Method for controlling gas injection device

Abstract

To provide a control method of a gas injection device capable of suppressing damage to a ceramic member under a high temperature environment.SOLUTION: A method for controlling a gas ejection device (30) including a gas wiping nozzle (31) configured to eject a wiping gas to a steel strip (S) pulled upward from a molten metal plating bath to adjust a film thickness of a molten metal adhering to a surface of the steel strip, the gas wiping nozzle including a non-metal material and a metal material mechanically connected to the non-metal material, the method including acquiring input data including a linear expansion coefficient of the non-metal material, a bending strength of the non-metal material, a Young's modulus of the non-metal material, a thermal conductivity of the non-metal material, a linear expansion coefficient of the metal material, and a temperature rise amount of a wiping gas, and determining a temperature rise rate of the wiping gas based on the input data.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] TECHNICAL FIELD The present disclosure relates to a method for controlling a gas injection device, and more particularly to a method for controlling a gas injection device that sprays wiping gas onto a metal strip. [Background technology]

[0002] Hot-dip galvanized metal strips, which are a type of hot-dip metal-coated metal strip, are widely used in fields such as building materials, automobiles, and home appliances. Hot-dip galvanized metal strips are required to have excellent appearance. 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, in which a metal strip is continuously introduced into molten metal stored in a plating tank, a wiping gas is sprayed onto the metal strip from a gas wiping nozzle to adjust the plating thickness, and the metal strip is cooled and then subjected to post-processing.

[0004] A pair of gas wiping nozzles are arranged above a plating tank, for example, with the metal strip sandwiched between them. The molten metal scattered by the wiping gas is 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 prevents the wiping gas from being sprayed uniformly from the gas wiping nozzle, resulting in surface defects such as uneven film thickness.

[0005] Patent Document 1 discloses spraying ceramics that do not undergo alloying reaction with molten metal onto the tip of a gas wiping nozzle to suppress adhesion of splashes into the slit. Patent Document 2, based on a similar concept, discloses bonding ceramics to the tip of the gas wiping nozzle. Patent Document 3 discloses a gas wiping nozzle whose nozzle tip is made of ceramics. [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 Utility Model Application Publication No. 01-147252 Summary of the Invention [Problem to be solved by the invention]

[0007] When manufacturing thick-plated products prone to wavy, flowing molten metal wrinkles on the plating surface of hot-dip metal strips, wiping with high-temperature gas is effective in suppressing defects. However, Patent Documents 1 to 3 do not anticipate the use of high-temperature gas and do not disclose how to control the use of high-temperature gas. When wiping with high-temperature gas, the difference in the linear expansion coefficients of the metal and ceramic components causes a difference in the amount of thermal expansion at the boundary between the metal and ceramic components. When high-temperature gas is used with the gas wiping nozzles described in Patent Documents 1 to 3, thermal stress is generated at the interface between the metal and ceramic components, causing damage to the ceramic component. The damage causes unevenness in the wiping gas, resulting in new defects on the plating surface.

[0008] In view of the above problems, the present disclosure has an object to provide a method for controlling a gas injection device that can suppress damage to ceramic members in a high-temperature environment. [Means for solving the problem]

[0009] (1) A method for controlling a gas injection device according to an embodiment of the present disclosure includes: A method for controlling a gas injection device having a gas wiping nozzle that sprays wiping gas onto a steel strip pulled up from a molten metal coating bath and adjusts the film thickness of molten metal adhering to the surface of the steel strip, comprising: The gas wiping nozzle includes a non-metallic material and a metallic material mechanically coupled to the non-metallic material, acquiring input data including a linear expansion coefficient of the non-metallic material, a bending strength of the non-metallic material, a Young's modulus of the non-metallic material, a thermal conductivity of the non-metallic material, a linear expansion coefficient of the metallic material, and a temperature rise amount of the wiping gas; and determining a temperature rise rate of the wiping gas based on the input data.

