JPH10245665A - Device for promoting precipitation and separation of dross in hot dip galvanizing bath and hot dip galvanizing bath - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for cleaning a hot dip galvanizing bath which quickly precipitates and separates dross developed in the galvanizing bath onto the bottom part of the galvanizing bath and can prevent the refloat-up of the precipitated and piled dross even if the traveling speed, etc., of a strip changes, and a method for cleaning the galvanizing bath by using this device. SOLUTION: In the dross precipitation and separation promoting device 2 having opening hole parts 12 arranged between a sink roll 7 and a bottom part 14 of the galvanizing bath, the opening hole part 12 is inclined to >45 deg. downward in the horizontal direction to this side wall thereof and the horizontal opening cross sectional area thereof becomes smaller as coming to downward and the opening hole part at the bottom part has the opening hole area of 25-80% in area ratio. The molten zinc containing the dross is passed through the opening hole part 12 and introduced to the lower part of a dross precipitation and separation device 2, and after depositing and separating the dross, the cleaned molten zinc is returned to the galvanizing part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for cleaning a plating bath by removing dross in a plating bath generated when hot-dip plating of zinc as a main component is applied to a continuously running steel sheet. About the method.

[0002]

2. Description of the Related Art In a continuous hot-dip galvanizing method for a steel sheet, the steel sheet is continuously subjected to a pretreatment such as degreasing, heated to a high temperature in a predetermined heating pattern, cooled, passed through a plating bath, and adhered with a plating. A typical method is to control the amount and then cool to room temperature in a predetermined cooling pattern.

In a continuous hot-dip galvanizing method of a steel sheet represented by hot-dip galvanizing, iron elutes from a steel sheet in a plating bath,
Produces an intermetallic compound with a plating component, so-called dross. Since this dross contains an iron component, in general,
The density of the dross becomes larger than the density of the plating bath, so that the dross sinks in the plating bath. However, the dross has a small particle size due to an intermetallic compound with iron eluted from the steel sheet. Therefore, the sedimentation speed due to the density difference is extremely slow, and it is likely to adhere to the steel sheet during the sedimentation. If this dross adheres to the steel sheet, it not only degrades the surface quality but also impairs the smoothness of the surface when processing the steel sheet, so dross adhesion is a major problem in the quality of hot-dip galvanized steel sheet. is there.

On the other hand, in the continuous operation, the dross finally settles and deposits on the bottom of the molten zinc bath. When the amount of deposited dross increases, the dross that has settled may float again due to a change in the strip running speed, particularly when the speed is increased, due to the flow of molten zinc induced by the strip running. Is also undesirable in product quality.

For this reason, Japanese Patent Application Laid-Open No. 3-47956 proposes that an arc-shaped cover be provided below the sink roll in the molten zinc tank to prevent the dross wound from the bottom of the molten zinc tank from adhering to the strip. I have. In Japanese Unexamined Utility Model Publication No. 4-53048, as shown in FIG. 6, a rectifying plate 16 for rectifying the entrained flow of the plating bath is provided at the bottom of the molten zinc tank below the sink roll, and the sink roll and the bottom of the molten zinc tank are provided. By preventing the dross from accumulating, the dross is prevented from accumulating on the strip by using a highly corrosion-resistant substance having low wettability to molten zinc for the current plate 16. Proposed. Further, in Japanese Patent Application Laid-Open No. 3-247746,
It has been proposed to install a box as a dross diffusion preventer at the bottom of the bath, settle and deposit the dross in the box, and prevent the accumulated dross from rolling up again.

[0006]

However, there are many problems with these. In the technique proposed in Japanese Patent Application Laid-Open No. 3-47956, although effective at the beginning of operation, when there is a line stop or low-speed operation condition during operation, dross accumulates on the upper surface side of the cover, Thereafter, when the operation is again performed at a high speed, a large amount of dross defects may be generated.

The technique proposed in Japanese Utility Model Laid-Open No. 4-53048 has the same problem as described above, although it is structurally simpler than the above. In particular, as shown in FIG. 6, the position where the dross accumulates when the low-speed operation is continuous is different from the position where the dross accumulates during the high-speed operation. Due to the difference in the accumulation state, when the operation is shifted from the low-speed operation to the high-speed operation, a large amount of dross 17 deposited during the low-speed operation is agitated and diffuses into the molten zinc bath at a stretch. It may adhere and cause a large amount of dross defects.

