JP2018178158A - Method of manufacturing hot-dip metallized steel strip - Google Patents

Abstract

An object of the present invention is to provide a method of manufacturing a hot-dip metal-plated steel strip which can sufficiently suppress the generation of hot water wrinkles and can manufacture a high-quality hot-dip metal-plated steel strip at low cost. A method for producing a hot-dip metal-plated steel strip according to the present invention comprises continuously dipping a steel strip (S) in a molten metal bath (14), and a pair of gas wiping nozzles (20A) in the steel strip (S) pulled up from the molten metal bath (14). , 20B to adjust the amount of molten metal deposited on both sides of the steel strip S to continuously produce a hot-dip metal-plated steel strip. Is controlled so as to satisfy a predetermined condition according to the traveling speed L and the target plating thickness W. [Selection diagram] FIG.

Description

  The present invention relates to a method of manufacturing a molten metal plated steel strip, and more particularly to gas wiping for adjusting the amount of molten metal deposited on the surface of the steel strip (hereinafter, also referred to as a "plated amount of plating").

  In the continuous molten metal plating line, as shown in FIG. 1, the steel strip S annealed in the continuous annealing furnace in a reducing atmosphere passes through the inside of the snout 10 and continuously into the molten metal bath 14 in the plating tank 12. Introduced to Thereafter, the steel strip S is pulled up above the molten metal bath 14 through 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 gas wiping nozzles 20A and 20B, the steel strip S is cooled. It is led to the post process. The gas wiping nozzles 20A and 20B are disposed above the plating tank 12 so as to face each other across the steel strip S, and spray gas toward both surfaces of the steel strip S from the injection ports. By this gas wiping, the excess molten metal is scraped off, the plating adhesion amount on the surface of the steel strip is adjusted, and the molten metal adhering 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 to cope with various steel strip widths and to cope with positional deviation in the width direction at the time of pulling the steel strip, and the width direction end of the steel strip It extends to the outside of the part.

  In such a gas wiping method, the molten metal plated steel strip produced due to one or both of (1) vibration of the collision pressure of the wiping gas, and (2) viscosity unevenness due to oxidation / cooling of the molten metal. Corrugated, ruffled hot water wrinkles (hot water drips) are easily generated on the plating surface. The plated steel sheet in which such hot water wrinkles arose, in the application of the exterior plate, when the plating surface is used as the surface of the base for coating, the surface properties of the coating film, in particular, the smoothness is inhibited. Therefore, the plated steel plate in which hot water wrinkles arose can not be used for the exterior plate in which the coating process excellent in the external appearance is calculated | required, and it has big influence on the yield of a plated steel plate.

  The following method is known as a method of suppressing the plating surface defect of hot water wrinkles. Patent Document 1 describes a method of making hot water wrinkles inconspicuous by changing the surface properties and rolling conditions of a temper rolling roll in temper rolling which is a step after plating. In Patent Document 2, before introducing a steel plate into a hot dip galvanizing bath, the surface roughness of the steel plate is adjusted according to the amount of plating adhesion using a skin pass mill, tension leveler or the like to suppress the generation of hot water wrinkles. How to do it is described.

Unexamined-Japanese-Patent No. 2004-27263 JP-A-55-21564

  However, according to the study by the present inventors, although the method described in Patent Document 1 improves minor hot water wrinkles, no effect is seen against severe hot water wrinkles. Further, in the method disclosed in Patent Document 2, there is a cost problem due to the necessity of installing a skin pass mill, a tension leveler or the like in the previous step of the hot dip galvanizing bath. Also, even when these are installed, it is difficult to obtain the ideal surface roughness due to the chemical and physical changes of the zinc plating film accompanying the pickling and recrystallization in the pretreatment equipment and the annealing furnace, and hot water wrinkles It is considered difficult to sufficiently suppress the occurrence.

  Then, in view of the above-mentioned subject, an object of the present invention is to provide a manufacturing method of a molten metal plating steel strip which can suppress generation of a hot water wrinkle sufficiently and can manufacture a high quality molten metal plating steel strip at low cost. .

