JPH07145461A - Method and device for hot dip metal coating - Google Patents

Abstract

PURPOSE:To prevent generation of defects of the plated surface, in particular, failures on the surface appearance accompanied with the alloying reaction which is caused by the adhesion of foreign matters such as scums on the surface of a steel sheet or a plating bath when the steel sheet is passed through a snout part and dipped in the plating bath with an extremely simple device. CONSTITUTION:Adhesion of foreign matters of a plating bath on the steel sheet 1 is prevented by mounting a buffle plate 5 on the surface of the plating bath in a snout 2 where the steel sheet 1 is dipped in the plating bath at the snout part 2 for the hot dip metal coating. The galvealed steel sheet where the surface appearance is extremely excellent can be obtained especially in the alloying treated steel sheet.

Description

Detailed Description of the Invention

[0001]

The present invention relates to hot dip galvanizing, hot dip galvanizing, hot dip aluminum coating, hot dip galvanizing-
The present invention relates to a method for hot-dip metal plating such as aluminum alloy plating and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, as a hot dip metal plating method, a steel sheet to be plated is heated and annealed, an upper part thereof is connected to an annealing furnace, and a lower end thereof is passed through an inside of a snout immersed in the hot dip metal plating bath to form a hot dip metal bath. It is a method of obtaining a hot-dip metal-plated steel sheet by immersing it inside, changing the direction of travel by a pot roll in a bath and pulling it upward, and controlling the amount of hot-dip metal plating adhered by a gas drawing method. When the steel sheet is immersed in the plating bath through the snout portion, if foreign matter such as dust, scum, dross, fragments of annealing furnace refractory bricks, powder, etc. adheres to the steel plate surface or plating bath surface, plating surface defects and alloying Problems such as abnormal reaction occur.

In order to solve these problems, various methods have been conventionally proposed. For example, Japanese Patent Publication 2-25
As in Japanese Patent Publication No. 981 and Japanese Patent Publication No. 3-49981,
As described in JP-A-61-186463 and a method of preventing the generation of scum by setting an atmosphere of hydrogen and oxygen in the atmosphere to be introduced into the snout to an inert gas atmosphere having a specific concentration or less, dipping into the snout. Molten zinc is discharged toward the steel plate width direction from the discharge port arranged on one side in the width direction of the steel plate, and floating substances such as floating dross on the bath surface are stripped along the strip width direction in the other side of the snout width direction. To the side of
In addition, a method is known in which floating material is collected from the other end side to prevent steel plate plating defects due to floating dross in the snout.

Further, as in JP-A-4-276051 and JP-A-4-276052, an inert gas is applied on the plating bath surface from one end side to the other end side in the width direction of the steel plate immersed in the snout. By spraying the scum on the surface of the bath and discharging the scum on the other end to the outside of the snout, and the method of preventing the scum from adhering to the steel sheet and Japanese Patent Publication No. 60-2654. Thus, by providing a slit nozzle across the entire width of the steel plate below the surface of the molten metal plating bath and ejecting the molten plating solution toward the steel plate in the vicinity where the steel plate enters the plating bath, the surface of the plated steel plate is It is intended to prevent the adhesion of foreign matter. Further, in Japanese Patent Laid-Open No. 3-134146, a continuous molten metal plating device that allows the position of the snout to be changed back and forth with the upper part of the snout as a fulcrum is moved forward and backward slightly to move the steel strip and one side of the snout. By alternately increasing the intervals between, the placement of the dross remover becomes easier,
It makes it easier to remove dross inside the snout.

However, each of the methods has its respective drawbacks, and cannot prevent foreign matter from adhering to the steel sheet.
That is, Japanese Patent Publication No. 2-25981 and Japanese Patent Publication No. 3-4
The method according to the Japanese Patent Publication No. 9981 has a problem in that it is impossible to remove foreign substances adhering to the steel plate and foreign substances falling from the inner wall of the snout to the plating bath surface simply by regulating the atmospheric gas composition in the snout. . Further, JP-A-61-186463 and JP-A-4-276051.
Although the method of Japanese Patent Laid-Open No. 4-276052 and JP-A-4-276052 can obtain the effect of reducing the amount of foreign matter on the bath surface, a part of the foreign matter adheres to the steel plate in the process of wiping the foreign matter from one end to the other end in the snout. In addition, there is a problem that it does not completely prevent foreign matter from adhering.