In the technique proposed in Japanese Patent Application Laid-Open No. 3-247746, dross is settled and deposited in the box, so that it is difficult to remove the deposited dross. In particular, as the depth of the box increases, the amount of deposition increases, and even if aluminum is put into the molten zinc bath to remove dross consisting of zinc-aluminum-based intermetallic compounds that settled and deposited in the box, Since it becomes impossible to convert the dross into an aluminum iron-based top dross having a lower specific gravity than the molten zinc and remove it by floating, there is also a problem in the method of removing the deposited dross.

The present invention has been made in view of such circumstances, and it is an object of the present invention to quickly settle and separate dross generated in a hot-dip zinc bath in hot-dip galvanizing at the bottom of a hot-dip zinc bath. Another object of the present invention is to provide an apparatus for cleaning a molten zinc bath capable of preventing re-floating of dross settled and deposited even when a running speed of a strip changes, and a method for cleaning a molten zinc bath using the apparatus.

[0010]

Means for Solving the Problems The present inventors investigated the flow of molten zinc in a molten zinc bath used in normal operation, the mechanism of dross generation, and the behavior of dross in the molten zinc bath. As a result, the following was confirmed.

First, the driving force of the flow of the molten zinc in the molten zinc bath is due to the stirring flow of the molten zinc generated by the strip running in the molten zinc bath and the heat retention or heating of the molten zinc. And the flow by natural convection due to uneven temperature of molten zinc generated near the inlet of the ingot for supplying solid phase zinc.

Among them, the flow that governs the behavior of dross is:
Only the agitated flow generated by the strip running supplying the molten zinc to the plated part, the other flows are not dominant to the dross behavior.

[0013] The dross is first generated by the formation of an intermetallic compound due to the reaction between iron powder and iron which elutes into the molten zinc bath from the strip and iron powder adhering to the strip entering the molten zinc bath. The intermetallic compounds are fine dross, which are flowed into the entrained flow of the strip and once reach the bottom of the molten zinc bath, mix with the low temperature molten zinc bath at the bottom of the bath, and reduce the iron to molten zinc. It was found that there was a tendency to grow into large zinc-aluminum iron-based dross due to changes in solubility and intermetallic compound structure.

In order to produce a high-quality hot-dip galvanized steel sheet with less quality defects due to dross adhesion, highly clean hot-dip galvanized zinc is supplied to the plating portion above the hot-dip zinc bath, and dross generated by the plating is removed. It is necessary to clean the contained molten zinc bath.

Therefore, the molten zinc containing the dross generated is quickly separated from the plating portion and led to the bottom of the molten zinc bath, where the dross is settled and separated to obtain highly clean molten zinc. Various methods and devices for returning to the plated part were examined from thought experiments and experiments using actual machines.

As a result, by providing a device for promoting the sedimentation and separation of dross of a specific shape between the sink roll in the molten zinc bath and the bottom of the bath, it is easy to settle and separate the dross at the lower part of the device. In addition, by utilizing the agitated flow of molten zinc generated by the running of the strip, regardless of the strip running speed, the molten zinc containing dross is quickly separated from the plated portion and reliably led to the bottom of the molten zinc bath. The present invention has been found that the hot-dip zinc can be returned to the plated portion after the dross has been removed.

Means of the present invention for solving the above problems are as follows. (1) A dross settling / separation promoting device having an opening provided between a sink roll in a molten zinc bath and the bottom of the molten zinc bath, wherein the opening has a side wall extending downward in the horizontal direction.
An apparatus for accelerating dross sedimentation and separation of a molten zinc bath, wherein the apparatus is inclined at an angle of 5 degrees or more and has a smaller horizontal opening cross-sectional area as it goes downward, and has an opening area of 25% to 80% in area ratio. (2) In the above (1), when the lower opening shape is a slit, the slit width is an opening having a width of 5 mm or more and 100 mm or less, and when the lower opening shape is a circle or a polygon,
An apparatus for promoting dross sedimentation and separation of a molten zinc bath, wherein the minimum size of the lower opening is 5 mm or more and 50 mm or less. (3) The molten zinc containing dross generated in the molten zinc bath is passed through the opening of the dross sedimentation / sedimentation promotion device by using the dross sedimentation / separation promotion device of the molten zinc bath according to (1) or (3). Cleaning the molten zinc bath, wherein the dross is settled and separated therefrom.

Hereinafter, the reasons for limitation and the operation of the present invention will be described. The molten zinc containing the dross is caused to collide with the bottom of the molten zinc bath along with the accompanying flow of the strip, but after the collision, only the molten zinc flows off and the sink roll in the molten zinc tank is settled down to the bottom of the bath. A dross sedimentation and separation accelerating device is installed between the and the bottom of the molten zinc tank. The dross sedimentation separation promotion device has a structure having an opening in a part. By providing an opening in a part of the dross sedimentation separation accelerating device, a stagnation region of the molten zinc flow is generated at the bottom of the molten zinc bath, and sedimentation of the dross can be promoted.

