JPH11286761A - Hot dip galvanizing device and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot dip galvanizing method in which the structure of a hot dip galvanizing device is simple, furthermore efficiently removing dross in a plating tank and moreover, capable of preventing the deposition of dross, and to provide the device therefor. SOLUTION: In the hot dip galvanizing device provided with a plating pot 12 housing zinc series molten metal contg. >=0.05 wt.% aluminum, dipped with a steel strip and applying plating thereto, a melting pot 13 melting an ingot 14 to be used for plating and a passage 22 connecting the plating pot 12 and the melting pot 13 in the same bath face, the melting pot 13 is provided with a heating means 16 capable of heating the molten metal in the melting pot 13 to above the average temp. of the molten metal bath in the plating pot 12, and moreover, the passage is provided with a heating means 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanizing apparatus and method, and more particularly to an apparatus and method suitable for producing high-quality hot-dip galvanized steel strip containing zinc as a main component.

[0002]

2. Description of the Related Art Conventionally, a hot-dip galvanized steel strip is manufactured by a plating apparatus shown in FIG. That is, the steel strip S runs in the direction of the arrow and is immersed in the plating tank 4 from the snout 1,
After the direction is changed by the sink roll 2, it is pulled up from the plating bath 3, the coating amount is adjusted by a coating amount control device (not shown), cooled, subjected to a predetermined post-treatment, and formed into a required plated steel strip. The zinc-based solid metal ingot 14 is melted in the plating bath 4 in order to compensate for the plating metal that is attached to the steel strip S and reduced.

[0003] While the steel strip S passes through the plating bath 4, iron eluted from the steel strip S reacts with zinc as a main component in the plating bath 3 or aluminum added in a small amount to form zinc iron aluminum or the like. To form an intermetallic compound, so-called dross.

[0004] The surface defect of the hot-dip galvanized steel strip due to the so-called dross is the most serious problem among hot-dip galvanized steel strips. Particularly serious is the intermetallic compound (FeZ) formed by the reaction between iron and zinc eluted from the steel strip.
n ₇ is what is called bottom dross etc.), its size is 5 to 300 microns in diameter spherical conversion.
This bottom dross will be deposited on the bottom of the plating tank in a stationary state where there is no flow of the plating bath. However, the plating bath in the bath is stirred by the running of the steel strip, the rotation of the roll in the bath in the plating bath, or the natural convection of the plating bath caused by the dissolution of the ingot. As a result, dross having a small difference in specific gravity from the plating bath cannot be deposited on the bottom, or the deposited dross is rolled up and adheres to the plated steel strip, resulting in surface defects of the hot-dip galvanized steel strip due to the dross.

Conventionally, there have been many proposals for removing the dross. Many of these suggestions are
This is a method in which molten zinc is once pumped out of the plating tank to settle and separate dross, or a method in which dross is separated by filtration.

However, despite many proposals, none of the conventional proposals have been put to practical use. The reason for this is that, although these proposed technologies can be realized on a desk, there are many problems in the complexity, durability, and operability of the mechanism in actual equipment, and it is practically impossible.

With respect to the sedimentation and separation of dross proposed so far, it is important to design an apparatus so that the molten zinc being transported outside the tank does not solidify, and even if molten zinc leaks from the transport piping, Since the equipment must be designed on the assumption, the equipment is enormously expensive and not realistic.

In the method of filtering dross, there is a large difference in the size of dross that can be filtered between when filtration is first started and when the filtration device is clogged, and dross that causes quality defects is efficiently removed. It cannot be removed, and when replacing the filter of the filtration device, it is necessary to remove the filter in some way in a molten zinc bath, which is costly and practical as in the case of transferring the molten zinc. Absent.

[0009] Recently, the point of view has been changed from that of the conventional method, and the generated bottom dross is immediately removed from the plating tank, for example, Japanese Patent Application Laid-Open No. 5-222500 (hereinafter referred to as prior art 1), and a method for reducing the dross generation, For example, JP-A-5
No. 186857 (hereinafter referred to as Prior Document 2) has been proposed.

