JP6635086B2 - Manufacturing method of hot-dip galvanized steel strip - Google Patents

Description

  The present invention relates to a method for producing a hot-dip metal-plated steel strip, and more particularly to gas wiping for adjusting the amount of hot-metal deposited on the surface of a steel strip (hereinafter, also referred to as “plated coating amount”).

  In the continuous molten metal plating line, as shown in FIG. 1, the steel strip S annealed in the continuous annealing furnace in the reducing atmosphere passes through the snout 10 and continuously enters the molten metal bath 14 in the plating tank 12. Will be introduced. Thereafter, the steel strip S is pulled up above the molten metal bath 14 via the sink roll 16 and the support roll 18 in the molten metal bath 14, adjusted to a predetermined plating thickness by the gas wiping nozzles 20 </ b> A, 20 </ b> B, and then cooled. Then, it is led to a subsequent process. The gas wiping nozzles 20A and 20B are arranged above the plating tank 12 so as to face each other with the steel strip S interposed therebetween, and spray gas from the injection ports toward both surfaces of the steel strip S. By this gas wiping, excess molten metal is scraped off, the amount of plating applied to the surface of the steel strip is adjusted, and the molten metal attached to the surface of the steel strip is made uniform in the sheet width direction and the sheet longitudinal direction. The gas wiping nozzles 20A and 20B are generally configured to be wider than the steel strip width in order to cope with various steel strip widths and to cope with a positional deviation in the width direction when the steel strip is pulled up. Extending beyond the part.

  In such a gas wiping method, one or both of (1) the vibration of the collision pressure of the wiping gas and (2) the unevenness in the viscosity due to oxidation / cooling of the molten metal causes the produced molten metal-plated steel strip to be produced. Wavy wrinkles in the shape of a wave pattern are easily generated on the plating surface. The plated steel sheet having such hot water wrinkles impairs the surface properties, particularly the smoothness, of the coating film when the plating surface is used as a coating base surface in the use of an exterior plate. For this reason, the plated steel sheet having the hot water wrinkles cannot be used as an exterior sheet requiring a coating treatment with excellent appearance, which greatly affects the yield of the plated steel sheet.

  The following methods are known as methods for suppressing plating surface defects called hot water wrinkles. Patent Literature 1 describes a method of making surface wrinkles less noticeable by changing the surface properties and rolling conditions of a temper rolling roll during temper rolling, which is a step after plating. Patent Document 2 discloses that before introducing a steel sheet into a hot-dip galvanizing bath, the surface roughness of the steel sheet is adjusted using a skin pass mill, a tension leveler or the like in accordance with the amount of coating to suppress the occurrence of hot water wrinkles. A method is described.

JP 2004-27263 A JP-A-55-21564

  However, according to studies by the present inventors, the method disclosed in Patent Document 1 improves minor hot water wrinkles, but has no effect on severe hot water wrinkles. In addition, the method disclosed in Patent Document 2 has a problem in cost due to the necessity of installing a skin pass mill, a tension leveler, and the like in a pre-process of a hot-dip galvanizing bath. In addition, even when these are installed, it is difficult to obtain the ideal surface roughness due to the chemical and physical changes of the galvanized film due to the pickling and recrystallization in the pretreatment equipment and the annealing furnace, and the hot water It is considered that it is difficult to sufficiently suppress the occurrence.

  In view of the above problems, an object of the present invention is to provide a method of manufacturing a hot-dip metal-plated steel strip that can sufficiently suppress the generation of hot water wrinkles and can manufacture a high-quality hot-dip metal-plated steel strip at low cost. .

  The present inventors have conducted intensive studies to solve the above-described problems, and found that there is a positive linear correlation between the header pressure of the gas wiping nozzle and the amount of gas collision pressure fluctuation, that is, by controlling the header pressure, It was found for the first time that the amount of fluctuation in the collision pressure could be controlled. By setting the gas collision pressure fluctuation amount to a predetermined value in consideration of the running speed of the steel strip and the target plating thickness, it has been found that generation of hot water wrinkles can be sufficiently suppressed. Obtained.