[0010] (2) As one embodiment of the present disclosure, in (1), The linear expansion coefficient of the nonmetallic material is α c [×10 -6 / K], the bending strength of the non-metallic material is σ [MPa], the Young's modulus of the non-metallic material is E [GPa], the thermal conductivity of the non-metallic material is k [W / m·K], and the linear expansion coefficient of the metallic material is α m [×10 -6 / K] and the temperature rise amount of the wiping gas is ΔT [K], the temperature rise rate of the wiping gas, β [°C / hr], is determined so as to satisfy the following formula.

[0011]

number

[0012] According to the present disclosure, it is possible to provide a method for controlling a gas injection device that can suppress damage to ceramic members in a high-temperature environment. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing the general configuration of a manufacturing facility for hot-dip metal-plated steel sheets. [Figure 2] FIG. 2 is a perspective view showing a schematic configuration of a gas wiping nozzle used in the manufacturing facility for hot-dip metal-plated steel sheets shown in FIG. [Figure 3] FIG. 3 is a diagram for explaining thermal deformation of the gas wiping nozzle. [Figure 4] FIG. 4 is a flowchart illustrating the process of a gas injection device control method according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] A control method for a gas injection device 30 (see FIG. 1) according to one embodiment of the present disclosure will be described below with reference to the drawings. In each drawing, identical or corresponding parts are designated by the same reference numerals. In the following description of the embodiment, the description of identical or corresponding parts will be omitted or simplified as appropriate.

[0015] <Equipment configuration> FIG. 1 shows a manufacturing facility 100 (continuous hot-dip metal coating facility) for hot-dip metal coated steel sheets, which is equipped with a gas injection device 30.

[0016] As shown in FIG. 1, the manufacturing equipment 100 for hot-dip metal-plated steel sheets is equipment for manufacturing hot-dip metal-plated steel sheets by immersing a steel strip S (an example of a metal strip) in molten metal M, thereby continuously depositing the molten metal M on the front and back surfaces of the steel strip S.

[0017] Although the metal strip is not particularly limited, the present embodiment will be described as a steel strip S. As the steel strip S, for example, one that has been annealed in a continuous annealing furnace in a reducing atmosphere is used.

[0018] The manufacturing equipment 100 for hot-dip metal-plated steel sheets 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.

[0019] The snout 20 is a hollow cylindrical member. The snout 20 is provided so as to cover the periphery of the steel strip S. 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.

[0020] 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.

[0021] The molten metal M is not particularly limited, and may be, for example, zinc, aluminum, or tin. 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.

[0022] The gas injection device 30 has a gas wiping nozzle 31 that sprays gas (wiping gas) onto the steel strip S pulled upward from the molten metal coating bath (coating tank 10) to adjust the film thickness of the molten metal M adhering to the surface of the steel strip S. 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.

[0023] The temperature T (°C) of the wiping gas immediately after being discharged from the tip of the wiping nozzle is preferably controlled to satisfy the relationship TM - 150 ≦ T ≦ TM + 250 in relation to the melting point TM (°C) of the molten metal M. Controlling the temperature T within the above range can suppress the cooling and solidification of the molten metal M, making it difficult for viscosity variations to occur and suppressing the occurrence of molten metal wrinkles. On the other hand, if the temperature T is less than TM - 150 (°C), it does not affect the fluidity of the molten metal M and is therefore ineffective in suppressing the occurrence of molten metal wrinkles. Furthermore, if the temperature T is higher than TM + 250°C, alloying is promoted, deteriorating the appearance of the steel sheet.

[0024] The control device controls the overall operation of the gas injection device 30, including the temperature T and temperature rise rate of the wiping gas. The control device may be configured as hardware, for example, a computer. The control device executes the process of a control method for the gas injection device 30, which will be described later, and controls the temperature rise rate of the wiping gas so as not to damage the ceramic member.

[0025] 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.

[0026] Excess molten metal M adhering to the steel strip S is removed by wiping gas injected from a gas injection device 30. The steel strip S is then cooled by cooling equipment (not shown) and is then guided to a subsequent process. In this manner, hot-dip metal coated steel strips are continuously produced. The subsequent process also includes shearing, and steel sheets are produced from the steel strip S.

