Gas injection device, facility for manufacturing hot-dip plated metal strip, method for manufacturing hot-dip plated metal strip, and method for cleaning gas injection device

Abstract

Provided is a gas injection device capable of suppressing the occurrence of chipping even in a case where a non-metal material such as a ceramic is used as the material of a gas wiping nozzle. The gas injection device blows a wiping gas onto a metal strip. The gas injection device has a gas wiping nozzle which is formed of a material having heat resistance to molten metal and which has a gas injection port through which the wiping gas is injected. An edge surface of the gas injection port in which the injection port is formed is a curved surface or is formed such that there is an obtuse angle between the edge surface and a surface adjacent to the edge surface. According to the gas injection device of the present invention, the gas-injection port edge surface in which the injection port is formed is a curved surface or is formed such that there is an obtuse angle between the edge surface and the surface adjacent to the edge surface, and therefore the load received from a cleaning tool or the like can be dispersed, thus enabling chipping of the wiping nozzle to be suppressed.

Description

Gas injection device, hot-dip plated metal strip manufacturing equipment, hot-dip plated metal strip manufacturing method, and gas injection device cleaning method

[0001] The present invention relates to a gas injection device for spraying wiping gas onto a metal strip, a manufacturing facility for a hot-dip galvanized metal strip, a manufacturing method for a hot-dip galvanized metal strip, and a cleaning method for a gas injection device.

[0002] Hot-dip galvanized metal strips, which are a type of hot-dip metal coated metal strip, are widely used in the fields of building materials, automobiles, home appliances, etc. Hot-dip galvanized metal strips are required to have excellent appearances for these applications. The appearance of hot-dip galvanized metal strips after painting is strongly affected by surface defects such as uneven coating thickness, scratches, and foreign matter adhesion. Therefore, hot-dip galvanized metal strips are required to be free of surface defects.

[0003] Hot-dip metal-plated metal strips are generally produced in a continuous hot-dip metal plating line, which involves continuously introducing a metal strip into molten metal stored in a plating tank, spraying wiping gas from a gas wiping nozzle onto the metal strip to adjust the plating thickness, cooling the metal strip, and then performing post-processing.

[0004] For example, a pair of gas wiping nozzles are arranged above the plating tank, sandwiching the metal strip. The molten metal scattered by the sprayed wiping gas is also called splash. If the splash adheres to the inside of the slit of the gas wiping nozzle, the flow path of the wiping gas is blocked. This makes it impossible to spray the wiping gas uniformly from the gas wiping nozzle, resulting in surface defects such as uneven film thickness.

[0005] Therefore, in Patent Documents 1 and 2, ceramics that do not undergo an alloying reaction with the molten metal are used as the material for the gas wiping nozzle to prevent the adhesion of splashes inside the slit. Also, in Patent Document 3, a cleaning jig made of a long, thin metal plate is inserted into the slit and moved in the width direction of the metal strip to remove the molten metal splashes.

[0006] Japanese Utility Model Application Publication No. 62-203260 Japanese Utility Model Application Publication No. 62-203261 Japanese Patent Application Publication No. 2018-70904

[0007] However, the gas wiping nozzles described in Patent Documents 1 and 2 have a problem in that they cannot completely remove molten metal droplets. Furthermore, when a gas wiping nozzle was cleaned using the cleaning tool described in Patent Document 3, chipping occurred. When a chip is formed in the gas wiping nozzle, it causes a disturbance in the flow of wiping gas. When the flow of wiping gas is disturbed, unevenness in the amount of molten metal adhered occurs, and there is a risk of a surface defect forming a linear mark in the direction of travel of the metal strip. When a chip is formed in the gas wiping nozzle to the extent that a surface defect occurs, the gas wiping nozzle must be replaced, resulting in a problem of reduced productivity.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a gas injection device etc. that can suppress the occurrence of chipping even when a non-metallic material such as ceramics is used as the material for the gas wiping nozzle.

[0009] In order to solve the above problems, the present invention has the following features.