  In order to solve the above-mentioned problems, the inventors of the present invention have conducted intensive studies and found that there is a positive linear correlation between the header pressure of the gas wiping nozzle and the gas collision pressure fluctuation amount, that is, the gas by controlling the header pressure. It has been found for the first time that the amount of impact pressure fluctuation can be controlled. And, by setting the collision pressure fluctuation amount of gas to a predetermined value in consideration of the traveling speed of the steel strip and the target plating thickness, it has been found that the generation of the hot water wrinkle 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 essential features of the present invention completed based on the above findings are as follows.
[1] Continuously immerse the steel strip in the molten metal bath,
A gas is blown from a pair of gas wiping nozzles disposed across the steel strip to the steel strip pulled up from the molten metal bath to adjust the adhesion amount of the molten metal on both sides of the steel strip,
A method for producing a molten metal plated steel strip for continuously producing a molten metal plated steel strip, comprising:
The molten metal plating characterized in that the collision pressure fluctuation amount σ of the gas is controlled to satisfy the following equation (1) according to the traveling speed L of the steel strip and the target plating thickness W. Steel strip manufacturing method.

σ: Collision pressure fluctuation of gas [Pa]
L: Travel speed of steel strip [m / min]
W: Target plating thickness [μm]
α, β: Constant

[2] The relationship between the header pressure P [kPa] of the gas wiping nozzle and the collision pressure fluctuation amount σ of the gas is determined in advance,
The method of manufacturing a molten 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 the formula (1).

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

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

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

  According to the method of manufacturing a molten metal plated steel strip of the present invention, the generation of hot water wrinkles can be sufficiently suppressed, and a high quality molten 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 installation. It is an enlarged view of the periphery of the front-end | tip part of gas wiping nozzle 20A in the continuous molten metal plating installation shown in FIG. It is a perspective view which shows the structure of the width direction edge part vicinity of steel strip S in the continuous molten metal plating installation used by this embodiment. It is a graph which shows the relationship between the header pressure P and the collision pressure fluctuation amount (sigma) of gas in one experimental example.

  With reference to FIG. 1, a continuous molten metal plating facility 100 (hereinafter, also simply referred to as a "plating facility") that can be used in the method of manufacturing a molten metal plated steel strip according to an embodiment of the present invention will be described.

  Referring to FIG. 1, the plating apparatus 100 of the present embodiment includes a snout 10, a plating tank 12 for containing a molten metal, a sink roll 16, and a support roll 18. The snout 10 is a member having a rectangular cross section perpendicular to the traveling direction of the steel strip, which defines a space through which the steel strip S passes, and its tip is immersed in the molten metal bath 14 formed in the plating tank 12 There is. In one embodiment, the steel strip S annealed in the continuous annealing furnace in a 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 through 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. It is cooled and led to the post process.

  The pair of gas wiping nozzles 20A and 20B (hereinafter, also simply referred to as "nozzles") are disposed above the plating tank 12 so as to face each other with the steel strip S interposed therebetween. With reference to FIG. 2 in addition to FIG. 1, the nozzle 20A sprays gas toward the steel strip S from the injection port 26 (nozzle slit) extending in the plate width direction of the steel strip at its tip, Adjust the amount of plating on the surface. The other nozzle 20B is also the same, and excess molten metal is scraped off by the pair of nozzles 20A and 20B, and the plating adhesion amount of both sides of the steel strip S is adjusted, and the plate width direction and the plate longitudinal direction Uniform.

  The nozzles 20A and 20B are generally configured longer than the steel strip width in order to cope with various steel strip widths and to cope with positional deviation in the width direction at the time of pulling up the steel strip, and from the width direction end of the steel strip 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 end portions of the upper and lower nozzle members 24A and 24B have surfaces facing each other in parallel in a cross sectional view 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 longitudinal cross-sectional shape of the nozzle 20A is a tapered shape that tapers toward the tip. The thickness of the tip of the upper and lower nozzle members 24A and 24B may be about 1 to 3 mm. Further, 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 and further passes through the gas flow path defined by the upper and lower nozzle members 24A and 24B, and is injected from the injection port 26 to the surface of the steel strip S. Be blown to The other nozzle 20B has a similar configuration. In the present invention, the pressure of the gas in the nozzle header 22 is defined as “header pressure P”.

  In the method of manufacturing a molten metal plated steel strip according to the present embodiment, the steel strip S is continuously immersed in the molten metal bath 14 and disposed so as to sandwich the steel strip S in the steel strip S pulled up from the molten metal bath 14. Gas is blown from a pair of gas wiping nozzles 20A and 20B to adjust the amount of adhesion of the molten metal on both sides of the steel strip S, and continuously manufacture a molten metal plated steel strip.

