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

Abstract

Provided is a gas injection device capable of suppressing the occurrence of chipping and preventing surface defects on a metal strip that accompany the generation of splashing, 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 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. The edge surface of the injection port is subjected to C surface chamfering of C0.10 or more and less than C1.10, or the edge surface of the injection port is subjected to R chamfering of R0.05 or more and R0.50 or less.

Description

[Technical Field]

[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. [Background technology]

[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 molten metal are used as the material for the gas wiping nozzle to prevent splashes from adhering inside the slit. In addition, 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. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Utility Model Application Publication No. 62-203260 [Patent Document 2] Japanese Utility Model Application Publication No. 62-203261 [Patent Document 3] Japanese Patent Application Publication No. 2018-70904 Summary of the Invention [Problem to be solved by the invention]

[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, chips occurred. When chips form in the gas wiping nozzle, they cause disturbances 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 surface defects forming linear streaks in the direction of travel of the metal strip. When chips form in the gas wiping nozzle to the extent that surface defects occur, 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 or the like that can suppress the occurrence of chipping and surface defects on a metal strip caused by splashing, even when a non-metallic material such as ceramics is used for the gas wiping nozzle. [Means for solving the problem]

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

[0010] [1] A gas injection device that sprays wiping gas onto a metal strip, a gas wiping nozzle formed of a material having heat resistance against molten metal and having a gas jetting port through which the wiping gas is jetted; 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, The edge surface of the gas injection port is chamfered to a C of not less than C0.10 and not more than C1.10, or A gas injection device, wherein the edge surface of the gas injection port is chamfered with an R of 0.05 or more and R of 0.50 or less. [2] a plating tank configured to be able to store molten metal; a gas injection device provided above the plating tank; A manufacturing facility for a hot-dip galvanized metal strip, comprising the coating tank and a conveying unit that conveys the metal strip toward the gas injection device, the gas injection device is formed of a material having heat resistance against molten metal and has a gas wiping nozzle having a gas injection port from which a wiping gas is injected; 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, The edge surface of the gas injection port is chamfered to a C of not less than C0.10 and not more than C1.10, or The edge surface of the gas injection port is chamfered to have an R of 0.05 or more and R of 0.50 or less. [3] A method for manufacturing a metal strip, comprising blowing 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 method comprising: [1] A method for manufacturing a hot-dip plated metal strip, comprising an adjusting step of injecting the wiping gas from the gas wiping nozzle of the gas injection device described in [1] to adjust the amount of molten metal adhering to the metal strip. [4] [1] 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 described in [1] to remove molten metal adhering to the gas injection nozzle. [Effects of the Invention]

[0011] According to the gas injection device of the present invention, the edge surface of the gas injection port is curved or the angle between the edge surface and the adjacent surface is formed at an obtuse angle, thereby dispersing the load received from a cleaning tool or the like. This makes it possible to prevent chipping of the wiping nozzle. As a result, the 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. Furthermore, the edge surface of the gas injection port is chamfered with a C chamfer of C0.10 or more and less than C1.10, or with an R chamfer of R0.05 or more and R0.50 or less. This makes it possible to suppress the occurrence of splashing. Therefore, it is possible to suppress surface defects associated with the occurrence of splashing. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram of a continuous hot-dip metal plating facility equipped with a gas injection device. [Figure 2] FIG. 2 is an explanatory diagram showing a gas wiping nozzle. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the first nozzle member taken along line AA' in FIG. 2. [Figure 4] 3 is an enlarged cross-sectional view of another first nozzle member taken along line AA' in FIG. 2. FIG. [Figure 5] FIG. [Figure 6] FIG. 10 is an explanatory diagram showing an aspect of cleaning the gas wiping nozzle using a cleaning jig. [Figure 7] 10 is a graph showing the occurrence of chipping in a gas wiping nozzle having a C-chamfered edge surface. [Figure 8] 10 is a graph showing the occurrence of chipping in a gas wiping nozzle with R-chamfered edge surfaces. [Figure 9] FIG. 1 is an explanatory diagram showing an outline of a defect meter. DETAILED DESCRIPTION OF THE INVENTION

[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, with a rectangular cross section perpendicular to its axial direction. 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 over 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 33a and a second nozzle member 33b arranged opposite each other. In this embodiment, the first nozzle member 33a is arranged on the upper side, and the second nozzle member 33b is arranged on the lower side.

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

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

[0029] The gas ejection port 35 has a slit-shaped opening that extends in the direction DX. The gas ejection 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 ejection 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 ejection port 35 has a slit-shaped opening that extends in the direction DY and is connected to the nozzle header 34.

