Method for manufacturing molten metal plating steel strip, and gas wiping apparatus

Abstract

To provide a method for manufacturing a molten metal plating steel strip, capable of easily controlling the spray pressure of wiping gas even when pressure loss to a wiping nozzle tip changes.SOLUTION: A method for manufacturing a molten metal plating steel strip, capable of spraying wiping gas from a pair of wiping nozzles arranged to sandwich a steel strip and face both surfaces thereof on the surface of the steel strip immersed in a molten metal plating bath to control a molten metal plating weight, comprises measuring the spray pressure of the wiping gas sprayed from the pair of wiping nozzles using a pressure gauge installed on the outside of an end part in the width direction of the steel strip between the pair of wiping nozzles.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a manufacturing method of hot-dip metal-plated steel strip and a gas wiping device that, in the production of hot-dip metal-plated steel strip, measures the spray pressure from a wiping nozzle and controls the amount of hot-dip metal coating that adheres to the front and back surfaces of the steel strip. [Background technology]

[0002] In a hot-dip metal-plated steel strip production line, a steel strip is immersed in a plating bath containing molten metal, and the molten metal is deposited on the steel strip. The steel strip is then turned by a sink roll and pulled vertically upward. Gas is sprayed onto the surface of the steel strip from a pair of wiping nozzles arranged opposite each other across the steel strip to wipe off excess molten metal, thereby controlling the amount of hot-dip metal deposition on the steel strip.

[0003] The amount of hot-dip metal coating applied is determined by the distance L between the tip of the wiping nozzle and the steel strip surface and the pressure P of the gas sprayed from the wiping nozzle. As a technique for controlling the distance L between the tip of the wiping nozzle and the steel strip surface, Patent Document 1 discloses a non-contact control device for a metal strip that adjusts the distance L using a non-contact position sensor and an electromagnet. According to Patent Document 1, the distance L can be controlled to a target distance by adjusting the magnetic force of the electromagnet.

[0004] As a technique for controlling the pressure P of the gas sprayed from the wiping nozzle, Patent Document 2 discloses a technique for detecting and controlling the (primary) pressure of a pipe connected to the wiping nozzle. Patent Document 3 discloses a technique for installing a pressure gauge inside the wiping nozzle to detect fluctuations in the pressure inside the wiping nozzle and suppress the fluctuations. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-160959 [Patent Document 2] Japanese Patent Application Publication No. 2018-204055 [Patent Document 3] Japanese Patent Application Publication No. 05-171394 Summary of the Invention [Problem to be solved by the invention]

[0006] To control the coating weight of the hot-dip metal coating in the longitudinal direction of the steel strip, it is necessary to appropriately control the distance L between the tip of the wiping nozzle and the steel strip surface and the pressure P of the gas sprayed onto the steel strip surface in accordance with the conveying speed of the steel strip and the width and thickness of the steel strip being continuously threaded. As disclosed in Patent Document 1, the distance L between the tip of the wiping nozzle and the steel strip surface can be controlled by adjusting the magnetic force of the electromagnet in accordance with the conveying speed of the steel strip and the width and thickness of the steel strip while the steel strip is being threaded.

[0007] On the other hand, the pressure P of the gas sprayed onto the steel strip surface is controlled based on the pressure measured in the piping that supplies the wiping gas to the wiping nozzle and the pressure inside the wiping nozzle, as in the technology disclosed in Patent Document 2 or Patent Document 3. However, because the spray pressure of the wiping gas is not actually measured, there is a problem that if rust or dust clogs the piping or part of the inside of the wiping nozzle, causing a change in pressure loss up to the tip of the wiping nozzle, it becomes difficult to control the spray pressure of the wiping gas.