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

  Therefore, the present inventors examined a method of suppressing the fluctuation amount of the collision pressure of the wiping gas. Specifically, wiping was performed while changing the header pressure P, and measurement of the collision pressure fluctuation amount σ of the wiping gas and inspection of the surface appearance after wiping were performed. The collision pressure of the wiping gas can be measured by measuring with a microphone the sound pressure generated at the point where the wiping gas collides with the surface of the molten metal (the stagnation point). The collision pressure slightly fluctuates with time around a certain pressure value even though the wiping gas is injected at a certain header pressure. In the present invention, the collision pressure fluctuation amount σ is defined as the standard deviation of the values of the collision pressure measured during a predetermined period. The predetermined period is 0.1 seconds or more. This is because variation in collision pressure can be accurately evaluated if the standard deviation is taken in a period of 0.1 seconds or more. In addition, although it is preferable to measure a collision pressure in the width direction center part of a steel strip, if it is 100 mm or more inside from the steel strip width direction edge part, a measured value is equivalent. At the end of the steel plate, the wiping gas which has collided is disturbed and thus not suitable for measurement.

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

  When the collision pressure fluctuation amount σ is large, it is considered that the fluctuation of the collision pressure causes the initial unevenness of the plating to be a hot water wrinkle defect. Therefore, it is effective to reduce the collision pressure fluctuation amount σ for the suppression of hot water wrinkles. And according to the knowledge shown in FIG. 4, it turns out that the collision pressure fluctuation amount of gas can be controlled by controlling the header pressure. By controlling the collision pressure fluctuation amount σ, the target plating adhesion amount can be easily realized with high accuracy, the generation of hot water wrinkles can be sufficiently suppressed, and a high quality molten metal plated steel strip can be manufactured at low cost.

  However, although the relationship between the header pressure P and the collision pressure fluctuation amount σ does not change that there is a positive linear correlation, regarding the specific value relationship, the shape of the nozzle, the slit gap B of the nozzle, and the nozzle angle It depends on θ. Further, it was found that the threshold value of the collision pressure fluctuation amount at which hot water wrinkle starts to be generated differs depending on the traveling 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, as the inventors of the present invention further studied, the following equation (1) is satisfied so that the collision pressure fluctuation amount σ of the gas satisfies the following equation (1) according to the traveling speed L of the steel strip and the target plating thickness W It was found that the generation of hot water wrinkles can be sufficiently suppressed and high quality hot-dip galvanized steel strip can be manufactured by controlling the above.

σ: Collision pressure fluctuation of gas [Pa]
L: Travel speed of steel strip [m / min]
W: Target plating thickness [μm]
α, β: Constant

Hereinafter, an example of the determination method of the operating condition using Formula (1) is described.
(A) In the used plating facility in which the nozzle shape, the slit gap B of the nozzle, 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, the target plating thickness W is set.
(C) Next, according to the thickness and width of the steel strip, an appropriate traveling speed L of the steel strip is appropriately determined.
(D) Next, the target target plating thickness W and traveling speed L of the steel strip are substituted into the equation (1) to determine the preferable range of the collision pressure fluctuation amount σ of gas.
(E) Next, the header pressure P which satisfies the equation (1) is determined based on the relationship between the header pressure P and the collision pressure fluctuation amount σ which has been obtained in advance.
(F) Next, in consideration of the travel speed L of the steel strip and the header pressure P, the distance D (see FIG. 2) between the nozzle tip and the steel strip to obtain the target plating thickness W is determined. Do.

  Although the distance D is about 3 to 40 mm under general operating conditions, 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 within this range. The present inventors confirmed. Therefore, the operation which suppressed generation | occurrence | production of hot water wrinkles sufficiently is possible by the procedure of said (A)-(F).

  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 by an on-line experiment. Hereinafter, how to obtain these constants and the technical meaning of the equation (1) will be described.

  Here, the right side of the equation (1) indicates the upper limit value of the collision pressure fluctuation amount σ at which the hot water wrinkle does not occur. The meaning of each parameter in the right side of Formula (1) is described. When the target plating thickness W increases, hot water wrinkles are easily generated, so 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 short, and it becomes difficult to generate hot water wrinkles, so the upper limit value of the collision pressure fluctuation amount σ increases.

