JP2005344178A - Method for controlling coating weight of hot dip plating and gas wiping nozzle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce surface defects caused by splashes by increasing the squeezing force for molten metal in a gas wiping nozzle, and attaining the operation under low nozzle pressure. <P>SOLUTION: In a gas wiping method where the surface of a steel strip continuously taken up from a hot dip plating metal bath is ejected with gas from a wiping nozzle, so as to control the coating weight of hot dip plating metal, a main nozzle provided with an ejector in the wide direction of the steel strip and ejecting a main jet mainly controlling the coating weight of the hot dip plating metal and auxiliary nozzles each ejecting a pulsating flow from an ejector parallel to the ejector of the main nozzle are provided, both the surface and back faces of the steel strip taken up from the hot dip plating metal bath are ejected with the main jet from the main nozzle and the pulsating flows from the auxiliary nozzles, and the pulsating frequency of the pulsating flows ejected from the auxiliary nozzles is controlled to the one higher than the shearing eddy frequency of the main jet ejected from the main nozzle. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hot dip coating amount control method in a hot dip plating process and the like, and to a gas wiping nozzle used for control of a galvanizing amount. More specifically, the present invention relates to a hot-dip coating amount control method and a gas wiping nozzle suitable for controlling the basis weight in the plate width direction uniformly, suppressing the occurrence of splash, and performing efficient operation.

  For example, in a continuous hot dipping process or the like, as shown in FIG. 1, after the steel strip 10 is immersed in a plating bath 25 generally filled with a molten metal, the steel strip 10 is pulled up vertically upward. After that, the molten metal adhering to the surface of the steel strip 10 is opposed to the steel strip 10 in a plane parallel to the steel strip 10 so as to have a predetermined plating thickness uniformly in the plate width direction and the plate longitudinal direction. Gas wiping device for controlling the amount of molten metal attached by squeezing excess molten metal by jetting gas (wiping gas) from a wiping nozzle 22 extending in the width direction of the belt provided toward the steel strip Is provided.

  The wiping nozzle 22 is usually longer than the width of the steel strip 10, that is, the width of the steel strip 10, in order to cope with various widths of the steel strip 10 and at the same time cope with the displacement in the width direction when the steel strip 10 is pulled up. It extends from the end to the outside. In such a gas wiping device, since the jet that collides with the steel strip edge portion faces slightly outside and the impact force decreases, the edge where the plating thickness of the steel strip edge portion becomes thicker than the central portion of the steel strip As a result of overcoating and uneven adhesion, or so-called splash, in which molten metal falling below the steel strip scatters due to turbulence of the jet that collided with the steel strip 10, the surface quality of the steel strip deteriorates. Invite.

  In order to solve the above problem, an auxiliary nozzle (sub nozzle) is arranged around the wiping nozzle (main nozzle) that mainly controls the amount of molten metal adhering to the steel strip. A method for improving nozzle performance is disclosed.

  In the method disclosed in Patent Document 1, the main nozzle is formed by providing auxiliary nozzles (sub-nozzles) that are independently controllable and sprayed on the upper and lower portions of the main nozzle and divided into three or more in the width direction. It is said that the main jet flow from is suppressed from spreading, and the gas flowing along the steel plate after the collision is stabilized.

  The method disclosed in Patent Document 2 is a result of making the front end of the partition nozzle of the main nozzle and the sub nozzle an acute angle, tilting the sub nozzle 5 to 20 degrees with respect to the main nozzle, and lengthening the potential core. The volume controllability increases and the jet flow stabilizes, so noise is also reduced.

  In the method disclosed in Patent Document 3, when the main jet is injected, the main jet is surrounded by a high-temperature gas by radiating a flame as a cutoff gas for blocking the main jet from the surrounding air. The flow resistance of the jet is reduced, and the impact force can be improved by extending the potential core.

