The present invention relates to a hot-dip plating method for a metal material, and more particularly to a hot-dip plating method for a steel material.
Background technology
[0002]
　The methods currently used for manufacturing hot-dip plating products (hot-dip plating methods) are roughly classified into continuous hot-dip plating methods and dip-plating methods. In the following, a steel material will be illustrated as a representative of the metal material, and a hot-dip plating method for the steel material will be described.
[0003]
　The continuous hot-dip plating method is a method in which a coiled steel material (metal band) is continuously passed through a hot-dip plating bath (immersion and passage) to plate the steel material. The immersion plating method is a so-called "deep-dip plating" method, in which flux is attached to a preformed steel material and then the steel material is immersed in a hot-dip plating bath for plating. ..
[0004]
　The equipment used to carry out the continuous hot-dip plating method (continuous hot-dip plating equipment) usually includes pretreatment equipment, a reduction heating furnace, a hot-dip plating bath (molten metal pot), and post-treatment equipment. In the pretreatment equipment, a process of removing rolling oil and dirt adhering to the steel material is performed. In the reduction heating furnace, the Fe oxide present on the surface of the steel material is reduced by heating the steel material in an atmosphere containing H 2 . In the hot-dip plating bath portion, the steel material treated in the reduction heating furnace is immersed and passed through the hot-dip plating bath while being maintained in a reducing atmosphere or an atmosphere for preventing reoxidation of the steel material surface. Is hot-dip plated. In the above post-treatment equipment, various treatments are applied to the hot-dip plated steel material depending on the application.
[0005]
　On the other hand, the equipment used for performing dobu-zuke plating (dobu-zuke plating equipment) is a degreasing equipment that removes oil and dirt from preformed steel materials, and removes Fe oxide layers (called rust or black skin). It includes a pickling facility for pickling, a flux facility for adhering flux to a pickled steel material, and a hot-dip plating bath portion for hot-plating the dried steel material of the flux. If necessary, a post-treatment facility may be added to the ditch-pickled plating facility as in the case of the continuous hot-dip plating facility. The flux is used to improve the reactivity between the steel material and the hot-dip plating bath.
[0006]
　Conventionally, in the hot-dip plating method, there may be a problem that plating defects (called non-plating or pinholes) occur on the surface of the plated product (semi-finished product) after hot-dip plating. The plating defect is a portion where the molten metal does not adhere to the steel material and the plating metal does not exist on the surface of the steel material. Various factors are considered for the occurrence of plating defects, and countermeasures have been taken for many years. For example, as one of the countermeasures, a technique of performing hot-dip plating in a state where ultrasonic vibration is applied to a metal band after heat treatment (reduction treatment) in a continuous hot-dip plating method has been proposed (Patent Documents 1 and 2). See). In the case of dobu-dip plating, a technique for performing dobu-dip plating using ultrasonic waves has been proposed to solve the problem that non-plating occurs due to burning (exposure of the alloy layer) (Patent Document 3). See).
[0007]
　Generally, in the continuous hot-dip plating method, the metal strip material itself is annealed and the oxide film existing on the metal strip surface is reduced by the reduction heating furnace before the metal strip is immersed in the molten metal pot. .. In the reduction heating furnace, the metal band is heat-treated in a mixed atmosphere of nitrogen and hydrogen, for example, in order to reduce the oxide film. In this heat treatment, the heating temperature of the metal band is set according to the purpose of use of the plated product, and in order to improve the reactivity between the metal band and the hot-dip plating bath, the metal band is at least above the temperature of the hot-dip plating bath. It is heated.
[0008]
　Since the oxide film on the surface of the metal band is removed by the treatment in the reduction heating furnace, the reactivity between the metal band and the hot-dip plating bath is improved in the hot-dip plating bath. Therefore, it is possible to stably produce a metal band subjected to hot-dip plating.
Prior art literature
Patent documents
[0009]
Patent Document 1: Japanese Patent Publication "Japanese Patent Application Laid-Open No. 2-125850"
Patent Document 2: Japanese Patent Publication "Japanese Patent Application Laid-Open No. 2-282456"
Patent Document 3: Japanese Patent Publication "Japanese Patent Application Laid-Open No. 2000-" 064020 Publication "
Outline of the invention
Problems to be solved by the invention
[0010]
　However, plating defects may occur on the surface of the plated product due to various factors such as the composition of the metal material or the manufacturing conditions, and this is not only the case of continuous hot-dip plating, but also the case of dobu-dip plating. The same applies to the case of manufacturing a plated product.
[0011]
　Further, in recent years, there has been an increasing demand for (i) energy saving of the hot-dip plating method and (ii) for workers to engage in hot-dip plating work in a clean working environment.
[0012]
　The reduction heating furnace in the continuous hot-dip plating facility requires a very large amount of heat and consumes a large amount of nitrogen and hydrogen used as atmospheric gases. This also applies to the techniques described in Patent Documents 1 and 2. In the conventional continuous hot-dip plating method, it is not easy to reduce the energy consumption while satisfying the requirements for hot-dip plating products (small plating defects, etc.).
[0013]
　Further, in the sewage plating equipment, a flux equipment is usually provided in order to ensure good plating performance. In this case, there are the following problems from the viewpoint of the working environment. That is, (i) it is necessary to handle chlorides (including ZnCl 2 , NH 4 Cl, etc.) which are the main components of the flux , and (ii) when the metal material after the flux has dried is immersed in the hot-dip plating bath. There are problems such as the generation of a large amount of white smoke and odor. It is difficult to improve the working environment while satisfying the requirements for hot-dip plating products in the sewage plating equipment.
[0014]
　One aspect of the present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to have good plating wettability between a metal material and a hot-dip plating bath and to reduce energy consumption as compared with the conventional one. And to provide a hot-dip plating method that can improve the working environment.
Means to solve problems
[0015]
　In order to solve the above problems, the hot-dip plating method according to one aspect of the present invention is to allow a metal material to enter a plating bath which is a hot-dip metal, and while the metal material is in contact with the hot-dip metal, the above-mentioned In the plating step, the metal material is coated with the molten metal while applying vibration during the plating bath, and the frequency of the vibration applied to the plating bath is used as a basic frequency. It is characterized in that the vibration is applied so that the measured acoustic spectrum satisfies the relationship of the following equation (1).
[0016]
　(IB-NB) / (IA-NA)> 0.2 ... (1)
　(Here,
　IA: average value of sound pressure over the entire measurement frequency band
　IB: (i) Peak of sound pressure at the above basic frequency Average value of sound pressure in a specific frequency band between (ii) peaks of sound pressure at a plurality of harmonic frequencies and between adjacent peaks of sound pressure peaks at a plurality of harmonic frequencies
　NA: The above-mentioned measurement frequency band Overall, the average value of the sound pressure when the vibration is not applied
　NB: The average value of the sound pressure when the vibration is not applied in the specific frequency band defined for the IB
).
[0017]
　In the present specification, the intensity ratio determined by (IB-NB) / (IA-NA) as described above may be referred to as a characteristic intensity ratio. The present inventors have found that the plating property of a metal material is improved by performing hot-dip plating under the condition that the characteristic strength ratio is larger than 0.2.
The invention's effect
[0018]
　According to one aspect of the present invention, there is provided a hot-dip plating method capable of reducing the energy consumption and improving the working environment as compared with the conventional case, while having good plating wettability between the metal material and the hot-dip plating bath. be able to.
A brief description of the drawing
[0019]
FIG. 1 is a schematic view showing an example of a hot-dip plating apparatus that implements the hot-dip plating method according to the first embodiment of the present invention.
FIG. 2 is a graph showing an example of an acoustic spectrum measured by a spectrum analyzer included in the hot-dip plating apparatus.
FIG. 3 is a graph showing an example of an acoustic spectrum measured by the spectrum analyzer when the ultrasonic output is changed.
FIG. 4A is a graph showing the effect of ultrasonic output on the average intensity of the entire measurement frequency band in the acoustic spectrum and the average intensity between overtones, and FIG. 4B is a graph showing the influence of the ultrasonic output on the entire measurement frequency band in the acoustic spectrum. It is a graph which shows the influence of the ultrasonic output on the ratio of the average intensity between harmonics with respect to the average intensity of.
FIG. 5 is a schematic view showing an example of a hot-dip plating apparatus that implements the hot-dip plating method according to the first embodiment of the present invention.
[Fig. 6] Fig. 6 is a side view showing the state of the test material after plating.
FIG. 7 is a graph showing an acoustic spectrum measured by changing the output of an ultrasonic vibrator at each distance when the position of the tip of the waveguide and the distance between the steel plate are changed. (A) Indicates a case where the distance is 1 mm, (b) is a distance of 5 mm, (c) is a distance of 10 mm, (d) is a distance of 30 mm, and (e) is a case of a distance of 80 mm.
FIG. 8 is a graph showing the relationship between the above distance and the characteristic intensity ratio.
FIG. 9 is a schematic view showing an example of a hot-dip plating apparatus that implements the hot-dip plating method according to the third embodiment of the present invention.
FIG. 10 is a schematic view showing an example of a hot-dip plating apparatus that implements the hot-dip plating method according to the fifth embodiment of the present invention.
FIG. 11 is a schematic view showing an example of a hot-dip plating facility that implements the hot-dip plating method according to the sixth embodiment of the present invention.
FIG. 12 is a schematic view showing a modified example of the hot-dip plating equipment.
[Fig. 13] (a) is a schematic view showing a state in which a steel sheet is allowed to enter a hot-dip plating bath in an atmospheric atmosphere, and (b) is an enlarged schematic view of a region (A1) in the figure shown in (a). It is a partially enlarged view shown in the above.
FIG. 14 is an acoustic spectrum observed when vibration is applied to a hot-dip plating bath using an ultrasonic vibrator having an output of 380 W.
Mode for carrying out the invention
[0020]
　Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description is for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Further, in the present application, "A to B" indicates that it is A or more and B or less. The shapes and dimensions of the configurations described in each drawing in the present application do not necessarily reflect the actual shapes and dimensions, and are appropriately changed for the sake of clarity and simplification of the drawings.