[0010] [1] A gas injection device for spraying wiping gas onto a metal strip, comprising a gas wiping nozzle formed of a material having heat resistance to molten metal and having a gas injection port through which the wiping gas is injected, wherein an edge surface of the gas injection port is curved or an angle formed between the edge surface and an adjacent surface is an obtuse angle. [2] The gas injection device according to [1], wherein the edge surface of the gas injection port is chamfered with a C chamfer of C0.10 or more, or the edge surface of the gas injection port is chamfered with an R chamfer of R0.05 or more. [3] A manufacturing facility for a hot-dip galvanized metal strip, comprising: a coating tank configured to store molten metal, a gas injection device provided above the coating tank, and a transport section that transports the metal strip toward the coating tank and the gas injection device, wherein the gas injection device is formed of a material that is heat resistant to the molten metal and has a gas wiping nozzle having a gas injection port through which a wiping gas is injected, and wherein the edge surface of the gas injection port through which the gas injection port is formed is curved or the angle formed between the edge surface and an adjacent surface is an obtuse angle. [4] A manufacturing method for a metal strip, comprising: a manufacturing step of manufacturing a hot-dip galvanized metal strip by spraying a wiping gas onto a metal strip pulled up from molten metal to adjust the amount of molten metal adhering to the surface of the metal strip, the manufacturing method comprising: an adjustment step of spraying the wiping gas from the gas wiping nozzle of the gas injection device described in [1] or [2] to adjust the amount of molten metal adhering to the metal strip. [5] A method for cleaning the gas injection device, comprising a removal step of inserting a cleaning tool into the gas wiping nozzle of the gas injection device according to [1] or [2] to remove molten metal adhering to the gas injection nozzle.

[0011] According to the gas injection device of the present invention, the edge surface of the injection port where the gas injection port is formed is curved, or the angle between the edge surface and the adjacent surface is obtuse, so that the load received from the cleaning tool or the like can be dispersed. This makes it possible to prevent chipping of the edge surface of the injection port. As a result, the gas wiping nozzle of the gas injection device can be used repeatedly and for a long period of time, thereby improving productivity and reducing running costs.

[0012] 2. An explanatory diagram of continuous hot-dip metal plating equipment equipped with a gas injection device. An explanatory diagram showing a gas wiping nozzle. An enlarged cross-sectional view of a first nozzle member taken along line A-A' in FIG. 2. An enlarged cross-sectional view of another first nozzle member taken along line A-A' in FIG. 2. A perspective view of a cleaning jig. An explanatory diagram showing an aspect of cleaning a gas wiping nozzle using a cleaning jig. A graph showing the occurrence of chipping in a gas wiping nozzle with C-chamfered edge surfaces. A graph showing the occurrence of chipping in a gas wiping nozzle with R-chamfered edge surfaces.

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 shows a continuous hot-dip galvanized metal strip manufacturing facility 100 equipped with a gas injection device according to one embodiment of the present invention.

[0014] As shown in FIG. 1, the continuous hot-dip plated metal strip manufacturing equipment 100 is equipment for manufacturing a hot-dip plated metal strip by immersing a metal strip S in molten metal M, thereby continuously depositing the molten metal M on the front and back surfaces of the metal strip S.

[0015] Although the metal strip is not particularly limited, an example using a steel strip S will be described in this embodiment. The steel strip S is, for example, one that has been annealed in a continuous annealing furnace in a reducing atmosphere.

[0016] The continuous hot-dip plated metal strip manufacturing equipment 100 includes a plating tank 10 in which molten metal M is stored, a snout 20 that supplies steel strip S to the plating tank 10, and a gas injection device 30 that adjusts the amount of molten metal M adhering to the steel strip S.

[0017] The snout 20 is a member formed in a hollow cylindrical shape. The snout 20 is provided so as to cover the periphery of the steel strip S. Therefore, the snout 20 is a member that partitions the space through which the steel strip S passes. The snout 20 is formed, for example, so that the cross section perpendicular to its axial direction is rectangular. The upper end side of the snout 20 is connected to, for example, the outlet side of a continuous annealing furnace, and the lower end side is connected to the inside of the coating tank 10.

[0018] The plating tank 10 is formed in the shape of a tank with a bottom so that it can store molten metal M. The plating tank 10 is formed with an open top. The lower end side of the snout 20 is inserted so as to be immersed in the molten metal M stored in the plating tank 10. A sink roll 40 and a support roll 50 are arranged in the plating tank 10. The steel strip S is stretched across the sink roll 40, passes through the support roll 50, and is discharged to the outside from the opening of the plating tank 10. The sink roll 40 applies an appropriate tension to the steel strip S and functions as a transport section that transports the steel strip S toward the plating tank 10 and the gas injection device 30.