The prior art document information is described below. Non-patent document 1 and non-patent document 2 will be described in the section of the best mode for carrying out the invention for convenience of explanation.
JP-A-1-230758 (first page) JP-A-10-204599 (pages 2 and 3) JP 2002-348650 A (second page) N. Rajaratnam, Yasumasa Nomura, “Journey”, Morikita Publishing, July 31, 1981, p. 1-3 Kozo Sudo, et al., “Dynamics of Fluids”, Corona, September 30, 1994, p. 187-190

  However, in the method disclosed in Patent Document 1, an unstable vortex is generated in the vicinity of the partition plate between the main nozzle and the sub nozzle, and the shear vortex increases due to the mixing action of the vortex, thereby inhibiting the growth of the potential core. Therefore, in order to control the amount of adhesion, the injection pressure of the main nozzle must be increased, and the splash is deteriorated.

  The method disclosed in Patent Document 2 has been implemented to solve the problems of Patent Document 1. When the sub-jet is given from the vicinity of the main jet, the three jets are immediately combined to form one jet, so the straightness of the jet is thought to increase due to the rectifying effect, but in effect one slightly wider jet This is not the same as the jet flow control from a nozzle having a nozzle, and is not suitable for controlling the thinning of molten metal.

  The method disclosed in Patent Document 3 shows that uneven mixing due to the difference in specific gravity works between the main jet (low temperature gas) and the sub jet (high temperature gas), and uneven adhesion amount is likely to occur. It was.

  The present invention has been devised to solve the above-described problems. The pulsating flow from the sub-nozzle actively excites the shear vortex of the main jet at a constant frequency, thereby reducing the shear force of the main jet. The aim is to reduce surface defects due to splash by strengthening uniformly in the direction, increasing the squeezing power of the molten metal, and enabling operation at low nozzle pressure.

  Means of the present invention for solving the above-mentioned problems are as follows.

  A first aspect of the present invention is a gas wiping method for controlling the amount of adhesion of a molten plating metal by spraying a gas from a wiping nozzle onto the surface of a steel strip that is continuously pulled up from a hot dipped metal bath. A pulsating flow is jetted from a jet nozzle parallel to the jet nozzle of the main nozzle on at least one of the main nozzle that is provided and mainly controls the amount of adhesion of hot-dip plated metal and the upper and lower sides of the main nozzle. The pulsating frequency of the pulsating flow that is sprayed from the sub nozzle by spraying the main jet flow from the main nozzle and the pulsating flow from the sub nozzle onto both the front and back surfaces of the steel strip pulled up from the hot dipped metal bath. Is a method for controlling the amount of hot dip coating, characterized in that the frequency is equal to or higher than the shear vortex frequency of the main jet injected from the main nozzle.

  A second aspect of the present invention is the method of controlling a hot-dip coating amount according to the first aspect of the present invention, wherein the pulsating flow of the sub-jet is a pulsating flow based on gas suction and discharge at the sub-nozzle outlet. is there.

  According to a third invention, in the first invention, when the gas flow direction at the outlet of the sub nozzle is a positive direction of the gas discharge direction, the gas flow direction of the pulsating flow at the outlet of the sub nozzle is always the positive direction. This is a method of controlling the amount of hot dip coating that is characterized by the following.

  According to a fourth invention, in the second invention or the third invention, the pulsation frequency of the pulsating flow injected from the sub nozzle is set to a frequency range of 1 to 10 times the shear vortex frequency of the main jet injected from the main nozzle. This is a method for controlling the amount of hot-dip plating deposited.

  5th invention is a gas wiping nozzle which controls the thickness of a deposit metal by spraying gas from a wiping nozzle on the surface of a steel strip pulled up continuously from a molten metal plating bath. A main nozzle that ejects a main jet that mainly adjusts the amount of hot-dip plated metal, and a sub-nozzle that ejects a pulsating flow above and below the main nozzle from a jet parallel to the jet nozzle of the main nozzle. It is a gas wiping nozzle characterized by having.