[0021]
　(Definition of Terms) In the
　present specification, various molten metals (molten metals) constituting the hot-dip plating bath may be referred to as "hot-dip plating bath metal". Further, in the present specification, the material and shape of the steel material to be subjected to hot-dip plating using the hot-dip plating bath are not particularly limited unless otherwise specified. Further, "steel plate" may be read as "steel strip" as long as there is no inconvenience.
[0022]
　In general, in the hot-dip plating method, "platability" means both the wettability of plating between a metal material and a hot-dip plating bath and the adhesion of plating between a metal material and a plating layer formed on the surface of the metal material. Is sometimes referred to as plating property. However, in the present specification, the plating property is used to mean the plating wettability.
[0023]
　
　Generally, (i) a steel plate (steel strip) that has not been subjected to reduction treatment is allowed to enter a hot-dip plating bath, or (ii) the atmosphere (high oxygen concentration) without using a snout. When the steel sheet is allowed to enter the hot-dip plating bath in an atmosphere, the reaction between the steel sheet and the hot-dip plating bath metal is hindered, and good plating properties cannot be obtained. The reason for this will be described in detail with reference to FIG. FIG. 13A is a schematic view showing how a steel sheet is allowed to enter a hot-dip plating bath in an atmospheric atmosphere. FIG. 13B is a partially enlarged view schematically showing an enlarged area (A1) of the figure shown in FIG. 13A.
[0024]
　As shown in FIG. 13A, the steel sheet 100 that has not been reduced is allowed to enter the hot-dip plating bath 110 under an atmospheric atmosphere. An oxide film is formed on the surface of the steel sheet 100. Further, the bath surface oxide 112 is present at the boundary (that is, the surface of the hot-dip plating bath 110) between the hot-dip plating bath metal 111 inside the hot-dip plating bath 110 and the outside atmosphere (atmosphere) of the hot-dip plating bath 110. do.
[0025]
　As shown in FIG. 13B, the steel plate 100 entraps (i) the bath surface oxide 112 and (ii) the air entrainment layer 120 formed by the atmospheric gas (air) on the surface of the hot-dip plating bath 110. It enters the hot-dip plating bath 110 so as to be involved. As a result, the reaction inhibiting portion 130 is formed between the hot-dip plating bath metal 111 and the oxide film 101 of the steel sheet 100 inside the hot-dip plating bath 110. The reaction inhibiting portion 130 is compoundly formed by the bath surface oxide 112 and the air entrainment layer 120. The oxide film 101 and the reaction inhibiting portion 130 inhibit the reaction between the steel sheet 100 and the hot-dip plating bath metal 111, so that the surface of the plated product after being pulled up from the hot-dip plating bath 110 has plating defects (pinholes or non-plating). Etc.) easily occur.
[0026]
　Therefore, in the hot-dip plating method in the prior art, as described above, the steel sheet in which the oxide film on the steel sheet surface is reduced by using a heating furnace is made to enter the hot-dip plating bath through the snout maintained in the reducing atmosphere (). For example, see Patent Documents 1 and 2). In this case, when the steel sheet enters the hot-dip plating bath, the reaction between the steel sheet and the hot-dip plating bath metal proceeds rapidly.
[0027]
　The present inventors have diligently studied a hot-dip plating method capable of reducing energy consumption by a new method different from the conventional technique as described above. As a result, when the steel material is brought into the hot-dip plating bath, the reactivity between the steel material and the hot-dip plating bath metal can be enhanced by the vibration activation effect generated by applying vibration under specific conditions to the hot-dip plating bath. I found a new finding. According to this knowledge, the plating property of the steel material can be improved even when the steel material at room temperature is allowed to enter the hot-dip plating bath in the air atmosphere. Such a phenomenon is a phenomenon that was not expected by the prior art at all, as can be seen from the fact that the conventional hot-dip plating equipment has a configuration in which the reduction heating furnace is arranged in the stage before the hot-dip plating portion.
[0028]
　The differences between the findings found by the present inventors and the prior art will be described in more detail as follows. That is, conventionally, a technique has been proposed in which a high sound pressure vibration is applied to a hot-dip plating bath using a high-power (for example, several hundred W class) ultrasonic vibrator. In this case, for example, as shown in FIG. An acoustic spectrum (a white noise-like spectrum with few characteristic peaks) is observed. FIG. 14 is an acoustic spectrum observed when vibration is applied to the hot-dip plating bath using an ultrasonic vibrator having an output of 380 W. In this type of technology, the cavitation effect of high-power ultrasonic irradiation of the hot-dip plating bath is used to physically remove the oxide film existing on the surface of the steel sheet (or the oxide film remaining on the surface of the steel sheet after reduction treatment). By breaking, the plating property of the steel sheet was improved.
[0029]
　On the other hand, the present inventors have found that the vibration activating effect of the present invention is recognized even when a low-power ultrasonic vibrator is used, and the plating property of the steel sheet is effectively improved. I found it. In this case, as will be described in detail later, a peak characteristic of the acoustic spectrum is observed. The present inventors consider the vibration activating effect that is exhibited even at a low sound pressure, which is different from the prior art, as follows.
[0030]
　Specifically, although it is not clear yet, even when a low sound pressure is applied to the hot-dip plating bath, the hot-dip plated metal in the molten state vibrates under pressure due to sound waves, and due to this pressure vibration, the hot-dip plating bath is subjected to pressure vibration. Bubbles are generated. Then, when the generated bubbles are crushed by the pressure vibration, it is considered that a shock wave is generated toward the periphery of the bubbles. Further, it is considered that the bubbles repeat expansion and contraction due to the pressure vibration, and it is also conceivable that the expansion and contraction causes a local flow of the molten plated metal around the bubbles. The action of the shock wave and the local flow based on the acoustic energy promotes mass transfer at the interface between the steel material and the plating bath, resulting in effects such as a decrease in the thickness of the boundary layer or an increase in the mass transfer rate. As a result, a mechanism is conceivable in which the plating wettability between the steel material and the hot-dip plating bath is ensured.
[0031]
　Even in the conventional technique (when high sound pressure vibration is applied to the hot-dip plating bath), it is considered that the phenomenon of promoting mass transfer at the interface between the steel material and the hot-dip plating bath occurs. However, according to the findings of the present invention, it is not necessary to apply high sound pressure vibration to the hot-dip plating bath, and the vibration energy has a vibration activating effect that can secure the plating wettability between the steel material and the hot-dip plating bath. It turned out that it should be enough to occur. Further, the conventional technique of applying high sound pressure vibration to the plating bath has disadvantages from the following points.
[0032]
　That is, when a high sound pressure vibration is applied to the hot-dip plating bath, the steel material is rapidly melted in the hot-dip plating bath due to the cavitation effect that occurs at the same time as the shock wave and the local flow, and a corrosion phenomenon called erosion occurs. The inconvenience of being more likely to occur occurs. This means that when the steel material is a steel sheet, the thickness of the steel sheet after hot-dip plating is smaller than that before it enters the hot-dip plating bath, and it becomes difficult to guarantee the product thickness of the hot-dip galvanized steel sheet. There are concerns. In addition, the reaction in which the steel material dissolves in the hot-dip plating bath is that the concentration of iron (Fe) and other steel material components in the hot-dip plating bath increases, and as a result, dross is likely to occur. There are also concerns. Further, erosion of a member (ultrasonic horn) or the like immersed in the hot-dip plating bath in order to apply high sound pressure vibration to the hot-dip plating bath is likely to occur, and maintenance of these members becomes complicated.
[0033]
　The hot-dip plating method (hereinafter, may be simply referred to as the main hot-dip plating method) in one embodiment of the present invention based on the findings found by the present inventors will be roughly described as follows. That is, by (i) applying ultrasonic vibration to the steel material, or (ii) applying ultrasonic vibration to the hot-dip plating bath using, for example, a diaphragm, low sound pressure vibration is applied to the hot-dip plating bath. Give. Then, the acoustic spectrum is measured using an acoustic measuring instrument immersed in a hot-dip plating bath. In this hot-dip plating method, the ultrasonic vibration is applied to the hot-dip plating bath so that the acoustic spectrum satisfies a predetermined condition. The ultrasonic vibration applied to the steel material or the diaphragm produces a vibration activating effect in the hot-dip plating bath. The above-mentioned predetermined conditions are defined in order to indirectly specify the degree of the strength of the vibration activating effect by using the acoustic spectrum in the hot-dip plating bath so that the vibration activating effect of a certain level or more is generated.
[0034]
　[Embodiment 1]
　Hereinafter, embodiments of the present invention will be described in detail.
[0035]
　In the present embodiment, a plate-shaped steel material (steel plate) among metal materials is used, and the steel plate is immersed in a hot-dip plating bath and then pulled up to apply hot-dip plating to the steel plate (so-called dobu-dip plating). Will be described. Further, in the hot-dip plating method of the present embodiment, the above-mentioned sewage plating is performed in an air atmosphere. The hot-dip plating method in one aspect of the present invention is not necessarily limited to this. This hot-dip plating method can be applied to, for example, various metal materials that are generally subject to hot-dip plating. Further, this hot-dip plating method can be applied to a continuous hot-dip plating method in which a steel strip is used as a steel material and hot-dip plating is continuously applied to the steel strip. Further, this hot-dip plating method can also be applied to the case where a steel wire is used as a steel material and the steel wire is subjected to dove-dip plating or continuous hot-dip plating.
[0036]
　(
　Steel sheet) The steel sheet used in the hot-dip plating method of the present embodiment may be appropriately selected from various known steel sheets according to the intended use, and examples of the steel type constituting the steel sheet include carbon steel (ordinary steel, high steel). Strong steel (high Si / high Mn steel)), stainless steel, and the like can be mentioned. The thickness of the steel plate is not particularly limited, but may be, for example, 0.2 mm to 6.0 mm. The shape of the steel plate is not particularly limited, but may be, for example, a rectangle. A steel plate generally used for hot-dip plating can be used for the hot-dip plating method of the present embodiment.
