JP4862479B2 - Manufacturing method of molten metal plated steel strip - Google Patents

Description

  The present invention relates to a method for producing a molten metal plated steel strip in which a gas wiping nozzle is sprayed with a gas onto the surface of a steel strip that is continuously pulled up from a molten metal plating bath to control the amount of coating on the surface of the steel strip. is there.

  In a continuous hot dipping process, a steel strip is generally immersed in a plating bath filled with molten metal, and the steel strip is pulled vertically upward from the plating bath, and then a gas provided opposite to the steel strip. Gas wiping in which gas is blown from the wiping nozzle onto the steel strip surface is performed. By this gas wiping, excess molten metal is scraped off and the amount of plating adhesion is controlled, and the molten metal adhering to the steel strip surface is made uniform in the plate width direction and the plate longitudinal direction. The gas wiping nozzle is usually configured to be longer than the width of the steel strip and to the outside of the width end of the steel strip in order to cope with various widths of the steel strip as well as misalignment in the width direction when the steel strip is pulled up. It extends.

In such a gas wiping method, a so-called splash is generated in which molten metal falling below the steel strip is scattered around due to the turbulence of the gas jet that collided with the steel strip, which adheres to the surface of the steel strip and adheres to the surface of the plated steel strip. There is a problem that the quality is degraded.
In order to increase the production amount in the continuous processing process of the steel strip, the steel strip passing speed (line speed) may be increased. However, when controlling the coating amount by gas wiping method in the continuous hot dipping process, if the line speed is increased, the initial coating amount immediately after passing through the plating bath of the steel strip increases due to the viscosity of the molten metal. In order to control within a certain range, it is necessary to set the gas pressure blown from the gas wiping nozzle to the steel strip surface to a higher pressure, which greatly increases the splash and makes it impossible to maintain good surface quality.

In order to solve such problems, auxiliary nozzles (sub nozzles) are provided above and below the gas wiping nozzle (main nozzle) which mainly controls the amount of molten metal adhering to the steel strip, and the action of the sub nozzles The following method has been proposed which aims to improve the performance of the main nozzle.
The method disclosed in Patent Document 1 is provided with auxiliary nozzles (sub nozzles) that are divided into three or more in the width direction above and below the main nozzle, and each divided part can independently control pressure, and gas is supplied from the auxiliary nozzle. The jet of gas from the auxiliary nozzle suppresses the spread of the gas jet from the main nozzle and stabilizes the gas flowing along the steel strip after the collision.

In the method disclosed in Patent Document 2, the front end of the partition plate between the main nozzle and the sub nozzle has an acute angle, and the sub nozzle is inclined by 5 to 20 ° with respect to the main nozzle. By making it longer, the adhesion amount controllability is improved, and the gas jet is stabilized, so that noise is also reduced.
In the method disclosed in Patent Document 3, when a main gas jet is injected, a flame is radiated as a cut-off gas for blocking the main gas jet from the surrounding air. The flow resistance of the main gas jet is reduced by enclosing it in a circle, and the impact force can be improved by extending the potential core.
JP-A-1-230758 JP-A-10-204599 JP 2002-348650 A

However, it is practically difficult to apply these prior art methods in actual operation. This is because the nozzles used in these prior art methods are each provided with a plurality of nozzle slits (main nozzles and sub nozzles), and thus are generated at a frequency that is also a conventional single nozzle type gas wiping nozzle. This is because there is a high risk that nozzle clogging will occur frequently.
Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art and to make the steel strip pass at high speed in the manufacturing method of the molten metal plated steel strip in which the amount of plating adhesion is controlled using the gas wiping nozzle. However, an object of the present invention is to provide a manufacturing method capable of appropriately suppressing the occurrence of plating surface defects due to splash and nozzle clogging and stably manufacturing a high-quality molten metal-plated steel strip.

