom dross generated in the plating bath can be effectively reduced.

Hereinafter, the manufacturing method of the hot dip galvanized steel strip which concerns on embodiment of this invention is demonstrated with reference to drawings.
FIG. 1 schematically shows a hot dip galvanizing facility according to an embodiment of the present invention. The hot dip galvanizing facility 10 includes an annealing furnace 14 that performs an annealing process on the steel strip 12 while conveying the strip-shaped steel strip 12. The annealing furnace 14 is provided with a heating zone 16 and a quenching zone 18 in order from the upstream side along the conveying direction of the steel strip 12 (arrow F direction). In the hot dip galvanizing facility 10, a cooling zone 20, a plating pot 22, a gas wiping device 32, and an alloying device 34 are arranged in this order along the conveying direction F on the downstream side of the annealing furnace 14.

A plating bath 24 in which zinc, which is a plating metal, is in a molten state is stored in the plating pot 22. Further, a sink roll 26 is rotatably disposed in the plating pot 22, and the sink roll 26 is immersed in the plating bath 24.
In the hot dip galvanizing equipment 10, the steel strip 12 is heated to a predetermined annealing temperature in a reducing atmosphere in the heating zone 16 of the annealing furnace 14, quenched in the quenching zone 18 and subjected to annealing treatment, and then the steel strip 12. Is adjusted to a predetermined temperature in the cooling zone 20. The steel strip 12 is guided into a cylindrical snout 30 via a turn-down roll 28 arranged at the outlet of the cooling zone 20 and enters the plating bath 24 through the snout 30. In the plating bath 24, the steel strip 12 is redirected by the sink roll 26 and pulled up from the plating bath 24. At this time, the molten zinc forming the plating bath 24 adheres to the surface of the steel strip 12 to form a plating layer.

The gas wiping device 32 adjusts the thickness of the plating layer attached to the surface of the steel strip 12 by blowing a gas flow onto the steel strip 12 conveyed upward. The alloying device 34 performs an alloying process (heating process) on the steel strip 12 having a plating layer formed on the surface thereof.
A plate temperature sensor 36 is disposed in the snout 30, and this plate temperature sensor 36 detects the temperature of the steel strip 12 (intrusion plate temperature TI) conveyed in the snout 30 and corresponds to the intrusion plate temperature TI. A plate temperature detection signal SS is output to the temperature control device 48. In the plating pot 22, a heating device 38 for heating the plating bath 24 is disposed, for example, on the side wall of the plating pot 22, and the heating device 38 is in accordance with the output control signal SI from the temperature control device 48. Change the heating amount for.

  As shown in FIG. 2, the plating pot 22 extends along the width direction (the arrow X direction in FIG. 2A) and the vertical direction (the arrow Z direction in FIG. 2B) of the plating pot 22. Twenty-four bath temperature sensors 40 each having three or two bath temperature sensors 40 are arranged at nine locations as viewed in section (ZX section). The bath temperature sensors 40 at the same position in the ZX cross section are arranged along the depth direction of the plating pot 22 (the arrow Y direction in FIG. 2B), and the sink roll 26 along the width direction. Are disposed at symmetrical positions on the outer side in the axial direction and at substantially the center position in the width direction.

  In addition, when it is necessary to distinguish and explain the 24 bath temperature sensors 40 according to the installation positions in the plating pot 22, the coordinate points of the bath temperature sensors 40 located at the lower left corner in FIG. 0, 0, 0), and the relative position of the other bath temperature sensor 40 with respect to the bath temperature sensor 40 is represented by three-dimensional coordinates (x, y, z) (where x = 0, 1, 2, y = 0, 1, 2, z = 0, 1, 2), and these three-dimensional coordinates are given before the bath temperature sensor 40.

  The bath temperature sensor 40 is arranged in a rectangular matrix as a whole in the Z-X cross-sectional view. Among these, the bath temperature sensor 40 of (x, y, 0) is arranged in the middle between the bottom surface of the plating pot 22 and the sink roll 26 along the vertical direction, and the bath temperature of (x, y, 1). The sensor 40 is disposed at substantially the same position as the axis of the sink roll 26 along the vertical direction, and the bath temperature sensor 40 of (x, y, 2) is aligned with the surface of the plating bath 24 and the sink along the vertical direction. Arranged in the middle of the roll 26.