[0019] The molten metal M is not particularly limited, and may be, for example, aluminum, tin, or the like in addition to zinc. When zinc is used as the molten metal M, the steel strip S is produced as a hot-dip galvanized metal strip. The hot-dip galvanized metal strip may be, for example, a galvanized steel sheet (GI) that is not subjected to an alloying treatment after the hot-dip galvanizing treatment, or a galvanized steel sheet (GA) that is subjected to an alloying treatment.

[0020] The gas injection device 30 has a gas wiping nozzle 31 that injects wiping gas. In this embodiment, a pair of gas wiping nozzles 31 are arranged so as to sandwich the front and back surfaces of the steel strip S. The wiping gas is not particularly limited, but for example, a mixture of exhaust gas from a combustor and air can be used.

[0021] The steel strip S passes through the snout 20 and is continuously introduced into the molten metal M in the coating tank 10. Thereafter, the steel strip S is pulled up from the molten metal M in the coating tank 10 via the sink roll 40 and support roll 50 of the molten metal M.

[0022] Excess molten metal M adhering to the steel strip S is removed by wiping gas injected from a gas injection device 30. Thereafter, the steel strip S is cooled by cooling equipment (not shown) and is led to a subsequent process, where hot-dip metal-plated steel strip S is continuously produced.

[0023] In this manner, the wiping gas is sprayed onto both sides of the steel strip S, thereby scraping off excess molten metal M. As a result, the amount of molten metal M deposited on the steel strip S is made uniform in the width direction and the length direction.

[0024] Fig. 2 shows an overview of the gas wiping nozzle 31. As shown in Fig. 2, the gas wiping nozzle 31 has a gas supply unit 32 that supplies a wiping gas and a nozzle header 34 that connects a nozzle unit 33 that sprays the wiping gas.

[0025] The nozzle header 34 is formed in a substantially rectangular shape extending in the length direction DX, the depth direction DY, and the width direction DZ. A gas supply pipe is connected to the base end (rear end) of the nozzle header 34.

[0026] The nozzle section 33 has a first nozzle member 33 a and a second nozzle member 33 b that are arranged opposite each other. In this embodiment, the first nozzle member 33 a is arranged on the upper side, and the second nozzle member 33 b is arranged on the lower side.

[0027] The first nozzle member 33 a and the second nozzle member 33 b are provided with a gap between them, so that a slit-shaped gas injection port 35 is formed between the first nozzle member 33 a and the second nozzle member 33 b.

[0028] Direction DX is a direction along the width direction of the steel strip S. Direction DZ is a direction along the conveying direction of the steel strip S, i.e., the plate length direction of the steel strip S. Direction DZ is also a direction perpendicular to direction DX. Direction DY is a direction along the plate thickness direction of the steel strip S. Direction DY is a direction perpendicular to direction DX and direction DZ.

[0029] The gas injection port 35 has a slit-shaped opening extending in the direction DX. The gas injection port 35 is formed by the first nozzle member 33a and the second nozzle member 33b facing each other in the direction DZ. That is, the gas injection port 35 is formed so that the distance between the first nozzle member 33a and the second nozzle member 33b in the direction DZ is the opening height. The gas injection port 35 has a slit-shaped opening extending in the direction DY and is connected to the nozzle header 34.

[0030] The gas injection port 35 is formed so that its length along the direction DX is longer than the width of the steel strip S. By forming the gas injection port 35 in this manner, it is possible to accommodate a variety of widths of the steel strip S. Furthermore, even if the steel strip S shifts in the width direction when being pulled up from the plating tank 10, for example, the gas injection port 35 is formed to be of sufficient length, so that the wiping gas can be injected across the entire width direction of the steel strip S.

[0031] The gas wiping nozzle 31 is made of a material that is heat resistant to molten metal. For example, the material has a fracture toughness of 3 MPa m １／２ More than 5 MPa m １／２ More preferably, it is 7 MPa m １／２ It would be good if that were the case.

