JPH07157853A - Method for removing zinc fume in snout of hot dip metal coating and device therefor - Google Patents

Abstract

PURPOSE:To eliminate the trouble such as defective plating surface, especially a defective surface appearance due to an alloying reaction, by excluding the zinc fume produced on the surface of a plating bath when a steel sheet is dipped into the bath through a snout. CONSTITUTION:A couple of circulating ports 9 and a couple of suction pots 8 are vertically arranged on the front and rear of a steel sheet 1 in a snout 2 to remove the zinc fume produced from the surface of a plating bath in the snout of hot-dip metal coating where the steel sheet 1 is dipped into the plating bath 3 or the circulating port 9 and suction port 8 are vertically provided on the side face of a snout, and the suction ports are furnished on the front and rear of the steel sheet over the full width of the sheet. Consequently, the flaws of the plated steel sheet due to the zinc fume and scum are remarkably reduced, especially in an alloyed steel sheet, and a galvannealed steel sheet excellent in surface appearance is obtained.

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 and an apparatus for removing zinc fume in snout of molten metal plating such as aluminum alloy plating.

[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 the Japanese Patent Publication No. 9981, scum generation can be reduced but not completely eliminated by simply controlling the hydrogen and oxygen atmosphere gas composition in the snout, and if it is possible, it will adhere to the steel plate. However, there is a problem in that it is impossible to remove foreign matter that is brought in as a result and foreign matter that falls from the inner wall of the snout to the plating bath surface. In addition, JP-A-6
Although the effects of reducing the amount of foreign matter on the bath surface can be obtained by the methods of JP-A 1-186463, JP-A-4-276051 and JP-A-4-276052, the foreign matter is wiped from one end side to the other end side in the snout. There is a problem that foreign matter is not completely prevented from adhering to the steel sheet in part during the process.

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, a reflux port and a suction port are provided on the front and back surfaces of the steel sheet in the snout. One pair is provided above and below each side of the snout, and the suction ports are arranged on the front and back surfaces of the steel plate over the entire width of the snout, so that zinc fume generated on the plating bath surface is removed by suction. By doing so, it is intended to prevent plating surface defects, particularly problems of surface appearance due to alloying reaction from occurring.

[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. Zinc in a snout for hot-dip galvanizing, characterized in that a pair of a reflux port and a suction port for removing zinc fume generated from the bath surface in the snout are arranged above and below the steel plate in the snout, respectively. Fume removal method. (2) The steel sheet is immersed in the plating bath at the snout portion of the molten metal plating. A reflux port and a suction port for removing zinc fume generated from the bath surface in the snout are provided above and below the snout side surface, and the suction is performed. A method for removing zinc fume in a snout of molten metal plating, characterized in that the mouths are arranged on the front and back surfaces of the steel plate over the entire width of the snout. (3) At the snout part of the molten metal plating, the steel plate is immersed in the plating bath. In the snout, a reflux port and a suction port are placed on the front and back sides of the steel plate in pairs, respectively, or the reflux port and the suction port are placed above and below the snout side face. In addition, the suction port is provided on the front and back surfaces of the steel sheet over the entire width of the snout.

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 sheet 1 discharged from a continuous annealing furnace passes through a snout 2 and is immersed in a plating bath 3 in a plating bath 5 and then passes through a pot roll 4 and a plating bath. 3. The gas wiping nozzle 6 outside the bath 3 wipes off the excessively deposited plating layer on 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]

By the way, conventionally, in hot dip galvanizing, a small amount of Al is added to the plating bath in order to improve the adhesion of zinc to the steel sheet. This Al reacts with Fe precipitated from the steel sheet to form Fe ₂ Al ₅ and floats on the bath surface as so-called top dross. Further, on the bath surface in the snout, foreign substances carried from the furnace by the steel plate and floating foreign substances due to zinc vapor in the snout are present. All of these foreign substances are transported to the vicinity of the steel sheet by the surface flow from the snout wall surface toward the steel sheet caused by the intrusion of the steel sheet into the bath, and adhere to the steel sheet in progress. 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, in particular, when the zinc-plated steel sheet adhered to the steel sheet due to the penetration of zinc vapor into the steel sheet bath by the zinc vapor in the snout is alloyed, the galvanized steel sheet directly adheres to the steel sheet and is alloyed. Of the steel sheet
When the foreign matter is diffused, the foreign matter is prevented from diffusing into the galvanized layer, resulting in a new problem of poor appearance. In order to solve these problems, zinc fume in the snout is removed to prevent the generation of floating foreign substances on the plating bath surface.