Further, according to the method disclosed in Japanese Patent Publication No. 60-2654, it is necessary to eject the plating bath with a strong pressure in order to remove the foreign matter in the vicinity of the steel sheet. Since the plating droplets from the slit nozzles on both sides collide with each other, the effect of eliminating foreign matter is lost, and problems such as entrainment of foreign matter due to ripples in the plating bath surface occur. Further, in Japanese Patent Laid-Open No. 3-134146, there is a working problem that an operation of moving the snout position forward and backward must be performed every time the dross is removed.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the problems described above, and when a steel sheet is immersed in a plating bath through a snout portion by a very simple device, the steel sheet surface or the plating bath surface is It is intended to prevent dust, scum, dross, debris from annealing furnace refractory bricks, and foreign matter such as powders from adhering to the surface defects of plating, especially the problem of surface appearance due to alloying reaction. is there.

[0008]

Means for Solving the Problems In order to achieve the above-mentioned objects, the gist of the invention is as follows: (1) A steel sheet is immersed in a plating bath at a snout portion of hot dip metal plating. A hot dip metal plating method, wherein a shielding plate is installed on the plating bath surface in the snout to prevent foreign matter from adhering to the steel plate on the bath surface. (2) In the snout part of the molten metal plating, the steel plate is immersed in the plating bath. A removable shield plate is installed on the plating bath surface in the snout and foreign substances accumulated on the plating bath surface surrounded by the shield plate are discharged. The apparatus for hot-dip metal plating is characterized in that the above apparatus is provided.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a vertical sectional view showing a plating process according to the present invention. In the continuous hot-dip galvanizing apparatus, as shown in FIG. 1, a steel plate 1 discharged from a continuous annealing furnace is passed through a snout 2 and immersed in a plating bath 3 in a plating tank, and then a pot roll 4 is passed through the plating bath 3. Then, the gas wiping nozzle (not shown) outside the bath blows off the excess plating layer adhering to the surface, so that the surface of the steel sheet 1 is plated with a predetermined thickness. When the alloying treatment is performed thereafter, an alloying heating device is provided.

[0010]

[Function] In molten metal plating, iron powder carried from the furnace by the steel plate on the plating bath surface in the snout, fragments of annealing refractory bricks, foreign substances such as powder, and the molten metal evaporating from the bath surface. Floating oxides generated by reaction with trace oxygen or water vapor in the atmosphere thereafter, or so-called bath surface scum generated by direct reaction between molten metal and oxygen or water vapor contained in the atmosphere in the plating bath surface portion in the snout Existing.
These foreign substances float on or above the plating bath surface in the snout and adhere to the steel sheet immediately before plating, or as the steel sheet penetrates into the bath, the plating bath surface near the steel sheet is accompanied by the accompanying flow caused by the steel sheet entering. This causes a surface flow from the wall surface of the snout to the steel plate side, is drawn into the bath, and adheres to the steel plate. As a result, plating defects such as indentation defects due to non-plating and dross adhesion occur. Even if these are not the major causes, the following new problems arise.

That is, especially, the foreign particles floating on the bath surface grow in size and increase in size with the passage of time, and the zinc-plated steel sheet adhered to the steel sheet is alloyed as it penetrates into the steel sheet bath. In this case, the scum directly attached to the steel sheet is alloyed to prevent the foreign matter from adhering to the galvanized layer when Fe in the steel sheet diffuses, resulting in poor appearance. That caused a new problem. In order to eliminate these, it is necessary to prevent adhesion of foreign matter to the steel sheet that has become coarse, prevent the coarsening of foreign matter between the steel sheet and the shielding plate by the shielding plate of the present invention, and foreign matter to the steel sheet It also prevents adhesion.