[0008] The present invention has been made in consideration of the problems of the prior art, and an object of the present invention is to provide a method for producing a hot-dip metal coated steel strip in which the spray pressure of the wiping gas can be easily controlled even if the pressure drop up to the tip of the wiping nozzle changes. Another object of the present invention is to provide a gas wiping device for use in the method for producing a hot-dip metal coated steel strip. [Means for solving the problem]

[0009] The means for solving the above problems are as follows. [1] A method for manufacturing a hot-dip metal-plated steel strip, in which a wiping gas is sprayed from a pair of wiping nozzles arranged opposite the front and back surfaces of a steel strip immersed in a hot-dip metal plating bath to control the amount of hot-dip metal plating applied, with the steel strip sandwiched between the pair of wiping nozzles and the pressure gauge installed outside the widthwise ends of the steel strip between the pair of wiping nozzles to measure the spray pressure of the wiping gas sprayed from the pair of wiping nozzles. [2] The method for producing a hot-dip metal coated steel strip according to [1], wherein the spray pressure of the wiping gas is measured while the steel strip is being threaded. [3] A method for manufacturing a hot-dip metal-plated steel strip according to [1] or [2], wherein the supply pressure of the wiping gas to the wiping nozzle is adjusted so that the spray pressure of the wiping gas is within a predetermined range. [4] A method for producing a hot-dip metal-plated steel strip described in any one of [1] to [3], wherein the pressure gauge is plate-shaped and is inclined so that the thickness of the lower surface and back surface decreases downward. [5] A gas wiping device that controls the amount of molten metal coating by spraying wiping gas onto a steel strip immersed in a molten metal coating bath, comprising: a pair of wiping nozzles that are arranged opposite the front and back surfaces of the steel strip across the steel strip and spray wiping gas onto the front and back surfaces; and a pressure gauge that is installed between the pair of wiping nozzles and outside the widthwise ends of the steel strip and measures the spray pressure of the wiping gas. [6] A gas wiping device as described in [5], further comprising a control device for controlling the spraying pressure of the wiping gas, wherein the control device adjusts the supply pressure to the wiping nozzle so that the spraying pressure measured by the pressure gauge is within a predetermined range. [7] The pressure gauge has a plate-shaped portion, an inclined portion inclined so that the thickness of the plate decreases downward on the front and back surfaces, and a sensor portion for measuring the pressure of the wiping gas, wherein the inclined portion is provided below the plate-shaped portion and the sensor portion is provided on the front and back surfaces of the plate-shaped portion, in a gas wiping device described in [5] or [6]. [Effects of the Invention]

[0010] In the manufacturing method of hot-dip metal-plated steel strip according to the present invention, the spray pressure of the wiping gas is measured at the position of the steel strip, so that even if the pressure loss to the tip of the wiping nozzle changes, the spray pressure of the wiping gas can be easily controlled. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional schematic view showing an example of a production line for a hot-dip metal coated steel strip including a gas wiping device according to this embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of the gas wiping device taken along line AA. [Figure 3] FIG. 3 is a schematic diagram showing an example of a pressure gauge. [Figure 4] FIG. 4 is a schematic diagram showing an example of the configuration of the control device. [Figure 5] FIG. 5 is a cross-sectional view of a gas wiping device according to another embodiment of the present invention. [Figure 6] FIG. 6 is a schematic diagram showing another example of a pressure gauge included in the gas wiping device according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be specifically described below through embodiments of the present invention. The following embodiments are preferred examples of the present invention, and the present invention is not limited to these embodiments.

[0013] Fig. 1 is a cross-sectional view showing an example of a production line for a hot-dip metal-plated steel strip including a gas wiping device 60 according to this embodiment. Fig. 2 is a cross-sectional view taken along line AA of the gas wiping device 60. The production line for a hot-dip metal-plated steel strip and the gas wiping device 60 according to this embodiment will be described with reference to Figs. 1 and 2.