The gist of the production method of the present invention for solving the above problems is as follows.
[1] The surface of the steel strip pulled up continuously from the molten metal plating bath is provided with a sub nozzle portion on the upper side and / or lower side of the main nozzle portion, The gas injection direction is inclined, and gas is blown from a gas wiping nozzle configured so that the gas jet jetted from the sub nozzle unit joins the gas jet jetted from the main nozzle unit, and the amount of plating adhesion on the surface of the steel strip In the manufacturing method of the molten metal plating steel strip that performs control,
The gas injection port of the sub nozzle part is separated from the gas injection port of the main nozzle part by 5 mm or more in the anti-steel strip direction, and the gas jet injected from the sub nozzle part is jetted from the main nozzle part. A method for producing a molten metal-plated steel strip, characterized by injecting a gas from the sub-nozzle portion so that a flow velocity of 10 m / s or more is obtained at the merging portion.

[2] In the manufacturing method of [1], the sub nozzle portion is formed between a first nozzle wall body constituting the main nozzle portion and a second nozzle wall body arranged outside thereof, and the sub nozzle portion A method for producing a molten metal-plated steel strip, wherein gas is jetted along the outer surface of the first nozzle wall from a gas jetting port of the part.
[3] In the manufacturing method of [1] or [2] above, the distance that the gas injection port of the sub nozzle portion is separated from the gas injection port of the main nozzle portion in the anti-steel strip direction is 100 mm or less. A method for producing a hot-dip metal-plated steel strip.
[4] In the manufacturing method according to any one of [1] to [3], the thickness of the tip of the first nozzle wall body forming the gas injection port of the main nozzle portion is 2 mm or less. Steel strip manufacturing method.

  According to the present invention, by injecting gas from the sub-nozzle part under a predetermined condition, the collision pressure of the gas jet increases on the surface of the steel strip, and the pressure gradient of the collision pressure distribution in the steel strip passage direction is steep. Therefore, the scraping power of the molten metal by the gas jet is improved, and even when the steel strip is passed at high speed, the scraping of the molten metal can be performed without excessively increasing the gas pressure. It can be effectively suppressed. On the other hand, since the gas injection port of the sub-nozzle part is separated from the gas injection port of the main nozzle part in the anti-steel strip direction, occurrence of nozzle clogging can also be suppressed. For this reason, the occurrence of plating surface defects due to splash and nozzle clogging can be appropriately suppressed even during the high-speed feeding of the steel strip, and a high-quality molten metal-plated steel strip can be stably produced.

  When controlling the coating amount by blowing gas from the gas wiping nozzle onto the surface of the steel strip that is continuously pulled up from the molten metal plating bath and scraping off the molten metal adhering to the surface of the steel strip, the plating scraping power is reduced. In order to improve the adhesion amount controllability by increasing it, it is effective not only to increase the maximum collision pressure of the gas jet on the steel strip surface, but also to make the pressure gradient of the collision pressure distribution curve in the steel strip passage direction steep It is. As a method for realizing this, as shown in FIG. 4, sub nozzle portions 20 a and 20 b are provided on the upper and lower sides of the main nozzle portion 10, and the gas in the sub nozzle portions 20 a and 20 b with respect to the gas injection direction of the main nozzle portion 10. It is conceivable to use a gas wiping nozzle configured such that the jet direction is inclined and the gas jet jetted from the sub-nozzle portions 20a and 20b joins the gas jet jetted from the main nozzle portion 10.

