JPH1150218A - Hot dip galvanizing equipment and hot dip galvanizing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot dip galvanizing facility and a hot dip galvanizing method in which dross can be efficiently discharged out of a galvanizing tank, dross deposition preventive effect in the galvanizing tank is excellent, generation of the dross can be reduced to low level, the structure is simple and durable, and no troubles are encountered during the operation. SOLUTION: In a hot dip galvanizing equipment of a steel strip to be continuously hot dip galvanized by dipping the steel strip in a hot dip galvanizing tank, an inner wall of a hot dip galvanizing tank 2 to achieve the hot dip galvanizing is within 200 mm in distance from the steel strip and within 100 mm in distance from a lower part of a sink roll 4 at a tank bottom part within 300 mm in distance from a member to be brought into contact with the steel strip, or the inner wall of the hot dip galvanizing tank is >=45 deg.C in gradient. A dross deposition space in the galvanizing tank is reduced, the flow of the molten zinc 3 in the galvanizing tank becomes twodimensional, the flow of the molten zinc can be constantly induced at the bottom part of the galvanizing tank, and no bottom dross is deposited on the tank bottom part. Because the inner wall is >=45 deg.C in gradient, no bottom dross can be deposited on the side of the galvanizing tank.

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 a hot-dip galvanizing method which are excellent in dross deposition preventing effect and dross forming preventing effect in a hot-dip zinc bath.

[0002]

2. Description of the Related Art Dross surface defects of hot-dip galvanized steel strip are the most serious of the surface defects of hot-dip galvanized steel strip. Dross is an intermetallic compound (FeZ) formed by the reaction between iron and zinc eluted from the steel strip to be plated.
n _7, an FeZn _13, Fe ₅ Zn _21, etc.), its size is 5 to 300 microns in diameter spherical conversion. If this dross is stationary with no flow of molten zinc,
Deposits on the bottom of the plating tank.

However, due to the natural convection of the molten zinc caused by the running of the steel strip, the rotation of the rolls in the bath in the plating tank, or the dissolution of the zinc ingot that supplies the molten zinc consumed by the plating, the molten zinc in the plating tank is removed. It is stirred.
As a result, dross having a small specific gravity difference from molten zinc cannot be deposited on the bottom of the plating tank. Alternatively, the deposited dross is wound up and adheres to the galvanized steel strip, resulting in a surface defect due to the dross of the galvanized steel strip.

Heretofore, there have been numerous proposals for removing dross. These proposals include a method in which molten zinc is pumped out of a plating tank to precipitate dross, a method in which dross is precipitated, a method in which aluminum is added and flotation is performed, and the like.

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. Recently, as a method that changed the viewpoint from the conventional method,
A method of immediately removing generated dross from a plating tank has been proposed. A typical example is disclosed in
There are methods disclosed in JP-A-9690 and JP-A-8-3709.

[0006] Japanese Patent Application Laid-Open No. Hei 5-9690 (hereinafter referred to as Reference 1) discloses that the distance between the bottom of a plating tank and the lower surface of a sink roll is 200 mm or less, and the length of time until a steel strip entering the plating tank comes into contact with the sink roll. The distance between the steel strip and the inner wall of the plating tank was 200 mm or less, and after changing the direction by the sink roll, the distance between the steel strip and the inner wall of the plating tank was limited to 700 mm or less to secure a space for dissolving the zinc ingot. It discloses that a steel strip is subjected to hot-dip galvanizing as a plating tank.

According to this method, since the capacity of the plating tank is reduced, even if a steel strip passes through the plating tank to produce an iron-zinc intermetallic compound which causes bottom dross, the growth of the steel strip is prevented. Before proceeding, the intermetallic compound adheres to the plated steel strip and is taken out of the system, and the dross generated in the plating tank performing plating is not accumulated or grown in the plating tank. It is said that the large diameter bottom dross can be prevented from adhering to the steel strip.