In the prior art document 1, as shown in FIG.
Ingot 1 separately from main pot 40 for plating on
A sub-pot 41 for dissolving 4 is provided, and the main pot 40 and the sub-pot 41 are connected at the side and bottom below the bath surface. That is, a molten metal introduction pipe 42 to the main pot 40 is provided at an upper position below the bath surface, and a molten metal outlet pipe 43 from the main pot and a stirring gas injection nozzle 46 provided in the sub pot 41 are provided below the pipe. The inlet pipe 42 and the molten metal outlet pipe 43 include heating devices 44 and 45, respectively.

In the above apparatus, the main pot 40 and the molten metal outlet pipe 4 are provided between the main pot 40 and the sub-pot 41.
A circulation flow is formed in the order of 3 → sub pot 41 → molten metal introduction pipe 42 → main pot 40. The dross generated in the main pot 40 is quickly transferred to the sub-pot 41 by a stirring gas injection nozzle 46 or the like, and the ingot 14 is dissolved and the dross is settled and separated in the sub-pot 41, and the purified molten zinc is returned to the main pot 40. Thereby, dross accumulation in the main pot 40 is prevented.

Further, in the prior art document 2, as shown in FIG. 7, a weir 51 is provided in a plating tank 50 to form a double structure.
A portion 52 for dissolving the ingot 14 with the plating tank 50;
In addition to being separated into a portion 53 for plating on the steel strip S, a communication hole 54 for a portion 52 for dissolving the ingot 14 and a portion 53 for plating is provided in the weir 51.
The heating means 56 is disposed in the vicinity of the ingot charging portion.
When the ingot 14 is melted, the heating means 56 is used to prevent the temperature of the portion 52 where the ingot 14 is melted from being locally reduced, thereby reducing the generation of dross.

[0013]

However, in the prior art document 1, the main pot 40 and the sub pot 41 are connected by pipes 42 and 43 provided at the bottom and side portions, respectively, to circulate the plating bath. Further, when the plating bath leaks from the pipe, there is no measure to stop the leak. Further, in a situation where the plating bath is insufficiently heated, for example, when a power failure occurs, the plating bath in the pipe is easily solidified. That is, not only is the facility complicated and hinders operation, but also there are many engineering problems that need to be solved, so that application to actual equipment is not easy.

In the prior art 2, the ingot 14 is connected to the weir 51
Although the non-uniformity of the temperature distribution of the plating bath is eliminated by melting while controlling the temperature using the heating device 56 in the portion 52 partitioned by the above, no consideration has been given to the generation or growth of dross itself. Therefore, it is impossible to sufficiently reduce dross in the plating tank 51.

The present invention has been made in view of such circumstances, and has a simple structure, a dross in a plating tank can be efficiently removed, and a method and an apparatus for hot-dip galvanizing can prevent the accumulation of dross. The purpose is to provide.

[0016]

The above-mentioned prior art documents 1 and 2 are as follows.
In each case, the conventional processes such as sedimentation, stirring, and uniform temperature distribution are examined to prevent dross from being generated or dross is removed. It does not do.

The present invention proposes an innovative process capable of efficiently removing dross in consideration of a change in iron solubility of a plating bath with temperature and a reaction between aluminum and iron, which have not been studied in the past. The gist of the invention is as follows.

The first invention is a plating pot for containing a zinc-based molten metal containing 0.05% by weight or more of aluminum and dipping a steel strip for plating, a dissolving pot for dissolving an ingot used for plating, and the plating pot. A hot-dip galvanizing apparatus provided with a flow path that connects a pot and the melting pot on the same bath surface, wherein the melting metal in the melting pot is set to a temperature higher than the molten metal bath average temperature in the plating pot. A hot-dip galvanizing apparatus for a steel strip, wherein a heating means capable of heating is provided, and a heating means is further provided in a flow path.

According to a second aspect of the present invention, the cross section of the flow path has a hydraulic diameter defined by the following formula of 0.1 m or more and 0.3 m or less, and the length of the flow path is at least 5 times the hydraulic diameter. The steel strip according to the first invention, wherein the passage is provided with a heating means capable of heating at least a part of the molten metal bath in the flow path to a temperature equal to or higher than the temperature of the molten metal bath in the plating pot. Hot-dip galvanizing apparatus.