σ：ガスの衝突圧変動量［Pa］
Ｌ：鋼帯の走行速度［m/min］
Ｗ：目標のめっき厚さ［μm］
α，β：定数 The gist configuration of the present invention completed on the basis of the above findings is as follows.
[1] A steel strip is continuously immersed in a molten metal bath,
Gas is blown from a pair of gas wiping nozzles disposed on the steel strip with the steel strip interposed between the steel strip pulled up from the molten metal bath, and the amount of molten metal deposited on both surfaces of the steel strip is adjusted.
A method for manufacturing a hot-dip metal-plated steel strip for continuously manufacturing a hot-dip metal-plated steel strip,
The molten metal plating is characterized in that the collision pressure fluctuation amount σ of the gas is controlled so as to satisfy the following expression (1) according to the running speed L of the steel strip and the target plating thickness W. Steel strip manufacturing method.

σ: Gas impact pressure fluctuation [Pa]
L: Running speed of steel strip [m / min]
W: Target plating thickness [μm]
α, β: constant

[2] The relation between the header pressure P [kPa] of the gas wiping nozzle and the collision pressure fluctuation amount σ of the gas is obtained in advance,
The method for producing a hot-dip metal-plated steel strip according to the above [1], wherein the header pressure P is set such that the collision pressure fluctuation amount σ of the gas satisfies Expression (1).

  [3] The method for producing a hot-dip metal-plated steel strip according to the above [1] or [2], wherein a height of a tip of the gas wiping nozzle is 250 mm or less from a surface of the hot-dip metal bath.

  [4] A baffle plate for avoiding collision between gases injected from the pair of gas wiping nozzles is installed on a steel strip extension surface near an end in the width direction of the steel strip, [1] to [3]. ] The manufacturing method of the hot-dip metal-plated steel strip as described in any one of the above.

  [5] The above-mentioned [1] wherein the component of the molten metal contains 1.0 to 10% by mass of Al, 0.2 to 1% by mass of Mg, and 0 to 0.1% by mass of Ni, with the balance being Zn and unavoidable impurities. ] The manufacturing method of the hot-dip metal-plated steel strip as described in any one of-[4].

  ADVANTAGE OF THE INVENTION According to the manufacturing method of the hot-dip metal-plated steel strip of this invention, generation | occurrence | production of hot water wrinkles is fully suppressed, and a high-quality hot-dip metal-plated steel strip can be manufactured at low cost.

It is a schematic diagram which shows the structure of a continuous molten metal plating facility. FIG. 2 is an enlarged view of the vicinity of a tip end of a gas wiping nozzle 20A in the continuous hot-dip metal plating equipment shown in FIG. 1. It is a perspective view showing the composition near the width direction end of steel strip S in the continuous molten metal plating equipment used in this embodiment. 6 is a graph showing a relationship between a header pressure P and a gas collision pressure fluctuation amount σ in one experimental example.

  With reference to FIG. 1, a continuous hot-dip metal plating facility 100 (hereinafter, also simply referred to as “plating facility”) that can be used in the method for producing a hot-dip metal-plated steel strip according to one embodiment of the present invention will be described.

  Referring to FIG. 1, a plating facility 100 of the present embodiment includes a snout 10, a plating tank 12 for storing a molten metal, a sink roll 16, and a support roll 18. The snout 10 is a member that defines a space through which the steel strip S passes and whose cross section perpendicular to the steel strip traveling direction has a rectangular shape, and whose tip is immersed in a molten metal bath 14 formed in the plating tank 12. I have. In one embodiment, the steel strip S annealed in the continuous annealing furnace in the reducing atmosphere passes through the snout 10 and is continuously introduced into the molten metal bath 14 in the plating tank 12. Thereafter, the steel strip S is pulled up above the molten metal bath 14 via the sink roll 16 and the support roll 18 in the molten metal bath 14, and after being adjusted to a predetermined plating thickness by the pair of gas wiping nozzles 20A and 20B. , Is cooled and led to the subsequent process.