  According to the present invention, since the above means is provided, the shear vortex of the main jet is fixed at a constant frequency by the pulsating sub-jet from at least one of the upper and lower sides of the main jet, so that the main jet having a stable and strong shear force can be obtained. It can be formed and the amount of hot-dip plating can be controlled efficiently.

  According to the present invention, by setting the pulsating flow from the sub nozzle to the optimum frequency range, the main jet shear layer is fixed, the potential core is extended further downstream, and the shear force of the shear vortex is reduced. Since it increases, the spreading angle of the main jet can be narrowed, and the wiping force for controlling the adhesion amount of the hot dipping can be increased. Therefore, even if the discharge pressure of the main jet flow is lowered, wiping can be performed efficiently, and the basis weight controllability can be improved and splash can be reduced.

  Hereinafter, the hot dipping control method and gas wiping apparatus of the present invention will be described with reference to the drawings.

  FIG. 2 is a schematic diagram illustrating a configuration example of the gas wiping nozzle according to the embodiment of the present invention. As shown in FIG. 2, the gas wiping nozzle 1 uses a rectifying plate 4 having a gas passage port (not shown) to feed a wiping gas (main jet) 8 supplied from the gas supply port 2 to the pressure header 3. The pressure distribution in the width direction is made uniform, and injection is performed from the main nozzle 5 toward the steel strip 10. The sub nozzles 7 are arranged above and below the main nozzle 5, and each outlet of the sub nozzle 7 is installed in parallel with the outlet of the main nozzle 5 and has an effective length equivalent to that of the main nozzle 5. The pulsating flow discharged from the injection port of the sub nozzle 7 (in this specification, the gas flow injected from the sub nozzle 7 is also referred to as “sub jet”) is injected with a slight inclination with respect to the main jet. It pulsates with a constant frequency and amplitude, and immediately after the injection, it becomes a small vortex 9 having a constant frequency (pulsation frequency) and acts on the main jet.

In order to evaluate the performance of this wiping nozzle, wind speed measurement (potential core length measurement) at the nozzle outlet was performed off-line. Here, the characteristics of the two-dimensional jet and the measurement method will be briefly described. The description regarding the two-dimensional jet is based on Non-Patent Document 1. As shown in FIG. 3, the jet flow from the nozzle can be divided into two parts of “development region” and “development region” in the axial direction. The development region is a region where turbulence from the outside gradually permeates toward the center line of the jet, and there is a wedge-shaped region where the average velocity of the jet initial velocity U ₀ does not decrease at all. This wedge-shaped region is called a potential core and is surrounded by a mixed region on both sides. As shown in FIG. 3, in the development region, the velocity distribution in the cross section perpendicular to the jet axis direction is similar.

  In order to measure the velocity distribution of such a jet in the gas wiping nozzle described above, a hot-wire anemometer having high spatial resolution and frequency resolution and generally used for turbulent flow measurement was used in this measurement experiment. A hot-wire anemometer is a measuring device that arranges a heated metal wire (hot-wire probe) in an air stream and measures the flow velocity by the cooling effect of the air stream.

The data obtained from the hot-wire anemometer is time-series data u _i having a large change speed as shown in FIG. 4, and the average speed Uavg is obtained from equation (1) (n: number of samples). Further, frequency analysis can be performed by performing FFT (Fast Fourier Transform) processing on the time series data u _i of the velocity.

  In this measurement, in the coordinate system shown in FIG. 5, along the central axis of the jet, that is, the line of y = 0, a hot wire probe that is a measurement sensor of the hot wire anemometer is installed, and the average flow velocity Uavg of the wiping gas is measured. Thus, the potential core length was measured.