[0030] The gas ejection 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 ejection 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 coating tank 10, for example, the gas ejection port 35 is formed to be of sufficient length, so that it is possible to eject the wiping gas 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 or more, preferably 5 MPa m 1 / 2 More preferably, 7 MPa m 1 / 2 It would be good if that were the case.

[0032] The material preferably has the following characteristics: low wettability with molten metal, low plastic deformability, and low coefficient of linear expansion. Examples of such materials include 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, 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, 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. The nozzle header 34 can be made of, for example, stainless steel or chrome-molybdenum steel. The linear expansion coefficients of stainless steel and chrome-molybdenum steel are in the range of 10 to 18×10. -6 / K.

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

[0040] This causes a difference in expansion between the tip and base ends of the gas wiping nozzle, which can lead to uneven deformation of the gas wiping nozzle. When the gas wiping nozzle 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 gas wiping nozzle replacement, resulting in problems such as high maintenance costs. For these reasons, it is preferable to use the above-mentioned ceramic materials, i.e., sintered bodies.

[0041] FIG. 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 ejection port 35 is a surface that is formed inward from the edge 35a of the gas ejection port 35. The edge surface 36 of the gas ejection port 35 is formed as a curved surface.

[0042] The edge surface 36 of the gas injection port 35 is preferably chamfered with an R of 0.05 or more and R of 0.50 or less, more preferably with an R of 0.10 or more and R of 0.50 or less, and even more preferably with an R of 0.25 or more and R of 0.35 or less.

[0043] By chamfering the edge with an R of 0.05 or more, the load from cleaning tools and the like can be dispersed, preventing chipping of the gas wiping nozzle. In addition, by chamfering the edge surface 36 with an R of 0.50 or less, splashing can be prevented.

[0044] In terms of preventing chipping of the gas wiping nozzle, a radius of 0.05 or greater is sufficient to prevent chipping. However, since it is difficult to process large ceramics with a radius of less than 0.05, the practical lower limit is 0.05.

[0045] 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 surfaces 36 of the first nozzle member 33a and the second nozzle member 33b are not limited to being formed as curved surfaces as shown in FIG. 3, and the angle formed between the edge surface 36 and the 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.

[0046] The edge surface 36 of the gas wiping nozzle is preferably chamfered to a C of not less than C0.10 and not more than C1.10, more preferably to a C of not less than C0.20 and not more than C0.80, and even more preferably to a C of not less than C0.30 and not more than C0.50.

[0047] The edge surface 36 is chamfered to a C of 0.10 or more, which can distribute the load received from cleaning tools and the like, thereby preventing chipping of the gas wiping nozzle. From the viewpoint of preventing chipping of the gas wiping nozzle, a chamfer of C of 0.10 or more can be effectively achieved without any problems. Furthermore, the edge surface 36 is chamfered to a C of less than C of 1.10, which can prevent splashing.

[0048] A description will now be given of a method for manufacturing a hot-dip galvanized metal strip using the above-described gas injection device 30. When transportation 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.

[0049] That is, the gas injection device 30 performs an adjustment step 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.

[0050] 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)

[0051] 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 creases can be suppressed.

[0052] If the temperature T (°C) of the wiping gas is less than the lower limit of formula (1), the wiping gas will have less effect on the fluidity of the molten metal M, and the effect of suppressing the occurrence of wrinkles will tend to be less pronounced. Also, if the temperature T (°C) of the wiping gas exceeds the upper limit of formula (1), alloying with the molten metal M will be promoted, which may deteriorate the appearance of the steel strip S.

[0053] 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.

[0054] A cleaning jig is preferably used to clean the gas wiping nozzle 31 of the gas injection device 30. 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.

[0055] 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.

[0056] Fig. 6 shows an example of cleaning the gas wiping nozzle using a cleaning jig. As shown in Fig. 6, cleaning is performed by inserting the insertion portion 61 of the cleaning jig 60 into the gas jet nozzle 35 and moving the cleaning jig 60 from one end of the opening of the gas jet nozzle 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 nozzle 35.

[0057] 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 or the like can be dispersed. This makes it possible to prevent chipping of the gas wiping nozzle 31. 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. [Example]

[0058] (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 the cleaning jig, chipping occurred.

[0059] 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 to the holding part rubbing against the gas wiping nozzle when cleaning the gas wiping nozzle. In addition, chipping of the gas wiping nozzle tends to occur when the metal strip is both poorly shaped and meandering, or when the gas wiping nozzle is subjected to an impact.