Here, the constants α and β are determined as follows. The header pressure P is variously changed in the combination (W ₁ , L ₁ ) of the target plating thickness W and the traveling speed L of the steel strip determined by the method (B) or (C) described above. The collision pressure fluctuation amount σ ₁ at the boundary where hot water wrinkles start to occur is determined. The plating thickness depends on the header pressure P, the distance D, and the traveling 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 method of (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 determined. Similarly, in a plurality of combinations (W _k , L _k ) (k; an integer of 1 to n) of the values of W and L, the collision pressure fluctuation amount σ _k at the boundary where hot water wrinkles start to occur is determined. 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 n-point plot, a line with the smallest residual sum of squares is determined by the least squares method, the value of the slope is α, and the intercept of the vertical axis is β. The term "collision pressure fluctuation at the boundary where hot water wrinkles start to occur" refers to a slit gap where the arithmetic mean waviness Wa measured based on the standard of JIS B0601-2001 on the steel strip surface after wiping is 1.00 μm. Shall be meant. When Wa exceeds 1.00 μm, small hot water wrinkles can be visually confirmed. In terms of the accuracy of the constants α and β, n is preferably 4 or more.

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

  The relationship between the header pressure P of the gas wiping nozzle and the collision pressure fluctuation amount σ of the gas as shown in FIG. 4 for each of the plating equipment conditions (the shape of the nozzle, the slit gap B of the nozzle, and the nozzle angle θ) used. Are determined in advance, and constants α and β are determined in advance by on-line experiments. Then, when at least one of the traveling speed L of the steel strip and the target plating thickness W as the operating conditions is changed, the preferable range of the collision pressure fluctuation amount σ and the corresponding header pressure accordingly Change the preferred range of P.

  According to the knowledge shown in FIG. 4, the collision pressure fluctuation amount .sigma., That is, the header pressure P may be set as small as possible to prevent the generation of hot water wrinkles, and in particular, the hot water wrinkles It is not necessary to grasp the upper limit value of the collision pressure fluctuation amount σ which 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 realize the target plating thickness W. Then, when warpage of the steel strip occurs, the nozzle may come in contact with the steel strip, or the splash may easily adhere to the nozzle, which may cause scratches or defects on the plated surface. In addition, when the header pressure P is reduced, in particular, the collision pressure at the edge portion of the steel strip weakens, and the adhesion amount at the edge portion becomes too thick, which may result in an uneven adhesion amount in the steel strip width direction. This current state is referred to herein as edge overcoat. From such a viewpoint, it is preferable to set the header pressure P as large as possible within the range in which the collision pressure fluctuation amount σ satisfies the equation (1). Therefore, in the present invention, it is significant to grasp the upper limit value of the collision pressure fluctuation amount σ at which the hot water wrinkle does not occur in the equation (1).

  Also, effective measures to prevent edge overcoating include the reduction of the nozzle height from the bath surface and the use of baffle plates. By implementing one or both of these means, it becomes possible to obtain a more beautiful appearance without hot water wrinkles and edge overcoats.

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

  Further, referring to FIG. 3, baffle plate 28 refers to a plate disposed on the steel strip extension surface near the widthwise end of steel strip S. By installing the baffle plate, it is possible to prevent the collision of the gases injected from the pair of gas wiping nozzles, so that edge overcoating can be prevented. Although FIG. 3 illustrates the baffle plates 28 disposed in the vicinity of the widthwise one side end of the steel strip S, it is preferable to dispose the baffle plates in the vicinity of the both ends of the steel strip in the width direction. 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, it is possible to prevent the oxidation of the molten metal on the surface of the steel strip, so it is possible to further suppress the viscosity unevenness of the molten metal. The inert gas includes, but is not limited to, nitrogen, argon, helium, carbon dioxide and the like.

  In the present embodiment, it is preferable that the components of the molten metal contain Al: 1.0 to 10% by mass, Mg: 0.2 to 1% by mass, Ni: 0 to 0.1% by mass, with the balance being Zn and unavoidable impurities . Thus, it is confirmed that when Mg is contained, viscosity unevenness due to oxidation / cooling of the molten metal is likely to occur, and hot water wrinkles are easily generated. Further, in the above component system, the viscosity is lower than that of the molten metal of 100% Zn, so when the initial unevenness occurs at the stagnation point, the initial unevenness grows larger before the molten metal solidifies, so that hot water wrinkles occur It becomes easy to do. Therefore, when a molten metal has the said component composition, the effect which suppresses the hot water wrinkle of this invention appears notably. In addition, even when the composition of the molten metal is 5% by mass Al-Zn or 55% by mass Al-Zn, the effect of suppressing the hot water wrinkle of the present invention can be obtained.

  Examples of the hot-dip galvanized steel strip produced by the production method of the present invention include a hot-dip galvanized steel sheet, which comprises a galvanized steel sheet (GI) not subjected to an alloying treatment after hot-dip galvanizing treatment and an alloyed steel sheet. It includes any of plated steel sheets (GA) to be treated.