[0037]
　The steel sheet does not need to be subjected to a reduction heat treatment or the like before the hot-dip plating treatment. Therefore, the steel sheet may have an oxide film on its surface at the time of being put into the hot-dip plating bath. The thickness of the oxide film depends on the type of steel constituting the steel sheet, but is, for example, about several tens of nm to several hundreds of nm.
[0038]
　Further, in the hot-dip plating method of the present embodiment, the temperature of the steel sheet before entering the hot-dip plating bath may be normal temperature. In other words, the temperature of the steel sheet may be, for example, normal temperature to 700 ° C.
[0039]
　In the hot-dip plating method of the present embodiment, the steel sheet does not need to be subjected to a flux treatment or the like before the hot-dip plating treatment. However, the steel sheet may be heat-treated, reduced, flux-treated, or the like, if necessary, before the hot-dip plating treatment.
[0040]
　(Hot-dip plating bath) As the hot-dip plating bath in the
　present embodiment, various known hot-dip plating baths can be used. Examples of the hot-dip plating bath include a zinc (Zn) -based plating bath, a Zn-aluminum (Al) -based plating bath, a Zn-Al-magnesium (Mg) -based plating bath, and a Zn-Al-Mg-silicon (Si) -based plating. Examples thereof include a bath, an Al-based plating bath, an Al-Si-based plating bath, a Zn-Al-Si-based plating bath, a Zn-Al-Si-Mg-based plating bath, and a tin (Sn) -Zn-based plating bath.
[0041]
　The temperature of the hot-dip plating bath in this hot-dip plating method may be the same as the temperature of the hot-dip plating bath used in the known hot-dip plating method.
[0042]
　(Hot-dip plating device)
　The hot-dip plating device 1 that implements the hot-dip plating method according to the present embodiment will be described with reference to FIGS. 1 and 2. The hot-dip plating apparatus 1 is an example, and the apparatus for carrying out this hot-dip plating method is not particularly limited. FIG. 1 is a schematic view showing a hot-dip plating apparatus 1 that implements the hot-dip plating method according to the present embodiment.
[0043]
　As shown in FIG. 1, the hot-dip plating device 1 includes an ultrasonic horn (vibration generator) 10, an ultrasonic power supply device D1, a hot-dip plating bath 20, and a measuring device 30. The ultrasonic horn 10 is provided with an ultrasonic vibrator 11. A steel plate 2 is fixed to the tip of the ultrasonic horn 10 by a bolt 12.
[0044]
　The ultrasonic power supply device D1 includes an oscillator 13, a power amplifier 14, and a power meter 15. The oscillator 13 generates an AC signal of an arbitrary frequency, and the power amplifier 14 amplifies the AC signal to generate an ultrasonic signal. The ultrasonic horn 10 receives the ultrasonic signal supplied via the power meter 15. As a result, the ultrasonic vibrator 11 vibrates ultrasonically. The vibration of the ultrasonic vibrator 11 causes the steel plate 2 connected to the ultrasonic horn 10 to vibrate.
[0045]
　The vibration of the steel plate 2 produces a vibration activation effect in the hot-dip plating bath 20, and a vibration activation region 23 is generated in the vicinity of the steel plate 2 inside the hot-dip plating bath 20. The hot-dip plating bath 20 is stored in the pot 24 and contains the hot-dip plating bath metal 21 and the bath surface oxide 22. The vibration activation region 23 occurs in both the hot-dip plating bath metal 21 and the bath surface oxide 22 in the hot-dip plating bath 20.
[0046]
　A waveguide 31 is inserted in the hot-dip plating bath 20. One end of the waveguide rod 31 is arranged at an appropriate position inside the hot-dip plating bath 20 so that the vibration frequency of the hot-dip plating bath metal 21 can be acquired, and the other end is connected to the vibration sensor 32. The vibration sensor 32 is a device that converts the vibration of the waveguide 31 into an electric signal by using a piezoelectric element. The electric signal transmitted from the vibration sensor 32 is amplified via the amplifier 33 and then transmitted to the spectrum analyzer 34. The spectrum analyzer 34 includes a display unit 34a. In the present embodiment, the case where the spectrum analyzer 34 includes the display unit 34a will be described, but the display unit 34a may be replaced by an external device connected to the spectrum analyzer 34.
[0047]
　For example, the frequency of the ultrasonic vibrator 11 is set to 20 kHz, the output of the ultrasonic vibrator 11 is reduced, and low sound pressure vibration is applied to the hot-dip plating bath 20. When dip plating is performed, the acoustic spectrum as shown in FIG. 2 is typically displayed on the display unit 34a. Here, the distance L1 between the waveguide rod 31 and the steel plate 2 is 10 mm, and the depth D1 of the tip of the waveguide rod 31 (the distance from the tip to the bath surface of the hot-dip plating bath 20) is 30 mm. FIG. 2 is a graph showing an example of an acoustic spectrum measured by a spectrum analyzer 34 included in the hot-dip plating apparatus 1. In the graph of FIG. 2, the horizontal axis is the frequency and the vertical axis is the power value measured by the spectrum analyzer 34. The unit of this electric power value, dBm (more accurately, dBmW: Digibel milliwatt), expresses the electric power as a decibel value with 1 mW as a reference. Such a power value can be used as an index showing the intensity of the acoustic spectrum. Further, the magnitude of the value of the intensity (vertical axis in FIG. 2) in the acoustic spectrum corresponds to the magnitude of the sound pressure in the hot-dip plating bath 20. Therefore, the intensity peak in the acoustic spectrum corresponds to the sound pressure peak.
[0048]
　As shown in FIG. 2, the acoustic spectrum mainly has a peak showing a fundamental tone (frequency: 20 kHz) corresponding to the vibration applied to the hot-dip plating bath 20 and a peak showing a harmonic overtone (frequency that is an integral multiple of the fundamental tone). It appears in. Here, the frequency of the fundamental tone is defined as the fundamental frequency f, and the frequency range (width) at which the acoustic spectrum is measured is defined as the measurement frequency band. Further, it is determined from the intermediate frequencies (specifically, 3 / 2f, 5 / 2f, 7 / 2f, 9 / 2f) of the fundamental frequency f and the plurality of overtone frequencies (integer overtones: 2f, 3f, 4f, 5f). The range of the width of is defined as the inter-overtone band (specific frequency band). In this specification, for convenience of explanation, the range from the intermediate frequency between the fundamental frequency f and the second harmonic frequency 2f to a predetermined width is also referred to as an interharmonic band.
[0049]
　In the present embodiment, the predetermined width of the interharmonic band is set to the range of 1/3 f centering on the intermediate frequency. However, this predetermined width is not necessarily limited to this, and is appropriately set so as to be a frequency band between adjacent peaks among a plurality of main peaks (a peak at a fundamental frequency and a plurality of peaks at a harmonic frequency) in an acoustic spectrum. do it.
[0050]
　When a vibration with a low sound pressure (for example, an output of 10 W) is applied to the hot-dip plating bath 20, as shown in FIG. 2, in the acoustic spectrum, the frequency between the overtones (for example, 3/2 times the fundamental tone (here, here)) A peak also appears in the region of 1 / 3f centered on 30 kHz). Then, as the output of the ultrasonic vibrator 11 is increased, the intensity of the interharmonic band also increases (see FIG. 3 described later). The reason why such an increase in strength occurs is not clear, but it is considered that it may be caused by, for example, the generation and disappearance of bubbles due to vibration in the hot-dip plating bath 20.
[0051]
　By the way, even if the steel plate 2 is vibrated by using the ultrasonic horn 10, what kind of vibration is generated in the hot-dip plating bath metal 21 due to the vibration, in other words, how active it is in the vicinity of the steel plate 2. It is not easy to evaluate whether the vibration activation region 23 is formed. This is because, for example, the viscosity, vapor pressure, density, vibration propagation speed, acoustic impedance, etc. of the hot-dip plating bath metal 21 change depending on the component composition and temperature of the hot-dip plating bath 20. That is, since the way the vibration of the steel sheet 2 is transmitted to the hot-dip plating bath metal 21 is affected by various conditions, the range, activity, etc. of the vibration activation region 23 are evaluated based only on the output of the ultrasonic vibrator 11. And difficult to control.
[0052]
　Therefore, the present inventors have focused on the ratio of the spectral intensity of the interharmonic band in the acoustic spectrum to the overall spectral intensity of the acoustic spectrum. This will be described below with reference to FIG. FIG. 3 is a graph showing an example of an acoustic spectrum measured by a spectrum analyzer included in the hot-dip plating apparatus 1 when the ultrasonic output is changed. In FIG. 3, the horizontal axis shows the frequency (Hz) and the vertical axis shows the intensity (dBm). Further, here, the result of changing the fundamental frequency to 20 kHz and the ultrasonic output to 0.1 W to 30 W is shown.
[0053]
　As shown in FIG. 3, when the output of the ultrasonic transducer 11 was changed from 0.1 W to 30 W, the higher the output, the higher the intensity of the acoustic spectrum as a whole over the entire frequency range. Further, when vibration is not applied to the hot-dip plating bath 20 (the output of the ultrasonic vibrator 11 is 0 W), the intensity of the acoustic spectrum measured by the spectrum analyzer can be regarded as noise. In this measurement system, the level (noise level) when ultrasonic vibration was not applied was -100 dBm.
[0054]
　At any output, in the acoustic spectrum measured by the spectrum analyzer, a peak at the fundamental frequency (20 kHz) and a peak at the overtone frequency appear prominently, and the intensity is also between these peaks (interharmonic band). Is increasing and decreasing. In the inter-overtone band, there are some peaks with relatively low intensities, and the peak frequencies of these peaks fluctuate variously depending on the output. The present inventors have found that there is a relationship between the strength (increase and decrease in strength) in this interharmonic band and the plating property of the steel sheet immersed in the hot-dip plating bath 20. Specifically, it is as follows. In the present specification, the average value of the intensity in the interharmonic band may be referred to as the interharmonic average intensity.
[0055]
　FIG. 4A is a graph showing the influence of the ultrasonic output on the average intensity of the entire measurement frequency band and the average intensity between overtones in the acoustic spectrum. In FIG. 4A, the horizontal axis shows the ultrasonic output and the vertical axis shows the average intensity. As shown in FIG. 4A, when the ultrasonic output is 10 W or less, the average intensity between harmonics is smaller than the average intensity in the entire measurement frequency band. On the other hand, when the ultrasonic output becomes 20 W or more, the average intensity in the entire measurement frequency band and the average intensity between harmonics become equal to each other.
[0056]
　In order to more accurately evaluate the average intensity and the average intensity between overtones in the entire measurement frequency band, the noise level was evaluated as a reference. That is, the average intensity of the entire measurement frequency band and the average intensity between overtones are evaluated as the signal intensity ratio to the noise level. Then, the relationship between the ratio of these average intensities and the output was summarized. The result will be described below with reference to FIG. 4 (b).
[0057]
