JPH07150321A - Hot dip metal coating device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of trouble on the outward appearance of surface accompanying the stickiness of scum on the hot dip coating steel sheet, particularly alloying reaction by restraining the growth of the scum in the plating bath surface in a snout with an extremely simple device, at the time of dipping the steel sheet into the plating bath through the snout. CONSTITUTION:In the hot dip metal coating device arranged with the snout through which the steel sheet 1 is dipped into the plating bath 3 to be subjected to the hot dip metal coating, the snout is constituted so as to satisfy the inequality d<=20Xsq. rt. S (wherein, d(mm): the interval between the steel sheet 1 and the snout wall surface on the outlet side, facing the plating bath side, of the snout 2, S(m/min): line speed). By this method, particularly, in the alloying treated steel sheet, galvannealed steel sheet having extremely excellent external appearance of the surface can be obtd.

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 molten metal plating apparatus for aluminum alloy plating and the like.

[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.

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
In the method according to Japanese Patent Publication No. 9981, scum generation can be reduced but not completely eliminated by simply controlling the atmosphere gas composition in the snout, and if it is possible, it will be attached to the steel sheet and brought in. There is a problem in that it is impossible to remove foreign matter or foreign matter that falls from the inner wall of the snout to the plating bath surface. Also, JP-A-61-1864
63, JP-A-4-276051 and JP-A-4-276051.
Although the method of Japanese Patent No. 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 side to the other end side in the snout, so that the foreign matter is completely attached. There was a problem that it did not prevent.

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.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and when a steel sheet is immersed in a plating bath through a snout portion by a very simple apparatus, the plating bath surface inside the snout is It is an object of the present invention to suppress scum growth and prevent deterioration of surface appearance quality due to adhesion of scum on a hot-dipped steel sheet, particularly due to alloying reaction.

[0008]

In order to achieve the above-mentioned object, the gist of the invention is that the plating of a snout in which a steel sheet is immersed in a plating bath at the snout portion of the molten metal plating. A hot-dip galvanizing apparatus is characterized in that it comprises a steel plate at the exit on the bath surface side and a snout having a distance d between the snout wall surfaces narrowed so as to satisfy the following formula. d (mm) ≦ 20 × √S (m / min) where d: distance between steel plate and snout wall surface (one side) S: line speed

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 6 outside the bath wipes off the excess plating layer on the surface, and the surface of the steel plate 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 refractory bricks in the annealing furnace, foreign substances such as powder, and molten metal evaporated 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 the plating bath surface near the steel sheet is caused by the penetration of the steel sheet as the steel sheet enters the bath. The flow 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 non-plating and indentation flaws due to the adhesion of foreign matter 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 foreign matter directly adhered 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 solve these problems, it is necessary to prevent the generation of foreign matter and prevent coarsening of the foreign matter. By narrowing the plating bath in the snout by the snout structure of the present invention, the generation of scum on the plating bath surface and coarsening It is to prevent the change.

Although FIG. 1 shows the steps described above,
In such a process, the space between the steel plate 1 at the snout outlet and the snout wall surface (one side) near the plating bath surface in the snout 2
Is d (mm), d (mm) ≦ 20 × √S (m /
min) is regulated. Here, S (m / min) is a line speed, and a value for passing a product that requires a good surface appearance is used.
The constant 20 is a value obtained from experience. That is, on the plating bath surface in the vicinity of the steel sheet, a surface flow occurs from the snout wall surface to the steel sheet side by the accompanying flow caused by the intrusion of the steel sheet. In this case, if the steel sheet has a large gap between the wall surfaces of the snout, scum grows large on the plating bath surface between them and then adheres to the steel sheet, thus deteriorating the surface appearance quality. Therefore, the scum particle size can be reduced by reducing d based on the above equation. However, if the value of d is made infinitely small, it will be close to the steel plate, and it will cause contact when the shape of the steel plate is defective or the steel plate vibrates. If this is not avoided, the risk of contact increases. Therefore, the lower limit naturally becomes the minimum value that does not cause contact with the steel sheet.

Since the accompanying flow occurring on the steel plate surface has a great influence on the line speed, the growth of scum on the snout bath surface is suppressed in relation to the line speed, and the range that does not affect the surface appearance is regulated. It is a thing. Further, if the support rolls 5 are arranged to stabilize the passing position of the steel plate, more stable passing can be achieved. FIG. 2 is a plan view of the snout portion according to the present invention. As shown in FIG. 2, by making the interval of the snout wall surface passing through the plating bath surface of the snout 2 at both ends of the steel plate 1 extremely narrow, the generation of scum is reduced and at the same time, the growth of scum on the bath surface is reduced. Is to be suppressed as much as possible.

[0014]

[Example] A steel plate of 0.8 mm (thickness) x 1219 mm (width) was line speed 80 mpm, 100 mpm, 15
The d value in each case of 0 mpm is 50 mm and 60, respectively.
mm, 100 mm, through a facility with snout wall spacing, Zn-0.1-0.3% Al, dipping in a hot dip galvanizing bath with a bath temperature of 460 ° C., and after plating to a prescribed plating thickness The surface appearance of the wiped hot dip galvanized steel sheet after the alloying treatment was observed. The result is shown in FIG. Figure 3
Shows the occurrence rate of defective surface appearance due to scum adhesion in the present invention and the comparative example. As shown in FIG. 3, by adopting an equipment configuration that satisfies the equation defining the snout wall surface distance d according to the present invention, it is possible to reduce the particles having a larger scum than the conventional method. As a result, it was possible to significantly reduce the incidence of surface appearance defects due to scum adhesion.

[0015]

As described above, according to the present invention, the generation of scum on the bath surface can be prevented and the growth of scum can be suppressed. Further, even if a slight amount is generated, the grain size is small, so that alloying is performed. Also has an excellent effect that a hot-dip galvanized steel sheet having an excellent surface appearance in which no abnormalities are observed in the surface appearance can be obtained.

[Brief description of drawings]

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

FIG. 2 is a plan view of a snout portion according to the present invention,

FIG. 3 is a diagram showing a surface appearance defect occurrence rate due to scum adhesion of the present invention and a comparative example.

[Explanation of symbols]

 1 Steel plate 2 Snout 3 Plating bath 4 Pot roll 5 Support roll 6 Gas wiping nozzle

Claims (1)

[Claims] 1. A steel plate at the exit of the plating bath surface side of the snout where the steel plate is immersed in the plating bath at the snout portion of the molten metal plating, and a snout wall space distance d is configured to be a narrow space so as to satisfy the following formula. A molten metal plating apparatus characterized by the above. d (mm) ≦ 20 × √S (m / min) where d: distance between steel plate and snout wall surface (one side) S: line speed