[0014] In a hot-dip metal coated steel strip production line, a steel strip 10 immersed in a coating bath 12 of molten metal 14 is redirected by a sink roll 16 and then pulled vertically upward. A pair of wiping nozzles 24, positioned opposite the front and back surfaces of the steel strip 10 and sandwiching the steel strip 10, sprays wiping gas onto the front and back surfaces of the steel strip 10 to wipe away excess molten metal 14. By spraying wiping gas onto the front and back surfaces of the steel strip 10 in this manner to wipe away excess molten metal 14, the amount of hot-dip metal coating applied to the front and back surfaces of the steel strip 10 is controlled. It is preferable to use dry air or nitrogen as the wiping gas sprayed onto the front and back surfaces of the steel strip 10.

[0015] The gas wiping device 60 according to this embodiment includes wiping nozzle units 20, 22 each having a pair of wiping nozzles 24 arranged opposite each other on the front and back sides of the steel strip 10, a pressure gauge 28, and a control device 40. Since the wiping nozzle units 20, 22 have the same configuration, in this embodiment, only the wiping nozzle unit 20 will be described, and a description of the wiping nozzle unit 22 will be omitted.

[0016] The wiping nozzle unit 20 has a wiping nozzle 24 and an adjustment valve 26 that adjusts the supply pressure of the wiping gas supplied to the wiping nozzle 24. The adjustment valve 26 is provided in a transport path along which the wiping gas is transported from a wiping gas supply source 70 to the wiping nozzle 24. The adjustment valve 26 is, for example, a pressure reducing valve that reduces the pressure of the wiping gas supplied from the wiping gas supply source 70. By opening the adjustment valve 26, the supply pressure of the wiping gas increases, and by closing the adjustment valve 26, the supply pressure of the wiping gas decreases.

[0017] The wiping nozzle 24 sprays wiping gas onto the front or back surface of the steel strip 10. The width dimension of the wiping nozzle 24 is larger than the width dimension of the steel strip 10 so that it can accommodate a variety of steel strips and can also accommodate widthwise misalignment of the steel strip 10 when pulled up. The pressure gauge 28 is installed between the pair of wiping nozzles 24 at a position where the wiping gas is sprayed outside the widthwise end of the steel strip 10.

[0018] FIG. 3 is a schematic diagram showing an example of a pressure gauge 28. FIG. 3(a) is a schematic diagram of the pressure gauge 28 as seen from the direction of arrow B in FIG. 2, and FIG. 3(b) is a schematic front view of the pressure gauge 28. The pressure gauge 28 has a plate-shaped portion 30 and sensor portions 32 and 33 provided on the front and back surfaces of the plate-shaped portion 30. The plate-shaped portion 30 is provided to fix the sensor portions. The plate-shaped portion 30 is formed, for example, from a rectangular flat plate.

[0019] The sensor units 32, 33 measure the spray pressure of the wiping gas sprayed from the wiping nozzle 24 online at predetermined measurement intervals while the steel strip 10 is being threaded. The sensor units 32, 33 measure the spray pressure of the wiping gas at a measurement interval of, for example, 10 times per second, and output spray pressure data indicating the spray pressure to the control device 40 at the same intervals as the measurement intervals. In this embodiment, the sensor unit 32 measures the spray pressure of the wiping gas sprayed from the wiping nozzle unit 20, and the sensor unit 33 measures the spray pressure of the wiping gas sprayed from the wiping nozzle unit 22. The sensor units 32, 33 are configured, for example, with sheet-like pressure sensors.

[0020] The control device 40 adjusts the supply pressure of the wiping gas to the wiping nozzle 24 so that the spray pressure of the wiping gas sprayed onto the steel strip 10 falls within a predetermined range. The predetermined range is a target spray pressure range determined in a hot-dip metal-plated steel strip production line. The target spray pressure range is determined so that the coating weight of the hot-dip metal coating on the produced hot-dip metal-plated steel strip falls within an allowable range (within a range of the target value ± tolerance).