As a result of the experiment, we discovered a phenomenon in which the potential core length of the main jet increases and decreases when the pulsation frequency of the sub nozzle is changed. The result of carrying out the experiment in detail is shown in FIG. Here, D: nozzle gap (main nozzle gap), F: pulsation frequency, F ₀ : main jet shear vortex frequency, and P: potential core length. Note that F / F ₀ = 0 is a state where there is no injection of the sub nozzle. The main jet shear vortex frequency F ₀ is a numerical value that varies depending on the main jet velocity and the nozzle outlet shape. In the present invention, the dominant frequency (as shown in FIG. 7) obtained by frequency analysis of velocity data at the Y direction end of the potential core. Power spectrum peak). The pulsation strength (pulsation fluctuation amplitude Vr) of the sub-jet will be described later.

As described above, the reason why the potential core length changes with the pulsation frequency is estimated as follows. When the vortex 9 is generated, the shear vortex of the main jet is excited, and the main jet shear layer is fixed at the frequency of the vortex 9 (= pulsation frequency). When the pulsation frequency is set within a predetermined range, that is, F / F ₀ ≧ 1, the potential core of the main jet is extended further downstream by the fixed shear layer. However, if the pulsation frequency is not set within the predetermined range, that is, if F / F ₀ <1, the main jet itself starts to vibrate up and down, the potential core decreases, and the jet flow is unsuitable for controlling the amount of coating. Become. This tendency was observed regardless of the average velocity of the secondary jet. The fact that the shear vortex of the main jet is fixed means that the shear force of the shear vortex has increased, and the so-called “wiping force” that controls the adhesion amount of hot dipped plating by narrowing the spread angle of the main jet It shows that the increase. An increase in the wiping force means that the amount of plating adhesion decreases even if the main jet flow is the same. Therefore, it is possible to perform wiping efficiently even if the gas header pressure of the main jet flow is lowered, so that the adhesion amount controllability is improved and the splash can be reduced.

It is considered that a longer potential core length is more advantageous for controlling the amount of plating adhesion. Based on the results shown in FIG. 6, the preferable range of the pulsation frequency is 1 ≦ F / F ₀ ≦ 10. A more preferable range of the pulsation frequency is 3 ≦ F / F ₀ ≦ 7, and an optimal range is 3 ≦ F / F ₀ ≦ 5.

The present invention is directed to a wiping nozzle for molten metal plating, and the nozzle pressure is usually about 0.1 to 1.5 kgf / cm ² . At this time, the nozzle exit wind speed is 120 to 360 m / s, and it is known that the shear vortex frequency at the measurement position ranges from approximately 100 Hz to 50000 Hz. Therefore, if the optimum range of the pulsation frequency is selected, it is appropriate to control in the range of 150,000 ≦ F ≦ 250,000 Hz if F ₀ = 100 Hz and 300 Hz ≦ F ≦ 500 Hz and F ₀ = 50000 Hz.

  The above investigation was performed by setting the fluctuation amplitude Vr (see FIGS. 9 and 12 for Vr for the flow velocity) of the pulsating sub-jet to 20% of the main jet outlet wind speed.

FIG. 8 shows a detailed investigation result regarding the optimum value of the fluctuation amplitude Vr of the flow velocity of the secondary jet. For measuring the fluctuation amplitude Vr of the sub-jet flow velocity, a hot-wire probe was placed at the sub-nozzle outlet, and the fluctuation amplitude of the sub-jet flow velocity was quantified without the main jet. The pulsation frequency F at this time was fixed to F / F ₀ = 4. From FIG. 8, it is preferable that the fluctuation velocity Vr of the sub-jet flow velocity satisfies Vr / U ≧ 0.05, and the optimum range is Vr / U ≧ 0.2. However, U: It is the main jet outlet average velocity.

  The above investigation was performed by injecting gas from all of the main jet and the two sub jets above and below the main jet. When only one of the sub-jets was used, the effect of extending the potential core was seen, although the degree of influence decreased somewhat. However, there was no difference in the extension of the potential core between the top and bottom.

