JPH07145464A - 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 by preventing generation of scum, dross or the like 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:Generation of scums on the surface of a plating bath is prevented by connecting one end of the plating bath surface covering material 5 to a snout part, or floating the plating bath surface covering balls on the surface of the plating bath in the snout to cover the plating bath surface where the steel sheet 1 is dipped in the plating bath at the snout part 2 for the hot dip metal coating to cover the plating bath surface. The galvannealed 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.

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 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 By preventing the above-mentioned scum and dross from occurring, it is intended to prevent the occurrence of plating surface defects, particularly problems of surface appearance due to alloying reaction.

[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 molten metal plating method, wherein one end of a bath surface coating material is connected to a snout portion in a snout to cover the bath surface, thereby preventing scum from occurring on the bath surface. (2) The steel plate is immersed in the plating bath at the snout portion of the molten metal plating. A bath surface coating sphere is floated on the plating bath surface in the snout to cover the bath surface, thereby preventing scum from occurring on the bath surface. A method for hot-dip metal plating, which comprises: (3) In the molten metal plating apparatus for the description of (1) and (2), the bath surface coating material and the bath surface coating sphere are arranged in the snout in which the steel plate is immersed in the plating bath at the snout portion of the hot dip metal plating. .

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 7 outside the bath wipes away the excessive plating layer adhered to the surface, so that 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 matters 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 due to scum adhesion occur. Even if these are not the major causes, the following new problems arise.

That is, in particular, the scum floating on the bath surface grows in size and grows in size with the passage of time, and as it penetrates into the steel plate bath, the galvanized steel plate adhered to the steel plate is alloyed. In this case, the scum directly adhered to the steel plate is alloyed to prevent diffusion of the scum to the galvanized layer when Fe of the steel plate diffuses, resulting in poor appearance. That caused a new problem. In order to solve these problems, it is necessary to prevent scum from occurring and prevent coarsening of scum. The bath surface coating material and the bath surface coating sphere of the present invention cover the bath surface in the plating bath in the snout. This prevents the generation of scum on the plating bath surface.

Although FIG. 1 shows the steps described above,
In such a step, one end of the bath surface covering material is connected to the snout portion in the snout to cover the bath surface. That is, in the present invention, one end of the bath surface coating material is connected to the snout portion in the snout, the bath surface coating material 5 is hung on the steel plate side, and the bath surface is covered, so that oxygen on the bath surface in the snout Blocks contact, prevents scumming and
Even for a small amount of scum generated, it is possible to prevent the scum from growing large on the plating bath surface.

The bath surface coating material is required to have heat resistance and corrosion resistance to the molten metal. For example, ceramics, stainless steel which is a metal having heat resistance and corrosion resistance, and a cermet coating material for the metal and heat resistance. Use a plate-shaped open / close function that uses resin. And
The plate-shaped bath surface covering member 5 is composed of an opening / closing mechanism that can narrow the space between the bath surface snout and the steel plate around a fulcrum 8 that connects one end of the bath surface coating material 5 to the snout portion. Further, since the molten metal adheres to the bath surface coating material, it is preferable to provide a heating mechanism having a function of preventing molten metal adhesion, and further a detaching mechanism to facilitate replacement.

FIG. 2 is a plan view of the snout portion according to the present invention. As shown in FIG. 2, bath surface coating materials 5 are arranged on the plating bath surfaces in the snouts 2 on both sides of the steel sheet 1 so as to surround both sides of the steel sheet 1. As a result, the contact with oxygen on the bath surface is blocked to prevent the generation of scum. FIG. 3 is a vertical sectional view showing a plating process which is another embodiment according to the present invention. 3 is basically the same device as FIG. 1,
The steel sheet 1 discharged from the continuous annealing furnace passes through the snout 2 and is immersed in the plating bath 3 in the plating tank, and is then drawn out of the plating bath 3 through the pot roll 4. In this case, The plating bath surface coating sphere 6 is floated to prevent Zn evaporation.

The bath surface coated sphere has heat resistance and corrosion resistance to the molten metal, and for example, ceramics, hollow stainless steel spheres which are metal having heat resistance and corrosion resistance, heat resistant glass and the like are used. Its size is 5 mm to 50 mm. The reason for this is that if it is less than 5 mm, it adheres to the steel plate and becomes defective. On the other hand, if it exceeds 50 mm, the coverage of the bath surface is lowered and the function of preventing scum is lowered. This is because the spherical shape makes it difficult for the steel sheet to be flawed even if it comes into contact with the steel sheet. FIG. 4 is a plan view showing a state in which the bath surface coating sphere according to the present invention is provided. As shown in FIG. 4, bath surface coating spheres 6 are arranged on the plating bath surfaces in the snouts 2 on both sides of the steel sheet 1 so as to surround the steel sheet 1. As a result, the contact with oxygen on the bath surface is blocked to prevent the generation of scum.

[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, dipped in a hot dip galvanizing bath having a Zn-0.1 to 0.3% Al and bath temperature of 460 ° C., and plated to a predetermined 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. FIG. 5 shows the occurrence rates of surface appearance defects due to the scum adhesion of the method of the present invention and the conventional method. As shown in FIG. 5, by applying the method of the present invention as compared with the conventional method in which the bath surface coating material is not used, it was possible to significantly reduce the occurrence rate of surface appearance defects due to scum adhesion.

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, dipped in a hot dip galvanizing bath having a Zn-0.1 to 0.3% Al and bath temperature of 460 ° C., and plated to a predetermined 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. FIG. 6 shows the surface appearance defect occurrence rate due to the scum adhesion of the method of the present invention and the conventional method. As shown in FIG. 6, by applying the method of the present invention as compared with the conventional method having no bath surface coating material as in FIG. 5, it was possible to significantly reduce the incidence of surface appearance defects due to scum adhesion. ..

[0018]

As described above, according to the present invention, it is possible to prevent the generation of scum on the bath surface, and even if a slight amount is generated, it is alloyed because the grain size is small, but the surface appearance is It has the excellent effect of being able to obtain a hot-dip galvanized steel sheet having an excellent surface appearance in which no abnormalities are observed.

[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 vertical sectional view showing a plating process which is another embodiment of the present invention,

FIG. 4 is a plan view showing a state in which a bath surface coating sphere according to the present invention is provided,

FIG. 5 is a graph showing a surface appearance defect occurrence rate due to scum adhesion according to the method of the present invention and the conventional method;

FIG. 6 is a diagram showing a surface appearance defect occurrence rate due to scum adhesion in the method of the present invention and the conventional method.

[Explanation of symbols]

 1 Steel plate 2 Snout 3 Plating bath 4 Pot roll 5 Bath surface coating material 6 Bath surface coating ball 7 Gas wiping nozzle 8 Support point

Claims (3)

[Claims] 1. A scum on the bath surface is prevented by connecting one end of the bath surface coating material to the snout portion in the snout where the steel plate is immersed in the plating bath at the snout portion of the molten metal plating and covering the bath surface. A method for hot dip metal plating, comprising: 2. The scum on the bath surface is prevented by floating the bath surface coating ball 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 covering the bath surface. A method for hot dip metal plating, comprising: 3. The hot-dip galvanizing apparatus according to claim 1, wherein the bath surface coating material and the bath surface coating sphere are arranged in the snout where the steel sheet is immersed in the plating bath at the snout portion of the hot dip metal plating.