  The pair of gas wiping nozzles 20A and 20B (hereinafter, also simply referred to as “nozzles”) are arranged above the plating tank 12 to face each other with the steel strip S interposed therebetween. Referring to FIG. 2 in addition to FIG. 1, nozzle 20A blows gas toward steel strip S from an injection port 26 (nozzle slit) extending in the plate width direction of the steel strip at its tip, and Adjust the amount of plating on the surface. The same applies to the other nozzle 20B. The excess molten metal is scraped off by the pair of nozzles 20A and 20B, the amount of plating applied to both surfaces of the steel strip S is adjusted, and the sheet width direction and the sheet longitudinal direction are adjusted. Is uniformed.

  The nozzles 20A and 20B are generally configured to be longer than the width of the steel strip in order to cope with various widths of the steel strip and to cope with a positional deviation in the width direction when the steel strip is pulled up. It extends to the outside. Further, as shown in FIG. 2, the nozzle 20A has a nozzle header 22, and an upper nozzle member 24A and a lower nozzle member 24B connected to the nozzle header 22. The tip portions of the upper and lower nozzle members 24A, 24B have surfaces facing each other parallel to each other in a cross section perpendicular to the steel strip S, thereby forming a gas injection port 26 (nozzle slit). The injection port 26 extends in the plate width direction of the steel strip S. The vertical cross-sectional shape of the nozzle 20A has a tapered shape tapering toward the tip. The thickness of the tip portions of the upper and lower nozzle members 24A and 24B may be about 1 to 3 mm. The opening width (nozzle gap B) of the injection port is not particularly limited, but can be about 0.5 to 3.0 mm. A gas supplied from a gas supply mechanism (not shown) passes through the inside of the header 22, further passes through a gas flow path defined by the upper and lower nozzle members 24A and 24B, is injected from the injection port 26, and Sprayed on. The other nozzle 20B has a similar configuration. In the present invention, the gas pressure inside the nozzle header 22 is defined as “header pressure P”.

  In the method for manufacturing a hot-dip metal-plated steel strip of the present embodiment, the steel strip S is continuously immersed in the hot-dip metal bath 14, and the hot-dip steel strip S is disposed on the hot-dip steel strip S with the steel strip S interposed therebetween. Gas is blown from a pair of gas wiping nozzles 20A and 20B to adjust the amount of molten metal adhered to both sides of the steel strip S, thereby continuously producing a hot-dip metal-plated steel strip.

  Here, as a cause of the occurrence of hot water wrinkles described above, generation of initial irregularities at a point (stagnation point) where the wiping gas collides with the surface of the molten metal can be cited. The initial irregularities are generated by one or both of (1) the vibration of the collision pressure of the wiping gas and (2) the unevenness of the viscosity due to the oxidation / cooling of the molten metal, and the molten metal is irregularly formed on the steel strip. It is thought to be flowing. The present invention is intended to suppress the occurrence of hot water wrinkles by suppressing the above phenomenon (1).

  Therefore, the present inventors have studied a method for suppressing the fluctuation amount of the collision pressure of the wiping gas. Specifically, the wiping was performed while changing the header pressure P, and the measurement of the collision pressure fluctuation amount σ of the wiping gas and the inspection of the surface appearance after the wiping were performed. The collision pressure of the wiping gas can be measured by measuring the sound pressure generated at the point where the wiping gas collides with the surface of the molten metal (stagnation point) with a microphone. The collision pressure slightly fluctuates with time around a certain pressure value even when the wiping gas is injected at a certain header pressure. In the present invention, the collision pressure fluctuation amount σ is defined as a standard deviation of the value of the collision pressure measured during a predetermined period. This predetermined period is set to 0.1 second or more. This is because if the standard deviation is obtained in a period of 0.1 second or more, the variation in the collision pressure can be accurately evaluated. The collision pressure is preferably measured at the center in the width direction of the steel strip. However, the measurement value is equivalent if the impact pressure is 100 mm or more inside from the end in the width direction of the steel strip. At the end of the steel sheet, the wiping gas that has collided is disturbed and is not suitable for measurement.