[0032] The material preferably has the properties of low wettability with molten metal, low plastic deformability, and a low coefficient of linear expansion, such as ceramic materials, carbon materials, carbon fiber reinforced carbon composite materials, and ceramic matrix composite materials (hereinafter also referred to as ceramic materials or sintered bodies).

[0033] The ceramic material is not particularly limited, but examples thereof include alumina, sialon, silicon nitride, zirconia, barium titanate, hydroxyapatite, silicon carbide (SiC), and fluorite.

[0034] The carbon material is not particularly limited, but examples thereof include graphite. Note that graphite oxidizes and volatilizes in a highly oxidizing atmosphere, so it is preferable to coat the surface with silica or the like.

[0035] Furthermore, ceramic materials, i.e., sintered bodies, preferably have a bending strength of 600 MPa or more, and more preferably 800 MPa or more. Examples of ceramic materials that satisfy this bending strength include zirconia, silicon nitride, and sialon. These materials are less susceptible to plastic deformation, and substantial deformation can be suppressed if the strength is below the breaking strength. Other desirable properties include a Vickers hardness of 800 HV or more, and more preferably 1000 HV or more.

[0036] Furthermore, if the thermal shock resistance of the ceramic material, i.e., the sintered body, is lower than the temperature of the wiping gas, it may crack. Therefore, it is preferable that the thermal shock resistance of the ceramic material be equal to or higher than the temperature of the supplied wiping gas. In particular, when a high-temperature gas is used as the wiping gas, the thermal shock resistance of the ceramic material is preferably 430°C or higher, and more preferably 600°C or higher.

[0037] In particular, the linear expansion coefficient of the first nozzle member 33a and the second nozzle member 33b is preferably 1 / 2 or less, and more preferably 1 / 3 or less, of the linear expansion coefficient of the nozzle header .

[0038] By setting the linear expansion coefficients of the first nozzle member 33a and the second nozzle member 33b in this manner, it is possible to prevent the first nozzle member 33a and the second nozzle member 33b from being deformed by the influence of heat. Note that, for example, stainless steel or chrome molybdenum steel can be used as the material for the nozzle header 34. The linear expansion coefficients of stainless steel and chrome molybdenum steel are 10 to 18 × 10 －６ / K.

[0039] The flow velocity of the discharged gas differs between the tip end and the base end of the gas wiping nozzle 31. Therefore, when a metal such as chromium-molybdenum steel or stainless steel is used as the material for the gas wiping nozzle 31, a difference in heat transfer coefficient occurs between the tip end and the base end of the gas wiping nozzle in a high-temperature environment. As a result, the rate of temperature rise differs between the tip end and the base end of the gas wiping nozzle.

[0040] This causes a difference in expansion between the tip and base ends of the gas wiping nozzle 31, which may result in uneven deformation of the gas wiping nozzle. When the gas wiping nozzle 31 deforms, deviations in the opening length in the width direction, i.e., deviations in the slit gap, occur. As a result, variations in the plating deposition amount in the plate width direction occur. This increases the frequency of replacement of the gas wiping nozzle 31, resulting in problems such as higher maintenance costs. For these reasons, it is preferable to use the above-mentioned ceramic materials, i.e., sintered bodies, used for the gas wiping nozzle 31.

[0041] 3 shows an enlarged cross section of the first nozzle member 33a. The second nozzle member 33b is formed symmetrically to the first nozzle member 33a. Therefore, the first nozzle member 33a and the second nozzle member 33b will be described together using this figure. As shown in FIG. 3, the edge surface 36 of the gas injection port 35 is a surface that is formed inward from the edge of the gas injection port 35. The edge surface 36 of the gas injection port 35 is formed as a curved surface.

[0042] The edge surface 36 of the gas jet nozzle 35 is preferably chamfered with an R of 0.05 or more. Such chamfering also makes it possible to distribute the load received from a cleaning tool or the like, and to prevent chipping of the gas wiping nozzle.

[0043] In terms of preventing chipping of the gas wiping nozzle, a radius of 0.05 or more is sufficient to provide the desired effect. However, since it is difficult to process large ceramics with a radius of less than 0.05, the practical lower limit is 0.05.

