JPH0813112A - Method and equipment for producing hot dip metal-coated steel sheet - Google Patents

Abstract

PURPOSE:To prevent the effusion of zinc bath from the sealing part other than a sheet passage at the time of changing sheet width by using an aerial pot, at the time of producing a hot dip metal-coated steel sheet. CONSTITUTION:The bottom 9 of an aerial pot 8 is formed so that it is inclined upward from the center of the passage of a steel sheet 2 in a sheet width direction, and a bath surface meter 12 makes a plunger 15 go into and out of an auxiliary vessel 1, communicating with the aerial pot 8, by means of a control device 13 and a driving device 14 according to the width of the steel sheet 2 to be passed, by which the surface of a molten bath 6 is moved up and down and the width of the surface of the molten bath 6 is made to correspond to the width of the steel sheet 2. The width-direction position of the steel sheet 2 is detected by a sheet passage detector 16, and the aerial pot 8 and the auxiliary vessel 1 are moved by using a control device 17 and a driving device 18 so that the steel sheet 2 corresponds with the width of the molten bath. Because the width of the bath surface corresponds to the width of the steel sheet, the effusion of the molten bath 6 from the sealing part other than the sheet passage can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for continuously producing hot-dip galvanized steel sheet or hot-dip galvanized steel sheet such as alloyed hot-dip galvanized steel sheet. The present invention relates to a manufacturing method excellent in operability for plating on the surface of a thin steel sheet and a manufacturing apparatus around a plating bath.

[0002]

2. Description of the Related Art Hot-dip galvanized steel sheets are widely used in the fields of building materials and home appliances because they have excellent corrosion resistance and are relatively inexpensive. Further, the alloyed hot-dip galvanized steel sheet has excellent corrosion resistance and can withstand press working with a large degree of working, so that the demand as a steel sheet for automobiles is rapidly expanding in recent years.

A general method for producing a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet is as follows. That is, after the surface of the cold-rolled thin steel sheet is cleaned in a pretreatment step, the surface oxide film is removed by annealing in a non-oxidizing furnace or in a reducing atmosphere, and then the steel sheet is oxidized almost without zinc. The plate temperature is cooled to the temperature of the bath and then penetrated into the zinc bath. Excessive molten zinc adhering to the steel sheet surface in the zinc bath is removed with a gas wiper to adjust the zinc basis weight, and then cooled as it is to obtain a hot dip galvanized steel sheet. On the other hand, an alloyed hot-dip galvanized steel sheet is one in which the hot-dip galvanized amount is adjusted and then heat-treated for alloying the galvanized layer.

An example of a hot dip galvanizing apparatus having a sink roll is shown in FIG. The steel plate 2 is drawn into the zinc bath 6 from the snout 11, wound around the sink roll 10, and then pulled up in the vertical direction via the support roll 3. The synchro 10 in the zinc bath conveys the steel sheet 2 without contacting the roll until the molten zinc on the steel sheet surface is solidified by changing the passage direction of the steel sheet 2 to which the molten zinc adheres to the vertical direction. Thus, it is an important device for preventing the occurrence of surface defects such as scratches. The steel plate surface pulled up from the molten zinc bath is adjusted to an appropriate basis weight by the gas wiper 7.

Since the sink roll 10 is always held in the molten zinc bath 6 at about 460 ° C., it is naturally necessary that it has excellent erosion resistance. When deposits are formed on the surface of the sink roll 10, a flaw may be created on the steel plate surface, or the deposits may migrate to the steel plate surface, resulting in surface defects. In many cases, the sink roll has no drive system, so if the steel plate slips and the sink roll becomes discontinuous,
Scratches will be formed on the steel plate surface. Furthermore, if the plating operation is continued for a long time, the sink roll surface will have irregularities, so it is necessary to take it out of the zinc bath for maintenance.

As described above, the conventional hot dip galvanizing apparatus having the sink roll has a drawback that the operability is deteriorated due to the presence of the equipment in the bath. Also, because of the presence of sink equipment such as sink rolls, the container of molten zinc becomes extremely large,
Since the amount of molten zinc is large, there is a problem that the degree of freedom is reduced when changing the type of plating. In order to solve such a problem, the technique which does not use a sink roll has been proposed so far.