  Further, the (0, y, z) bath temperature sensor 40 is disposed along the width direction X of the plating pot 22 at a position substantially coinciding with the immersion portion (tip portion) of the plating bath 24 in the snout 30 (1 , Y, z) is disposed at a position substantially coincident with the axis of the sink roll 26 along the width direction X of the plating pot 22, and the bath temperature sensor 40 of (2, y, z) is Along the width direction X of the plating pot 22, the plating pot 22 is disposed between the front side (right side in FIG. 2) side wall portion and the sink roll 26.

The 24 bath temperature sensors 40 respectively detect the temperature (plating bath temperature) of the plating bath 24 at a position (measurement point) corresponding to the coordinate point, and control the temperature detection signal SM corresponding to the plating bath temperature. Output to device 48.
As shown in FIG. 1, a cooling fan 42 is connected to the cooling zone 20 through a ventilation pipe 44, and the amount of cooling air supplied to the cooling zone 20 by the cooling fan 42 is set in the middle of the ventilation pipe 44. A control damper 46 for adjustment is arranged. Here, the opening degree of the control damper 46 is controlled by an opening degree control signal SD output from the temperature control device 48.

  Next, the heat balance of the plating bath 24 in the hot dip galvanizing facility 10 will be described. Regarding heat input to the plating bath 24, heat input amount Q1 from the steel strip 12, heating amount Q2 by the heating device 38, and regarding heat output, heat dissipation amount Q3 due to radiation from the surface of the plating bath 24, plating bath equipment ( A heat dissipation amount Q4 due to radiation from the surface, and a heat output amount Q5 due to charging an ingot for supplying the plating bath 24.

  Accordingly, when the average temperature of the entire plating bath 24 is considered, in order to keep this average temperature constant, a heating device is set so that the heat input amount Q1 + the heating amount Q2 = the heat dissipation amount Q3 + the heat dissipation amount Q4 + the heat output amount Q5. What is necessary is just to change the heating amount Q2 by 38. Of these, for Q3 and Q4, there is little variation due to changes in the temperature of the plating bath 24. Also for Q5, the bath temperature is lowered by installing an ingot box or an induction heating device dedicated to melting. The influence by can be reduced. Therefore, it is the change in the heat input Q1 from the steel strip 12 that has the greatest effect on the average temperature of the plating bath 24 during steady operation.

  Specifically, for example, the difference between the intrusion plate temperature of the steel strip 12 and the plating bath temperature of the plating bath 24 is 10 ° C., the plate thickness is 0.4 to 3.2 mm, the plate width is 700 to 1800 mm, the steel strip 12 is When the line speed LS is in the range of LS 50 to 150 mpm, the heat input Q1 from the steel strip 12 to the plating bath 24 varies in a large range of 8.8 kW to 540 kW in calculation.

On the other hand, according to the heat flow analysis and experiments by the inventors of the present application, the temperature distribution in the plating bath 24 during operation is not uniform, and roughly divided as shown in FIG. In particular, it is divided into a flow region FF which is a high temperature region and a stagnation region FS which is a relatively low temperature region.
Here, the flow region FF is a melting flow caused by a contact flow (associated flow) of molten zinc flowing while contacting the surface of the steel strip 12 conveyed in the plating bath 24 and convection caused by temperature nonuniformity of the plating bath 24. This is a region including the flow of zinc, and most of the heat input amount Q1 directly enters the flow region FF from the steel strip 12. Further, the stagnation region FS usually exists in a plurality of locations in the plating bath 24 due to the influence of the viscosity of molten zinc, etc., but the large stagnation region FS which is a problem in quality is near the bottom surface of the plating pot 22. And located adjacent to the flow region FF.

  FIG. 3A schematically shows the flow region FF and the stagnation region FS in a substantially steady state. An arrow LM shown in FIG. 3 (A) schematically shows main stream lines of molten zinc generated by the accompanying flow and convection accompanying the movement of the steel strip 12 when the flow region FF is in a substantially steady state. . The main flow LM is a circulation flow that flows along a concave-shaped trajectory as a whole, and a part of the main flow LM is formed by an accompanying flow that flows along the steel strip 12 whose direction is changed by the sink roll 26. And the area | region enclosed by the streamline of this mainstream LM has overlapped substantially with flow area | region FF (area | region which attached | subjected hatching). Further, a stagnation region FS is formed between the flow region FF and the bottom surface of the plating pot 22.