Hydraulic diameter = (cross-sectional area of flow path / wet length of flow path) × 4 where the wet length of the flow path is the length around the cross-section of the flow path.

A third invention is characterized in that a heating means for heating the molten metal bath is further provided in the plating pot, and the flow path is a flow path whose upper part is open. It is a hot-dip galvanizing apparatus for a steel strip according to the invention.

According to a fourth aspect of the present invention, when a steel strip is immersed in a plating tank containing a zinc-based molten metal containing 0.05% by weight or more of aluminum to perform continuous hot-dip galvanizing, the steel strip is immersed in the plating tank. And a melting pot in which an ingot used for plating is melted, and a molten metal bath average temperature Ts melted in the melting pot.
(° C.), average temperature Tm of the molten metal bath of the plating pot
(° C.) satisfies Ts> Tm, transfer the molten metal bath dissolved in the melting pot to the plating pot on the same bath surface through a flow path, and heat the molten metal bath in the flow path. This is a hot-dip galvanizing method for a steel strip.

According to a fifth aspect of the present invention, there is provided a fuel cell system comprising: The hot-dip galvanizing method for a steel strip according to the fourth aspect, wherein the steel strip is transferred to a plating pot on the same bath surface.

Hydraulic diameter = (cross-sectional area of channel / wetting length of channel) × 4 where the wet length of the channel is the length around the cross-section of the channel.

According to a sixth aspect of the present invention, a molten metal bath average temperature Ts (° C.) of a plating pot is set to 440 ° C. or more, a molten metal bath average temperature Tm (° C.) of a melting pot is set to 460 ° C. 6. The hot-dip galvanizing method for a steel strip according to claim 4, wherein the flow path is an open channel.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION In order to improve the workability of a plating film of a hot-dip galvanized steel strip, a plating bath containing zinc as a main component contains 0.05% (hereinafter, wt%) of aluminum. When the steel strip is immersed in the plating bath, iron is eluted from the steel strip.

When iron eluted from the steel strip forms zinc and an intermetallic compound, the specific gravity is higher than that of the plating bath, and the bottom dross settles. On the other hand, when iron forms an intermetallic compound with aluminum, the specific gravity is lower than that of the plating bath, and the iron becomes a top dross that floats. The dross that usually becomes a problem is that the sinking bottom dross emerges for some reason,
Adhering to steel strip. Even if the floating top dross adheres to the steel strip, there is little problem.

The solubility of iron in molten zinc is proportional to the temperature of the plating bath. The higher the temperature, the better the iron dissolves in the plating bath, and the lower the temperature, the more supersaturated iron forms intermetallic compounds with zinc and precipitates. In addition, the amount of iron dissolved is appropriate for the temperature of the plating bath.

The iron eluted from the steel strip does not exist in the vicinity of the steel strip, but is dissolved while being sufficiently stirred in the plating bath with the movement of the steel strip. It is always saturated. If there is a low-temperature part in the plating tank, iron reacts with zinc in that part to produce bottom dross, or the iron-zinc intermetallic compound formed by the plating reaction that has fallen off the steel strip surface cannot dissolve, resulting in bottom dross. Become.

In a normal operation, a low-temperature ingot is supplied to a plating bath maintained at a constant temperature. In this case, as shown in FIG. 1, non-uniform temperature distribution occurs,
The temperature around the ingot 14 becomes lower than the plating bath temperature. Iron in the plating bath generates intermetallic compounds with zinc or aluminum contained in the ingot in the region where the temperature is lowered.

For example, the solubility of iron in a plating bath at 420 ° C. becomes smaller as it approaches zero, but at 460 ° C., 0.03% of iron can be dissolved in the plating bath. Therefore, when the plating bath of 460 ° C. flows on the surface of the ingot 14 and becomes a low temperature of about 420 ° C., the dissolved 0.03% of iron cannot be dissolved in the plating bath. It reacts with aluminum in 14 to become an intermetallic compound of iron aluminum or an intermetallic compound of iron zinc. Once formed, these intermetallic compounds have a high melting temperature, so that the plating bath
It does not completely dissolve even after returning to 60 ° C.