[0027] 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 and length directions.

[0028] <Gas wiping nozzle> FIG. 2 shows a schematic configuration of the gas wiping nozzle 31. The gas wiping nozzle 31 includes a non-metallic material and a metallic material mechanically coupled to the non-metallic material. As shown in FIG. 2, the gas wiping nozzle 31 includes a ceramic nozzle portion 33 (ceramic member) that sprays wiping gas. The nozzle portion 33 has a supply port 32 through which gas is supplied and an injection port 35 that sprays the supplied gas. In this embodiment, the gas wiping nozzle 31 further includes a flange 36 to which gas is supplied through a pipe 38 and a flow rectifier 34 connected to the nozzle portion 33. The flange 36 is a member that receives gas sent to the gas wiping nozzle 31 through the pipe 38. The flange 36 is a member that constitutes a nozzle header and is also referred to as a secondary header. In this embodiment, the gas wiping nozzle 31 also includes a primary header 37, which is composed of the flange 36 and the primary header 37. In this embodiment, the gas wiping nozzle 31 is also provided with a thermocouple 61 (see FIG. 3) for measuring the temperature of the gas.

[0029] The current plate 34 is formed in a substantially rectangular shape extending in the length direction DX, the depth direction DY, and the width direction DZ. The base end (rear end) of the current plate 34 is connected to a flange 36. As shown in Fig. 2, the metal flange 36 is mechanically connected to a side of the current plate 34 different from the side to which the nozzle portion 33 is connected. Here, the mechanical connection is made by using members such as bolts and screws.

[0030] 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.

[0031] The first nozzle member 33a and the second nozzle member 33b are provided with a gap between them, so that a slit-shaped injection port 35 is formed between the first nozzle member 33a and the second nozzle member 33b.

[0032] The length direction DX is the direction along the width direction of the steel strip S. The width direction DZ is the direction along the length direction of the steel strip S, i.e., the conveying direction. The width direction DZ is also a direction perpendicular to the length direction DX. The depth direction DY is the direction along the thickness direction of the steel strip S. The depth direction DY is also a direction perpendicular to the length direction DX and the width direction DZ.

[0033] The injection port 35 has a slit-shaped opening that extends in the longitudinal direction DX. The injection port 35 is formed by the first nozzle member 33a and the second nozzle member 33b facing each other in the width direction DZ. That is, the injection port 35 is formed so that the distance between the first nozzle member 33a and the second nozzle member 33b in the width direction DZ is the opening height.

[0034] The injection port 35 is formed so that its length along the longitudinal direction DX is longer than the width of the steel strip S. For example, even if the steel strip S shifts in the longitudinal direction DX when being pulled up from the coating tank 10, the injection port 35 is formed to be sufficiently long, so that the wiping gas can be injected across the entire width of the steel strip S.

[0035] <Nozzle section> As described above, the nozzle section 33 is composed of the first nozzle member 33a and the second nozzle member 33b. Wiping gas is sprayed from the gap between the first nozzle member 33a and the second nozzle member 33b to adjust the film thickness of the molten metal M adhering to the steel strip surface. The first nozzle member 33a and the second nozzle member 33b are formed from a material that is heat resistant to the molten metal M. The material may have a fracture toughness value of, for example, 3 MPa m 1 / 2 The fracture toughness of the material is selected to be greater than or equal to 5 MPa m 1 / 2 It is more preferable that the fracture toughness of the material is 7 MPa m 1 / 2 More preferably, it is equal to or greater than this.

[0036] Furthermore, the material of the first nozzle member 33a and the second nozzle member 33b preferably has low wettability with respect to the molten metal M, low plastic deformability, and a low linear expansion coefficient. Examples of materials that satisfy these conditions include ceramic materials and ceramic-based composite materials (hereinafter referred to as ceramic materials, etc.).

