JPH0770722A - Continuous galvanizing method - Google Patents

Abstract

PURPOSE:To prevent the degradation in the efficiency of a plating operation by bottom dross and the degradation in the quality of a plating surface by gathering the bottom dross formed in a galvanizing tank to the bottom of a plating tank. CONSTITUTION:The plating tank 1 is separated by a partition wall 3 to a galvanizing bath tank 4 and a reaction treating tank 5 and an open part 7 is disposed between the bottom end of the partition wall 3 and the bottom of the plating tank 1 at the time of galvanizing a steel strip, etc. The bottom dross BD of a heavy sp. gr. is produced by the Fe eluted from the steel strip and molten Zn during the galvanizing operation of the steel strip. The bottom dross accumulates on the inclined bottom face of the bottom of the plating tank 1 and fills the open part 7, thereby forming a reaction treating vessel part 5 on the right side of the partition wall 3. Al is added to the part and the galvanizing bath in the plating tank 1 is transferred thereto by a pump 8. The Al-rich Zn bath in the reaction treating vessel 5 is diffused into the bottom dross BD and is floated as the top dross TD of a low sp. gr. which is then easily removed. The degradation in the quality of the galvanized steel sheet by integration of the bottom dross BD is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hot dip galvanizing a continuous strip steel sheet, and more particularly to prevention of dross defects caused by bottom dross deposited on the bottom of a plating bath in the hot dip galvanizing method.

[0002]

2. Description of the Related Art In a hot-dip galvanizing apparatus, as means for preventing the occurrence of this dross flaw, Japanese Patent Laid-Open No. 55-1285.
In Japanese Patent Publication No. 69, a molten zinc bath is divided into a zinc bath and a reaction bath by a partition having an open bottom, the inner bottom of which is inclined downward toward the reaction bath, and the reaction The tank has a structure with a stirrer, and aluminum is added to molten zinc in the reaction tank and stirred to react the following 2FeZn ₇ + 5Al → Fe ₂ Al ₅ + 14Zn with FeZn ₇ which is the main component of the bottom dross and aluminum. Is maintained at equilibrium and the aluminum concentration is adjusted to 0.1
It is described that the dross is floated (converted to a top dross) to be removed by maintaining it at 2 to 0.14, and the zinc content in the dross is returned to metallic zinc for reuse.

However, in this method, the amount of aluminum must be added so as to be in an equilibrium state in a narrow range of 0.1 to 0.14%, which is extremely difficult to adjust, and the lower part of the partition wall is opened. Therefore, when the aluminum concentration becomes high, the aluminum diffuses to the plating bath side, which has a drawback that the plating is adversely affected.

Therefore, the bottom open portion of the partition wall is filled with the formed bottom dross and sealed, and the addition amount of aluminum to the reaction tank portion separated from the plating tank portion by the partition wall is 0.1 to 0.14%. , A method has also been proposed in which the Botro dross can be brought into a floating state without having to control it within an extremely narrow range.

[0005]

However, the reaction of top dross formation in the reaction tank portion isolated by the partition wall does not cause the seal at the lower open portion of the partition wall to break, and the inside of the aluminum plating tank is prevented. In order to prevent the invasion into the bottom dross, it is necessary to do so while the bottom dross is in a stationary state, and the reaction speed of the dross is inevitably slow, and there is a drawback that it cannot cope with the formation of a large amount of dross by high speed plating. .

On the other hand, if the reaction of dross in the reaction vessel is attempted to be promoted by means such as stirring, the sealing mechanism due to the bottom dross is destroyed and aluminum added in the plating bath for the reaction with dross. Occurs and contaminates the plating bath.

An object of the present invention is to separate a plating tank into a plating bath portion and a reaction tank portion by a partition wall having an open portion below and deposit bottom dross generated in the plating process on the open portion below the partition wall to seal the bottom dross. As it forms
An object of the present invention is to provide a means for preventing the seal structure from being destroyed even when the reaction of the bottom dross in the reaction tank is promoted in the hot dipping method in which aluminum is added to the reaction tank to turn the bottom dross into a floating dross.

[0008]

According to the present invention, in a hot dip plating method in which such a bottom dross is made into a floating dross, the molten zinc composing the plating bath is forcibly transferred from the plating tank to the reaction tank. It is characterized by sending zinc of the bottom dross.

[0009]

The action of bottom dross conversion to top dross by the addition of aluminum to the reaction tank is promoted while maintaining the sealed state of the lower opening of the partition wall by botro dross.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of an apparatus to which the present invention is applied.

In FIG. 1, 1 contains molten zinc,
Roll 2 in the plating bath for rotating the strip steel plate S
The plating tank in which is arranged is shown. Zinc capacity is 180 tons
The size of the steel plate S is 0.8 mm in thickness and 160 in width.
0 mm, and the plate passing speed is 90 mpm. A partition 3 having an open bottom is provided in the plating tank 1, and the partition 3 allows the plating tank 1 to have a plating bath portion 4 having a capacity of 155 tons and 25 tons for processing bottom dross BD.
n reaction treatment tank portion 5. And it is preferable that the bottom surface 6 is formed so as to be inclined downward toward the reaction treatment tank portion 5. The inclination angle is preferably 30 ° to 45 ° so that the bottom dross flows quickly and the pot capacity can be maintained. The distance between the bottom surface of the opening 7 formed at the lower end of the partition wall 3 and the inclined bottom surface is such that the bottom dross is sufficiently moved to the reaction treatment tank portion 5, and the sealing bottom dross described below is relatively small. It is formed to a small extent. Desirably 50-
It is about 200 mm. Furthermore, this plating apparatus is provided with a device (metal pump 8 etc.) for forcibly transferring zinc from the plating bath portion 4 to the reaction treatment bath portion 5 to diffuse aluminum-rich zinc into the bottom dross BD. The moving amount of zinc by the metal pump 8 is about 1 to ³ m ³ / hr, although it depends on the amount of bottom dross generated.