  In FIG. 3B, the temperature distribution in the plating bath when the flow state of the flow region FF is in a substantially steady state is schematically shown by an isotherm. Here, the numerical value attached to the isotherm shown in FIG. 3B indicates a relative temperature difference in the plating bath 24. As is apparent from this figure, ± 0 ° C. isotherms overlap in the vicinity of the region where the accompanying flow accompanying the movement of the steel strip 12 occurs. This indicates that the steel strip 12 and the plating bath 24 (molten zinc) are in a substantially thermal equilibrium state in the vicinity of the region where the accompanying flow is generated. Near the bottom surface of the plating pot 22, there is a relatively low temperature region overlapping the stagnation region FS.

That is, in the plating bath 24, most of the heat input amount Q1 from the steel strip 12 moves to the flow region FF, so that the heat input amount as a whole is larger in the flow region FF than in the stagnation region FS. Thereby, in the plating bath 24, the flow region FF becomes a relatively high temperature region, and the stagnation region FS becomes a relatively low temperature region.
In the plating bath 24, the bath temperature sensor 40 (see FIG. 2) of (0, 0, 0), (0, 1, 0) and (0, 2, 0) mainly has a stagnation area FS (low temperature area) bath degree. (0, 0, 1), (0, 1, 1), (0, 2, 1), (2, 0, 1), (2, 1, 1), (2, 2, 1 ), (2, 0, 2), (2, 1, 2) and (2, 2, 2) bath temperature sensors 40 detect the bath temperature in the flow region FF (high temperature region).

  When the flow state of the flow region FF is in a substantially steady state, for example, a measurement bath detected by the bath temperature sensor 40 of (0, 0, 0), (0, 1, 0) and (0, 1, 2). Average value of temperature and (0,0,1), (0,1,1), (0,2,1), (2,0,1), (2,1,1), (2,2 , 1), (2, 0, 2), (2, 1, 2) and (2, 2, 2), the difference from the average value of the measured bath temperature detected by the bath temperature sensor 40 is about 2 ° C. or less. It is clear that

On the other hand, for example, the average value of the measured bath temperature detected by the bath temperature sensor 40 of (0, 0, 0), (0, 1, 0) and (0, 2, 0), and (0, 0, 1 ), (0,1,1), (0,2,1), (2,0,1), (2,1,1), (2,2,1), (2,0,2), As the difference from the average value of the measured bath temperature detected by the bath temperature sensor 40 of (2, 1, 2) and (2, 2, 2) increases from about 2 ° C., from the vicinity of the bottom surface of the plating pot 22 It is understood that the upward flow FR (see FIG. 4A) flowing toward the sink roll 26 side is likely to be generated, and the flow state of the flow region FF becomes unstable (unsteady state) due to the influence of the upward flow FR. Yes.
FIG. 4A schematically shows the flow region FF and the stagnation region FS in an unsteady state, and FIG. 4B shows plating when the flow state of the flow region FF is in an unsteady state. The temperature distribution in the bath is schematically shown by the isotherm.

For example, the average value of the measured bath temperature detected by the bath temperature sensor 40 of (0, 0, 0), (0, 1, 0) and (0, 2, 0), and (0, 0, 1), (0,1,1), (0,2,1), (2,0,1), (2,1,1), (2,2,1) (2,0,2), (2, When the difference from the average value of the measured bath temperature detected by the bath temperature sensor 40 of (1, 2,) and (2, 2, 2) exceeds about 5 ° C., as shown in FIG. A strong upward flow FR that flows from the vicinity of the bottom surface of the plating pot 22 toward the sink roll 26 is generated, and the main flow LM is divided into a front side and a back side due to the influence of the upward flow FR and the like. In such a state, the bottom dross accumulated in the vicinity of the bottom surface of the plating pot 22 is wound up by the upward flow FR and may be diffused to a wide area in the plating bath 24.
Further, as shown in FIG. 4 (B), compared to the case where the flow region FF is in a substantially steady state, the −2 ° C. isotherm retreats to the back side (left side in FIG. 4 (B)), You can see that it swells upward.