The production test of the hot-dip galvanized steel strip was conducted in the production line of the hot-dip galvanized steel strip. The plating equipment shown in FIG. 1 was used in each of the invention examples and the comparative examples. 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, the pressure of the wiping gas The collision 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 presence or absence of the baffle plate are shown in Table 1. The distance D between the nozzle tip and the steel strip was set in consideration of the steel strip traveling speed L and the header pressure P so that the plating adhesion amount at the central portion of one side of the steel strip satisfies W.

  As a gas supply method to the gas wiping nozzle, a method of supplying one pressurized to a predetermined pressure by a compressor was adopted. Thus, a hot-dip galvanized steel strip was manufactured by passing a steel strip having a thickness of 1.2 mm and a width of 1000 mm.

  In addition, when the constant in Formula (1) was each calculated | required by the prior online test, it was (alpha) = 1725 and (beta) =-60. The preferable range of the collision pressure fluctuation amount σ calculated from the equation (1) is also shown in Table 1.

In addition, the appearance of the produced hot-dip galvanized steel strip and the total plating adhesion amount on both sides were evaluated. About the appearance evaluation of a steel plate, the following references | standards determined the pass / fail. The results are shown in Table 1.
X: Rejected = Galvanized steel sheet where large hot water wrinkles can be visually confirmed (1.50 <Wa)
:: Rejected = Galvanized steel sheet where small hot water wrinkles can be visually confirmed (1.00 <Wa ≦ 1.50)
○: Passing = Beautiful galvanized steel sheet (0.50 <Wa ≦ 1.00) where hot water wrinkles can not be confirmed visually
◎: Passing = Very beautiful galvanized steel sheet where hot water wrinkles can not be confirmed visually (0 <Wa ≦ 0.50)
Wa is a value of arithmetic mean waviness Wa [μm] measured based on the standard of JIS B0601-2001.

  Further, C in Table 1 is C = (adhesion amount of steel strip end-adhesion amount of steel strip central portion) / adhesion amount of steel strip central portion x 100, steel strip center and steel strip end Plating adhesion amount deviation [%].

  As apparent from Table 1, when the collision pressure fluctuation amount σ satisfies the expression (1), the Wa is low and a beautiful surface appearance is obtained, whereas the collision pressure fluctuation amount σ is given by the expression (1). If not satisfied, Wa has become large. In particular, in the plating types B and E, the effects obtained when the collision pressure fluctuation amount σ was in the range of the present invention were significantly obtained.

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

  According to the method of manufacturing a molten metal plated steel strip of the present invention, the generation of hot water wrinkles can be sufficiently suppressed, and a high quality molten metal plated steel strip can be manufactured at low cost.

100 continuous molten metal plating equipment 10 snout 12 plating tank 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 (5)

Immerse the steel strip continuously in a molten metal bath,
A gas is blown from a pair of gas wiping nozzles disposed across the steel strip to the steel strip pulled up from the molten metal bath to adjust the adhesion amount of the molten metal on both sides of the steel strip,
A method for producing a molten metal plated steel strip for continuously producing a molten metal plated steel strip, comprising:
The molten metal plating characterized in that the collision pressure fluctuation amount σ of the gas is controlled to satisfy the following equation (1) according to the traveling speed L of the steel strip and the target plating thickness W. Steel strip manufacturing method.

σ: Collision pressure fluctuation of gas [Pa]
L: Travel speed of steel strip [m / min]
W: Target plating thickness [μm]
α, β: Constant The relationship between the header pressure P [kPa] of the gas wiping nozzle and the collision pressure fluctuation amount σ of the gas is determined in advance,
The method for manufacturing a hot-dip metal plated steel strip according to claim 1, wherein the header pressure P is set such that the collision pressure fluctuation amount σ of the gas satisfies the equation (1).   The manufacturing method of the molten metal plated steel strip according to claim 1 or 2 which makes height of a tip of said gas wiping nozzle 250 mm or less from a surface of said molten metal bath.   The baffle plate which avoids the collision of the gas injected from said pair of gas wiping nozzles is installed on the steel strip extension surface of the width direction edge part vicinity of the said steel strip, The any one of Claims 1-3 The manufacturing method of the molten metal plated steel strip as described in 4.   The component of the molten metal contains Al: 1.0 to 10% by mass, Mg: 0.2 to 1% by mass, Ni: 0 to 0.1% by mass, and the balance consists of Zn and unavoidable impurities. The manufacturing method of the molten metal plated steel strip as described in any one of Claims.

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