[0044] FIG. 4 shows an enlarged cross section of another embodiment of the first nozzle member 33a. The second nozzle member 33b is formed symmetrically to the first nozzle member 33a. Therefore, the first nozzle member 33a and the second nozzle member 33b will be described together using this figure. As shown in FIG. 4, the edge surface 36 of the gas ejection port 35 is not limited to being formed by a curved surface as shown in FIG. 3, and the angle formed between the edge surface 36 and an adjacent surface 37 may be an obtuse angle. Note that the surface 37 adjacent to the edge surface 36 is a surface formed from the edge surface 36 toward the inside of the gas ejection port 35.

[0045] The edge surface 36 of the gas jet nozzle 35 is preferably chamfered to a chamfering angle of C0.10 or greater. By chamfering the edge surface 36 to a chamfering angle of C0.10 or greater, the load applied by a cleaning tool or the like can be dispersed, and chipping of the gas wiping nozzle can be suppressed. Note that a chamfering angle of C0.10 or greater is sufficient to prevent chipping of the gas wiping nozzle.

[0046] A method for manufacturing a hot-dip galvanized metal strip using the gas injection device 30 described above will now be described. When the conveyance of the steel strip S begins, the gas injection device 30 injects wiping gas from the gas wiping nozzle 31 toward the steel strip S.

[0047] That is, the gas injection device 30 performs an adjustment process in which wiping gas is sprayed onto the steel strip S pulled up from the molten metal M to adjust the amount of molten metal M adhering to the front and back surfaces of the steel strip S.

[0048] It is preferable that the temperature T (°C) of the wiping gas injected from the gas injection device 30 and the melting point TM (°C) of the molten metal satisfy the relationship of the following formula (1): TM-150≦T≦TM+250 (1)

[0049] When the temperature T (°C) of the wiping gas satisfies the relationship of formula (1), it is possible to suppress the cooling and solidification of the molten metal M. As a result, the viscosity of the molten metal is less likely to vary, and the occurrence of molten metal wrinkles can be suppressed.

[0050] If the temperature T (°C) of the wiping gas is less than the lower limit of formula (1), the wiping gas is less likely to affect the fluidity of the molten metal M, and therefore the effect of suppressing the occurrence of molten metal wrinkles tends to be less likely to be obtained. Also, if the temperature T (°C) of the wiping gas exceeds the upper limit of formula (1), alloying with the molten metal M is promoted, which may deteriorate the appearance of the steel strip S.

[0051] The method for increasing the temperature of the wiping gas is not particularly limited. For example, the temperature may be increased using a heat exchanger, or the temperature may be increased by mixing the combustion exhaust gas from the annealing furnace with air.

[0052] The gas wiping nozzle 31 of the gas injection device 30 may be cleaned using a cleaning jig. Fig. 5 shows the configuration of the cleaning jig. As shown in Fig. 5, the cleaning jig 60 has an insertion portion 61 formed in a plate shape and a holding portion 62 that holds the insertion portion 61.

[0053] For example, a stainless steel metal plate can be used as the insertion portion 61. The holding portion 62 is formed in a rod shape. The insertion portion 61 is fixed to one axial end of the holding portion 62 with two bolts.

[0054] Fig. 6 shows an example of cleaning the gas wiping nozzle using a cleaning tool. As shown in Fig. 6, cleaning is performed by inserting the insertion portion 61 of the cleaning tool 60 into the gas jet port 35 and moving the cleaning tool 60 from one end of the opening of the gas jet port 35, i.e., from one end in the direction DX shown in Fig. 2 to the other end in the direction DX. This executes the removal step in the method for cleaning the gas injection device 30, and removes the molten metal M adhering to the gas jet port 35.

[0055] As described above, according to the gas injection device 30 etc. of the present invention, the edge surface 36 of the gas injection port 35 where the gas injection port 35 is formed is curved, or the angle formed between the edge surface 36 and the adjacent surface is an obtuse angle, so that the load received from a cleaning tool etc. can be dispersed. This makes it possible to prevent chipping of the edge surface 36 of the gas injection port 35. As a result, the gas wiping nozzle 31 of the gas injection device 30 can be used repeatedly and for a long period of time, thereby improving productivity and reducing running costs.

[0056] (Test Example 1: Chipping of Gas Wiping Nozzle) As a control, a ceramic gas wiping nozzle with an unchamfered tip was used. When the control gas wiping nozzle was cleaned using a cleaning jig, chipping occurred.