  Next, temperature control of the steel strip 12 performed by the temperature control device 48 will be described. The temperature control device 48 determines the intrusion plate temperature TI of the steel strip 12 based on the plate temperature detection signal SS output from the plate temperature sensor 36 disposed in the snout 30, and the intrusion temperature TI is a predetermined target intrusion plate. The cooling amount for the steel strip 12 in the cooling zone 20 is controlled (feedback control) so that the temperature TS is reached. At this time, the temperature control device 48 calculates the difference (deviation) between the infiltration plate temperature TI and the target infiltration plate temperature TS, and changes the value of the opening control signal SD output to the control damper 46 in accordance with this deviation. .

At this time, the temperature control device 48 measures the target intrusion plate temperature TS by the bath temperature sensor 40 having measurement points in the plate thickness t, plate width w, line speed LS, and flow region FF of the steel strip 12. The calculation is based on the bath temperature deviation DT between the average value of the bath temperature and the average value of the measured bath temperature measured by the bath temperature sensor 40 having a measurement point in the stagnation region FS.
That is, the heat input Q1 from the steel strip 12 to the plating bath 24 is obtained by the following equation.

Q1 = plate thickness t × plate width w × line speed LS × (measurement bath temperature−penetration plate temperature TI) × factor α
Further, the temperature control device 48 determines whether the flow region FF is in a substantially steady state or an unsteady state based on the bath temperature deviation DT in the plating bath 24. When the temperature control device 48 determines that the flow region FF is in a substantially steady state, the temperature control device 48 sets the target infiltration plate temperature TS so that the heat input amount Q1 from the steel strip 12 is kept constant.

  On the other hand, when the temperature control device 48 determines that the flow region FF is in an unsteady state, that is, when the bath temperature deviation DT becomes larger than a predetermined threshold (for example, 3 ° C.), the bath temperature deviation DT. The amount of heat input Q1 from the steel strip 12 to the plating bath 24 is changed (increased or decreased) so that becomes smaller. That is, when the plate thickness t, the plate width w, the line speed LS, and the heating amount Q2 of the heating device 38 are constant, the heat input amount Q1 is changed by changing (increasing or decreasing) the target infiltration plate temperature TS. Let

In the present invention, when the infiltration plate temperature TS is controlled so that the bath temperature deviation DT is maintained at 5 ° C. or less, the flow of the flow region FF in the plating bath 24 is stabilized as described above, This is preferable. Furthermore, it is preferable to control so that it may maintain at 2 degrees C or less.
Specifically, the temperature control device 48 uses, for example, an average value of the measured bath temperature measured by the bath temperature sensor 40 having the measurement point in the flow region FF and the bath temperature sensor 40 having the measurement point in the stagnation region FS. The size and position of a relatively high temperature region (flow region FF) are determined based on, for example, an average value of the measured bath temperature, and the size and position of the flow region FF are substantially equal to the steady state flow region FF. The amount of heat input Q1 is changed so as to change to the size and position.

Therefore, the temperature control device 48 has a control data table in which the value of the bath temperature deviation DT and the appropriate value of the heat input Q1 corresponding to the value of the bath temperature deviation DT are set. The appropriate value of the heat input amount Q1 corresponding to the bath temperature deviation DT calculated from is read, and the target infiltration plate temperature TS is calculated based on the heat input amount Q1.
When the temperature control device 48 determines that the flow region FF is in an unsteady state, the temperature control device 48 changes the heat input amount Q1 and also changes the heating amount Q2 by the heating device 38 to supplement the bath temperature deviation. You may make it reduce DT.

In the manufacturing method of the hot dip galvanized steel strip according to the embodiment of the present invention described above, the temperature control device 48 determines the intrusion plate temperature TI of the steel strip 12 entering the plating bath 24, the width w and the thickness of the steel strip. t, the line speed LS, the measurement bath temperature of the flow region FF in the plating bath 24, and the bath temperature deviation DT between the bath temperature of the flow region FF and the stagnation region FS. Since the amount of heat input that moves to the flow region FF of the plating bath 24 can be appropriately controlled, it is possible to suppress a rise in the bath temperature in the vicinity of the flow region FF in the plating bath 24 and to flow in the plating bath 24. It is possible to suppress an increase in the bath temperature deviation DT between the region FF and the stagnation region FS, and to effectively generate bottom dross and diffuse the bottom dross into the plating bath 24 by the upward flow FR. It can be suppressed to. As a result, surface defects of the hot dip galvanized steel sheet due to bottom dross generated in the plating bath 24 can be effectively reduced.
In addition, embodiment described above shows an example of this invention and is not limited to this embodiment. The number, position, and the like of the bath temperature sensor 40 can be changed as long as the same effect can be obtained.