However, the present inventors have experimentally confirmed that iron in the intermetallic compound dissolves in the plating bath when only the iron having a solubility equal to or lower than the saturation solubility is dissolved in the plating bath.
The present invention utilizes this phenomenon effectively, that is,
By bringing the plating bath containing the intermetallic compound into contact with a high-temperature plating bath in which iron is not saturated, it is possible to remove iron in the intermetallic compound and the plating bath and reduce quality defects due to dross. It was done.

Since it is inevitable that the temperature change during melting of the ingot and the resulting change in iron solubility, not dissolving this in the plating pot is an effective method for preventing dross from being generated. However, this improvement alone does not significantly reduce the dross of the plating pot, but merely reduces the amount of dross generated when the ingot is melted, and is therefore insufficient as a dross removal measure.

Therefore, first, the melting pot and the plating pot are separated from each other, and accordingly, a heating device is provided in each of the melting pot and the plating pot so that the temperature of each pot can be controlled by heating. In order to improve plating workability and obtain excellent plating quality, the temperature (average temperature) of the plating pot is set to 440 ° C. or higher. Also,
In order to dissolve the required amount of ingot and efficiently remove the dissolved iron transferred from the plating pot as dross, the melting pot temperature (average temperature) is 460 ° C.
Above.

When the pots are separated, it is necessary to transfer the plating bath between the pots by some method. The present inventors have learned from the operation analysis data that it is important for the operation not to generate zinc oxide by mixing air into the molten zinc. The transfer of the plating bath is generally performed by a pump or an overflow. However, when the plating bath is simply transferred by the pump or the overflow, a large amount of zinc oxide is generated on the surface of the plating bath, which is a factor that hinders the operation. The present inventors have succeeded in suppressing the generation of zinc oxide during transfer of the plating bath by providing a flow path and transferring the plating solution with the same bath surface between both pots.

Regarding the use of the same bath surface, refer to the prior art document 1.
However, in the present invention, it is important to secure a flow path in the vicinity of the plating bath surface, avoiding providing a communication portion at the bottom or side of the pot as in the prior art document 1. In particular, solidification of the plating bath in the flow path is a problem that is unacceptable in operation, and therefore, it is desirable to use a flow path with an open top.

When the temperature of the plating bath in the flow path is maintained at the same temperature as the temperature of the plating pot, as described in the prior art document 2, dross generation due to a decrease in temperature during melting of the ingot is only suppressed. If the temperature of the plating bath in the flow path is higher than the temperature of the plating pot, the situation will change drastically.
In other words, the iron in the plating bath in the pot is saturated, but the plating bath in the flow channel flowing from the melting pot in which the ingot has been dissolved is not saturated with iron and has a high temperature because the iron is not saturated. Is getting bigger. Therefore, the iron in the plating pot saturated with iron and the iron that has become an intermetallic compound dissolve, and the iron diffuses into the plating bath in the unsaturated flow path. This means that the iron in the agitated plating pot reacts with the plating bath in the flow channel, and when the aluminum concentration of the ingot is high, it becomes an iron-aluminum intermetallic compound and Surface of the plating bath. In addition, part of the diffused iron moves from the flow channel into the melting pot and spreads, generating iron zinc bottom dross and iron aluminum top dross in the bath temperature drop area around the ingot to reduce iron in the plating bath. It becomes possible to do.
That is, dross in the plating pot can be reduced. Further, since the reduced dross is removed outside the system as a top dross or a bottom dross in the dissolving pot, these do not affect the plating pot.

Even when the temperature of the flow channel is the same as the temperature of the plating pot, the same phenomenon as described above occurs because iron is not dissolved in the plating bath in the flow channel. The iron in the plating pot cannot be moved to the melting pot. As a result of much trial and error,
With the synergistic effect of increasing the flow channel temperature to increase the amount of iron dissolved in the plating bath and diffusing the dissolved iron into the plating bath in which the iron is not dissolved, the iron in the plating pot is removed. It has been experimentally confirmed that it can be removed.