[0060] 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 gas jet nozzle, it induces disturbances in the wind speed of the wiping gas. They also found that disturbances in the wind speed of the wiping gas cause unevenness in the amount of molten metal adhered. 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.

[0061] The opening height, which is 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 1.3 mm thick stainless steel (SUS304) metal plate.

[0062] 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 times the gas wiping nozzle was cleaned in one operating cycle.

[0063] Cleaning was performed by inserting the inserting part 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.

[0064] The number of chips was determined by observing the gas wiping nozzle after the experiment. The number of chips on the gas wiping nozzle with C-chamfered edges is shown in Figure 7. The number of chips on the gas wiping nozzle with R-chamfered edges is shown in Figure 8.

[0065] As shown in Figure 7, the control C0, where the gas wiping nozzle was not chamfered, had 29 chips of Φ0.5 mm or larger. In addition, the gas wiping nozzle C0.05, where the gas wiping nozzle was chamfered, had 16 chips of Φ0.5 mm or larger. This shows that applying C-chamfering to the gas wiping nozzle significantly reduces the occurrence of chips.

[0066] 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 cases of C0.3, where the gas wiping nozzle was chamfered to C0.30, to C2, where the gas wiping nozzle was chamfered 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.

[0067] As shown in Figure 8, the control C0, where the gas wiping nozzle was not chamfered, had 29 chips of Φ0.5 mm or larger. In addition, the gas wiping nozzle with R0.05 chamfering had 6 chips of Φ0.5 mm or larger. This shows that applying R chamfering to the gas wiping nozzle significantly reduces the occurrence of chips.

[0068] Furthermore, when the gas wiping nozzle was chamfered from R0.10 to R0.50, there were no chips of Φ0.5 mm or more. This shows that the number of chips decreases as the chamfering increases.

[0069] 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 contact with the jig decreasing as the contact area increased. In other words, it was found that chipping of the gas wiping nozzle could be suppressed by dispersing the stress through chamfering.

[0070] Furthermore, when the chamfering amount is C0.10 or more and R0.05 or more, it is possible to obtain a particularly effective stress dispersion effect, and it was found that this can prevent chipping of more than φ0.5 mm when an external force acts on the edge surface of the gas injection port. In particular, R-chamfering is effective even with a smaller chamfering amount than C-chamfering, because no corners are created during the chamfering process.

[0071] 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.

[0072] (Test example 2: Cleaning frequency test) Using continuous hot-dip plated metal strip manufacturing equipment, hot-dip plated metal strips were manufactured by continuously depositing molten metal on the front and back surfaces of a metal strip. When linear streaks appeared on the metal strip during the manufacturing of the hot-dip plated metal strip, cleaning was performed to determine the number of cleanings required to remove the linear streaks. It was also investigated whether linear streaks appeared again on the metal strip immediately after cleaning. Furthermore, it was investigated whether chipping occurred in the gas wiping nozzle when cleaning was performed. Furthermore, the incidence of splash defects on the metal strip during the manufacturing of the hot-dip plated metal strip was investigated.

[0073] The metal strip used had a width of 900 mm and a thickness of 1 mm. Gas wiping nozzles were manufactured with C-chamfering and R-chamfering on the edge surfaces as shown in Table 1. The opening height of the injection port, which is the slit width of the gas wiping nozzle, and the width of the gas wiping nozzle were the same as in Test Example 1.

[0074] [Table 1]

[0075] The distance from the tip of the gas wiping nozzle to the metal strip was 10 mm. The metal strip was passed through at a speed of 130 mpm. The gas wiping nozzle was cleaned using the same cleaning tool as in Test Example 1. The wiping gas used was a mixture of exhaust gas from the combustor and air. The wiping gas had a temperature of 500°C and a deposition amount at the strip width center of 50 g / m. 2 The gas pressure was adjusted so that

[0076] (Evaluation of surface defect occurrence) When linear streaks appeared on the metal strip, the gas wiping nozzle was cleaned, and the number of cleanings required to remove the linear streaks was investigated. The linear streaks that appeared on the metal strip were caused by at least one of adhesion of molten zinc to the gas wiping nozzle and chipping of the gas wiping nozzle.

[0077] Among these factors, when linear streaks were removed by cleaning, they were determined to be caused by molten zinc adhering to the gas wiping nozzle.Furthermore, when linear streaks were not removed even after cleaning, they were determined to be caused by chipping of the gas wiping nozzle.

[0078] (Evaluation of chipping) Next, the gas wiping nozzles in Table 1 were evaluated for chipping when cleaned with a cleaning jig.