　FIG. 4B is a graph showing the effect of ultrasonic output on the intensity ratio of the average intensity between overtones (noise reference) to the average intensity (noise reference) of the entire measurement frequency band in the acoustic spectrum. In FIG. 4B, the horizontal axis shows the ultrasonic output and the vertical axis shows the intensity ratio. In the present specification, the strength ratio (formula (1) described later) may be referred to as a characteristic strength ratio.
[0058]
　As shown in FIG. 4B, the characteristic intensity ratio increased as the ultrasonic output increased from 0.1 W to 20 W. When the ultrasonic output increased to 20 W or more, the characteristic intensity ratio became about 1 and became substantially constant.
[0059]
　The present inventors used the hot-dip plating apparatus 1 to perform hot-dip plating on the steel sheet 2 by variously changing the ultrasonic output. As a result, it was found that the plating property of the steel sheet 2 is improved when the hot-dip plating is performed under the condition that the characteristic strength ratio is larger than 0.2. That is, the reactivity between the surface of the steel plate 2 and the hot-dip plating bath metal 21 can be improved by applying vibration that satisfies the above conditions to the hot-dip plating bath 20. Specifically, the non-plating rate on the surface of the plated product after hot-dip plating can be set to less than 10%.
[0060]
　The above can be organized as follows.
[0061]
　That is, in the hot-dip plating method according to one aspect of the present invention, the steel material is allowed to enter the plating bath which is a molten metal, and vibration is applied to the plating bath while the steel material is in contact with the hot metal. It includes a plating step of coating the steel material with the molten metal. The frequency of the vibration applied to the plating bath is used as the fundamental frequency. In the plating step, the vibration is applied so that the acoustic spectrum measured in the plating bath satisfies the relationship of the following formula (1):
　(IB-NB) / (IA-NA)> 0.2. (1)
Here,
　IA: average value of sound pressure in the entire measurement frequency band
　IB: (i) between the peak of sound pressure at the above basic frequency and the peak of sound pressure at the second harmonic frequency, and (ii). ) Average value of sound pressure in a specific frequency band between adjacent peaks of sound pressure peaks at a plurality of integer harmonic frequencies (integer of 2 or more)
　NA: The vibration is not applied in the entire measurement frequency band. Average value of sound pressure in the case
　NB: The average value of the sound pressure in the specific frequency band defined for the IB when the vibration is not applied
.
[0062]
　(Vibration Frequency / Output) In the
　above example, the ultrasonic horn 10 applies vibration having a frequency of 20 kHz to the steel plate 2 by vibrating the ultrasonic vibrator 11. However, the present invention is not limited to this, and the ultrasonic horn 10 may apply vibration having a frequency of, for example, 15 kHz to 150 kHz to the steel plate 2. Further, if the vibration intensity (output of the ultrasonic vibrator 11) applied to the steel plate 2 by the ultrasonic horn 10 is set so that an acoustic spectrum satisfying the relationship of the above equation (1) is generated in the hot-dip plating bath. good. For example, the output of the ultrasonic vibrator 11 determines whether an acoustic spectrum satisfying the relationship of the above formula (1) is generated in the hot-dip plating bath for each of various conditions such as the steel plate and the hot-dip plating bath 20. You should check in advance.
[0063]
　(Advantageous Effect) As described
　above, according to the hot-dip plating method in one aspect of the present invention, predetermined conditions are met while the steel sheet 2 and the hot-dip plating bath 20 are in contact with each other (in the above formula (1)). (Satisfying the relationship) is applied to the steel sheet 2. As a result, the bath surface oxide 22 and the atmosphere entrained in the hot-dip plating bath 20 are dispersed in the bath. That is, the reaction inhibitor is dispersed in the bath. In addition, mass transfer is promoted at the interface between the steel plate 2 and the hot-dip plating bath 20, which has the effect of reducing the thickness of the boundary layer or increasing the mass transfer rate. As a result, the plating wettability between the steel plate 2 and the hot-dip plating bath 20 is ensured. Therefore, the reaction between the hot-dip plating bath metal 21 and the steel plate 2 proceeds smoothly. As a result, even when the steel sheet 2 which has not been heat-treated (reduced) in advance is used, the plating property of the steel sheet 2 can be improved. Therefore, it is possible to provide a hot-dip plating method in which the hot-dip plating bath metal 21 and the steel plate 2 have good plating wettability and can reduce energy consumption as compared with the conventional case.
[0064]
　Further, according to the hot-dip plating method in one aspect of the present invention, it is not necessary to perform flux treatment. Therefore, the running cost can be reduced and the working environment can be improved.
[0065]
　Then, according to the hot-dip plating method in one aspect of the present invention, when a hot-dip plating facility is newly introduced, the cost and material for installing the heating furnace are not required, and the introduction cost can be reduced. Further, since the heating furnace has a long furnace length, the total length of the hot-dip plating equipment can be shortened by eliminating the need to install a heating furnace.
[0066]
　(Pretreatment) In
　the hot-dip plating method of the present embodiment, either the heat treatment or the reduction treatment before the hot-dip plating treatment (plating step) may be omitted, or both of them may be omitted. Further, in the hot-dip plating method of the present embodiment, the steel sheet 2 may be subjected to a lighter heat treatment and a reduction treatment than before before the plating step, and in this case, energy consumption in both of these treatments is consumed. The amount can be reduced.
[0067]
　The steel sheet 2 may be subjected to various pretreatments before the hot-dip plating treatment. For example, it does not matter if the reduction treatment is performed as the pretreatment of the plating process. Further, if necessary, the steel sheet 2 may be subjected to a degreasing treatment or a pickling treatment, or both of them may be carried out. In this hot-dip plating method, the steel sheet 2 may be degreased and pickled as a pretreatment for the plating step, and at least degreasing is particularly preferable. The degreasing treatment may be followed by a pickling treatment.
[0068]
　(Other Configuration) In
　the hot-dip plating method according to one aspect of the present invention, the measurement frequency band may include the fundamental frequency and have a frequency width four times or more the fundamental frequency. For example, the measurement frequency band may be 10 kHz or more and 90 kHz or less.
[0069]
　Further, between each peak in the specific frequency band, the fundamental frequency is f, and the frequency width of (1/3) f is centered on the frequency of (n + (1/2)) f (n is a natural number). You may.
[0070]
　In the plating step, the vibration generator (ultrasonic horn 10) may be used to apply the vibration to the plating bath, and the output of the vibration generator may be 0.5 W or more. In this hot-dip plating method, the output of the vibration generator may be 0.5 W or more and 30 W or less, and the frequency of vibration applied to the hot-dip plating bath 20 via the steel plate 2 may be 15 kHz or more and 150 kHz or less. Further, the vibration generator applies vibration having a frequency of 15 kHz or more and 150 kHz or less to the hot-dip plating bath 20, and the output may be 1 W or more and 30 W or less, or 5 W or more and 30 W or less.
[0071]
　Further, in the plating step, the time for applying the vibration to the plating bath using the vibration generator may be 2 seconds or more and 90 seconds or less. Then, in the plating step, the temperature (inlet temperature) immediately before the steel sheet 2 is immersed in the hot-dip plating bath 20 may be room temperature, for example, 100 ° C. or lower, or 50 ° C. or lower. You may.
[0072]
　In the plating step, a vibration detection device (for example, a vibration sensor 32, an amplifier 33, a spectrum analyzer 34) is used to measure the acoustic spectrum in the plating bath. The distance between the vibration detection location and the steel plate 2 in the plating bath may be 1 mm or more and 10 mm or less. The above distance is measured in a state where the steel plate 2 is immersed in the hot-dip plating bath 20 before the vibration of the ultrasonic horn 10 is started.
[0073]
　[Example 1] An example
　of the hot-dip plating method according to the first embodiment of the present invention will be described below.
[0074]
　In this embodiment, the hot-dip plating apparatus shown in FIG. 5 was used as an apparatus for carrying out the hot-dip plating method according to the first embodiment of the present invention. FIG. 5 is a schematic view showing an example of a hot-dip plating apparatus used when the hot-dip plating method according to one aspect of the present invention is applied to dobu-dip plating in an air atmosphere.
[0075]
　As shown in FIG. 5, in the hot-dip plating apparatus 40, the carbon crucible 42 is housed inside the crucible furnace 41, and the carbon crucible 42 is heated by causing resistance heating in the heating zone 43. The hot-dip plating bath metal 21 is stored in the carbon crucible 42, and the bath surface oxide 22 is generated on the surface of the hot-dip plating bath metal 21. In the hot-dip plating apparatus 40, the surface of the hot-dip plating bath metal 21 has an atmospheric atmosphere.
[0076]
　Similar to the hot-dip plating device 1 (see FIG. 1) described above, the hot-dip plating device 40 includes an ultrasonic horn 10, and a steel plate 2 is fixed to the tip of the ultrasonic horn 10. The ultrasonic vibrator 11 of the ultrasonic horn 10 receives the ultrasonic signal supplied from the ultrasonic power supply device D1 (including the oscillator 13, the power amplifier 14, and the power meter 15), and the ultrasonic power supply device D1 receives the ultrasonic signal. Vibration is applied to the steel plate 2 at the set output.
[0077]
　As the ultrasonic vibrator 11, a commercially available bolt-tightened Langevin type vibrator can be used. Further, as the ultrasonic horn 10, an ultrasonic horn made of aluminum, titanium, ceramics or the like can be used.
[0078]
　Further, the hot-dip plating apparatus 40 includes a waveguide 51, an acoustic emission sensor (hereinafter, may be referred to as an AE sensor) 52, and a measuring apparatus 50 (corresponding to the measuring apparatus 30 in FIG. 1) for measuring an acoustic spectrum. The measuring unit 53 is provided. The measuring unit 53 includes a spectrum analyzer and an amplifier. One end of the waveguide 51 is immersed in the hot-dip plating bath metal 21, and the other end is connected to the AE sensor 52.
[0079]
　Specifically, the various devices used in the hot-dip plating apparatus 40 in this embodiment are as follows.
[0080]
　(Ultrasonic vibration supply system)
　・ Ultrasonic vibrator 11: Honda Electronics, bolt-tightened
　spectrum analyzer
　・Ultrasonic horn 10: Material ・ Oscillator 13: Azirent Technology Co., Ltd., 33220A
　, power amplifier 14: Mestec Co., Ltd., M-2141
　, power meter 15: Hioki Electric Co., Ltd., PW-3335
　(ultrasonic vibration measurement system)
　, waveguide 51: Material , φ6 mm × 300 mm
　・ AE sensor 52: manufactured by NF Circuit Design Block Co., Ltd., AE-900M
　・ Amplifier: manufactured by NF Circuit Design Block Co., Ltd., AE9922
　・ Spectrum analyzer: manufactured by Azilent Technology Co., Ltd., E4408B.
[0081]
　Further, in this embodiment, carbon steel (steel type A and steel type B) shown in Table 1 below or stainless steel (steel type C to steel type F) shown in Table 2 below was used as the steel plate 2 (plating base material). Steel types A to F are all annealed materials.
[table 1]