A roll coater method, a meniscus method, a curtain flow method and the like are typical sink rollless type hot dipping methods. These are suitable for single-sided plating, but when hot-dip plating is performed on both sides of the steel sheet, the heat treatment before plating is duplicated and the mechanical properties of the steel sheet cannot be ensured, so that it is not an appropriate plating method. Without using Syncroll
An air pot has been proposed as a method applicable to double-sided plating. That is, it is a manufacturing apparatus in which molten zinc is held in a relatively small container, a steel plate is introduced from the bottom of the container, and molten zinc is attached to the steel plate surface. The eyes of this manufacturing apparatus are the means for preventing leakage of molten zinc at the bottom of the container into which the steel sheet enters and the means for removing excess molten zinc adhering to the steel sheet.

In JP-A-63-109149 and JP-A-63-310949, electromagnetic force is used to hold the zinc bath at the bottom of the container, and JP-A-63-109148.
In JP-A-63-303045 and JP-A-63-303045, an electromagnetic force and a static pressure seal are used together to hold the zinc bath at the bottom of the container. If electromagnetic force can be used successfully, there is no mechanical contact with the steel sheet surface, so it is an ideal device without generating defects on the steel sheet surface, but if you try to completely suppress the outflow of molten zinc, Not only does the capacity of the excitation power supply become extremely large, but there is also a problem that the magnetic force exerts an attractive force or a repulsive force on the steel sheet, thereby impairing the stable passing of the steel sheet. Further, JP-A-63-162847 and JP-A-1-139.
Japanese Patent No. 744 proposes a method in which a steel plate is sandwiched between seal rolls to suppress the outflow of molten metal.

Further, the applicant of the present invention discloses in Japanese Patent Application Laid-Open No. 4-356 that a seal plate is arranged with a slight gap between the steel plate and the surface tension and viscous flow of the bath to flow out molten metal. We are proposing a means to suppress this. In addition, Japanese Patent Laid-Open No. 4-364
51, JP-A-4-36446, and JP-A-4-36446.
Japanese Patent No. 36447 proposes an operation method, a bath surface control method, and a bath supply method for preventing the outflow of the bath.

Although these various proposals have been made, it is considered that the aerial pot has not been put into practical use at an actual industrial level, and industrial studies are still insufficient.

[0011]

When manufacturing hot-dip galvanized steel sheets or alloyed hot-dip galvanized steel sheets, as a result of studying the problems in the prior art around the zinc bath, in the present invention, the double-side plating is omitted while the sink roll is omitted. With the goal of doing so, we decided to adopt an aerial pot in the manufacturing equipment. Regarding the important bath retention in the air pot, we propose a measure to prevent the zinc bath outflow outside the board road especially when changing the board width which is indispensable industrially.

[0012]

The present invention has been proposed in order to solve the above-mentioned problems, in which a steel sheet to be plated is continuously bathed through an opening at the bottom of a container holding a hot dip metal bath. When manufacturing a hot-dip galvanized steel sheet by passing the above, while expanding and contracting the bath surface upper surface width, the container and the steel sheet are relatively moved, and the width direction position of the steel sheet to be plated is made to coincide with the bath surface upper surface. It is a method for producing a hot-dip galvanized steel sheet, which is characterized by performing plating. In this case, as a means for expanding and contracting the width of the upper surface of the bath, a container having a shape in which the width of the upper surface of the bath changes according to the height of the surface of the bath is used, and the height of the surface of the bath is set so that the width of the upper surface of the bath matches the plate width. It is preferable to perform plating while maintaining the bath surface height.

The apparatus of the present invention capable of suitably carrying out the above invention is a hot-dip galvanized steel sheet manufacturing apparatus having an opening at the bottom of a hot-dip galvanized metal bath holding vessel for allowing the steel sheet to be plated into the bath, The hot dip metal bath holding container has a bottom portion that is inclined upward toward the plate width end direction around the plate path, and has a shape in which the bath surface upper surface width changes depending on the bath surface height, and the metal in the container is The apparatus for producing a hot-dip galvanized steel sheet is characterized in that a height adjusting device for the bath surface is additionally provided. This height adjusting device communicates with the metal bath holding container,
It is preferable to use an auxiliary container provided with a bath surface height adjusting means,
Further, the bath surface height adjusting means may be a plunger that can be freely pushed into the auxiliary container, or may be means for moving up and down the entire auxiliary container.