[0037] The ceramic material is not particularly limited, but may be, for example, alumina, sialon, silicon nitride, or zirconia.

[0038] The bending strength of the ceramic material is preferably 600 MPa or more. More preferably, the bending strength of the ceramic material is 800 MPa or more. Examples of ceramic materials that satisfy this condition include zirconia, silicon nitride, and sialon. These ceramic materials are resistant to plastic deformation, and substantial deformation can be suppressed if the strength is below the fracture strength. Furthermore, the Vickers hardness of the ceramic material is preferably 800 HV or more. More preferably, the Vickers hardness of the ceramic material is 1000 HV or more.

[0039] Ceramic materials and the like may crack if their thermal shock resistance is below the temperature of the wiping gas. Therefore, it is preferable that the thermal shock resistance of the ceramic material and the like be equal to or higher than the temperature of the supplied wiping gas. In particular, when high-temperature wiping gas is used, the thermal shock resistance of the ceramic material and the like is preferably 430°C or higher. It is more preferable that the thermal shock resistance of the ceramic material and the like be 600°C or higher.

[0040] Furthermore, the linear expansion coefficients of the first nozzle member 33a and the second nozzle member 33b are preferably not more than half the linear expansion coefficient of the rectifying plate 34. It is more preferable that the linear expansion coefficients of the first nozzle member 33a and the second nozzle member 33b are not more than one-third the linear expansion coefficient of the rectifying plate 34. By satisfying such conditions for the linear expansion coefficients, it is possible to suppress deformation of the first nozzle member 33a and the second nozzle member 33b due to the influence of heat.

[0041] <Rectifier plate> The gas blown to the flange 36 is subject to considerable turbulence as it passes through the piping 38, and if it is introduced into the nozzle portion 33 as is, the turbulence will cause a bias in the wind speed in the width direction DZ. The rectifying plate 34 is, for example, a metal plate with holes or slits, and the holes or slits have the function of narrowing the gas flow path. The gas that reaches the rectifying plate 34 passes through the holes or slits provided in the rectifying plate 34 and is discharged uniformly from the outlet of the rectifying plate 34. As a result, wiping gas is discharged uniformly from the outlet of the nozzle portion 33.

[0042] The material of the rectifying plate 34 may be, for example, stainless steel (SUS steel) or chrome molybdenum steel. Similarly, the material of the flange 36 may be stainless steel or chrome molybdenum steel. The linear expansion coefficients of stainless steel and chrome molybdenum steel are approximately 10×10 -6 / K~18×10 -6 / K.

[0043] <Control method> When the gas injection device 30 is used in a high-temperature environment (i.e., when high-temperature wiping gas is sprayed from the gas wiping nozzle 31), the temperature of the wiping gas is controlled to rise to a target temperature. At this time, the nozzle portion 33 and the rectifying plate 34 have different linear expansion coefficients and thermal conductivities, resulting in differences in the way they deform (expand). For example, as shown in Figure 3, when the nozzle portion 33 thermally deforms, the rectifying plate 34 thermally deforms in different directions and to different degrees. If the temperature rise rate of the wiping gas is rapid, the nozzle portion 33 and the rectifying plate 34 expand rapidly, resulting in a large difference in expansion and causing cracks in the nozzle portion 33 at their interface. However, if the temperature rise rate is slow, slippage occurs at the interface between the nozzle portion 33 and the rectifying plate 34, preventing damage to the nozzle portion 33. Therefore, damage to the nozzle portion 33 can be avoided by specifying the temperature rise rate of the wiping gas based on the physical properties of the non-metallic material (nozzle portion 33) and the physical properties of the metallic material (rectifying plate 34) mechanically connected to the non-metallic material.

[0044] The inventors changed the material of the nozzle portion 33, attached a thermocouple 61 to the primary header 37 as shown in Fig. 3, and changed the heating rate while measuring the gas temperature, to check for damage to the nozzle portion 33. As a result, it was confirmed that damage to the ceramic nozzle portion 33 can be avoided by determining the heating rate β [°C / hr] of the wiping gas so as to satisfy the following formula (1).