FIG. 2 is a sectional view of the vicinity of the shield plate installed in the snout according to the present invention. As shown in FIG. 2, the shielding plate 5 is arranged as close to the steel plate 1 as possible to prevent foreign matters and the like from the bath surface from coming close to the steel plate. Figure 3
FIG. 6 is a cross-sectional view of the vicinity of a shield plate showing another embodiment according to the present invention. As shown in FIG. 3, the snouts 2 on both ends of the steel plate 1
A suction port 6 is provided at a symmetrical position inside the suction port 6, and a suction pipe 7 such as a metal pump or an electromagnetic pump is provided at the suction port 6 to operate the metal pump or the like (not shown) during operation to shield the shield plate 5.
Foreign matter floating on the zinc bath surface in the suction tube 7 together with molten zinc
The suction pipe is used to discharge the air from the discharge pipe to the outside of the snout.

In this way, the snout 2 is driven by the metal pump.
By discharging the foreign matters floating inside the zinc bath surface 3 inside the shield plate 5 together with the molten zinc to the outside of the snout 2, clean molten zinc flows into the shield plate 5 and the shield plate is activated during the operation of the metal pump. It is possible to keep the zinc bath surface 3 in 5 clean. Moreover, the shield plates 5 are provided near both sides of the steel plate 1.
As a result, the foreign substances such as scum on the zinc bath surface are cut off from the steel plate, and the amount of scum generated is extremely small.It is sufficient to suck a small amount of such foreign substances such as scum by the operation of the metal pump. It is an extremely small amount and can always maintain a clean state.

The shielding plate is required to have heat resistance and corrosion resistance to the molten metal, and for example, ceramics, stainless steel which is a metal having heat resistance and corrosion resistance, and a cermet coating material for the metal are used. It Further, since the molten metal is adhered to the shield plate, it is preferable to provide a heating mechanism having a function of preventing molten metal from adhering. Further, a detaching mechanism is provided to facilitate replacement.

[0015]

EXAMPLE A 0.8 mm (thickness) × 1219 mm (width) steel plate was used at a line speed of 80 by using the apparatus shown in FIG.
It is passed through the plate at mpm, dipped in a hot dip galvanizing bath with Zn-0.1 to 0.3% Al and a bath temperature of 460 ° C, plated, and then wiped to a predetermined plating thickness to form a galvanized steel sheet which is alloyed. The surface appearance after the treatment was observed. As a result, as shown in FIG. 4, compared with the conventional method without a shielding plate, the present invention has a significantly smaller particle size of the foreign matter, and the appearance defect rate is about 16% compared with the conventional method. It can be seen that the invention is extremely small, about 3%.

[0016]

As described above, according to the present invention, it is possible to prevent foreign matter on the bath surface from adhering to the steel sheet, and even if it adheres, the amount of foreign matter and the particle size that are extremely generated are small, so that the alloy However, no abnormalities are observed in the surface appearance, and it is possible to obtain a hot-dip galvanized steel sheet having an excellent surface appearance.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a plating process according to the present invention,

FIG. 2 is a cross-sectional view of the vicinity of the shield plate installed in the snout according to the present invention,

FIG. 3 is a cross-sectional view of the vicinity of a shield plate showing another embodiment according to the present invention,

FIG. 4 is a diagram showing the relationship between the surface appearance after the alloying treatment according to the present invention and the generated scum particle size.

[Explanation of symbols]

 1 Steel plate 2 Snout 3 Plating bath 4 Pot roll 5 Shielding plate 6 Suction port 7 Suction tube

Claims (2)

[Claims] 1. A feature of preventing foreign matter from adhering to the bath surface on the steel sheet by installing a shielding plate on the plating bath surface in the snout where the steel sheet is immersed in the plating bath at the snout portion of the molten metal plating. Hot metal plating method. 2. A detachable shield plate is installed on the plating bath surface in the snout where the steel plate is immersed in the plating bath at the snout portion of the molten metal plating, and foreign substances accumulated on the plating bath surface surrounded by the shield plate are discharged. An apparatus for hot-dip metal plating, which is provided with a device for