  FIG. 4 shows the relationship between the header pressure P and the gas collision pressure fluctuation amount σ in one experimental example. As is clear from FIG. 4, it has been found that there is a positive linear correlation between the header pressure P and the gas collision pressure fluctuation amount σ. It is obvious that if the header pressure P is increased, the collision pressure itself is also increased. However, the present inventors have found for the first time that the collision pressure fluctuation amount σ also increases as the header pressure increases, as shown in FIG. In this experimental example, occurrence of hot water wrinkles was confirmed in the range where the collision pressure fluctuation amount σ was 300 Pa or more.

  When the collision pressure fluctuation amount σ is large, it is considered that the fluctuation of the collision pressure generates initial unevenness of the plating and causes a wrinkle defect. Therefore, reduction of the collision pressure fluctuation amount σ is effective for suppressing hot water wrinkles. Then, according to the knowledge shown in FIG. 4, it can be understood that the collision pressure fluctuation amount of the gas can be controlled by controlling the header pressure. By controlling the impact pressure fluctuation amount σ, it becomes easy to achieve the target plating adhesion amount with high accuracy, the occurrence of hot water wrinkles can be sufficiently suppressed, and a high-quality hot-dip coated steel strip can be manufactured at low cost.

  However, although the relationship between the header pressure P and the collision pressure fluctuation amount σ still has a positive linear correlation, the specific value relationship is determined by the nozzle shape, the nozzle slit gap B, and the nozzle angle. Depends on θ. Further, it was found that the threshold value of the collision pressure fluctuation amount at which the occurrence of hot water wrinkles differs depending on the running speed L of the steel strip and the target plating thickness W.

σ：ガスの衝突圧変動量［Pa］
Ｌ：鋼帯の走行速度［m/min］
Ｗ：目標のめっき厚さ［μm］
α，β：定数 Therefore, the present inventors have further studied and found that the gas collision pressure fluctuation amount σ satisfies the following expression (1) according to the traveling speed L of the steel strip and the target plating thickness W. It was found that by controlling the temperature, the generation of hot water wrinkles was sufficiently suppressed, and a high-quality hot-dip coated steel strip could be produced.

σ: Gas impact pressure fluctuation [Pa]
L: Running speed of steel strip [m / min]
W: Target plating thickness [μm]
α, β: constant

Hereinafter, an example of a method for determining operating conditions using Expression (1) will be described.
(A) In the plating equipment used in which the nozzle shape, the nozzle slit gap B, and the nozzle angle θ are determined, the relationship between the header pressure P and the collision pressure fluctuation amount σ as shown in FIG. 4 is obtained in advance.
(B) Next, a target plating thickness W is set.
(C) Next, an appropriate traveling speed L of the steel strip is appropriately determined according to the thickness and the width of the steel strip.
(D) Next, the set target plating thickness W and running speed L of the steel strip are substituted into the equation (1) to determine a suitable range of the gas collision pressure fluctuation amount σ.
(E) Next, the header pressure P that satisfies the expression (1) is determined based on the relationship between the header pressure P and the collision pressure fluctuation amount σ obtained in advance.
(F) Next, in consideration of the determined traveling speed L and header pressure P of the steel strip, a distance D (see FIG. 2) between the nozzle tip and the steel strip for obtaining the target plating thickness W is determined. I do.

  Under general operating conditions, the distance D is about 3 to 40 mm. However, within this range, the relationship between the header pressure P and the collision pressure fluctuation amount σ does not change regardless of the value of the distance D. Have been confirmed by the present inventors. Therefore, by the above-described procedures (A) to (F), it is possible to perform an operation in which generation of hot water wrinkles is sufficiently suppressed.

  Here, since the constants α and β in the equation (1) differ depending on the shape of the nozzle, the slit gap B of the nozzle, and the nozzle angle θ, they are determined in advance in an online experiment. Hereinafter, how to determine these constants and the technical meaning of equation (1) will be described.