[0021] 4 is a schematic diagram showing an example configuration of the control device 40. The control device 40 is, for example, a general-purpose computer such as a workstation or a personal computer. The control device 40 has a control unit 42, an input unit 44, an output unit 46, and a storage unit 48. The control unit 42 is, for example, a CPU, and functions as a pressure determination unit 50 and a pressure adjustment unit 52 by executing a program stored in the storage unit 48.

[0022] The input unit 44 is, for example, a keyboard, a touch panel integrated with a display, or the like. The output unit 46 is, for example, an LCD or CRT display, or the like. The storage unit 48 is, for example, an updatable flash memory, a built-in hard disk or a hard disk connected via a data communication terminal, an information recording medium such as a memory card, and a read / write device for the same. The storage unit 48 stores programs and data for realizing the various functions of the control device 40. Specifically, the storage unit 48 stores the range of the target spray pressure, the unit for adjusting the opening of the regulating valve 26, and the like. These data may be determined in advance by an operator and stored in the storage unit 48 by the operator via the input unit 44.

[0023] Next, the processes executed by the pressure determination unit 50 and the pressure adjustment unit 52 will be described. When the pressure determination unit 50 acquires spray pressure data from the sensor units 32 and 33, it reads the target spray pressure range from the storage unit 48 and determines whether the pressure indicated by the spray pressure data is within the target spray pressure range. The pressure determination unit 50 compares the spray pressure with the target spray pressure range and generates ternary data that distinguishes between, for example, a case where the acquired spray pressure is lower than the target, a case where the acquired spray pressure is within the target range, and a case where the acquired spray pressure is higher than the target. The pressure determination unit 50 outputs the generated ternary data to the pressure adjustment unit 52 together with information identifying the sensor units 32 and 33. The pressure determination unit 50 may display the spray pressure acquired from the sensor units 32 and 33 and / or the generated ternary data on the output unit 46.

[0024] If the ternary data acquired from the pressure determination unit 50 indicates that the spray pressure is lower than the target range, the pressure adjustment unit 52 outputs a signal to increase the opening degree by one unit to the adjustment valve 26 of the wiping nozzle unit corresponding to the sensor units 32 and 33. That is, if spray pressure data is acquired from the sensor unit 32, the pressure adjustment unit 52 outputs that signal to the adjustment valve 26 of the wiping nozzle unit 20, and if spray pressure data is acquired from the sensor unit 33, the pressure adjustment unit 52 outputs that signal to the adjustment valve 26 of the wiping nozzle unit 22. As a result, the supply pressure of the wiping gas supplied to each wiping nozzle 24 increases, and the spray pressure measured by the sensor units 32 and 33 also increases.

[0025] Furthermore, if the ternary data acquired from the pressure determination unit 50 indicates that the spray pressure is higher than the target range, the pressure adjustment unit 52 outputs a signal to close the opening by one unit to the adjustment valve 26 of the wiping nozzle unit corresponding to the sensor units 32 and 33. This reduces the supply pressure of the wiping gas supplied to the wiping nozzle 24, and therefore the spray pressure measured by the sensor units 32 and 33 also reduces.

[0026] On the other hand, if the ternary data acquired from the pressure determination unit 50 indicates that the spray pressure is within the target range, the pressure adjustment unit 52 does not send a signal to the adjustment valve 26. As a result, the supply pressure of the wiping gas supplied to the wiping nozzle 24 does not change, and the spray pressure is maintained within the target pressure range. By repeatedly executing the processes by the pressure determination unit 50 and the pressure adjustment unit 52, the supply pressure of the wiping gas is adjusted so that the spray pressure of the wiping gas falls within the target pressure range. In this way, the control device 40 controls the spray pressure of the wiping gas so that it falls within the target pressure range.