In the present invention, in order to remove iron in the plating pot, it is necessary to heat the temperature of the plating bath in the flow channel to a temperature equal to or higher than the plating pot temperature. Although the inside of the flow path may be heated to a high temperature, the heating equipment becomes large and it may be difficult to control the temperature of the plating pot.Therefore, a part of the plating bath is plated using an induction heating device or a heating burner. What is necessary is just to heat to the temperature more than a pot temperature.

An embodiment of the present invention will be described with reference to FIG. In FIG. 2, 1 is a snout, 2 is a sink roll, 3 is a plating bath, 12 is a plating pot, 13 is a melting pot, and 14 is an ingot. The steel strip S travels in the direction of the arrow and enters the plating pot 12 from the snout 1,
After the direction is changed by the sink roll 2, it is pulled up from the plating bath 3, and the adhesion amount is adjusted by an adhesion amount adjusting device (not shown).
After cooling and performing a predetermined post-treatment, a required plated steel strip is obtained.

The plating pot 12 for plating the steel strip S has a capacity of 15 m ³ , and the melting pot 13 has a capacity of 10 m ^3. Both sides of the plating pot 12 and the melting pot 13 have induction heating for controlling the respective plating bath temperatures. Devices 15 and 16 are provided. The plating bath 3 melted in the melting pot 13 flows from above into the plating pot 12 on the same bath surface through the flow path 22 heated by the burner 21.

As shown in FIG. 3, the heating device 21
a may be provided, and the flow path 22a may not be open at the top. However, in consideration of the fact that an intermetallic compound of iron and aluminum generated in the flow path 22a may cause clogging of the flow path, or a problem of maintenance. In the apparatus shown in FIG.
Is opened so that the plating pot 12 and the melting pot 13 have the same plating bath surface. In other words, it goes without saying that the channel does not have to be opened unless there is a problem of clogging of the channel.

The molten metal adhered to and taken out of the steel strip S dissolves and replenishes the ingot 14 into the melting pot 13 to keep the plating bath surface constant. In this case, in consideration of the fact that aluminum reacts with iron to be consumed as an intermetallic compound of iron aluminum, an ingot having a higher aluminum concentration than the plating pot 12 is used.
In the present embodiment, the aluminum concentration of the plating pot 12 is set to 0.1
Since it was set to 2%, the ingot 14 used had an aluminum concentration of 0.15%. It does not necessarily mean that an ingot having a constant aluminum concentration is used, but a combination of an ingot having an aluminum concentration of 0.2% and 0.1% or an ingot having an aluminum concentration of 0% and 0.3%. The ingots 14 may be sequentially put into the melting pot 13 in combination. It suffices that the aluminum concentration in the plating pot 12 eventually reaches a predetermined value, and thus there is no specification on the method of adding aluminum.

As shown in FIG. 4, when an ingot having a high aluminum concentration is dissolved, the iron solubility is lower than when an ingot having a low aluminum concentration is dissolved, so that more iron can be removed from the plating bath. However, when an ingot having a high aluminum concentration is dissolved, it is necessary to pay attention to the fact that the amount of aluminum consumed in the ingot increases because the intermetallic compound generated contains more iron aluminum than iron zinc.

In the vicinity of the ingot 14 of the melting pot 13, iron reacts with aluminum to form top dross 31, and iron reacts with zinc to form bottom dross 32. In addition, channel 2
A slightly rising top dross 31 is also formed at the upper part of the second dross 2. Here, when the ingot 14 having a low aluminum concentration is used, iron and zinc may react and generate bottom dross 32 at the bottom of the melting pot 13 or the flow path 22. Some of these react with the aluminum again to form the top dross 31 when the ingot 14 having a high aluminum concentration is introduced, and others remain as the bottom dross 32. The situation changes with the introduction of the ingot 14, but finally, the situation changes. The dross can be intensively deposited on the melting pot 13 or the flow path 22 and removed, and the generation of dross in the plating pot 12 can be largely suppressed.

When the flow path 22 becomes large, the structure becomes the same as that of the ordinary plating tank 4 as shown in FIG.
There is some optimum value for the dimension of. Since various shapes such as a circular shape and a rectangular shape can be considered as the cross-sectional shape of the flow channel 22, the present inventors have studied using the hydraulic diameter used in hydraulics. The hydraulic diameter is obtained by dividing the cross-sectional area of the flow path 22 by the wetting length of the flow path 22, that is, the peripheral length of the flow path cross section, and multiplying by four. For a circular cross section, the hydraulic diameter corresponds to the diameter of the circular cross section. In the case of a square cross section, the length is equal to the length of one side of the square.