  Here, the right side of Expression (1) indicates the upper limit of the collision pressure fluctuation amount σ at which hot water wrinkles do not occur. The meaning of each parameter on the right side of Expression (1) will be described. When the target plating thickness W increases, hot water wrinkles easily occur, and the upper limit value of the collision pressure fluctuation amount σ decreases. When the steel strip traveling speed L increases, the time during which the wiping gas collides becomes shorter, and it becomes difficult to generate hot water wrinkles, so that the upper limit of the collision pressure fluctuation amount σ increases.

Here, the constants α and β are obtained as follows. In the combination (W ₁ , L ₁ ) of the target plating thickness W and the value of the running speed L of the steel strip determined by the methods (B) and (C) described above, the header pressure P is variously changed. The collision pressure fluctuation amount σ ₁ at the boundary where the hot water wrinkles begin to be generated is determined. The plating thickness depends on the header pressure P, the distance D, and the running speed L of the steel strip. Therefore, in the operation of a running speed L _1, the combined header pressure P to variously changed, so that it can realize the target plating thickness W _1, the distance D must be changed as appropriate.

Furthermore, in another combination (W ₂ , L ₂ ) of the values of W and L determined by the methods (B) and (C) described above, the header pressure P is variously changed, and hot water wrinkles begin to occur. The collision pressure fluctuation amount σ ₂ at the boundary is obtained. Similarly, in a plurality of combinations of the values of W and L (W _k , L _k ) (k; an integer of 1 to n), the collision pressure fluctuation amount σ _k at the boundary where the hot water wrinkle starts to be generated is _obtained . The obtained n points are plotted on a graph in which the horizontal axis is L / W ² and the vertical axis is σ. From the plot of n points, a straight line that minimizes the residual sum of squares is obtained by the least squares method, the value of the slope is α, and the intercept of the vertical axis is β. Note that the "impact pressure variation boundaries Yu wrinkles begin to occur" in the steel strip surface after wiping, the arithmetic mean waviness Wa is 1.00μm impact pressure variations measured based on the standard of JIS B0601-2001 Shall mean quantity . This is because if Wa exceeds 1.00 μm, small hot water wrinkles can be visually confirmed. From the viewpoint of the accuracy of the constants α and β, n is preferably 4 or more.

  As described above, in order to suppress hot water wrinkle defects, it is necessary to control the gas collision pressure fluctuation amount σ according to the running speed L of the steel strip and the target plating thickness W. More specifically, the relationship between the header pressure P of the gas wiping nozzle and the gas collision pressure fluctuation amount σ as shown in FIG. 4 is obtained in advance, and the gas collision pressure fluctuation amount satisfies Expression (1). The header pressure P can be set as described above.

  Then, the relationship between the header pressure P of the gas wiping nozzle and the gas collision pressure fluctuation amount σ as shown in FIG. 4 for each plating equipment condition (nozzle shape, nozzle slit gap B, and nozzle angle θ) used. Are determined in advance, and the constants α and β are determined in advance in an online experiment. When at least one of the running speed L of the steel strip and the target plating thickness W as operating conditions is changed, a suitable range of the collision pressure fluctuation amount σ and a corresponding header pressure are changed. Change the preferred range of P.

  According to the knowledge shown in FIG. 4, if only the occurrence of hot water wrinkles is to be prevented, the collision pressure fluctuation amount σ, that is, the header pressure P may be set as small as possible. It is not necessary to know the upper limit of the collision pressure fluctuation amount σ that does not occur. However, if the header pressure P is reduced to reduce the collision pressure fluctuation amount σ, the distance D must be reduced in order to achieve the target plating thickness W. Then, when the steel strip is warped, there is a concern that the nozzle may come into contact with the steel strip, splash may easily adhere to the nozzle, and scratches or defects may occur on the plating surface. In addition, when the header pressure P is reduced, the collision pressure particularly at the edge portion of the steel strip is weakened, and the adhesion amount at the edge portion becomes too thick, so that the adhesion amount may be uneven in the steel strip width direction. This situation is referred to herein as an edge overcoat. From such a viewpoint, it is preferable that the header pressure P is set as large as possible as long as the collision pressure fluctuation amount satisfies the expression (1). Therefore, in the present invention, it is significant to know the upper limit value of the collision pressure fluctuation amount σ at which the hot water wrinkle does not occur in Expression (1).