[0027] As described above, the gas wiping device 60 according to this embodiment has a pressure gauge 28 installed between the pair of wiping nozzles 24 and outside the widthwise end of the steel strip 10. By measuring the spray pressure of the wiping gas sprayed onto the steel strip 10 with this pressure gauge 28, the spray pressure can be determined, making it easy to control the spray pressure within a target spray pressure range. On the other hand, with conventional configurations, if the pressure loss up to the tip of the wiping nozzle 24 changes, it is not possible to determine the extent to which the wiping gas spray pressure will change due to this change, making it difficult to control the spray pressure within a target spray pressure range.

[0028] Furthermore, by measuring the spray pressure of the wiping gas sprayed onto the steel strip 10 with the pressure gauge 28 while the strip is being threaded, the spray pressure can be grasped online while the strip is being threaded. This makes it possible to detect any changes in the pressure drop up to the tip of the wiping nozzle 24 while the strip is being threaded, and to control the spray pressure of the wiping gas within a target spray pressure range.

[0029] Furthermore, even if the distance L between the wiping nozzle 24 and the surface of the steel strip 10 changes depending on the shape of the steel strip 10, the use of the pressure gauge 28 makes it easy to control the spray pressure of the wiping gas sprayed onto the steel strip 10 within a target spray pressure range. Furthermore, even for steel strips with different hot-dip metal coating weights on the front and back surfaces of the steel strip 10, they can be easily manufactured by setting the target spray pressure ranges for the sensor units 32, 33 to different ranges on the front and back surfaces. As a result, hot-dip metal-coated steel strips in which the coating weight of hot-dip metal coating is controlled within an allowable range (within the target value ± tolerance) can be stably manufactured.

[0030] The embodiments of the present invention are not limited to the above-described embodiments and various modifications can be made. The wiping nozzle units 20, 22 may have a gas pressure gauge that measures the supply pressure of the wiping gas downstream of the adjustment valve 26 in the direction of wiping gas transport. By having the wiping nozzle units 20, 22 have a gas pressure gauge, it is possible to spray the wiping gas onto the steel strip 10 while managing the supply pressure of the wiping gas. Furthermore, by having the wiping nozzle units 20, 22 have a gas pressure gauge, it is possible to grasp the pressure loss up to the tip of the wiping nozzle 24. If the wiping nozzle 24 becomes clogged with rust or dust, the pressure loss increases, so understanding this pressure loss makes it possible to determine the need for maintenance of the wiping nozzle 24.

[0031] Figure 5 is a cross-sectional schematic view of a gas wiping device 62 showing another embodiment of the present invention. In the gas wiping device 62 shown in Figure 5, the same components as those in the gas wiping device 60 shown in Figure 2 are given the same reference numerals, and their description will be omitted. The gas wiping device 62 shown in Figure 5 differs from the gas wiping device 60 shown in Figure 2 in that it has pressure gauges 28, 34 installed between a pair of wiping nozzles 24 and on the outside of both ends of the steel strip 10 in the width direction.

[0032] As shown in Figure 5, the gas wiping device 62 may have two pressure gauges 28, 34 installed outside both ends of the steel strip 10 in the width direction. In this case, the pressure determination unit 50 uses, for example, the average value of the spray pressure measured by two sensor units provided on the wiping nozzle unit 20 side to determine whether the average value is within the range of the target spray pressure. The pressure adjustment unit 52 uses the determination result to adjust the supply pressure of the wiping gas. This allows the spray pressure of the wiping gas to be controlled so that it falls within the range of the target spray pressure.

[0033] The spray pressure of the wiping nozzle 24 may fluctuate in the width direction of the steel strip 10. Even if the spray pressure fluctuates in this way, by providing two pressure gauges 28, 34 and controlling the supply pressure of the wiping gas based on the spray pressure at both ends, it becomes possible to control the spray pressure of the wiping gas with high precision.