According to a study by the present inventors, by using such a gas wiping nozzle, the collision pressure of the gas jet rises on the surface of the steel strip, and the pressure gradient of the collision pressure distribution in the direction of the steel strip passes through. It becomes steep. This gas jet improves the plating scraping power, and even when the steel strip passes through at high speed, it can scrape the molten metal without excessively increasing the gas pressure, effectively suppressing the occurrence of splash. can do. FIG. 5 shows a comparison between collision pressure distribution curves of a conventional single nozzle type gas wiping nozzle (gas wiping nozzle having no sub-nozzle portion) and the gas wiping nozzle shown in FIG. a) shows the former, and (b) shows the latter collision pressure distribution curve. In y / b on the horizontal axis of the graph, b is the nozzle slit width (slit gap), and y is the distance from the gas jet center (y = 0). Further, the collision pressure ratio on the vertical axis is a pressure ratio with respect to the maximum pressure with the maximum pressure of the collision pressure distribution curve of (a) as the reference (1.0). y <0 is the lower side from the center of the gas jet (on the hot dip plating tank side), and y> 0 is the upper side from the center of the gas jet (on the anti-hot dip plating tank side).
As shown in FIG. 5, the collision pressure distribution of (b) by the gas wiping nozzle of FIG. 4 is a diffusion of the gas jet compared with the collision pressure distribution of (a) by the conventional single nozzle type gas wiping nozzle. Is suppressed, the pressure gradient of the collision pressure distribution curve changes steeply, and the collision pressure increases, which indicates that the plating scraping power is improved as compared with (a).

However, in the method using the gas wiping nozzle as shown in FIG. 4, a plurality of nozzle slits (main nozzle and sub nozzle) are present at a position very close to the steel strip surface, so that nozzle clogging may occur frequently. Is not suitable for actual operation.
Therefore, in the present invention, nozzle clogging is prevented by separating the gas injection port of the sub nozzle portion by an appropriate distance in the anti-steel strip direction from the gas injection port of the main nozzle portion, and the sub nozzle portion is injected from the sub nozzle portion. By controlling the flow rate of the gas jet (hereinafter referred to as the sub-gas jet) to a predetermined condition, the diffusion of the gas jet (hereinafter referred to as the main gas jet) ejected from the main nozzle portion is suppressed, thereby FIG. (B) As shown in (b), the pressure gradient of the collision pressure distribution curve is steepened, the collision pressure is increased, and the plating scraping power is improved, thereby preventing the occurrence of splash without excessively increasing the gas pressure. To do.
Here, the above-described action by the sub-gas jet from the sub-nozzle part has no essential difference regardless of whether the sub-nozzle part is provided on the upper side or the lower side of the main nozzle part. Therefore, in the present invention, the sub nozzle part may be provided only on either the upper side or the lower side of the main nozzle part, and the sub nozzles may be provided on the upper side and the lower side of the main nozzle part, respectively.

Hereinafter, details and preferred embodiments of the production method of the present invention will be described.
The gas wiping nozzle used in the present invention includes a main nozzle portion and a sub nozzle portion provided above and / or below the main nozzle portion, and the gas injection direction of the sub nozzle portion is inclined with respect to the gas injection direction of the main nozzle portion. The gas jet jetted from the sub nozzle unit is joined to the gas jet jetted from the main nozzle unit, and the gas is applied to the surface of the steel strip that is continuously pulled up from the molten metal plating bath. Gas is blown from the wiping nozzle to control the amount of plating on the steel strip surface.
In the manufacturing method of the present invention, the gas injection port of the sub nozzle part is separated from the gas injection port of the main nozzle part by 5 mm or more in the anti-steel strip direction, and the gas jet injected from the sub nozzle part is separated from the main nozzle part. Gas is jetted from the sub-nozzle portion so that the flow velocity is 10 m / s or more at the junction with the jetted gas jet.