Further, Japanese Patent Application Laid-Open No. H8-3709 (hereinafter, referred to as Japanese Patent Application Laid-Open No.
Prior art document 2) discloses a plating tank having a bottom and inclined portions on both sides thereof along a traveling path of a steel strip wound around a sink roll, a sedimentation tank communicating with the plating tank through a shallow flow path, and a sedimentation tank. Hot dip galvanizing equipment equipped with a pump that refluxes the hot dip zinc to the plating tank,
Even if iron-zinc intermetallic compounds that cause bottom dross are generated, the molten zinc in the plating tank is quickly discharged from the shallow channel to the settling tank before the growth proceeds, and the dross settles in the settling tank. It is disclosed that after removal, the molten zinc in the precipitation tank is returned to the plating tank by a pump to prevent the bottom dross having a large diameter from adhering to the steel strip.

[0009]

However, prior art documents 1 and 2 have many problems. (1) Prior art documents 1 and 2 have a problem that the temperature of the plating tank changes greatly due to the reduced capacity of the plating tank, and dross is more likely to occur.

[0010] Since the molten zinc in the plating tank adheres to the steel strip and decreases, zinc must be replenished. Zinc is replenished by dissolving solid phase zinc (zinc ingot).

For example, 1800 running at 120 mpm
When a steel strip having a width of 0.8 mm and a thickness of 0.8 mm is plated with a coating amount of 60 g / m ² on both sides, the amount of zinc used is approximately 1.5 tons per hour as calculated below. 120 (m / min) x 60 (min / h) x 1.8
(M) × 2 (front and back) × 60 (g / m ² ) / 1000 (g)
/ Kg) = 1555.2 kg / h In this case, assuming that the heat of fusion of zinc is 102 kJ / kg and the specific heat of normal zinc is 0.5 kJ / kgK, the heat quantity required for dissolving zinc is calculated as follows. 129 kW. 1555.2 (kg / h) × 102 (kJ / kg) +1
555.2 (kg / h) x 0.5 (kJ / kgK) x
(419-20) (° C) = 463450 kJ / h = 12
9kW

On the other hand, the capacity of the operating plating tank is 10
m ^3, the density of the zinc and 1 m ³ per 6.66 tons, when operating the temperature of molten zinc at 460 ° C., the amount of heat to be used for the temperature holding of the plating tank is equal to the amount of heat dissipated from approximately the plating bath, plating The amount of heat released from the tank is substantially equal to the amount of radiant heat transferred from the plating tank surface.

Assuming that the radiation coefficient of the zinc surface is 0.6 and the surface area is 10 m ² , the amount of heat transferred from the surface of the plating tank is calculated as follows. 4.88 (kcal / hK ⁴ m ² ) × (((460 + 2
73) / 100) ⁴ -((20 + 273) / 100)
⁴ (K ⁴ ) × 0.6 × 10 (m ² ) = 82000 (Kca
1 / h) = 95800 (kW) On the other hand, the steel density was 7000 kg / m ³ and the specific heat was 0.2 K.
When cal / kgK and the temperature of the steel strip immersed in the plating tank is 5 ° C. higher than the molten zinc, the calorie carried by the steel strip is calculated as follows. 120 (m / min) x 60 (min / h) x 1.8
(M) × 0.0008 (m) × 7000 (kg / m ³ )
× 0.2 (Kcal / kgK) × 5 (° C) = 72600
(Kcal / h) = 84670 kW That is, there is no large difference between the amount of heat introduced by the steel strip and the amount of heat released from the plating tank. The temperature may change.

The smaller the size of the plating bath, the smaller the amount of sensible heat of the molten zinc serving as a buffer. Therefore, fluctuations in the sensible heat brought in by the steel strip and changes in the temperature of the plating bath due to the addition of solid phase zinc are more remarkable. Will be transformed.