[0045]

number

[0046] where α c [×10 -6 / K] is the linear expansion coefficient of the nonmetallic material. σ [MPa] is the bending strength of the nonmetallic material. E [GPa] is the Young's modulus of the nonmetallic material. k [W / m·K] is the thermal conductivity of the nonmetallic material. α m [×10 -6 / K] is the linear expansion coefficient of the metal material. ΔT [K] is the temperature rise of the wiping gas. The temperature rise of the wiping gas is the amount of rise from the current temperature to the target temperature (the difference between the target temperature and the current temperature). The current temperature of the wiping gas can be obtained, for example, as a measurement value using a thermocouple 61.

[0047] When the nonmetallic material has a high thermal conductivity, a high bending strength, or a high linear expansion coefficient, the temperature rise rate can be set high. c -α m " is a negative value, so the smaller the amount of temperature rise of the wiping gas, the higher the temperature rise rate can be set.

[0048] The control device executes the process of the control method for the gas injection device 30 using the above formula (1). FIG. 4 is a flowchart illustrating an example of the control method for the gas injection device 30 according to this embodiment. The control device acquires input data including the linear expansion coefficient of the non-metallic material, the bending strength of the non-metallic material, the Young's modulus of the non-metallic material, the thermal conductivity of the non-metallic material, the linear expansion coefficient of the metallic material, and the temperature rise amount of the wiping gas (step S1). The control device determines the temperature rise rate of the wiping gas based on the input data (step S2). That is, the control device determines the temperature rise rate of the wiping gas so that the above formula (1) is satisfied. Then, the control device controls the gas injection device 30 so as to achieve the determined temperature rise rate (step S3). For example, the control of the gas injection device 30 may involve adjusting the amount of air to be diluted with the exhaust gas and the gas pressure to achieve a desired temperature rise rate.

[0049] Here, as described above, the control device is, for example, a computer. In this case, the processing of the control method for the gas injection device 30 may be executed by a program. One or more programs used to control the operation of the gas injection device 30 are stored in a storage device (for example, a memory) accessible by the control device. When the program stored in the storage device is read by the processor of the control device, it may cause the processor to execute the processing of steps S1 to S3 described above.

[0050] (Example) The gas injection device 30 was installed in the manufacturing facility 100 for hot-dip metal-coated steel sheets shown in Figure 1, and the presence or absence of damage to the ceramics was measured. More specifically, as shown in Table 1, an evaluation was conducted for a case in which the gas injection device 30 was controlled so that the temperature rise rate (β) of the wiping gas did not satisfy the above formula (1) (Comparative Example), and a case in which the gas injection device 30 was controlled so that the above formula (1) was satisfied (Example).

[0051] High-temperature gas was generated by mixing air with exhaust gas obtained from the combustor located behind the gas wiping nozzle 31, and the high-temperature gas was discharged from the nozzle section 33. The gas temperature was measured by a thermocouple 61 attached to the primary header 37, and the rate at which the gas temperature rose from 100°C to 550°C was controlled by a control device. The rate at which the gas temperature rose was controlled was by adjusting the amount of air used to dilute the exhaust gas and the gas pressure based on the measured gas temperature, so as to achieve the desired rate of rise in temperature.