[0082]
[Table 2] In

　the description in Table 2, "-" indicates that the component analysis was not performed, and "tr." Indicates that it was below the detection limit of the analysis.
[0083]
　(Example 1-1: Zn-Al-Mg-based hot-dip plating bath type is used)
　The steel sheets A to F shown in Tables 1 and 2 are pickled with alkaline degreasing and 10% hydrochloric acid as pretreatments, respectively. Was done. The pretreated steel sheets are attached to the tips of the ultrasonic horns 10 and immersed in a Zn—Al—Mg-based hot-dip plating bath to a depth of 60 mm (in other words, in the bath in the depth direction of the plating bath). It was immersed to the length of the steel sheet), and the immersion plating was performed with the immersion time set to 100 seconds. When applying vibration to the steel plate, the vibration was applied 10 seconds after the steel plate attached to the tip of the ultrasonic horn 10 was immersed in the hot-dip plating bath, and the vibration was applied for 90 seconds.
[0084]
　The composition of the hot-dip plating bath was 6% by mass Al, 3% by mass Mg, 0.025% by mass Si, and the balance Zn. The temperature of the hot-dip plating bath was 380 ° C. to 550 ° C., and when vibration was applied to the hot-dip plating bath, the fundamental frequency and the output of the ultrasonic vibrator 11 were changed. Further, as a comparative example, sewage plating was performed without applying vibration to the hot-dip plating bath.
[0085]
　Using the sample after sewage plating as a test material, the plating property was evaluated as follows. FIG. 6 is a side view showing the state of the test material 3 after plating. As shown in FIG. 6, a plating region 3a subjected to hot-dip plating is formed on the test material 3 after plating. Further, a non-plated portion 4 that has not been subjected to hot-dip plating may be present in a part of the plated region 3a.
[0086]
　For example, the depth of the portion of the test material 3 immersed in the hot-dip plating bath is L11, and the width of the test material 3 is L12. In this case, L11 × L12 × 2 is the ideal plating area area α on the plate surface (both sides) shown in FIG. Further, the area β of the non-plated portion 4 is measured by using a known area measuring means. The area β of the non-plated portion 4 is an area measured for both plated surfaces (both plate surfaces) of the test material 3. Then, the non-plating rate was calculated by calculating (β / α) × 100. The plating property of the test material 3 was evaluated according to the following criteria, and a result of Δ or higher was evaluated as acceptable.
[0087]
　◎:% non-coating rate 0
　○: less than 1% non-coating rate is greater than 0%
　△: non-coating ratio is 10% or more and less than 1%
　×: non-coating rate is less than 10% to 80%
　××: non-coating The rate is 80% or more.
[0088]
　The results of the above tests are summarized in Table 3. In Table 3, the plating base material is a steel plate, and the presence or absence of heating of the plating base material means the presence or absence of heating of the steel plate in the stage prior to hot-dip plating. Further, the inlet temperature means the temperature of the steel sheet at the time of charging into the hot-dip plating bath. The acoustic intensity (noise standard) in the table is determined by IA-NA, and the average intensity between integer harmonics (that is, the average intensity between harmonics based on noise) is determined by IB-NB, and the average intensity between integer harmonics with respect to the acoustic intensity. The ratio (characteristic intensity ratio) of is obtained by (IB-NB) / (IA-NA) (for these symbols, refer to the above-mentioned formula (1)). The above is the same in the present specification.
[0089]
[Table 3]

　No. in Table 3 As shown in 1 to 21, when the steel sheet is dipped-plated while applying vibration in the hot-dip plating bath under the condition that the acoustic spectrum within the range of the present invention is measured in the hot-dip plating bath. The plating property of the steel sheet was improved, and the non-plating rate of the plated product was less than 10%. In addition, No. 1 having an output of 5 W to 20 W. In the examples shown in 3 to 21, the non-plating rate of the plated product was 0%.
[0090]
　On the other hand, when the vibration applied in the hot-dip plating bath is too weak (sound pressure is too low), the acoustic spectrum within the range of the present invention is not measured in the hot-dip plating bath, and No. As shown in 22 to 24, the non-plating rate of the plated product was 10% or more. In addition, when hot-dip plating was performed in the hot-dip plating bath without applying vibration, No. As shown in 25 to 30, the non-plating rate of the plated product was 80% or more.
[0091]
　(Example 1-2: Al—Si-based hot-dip plating bath type is used)
　Various types shown in Tables 1 and 2 are used as the hot-dip plating bath using an Al-9 mass% Si-2 mass% Fe-based plating bath. The steel plate was soaked and plated. The temperature of the hot-dip plating bath is 630 ° C to 700 ° C, the immersion time of the steel sheet in the hot-dip plating bath is 12 seconds, and when the steel sheet is vibrated, vibration is applied 10 seconds after the start of immersion of the steel sheet in the hot-dip plating bath. Was started, and vibration was applied for 2 seconds. When the steel plate was vibrated, the fundamental frequency was set to 15 kHz, and the output of the ultrasonic transducer 11 was changed to 10 W or 0.05 W to 0.3 W. The conditions other than these were the same as in Example 1-1 above. The test results are summarized in Table 4.
[0092]
[Table 4]

　No. in Table 4 As shown in 41 to 48, when the steel sheet is dipped-plated while applying vibration in the hot-dip plating bath under the condition that the acoustic spectrum within the range of the present invention is measured in the hot-dip plating bath. The plating property of the steel sheet was improved, and the non-plating rate of the plated product became 0%.
[0093]
　On the other hand, when the vibration applied in the hot-dip plating bath is too weak (sound pressure is too low), the acoustic spectrum within the range of the present invention is not measured in the hot-dip plating bath, and No. As shown in 49 to 51, the non-plating rate of the plated product was 10% or more. In addition, when hot-dip plating was performed in the hot-dip plating bath without applying vibration, No. As shown in 52 to 57, the non-plating rate of the plated product was 80% or more.
[0094]
　(Example 1-3: Various hot-dip plating bath types are used) As the
　hot-dip plating bath, various hot-dip plating baths shown in Example 2 (Example 2-3) of the third embodiment are used in Tables 1 and 2. The various steel sheets A to F shown were soaked and plated. The compositions of the hot-dip plating baths M1 to M10 are shown in Table 8 of Example 2, and the compositions of the hot-dip plating baths M12 are shown in Table 9 of Example 2. The plating bath type M11 is an Al-2 mass% Fe-based plating bath, and the bath temperature is 700 ° C. (the plating bath type M11 is Al-9 mass% Si- used in the test shown in Table 4. Unlike the 2% by mass Fe-based plating bath, Si is not added).
[0095]
　The immersion time of the steel sheet in the hot-dip plating bath was 12 seconds, and when the steel sheet was vibrated, the vibration was applied 10 seconds after the start of immersion of the steel sheet in the hot-dip plating bath, and the vibration was applied for 2 seconds.
[0096]
　In the examples of Examples 1-3, the fundamental frequency was set to 15 kHz and the output of the ultrasonic transducer 11 was set to 20 W, respectively, and vibration was applied into the hot-dip plating bath. In the comparative example, sewage plating was performed without applying vibration to the hot-dip plating bath. Further, in Examples and Comparative Examples, steel plates A to F having a thickness of 0.8 mm were used.
[0097]
　Conditions other than the above were the same as in Example 1-1 above. The test results are summarized in Table 5.
[0098]
[Table 5]

　No. in Table 5 As shown in 231 to 302, when the steel sheet is dipped-plated while applying vibration in the hot-dip plating bath under the condition that the acoustic spectrum within the range of the present invention is measured in the hot-dip plating bath. The plating property of the steel sheet was improved, and the non-plating rate of the plated product was 0%.
[0099]
　On the other hand, when hot-dip plating was performed in the hot-dip plating bath without applying vibration, No. As shown in 303 to 314, the non-plating rate of the plated product was 80% or more.
[0100]
　[Embodiment 2]
　Other embodiments of the present invention will be described below. For convenience of explanation, the members having the same functions as the members described in the above-described embodiment are designated by the same reference numerals, and the description thereof will not be repeated.
[0101]
　In the hot-dip plating apparatus 1 (see FIG. 1) in the first embodiment, the distance L1 between the tip of the waveguide 31 and the surface of the steel plate 2 in the hot-dip plating bath 20 was fixed at 10 mm, and the acoustic spectrum was measured. According to a further study by the present inventor, it has been found that the characteristic intensity ratio in the acoustic spectrum can change with the change in the position where the acoustic spectrum is measured.
[0102]
　Therefore, the acoustic spectrum was measured by changing the distance L1 to 1 mm to 80 mm and changing the output of the ultrasonic vibrator 11 to 0.1 W to 20 W. The results are shown in FIGS. 7 (a) to 7 (e). 7 (a) to 7 (e) are graphs showing acoustic spectra measured by changing the output of the ultrasonic transducer 11 at each distance L1, where distance L1 is 1 mm and (b) is. The distance L1 is 5 mm, (c) is the case where the distance L1 is 10 mm, (d) is the case where the distance L1 is 30 mm, and (e) is the case where the distance L1 is 80 mm.
[0103]
　FIG. 8 is a graph showing the relationship between the distance L1 and the characteristic intensity ratio. As shown in FIG. 8, the characteristic intensity ratio tends to decrease as the distance L1 increases, and this tendency is particularly remarkable when the output is weak (specifically, 0.1 W, 0.5 W). be. From this, it can be said that, for example, when the output is 0.1 W or 0.5 W, it is preferable that the distance L1 is 10 mm or less in order to detect the acoustic spectrum.
[0104]
　Further, as shown in FIGS. 7A to 7E, if the distance L1 is too large, the signal intensity of the acoustic spectrum becomes small, and it may be difficult to detect the signal because it falls below the noise level. Therefore, it may be difficult to accurately evaluate the vibration state in the hot-dip plating bath 20. Therefore, in this hot-dip plating method, it is preferable that the output is 0.5 W or more and the distance L1 is 10 mm or less.
[0105]
　[Embodiment 3]
　Other embodiments of the present invention will be described below. For convenience of explanation, the members having the same functions as the members described in the above-described embodiment are designated by the same reference numerals, and the description thereof will not be repeated.
[0106]
　In the first and second embodiments, the ultrasonic horn 10 is used to apply vibration to the steel plate 2 in a state where the steel plate 2 is attached to the tip of the ultrasonic horn 10. On the other hand, in the present embodiment, in a state where the diaphragm is attached to the tip of the ultrasonic horn 10, vibration is applied to the diaphragm by using the ultrasonic horn 10, and the steel plate 2 is passed through the hot-dip plating bath 20. The difference is that it indirectly gives vibration to.
[0107]
　(Hot-dip plating device)
　A hot-dip plating device 60 that implements the hot-dip plating method according to the present embodiment will be described with reference to FIG. The hot-dip plating apparatus 60 is an example, and the apparatus for carrying out this hot-dip plating method is not particularly limited. FIG. 9 is a schematic view showing a hot-dip plating apparatus 60 that implements the hot-dip plating method according to the present embodiment.
[0108]
　As shown in FIG. 9, the hot-dip plating apparatus 60 includes a gas reduction heating zone 61, a hot-dip plating portion 62, an ultrasonic horn 10, and a measuring device 50 for measuring an acoustic spectrum. The gas reduction heating band 61 includes an atmospheric gas introduction section 61a and a heating section 61b, and can heat the steel sheet 2 in a desired atmosphere.
[0109]
　In the hot-dip plating section 62, the space above the crucible furnace 41 is shielded from the atmosphere by the port flange 64 and the O-ring 65. Further, an atmosphere gas introduction portion 66 is provided in a part of the port flange 64 so that the atmosphere in the hot-dip plating portion 62 can be controlled.
[0110]
　A gate valve 63 is provided between the gas reduction heating zone 61 and the hot-dip plating portion 62. The steel plate 2 treated in the gas reduction heating zone 61 opens the gate valve 63 and is transferred to the hot-dip plating section 62 without being exposed to the atmosphere. The steel plate 2 enters the plating bath 21 after undergoing pretreatment such as atmosphere control and heat treatment in the gas reduction heating zone 61 above the gate valve 63.
[0111]
　Further, in the hot-dip plating apparatus 60 of the present embodiment, the diaphragm 70 is fixed to the tip of the ultrasonic horn 10 instead of the steel plate 2. As the diaphragm 70, a plate of ordinary steel (same steel type as the steel plate A in Table 1) having a length of 150 mm, a width of 50 mm, and a thickness of 0.8 mm was used here. The vibration of the diaphragm 70 gives vibration to the hot-dip plating bath metal 21. As a result, vibration is applied to the steel sheet 2 via the hot-dip plating bath metal 21. That is, the hot-dip plating apparatus 60 indirectly applies vibration to the steel plate 2. The diaphragm 70 is not limited to the above materials. The diaphragm 70 is preferably made of a material that has strong erosion resistance when immersed in the hot-dip plating bath and does not have good wettability with respect to the hot-dip plating bath, and ceramics can be used, for example.
[0112]
　Since the configurations of the other measuring devices 50 and the like are the same as those of the hot-dip plating device 40 (see FIG. 5), detailed description thereof will be omitted.
[0113]
　The hot-dip plating apparatus 60 as described above can be applied to a continuous hot-dip plating method. That is, in the continuous hot-dip plating method, it is difficult to directly apply vibration to the steel sheet, but it is possible to indirectly apply vibration to the steel sheet 2 as in the hot-dip plating apparatus 60. Therefore, the results demonstrated using the hot-dip plating apparatus 60 as described above can be applied to the continuous hot-dip plating method. Specific examples of application to the continuous hot-dip plating method will be described later.
[0114]
　[Example 2] Examples
　of the hot-dip plating method according to the third embodiment of the present invention will be described below. In this embodiment, the hot-dip plating apparatus 60 shown in FIG. 9 described above was used.
[0115]
　Various steel plates A to F (see Tables 1 and 2) are used in the same manner as in Example 1, and a Zn—Al—Mg-based hot-dip plating bath or an Al-9 mass% Si-2 mass% Fe-based plating bath is used. Was used for hot-dip plating under various conditions.
[0116]
　(Example 2-1: No heat treatment in the gas reduction heating zone 61)
　Alkaline degreasing treatment was performed on each of the various steel sheets as a pretreatment. As the hot-dip plating bath, the Zn—Al—Mg-based plating bath in Example 1-1 of Example 1 and the Al-9% Si-based plating bath in Example 1-2 of Example 1 were used. The atmosphere in the hot-dip plating section 62 was changed to an atmospheric atmosphere, a nitrogen atmosphere, a 3% hydrogen-nitrogen atmosphere, or a 30% hydrogen-nitrogen atmosphere. Atmosphere control and heat treatment in the gas reduction heating zone 61 were not performed. The immersion time of the steel plate in the hot-dip plating bath is 12 seconds, and when the diaphragm 70 is vibrated by using the ultrasonic horn 10 to give vibration to the hot-dip plating bath, the steel plate is started to be dipped in the hot-dip plating bath. 10 seconds later, the vibration was applied, and the vibration was applied for 2 seconds. When the diaphragm 70 was vibrated, the fundamental frequency was set to 15 kHz, the output of the ultrasonic vibrator 11 was set to 30 W, and the vibration was applied to the hot-dip plating bath.
[0117]
　The arrangement of the steel plate and the diaphragm in the hot-dip plating bath was adjusted so that the distance (interval) between the diaphragm and the steel plate was 5 mm. The distance between the steel plate and the tip of the waveguide was 5 mm.
[0118]
　Further, as a comparative example, the steel sheet was dipped and plated using the hot-dip plating apparatus 60 without applying vibration to the hot-dip plating bath. The test results are summarized in Table 6.
[0119]
[Table 6]