Next, the case where the intrusion temperature TS of the steel strip 12 is controlled using the manufacturing method of the hot dip galvanized steel strip of the present invention will be described as Examples 1 to 3, and the conventional manufacturing method of the hot dip galvanized steel strip will be described. The case where the penetration temperature TS of the steel strip 12 is controlled using will be described as Comparative Examples 1 to 4. In the method for producing a hot dip galvanized steel strip according to the present invention, as shown in FIG. 2, 24 bath temperature sensors are used, and the infiltration plate temperature TS is controlled so that the bath temperature deviation DT is 5 ° C. or less. . The bath temperature deviation DT is defined as an average value of the three measured bath temperatures (0, 1, 1), (2, 1, 1) and (2, 1, 2) in FIG. The measurement bath temperature of (0, 1, 0) was defined as the temperature of the stagnation region, and the difference between these temperatures. In the conventional method of manufacturing a hot dip galvanized steel strip, the measurement bath temperature detected by one bath temperature sensor arranged at the position (2, 2, 2) is used as the representative temperature of the plating bath, and every minute. The intrusion temperature TS was controlled so that the heat input amount Q1 was constant from the deviation of the measurement bath temperature.
The results of Examples 1 to 3 and Comparative Examples 1 to 4 are shown below (Table 1), respectively.

  Next, the graph of FIG. 6 shows the relationship between the amount of bottom dross generated in the plating bath 24 and the bath temperature deviation DT. In FIG. 7, the amount of bottom dross generated when the bath temperature deviation DT is 10 ° C. is 1.0, and the amount of bottom dross generated when the bath temperature deviation DT is 5 ° C. and 2 ° C. is represented by an index. Yes.

It is a lineblock diagram showing typically the hot dip galvanization equipment concerning the embodiment of the present invention. It is the side surface cross section and top view which show arrangement | positioning of the bath temperature sensor in the plating pot shown by FIG. (A) is a side view of a plating pot schematically showing a flow region FF and a stagnation region FS in a substantially steady state, and (B) is a temperature distribution in the plating bath when the flow state of the flow region FF is in a substantially steady state. It is side surface sectional drawing of the plating pot which shows typically. (A) is a side view of a plating pot schematically showing a flow region FF and a stagnation region FS in an unsteady state, and (B) is a temperature distribution in the plating bath when the flow state of the flow region FF is in an unsteady state. It is side surface sectional drawing of the plating pot which shows typically. It is a side cross section which shows an example of the conventional continuous hot dip galvanization equipment. It is a graph which shows the relationship between the generation amount of the bottom dross in a plating bath, and bath temperature deviation DT.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Hot dip galvanization equipment 12 Steel strip 14 Annealing furnace 16 Heating zone 18 Quench zone 20 Cooling zone 22 Pot 24 Plating bath 26 Sink roll 28 Turndown roll 30 Snout 32 Gas wiping device 34 Alloying device 36 Plate temperature sensor 38 Heating device 40 Bath temperature sensor 42 Cooling fan 44 Ventilation pipe 46 Control damper 48 Temperature control device DT Bath temperature deviation FF Flow region FR Up flow FS Stagnation region LR Up flow LM Main flow LS Line speed TS Target intrusion plate temperature t Plate thickness w Plate width

Claims (2)

After being annealed in the annealing furnace, the steel strip cooled by the cooling zone is continuously infiltrated into the plating bath storing the molten metal, and then pulled upward from the plating bath to continuously plate the steel strip. A method for producing a hot dipped galvanized steel strip, comprising:
The intrusion plate temperature, which is the temperature of the steel strip entering the plating bath, the width and thickness of the steel strip, the transport speed of the steel strip in the plating bath, the contact flow and convection flowing while contacting the steel strip surface in the plating bath Production of hot dip galvanized steel strip characterized by controlling according to the temperature of the flow region of molten metal formed by the phenomenon and the temperature difference between the temperature of the flow region and the temperature of the stagnation region adjacent to the flow region Method.   The method for producing a hot-dip galvanized steel strip according to claim 1, wherein the temperature of the infiltration plate is controlled so that a temperature difference between the temperature of the flow region and the temperature of the stagnation region is maintained at 5 ° C or less. .

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