  FIG. 1 shows an embodiment of a gas wiping nozzle used in the present invention, and is a longitudinal sectional view of the nozzle. This gas wiping nozzle includes a main nozzle portion 1 and a sub nozzle portion 2 provided on the upper side thereof, and a sub nozzle with respect to the gas injection direction of the main nozzle portion 1 (usually substantially perpendicular to the steel strip surface). The gas jet direction of the part 2 is inclined, and the gas jet jetted from the sub nozzle part 2 is joined to the gas jet jetted from the main nozzle part 1. The main nozzle portion 1 includes upper and lower first nozzle wall bodies 3a and 3b (first nozzle members), and a gas injection port 4 (nozzle slit) is formed between the tips of the first nozzle wall bodies 3a and 3b. Yes. A second nozzle wall 5 (second nozzle member) is disposed outside (above) the first nozzle wall 3a, and the second nozzle wall 5 and the first nozzle wall 3a serve as a sub nozzle portion. 2 is formed. And between the front-end | tip of the 2nd nozzle wall body 5 and the 1st nozzle wall body 3a forms the gas injection port 6 (nozzle slit), gas flows along the outer surface of the said 1st nozzle wall body 3a from this gas injection port 6. Is injected.

  The gas injection port 6 of the sub-nozzle unit 2 is separated from the gas injection port 4 of the main nozzle unit 1 by 5 mm or more in the anti-steel strip direction (L: separation distance in the figure). Thereby, the nozzle clogging of the sub nozzle 2 due to the splash of molten metal can be appropriately suppressed. If the separation distance L of the gas injection port 6 of the sub-nozzle unit 2 with respect to the gas injection port 4 of the main nozzle unit 1 is less than 5 mm, the effect of preventing nozzle clogging is insufficient. A more preferable lower limit of the separation distance L is 10 mm.

On the other hand, if the separation distance L of the gas injection port 6 of the sub-nozzle unit 2 with respect to the gas injection port 4 of the main nozzle unit 1 becomes too large, not only will the required gas amount increase, but also the sub-gas from the sub-nozzle unit 2 This is not preferable because the effect of improving the plating scraping force by the jet flow is also reduced. It is generally known that the gas jet flows along the wall surface (Coanda effect). However, if the jet direction changes suddenly or flows over a long distance, the jet flow gradually separates or diffuses from the wall surface. Therefore, in order to suppress this, the amount of gas required increases. If the separation distance L of the gas injection port 6 of the sub nozzle unit 2 with respect to the gas injection port 4 of the main nozzle unit 1 is about 100 mm or less, an adhering jet is formed along the outer surface of the first nozzle wall 3a due to the Coanda effect. Therefore, the sub-gas jet from the sub-nozzle 2 is efficiently formed. However, when the thickness exceeds 100 mm, diffusion gradually occurs, and not only the necessary gas amount increases, but also the plating scraping force by the sub-gas jet from the sub-nozzle. The improvement effect is also reduced. For this reason, the separation distance L is 100 mm or less, preferably 50 mm or less.
The first nozzle walls 3a and 3b are desirably designed to have a shape that does not have a very abrupt angle change in order to prevent separation of the sub-gas jet.

Further, in the manufacturing method of the present invention, the gas from the sub-nozzle part 2 is gas so that the sub-gas jet from the sub-nozzle part 2 has a flow velocity of 10 m / s or more at the junction p with the main gas jet from the main nozzle part 1. Inject. When the flow velocity of the sub gas jet at the junction p is less than 10 m / s, the effect of preventing the diffusion of the main gas jet by the sub gas jet cannot be sufficiently obtained, and the effect of improving the plating scraping force is small. Moreover, the more preferable flow velocity of the subgas jet in the junction part p is 20 m / s or more.
In addition, the control of the flow velocity of the auxiliary gas jet at the merge portion p is to obtain the relationship between the header pressure and the actual flow velocity of the auxiliary gas jet at a position corresponding to the merge portion p in advance to control the header pressure. Can be performed.