The bottom dross is an intermetallic compound (FeZn ₇ , FeZn ₁₃ , Fe ₅ Zn _21, etc.) formed by the chemical reaction of iron as a solute with zinc as a solvent. The solubility of iron in molten zinc is greatly affected by the temperature of the molten zinc, for example, 0.04 wt.
% At 430 ° C. is 0.01 wt%. The change in solubility and the change in solute concentration greatly affect dross formation and growth. In addition, dross is thought to undergo a phase transformation as it grows. Different phases have different physical properties such as density. That is, when the temperature of the plating tank changes, the floating behavior of the dross generated in the plating tank changes accordingly.

According to the experiments of the inventors of the present invention, the introduction of solid phase zinc temporarily changes the temperature of the plating tank to confirm the occurrence of bottom dross, and there is also a problem in stable production of final quality. . A similar problem also occurs in the case of a change in the temperature of the plating tank caused by a change in the sensible heat carried by the steel strip.

In each of the prior arts 1 and 2, since the capacity of the plating tank is reduced, the temperature change of the plating tank due to the fluctuation of the sensible heat carried by the steel strip becomes large.
In this case, since solid phase zinc is directly dissolved in the plating tank, there is a problem that the temperature of the solid phase zinc changes during dissolution, and the bottom dross increases due to these. Prior Documents 1 and 2 do not consider any measures against this problem. (2) In Prior Document 2, molten zinc is circulated between the plating tank and the sedimentation tank using a transfer pipe equipped with a pump. The circulation of molten zinc using a pump is described below. So there is a big problem in practical use.

In a transfer pipe having a large specific surface area, heat loss is very large. Further, since the specific heat of the molten zinc is only about 25% of water, the amount of heat up to the temperature at which the molten zinc starts to solidify can be surprisingly small. Therefore, the molten zinc tends to solidify during the transfer. In order to prevent the molten zinc from solidifying during the transfer, it is necessary to transfer the molten zinc by overheating it by about 30 ° C. to 50 ° C. with respect to the melting temperature.

Heating is the easiest means to prevent solidification of the molten zinc. However, if the heated molten zinc is circulated for a long period of time, a large amount of fumes will be generated, and the transfer piping will be greatly damaged by heating. The running cost of equipment increases,
There is a problem that the device itself becomes complicated.

Further, molten zinc reacts very easily with other metals, forms a eutectic alloy with many metals, lowers the melting point, and melts the piping metal. Metals that do not react include gold and uranium, but these are not practical metals. Therefore, there is a problem that the cost is increased because the piping is often designed considering the pipe as a consumable.

In the field of aluminum refining technology, special steel has been used to achieve this requirement by using special steel. However, the material is very expensive, and the molten zinc plating equipment is difficult to use. It cannot be put to practical use because of the problem described above.

Therefore, a device for circulating molten zinc as described in the prior art 2 can be manufactured, but cannot be a practical facility.

(3) Further, in the prior art documents 1 and 2, as described below, there is a problem that dross accumulation in the plating tank cannot be fundamentally prevented. Prior document 1,
No. 2 only considers the flow of molten zinc in the plating tank only in the section of the plating facility in the running direction of the steel strip. FIGS. 6 and 7 schematically show the state of dross deposition distribution in the plating tank obtained from the water model and the actual machine data by the present inventors. 6 is a sectional view of the plating facility in the running direction of the steel strip, FIG. 7 is a sectional view taken along line AA of FIG. 6, and FIGS.
, 10 is a bottom dross.

As shown in FIG. 6 and FIG.
0 is deposited and distributed before and after the end of the sink roll in the axial direction and in the direction of rotation of the sink roll. That is, the flow of the molten zinc between the sink roll and the inner wall of the plating tank is not a simple flow shown only in one direction cross section in the running direction of the steel strip as shown in the prior art documents 1 and 2, but a three-dimensional complicated flow. It can be seen that a simple flow is formed. In addition, it can be seen from FIGS. 6 and 2 that, in many cases, bottom dross is deposited on a slope portion that is smaller than the angle of repose of the bottom dross.

Therefore, under the simple flow conditions studied only in one direction cross section in the running direction of the steel strip seen in the prior art documents 1 and 2, it is only necessary to change the place where the dross accumulates, and the Needless to say, it is not a fundamental solution to prevent dross accumulation.