[0034] Figure 6 is a schematic diagram showing another example of a pressure gauge included in the gas wiping device according to this embodiment. Figure 6(a) is a schematic side view of a pressure gauge 80, and Figure 6(b) is a schematic front view of the pressure gauge 80. In the pressure gauge 80 shown in Figure 6, the same components as those in the pressure gauge 28 shown in Figure 3 are given the same reference numerals, and their description will be omitted. The pressure gauge 80 shown in Figure 6 differs from the pressure gauge 28 shown in Figure 3 in that it has an inclined portion 84.

[0035] 6, the pressure gauge 80 has an inclined portion 84 below the plate-shaped portion 30, which is inclined so that the plate thickness of the front and back surfaces becomes thinner downward. The sensor portions 32, 33 are provided on the front and back surfaces of the plate-shaped portion 30.

[0036] At the widthwise ends of the steel strip 10 and outside the widthwise ends of the steel strip 10, the wiping gases tend to interfere with each other and become turbulent, causing defects due to splashing and degrading the surface quality of the steel strip 10. Furthermore, if a plate-shaped pressure gauge 28 is provided outside the widthwise ends of the steel strip 10, the lower component of the wiping gas that separates upon impact with the pressure gauge 28 may swirl at the bottom end of the pressure gauge 28, which may affect the ends of the steel strip 10 and cause splashing. Here, splashing refers to the phenomenon in which molten metal 14 that falls from the steel strip 10 is scattered around due to disturbances in the wiping gas that impacts the steel strip 10, and the occurrence of such splashing degrades the surface quality of the steel strip 10.

[0037] To prevent this splashing, if an inclined portion 84 is provided below the plate-shaped portion 30 so that the thickness of the front and back surfaces becomes thinner downward, the downward component of the wiping gas will smoothly merge at the lower end of the pressure gauge 28, and turbulence of the wiping gas at that end will be suppressed. This will suppress the occurrence of splashing and prevent deterioration of the surface quality of the steel strip 10. Therefore, it is preferable that the pressure gauge have an inclined portion 84 below the plate-shaped portion 30 so that the thickness of the front and back surfaces will become thinner downward. [Example]

[0038] Next, an example will be described. Using the continuous hot-dip metal coating line and gas wiping device 60 shown in Figures 1 and 2, a zinc alloy, which is a molten metal, was deposited on the surface of a steel strip 10 under the following conditions. The coating weight of the zinc alloy coating on the steel strip 10 during the coating process was continuously measured using a magnetic film thickness meter. <Zinc alloy adhesion conditions> Wiping nozzle 24 slit gap: 0.8 mm Distance between the tip of the wiping nozzle 24 and the surface of the steel strip 10: 8.0 mm Height from plating bath 12 to tip of wiping nozzle 24: 420 mm Temperature of zinc alloy in plating bath 12: 460°C Steel strip 10 thickness: 1.0mm Width of steel strip 10: 1240mm Steel strip 10 threading speed: 150 m / min Molten metal type: Zinc alloy Target range of zinc alloy plating coating weight: 48g±1g / m 2

[0039] In the example of the present invention, a pressure gauge 28 was installed at a position 10 mm away from the widthwise end of the steel strip 10, and the spray pressure from the wiping nozzles 24 arranged opposite to it was measured during the strip threading. The target range of the spray pressure was 0.45±0.0017 kgf / cm. 2The adjustment valve 26 was adjusted so that the spray pressure was within this range, and zinc alloy plated steel strips were produced. As a result, the zinc alloy coating weight at the position 100 m from the start of threading of the first steel strip 10 was 48 g / m, which was within the target range. 2 The zinc alloy coating weight at the 20,000m position, which is the 10th steel strip, was also within the target range of 48g / m 2 was maintained.