Although FIG. 1 shows the steps described above,
In such a process, in order to remove zinc fume in the snout, the reflux port 9 from the reflux pipe 7 and the suction pipe 8 is removed.
And suction port 10 are arranged one above the other on the front and back of the steel plate in the snout to form a circulating flow on the bath surface and seal the upward flow from the bath surface to the upstream furnace. To prevent zinc fume intrusion. FIG. 2 is an explanatory diagram of the lower part of the snout. FIG. 2A is an explanatory view showing a suction state on one of the front and back surfaces of the steel plate. As shown in FIG. 2 (A), when the suction pipe 8 is sucked on only one of the front and back surfaces of the steel plate, a suction-disabled region 11 is produced. That is, since the non-suctionable area 11 is formed, the circulation flow cannot be completely sucked together with the upward flow from the bath surface.

Therefore, according to the present invention, the suction pipes 8 are provided on the front and back surfaces of a steel plate as shown in FIG. 2 (B). That is, FIG. 2B shows a suction state in which suction pipes 8 are arranged on the front and back surfaces of the steel plate in the snout. This eliminates the non-suckable area, and the circulating flow can be completely sucked from the front and back surfaces of the steel sheet together with the rising flow from the bath surface, and prevents zinc fume from entering the annealing furnace upstream. In this case, the linear flow velocity at the suction port is preferably 2 m / sec or more, the diameters of the reflux port and the suction port are preferably close to the width of the snout, and the height of the suction port from the bath surface is 5 mm.
About 00 mm is desirable. Further, the suction amount (volume flow rate) is slightly smaller than the blowing amount by the N ₂ scarf (for example, 10%).
Increase) It is desirable to increase.

FIG. 3 is a detailed view of the lower part of the snout showing another embodiment according to the present invention. As shown in FIG. 3A, the reflux pipe 7 and the suction pipe 8 are provided above and below the side surface of the snout. That is, the reflux position is provided above the suction position so as to form a flow that is against the upward flow of zinc fume, and the suction pipe 8 is provided on the front and back surfaces of the steel sheet over the entire width of the snout. FIG. 3B is a diagram showing the suction port 10 having a slit shape. By providing this slit in the full width direction of the snout, all zinc fume generated from the bath surface inside the snout is sucked in the full width direction of the snout, and the zinc fume is filtered and discharged to the outside of the snout.

FIG. 4 is a graph showing the relationship between the linear flow velocity at the suction port and the defective product occurrence rate due to zinc fume according to the present invention. As shown in FIG. 4, the linear velocity at the suction port is 2 m / s.
It can be seen that in the case of ec or more, the defective product occurrence rate due to zinc fume is extremely low. From this result, it is desirable that the linear velocity at the suction port is 2 m / sec or more when the reflux port and the suction port are provided on the front and back surfaces of the steel plate in the snout, respectively, one pair above and below. FIG. 5 is a diagram showing the relationship between the linear flow velocity at the suction port and the defective product occurrence rate due to zinc fume according to another embodiment of the present invention. As shown in FIG. 5, it can be seen that the defective product occurrence rate due to zinc fume is extremely low when the linear flow velocity at the suction port is 1 m / sec or more. From this result, it is desirable that the linear velocity at the suction port is 1 m / sec or more when the suction port is formed in a slit shape in the width direction of the snout.