As described above, in the prior art documents 1 and 2, there is an increase in the generation of dross due to the reduction in the size of the plating tank. Therefore, the dross deposited in the plating tank changes the running speed of the steel strip and the temperature of the plating tank. If there is a change, it will be rolled up, adhere to the steel strip and become a surface defect due to dross,
The effect of preventing surface defects due to dross is insufficient.

The present invention has been made in view of such circumstances, and has a structure capable of efficiently discharging dross out of a plating tank, having a high dross accumulation preventing effect in the plating tank, and further reducing dross generation. It is an object of the present invention to provide a hot-dip galvanizing facility and a hot-dip galvanizing method that are simple, durable, and have no operational problems.

[0028]

SUMMARY OF THE INVENTION The present invention relates to a method for measuring a three-dimensional flow in a plating tank, which has been clarified by a number of water models and numerical analysis. It is based on the knowledge about the prevention of dross deposition, and the knowledge that the dross deposition prevention effect can be further improved by reducing the temperature change of the molten zinc in the plating tank. It is as follows.

The first to fourth inventions are inventions of hot-dip galvanizing equipment, and the fifth to eighth inventions are inventions of hot-dip galvanizing method.

According to a first aspect of the present invention, there is provided a hot-dip galvanizing apparatus for a steel strip in which a steel strip is immersed in a hot-dip galvanizing bath and is continuously subjected to hot-dip galvanizing. Is within 200 mm, the distance from the bottom of the tank to the bottom of the sink roll is within 100 mm, and the distance between the member in contact with the steel strip and the inner wall is within 300 mm.

A second invention is a hot-dip galvanizing apparatus according to the first invention, wherein the inner wall of the hot-dip galvanizing tank has a gradient of 45 degrees or more.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the molten zinc tank is provided at its bottom or side surface with a molten zinc for replenishing molten zinc used by plating from a zinc melting tank in which zinc is previously melted. This is a hot-dip galvanizing facility having a zinc supply unit.

According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, there is provided a coreless induction heating device for maintaining a constant temperature of the molten zinc in the molten zinc tank. It is a galvanizing facility.

According to a fifth aspect of the present invention, when a steel strip is immersed in a hot-dip galvanizing bath and continuously hot-dip galvanized, the distance between the inner wall of the hot-dip galvanizing bath to be plated and the steel strip is within 200 mm, and the bottom of the bath and the sink are The hot-dip galvanizing method is characterized in that the distance from the lower part of the roll is within 100 mm and the distance between the inner wall and the member in contact with the steel strip is within 300 mm.

A sixth invention is the hot-dip galvanizing method according to the fifth invention, wherein the hot-dip galvanizing is performed using a hot-dip galvanizing bath having an inner wall gradient of 45 ° or more.

According to a seventh aspect of the present invention, the molten zinc used in the plating according to the fifth or sixth aspect of the invention is melted from the bottom or side of the molten zinc tank by using molten zinc in a zinc melting tank in which zinc has been previously melted. A hot-dip galvanizing method characterized by replenishment.

According to an eighth aspect of the present invention, in any one of the fifth to seventh aspects, the temperature of the molten zinc in the molten zinc tank is kept constant by using a coreless induction heating device. This is a hot-dip galvanizing method.

According to the first and fifth aspects of the invention, dross generated in the molten zinc tank is prevented from being deposited at the bottom of the tank, and dross can be efficiently discharged from the plating tank together with the steel strip.

According to the second and sixth aspects of the present invention, since the bottom dross cannot be deposited on the side of the plating tank, the effect of the above-mentioned aspect can be further improved.

According to the third and seventh aspects of the invention, the molten zinc used for plating is supplied from the bottom or the side of the molten zinc tank using the molten zinc in the zinc melting tank in which zinc has been melted in advance. When replenishing the molten zinc, the temperature of the molten zinc in the molten zinc tank does not change. Therefore, there is no problem of dross generation due to a change in temperature of the molten zinc due to replenishment of the molten zinc. In addition, since the molten zinc is not circulated, the equipment for supplying the molten zinc is simple and inexpensive, and its durability and operational troubles are not a problem.