  FIG. 2 shows another embodiment of the gas wiping nozzle used in the present invention, and is a longitudinal sectional view of the nozzle. This gas wiping nozzle includes a main nozzle portion 1 and auxiliary nozzle portions 2a and 2b provided on the upper side and the lower side thereof, and a gas injection direction of the main nozzle portion 1 (usually in a direction substantially perpendicular to the steel strip surface). In contrast, the gas injection directions of the sub nozzle portions 2a and 2b are inclined so that the sub gas jet flow from the sub nozzle portions 2a and 2b merges with the main gas jet flow from the main nozzle portion 1. The configuration of the main nozzle portion 1 is the same as that shown in FIG. 1, but the second nozzle is disposed outside (upper and lower) of the first nozzle walls 3a and 3b (first nozzle member) constituting the main nozzle portion 1. Wall bodies 5a and 5b (second nozzle members) are arranged, and the sub nozzle portions 2a and 2b are formed by the second nozzle wall bodies 5a and 5b and the first nozzle wall bodies 3a and 3b. And between each front-end | tip of 2nd nozzle wall body 5a, 5b and 1st nozzle wall body 3a, 3b forms gas injection port 6a, 6b (nozzle slit), From said gas injection port 6a, 6b, said 1st nozzle Gas is jetted along the outer surfaces of the walls 3a, 3b.

  The gas injection ports 6a and 6b of the sub nozzle portions 2a and 2b are separated from the gas injection port 4 of the main nozzle portion 1 by 5 mm or more, preferably 10 mm or more in the anti-steel strip direction (L: separation distance in the figure). Let Thereby, the nozzle clogging of the sub nozzles 2a and 2b due to the splash of molten metal can be appropriately suppressed. The separation distance L is 100 mm or less, preferably 50 mm or less. Further, from the sub nozzle unit 2, the sub gas jet flow from the sub nozzle unit 2 has a flow velocity of 10 m / s or more, preferably 20 m / s or more at the junction p with the main gas jet from the main nozzle unit 1. Inject gas. The reasons for limiting the separation distance L and the flow velocity of the auxiliary gas jet are the same as in the embodiment of FIG.

FIG. 3 is a partially enlarged view of the nozzle tip portion of FIG. 1. The gas wiping nozzle used in the present invention is the thickness of the tip of the first nozzle wall bodies 3 a and 3 b forming the gas injection port 4 of the main nozzle portion 1. It is preferable that t is 2 mm or less, desirably 1 mm or less. Although depending on the degree of inclination of the gas injection direction of the sub nozzle with respect to the gas injection direction of the main nozzle part, when the thickness t of the tip of the first nozzle wall bodies 3a and 3b exceeds 2 mm, the main gas jet and the sub gas jet Therefore, the effect of preventing the diffusion of the main gas jet by the secondary gas jet is reduced, and the effect of improving the plating scraping force is reduced.
In general, the gas wiping nozzle is R-processed so that the corners of the gas wiping nozzle are in contact with an arc having a radius R in order to perform surface treatment such as Cr plating, but the inner and outer corners of the tips of the first nozzle walls 3a and 3b. The radius R is desirably as small as possible, and R0.5 or less is particularly preferable in order to sufficiently exhibit the effect of preventing the diffusion of the main gas jet by the sub-gas jet.

The gas wiping nozzle used in the present invention is usually configured so that the main nozzle portion 1 and the sub nozzle portions 2, 2a, 2b are individually provided so that the injection gas pressure of the main nozzle portion and the sub nozzle portion can be arbitrarily adjusted. While having a pressure chamber (not shown), each pressure chamber is individually supplied with pressure-controlled gas.
The nozzle slit width (slit gap) of the gas injection ports 4 and 6 of the main nozzle portion 1 and the sub nozzle portions 2, 2 a and 2 b is not particularly limited, but generally the nozzle slit width of the gas injection port 4 is 0.5˜. The nozzle slit width of the gas injection port 6 is about 0.1 to 2.5 mm. Further, the inclination angle of the gas injection direction of the sub nozzle portions 2, 2a, 2b with respect to the gas injection direction of the main nozzle portion 1 is not particularly limited, but is generally 5 ° to 70 °, preferably 10 ° to 70 °, particularly Preferably it is comprised at about 15 degrees-45 degrees.