In order to effectively settle and separate dross,
The dross sedimentation and separation accelerating device is 150 to 50 meters from the bottom of the bathtub.
0 mm, 150-500 mm below the sink roll, and generally horizontally.

In order to prevent the molten zinc from flowing back from the bottom of the zinc bathtub through the opening of the dross sedimentation and separation accelerating device and to prevent the molten zinc from flowing back from the bottom of the zinc bathtub, and to enhance the dross sedimentation and separation effect, the dross sedimentation is performed. It is necessary to set the opening area ratio of the minimum opening of the separation promoting device to 25% or more and 80% or less. Further, in order to prevent dross from being deposited on the apparatus, it is necessary to incline all side walls of the opening 45 degrees or more downward from the horizontal plane so that no horizontal portion is provided at the top of the apparatus.

There is no particular limitation on the shape of the opening,
The shape may be any shape such as a circle (including an ellipse), a rectangle, and other polygons. When the lower opening is formed by a slit, the slit interval is desirably 5 mm or more so that dross does not clog the slit, and 100 mm or less in order to prevent the backflow of molten zinc from the tank bottom.
The slit is desirably provided in the strip width direction.
When the lower opening has a polygonal or circular shape, it is preferable that the minimum dimension of the lower opening be 5 mm or more and 50 m or less in order to prevent dross clogging and backflow of the molten zinc as described above. Even in the case of the above-mentioned shape, in the test with the actual machine, by making the inclination of the opening side wall 45 degrees or more,
Dross accumulation was prevented.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS.

The dross settling / separation accelerating device 2 is installed 300 mm (L) from the bottom of the molten zinc bath 1 and approximately 400 mm below the sink roll 7. The dross sedimentation and separation accelerating device 2 is located two to the left and right of the body length of the sink roll 7.
The width is 00 mm wider. Further, the length of the dross sedimentation separation promoting device 2 in the strip running direction is 1080 mm, and it is disposed with respect to the center of the sink roll 7 so as to have a length of 540 mm before and after the strip running direction, respectively.
Five sets of slit-shaped openings 12 shown in FIG. 2 are arranged at substantially horizontal positions in the strip running direction (opening area ratio: 35%).

FIG. 2 shows the details of the main part of the opening of the dross settling / separation promoting device 2. In FIG. 2, (a) is a side view,
(B) is a plan view. As shown in FIG.
The width (W) is 100mm, the inclination angle (α) with respect to the horizontal plane
It is composed of two plates inclined at 45 degrees in opposite directions to each other, the lower interval (D) of the side wall 3 is 75 mm, and a slit-shaped opening 12 is formed.

The strip S enters the molten zinc bath 6 in the molten zinc bath 1 from the snout 5 whose lower part is immersed in the molten zinc bath 6, and is turned upward by the sink roll 7. 8 and a stabilizing roll 9, and is adjusted to a predetermined plating adhesion amount by a gas wiping nozzle 10.

The molten zinc 11 containing dross is guided by the agitated flow of the strip S through the opening of the dross settling / separation promoting device 2 to the bottom of the molten zinc bath 1 below the dross settling / separation promoting device 2. I will The backflow of the molten zinc from the molten zinc bath bottom 14 is prevented by the action of the dross sedimentation separation promoting device 2 having an opening in part, and as a result, the backflow of the dross is also prevented. Since the temperature of the molten zinc bath bottom 14 is lower than that of the plating portion at the top of the bath, the dross of the molten zinc 11 containing dross has a large diameter, and sedimentation and separation of the dross are promoted. In addition, since the opening is partially formed, a stagnation region of the molten zinc flow can be generated in the molten zinc bath bottom portion 14, so that the molten zinc bath temperature can be lowered and the dross settling can be further promoted.

The molten zinc 11 containing dross moves on the bottom 14 of the molten zinc bath under the dross sedimentation separation promoting device 2 in the direction of the side wall of the molten zinc bath 1 and the gap 15 between the dross sedimentation separation promoting device 2. . At that time, the dross 17 settles and separates and deposits on the molten zinc bath bottom 14. On the other hand, the molten zinc from which dross has been removed and which has been cleaned returns to the plating portion of the molten zinc bath again through the gap 15 between the dross settling / separation accelerating device 2 and the side wall of the molten zinc bath 1.

Even when the running speed of the strip is low, the molten zinc containing dross passes through the opening 12 of the dross settling / separation promoting device 2 due to the accompanying flow of the strip.
The dross 17 can be surely settled and separated by leading to the molten zinc bath bottom 14 below. In addition, even if the traveling speed of the strip changes, the dross sedimentation separation promoting device 2 operates
The re-floating of the dross 17 deposited on the molten zinc bath bottom 14 can be suppressed.