According to the fourth and eighth aspects of the present invention, since the coreless induction heating device is used for heating the molten zinc in the molten zinc tank, the entire molten zinc in the molten zinc tank can be uniformly heated. Temperature change can be reduced. As a result, dross generation due to the temperature change of the molten zinc can be reduced, and the final quality of the steel strip after plating is further stabilized.

Hereinafter, the reasons for limitation of the present invention will be described. In the present invention, the dross accumulation space around the member in contact with the steel strip such as a sink roll is reduced as much as possible in order to enhance the dross discharge effect in the plating tank and prevent dross from accumulating in the plating tank, By keeping the space small, the flow of the molten zinc in the plating tank is changed from a conventional three-dimensional flow to a two-dimensional flow. From such a viewpoint, the distance (d1, d) between the inner wall of the hot-dip galvanizing tank to be plated and the steel strip.
2) The distance (d3) between the bottom of the tank and the lower end of the sink roll, the distance (d4, d5) between the inner wall and the member in contact with the steel strip, and the gradient (θ) of the inner wall are limited. The distances d1 to d5 and the gradient θ are shown in FIGS.

The distance between the steel strip and the inner wall of the molten zinc tank (d1,
By setting d2) to 200 mm or less and the distance (d3) between the bottom of the tank and the lower end of the sink roll to 100 mm or less, the flow of molten zinc can be always induced at the bottom of the plating tank, so that dross does not accumulate on the bottom of the tank. .

By setting the distance (d4, d5) between the end of the member that comes into contact with the steel strip such as a sink roll and the inner wall (d4, d5) to 300 mm or less, the three-dimensional flow of the molten zinc is prevented, and the steel strip comes into contact with the steel strip. The bottom dross at the bottom of the plating tank as shown in FIG. 7 due to the pressure difference generated at the end of the member is eliminated.

By setting the gradient (θ) of the inner wall to 45 degrees or more, even if bottom dross is generated, the bottom dross cannot be deposited on the side surface of the plating tank.

[0046]

Next, an embodiment of the present invention will be specifically described with reference to FIGS. FIG.
FIG. 2 is a side view of the hot-dip galvanizing equipment according to the embodiment of the present invention, and FIG. 2 is a cross-sectional view of the equipment shown in FIG.

1 and 2, 1 is a snout, 2 is a molten zinc tank, 3 is molten zinc, 4 is a sink roll, 5 is a stabilizing roll, 6 is a collecting roll, 7
Is a gas wiping device, 9 is a molten zinc heating device, 11
Is sink roll support. In the apparatus shown in FIG. 1, the distance d4 between the sink roll where the sink roll support 11 is not located and the inner wall is smaller than the distance d5 between the sink roll where the sink roll support 11 is located and the inner wall. The lower end of the snout 1 is the molten zinc tank 2
The structure is connected to the upper edge.

In order to prevent bottom dross from accumulating anywhere in the molten zinc tank 2, the dross accumulation space around the rotating sink roll 4 is kept as small as possible. In order to change the flow from a flow to a two-dimensional flow, the distances d1 and d2 between the steel strip S and the inner wall of the molten zinc tank 2 are 200 mm or less, and the distance d3 between the tank bottom and the lower part of the sink roll 4 is 100 mm.
Hereinafter, distances d4 and d between the end of the sink roll in the axial direction and the inner wall.
5 is set to 300 mm or less, and the gradient θ of the inner wall is set to 45 degrees or more.

The flow of the molten zinc in the molten zinc tank 2 is changed from a conventional three-dimensional flow to a two-dimensional flow, and the pressure difference that has conventionally occurred at the axial end of the sink roll 4 is reduced. In addition, since the flow of molten zinc can be always induced at the bottom of the tank, bottom dross does not accumulate in the molten zinc tank. In the apparatus shown in FIG. 1, the distance d4 between the sink roll where the sink roll support 11 is not located and the inner wall is smaller than the distance d5 between the sink roll where the sink roll support 11 is located and the inner wall. Is better.