In the production line of hot dip galvanized steel strip, various gas wiping nozzles were installed at the gas wiping position above the hot dip galvanizing bath, and production tests of hot dip galvanized steel strip having a plate thickness of 1.0 mm and a plate width of 1200 mm were conducted. . The manufacturing conditions (common to all tests) were: gas wiping nozzle height from hot dip galvanizing bath surface: 400 mm, hot dip galvanizing bath temperature: 460 ° C., main gas jet pressure of gas wiping nozzle: 0.65 kgf / cm ² , gas The distance between the wiping nozzle and the steel strip was 8 mm, the steel strip passage speed was 120 mpm, and the coating adhesion amount and nozzle clogging occurrence frequency (times / hr) in each test were investigated. The results are shown in FIGS. In addition, as a gas wiping nozzle, the thing which has a sub nozzle on the upper side and the lower side of the main nozzle part as shown in FIG.2 and FIG.4 was used. These gas wiping nozzles have a nozzle slit width of the main nozzle portion: 1 mm, a nozzle slit width of the sub nozzle portion: 1 mm, and an outer wall angle of the main nozzle portion: 40 ° (angle θ in FIGS. 2 and 4).

  FIG. 6 shows the relationship between the separation distance L, the plating adhesion amount, and the nozzle clogging occurrence frequency when the gas injection port of the sub nozzle part is separated from the gas injection port of the main nozzle part in the anti-steel strip direction. It is a thing. FIG. 7 is an enlarged view of a part of FIG. 6 (region with a small separation distance L). In this test, as the gas wiping nozzle, a nozzle of the type shown in FIG. 4 (separation distance L = 0) and a nozzle of the type shown in FIG. In any gas wiping nozzle, the thickness t of the tip of the first nozzle wall constituting the main nozzle portion is 1 mm, and the flow velocity of the sub gas jet at the junction p with the main gas jet of the main nozzle portion is 20 m / s. Note that the reference plating adhesion amount shown in FIGS. 6 and 7 is the plating adhesion amount when gas wiping is performed only by gas injection from the main nozzle portion without gas injection from the sub nozzle portion. According to FIGS. 6 and 7, the number of clogged nozzles is remarkably reduced when the separation distance L is 5 mm or more, and particularly when it is 10 mm or more. On the other hand, if the separation distance L exceeds 100 mm, the effect of improving the plating scraping force due to the sub-gas jet from the sub-nozzle portion is reduced, and the plating adhesion amount approaches the reference plating adhesion amount. In particular, when the separation distance L is 50 mm or less, the effect of improving the plating scraping force by the sub-gas jet flow from the sub-nozzle portion is more appropriately obtained.

  FIG. 8 shows a gas wiping nozzle of the type shown in FIG. 2 (separation distance L = 20 mm, thickness t = 1 mm at the tip of the first nozzle wall constituting the main nozzle portion). The relationship between the flow velocity of the sub-gas jet at the junction p of the gas jet and the sub-gas jets from the sub-nozzle portions 2a and 2b, the plating adhesion amount, and the nozzle clogging frequency is shown. FIG. 9 is an enlarged view of a part of FIG. 8 (region with a small separation distance L). The reference plating adhesion amount shown in FIG. 8 and FIG. 9 is the plating adhesion amount when gas wiping is performed only by gas injection from the main nozzle portion without gas injection from the sub nozzle portion. According to FIG. 8 and FIG. 9, when the flow velocity of the sub-gas jet from the sub-nozzle portion at the confluence portion p is 10 m / s or more, the plating adhesion amount is effectively reduced, and particularly effectively at 20 m / s or more. is doing.