[0040] On the other hand, in the comparative example, the pressure gauge 28 was not provided, and a gas pressure gauge was provided to measure the supply pressure of the wiping gas supplied to the wiping nozzle 24, and the supply pressure of the wiping gas was 0.8±0.003 kgf / cm 2 As a result, the coating weight of the zinc alloy coating on the first steel strip 10 from the start of threading to the position of 100 m was 48 g / m, which was within the target range. 2 The zinc alloy coating weight of the steel strip 10 that was threaded thereafter was also within the target range. However, at the 20,000 m position of the 10th steel strip, the zinc alloy coating weight was 50 g / m, which was outside the target range. 2 When the cause was investigated, it was found that rust had clogged a part of the pipe connected to the wiping nozzle 24, reducing the supply pressure to 0.8±0.003 kgf / cm. 2 It was discovered that the wiping gas spray pressure was decreasing despite the pressure being controlled within the specified range.

[0041] From these results, it was confirmed that by using the manufacturing method of hot-dip metal-plated steel strip and gas wiping device of this embodiment, it is possible to stably manufacture hot-dip metal-plated steel strip in which the adhesion weight of hot-dip metal plating is controlled within an acceptable range (within the range of target value ± tolerance). [Explanation of symbols]

[0042] 10 Steel strips 12 Plating bath 14 Molten Metal 16 Sink Roll 20 Wiping nozzle unit 22 Wiping nozzle unit 24 Wiping nozzle 26 Regulating valve 28 Pressure gauge 30 Plate-shaped part 32 Sensor section 33 Sensor section 40 Control device 42 Control Unit 44 Input section 46 Output section 48 Storage area 50 Pressure determination unit 52 Pressure adjustment unit 60 Gas wiping device 62 Gas wiping device 70 Wiping gas supply source 80 Pressure Gauge 82 Plate-shaped part 84 Slope

Claims

1. A method for manufacturing a hot-dip metal-plated steel strip, comprising the steps of: spraying a wiping gas onto a front surface and a back surface of a steel strip immersed in a hot-dip metal plating bath from a pair of wiping nozzles disposed opposite the front surface and the back surface of the steel strip with the steel strip sandwiched therebetween, thereby controlling the amount of hot-dip metal plating applied; A method for manufacturing a hot-dip metal plated steel strip, wherein the spray pressure of the wiping gas sprayed from the pair of wiping nozzles is measured using a pressure gauge installed between the pair of wiping nozzles and outside the widthwise end of the steel strip.

2. The method for producing a hot-dip metal coated steel strip according to claim 1, wherein the spray pressure of the wiping gas is measured while the steel strip is threaded.

3. 3. The method for producing a hot-dip metal coated steel strip according to claim 1, wherein a supply pressure of the wiping gas to the wiping nozzle is adjusted so that the spray pressure of the wiping gas falls within a predetermined range.

4. 3. The method for producing a hot-dip metal coated steel strip according to claim 1, wherein the pressure gauge is plate-shaped and is inclined so that the thickness of the lower surface and back surface decreases downward.

5. 4. The method for producing a hot-dip metal coated steel strip according to claim 3, wherein the pressure gauge is plate-shaped and is inclined so that the thickness of the lower surface and back surface decreases downward.

6. A gas wiping device that controls the amount of molten metal coating by spraying wiping gas onto a steel strip immersed in a molten metal coating bath, a pair of wiping nozzles arranged opposite the front and back surfaces of the steel strip across the steel strip, and spraying wiping gas onto the front and back surfaces; a pressure gauge that is installed between the pair of wiping nozzles and on the outside of the end portion in the width direction of the steel strip, and that measures the spray pressure of the wiping gas; A gas wiping device comprising:

7. The wiping gas supply system further includes a control device for controlling the spray pressure of the wiping gas. The gas wiping device according to claim 6, wherein the control device adjusts the supply pressure to the wiping nozzle so that the spray pressure measured by the pressure gauge falls within a predetermined range.

8. The pressure gauge has a plate-like portion, an inclined portion inclined so that the plate thickness becomes thinner downward on the front and back surfaces, and a sensor portion for measuring the pressure of the wiping gas, 8. The gas wiping device according to claim 6, wherein the inclined portion is provided below the plate-like portion, and the sensor portions are provided on the front and back surfaces of the plate-like portion.

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