[0079] (Splash defect evaluation) Splash defects caused by molten zinc adhering to the metal strip were investigated using a defect meter installed at the outlet of a CGL (Continuous Galvanizing Line). The occurrence rate of splash defects was calculated as the ratio of the length of the metal strip where splash defects were determined by the defect meter to the length of the metal strip measured by the defect meter.

[0080] The defect meter will now be described. FIG. 9 shows an outline of a defect meter 80. As shown in FIG. 9, the defect meter 80 includes a projector 81 and a camera 82. The projector 81 is a device that irradiates a white beam or a monochromatic beam of inspection light toward the surface of the hot-dip galvanized steel sheet G. The projector 81 is disposed at a certain angle with respect to the traveling direction of the hot-dip galvanized steel sheet G. The projector 81 may be provided with a plurality of light-emitting elements so that the inspection light is uniformly irradiated in the width direction of the hot-dip galvanized steel sheet G. That is, the projectors 81 may be disposed so that the optical axes of the projectors 81 are parallel to each other. In this manner, the inspection lights are incident on the surface of the hot-dip galvanized steel sheet G as parallel light. The irradiation area of ​​each of the inspection lights is set as an inspection line L. The camera 82 is disposed so that its optical axis is directed toward the surface of the hot-dip galvanized steel sheet G and receives light reflected from the surface of the hot-dip galvanized steel sheet G. The camera 82 may have, for example, a plurality of light-receiving elements arranged in the width direction of the hot-dip galvanized steel sheet G. Alternatively, one light-receiving element may be provided for each camera 82. In this case, for example, about 20 cameras 82 may be provided. The cameras 82 may be arranged according to the angle formed by the hot-dip galvanized steel sheet G and the inspection light. If there is no defect on the surface of the hot-dip galvanized steel sheet G, the inspection light irradiated from the projector 81 is specularly reflected from the surface. If there is a defect on the surface of the hot-dip galvanized steel sheet G, the inspection light is diffusely reflected from the surface. By providing the camera 82 at a position where it can receive the diffusely reflected light, the defect meter 80 can detect splash defects. In the example of FIG. 9, the defect meter 80 detects splash defects based on the reception of light reflected by the inspection line L by the camera 82.

[0081] Splash defects are defects caused by splashes adhering to the metal strip. Specifically, a pair of gas wiping nozzles are arranged so that the wiping gas is ejected in directions opposite to each other. When the wiping gas ejected from both gas wiping nozzles collides near the widthwise end of the metal strip, it vibrates the metal strip. When the metal strip vibrates, a liquid film of molten metal is torn off from the metal strip. The torn off liquid film solidifies and becomes metal powder, which adheres to the metal strip and causes defects.

[0082] If the rate of occurrence of splash defects is 0.100% or less, the quality is sufficient for metal strips that require strict surface quality, such as steel sheets for automobiles. For this reason, a rate of occurrence of splash defects of 0.100% or less was evaluated as the quality standard.

[0083] (Evaluation of zinc adhesion amount) The amount of zinc deposited at the center of the coil's width and at both edges was evaluated. Samples were taken at the center of the coil's width and at a position 50 mm inward from both edges. Samples were taken using a sample (Φ48) for deposition amount analysis. The amount of zinc deposited was measured using fluorescent X-ray analysis. If the deviation of the deposition amount at both edges from the deposition amount at the center was within 20%, it was evaluated as passing.

[0084] (comprehensive evaluation) Products were deemed to have passed the test if they met all of the following criteria: linear streaks could be removed by cleaning, i.e., zinc adhering to the slits could be removed; the incidence of splash defects was 0.100% or less; and no chips of Φ0.5 mm or larger were observed on the gas wiping nozzle.

[0085] As shown in Table 1, in Comparative Examples 1 to 3, the linear streaks could be removed by cleaning. However, in Comparative Examples 1 to 3, new linear streaks subsequently appeared and could not be removed by cleaning, resulting in failure. When the gas wiping nozzles of Comparative Examples 1 to 3 were observed offline, the linear streaks on the metal band were found to have formed at positions corresponding to the positions where the chipping had occurred in the gas wiping nozzle.

[0086] In Comparative Examples 4 to 6, linear streaks could be removed by cleaning. Furthermore, in Comparative Examples 4 to 6, no chipping occurred in the gas wiping nozzle. Furthermore, the time required to clean these gas wiping nozzles was approximately 15 seconds per cleaning, and cleaning could be completed in less than two minutes. Furthermore, in Comparative Examples 4 to 6, the incidence of splash defects exceeded 0.100%, so all were rejected.