[0052] For each of the comparative examples and examples shown in Table 1, the nozzle portion 33 was removed after the temperature increase was completed, and the presence or absence of damage to the ceramic portion was confirmed. The presence or absence of damage was confirmed using fluorescent penetrant testing. The occurrence of cracks was determined as damage. That is, the presence or absence of damage was determined as "present (fail)" if even one crack occurred, and "absent (pass)" if no cracks occurred. The experimental results are shown in Table 1. Here, three types of material were used for the nozzle portion 33 (corresponding to non-metallic materials): alumina, sialon, and zirconia. SCM440 was used as the material for the straightening plate 34 (corresponding to metallic materials) mechanically connected to the nozzle portion 33. The physical properties of alumina, sialon, and zirconia are shown in Table 2. The physical properties of SCM440 are shown in Table 3. Here, SCM440 is based on the classification of SCM steel in the JIS standard. For example, regarding the right side of the formula (1), when the material of the nozzle portion 33 is alumina, (0.318k+0.708) / α c The value of is calculated as "1302558.14". Also, the value of σ / 0.7605E is calculated as "0.001690617". Also, (α c -α m The value of ΔT is calculated to be "-0.001575". Therefore, the value of the right side of formula (1) is "150.6". When the material of the nozzle portion 33 is sialon or zirconia, the values ​​of the right side of formula (1) are calculated to be "458.9" and "207.2", respectively.

[0053] In Comparative Examples 1 to 3, in which the temperature rise rate of the wiping gas exceeded the value of the right side of the above formula (1), cracks (fissures) occurred in the ceramics, and the results were unsuccessful. In contrast, in Examples 1 to 8, in which the temperature rise rate of the wiping gas satisfied the above formula (1), no damage occurred and the results were successful. It is believed that by limiting the temperature rise rate of the wiping gas, the nozzle part 33 and the straightening plate 34 deform (expand) so as to slide at the interface, preventing damage to the nozzle part 33.

[0054] [Table 1]

[0055] [Table 2]

[0056] [Table 3]

[0057] As described above, the control method for the gas injection device 30 according to this embodiment can suppress damage to the ceramic nozzle portion 33 in a high-temperature environment by using the above-described configuration. As a result, it is possible to eliminate uneven spray of wiping gas caused by damage to the nozzle portion 33 and reduce plating defects. In addition, because the nozzle portion 33 is made of ceramic, adhesion of splashes to the nozzle portion 33 can also be suppressed.

[0058] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art would easily be able to make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are included in the scope of the present disclosure. The embodiments of the present disclosure may also be realized as a program executed by a processor included in an apparatus or a storage medium on which a program is recorded. It should be understood that these are also included in the scope of the present disclosure.

[0059] In the above examples, three types of non-metallic materials, alumina, sialon, and zirconia, were used, but silicon nitride may also be used. The physical properties of silicon nitride are similar to those of sialon, and even when silicon nitride is used as the non-metallic material, the temperature rise rate of the wiping gas can be determined using the above formula (1). [Explanation of symbols]

[0060] 10 Plating tank 20 Snout 30 Gas Injector 31 Gas wiping nozzle 32 Supply port 33 Nozzle section 33a first nozzle member 33b second nozzle member 34 Rectifier plate 35 Nozzle 36 flange 37 Primary Header 38 Piping 40 Sink Roll 50 Support Rolls 61 Thermocouple 100 Manufacturing equipment for hot-dip metal coated steel sheets S steel strip M Molten metal

Claims

1. A method for controlling a gas injection device having a gas wiping nozzle that sprays wiping gas onto a steel strip pulled up from a hot-dip metal coating bath to adjust the film thickness of molten metal adhering to the surface of the steel strip, comprising: The gas wiping nozzle includes a non-metallic material and a metallic material mechanically coupled to the non-metallic material, acquiring input data including a linear expansion coefficient of the non-metallic material, a bending strength of the non-metallic material, a Young's modulus of the non-metallic material, a thermal conductivity of the non-metallic material, a linear expansion coefficient of the metallic material, and a temperature rise amount of the wiping gas; and determining a temperature rise rate of the wiping gas based on the input data.

2. The linear expansion coefficient of the nonmetallic material is α ｃ [x10 －６ / K], the bending strength of the non-metallic material is σ [MPa], the Young's modulus of the non-metallic material is E [GPa], the thermal conductivity of the non-metallic material is k [W / m·K], and the linear expansion coefficient of the metallic material is α ｍ [x10 －６ / K] and the temperature rise amount of the wiping gas is ΔT [K], and the temperature rise rate of the wiping gas, β [°C / hr], is determined so as to satisfy the following formula: [Equation 1]

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