Distance d from the top of sink roll 4 to the bath surface
6 depends on the running speed of the steel strip S, but may be any distance that does not cause ripples, and is actually 100 mm or more,
500 m or less is realistic. 12 for less than 100mm
Rippling was observed at a line speed of 0 mpm or more, and 500
If it exceeds mm, the stirring effect of the sink roll 4 in the molten zinc tank is reduced, and the effect of discharging dross from the molten zinc tank 2 is reduced.

Using the hot-dip galvanizing equipment, hot-dip galvanizing is performed as follows. That is, the steel strip S annealed in the previous step enters the molten zinc 3 filled in the molten zinc tank 2 from the snout 1 and sink rolls 4 in the molten zinc tank 2.
The traveling direction is changed by, and after exiting from the molten zinc tank 2 while being supported by the stabilizing roll 5 and the collecting roll 6, the amount is controlled to a predetermined amount by the gas wiping device 7, and the process proceeds to the next step.

The dross generated at the time of plating is immediately discharged from the molten zinc tank 2 together with the steel strip.
It does not accumulate and accumulate inside.

As for the replenishment of the molten zinc used for plating, when solid zinc is directly charged into the molten zinc tank 2, the temperature distribution and the concentration distribution of the molten zinc change, and dross is generated. It is preferable to provide a zinc dissolving tank separately from the zinc tank 2 and refill the molten zinc tank 2 with molten zinc previously dissolved in the zinc dissolving tank.

FIG. 3 shows an example of an apparatus for supplying molten zinc from a zinc dissolving tank to a molten zinc tank. In FIG. 3, the zinc dissolving tank 8 communicates with the bottom of the molten zinc tank 2 via a communication pipe 21. The molten zinc previously melted in the zinc dissolving tank 8 is supplied to the molten zinc tank 2 through the communication pipe 21 and the opening 20.

In this apparatus, since the liquid level in the zinc dissolving tank 8 matches the liquid level in the molten zinc tank 2 in operation, it is necessary to control the bath surface of the zinc dissolving tank 8 when the solid phase zinc is melted.
While performing liquid level control using a non-contact sensor or the like, a solid-phase zinc can be melted, for example, by a commonly used method.

On the other hand, when it is not desired to manage the bath surface in the zinc dissolving tank 8, the supply of the molten zinc to the molten zinc tank 2 is performed by using the pump 22 from the zinc dissolving tank 8, as shown in FIG. be able to. In this case, the bath surface management of the molten zinc tank 2 measures the bath surface of the molten zinc tank 2 with a non-contact sensor or the like,
A method of performing on / off control such that the pump 22 is operated when the bath surface reaches the lower limit value and the pump 22 is stopped when the bath surface reaches the upper limit value, and the pump 2 is controlled so as to fall within an allowable range.
For example, a method of performing PID control for the flow rate control 2 may be considered. It goes without saying that there is no problem with either method from the viewpoint of bath surface management.

Further, from the viewpoint of making the temperature of the molten zinc uniform, it is preferable to use, as the heating device 9, a coreless induction heating device in which a coil is wound around the entire molten zinc tank 2 to heat uniformly.

Conventionally, a groove-type induction heating device partially equipped with an induction heater has been employed for heating molten zinc. In this case, in order to maintain the temperature of the molten zinc in the molten zinc tank at a predetermined operating temperature, the temperature of the molten zinc in the induction heater portion needs to be about 50 ° C. higher than the temperature of the molten zinc in the molten zinc tank 2. Therefore, there is a problem that the temperature of the molten zinc in the molten zinc tank 2 becomes uneven, and dross is generated due to this. In the case of the coreless induction heating device, since the entire molten zinc tank 2 is uniformly heated, it is possible to prevent dross generation due to temperature fluctuation of the molten zinc.