When the examination was conducted using the hydraulic diameter,
In a flow path having a hydraulic diameter of about 50 mm or less, even when heating is performed so that the plating bath does not solidify in the flow path, the solidification often actually solidifies, and the dimensions were not applicable to an actual machine.
A hydraulic diameter of at least about 100 mm was required. On the other hand, as the flow path becomes larger, the functions of the plating pot 12 and the dissolving pot 13 are mixed, so that dross is generated in the plating pot 12 and the problem of leakage is increased structurally. In order to remove the dross with the dissolving pot 13 and to solve the problem of the occurrence of the leakage from an engineering point of view, it has been found that the hydraulic diameter is preferably 0.3 m or less. In the case of a flow path having an open upper part, if the depth exceeds 0.3 m, it is necessary to make the welded structure of the connection part strong. Therefore, in this embodiment, the depth is set to 0.3 m or less.

In the plating pot 12, the plating bath 3 is in a state of being appropriately stirred by the running of the steel strip S. In the melting pot 13, it is preferable that the plating bath is stationary so that the dross can easily settle or float.
The length of the flow path 22 needs to be a length that can cut off the influence of the flow between the two pots. From this point of view, the necessary length of the flow path 22 was examined, and it was found that if the length of the flow path 22 was set to five times or more the hydraulic diameter, the influence of the flow between the two pots could be cut off. Was confirmed. Therefore, in this embodiment, the width of the cross section is 2
The diameter was 00 mm, the depth was 150 mm, the length was 2 m, that is, the hydraulic diameter was 175 mm, and the length was about 11 times the hydraulic diameter.

From the plating pot 12 to the melting pot 13
In order to move the plating pot, the flow path 22 is heated and the plating pot 12 is heated.
It is important to keep the temperature above. FIG. 4 shows the iron solubility when the plating bath temperature and the aluminum concentration are specified. Iron solubility tends to increase with increasing plating bath temperature, and iron solubility tends to decrease with increasing aluminum concentration. Then, when the concentration of aluminum in the plating bath of the plating pot 12 was set to 0.12% and the flow path was heated, the temperature of the plating bath was set to be lower than the plating pot temperature by one.
Since there is a portion which is higher than 0 ° C., preferably 50 ° C. or more, the iron component can be transferred through the high temperature portion to the plating pot 12.
It can be seen from FIG.

Therefore, in this embodiment, the plating pot 12
Was set to 460 ° C., the temperature of the melting pot 13 was set to 470 ° C., and the surface was heated to 510 ° C. by heating with the burner 21 from the upper part of the flow path 22 whose upper part was opened. 460
At 500C, the iron solubility of the plating bath was 0.03%, whereas at 510C, the iron dissolving ability was 0.15%, which is five times as high, so that the intermetallic compound in the plating pot 12 was efficiently dissolved. In addition, the saturated iron in the plating bath can be efficiently diffused to the melting pot 13 side. Since the plating bath heated to 510 ° C. contains aluminum, it reacts with the aluminum to form an intermetallic compound of iron aluminum.
Also, since the average temperature of the plating bath actually flowing through the flow path 22 is lower by 1 to 2 ° C. than the temperature of the melting pot 13 (470 ° C.),
The molten iron can be transferred to the melting pot 13 by setting the surface temperature of the flow channel 22 to 510 ° C. and creating a local high-temperature region.

In the present embodiment, there was no dross defect in the plated steel strip, which was about 2% of the conventional production amount, and the dross problem was completely eliminated.

[0052]

According to the present invention, dross generated in a plating pot can be melted in a heated flow path, moved outside the plating pot, and removed as a top dross or a bottom dross. Generation can be reduced and bottom dross can be prevented from being deposited. ADVANTAGE OF THE INVENTION According to this invention, since the surface defect of the steel strip by dross can be prevented in a hot-dip galvanizing equipment, manufacture of a high quality hot-dip galvanized steel strip can be realized.