　No. in Table 6 As shown in 61 to 108, when the steel sheet is hot-dip plated while applying vibration in the hot-dip plating bath under the condition that the acoustic spectrum within the range of the present invention is measured in the hot-dip plating bath. The plating property of the steel sheet was improved, and the non-plating rate of the plated product became 0% under all various conditions.
[0120]
　On the other hand, when hot-dip plating was performed in the hot-dip plating bath without applying vibration, No. As shown in 109 to 124, the non-plating rate of the plated product was 80% or more under all of the various conditions.
[0121]
　(Example 2-2: With heat treatment in the
　gas reduction heating zone 61 ) Atmosphere control and heat treatment in the gas reduction heating zone 61 are performed, and vibration is applied 2 seconds after the start of immersion of the steel sheet in the hot-dip plating bath. From the start, hot-dip plating was performed in the same manner as in Example 2-1 above except that vibration was applied for 2 seconds. The test results are summarized in Table 7.
[0122]
[Table 7]

　No. in Table 7. As shown in 130 to 141, even when the steel sheet is heated in an atmospheric atmosphere and then entered into the hot-dip plating bath (when the steel sheet has a relatively thick oxide film on the surface), the hot-dip plating bath is used. By applying vibration under the condition that the acoustic spectrum within the range of the present invention is measured, the non-plating rate of the plated product is less than 1%.
[0123]
　In addition, No. As shown in 142 to 177, when the heating atmosphere in the gas reduction heating zone 61 and the atmosphere of the hot-dip plating bath are non-oxidizing atmospheres, even if the steel sheet is allowed to enter the hot-dip plating bath while the steel sheet is heated, it melts. By applying vibration in the plating bath under conditions such that the acoustic spectrum within the range of the present invention is measured, the non-plating rate of the plated product became 0%.
[0124]
　On the other hand, when the steel sheet was heated in an atmospheric atmosphere and then hot-dip plating was performed in the hot-dip plating bath without applying vibration, No. As shown in 178, 179, 186, and 187, the non-plating rate of the plated product was 80% or more.
[0125]
　In addition, No. As shown in 180 to 183 and 188 to 193, when the hot atmosphere in the gas reduction heating zone 61 and the atmosphere of the hot-dip plating bath are set as non-oxidizing atmospheres and hot-dip plating is performed in the hot-dip plating bath without applying vibration. The non-plating rate of the plated product was 10% or more and less than 80%.
[0126]
　When the steel sheet is subjected to reduction heat treatment and melt plating is performed in a reducing atmosphere as in the prior art, No. As shown in 184 and 185, the non-plating rate of the plated product was 0%.
[0127]
　(Example 2-3: No heat treatment in the gas reduction heating zone 61, various plating baths are used)
　Using the hot-dip plating baths having the compositions shown in Tables 8 and 9 below, the atmosphere in the hot-dip plating section 62 is 3% hydrogen-nitrogen. Melt plating was performed in the same manner as in Example 2-1 above except that the atmosphere was set. The plating bath type M11 is an Al-2 mass% Fe-based plating bath, and the bath temperature is 700 ° C. (The plating bath type M11 is Al-9 mass% Si-2 mass% Fe used in the test shown in Table 4. Unlike the system plating bath, Si is not added). The test results are summarized in Table 10.
[Table 8]

[Table 9]

[0128]
[Table 10]