[0014]

The operation of the present invention will be described below. 1 to 4 are explanatory views of an apparatus capable of suitably implementing the present invention. The aerial pot 8 is used as a molten metal container.
The auxiliary container 1 is arranged in communication with the aerial pot 8. It is necessary that these containers have a heating function for holding the molten metal. As shown in FIG. 2, the bottom portion 9 of the aerial pot 8 has an opening 4 through which the steel sheet 2 is continuously inserted via a bath sealant 5. As shown in Figure 1,
The bottom of the aerial pot 8 is inclined upward in the plate width direction from the center of the plate path, and the center is the lowest. Molten metal is attached to the surface of the steel plate 2 that has entered the aerial pot 8, and then the steel plate 2 is passed in a substantially vertical direction. A gas wiper 7 provided above the zinc bath 6 removes excess molten metal adhering to the steel plate surface. Since it is for the purpose of removing excess metal, not only gas but also electromagnetic type or mechanical type may be used. The sealing material 5 is installed to prevent the zinc bath from flowing out, and a ceramic material such as alumina, which is difficult to wet with the molten metal, is suitable. Further, the gap distance between the steel plate 2 and the seal material 5 is important for the outflow of molten metal, and in a device that handles various steel plates having different plate thicknesses, the seal material can be moved to make the opening gap distance variable. There is a need.

As shown in FIG. 1, the position of the passing steel plate 2 is detected by a plate road detector 16, and a controller 17 and a drive device 18 are used so that the plate road center is always the container center. The pot 8 and the auxiliary container 1 are moved. Bath surface total 12
Controls the bath surface using the control device 13, the drive device 14, and the plunger 15 according to the plate width known in advance.
By doing so, even when the plate width of the steel plate 2 is changed, by controlling the molten metal bath surface, it is possible to prevent the bath other than the plate passage from flowing out from the seal portion. In addition,
FIG. 2 shows a cross section of the center portion of the aerial pot 8. FIG.
Shows the cross section of the steel plate 2 end portion of the aerial pot 8. The steel sheet before plating needs to be contacted with the bath at about the same temperature as the molten metal without oxidizing the surface after annealing, so use of an inert gas wiper or seal box to prevent oxygen from entering from the top of the pot. Is effective.

In FIG. 4, the auxiliary container 1 is installed on the jack 20 in order to control the height of the bath surface in the aerial pot 8.
The jack 20 moves the auxiliary container 1 up and down in response to signals from the bath gauge 12 and the controller 13, so that the bath surface of the aerial pot 8 can be controlled as in the plunger system of FIG. Further, in FIG. 4, it is possible to input the detection value of the plate path detector 16 to the control device 17, operate the driving device 18, and constantly control the plate path to the center by the steering roll 19. The board path control method and the bath surface control method are
Each can be selected according to the installation space of the device of the present invention.

[0017]