  As for the flow direction of the sub-jet at the sub-nozzle outlet, when the flow discharged from the sub-nozzle is the forward flow and the reverse direction, that is, the flow sucked into the sub-nozzle is the negative flow, the sub-jet is ejected. As an example of an embodiment of the pulsating flow, as shown in FIG. 9, a pulsating flow in which the flow direction at the nozzle outlet alternately repeats positive and negative at a certain period, that is, discharge and suction are continuously repeated can be considered.

  As a specific method for generating such pulsating flow, pulsating flow applying means such as a piston mechanism, a vibrating body, or a speaker that reciprocates in the gas flow path (gas supply port, inside of nozzle, outlet, etc.) of the sub nozzle. And a method of applying a pulsating flow of an arbitrary frequency by inputting a sine wave signal from a signal generator to these devices can be exemplified, but the embodiment of the present invention may not be particularly in this form. When a vibration source such as a vibrating body or a speaker is installed in the nozzle, at the outlet or the like, the gas supply port may not be provided.

  FIG. 10 is an example in which a vibrating body 31 is attached in a nozzle near the gas outlet of the sub nozzle 7. An example of the vibrating body 31 is a piezoelectric element. As the vibrating body 31 reciprocates in the gas flow direction, an alternating gas flow in the forward direction and the reverse direction is generated at the sub nozzle gas outlet.

  FIG. 11 shows an example in which a speaker 32 is attached in the nozzle of the sub nozzle 7. By setting the output of the speaker 32 to a constant frequency within the range shown in FIG. 6, an alternating gas flow in the forward direction and the reverse direction is generated at the sub nozzle gas outlet.

  As another example of the embodiment of the pulsating flow injected from the sub nozzle, as shown in FIG. 12, the flow direction of the sub nozzle outlet is always a positive flow, and the vibration is generated by the vibration device or the vortex generator in the sub nozzle. A pulsating flow given vibration can be considered. The average speed Vavg of the sub nozzles is in the range of 0 <Vavg ≦ U. A specific method for supplying such a pulsating flow is to supply gas at a constant pressure from the gas supply port, and add it to the gas flow path (gas supply port, inside the nozzle, outlet, etc.) of the sub nozzle at a flow velocity U. A vibration device (piezoelectric element or speaker) is provided, or a rotating shaft with a protrusion is rotated against a thin elastic body (for example, a metal thin plate) that is cantilevered in the nozzle, and gas is generated by periodic collision between the protrusion and the elastic body. Although there is a method of generating a vortex by providing a simple protrusion or thin wire that does not operate itself, and generating a pressure fluctuation, this form is not particularly required. FIG. 13 shows an example in which a thin wire 33 is attached in the nozzle of the sub nozzle.

  For example, when a wire (cylindrical type) is installed in the vicinity of the sub-nozzle outlet, the vortex frequency generated behind the wire (sub-nozzle outlet side) is obtained from the following equation (2). Here, St: Strouhal number, f: Vortex frequency [Hz], d: Wire (cylinder) diameter [m], U: Outlet flow velocity [m / s].

  According to Non-Patent Document 2, the Strouhal number St is almost St = 0.21 over a wide flow velocity range. Therefore, when d = 3 mm and U = 50 m / s, the vortex frequency is simply f = 3500 Hz. Can be calculated.

  As a method for controlling the pulsating flow from the sub nozzles 7 located above and below the main nozzle 5, various controls can be assumed by combining two parameters of frequency and amplitude of speed fluctuation. Further, in the case of a main nozzle in which the width direction velocity profile of the main jet 8 from the main nozzle 5 has a non-uniform distribution, the sub-nozzle 7 is divided and controlled in the width direction to improve the width direction uniformity. It is also possible. In this embodiment, which will be described later, the frequency of the pulsating flow ejected from the sub-nozzle 7 and the amplitude of the speed fluctuation are controlled in an integrated manner, and the width profile of the main nozzle is within the allowable range. It was carried out with no direction division.