  Effective means for preventing edge overcoat include lowering the height of the nozzle from the bath surface and using a baffle plate. By implementing both or one of these means, it becomes possible to obtain a more beautiful appearance without hot water wrinkles or edge overcoats.

  If the height of the nozzle is reduced, wiping can be performed before the plating surface layer of the steel strip edge portion solidifies, so that edge overcoat can be prevented. From this viewpoint, it is preferable that the height of the tip of the gas wiping nozzle be 250 mm or less from the surface of the molten metal bath. However, if the height of the wiping nozzle is too low, a large amount of splash occurs on the bath surface, so that a height of 100 mm or more is desirable.

  Referring to FIG. 3, baffle plate 28 indicates a plate arranged on the steel strip extension surface near the widthwise end of steel strip S. By installing a baffle plate, collision between gases injected from a pair of gas wiping nozzles can be avoided, so that edge overcoat can be prevented. In FIG. 3, the baffle plates 28 arranged near one end in the width direction of the steel strip S are illustrated, but it is preferable to arrange the baffle plates near the ends on both sides in the width direction of the steel strip. The shortest distance d between the baffle plate 28 and the widthwise end of the steel strip S is preferably about 1 to 10 mm.

  The gas injected from the nozzles 20A and 20B is preferably an inert gas. By using an inert gas, oxidation of the molten metal on the surface of the steel strip can be prevented, so that uneven viscosity of the molten metal can be further suppressed. Examples of the inert gas include, but are not limited to, nitrogen, argon, helium, and carbon dioxide.

  In this embodiment, the components of the molten metal include Al: 1.0 to 10% by mass, Mg: 0.2 to 1% by mass, and Ni: 0 to 0.1% by mass, and the balance is preferably composed of Zn and inevitable impurities. . It has been confirmed that when Mg is contained as described above, unevenness in viscosity due to oxidation / cooling of the molten metal is likely to occur, and hot water wrinkles are likely to occur. In addition, in the above-mentioned component system, since the viscosity is lower than that of molten metal of 100% Zn, when initial unevenness occurs at the stagnation point, the initial unevenness grows larger before the molten metal solidifies, so that hot water wrinkles are generated. Easier to do. Therefore, when the molten metal has the above component composition, the effect of suppressing the hot water wrinkles of the present invention is remarkably exhibited. Further, even when the composition of the molten metal is 5% by mass Al—Zn or 55% by mass Al—Zn, the effect of suppressing hot water wrinkles of the present invention can be obtained.

  Examples of the hot-dip galvanized steel strip manufactured by the manufacturing method of the present invention include a hot-dip galvanized steel sheet. Includes any coated steel sheet (GA) to be treated.

A production test of a hot-dip galvanized steel strip was performed on a hot-dip galvanized steel strip manufacturing line. In each of the invention examples and the comparative examples, the plating equipment shown in FIG. 1 was used. The gas wiping nozzle used had a nozzle gap B of 1.2 mm. In each of the invention examples and comparative examples, the composition of the plating bath, the temperature T of the plating bath, the melting point T _{M of the} plating bath, the target plating thickness W, the traveling speed L of the steel strip, the header gas pressure P of the wiping nozzle, and the Table 1 shows the impact pressure fluctuation amount σ, the distance D between the nozzle tip and the steel strip, the nozzle angle θ, the nozzle height H, and the use of the baffle plate. The distance D between the nozzle tip and the steel strip was set in consideration of the values of the steel strip running speed L and the header pressure P such that the plating adhesion amount at the center of one side of the steel strip satisfies W.

  As a method of supplying gas to the gas wiping nozzle, a method of supplying a gas pressurized to a predetermined pressure by a compressor was employed. In this way, a steel strip having a thickness of 1.2 mm and a width of 1000 mm was passed through to produce a hot-dip galvanized steel strip.

  In addition, when the constants in the equation (1) were obtained by a preliminary online test, they were α = 1725 and β = -60. Table 1 also shows a preferred range of the collision pressure fluctuation amount σ calculated from the equation (1).