[0087] As shown in Table 1, this shows that the greater the chamfering of the edge surface of the gas jet nozzle, the more effective it is in suppressing chipping. On the other hand, it was found that the wiping gas jet tends to diffuse as the chamfering amount increases. When the wiping gas jet diffuses, the amount of zinc deposition tends to exceed the target deposition amount range. Therefore, in order to keep the zinc deposition amount within the target deposition amount range, it is necessary to increase the wiping gas pressure. When the wiping gas pressure increases, the molten zinc is more likely to splash, which tends to increase the incidence of splash defects.

[0088] Linear streaks were also removable in Examples 1 to 10. The splash defect incidence rate was also within the standard range in Examples 1 to 10, and all were evaluated as passing.

[0089] A similar test was also conducted using a gas wiping nozzle made of chrome molybdenum steel. Comparative Example 7 is an example in which chrome molybdenum steel was used as the material for the gas wiping nozzle. No chipping was observed in the gas wiping nozzle.

[0090] 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.

[0091] Furthermore, the deviation in the zinc deposition amount across the strip width was significantly worse than when a ceramic gas wiping nozzle was used. Specifically, the deviation in the zinc deposition amount exceeded 20%, resulting in a failure.

[0092] When the gas wiping nozzle was observed after removal, it was found that the gap in the center of the nozzle width had widened by approximately 1 mm from before the start of the test. It is believed that this gap was causing the deviation in the amount of molten zinc applied.

[0093] A similar test was carried out on a gas wiping nozzle made of austenite / ferrite two-layer stainless steel that had been HIP-treated. Comparative Example 8 is an example in which the gas wiping nozzle was made of the gas wiping nozzle described above. Almost no chipping was observed in the gas wiping nozzle of Comparative Example 8.

[0094] 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.

[0095] Furthermore, the deviation in the zinc deposition amount across the strip width was significantly worse than when a ceramic gas wiping nozzle was used. Specifically, the deviation in the zinc deposition amount exceeded 20%, resulting in a failure.

[0096] Furthermore, the deviation in the amount of zinc deposited in the strip width direction was significantly worse than when a ceramic gas wiping nozzle was used. When the gas wiping nozzle was observed after removal, it was found 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 this gap is the cause of the deviation in the amount of molten zinc deposited.

[0097] 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.

[0098] As described above, when performing C-chamfering on the edge surface of a gas injection port, it was found that the occurrence rate of splash defects can be reduced by setting the upper limit of C-chamfering to less than C1.10. In addition, R-chamfering reduces wiping ability more than C-chamfering. When performing R-chamfering on the edge surface of a gas injection port, it was found that the occurrence rate of splash defects can be reduced by setting the upper limit of R-chamfering to R0.50 or less. [Explanation of symbols]

[0099] 100 Continuous hot-dip galvanized metal strip manufacturing equipment 10 Plating tank 30 Gas Injector 31 Gas wiping nozzle 36 Edge surface 37 Adjacent faces 40 Sink Roll

Claims

1. A gas injection device that sprays wiping gas onto a metal strip, a gas wiping nozzle formed of a ceramic material, a carbon material, a carbon fiber reinforced carbon composite material, or a ceramic matrix composite material, the gas wiping nozzle having a gas injection port through which the wiping gas is injected; 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, The edge surface of the gas injection port is chamfered to a C of not less than C0.10 and not more than C1.10, or A gas injection device, wherein the edge surface of the gas injection port is chamfered with an R of 0.05 or more and R of 0.50 or less.

2. a plating tank configured to be able to store molten metal; a gas injection device provided above the plating tank; A manufacturing facility for a hot-dip galvanized metal strip, comprising the coating tank and a conveying unit that conveys the metal strip toward the gas injection device, the gas injection device is made of a ceramic material, a carbon material, a carbon fiber reinforced carbon composite material, or a ceramic matrix composite material, and has a gas wiping nozzle having a gas injection port from which a wiping gas is injected; 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, The edge surface of the gas injection port is chamfered to a C of not less than C0.10 and not more than C1.10, or The equipment for manufacturing hot-dip galvanized metal strips, wherein the edge surface of the gas injection port is chamfered with an R of 0.05 or more and R of 0.50 or less.

3. A method for manufacturing a metal strip, comprising blowing 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 method comprising:

2. A method for manufacturing a hot-dip plated metal strip, comprising an adjusting step of adjusting the amount of molten metal adhering to the metal strip by injecting the wiping gas from the gas wiping nozzle of the gas injection device according to claim 1.

4. A method for cleaning the gas injection device according to claim 1, comprising a removing 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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