[0057] It is believed that the chipping of the gas wiping nozzle was caused by the impact of contact with the cleaning tool. Specifically, it is believed that the chipping of the gas wiping nozzle was caused by the corners of the plate-shaped insertion part or the corners of the bolts securing the insertion part and the holding part rubbing against the edge surface of the gas jet orifice when cleaning the gas wiping nozzle. In addition, chipping tends to occur on the edge surface of the gas jet orifice when the metal strip is poorly shaped and meanders, or when an impact is applied.

[0058] As a result of the inventors' investigation of comparative examples, they found that when chipping of more than 0.5 mm occurs on the edge surface of the nozzle, disturbances in the wind speed of the wiping gas are induced. Furthermore, they found that disturbances in the wind speed of the wiping gas cause unevenness in the amount of molten metal deposited. Therefore, the inventors investigated the shape of the gas wiping nozzle to prevent chipping of more than 0.5 mm in the gas wiping nozzle.

[0059] The opening height, i.e., the slit width, of the gas wiping nozzle used in the test was 1.4 mm, and the width of the gas wiping nozzle was 1700 mm. The insertion part of the cleaning jig used for cleaning was a stainless steel (SUS304) metal plate with a thickness of 1.3 mm.

[0060] The gas wiping nozzle was cleaned 50 times, and the number of chips with a diameter of 0.5 mm or more was counted. The number of cleanings was determined as the average number of cleanings of the gas wiping nozzle in one operation cycle.

[0061] Cleaning was performed by inserting the insertion portion of the cleaning tool into the nozzle and sliding it. Sliding the cleaning tool from one end of the width of the gas wiping nozzle to the other was counted as one cleaning.

[0062] The number of chips was determined by observing the edge of the gas wiping nozzle's gas jet nozzle after the experiment. The number of chips on the gas wiping nozzle with C-chamfered edge is shown in Figure 7. The number of chips on the gas wiping nozzle with R-chamfered edge is shown in Figure 8.

[0063] As shown in Figure 7, the control C0, in which the gas wiping nozzle was not chamfered, had 29 chips with a diameter of 0.5 mm or larger. Furthermore, the gas wiping nozzle C0.05, in which the gas wiping nozzle was chamfered, had 16 chips with a diameter of 0.5 mm or larger. Thus, it was found that applying C-chamfering to the gas wiping nozzle significantly reduced the occurrence of chips.

[0064] Furthermore, in the case of C0.10, where the gas wiping nozzle was chamfered to C0.10, there were five chips with a diameter of 0.5 mm or larger. In the case of C0.20, where the gas wiping nozzle was chamfered to C0.20, there were three chips with a diameter of 0.5 mm or larger. In the case of C2, where the gas wiping nozzle was chamfered from C0.30 to C2.00, there were zero chips with a diameter of 0.5 mm or larger. As such, it was found that the number of chips decreased as the C chamfering increased. From these results, it can be seen that by performing C chamfering, the occurrence of chips with a diameter of 0.5 mm or larger in the gas wiping nozzle can be suppressed more effectively than in the case where C chamfering was not performed.

[0065] As shown in Figure 8, the control C0, in which the gas wiping nozzle was not chamfered, had 29 chips with a diameter of 0.5 mm or larger. Furthermore, the gas wiping nozzle with R0.05 chamfering had 6 chips with a diameter of 0.5 mm or larger. Thus, it was found that applying R-chamfering to the gas wiping nozzle significantly reduced the occurrence of chips.

[0066] Furthermore, when the gas wiping nozzle was chamfered to R0.10 (R0.10) to R0.50 (R0.50), there were no chips of Φ0.5 mm or more. Thus, it was found that the number of chips decreased as the chamfering increased. From these results, it can be seen that R-chamfering can suppress the occurrence of chips of Φ0.5 mm or more in the gas wiping nozzle compared to the case where R-chamfering was not performed.

[0067] As described above, it was found that the number of chips decreased as the chamfering increased, whether it was C-chamfered or R-chamfered. This is thought to be the result of the stress during jig contact decreasing as the contact area increased. In other words, it was found that chipping of the gas wiping nozzle can be suppressed by dispersing stress through chamfering.