According to the present invention, there is no need for a plating bath circulating system for removing dross, so that it is inexpensive. In addition, the operability is excellent because serious problems such as leakage and solidification of the plating bath in the flow path can be solved.

[Brief description of the drawings]

FIG. 1 is a view showing a plating bath temperature distribution around an ingot when the ingot is put into the plating bath.

FIG. 2 is a diagram showing a plating apparatus according to an embodiment of the present invention.

FIG. 3 is a view showing another flow channel provided in the plating apparatus according to the embodiment of the present invention.

FIG. 4 is a diagram showing iron solubility when a plating bath temperature and an aluminum concentration are specified.

FIG. 5 is a view showing a normal molten zinc pot.

FIG. 6 is a view showing a hot-dip galvanizing apparatus of Prior Document 1.

FIG. 7 is a diagram showing a hot-dip galvanizing apparatus of Prior Document 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Snout 2 Sink roll 3 Plating bath 4 Plating tank 12 Plating pot 13 Melting pot 14 Ingot 15, 16 Heating device (Induction heating device) 21 Burner (Heating device) 22 Channel 31 Top dross 32 Bottom dross S Steel strip

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Keishi Yamashita Nihon Kokan Co., Ltd. 1-2-1, Marunouchi, Chiyoda-ku, Tokyo

Claims (6)

[Claims] 1. A plating pot for containing a zinc-based molten metal containing 0.05% by weight or more of aluminum and plating by dipping a steel strip, a melting pot for dissolving an ingot used for plating, and the plating pot, What is claimed is: 1. A hot-dip galvanizing apparatus comprising a flow path connecting a melting pot on the same bath surface, wherein the melting pot is capable of heating the molten metal in the melting pot to a temperature higher than the average temperature of the molten metal bath in the plating pot. A hot-dip galvanizing apparatus for a steel strip, wherein a heating means is provided in the flow path. 2. The cross section of the flow path has a hydraulic diameter defined by the following equation of 0.1 m or more and 0.3 m or less, and the length of the flow path is at least 5 times the hydraulic diameter. 2. A hot-dip galvanized steel strip according to claim 1, wherein a heating means capable of heating at least a part of the molten metal bath in the flow channel to a temperature equal to or higher than the temperature of the molten metal bath in the plating pot is provided. System plating equipment. Hydraulic diameter = (cross-sectional area of flow path / wet length of flow path) × 4 where the wet length of the flow path is the length around the cross-section of the flow path. 3. The method according to claim 1, wherein a heating means for heating the molten metal bath is provided in the plating pot, and the flow path is a flow path whose upper part is open. Hot dip galvanizing equipment for steel strip. 4. When performing a continuous hot-dip galvanizing by immersing a steel strip in a plating tank containing a zinc-based molten metal containing 0.05% by weight or more of aluminum, the steel strip is immersed in the plating tank to perform plating. Is divided into a plating pot for dissolving the ingot used for plating and a melting pot for melting the ingot used for plating, and the average temperature Ts (° C.) of the molten metal bath melted in the melting pot and the average temperature Tm (° C.) of the molten metal bath of the plating pot are Ts.
> Tm, wherein the molten metal bath melted in the melting pot is transferred to the plating pot on the same bath surface through a flow path, and the molten metal bath in the flow path is heated. Hot-dip galvanizing method for belt. 5. The cross section of the flow path has a hydraulic diameter defined by the following formula of 0.1 m or more and 0.3 m or less, and the length of the flow path is equal to or more than 5 times the hydraulic diameter. 5. The hot-dip galvanizing method for a steel strip according to claim 4, wherein the hot-dip galvanizing method is carried out. Hydraulic diameter = (cross-sectional area of flow path / wet length of flow path) × 4 where the wet length of the flow path is the length around the cross-section of the flow path. 6. An average temperature Ts of a molten metal bath of a plating pot.
(4) the melting metal bath average temperature Tm (° C) of the melting pot is 440 ° C or higher, and the flow path is a flow path whose upper part is open.
Or the hot-dip galvanizing method of the steel strip of Claim 5.