EXAMPLES The present invention will now be described based on examples. Plate width 350 mm, 300 mm, 250 mm, plate thickness 0.7 m
m ultra-low carbon steel sheet was annealed at 800 ° C in a reducing atmosphere with a mixed gas of nitrogen and hydrogen, cooled to 465 ° C, then the progress of the steel sheet was changed vertically by a deflector roll, and then fixed by a support roll. After that, it was made to enter through the opening 4 at the bottom of the aerial pot 8 shown in FIG. Dissolve zinc in auxiliary container 1 and set molten zinc bath temperature to 465
After maintaining at ℃, the thin steel plate in the aerial pot 8
With the plate passed at a line speed of a minute, the plunger 15 is pushed in, the head height at the center of the molten zinc bath in the space-time pot 8 having a plate width of 350 mm is adjusted to 75 mm, and the N ₂ gas wiper is used. The amount of molten zinc deposited was controlled to 45 g / m ² . Here, the head height of the molten zinc bath in the aerial pot 8 is measured online by a laser liquid level gauge 12, and a controller 13 and a plunger driver 14 which control the pushing amount of the plunger 15 so that the head height becomes 100 mm. When adjusted, the head height during operation was maintained within 75 mm ± 1 mm. Continuing, 64 for widths of 300 mm and 250 mm, respectively
It was controlled to ± 1 mm and 54 ± 1 mm, and while maintaining this state, stable plating operation could be maintained for a long time. Then, when the plating operation is finished, the plunger 15 is pulled up while the steel plate 2 is being passed through at the same line speed to melt the molten zinc in the aerial pot 8 in the melting furnace 1.
When the line was stopped after retreating inside, the molten zinc did not flow out from the opening at the bottom of the aerial pot 8,
We were able to safely finish the plating operation.

In the above description, only the example of hot dip galvanizing on a thin steel sheet is described, but this applies the present invention to other hot dip coatings such as hot dip Al and hot Al alloy plating, and It does not prevent the steel sheet and the plated metal layer from being alloyed by heating after wiping the excess molten metal.

[0019]

As described above, according to the method for producing a hot-dip galvanized steel sheet of the present invention, the hot-dip galvanized steel sheet can be treated for a long time without using equipment in the bath such as a sink roll, which easily causes surface defects. Since it can be stably manufactured over a long period of time, its industrial significance is extremely large.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an apparatus capable of suitably implementing the present invention.

FIG. 2 is a sectional view of an aerial pot.

FIG. 3 is a cross-sectional view of an aerial pot.

FIG. 4 is a sectional view of another embodiment of the present invention.

FIG. 5 is an explanatory view of a cross section of a conventional device.

[Explanation of symbols]

1 Auxiliary Container 2 Steel Plate 3 Support Roll 4 Opening 5 Seal Plate 6 Zinc Bath 7 Gas Wiper 8 Air Pot (Container) 9 Bottom 10 Sink Roll 12 Liquid Level Gauge 13 Control Device 14 Drive Device 15 Plunger 16 Plate Road Detector 17 Control Device 18 Drive device 19 Steering roll 20 Jack

Claims (6)

[Claims] 1. When manufacturing a hot-dip galvanized steel sheet by continuously passing the steel sheet to be plated upward through an opening at the bottom of a container holding the hot-dip galvanized metal bath, the width of the upper surface of the bath surface is expanded or contracted. At the same time, the method of manufacturing a hot-dip galvanized steel sheet is characterized in that the container and the steel sheet are moved relative to each other, and plating is performed while the position of the steel sheet to be plated in the width direction is aligned with the upper surface of the bath surface. 2. A container having a shape in which the width of the upper surface of the bath surface changes according to the height of the surface of the bath is used as a means for expanding and contracting the width of the upper surface of the bath. Set,
The method for producing a hot-dip galvanized steel sheet according to claim 1, wherein plating is performed while maintaining the height of the bath surface. 3. A hot-dip galvanized steel sheet manufacturing apparatus having an opening for allowing a steel sheet to be plated to enter the bath at the bottom of the hot-dip galvanized metal bath holding vessel, wherein the hot-dip galvanized metal bath holding vessel is centered around a board path. It has a bottom portion that is inclined upward toward the plate width end direction, has a shape in which the top surface width of the bath surface changes depending on the bath surface height, and is equipped with a height adjusting device for the metal bath surface in the container. Hot-dip galvanized steel sheet manufacturing equipment. 4. The apparatus for manufacturing a hot-dip galvanized steel sheet according to claim 3, wherein the height adjusting device is an auxiliary container that is in communication with a metal bath holding container and is provided with bath surface height adjusting means. . 5. The apparatus for manufacturing a hot-dip galvanized steel sheet according to claim 4, wherein the bath surface height adjusting means is a plunger that can be pushed into the auxiliary container. 6. The hot-dip galvanized steel sheet manufacturing apparatus according to claim 4, wherein the bath surface height adjusting means is means for moving up and down the entire auxiliary container.