[0068] Furthermore, when the chamfering amount is C 0.10 or more and R 0.05 or more, it is possible to obtain a particularly effective stress dispersion effect, and it was found that it is possible to prevent the occurrence of chipping of the gas wiping nozzle exceeding φ 0.5 mm when an external force is applied. In particular, R-chamfering is effective even with a smaller chamfering amount than C-chamfering, because no corners are created during the chamfering process.

[0069] It has been found that by subjecting the gas wiping nozzle to such processing, the gas wiping nozzle is less likely to chip when cleaned, enabling it to be used for a long period of time.

[0070] A similar test was also conducted using a gas wiping nozzle made of chrome molybdenum steel. The gas wiping nozzle was not chamfered. No chipping was observed on the gas wiping nozzle.

[0071] In addition, a manufacturing test was conducted using this gas wiping nozzle. When the gas wiping nozzle was observed, molten zinc was found to be attached to the gas wiping nozzle. The zinc attached to the gas wiping nozzle could not be removed even by cleaning. In other words, it is believed that an alloying reaction occurred between the gas wiping nozzle and the molten zinc, making it difficult to remove the zinc.

[0072] Furthermore, the deviation in the amount of zinc deposited in the width direction of the plate was significantly worse than when a ceramic gas wiping nozzle was used. Observation of the gas wiping nozzle after removal revealed that the gap in the center of the nozzle width had expanded by approximately 1 mm from before the start of the test. It is believed that the deviation in the amount of molten zinc deposited was caused by this gap.

[0073] A similar test was conducted on a gas wiping nozzle made of austenitic / ferritic two-layer stainless steel that had been HIP-treated. The gas wiping nozzle was not chamfered. No chipping was observed on the gas wiping nozzle.

[0074] In addition, a manufacturing test was conducted using this gas wiping nozzle. When the gas wiping nozzle was observed, molten zinc was found to be attached to the gas wiping nozzle. The zinc attached to the gas wiping nozzle could be removed by cleaning.

[0075] Furthermore, the deviation in the amount of zinc deposited in the width direction of the plate was significantly worse than when a ceramic gas wiping nozzle was used. Observation of the gas wiping nozzle after removal revealed that the gap in the center of the nozzle width had expanded by approximately 1 mm from before the start of the test. It is believed that the deviation in the amount of molten zinc deposited was caused by this gap.

[0076] As described above, metal gas wiping nozzles are not suitable for use in high-temperature environments because they cause deviations in the amount of molten zinc deposited.

[0077] 100 Manufacturing equipment for continuous hot-dip galvanized metal strip 10 Galvanizing tank 30 Gas injection device 31 Gas wiping nozzle 36 Edge surface 37 Adjacent surface 40 Sink roll

Claims

1. A gas injection device for spraying wiping gas onto a metal strip, comprising a gas wiping nozzle formed of a material having heat resistance against molten metal and having a gas injection port from which the wiping gas is injected, wherein the edge surface of the gas injection port is curved or the angle between the edge surface and an adjacent surface is an obtuse angle.

2. A gas injection device as set forth in claim 1, wherein the edge surface of the gas injection port is chamfered with a C chamfer of C0.10 or more, or the edge surface of the gas injection port is chamfered with an R chamfer of R0.05 or more.

3. A manufacturing facility for hot-dip plated metal strip, comprising: a plating tank capable of storing molten metal; a gas injection device provided above the plating tank; and a transport section for transporting the metal strip toward the plating tank and the gas injection device, wherein the gas injection device is formed of a material having heat resistance to molten metal and has a gas wiping nozzle having a gas injection port from which a wiping gas is injected, and the edge surface of the gas injection port is curved or the angle between the edge surface and an adjacent surface is an obtuse angle.

4. A method for manufacturing a metal strip, in which a wiping gas is sprayed onto a metal strip pulled up from molten metal to adjust the amount of molten metal adhering to the surface of the metal strip, comprising an adjustment step of spraying the wiping gas from the gas wiping nozzle of the gas injection device described in claim 1 or 2 to adjust the amount of molten metal adhering to the metal strip.

5. A method for cleaning the gas injection device according to claim 1 or 2, comprising a removal step of inserting a cleaning tool into the gas wiping nozzle of the gas injection device to remove molten metal adhering to the gas injection nozzle.

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