In such equipment, the iron eluted from the steel strip S passing through the zinc bath ZB in the plating bath portion 4 reacts with the molten zinc forming the bath, so that FeZn ₇ having a high specific gravity is 95 kg / hr. Generated at the speed of, this becomes dross and slides down along the sloping bottom of the bathtub,
It moves to the lower part of the reaction treatment tank part 5. The dross that has moved to this reaction treatment tank portion 5 becomes a bottom dross BD and is deposited on the lower portion thereof and partially enters the plating bath portion 4 as well, closing the lower opening portion 7 of the partition 3 and closing the plating bath portion 4
And the reaction treatment tank portion 5 are sealed. Reaction treatment tank part 5
Aluminum for reaction is ingot from above
Alternatively, it is added by a wire or the like. Here, zinc is transferred from the plating bath portion 4 to the reaction treatment bath portion 5 by the metal pump 8. By this operation, the aluminum-rich zinc in the reaction treatment tank portion 5 is forcibly diffused into the bottom dross BD that seals the partition wall opening portion 7, and the contact between the aluminum and the bottom dross BD is increased, so that the bottom dross BD and the aluminum are separated. Accelerate the reaction. The reaction product becomes top dross TD, floats in the upper layer of the reaction treatment tank portion 5, and is discharged to the outside by an appropriate means.

In carrying out the present invention, it is not always necessary to add a small amount of aluminum at all times, and a sufficient amount of aluminum is zincated to form dross by being fed in a batch at regular intervals.
₂ Convert to Al ₅ and float. That is, the bottom dross and the top dross coexist in the reaction treatment tank portion 5, and the reaction products and aluminum in the reaction tank do not move to the plating bath side due to the sealing of the dross itself. In order to ensure the sealing of the opening of the partition wall, the thickness of the deposited dross is measured by a thickness measuring rod utilizing the difference in viscosity between zinc and bottom dross, or ultrasonic sonar, etc. The amount of aluminum to be added to the aluminum or the interval of addition is determined and a seal is always secured. Further, by transferring zinc from the plating bath portion 4 to the reaction treatment bath portion 5 by the metal pump 8, aluminum is diffused into the bottom dross and the change of FeZn ₇ to Fe ₂ Al ₅ is promoted.

FIG. 2 shows the transition of the aluminum concentration in the plating bath portion 4 and the reaction treatment bath portion 5 and the transition of the bottom dross deposition amount when the movement amount of zinc by the metal pump is changed in the present invention.

As shown in the figure, in the present invention, since the open portion 7 under the partition wall is sealed, even if the aluminum concentration in the reaction treatment tank portion 5 temporarily becomes high, aluminum diffuses into the plating bath portion 4. There is nothing to do. In addition, a metal pump 8 is provided from the plating bath portion 4 to the reaction treatment bath portion 5.
By transferring Zn and diffusing aluminum-rich Zn into the bottom dross BD, the top dross forming reaction of the bottom dross is promoted from the upper layer part of the bottom dross without rolling up the bottom dross. By increasing the migration amount of zinc, the reaction of bottom dross to top dross is further promoted.

On the other hand, in the conventional method in which the opening 7 at the lower part of the partition wall is not sealed, the aluminum concentration in the plating bath portion 4 and the reaction treatment bath portion 5 are equal, so that the reaction treatment bath portion 5 is always present. Aluminum concentration of 0.
Must be held between 1 and 0.14%. For this reason, it is necessary to frequently control the aluminum concentration and to add aluminum so that the aluminum concentration does not change little by little.

[0017]

The present invention has the following effects.

(1) Even when a large amount of bottom dross is generated due to high-speed plating, excessive accumulation of bottom dross in the plating tank is prevented, flaws caused by bottom dross are reduced, and great effects such as improved productivity and improved yield are achieved. Can be raised.

(2) Since aluminum added to the reaction tank does not diffuse into the plating tank, a large amount of aluminum can be added to the reaction tank at one time, and fine adjustment when adding aluminum is unnecessary. It will be easier to operate.

(3) By moving Zn from the plating tank to the reaction tank, diffusion of aluminum-rich Zn into the bottom dross is promoted, and the reaction of top dross is promoted, so that it is possible to sufficiently cope with high-speed operation.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of equipment to which the present invention is applied.

FIG. 2 shows changes in the aluminum concentration in the plating bath portion and the reaction treatment tank portion and changes in the bottom dross deposition amount when the amount of zinc transferred by the metal pump was changed.

[Explanation of symbols]

 1 Plating tank 2 Roll in bath 3 Partition wall 4 Plating bath part 5 Reaction bath part 6 Bottom surface of plating tank 7 Opening part of partition wall S Strip steel plate BD Bottom dross ZB Zinc bath TD Top dross

Claims (1)

[Claims] 1. A plating bath is divided into a plating bath portion and a reaction bath portion by a partition having an open portion below, and bottom dross generated in the plating process is deposited on the open portion below the partition to form a seal, In the continuous hot dip plating method in which aluminum is added to the reaction tank to make the bottom dross a floating dross, the molten zinc that constitutes the plating bath is forcibly transferred from the plating tank to the reaction tank to form aluminum-rich zinc as the bottom dross. Continuous hot dip galvanizing method to feed into.