[0016]

【Example】

Example 1 Using the device shown in FIG. 1, 0.8 mm (thickness) × 121
A 9 mm (width) steel plate is passed at a line speed of 80 mpm, and when the reflux port and the suction port are arranged on the front and back surfaces of the steel plate in the snout, respectively, one pair is arranged vertically, and the upward flow from the bath surface To form a circulating flow on the bath surface, and the generated rising zinc fume flow was sucked from the suction port to prevent zinc fume invasion upstream. The suction speed in this case is a linear velocity of 2 m / sec, and the height of the suction port from the bath surface is 500 m.
m and the reflux port were 700 mm. Steel plate is Zn-0.1
The surface appearance after immersing in a hot dip galvanizing bath having 0.3% Al and a bath temperature of 460 ° C., plating, and wiping to a predetermined plating thickness, after alloying treatment, was observed. As a result, by applying the method of the present invention as compared with the conventional method having no suction port, the flaws of the plated steel sheet due to zinc fume and scum could be significantly reduced.

Example 2 Using the apparatus shown in FIG. 3, 0.8 mm (thickness) × 121
A 9 mm (width) steel plate is passed at a line speed of 80 mpm, and the reflux position provided on the snout is provided above the suction position so that a flow that is against the upward flow of zinc fume is not formed. By providing the slit-shaped suction port in the full width direction of the snout, the fumes in the entire width direction of the steel sheet were completely filtered through the suction port together with the zinc fume generated from the bath surface inside the snout and discharged to the outside of the snout. The suction speed in this case is a linear flow velocity of 1 m / sec, the height of the suction port from the bath surface is 500 mm,
The reflux port was 700 mm. The steel sheet has Zn-0.1 to 0.
The surface appearance after immersing in a hot dip galvanizing bath having 3% Al and a bath temperature of 460 ° C., plating and then wiping the hot dip galvanized steel sheet to a predetermined plating thickness after alloying treatment was observed.
As a result, by applying the method of the present invention as compared with the conventional method having no suction port, the flaws of the plated steel sheet due to zinc fume and scum could be significantly reduced.

[0018]

As described above, by sucking the zinc fume generated by the present invention, the defects of the plated steel sheet due to the zinc fume and scum are significantly reduced, and the hot dip galvanized steel sheet having an excellent surface appearance is obtained. It is possible to obtain the excellent effect.

[Brief description of drawings]

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

FIG. 2 is an explanatory view of the lower part of the snout,

FIG. 3 is a detailed view of a lower part of a snout showing another embodiment according to the present invention,

FIG. 4 is a diagram showing the relationship between the linear flow velocity at the suction port and the defective product occurrence rate due to zinc fume according to the present invention;

FIG. 5 is a diagram showing a relationship between a linear flow velocity at a suction port and a defective product occurrence rate due to zinc fume according to another embodiment of the present invention.

[Explanation of symbols]

 1 Steel Plate 2 Snout 3 Plating Bath 4 Pot Roll 5 Plating Bath 6 Gas Wiping Nozzle 7 Reflux Pipe 8 Suction Pipe 9 Reflux Port 10 Suction Port 11 Non-Suction Area

Claims (3)

[Claims] 1. A reflow port and a suction port for removing zinc fume generated from the bath surface in the snout where the steel plate is immersed in the plating bath at the snout portion of the molten metal plating are provided on the front and back surfaces of the steel plate in the snout, respectively. A method for removing zinc fume in a snout of hot-dip galvanizing, characterized in that a pair is arranged vertically. 2. A reflux port and a suction port for removing zinc fume generated from the bath surface in the snout where the steel plate is immersed in the plating bath at the snout portion of the molten metal plating are provided above and below the snout side surface, and A method for removing zinc fume in a snout of a molten metal plating, characterized in that the suction ports are provided on the front and back surfaces of a steel plate over the entire width of the snout. 3. In the snout portion of the molten metal plating, the steel plate is immersed in the plating bath. In the snout, a reflux port and a suction port are respectively placed on the front and back sides of the steel plate, one pair up and down respectively, or the reflux port and the suction port with respect to the side surface of the snout. The zinc fume removing device in a molten metal plating snout, wherein the suction ports are provided on the front and back surfaces of the steel sheet over the entire width of the snout.