　No. in Table 10. As shown in 201, 203, 205, 207, 209, 211, 213, 215, 217, 219, 221 and 223, under the condition that the acoustic spectrum within the range of the present invention is measured in the hot-dip plating bath. When the steel sheet was dipped and plated while applying vibration in the hot-dip plating bath, the plating property of the steel sheet was improved and the non-plating rate of the plated product became 0%.
[0129]
　On the other hand, when hot-dip plating was performed in the hot-dip plating bath without applying vibration, No. As shown in 202, 204, 206, 208, 210, 212, 214, 216, 218, 220, 222, 224, the non-plating rate of the plated product was 10% or more.
[0130]
　[Embodiment 4] In
　the hot-dip galvanized steel sheet produced by the hot-dip plating method of the present invention, a base chemical conversion treatment film for improving corrosion resistance and film adhesion may be formed on the surface of the plating layer. As the base chemical conversion treatment film, an inorganic film is preferable, and more specifically, a film containing a valve metal oxide or hydroxide and a valve metal fluoride is preferable. Here, the "valve metal" refers to a metal whose oxide exhibits high insulation resistance. As the valve metal element, one or more elements selected from Ti, Zr, Hf, V, Nb, Ta, Mo and W are preferable. Further, the base chemical conversion treatment film may contain a soluble or sparingly soluble metal phosphate or a composite phosphate. Further, the base chemical conversion treatment film may contain an organic wax such as fluorine-based, polyethylene-based or styrene-based, or an inorganic lubricant such as silica, molybdenum disulfide and talc. The base chemical conversion treatment film may be an organic film based on a urethane resin, an acrylic resin, an epoxy resin, an olefin resin, a polyester resin, or the like.
[0131]
　Further, the hot-dip plated steel plate manufactured by the hot-dip plating method of the present invention has a resin-based material such as polyester-based, acrylic resin-based, fluororesin-based, vinyl chloride resin-based, urethane resin-based, and epoxy resin-based on the surface of the plating layer. The paint can be applied by a method such as roll coating, spray coating, curtain flow coating, or dip coating. Alternatively, it can also be used as a base material for film lamination when laminating a plastic film such as an acrylic resin film.
[0132]
　[Embodiment 5]
　Other embodiments of the present invention will be described below. For convenience of explanation, the members having the same functions as the members described in the above-described embodiment are designated by the same reference numerals, and the description thereof will not be repeated.
[0133]
　In the hot-dip plating method of the present embodiment, a part of the ultrasonic horn is immersed in the hot-dip plating bath, and vibration is applied to the hot-dip plating bath from the tip of the ultrasonic horn. As a result, vibration is indirectly transmitted from the tip of the ultrasonic horn to the steel sheet via the hot-dip plating bath, and the steel sheet is dipped and plated.
[0134]
　(Hot-dip plating device)
　The hot-dip plating device 80 that implements the hot-dip plating method according to the present embodiment will be described with reference to FIG. The hot-dip plating apparatus 80 is an example, and the apparatus for carrying out this hot-dip plating method is not particularly limited. FIG. 10 is a schematic view showing a hot-dip plating apparatus 80 that implements the hot-dip plating method according to the present embodiment.
[0135]
　As shown in FIG. 10, the hot-dip plating device 80 includes an elevating device 81, an ultrasonic horn 10A, a measuring device 50 for measuring an acoustic spectrum, and a carbon crucible 42 in which a hot-dip plating bath metal 21 is stored. ing. In the hot-dip plating apparatus 80, the steel plate 2 is immersed in the hot-dip plating bath 20 in the atmosphere without heating the steel plate 2.
[0136]
　The elevating device 81 is a device that enables the steel plate 2 to be immersed in the hot-dip plating bath 20 and the steel plate 2 to be pulled up from the hot-dip plating bath 20 while holding the steel plate 2. As the elevating device 81, a known device may be used, and detailed description thereof will be omitted.
[0137]
　The ultrasonic horn 10A includes an ultrasonic vibrator 11, a tip portion 17, and a connecting portion 16 for connecting the ultrasonic vibrator 11 and the tip portion 17. The ultrasonic vibrator 11 is fixed by a vibrator fixing stage 19. The connecting portion 16 has a length that easily resonates in response to the frequency of vibration generated by the ultrasonic vibrator 11. The connecting portion 16 may be a simple adapter, or may be a booster that amplifies the amplitude generated by the ultrasonic vibrator 11 and transmits it to the tip portion 17.
[0138]
　With at least a part of the tip portion 17 of the ultrasonic horn 10A immersed in the hot-dip plating bath 20, the ultrasonic vibrator 11 receives the ultrasonic signal transmitted from the ultrasonic power supply device D1 and ultrasonically vibrates. do. This ultrasonic vibration is transmitted to the tip portion 17 via the connecting portion 16, and the tip portion 17 imparts vibration to the hot-dip plating bath 20.
[0139]
　When the steel plate 2 is immersed in the hot-dip plating bath 20 by the elevating device 81, the steel plate 2 is arranged in front of the tip portion 17. A vibrating surface 17A is formed at the end of the tip 17 farther from the connecting portion 16 in the longitudinal direction so that the cross-sectional shape of the end is an isosceles triangle, and the vibrating surface 17A is melted. It faces the surface of the steel plate 2 immersed in the plating bath 20.
[0140]
　The tip portion 17 is preferably made of ceramic. This is to reduce the deterioration of the tip portion 17 that may occur due to the ultrasonic vibration of the tip portion 17 in the hot-dip plating bath 20.
[0141]
　The hot-dip plating apparatus 80 may use an integrated ultrasonic horn instead of the ultrasonic horn 10A. In this case, the tip of the ultrasonic horn may be made of ceramics.
[0142]
　The distance L2 between the vibrating surface 17A of the tip portion 17 and the surface of the steel plate 2 may be 0 mm, greater than 0 mm and 50 mm or less. The distance L2 of 0 mm means that the vibrating surface 17A and the surface of the steel plate 2 are in contact with each other at a time point before the ultrasonic horn 10A ultrasonically vibrates (that is, at the time of setting). For example, the elevating device 81 can move the steel plate 2 in the horizontal direction, and the distance L2 can be adjusted by moving the steel plate 2 in the horizontal direction using the elevating device 81. The distance L2 is preferably greater than 0 mm and less than or equal to 5 mm.
[0143]
　In the hot-dip plating apparatus 80, the frequency, output, and the like of vibration applied to the hot-dip plating bath 20 using the ultrasonic horn 10A are the same as those described in the first embodiment.
[0144]
　[Example 3] Examples
　of the hot-dip plating method according to the fifth embodiment of the present invention will be described below. In this embodiment, the hot-dip plating apparatus 80 shown in FIG. 10 described above was used.
[0145]
　Specifically, the various devices used in the hot-dip plating apparatus 80 in this embodiment are as follows.
[0146]
　(Ultrasonic vibration supply system)
　・ Ultrasonic vibrator 11: manufactured by hielscher, 20 kHz oscillator
　・ Connection part 16 (booster): Material , amplification factor 2.2 times, 1/2 wavelength type, length 126 mm
　・ Tip 17: Material , 1/2 wavelength type, length 250 mm
　・ Ultrasonic power supply device D1: manufactured by hielscher, 20 kHz, 2 kW power supply
　(ultrasonic vibration measurement system)
　・ Waveguide rod 51: Material , Φ6mm × 300mm
　・ AE sensor 52: NF circuit design block company, AE-900M
　・ Measurement unit 53
　　amplifier: NF circuit design block company, AE9922
　　spectrum analyzer: Azilent Technology Co., Ltd. Made by E4408B.
[0147]
　(Example 3-1: Use a Zn—Al—Mg-based hot-dip plating bath type)
　Various steel plates A to F (see Tables 1 and 2) are used in the same manner as in Example 1, and the hot-dip plating bath is described above. Using the Zn—Al—Mg-based hot-dip plating bath of Example 1-1 of Example 1, hot-dip plating was performed under various conditions.
[0148]
　When vibration was applied to the hot-dip plating bath using the ultrasonic horn 10A, the distance L2 was set to 0 mm to 50 mm, and the fundamental frequency was set to 20 kHz.
[0149]
　The ultrasonic vibrator 11 has a built-in amplitude sensor for monitoring the amplitude of the ultrasonic vibrator 11. Using the display device, the output from the amplitude sensor was received, and the output was displayed with the full scale set to 5V. Since the magnitude of the amplitude of the ultrasonic vibrator 11 is reflected in the output displayed by the display device, in the following, the full-scale 5V is set as 100% of the output, and an index showing the magnitude of the amplitude of the ultrasonic vibrator 11 is set. "Output%" was used as.
[0150]
　Here, in the method of directly vibrating the steel sheet (direct method), the load on the ultrasonic power supply is considered to be the steel sheet itself. On the other hand, in the case of the method of indirectly vibrating the steel sheet through the hot-dip plating bath (indirect method), the load on the ultrasonic power source is the steel sheet and the hot-dip plating bath. Therefore, the vibration imparting condition is expressed by using "output%" which is an index indicating the amplitude of the ultrasonic vibrator at the time of resonance, instead of the output (W) itself from the ultrasonic power source.
[0151]
　When vibration was applied to the hot-dip plating bath using the ultrasonic horn 10A, the vibration was started 10 seconds after the start of immersion of the steel plate 2 in the hot-dip plating bath, and the vibration was applied for 2 to 60 seconds. ..
[0152]
　Further, as a comparative example, each test material was dipped and plated using the hot-dip plating apparatus 80 without applying vibration to the hot-dip plating bath. Conditions other than the above were the same as in Example 1-1 described above. The test results are summarized in Table 11.
[0153]
[Table 11]

　No. in Table 11 As shown in 321 to 347, when the steel sheet is dipped-plated while applying vibration in the hot-dip plating bath under the condition that the acoustic spectrum within the range of the present invention is measured in the hot-dip plating bath. Even under various plating conditions, the plating property of the steel sheet was improved, and the non-plating rate of the plated product was less than 10%.
[0154]
　On the other hand, when hot-dip plating was performed in the hot-dip plating bath without applying vibration, No. As shown in 348 to 353, the non-plating rate of the plated product was 80% or more.
[0155]
　(Example 3-2: Al—Si-based hot-dip plating bath type is used)
　Various steel plates A to F (see Tables 1 and 2) are used in the same manner as in Example 1, and the hot-dip plating bath is used as the above-mentioned Example. Melt plating was performed under various conditions using the Al-9 mass% Si-2 mass% Fe-based plating bath in Example 1-2 of 1.
[0156]
　When vibration was applied to the hot-dip plating bath using the ultrasonic horn 10A, the distance L2 was set to 0 mm to 5 mm, and the fundamental frequency was set to 20 kHz. When vibration was applied to the hot-dip plating bath using the ultrasonic horn 10A, the vibration was started 10 seconds after the start of immersion of the steel sheet 2 in the hot-dip plating bath, and the vibration was applied for 2 seconds. The conditions other than these were the same as in Example 1-2 above. The test results are summarized in Table 12.
[0157]
[Table 12]

　No. in Table 12 As shown in 361 to 370, when the steel sheet is dipped-plated while applying vibration in the hot-dip plating bath under the condition that the acoustic spectrum within the range of the present invention is measured in the hot-dip plating bath. The plating property of the steel sheet was improved, and the non-plating rate of the plated product became 0%.
[0158]
　On the other hand, when hot-dip plating was performed in the hot-dip plating bath without applying vibration, No. As shown in 371 to 376, the non-plating rate of the plated product was 80% or more.
[0159]
　(Example 3-3: Various hot-dip plating bath types are used)
　Various steel plates A to F (see Tables 1 and 2) are used in the same manner as in Example 1, and the hot-dip plating bath according to the third embodiment. Hot-dip plating was performed under various conditions using various hot-dip plating baths shown in Example 2 (Example 2-3).
[0160]
　When vibration was applied to the hot-dip plating bath using the ultrasonic horn 10A, the distance L2 was set to 0 mm and the fundamental frequency was set to 20 kHz. Conditions other than these were the same as in Example 1-3 above. The test results are summarized in Table 13.
[0161]
[Table 13]