FIG. 10 is a gas wiping nozzle (separation distance L = 20 mm) of the type shown in FIG. 2, and the thickness t of the tip of the first nozzle walls 3a and 3b forming the gas injection port 4 of the main nozzle portion 1 is shown. The relationship between the thickness t, the plating adhesion amount, and the nozzle clogging frequency is shown. In this test, the flow velocity of the auxiliary gas jet at the junction p with the main gas jet of the main nozzle portion 1 was 20 m / s.
According to FIG. 10, if the thickness t of the tip of the first nozzle walls 3a and 3b is 2 mm or less, the effect of improving the plating scraping force by the sub-gas jet from the sub-nozzle part can be obtained, and the nozzle clogging Is also suppressed. In particular, when the thickness t is 1 mm or less, the effect of improving the plating scraping power is high.

The longitudinal cross-sectional view which shows one Embodiment of the gas wiping nozzle used by this invention The longitudinal cross-sectional view which shows other embodiment of the gas wiping nozzle used by this invention Partial enlarged view of the nozzle tip of the gas wiping nozzle of FIG. A longitudinal sectional view showing a gas wiping nozzle of a reference example provided with sub nozzles on the upper side and lower side of the main nozzle part A graph comparing the impact pressure distribution curves of the conventional single nozzle type gas wiping nozzle and the gas wiping nozzle shown in FIG. In a manufacturing test using the gas wiping nozzle of the type shown in FIG. 4 and the gas wiping nozzle of the type shown in FIG. 2 having a different separation distance L, the relationship between the separation distance L, the plating adhesion amount and the nozzle clogging occurrence frequency was shown. Graph The graph which expanded and showed a part (area | region where the separation distance L is small) of FIG. FIG. 2 is a graph showing the relationship between the flow velocity of the auxiliary gas jet at the junction p with the main gas jet, the amount of plating adhesion, and the frequency of nozzle clogging in the manufacturing test using the gas wiping nozzle of the type shown in FIG. The graph which expanded and showed a part (area | region where the separation distance L is small) of FIG. 2 shows the relationship between the thickness t of the tip of the first nozzle wall forming the gas injection port of the main nozzle part, the amount of plating adhesion, and the frequency of nozzle clogging in a manufacturing test using the gas wiping nozzle of the type shown in FIG. Graph

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main nozzle part 2,2a, 2b Sub nozzle part 3a, 3b 1st nozzle wall body 4,6 Gas injection port 5,5a, 5b 2nd nozzle wall body 10 Main nozzle part 20a, 20b Sub nozzle part p Merge part

Claims (4)

On the surface of the steel strip that is continuously pulled up from the molten metal plating bath, a sub nozzle part is provided above and / or below the main nozzle part, and the gas injection direction of the sub nozzle part with respect to the gas injection direction of the main nozzle part Is inclined, and gas is blown from a gas wiping nozzle configured so that the gas jet jetted from the sub-nozzle unit joins the gas jet jetted from the main nozzle unit, and the amount of plating adhesion on the steel strip surface is controlled. In the manufacturing method of the molten metal plating steel strip,
The gas injection port of the sub nozzle part is separated from the gas injection port of the main nozzle part by 5 mm or more in the anti-steel strip direction, and the gas jet injected from the sub nozzle part is jetted from the main nozzle part. A method for producing a molten metal-plated steel strip, characterized by injecting a gas from the sub-nozzle portion so that a flow velocity of 10 m / s or more is obtained at the merging portion.   The sub nozzle part is formed between the first nozzle wall body constituting the main nozzle part and the second nozzle wall body arranged on the outside thereof, and the first nozzle wall body is formed from the gas injection port of the sub nozzle part. The method for producing a hot-dip metal-plated steel strip according to claim 1, wherein gas is injected along the outer surface.   The molten metal plated steel strip according to claim 1 or 2, wherein a distance at which the gas injection port of the sub nozzle portion is separated from the gas injection port of the main nozzle portion in the anti-steel strip direction is 100 mm or less. Manufacturing method.   The thickness of the front-end | tip of the 1st nozzle wall which forms the gas injection port of a main nozzle part is 2 mm or less, The manufacturing method of the molten metal plating steel strip in any one of Claims 1-3 characterized by the above-mentioned.

Images