When the amount of dross settled and deposited on the bottom 14 of the molten zinc bath increases, the dross settling / separation accelerating device 2 is removed, and the dross 17 can be taken out of the tank by a usual method.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the case where the direction of entry of a strip into a molten zinc bath is 45 degrees downward from the horizontal direction, quality defects due to dross adhesion before and after the installation of the dross sedimentation and separation accelerating device 2 of the present invention shown in FIG. FIG. 3 shows the results of the investigation on the amount of the generation. The amount of quality defects caused by dross adhesion after installation is reduced by 95% compared to before installation.

Further, according to the present invention, the amount of quality defects caused by dross adhesion can be reduced. Therefore, the effect of reducing the quality defects by dross adhesion when the line speed is increased was examined. The examination result is shown in FIG.

From FIG. 4, it can be seen that in order to ensure the same level of quality as before the installation of the device of the present invention, the running speed of the strip is set to 1
It was found that the speed could be increased by 60% from 00 m / min to 160 m / min, that is, the production could be increased by 60%. Further, when considering a case where the traveling speed of the strip is increased while improving the quality, according to the present embodiment, a quality level of about 50% of the amount of quality defects caused by dross adhesion before installation of the apparatus of the present invention is secured. 30% while
It is possible to increase the speed by about 30%, that is, about 30%.

FIG. 5 shows another embodiment of the opening used in the dross sedimentation separation accelerating apparatus of the present invention. The opening in FIG. 5 is replaced with the slit opening shown in FIG. 2 and the upper opening and the lower opening are both regular hexagonal honeycombs, the inclination angle (α) of the side wall 3 is 45 degrees, and the upper opening dimension ( D ₁ ) is 200
mm, and the lower opening dimension (D ₂ ) is 100 mm (opening area ratio: 25%). In the case of the dross settling / separation accelerating device using this opening, the same effect as in the case of the above example was confirmed.

[0034]

According to the present invention, dross generated in a molten zinc bath can be quickly sedimented and separated at the bottom of the molten zinc bath to clean the molten zinc bath.
Even if the strip running speed changes, re-emerging dross settled and deposited on the bottom of the molten zinc bath can be suppressed. ADVANTAGE OF THE INVENTION According to this invention, a high quality molten zinc steel plate which reduced the quality defect by dross adhesion can be manufactured, or it can aim at increase in production, reducing occurrence of a quality defect.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a dross sedimentation separation accelerating device of the present invention.

FIG. 2 is a view showing an embodiment of an opening used in the dross sedimentation separation accelerating device of the present invention.

FIG. 3 is a diagram showing an effect of reducing the amount of quality defects generated by dross adhesion according to the present invention.

FIG. 4 is a diagram showing a relationship between a strip traveling speed and a quality defect generation amount due to dross adhesion.

FIG. 5 is a view showing another embodiment of the opening used in the dross sedimentation separation accelerating device of the present invention.

FIG. 6 is a diagram showing the state of dross accumulation in a molten zinc bath when the strip running speed changes in the prior art.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 molten zinc bath 2 dross settling / separation promoting device 3 side wall 5 snout 6 molten zinc bath 7 sink roll 8 collecting roll 9 stabilizing roll 10 gas wiping nozzle 11 molten zinc 12 opening 14 molten zinc bath bottom 15 dross settling / separation promoted device Gap between molten zinc bathtub side wall 16 Rectifier plate 17 Dross S strip

Claims (3)

[Claims] 1. A dross settling / separation promoting device having an opening provided between a sink roll in a molten zinc bath and a bottom of the molten zinc bath, wherein the opening has a side wall having a horizontal angle of 45 degrees or more. Inclined, the horizontal opening cross-sectional area decreases toward the bottom, and the area ratio is 25% or more and 80% or more.
An apparatus for accelerating dross sedimentation of a molten zinc bath having the following opening area. 2. When the shape of the lower opening is a slit, the opening has a slit width of 5 mm or more and 100 mm or less. When the shape of the lower opening is circular or polygonal, the minimum dimension of the lower opening is 5 mm or more and 50 mm or less. The dross sedimentation and separation accelerating apparatus for a molten zinc bath according to claim 1, wherein the apparatus is an opening. 3. An apparatus for promoting dross sedimentation separation in a molten zinc bath according to claim 1 or 2, wherein molten zinc containing dross generated in the molten zinc bath is passed through an opening of the dross sedimentation separation acceleration apparatus. A method for cleaning a molten zinc bath, characterized in that the dross is settled and separated therethrough by passing through.