Another embodiment of the present invention will be described with reference to FIG. In FIG. 5, reference numeral 10 denotes a zinc dissolving tank, and the other portions are denoted by the same reference numerals as those shown in FIGS. Zinc dissolution tank 10
Is provided so as to surround the molten zinc tank 2, and the heating device 9 is provided outside the zinc melting tank 10, and a coreless induction heating device is used.

The distance d1 between the side surface of the steel strip S in the traveling direction of the molten zinc tank 2 and the steel strip S is 150 mm, and the gradient θ is 45 degrees or more. Since the gradient θ is 45 degrees or more, even if bottom dross is generated, the bottom dross does not accumulate on the side surface. The exit side of the steel strip of the molten zinc tank 2 is substantially vertical, and the distance d2 from the side surface of the molten zinc tank 2 to the steel strip S is 150 mm. The distance d3 between the bottom of the tank and the lower part of the sink roll is 100 mm. Further, not shown, a molten zinc tank 2 facing the end of the sink roll in the axial direction.
The molten zinc tank 2 is manufactured such that the distance between the inner surface of the sink roll 4 and the end of the sink roll 4 is within 300 mm.

An opening 20 is provided at a part of the bottom of the molten zinc tank 2.
Is provided. The molten zinc dissolved in the zinc dissolving tank 10 passes through the opening 20 and is supplied to the molten zinc tank 2. Since the zinc dissolving tank 10 is heated using the coreless induction heating device, the temperature of the zinc dissolving tank 10 does not become uneven. Therefore, when replenishing zinc to the molten zinc tank 2,
The temperature of the molten zinc in the molten zinc tank 2 does not change.

In the equipment shown in FIG. 5, the opening 20 is provided at the bottom of the molten zinc tank 2; however, the location of the opening 20 is not limited to the bottom of the tank, and even if it is installed on the side. No problem. However, in general, molten zinc is often taken out of the system during maintenance, so an opening is installed at the bottom and used as a supply port for molten zinc during normal plating operations, and an outlet for discharging molten zinc during maintenance. It is more preferable to use them.

By promoting the flow of molten zinc entrained by the steel strip S running while being wound around the sink roll 4 from the snout 1, the bottom dross generated from the steel strip S adheres to the steel strip S and the molten zinc tank 2 is quickly taken out of the molten zinc tank 2 so that bottom dross does not accumulate in the molten zinc tank 2.

The zinc dissolving tank 10 has an apparatus (not shown) for supplying solid phase zinc, and supplies and dissolves solid phase zinc periodically. In this apparatus, the molten zinc tank 2 and the zinc melting tank 10
Are connected through the opening 20, so that the control of the bath surface of the molten zinc tank 2 depends on the supply form of the solid phase zinc to be charged into the zinc dissolving tank 10. When the solid phase zinc is inserted at once, the bath surface of the molten zinc tank 2 rises at once, which is not preferable in terms of quality. Therefore, the solid phase zinc is controlled and supplied so that the bath surface of the molten zinc bath 2 is at a constant level using a bath surface management system (not shown).

As a result, it is not necessary to keep the molten zinc tank 2 warm, and the supply of the molten zinc taken out to the steel strip S is automatically performed. This device is a simple and inexpensive device,
There is no operational trouble and the durability of the device does not matter.

[0066]

EXAMPLE Using the apparatus shown in FIGS. 1, 2 and 4, the sink roll diameter was 600 mm and the body length was 2500 m.
m, the distance between the inner wall of the molten zinc tank and the steel strip, the bottom of the tank and the lower part of the sink roll, and the distance between the upper part of the sink roll and the liquid surface are d1
To d4 are all 100 mm, d5 is 250 mm, d6
Was set to 150 mm. Then, a conventional induction heater was used as a heating device for the zinc melting tank 8, molten zinc was supplied to the molten zinc tank 2 by the pump 22, and a coreless heater was used as the heating device 9 for the molten zinc tank 2.

As a result, the conventional line speed of 120 mpm
As for the quality defect due to bottom dross, which was about 5% of the production volume, the rate of bottom dross defect of the same level was 5% or less even if the line speed was significantly increased to 160 mpm, and stable production was possible. did it.