　No. in Table 13. As shown in 381 to 452, when the steel sheet is dipped-plated while applying vibration in the hot-dip plating bath under the condition that the acoustic spectrum within the range of the present invention is measured in the hot-dip plating bath. The plating property of the steel sheet was improved, and the non-plating rate of the plated product was 0%.
[0162]
　On the other hand, when hot-dip plating was performed in the hot-dip plating bath without applying vibration, No. As shown in 453 to 464, the non-plating rate of the plated product was 80% or more.
[0163]
　[Embodiment 6]
　Other embodiments of the present invention will be described below. For convenience of explanation, the members having the same functions as the members described in the above-described embodiment are designated by the same reference numerals, and the description thereof will not be repeated.
[0164]
　In the hot-dip plating method of the present embodiment, a continuous hot-dip plating facility for continuously passing a steel strip through a hot-dip plating bath is used, and a part of an ultrasonic horn is immersed in the hot-dip plating bath to form a steel strip. Place the tip of the ultrasonic horn in the vicinity. While applying vibration to the hot-dip plating bath or steel strip from the tip of the ultrasonic horn, hot-dip plating is continuously applied to the steel strip.
[0165]
　(Hot-dip plating equipment)
　The hot-dip plating equipment 90A that implements the hot-dip plating method in the present embodiment will be described with reference to FIG. The hot-dip plating apparatus 90A is an example, and the apparatus for carrying out this hot-dip plating method is not particularly limited. FIG. 11 is a schematic view showing an example of a hot-dip plating facility 90A that implements the hot-dip plating method according to the present embodiment.
[0166]
　As shown in FIG. 11, the hot-dip plating equipment 90A has a configuration in which an ultrasonic horn 10B and a measuring device 50 are added to a general continuous hot-dip plating equipment. The steel strip 2A is immersed in the hot-dip plating bath 20 through the snout 91. The steel strip 2A is passed through the hot-dip plating bath 20 by the guide roll 92 and the support roll 93, and then pulled up to adjust the plating adhesion amount by gas spraying or the like.
[0167]
　The iron oxide layer on the surface of the steel strip 2A may be removed by a pickling treatment or the like as a pretreatment of the plating step on the steel strip 2A. Further, the hot-dip plating equipment 90A may be adapted to heat the steel strip 2A to a temperature suitable for hot-dip plating by a heating device (not shown) provided in front of the snout 91.
[0168]
　Here, unlike the general continuous hot-dip plating equipment, the hot-dip plating equipment 90A does not have to be provided with a reduction heating device in front of the snout 91. In the hot-dip plating equipment 90A, by applying ultrasonic vibration to the hot-dip plating bath 20 using the ultrasonic horn 10B, the plating wettability of the steel strip 2A is not obtained even if the surface of the steel strip 2A is not subjected to the reduction treatment. Can be enhanced.
[0169]
　In the present embodiment, the ultrasonic horn 10B is an integrally configured device including the ultrasonic vibrator 11, the tip portion 17, and the connecting portion 16 in the ultrasonic horn 10A described in the fifth embodiment. The hot-dip plating equipment 90A may use the ultrasonic horn 10A instead of the ultrasonic horn 10B.
[0170]
　In the hot-dip plating equipment 90A, the ultrasonic horn 10B is arranged so that the tip of the ultrasonic horn 10B is immersed in the hot-dip plating bath 20 and is located near the steel strip 2A near the outlet of the snout 91. There is.
[0171]
　It is preferable that the end of the ultrasonic horn 10B closer to the steel strip 2A in the longitudinal direction is chamfered to form the vibration surface 17A. The vibrating surface 17A faces the surface of the steel strip 2A through which the hot-dip plating bath 20 passes. As a result, the vibration can be efficiently transmitted from the ultrasonic horn 10B to the steel strip 2A by keeping the distance between the vibration surface 17A and the surface of the steel strip 2A constant according to the plate passing direction.
[0172]
　Further, in the hot-dip plating facility 90A, the lead is provided in the hot-dip plating bath 20 in the vicinity of the second surface of the steel strip 2A on the side opposite to the first surface of the steel strip 2A facing the vibrating surface 17A. The tip of the corrugated rod 51 is arranged. The waveguide 51 is preferably arranged along the plate-passing direction of the steel strip 2A. Further, the waveguide 51 may be provided with a protective tube or the like that covers a portion other than the tip in the hot-dip plating bath 20 in order to reduce noise or the like in the acoustic spectrum.
[0173]
　The distance L3 between the vibrating surface 17A and the surface of the steel strip 2A may be 0 mm, greater than 0 mm and 50 mm or less. The distance L3 of 0 mm means that the vibrating surface 17A and the surface of the steel strip 2A are in contact with each other at a time point before the ultrasonic horn 10B ultrasonically vibrates (that is, at the time of setting).
[0174]
　Despite applying ultrasonic vibration from the ultrasonic horn 10B to one side of the steel strip 2A, if the distance L3 is sufficiently close, the steel strip 2A vibrates at the same fundamental frequency as the ultrasonic horn 10B. It is possible to make it. As a result, the plating wettability can be enhanced not only on the first surface of the steel strip 2A but also on the second surface.
[0175]
　In the hot-dip plating equipment 90A, the frequency, output, and the like of vibration applied to the hot-dip plating bath 20 using the ultrasonic horn 10B are the same as those described in the first embodiment.
[0176]
　(
　Modification example of hot-dip plating equipment ) FIG. 12 is a schematic view showing a hot-dip plating equipment 90B and a hot-dip plating equipment 90C of one modified example.
[0177]
　The hot-dip plating equipment 90B and the hot-dip plating equipment 90C are different from the above-mentioned hot-dip plating equipment 90A in that the ultrasonic horn 10B is arranged in the vicinity of the support roll 93. In the hot-dip plating equipment 90B and the hot-dip plating equipment 90C, the ultrasonic horn 10B is arranged at a position after the steel strip 2A is passed through the hot-dip plating bath 20 and passed through the support roll 93. Even when the ultrasonic horn 10B is arranged in this way, the plating wettability of the steel strip 2A can be improved by applying ultrasonic vibration from the ultrasonic horn 10B to the hot-dip plating bath 20 or the steel strip 2A. ..
[0178]
　In addition, the arrangement of the ultrasonic horns 10B in the hot-dip plating facilities 90A to 90C may be combined to apply ultrasonic vibration to the hot-dip plating bath 20 or the steel strip 2A by using a plurality of ultrasonic horns 10B. .. A configuration that improves the plating property of the steel strip 2A may be appropriately selected.
[0179]
　Further, in the hot-dip plating facilities 90A to 90C, instead of specifically specifying the time for applying ultrasonic vibration to the steel strip 2A, the plate passing speed of the steel strip 2A is improved so that the plating property of the steel strip 2A is good. May be adjusted as appropriate.
[0180]
　[Example 4] Examples
　of the hot-dip plating method according to the sixth embodiment of the present invention will be described below. In this example, the hot-dip plating equipment 90A shown in FIG. 11 described above was used.
[0181]
　Specifically, the various devices used in the hot-dip plating facility 90A in this embodiment are as follows.
[0182]
　(Ultrasonic vibration supply system)
　・ Ultrasonic vibrator 11: manufactured by hielscher, 20 kHz oscillator
　・ Connection part 16 (adapter): Material , 1/2 wavelength type, length 126 mm
　, tip part 17: Material < Super Sialon>, 2-wavelength type, length 500 mm
　, ultrasonic power supply device D1: heelscher, 20 kHz, 2 kW power supply
　(ultrasonic vibration measurement system)
　, waveguide 51: Material , φ6 mm x 300 mm
　, AE sensor 52: NF Circuit Design Block Co., Ltd., AE-900M
　, Measuring Unit 53
　　Amplifier: NF Circuit Design Block Co., Ltd., AE9922
　　Spectrum Analyzer: Azilent Technology Co., Ltd., E4408B.
[0183]
　(Example 4-1: No heat treatment before the hot-dip plating step)
　Various steel sheets A to F (see Tables 1 and 2) are used in the same manner as in Example 1, and a Zn—Al—Mg-based hot-dip plating bath is used. Alternatively, melt plating was performed under various conditions using an Al-9 mass% Si-2 mass% Fe-based plating bath.
[0184]
　The atmosphere in the snout was changed to an atmospheric atmosphere, a nitrogen atmosphere, a 3% hydrogen-nitrogen atmosphere, or a 30% hydrogen-nitrogen atmosphere.
[0185]
　When vibration was applied to the hot-dip plating bath using the ultrasonic horn 10B, the distance L3 was set to 0 mm and the fundamental frequency was set to 20 kHz. The plate passing speed of the steel strip in the hot-dip plating bath was set to 20 m / min.
[0186]
　Further, as a comparative example, the steel strip 2A was subjected to continuous hot-dip plating using the hot-dip plating equipment 90A without applying vibration to the hot-dip plating bath. The test results are summarized in Table 14.
[0187]
[Table 14]

　No. of Table 14 As shown in 471 to 518, when the steel strip is hot-dip plated while applying vibration in the hot-dip plating bath under the condition that the acoustic spectrum within the range of the present invention is measured in the hot-dip plating bath. , The plating property of the steel strip was improved, and the non-plating rate of the plated product became 0% under all various conditions.
[0188]
　On the other hand, when hot-dip plating was performed in the hot-dip plating bath without applying vibration, No. As shown in 519 to 534, the non-plating rate of the plated product was 80% or more under any of the various conditions.
[0189]
　(Example 4-2: Heat treatment is performed before the hot-dip plating process) In
　the pre-snout stage, the steel strip is heat-treated in an air atmosphere, a nitrogen atmosphere, a 3% hydrogen-nitrogen atmosphere, or a 30% hydrogen-nitrogen atmosphere. Continuous hot-dip plating was performed in the same manner as in Example 4-1 above, except that the above-mentioned example 4-1 was performed. The test results are summarized in Table 15.
[0190]
[Table 15]

　No. in Table 15. As shown in 541 to 552, even when the steel strip is heated in an atmospheric atmosphere and then the steel strip is allowed to enter the hot-dip plating bath (when the steel sheet has a relatively thick oxide film), it melts. The passivation rate of the plated product was less than 1% by applying vibration in the plating bath under conditions such that the acoustic spectrum within the range of the present invention was measured.
[0191]
　In addition, No. As shown in 553 to 588, when the heating atmosphere in the previous stage of the snout and the atmosphere in the snout are non-oxidizing atmospheres, even if the steel strip is allowed to enter the hot-dip plating bath while the steel strip is heated, hot-dip plating is performed. By applying vibration under conditions such that the acoustic spectrum within the range of the present invention was measured in the bath, the non-plating rate of the plated product became 0%.
[0192]
　On the other hand, when the steel strip was heated in the atmospheric atmosphere and then the steel strip was melt-plated without applying vibration in the hot-dip plating bath, No. As shown in 589, 590, 579, 598, the non-plating rate of the plated product was 80% or more.
[0193]
　In addition, No. As shown in 591 to 594 and 599 to 604, when the steel strip is melt-plated without applying vibration in the hot-dip plating bath, with the heating atmosphere in the previous stage of the snout and the atmosphere in the snout as a non-oxidizing atmosphere. The non-plating rate of plated products was 1% or more.
[0194]
　In addition, as in the prior art, when the steel strip was subjected to the reduction heat treatment and the hot-dip plating was performed in the reducing atmosphere, the No. As shown in 595 and 596, the non-plating rate of the plated product was 0%.
[0195]
　[Appendix] The
　present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the technical means disclosed in the different embodiments may be appropriately combined. The obtained embodiments are also included in the technical scope of the present invention.
Code description
[0196]
　　2
　Steel plate (metal material) 2A Steel strip (metal material)
　20 Hot-dip plating bath (plating bath)
The scope of the claims
[Claim 1]
　Plating in which a metal material is allowed to enter a plating bath which is a molten metal, and the metal material is coated with the molten metal while applying vibration to the plating bath while the metal material is in contact with the molten metal. Including the step,
　the frequency of the vibration applied to the plating bath is used as a basic frequency, and in the
　plating step, the vibration is measured so that the acoustic spectrum measured in the plating bath satisfies the relationship of the following formula (1). A hot-dip plating method characterized by imparting.
　(IB-NB) / (IA-NA)> 0.2 ... (1)
　(Here,
　IA: average value of sound pressure over the entire measurement frequency band
　IB: (i) Peak of sound pressure at the above basic frequency Average value of sound pressure in a specific frequency band between (ii) peaks of sound pressure at a plurality of harmonic frequencies and between adjacent peaks of sound pressure peaks at a plurality of harmonic frequencies
　NA: The above-mentioned measurement frequency band The average value of the sound pressure when the vibration is not applied in the whole
　NB: The average value of the sound pressure when the vibration is not applied in the specific frequency band specified for the IB
)
[Claim 2]
　The melt plating method according to claim 1, wherein the metal material is subjected to a degreasing treatment or a pickling treatment as a pretreatment before the plating step.