The gas wiping nozzle of the present invention shown in FIG. 2 was installed in a hot dip galvanized steel plate production line, hot galvanizing production experiments were performed, and the amount of adhesion controllability and the degree of splash were compared with conventional nozzles. . The manufacturing conditions were: plate speed 90 mpm, main nozzle gap 0.8 mm, sub nozzle gap 0.8 mm, nozzle height from molten zinc bath 420 mm, molten zinc bath temperature 460 ° C., main nozzle wiping gas pressure 0.3 kgf / cm ² etc. were the same. Table 1 shows the evaluation results of other manufacturing conditions, the amount of adhesion, and the degree of occurrence of splash. The degree of occurrence of splash was monitored by a video camera installed on the side of the nozzle, quantified by the area of splash in the screen, and compared with 1.0 as the management standard for current operation (Comparative Example 1). As described above, in this embodiment, the pulsating flow from a total of four sub nozzles, one above and one below the main nozzle on one side, was tested with the same frequency and the same speed fluctuation amplitude.

When the gas wiping main nozzle of this example was jetted under the above manufacturing conditions, the shear vortex frequency F ₀ was about 400 Hz. In Invention Examples 1 to 4 and Comparative Examples 3 and 4 in Table 1, the gas supply ports of the sub nozzles were provided at 10 positions at regular intervals in the nozzle width direction, and piston devices using electromagnets were installed in the respective gas supply ports. By inputting the signal of the signal generator to the piston device, all the piston devices can be controlled at an arbitrary frequency and velocity fluctuation amplitude. With this mechanism, gas is discharged and sucked alternately and continuously at the sub nozzle outlet. In Invention Examples 5 to 8, a single φ5 mm wire (cylindrical type) was stretched inside the sub nozzle, thereby generating a vortex in the wake of the wire and jetting a pulsating flow from the sub nozzle outlet. In Invention Examples 5 and 6, the nozzle outlet average flow velocity was set to 38 m / s and a frequency of 1600 Hz, and in Invention Examples 7 and 8, the nozzle outlet average flow velocity was set to 76 m / s and a pulsating flow having a frequency of 3200 was realized. Inventive Examples 9 and 10 have a pulsation frequency similar to that of Inventive Example 5 and jetted pulsating flow from only one of the sub nozzles provided above and below the main nozzle. Comparative Examples 1 and 2 are the most basic wiping nozzles without a sub nozzle.

  From the results of Invention Example 1 and Comparative Example 1, the nozzle wiping force was increased according to the present invention example, a decrease in the adhesion amount was confirmed, and there was no adhesion amount unevenness. From Invention Example 2 and Comparative Example 2, this tendency was effective even when the nozzle-steel strip distance was increased, and the splash reduction was significant. Similar results were obtained from Invention Examples 5 and 6, and there was almost no difference between the discharge / suction system (Invention Examples 1 and 2) and the discharge system (Invention Examples 5 and 6). In Invention Examples 3 and 4 in which the pulsation frequency was increased by 8 times, the adhesion amount was slightly increased compared to Invention Examples 1 and 2, but an increase in wiping force from the prior art was confirmed. In Invention Examples 7 and 8, since the adhesion amount is slightly increased as compared with Invention Examples 3 and 4, the discharge / suction system is effective when the steel plate-nozzle distance is increased. When the sub-jet was jetted from only one of the sub-nozzles provided above and below the main nozzle (Invention Examples 9 and 10), both the amount of adhesion and the splash were reduced compared to Comparative Example 1. . Compared to Invention Examples 9 and 10, there was no difference in potential core length, but from the viewpoint of wiping, it is more advantageous to inject a sub jet from the sub nozzle below the main nozzle.

  On the other hand, Comparative Examples 3 and 4 in which the pulsation frequency was not controlled within the optimum range were deteriorated in both adhesion amount controllability and splash occurrence, and the results showed that control of the pulsation frequency is important. .

  The method of the present invention can be used as a method for controlling the plating adhesion amount in the hot dipping process.