[0068]

As described above, according to the present invention,
The dross is attached to the steel strip and can be efficiently discharged out of the molten zinc tank, and the dross accumulation prevention effect in the molten zinc tank is high. Also, circulation of molten zinc is not required for dross removal,
The structure is simple, inexpensive, and has excellent durability. There are no operational problems.

Further, since fluctuations in the sensible heat carried by the steel strip and changes in the temperature of the molten zinc tank caused by the dissolution of solid phase zinc can be prevented, dross generation due to this is eliminated, and dross accumulation in the molten zinc tank is prevented. The prevention effect can be further improved.

Further, according to the present invention, since dross deposition in the molten zinc tank can be prevented, the line speed at the time of plating can be increased as compared with the prior art.

[Brief description of the drawings]

FIG. 1 illustrates an embodiment of the present invention.

FIG. 2 is a diagram showing a BB cross section of the apparatus of FIG. 1;

FIG. 3 is a diagram showing an example of an apparatus for supplying molten zinc from a zinc dissolving tank to a molten zinc tank in the present invention.

FIG. 4 is a view showing another example of the apparatus for supplying molten zinc from the zinc dissolving tank to the molten zinc tank in the present invention.

FIG. 5 is a diagram illustrating another embodiment of the present invention.

FIG. 6 is a view showing a state of dross accumulation in a running section of a steel strip in a plating tank.

FIG. 7 is a diagram showing the state of dross accumulation in the plating tank in the section AA in FIG. 6;

[Explanation of symbols]

 1 Snout 2 Molten zinc tank 3 Molten zinc 4 Sink roll 5 Stabilizing roll 6 Collecting roll 7 Gas wiping device 8 Zinc melting tank 9 Heating device (Coreless induction heating device) 10 Bottom dross 20 Opening S Steel strip

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

Claims (8)

[Claims] 1. A hot-dip galvanizing apparatus for a steel strip in which a steel strip is immersed in a hot-dip galvanizing bath and subjected to continuous hot-dip galvanizing, wherein an inner wall of the hot-dip galvanizing bath to be plated has a distance from the steel strip of 200 mm or less. A hot-dip galvanizing facility, wherein the distance from the bottom of the sink roll to the bottom of the sink roll is within 100 mm, and the distance between a member in contact with the steel strip and the inner wall is within 300 mm. 2. The hot dip galvanizing equipment according to claim 1, wherein the inner wall of the hot dip galvanizing tank has a gradient of 45 degrees or more. 3. The molten zinc bath is provided on the bottom or side thereof.
The hot-dip galvanizing equipment according to claim 1 or 2, further comprising a hot-dip zinc supply unit that replenishes the hot-dip zinc used by plating from a zinc melting tank in which zinc has been melted in advance. 4. The hot-dip galvanizing equipment according to claim 1, further comprising a coreless induction heating device for keeping the temperature of the hot-dip zinc in the hot-dip zinc bath constant. . 5. When continuously immersing a steel strip in a hot-dip galvanizing bath and performing hot-dip galvanizing, the distance between the inner wall of the hot-dip galvanizing bath to be plated and the steel strip is within 200 mm, and the bottom of the bath and the bottom of the sink roll are connected. A hot-dip galvanizing method, wherein the distance between the inner wall and the member in contact with the steel strip is within 300 mm and the distance between the inner wall and the member is 100 mm or less. 6. The hot-dip galvanizing method according to claim 5, wherein the hot-dip galvanizing is performed using a hot-dip galvanizing bath having an inner wall gradient of 45 ° or more. 7. The hot-dip zinc used in the plating is
The hot-dip galvanizing method according to claim 5 or 6, wherein replenishment is performed from the bottom or the side of the hot-dip zinc bath by using hot-dip zinc in a hot-dip zinc melting bath. 8. The hot-dip galvanizing method according to claim 5, wherein the temperature of the hot-dip zinc in the hot-dip zinc bath is kept constant by using a coreless induction heating apparatus. .