In addition, the appearance of the manufactured hot-dip galvanized steel strip and the total coating weight of both sides were evaluated. Regarding the appearance evaluation of the steel sheet, pass / fail was determined based on the following criteria. Table 1 shows the results.
×: rejected = galvanized steel sheet (1.50 <Wa) where large hot water wrinkles can be visually confirmed
△: rejected = galvanized steel sheet (1.00 <Wa ≦ 1.50) where small wrinkles can be visually observed
：: Pass = beautiful galvanized steel sheet with no visible wrinkles (0.50 <Wa ≦ 1.00)
◎: Pass = Very beautiful galvanized steel sheet with no visible wrinkles (0 <Wa ≦ 0.50)
In addition, Wa is a value of the arithmetic mean waviness Wa [μm] measured based on the standard of JIS B0601-2001.

  C in Table 1 is C = (the amount of adhesion at the end of the steel strip−the amount of adhesion at the center of the steel strip) / the amount of adhesion at the center of the steel strip × 100. Is the value of the plating adhesion amount deviation [%].

  As is clear from Table 1, when the impact pressure fluctuation amount satisfies the expression (1), a beautiful surface appearance with a low Wa is obtained, whereas the collision pressure fluctuation amount σ is the expression (1). If not, Wa has increased. In particular, in the plating types B and E, the effect when the impact pressure fluctuation amount σ was within the range of the present invention was remarkably obtained.

  Further, when the nozzle height H was less than 250 mm or when a baffle plate was used, the adhesion amount deviation C in the width direction was reduced, and an effect of preventing edge overcoat was obtained.

  ADVANTAGE OF THE INVENTION According to the manufacturing method of the hot-dip metal-plated steel strip of this invention, generation | occurrence | production of hot water wrinkles is fully suppressed, and a high-quality hot-dip metal-plated steel strip can be manufactured at low cost.

REFERENCE SIGNS LIST 100 Continuous molten metal plating equipment 10 Snout 12 Plating bath 14 Molten metal bath 16 Sink roll 18 Support roll 20A, 20B Gas wiping nozzle 22 Nozzle header 24A Upper nozzle member 24B Lower nozzle member 26 Injection port (nozzle slit)
28 Baffle plate S Steel strip B Slit gap D Distance between tip of gas wiping nozzle and steel strip θ Nozzle angle

Claims (4)

Continuously immerse steel strip in molten metal bath,
A gas is blown from a pair of gas wiping nozzles arranged on the steel strip pulled up from the molten metal bath, with the steel strip interposed therebetween to adjust the amount of adhered molten metal on both surfaces of the steel strip,
A method for manufacturing a hot-dip metal-plated steel strip for continuously manufacturing a hot-dip metal-plated steel strip,
A relationship between a header pressure P [kPa] of the gas wiping nozzle and a collision pressure fluctuation amount σ of the gas is obtained in advance,
Based on the relationship, impact pressure variation of the gas σ is in accordance with the running speed L and the target of the plating thickness W of the steel strip, the header pressure P so as to satisfy the following equation (1) Decide,
Determine the distance D between the nozzle tip and the steel strip to obtain the target plating thickness W,
The method of manufacturing a hot-dip metal-plated steel strip , wherein the blowing of the gas is performed under the determined conditions of the header pressure P and the distance D.

σ: Gas impact pressure fluctuation [Pa]
L: Running speed of steel strip [m / min]
W: Target plating thickness [μm]
α, β: constant The height of the tip of the gas wiping nozzle, said to the surface of the molten metal bath and 250mm or less, the production method of the molten metal plated steel strip according to claim 1. On the steel strip extended surface in the width direction end portion vicinity of the steel strip, placing the baffle plate to avoid collisions of gas between ejected from said pair of gas wiping nozzle, the molten metal of claim 1 or 2 Manufacturing method of plated steel strip. Component of the molten metal, Al: 1.0 to 10 mass%, Mg: 0.2 to 1 mass%, Ni: 0 to 0.1 containing mass%, the balance being Zn and incidental impurities, according to claim 1 to 3 The method for producing a galvanized steel strip according to any one of the preceding claims.

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