  The gas wiping nozzle of the present invention can be used as a gas wiping nozzle for controlling the amount of plating adhesion in a hot dipping process.

It is a longitudinal cross-sectional view which shows the manufacturing apparatus of a general continuous molten metal plating steel plate. It is the schematic which shows the structural example of the gas wiping nozzle of the gas wiping apparatus which concerns on embodiment of this invention. It is a figure explaining the potential core of a two-dimensional jet. It is a figure which shows the velocity data of the gas wiping nozzle measured with the hot wire anemometer. It is a figure explaining the measuring method of the potential core length of the wiping nozzle which has the sub nozzle which injects a pulsating flow up and down the main nozzle. It is a figure explaining the preferable range of the pulsation frequency of the pulsating flow injected from a sub nozzle. It is a diagram illustrating the main jet shear vortex frequency F _0. It is a figure explaining the preferable range of amplitude Vr of the pulsating flow injected from a subjet. It is a figure explaining the example of the pulsating flow from a sub nozzle. It is the figure which attached the vibrating body in the nozzle of a sub nozzle. It is the figure which attached the speaker in the nozzle of a sub nozzle. It is a figure explaining another example of the pulsation flow from a sub nozzle. It is the figure which attached the thin wire | line in the nozzle of a sub nozzle.

Explanation of symbols

1 Gas Wiping Nozzle 2 Gas Supply Port 3 Pressure Header 4 Rectifier Plate 5 Main Nozzle 6 Sub Nozzle Gas Supply Port 7 Sub Nozzle 8 Main Jet 9 Vortex Flow 10 Injected from Sub Nozzle Steel Strip (Steel)
11 Molten metal 21 Roll 22 Gas wiping nozzle 23 Support roll 24 Sink roll 25 Molten metal (plating bath)
31 Vibrator 32 Speaker 33 Wire

Claims (5)

In a gas wiping method in which the amount of adhesion of molten plating metal is controlled by blowing gas from a wiping nozzle onto the surface of a steel strip that is continuously pulled up from a hot dipped metal bath, a jet outlet is provided in the width direction of the steel strip. A main nozzle for injecting a main jet for adjusting the amount of adhesion of the galvanized metal, and a sub-nozzle for injecting a pulsating flow from an outlet parallel to the outlet of the main nozzle on at least one of the upper and lower sides of the main nozzle. The pulsation frequency of the pulsating flow sprayed from the sub nozzle is sprayed from the sub nozzle by spraying the main jet flow from the main nozzle and the pulsating flow from the sub nozzle on both front and back surfaces of the steel strip pulled up from the hot dipped metal bath. A method for controlling the amount of hot dip coating, characterized in that the frequency is equal to or higher than the shear vortex frequency of the main jet jetted from the hot water. 2. The method of controlling the amount of hot-dip plating according to claim 1, wherein the pulsating flow of the sub-jet is a pulsating flow based on suction and discharge of gas at the jet nozzle of the sub-nozzle. The gas flow direction of the pulsating flow at the outlet of the sub nozzle is always a positive direction when the gas flow direction at the outlet of the sub nozzle is a positive direction of gas discharge. Method for controlling the amount of hot-dip plating. The hot dip plating according to claim 2 or 3, wherein the pulsation frequency of the pulsating flow ejected from the sub nozzle is in a frequency range of 1 to 10 times the shear vortex frequency of the main jet ejected from the main nozzle. How to control the amount of adhesion. In the gas wiping nozzle that controls the thickness of the deposited metal by blowing gas from the wiping nozzle onto the surface of the steel strip that is continuously pulled up from the molten metal plating bath, a jet nozzle is provided in the steel strip width direction as a wiping nozzle. In addition, a main nozzle for injecting a main jet mainly adjusting the amount of adhesion of the hot-dip plated metal, and a sub nozzle for injecting a pulsating flow from the outlet parallel to the main nozzle outlet above and below the main nozzle. Gas wiping nozzle.

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