KR20060074689A - Method for removing dross in hot dipping bath and apparatus for hot dipping - Google Patents

Abstract

Provided are a method of removing a bottom dross in a hot dip plating bath and a hot dip plating apparatus for use. The bottom dross removing method of the present invention is a method of removing a bottom dross generated in a process of drawing a steel plate into a plating bath by plating a sink roll provided in the plating bath, wherein the inner bottom surface of the plating bath is inclined. The bottom dross flows into the dross deposition part provided on the inner bottom of the plating bath by the inclined surface, and the dross floating material is introduced into the bottom dross deposited on the sedimentation part. To prevent the floating dross from leaking to the plating area of the sink roll by a separator provided between the dross sedimentation area and the plating area of the sink roll, and removing the wound dross. It consists of steps.

According to the present invention, the bottom dross of the hot dip plating bath can be removed throughout the plating bath without interruption of operation, and there is no change in the composition of the plating bath. In addition, dross does not adhere to the surface of the steel plate due to the effective removal of the bottom dross, so that a high quality product can be mass produced.

Hot dip plating, bottom dross, aluminum powder, nitrogen gas

Description

METHOD FOR REMOVING DROSS IN HOT DIPPING BATH AND APPARATUS FOR HOT DIPPING}

1 is an example of a conventional molten metal plating apparatus.

        1A is a case of Japanese Laid-Open Patent Publication No. 53-088633.

        Figure 1b is the case of Japanese Patent Laid-Open No. 3-47956

        1C is a case of Japanese Patent Laid-Open No. 2001-164349.

2 is an example of a molten metal plating apparatus that can be applied to the present invention.

3 is a graph showing the amount of removal of the bottom dross according to the amount of aluminum powder injected.

Explanation of symbols on the main parts of the drawings

1 ...... Steel Plate 2 ...... Plating Solution

4 ...... Top Dross 6 ...... Double Dross

10 ...... Sink Roll

20 ...... Plating Bath

22 ...... Slope 24 ...... Dross Sediment

26 ...... Separator 28 ...... Supply

The present invention relates to a method for removing the bottom dross in the hot dip plating bath and a hot dip plating apparatus therefor. More specifically, the present invention relates to a method of separating a bottom dross from a plating area by an inclined bottom surface of a plating bath, depositing it in a specific area of the plating bath, and removing floating floor dross from the plating bath, and a molten plating apparatus for the same.

In general, the hot dip plating process draws a steel plate into the plating bath by a sink roll installed in the plating bath to plate the plate. In the plating process, the steel sheet is dissolved by the plating bath, the iron is eluted, and the dross is generated by reacting with the eluted iron and the components of the plating bath. The dross is divided into a top dross that floats in the dog bath and a bottom dross that is deposited and deposited on the bottom of the plating bath. Top dross is easily removable, but bottom dross is difficult to remove. Bottom dross causes plating defects, so removal is important in terms of plating quality. Particular attention is paid to the removal of bottom dross in the technical field of the hot dip galvanizing process. Hereinafter, hot dip galvanizing, in particular, alloying hot dip galvanizing will be described in detail.

Hot dip galvanizing is performed by degreasing and washing the surface of the steel sheet, and then cooling it to near the plating temperature after annealing to immerse it in a zinc plating bath. After galvanizing, the coating amount of the coating is controlled by an air knife, and, if necessary, is also manufactured into an alloyed hot dip galvanized steel sheet through alloy heat treatment. An alloying heat treatment is a steel sheet which reheats an already formed plating layer and makes a pure zinc layer into an intermetallic compound of iron and zinc to improve workability, weldability and paintability. It is widely used in industrial fields such as home appliances, building materials, and automobiles.

In the production of alloyed hot-dip galvanized steel sheet, 0.1 to 0.18% of aluminum (Al) is included in the plating bath. This is because aluminum advantageously acts to control the thickness of the alloy layer by adjusting the plating deposition amount. The aluminum content control in the galvanizing bath is controlled by the aluminum content control in the zinc ingot.

The dross generated in the galvanized bath containing aluminum reacts with Fe (Al), zinc (Zn), and aluminum (Al), which are eluted from the plating bath, to form Fe-Al top dross (Fe ₂ Al ₅ ) and Fe-Zn. It is divided into a system bottom dross (FeZn ₇ ). Top dross having a smaller specific gravity than zinc floats in the vicinity of the bath surface of the plating bath by stirring and buoyancy of the plating liquid generated when the steel sheet enters the plating bath. On the other hand, the bottom dross having a higher specific gravity than zinc precipitates and deposits at the bottom of the plating bath. Some of the deposited dross is suspended in the plating bath, changing to a ternary compound of Fe-Al-Zn. The dross floating in the bottom dross causes damage due to adhesion of the dross to the surface of the alloyed hot-dip galvanized steel sheet manufactured by adhering to the surface of the steel sheet passing through the plating bath, thereby damaging the appearance of the product.

Therefore, various methods have been tried to remove the bottom dross in the hot dip galvanizing bath, and examples thereof include Japanese Patent Application Laid-open No. 53-088633, Hei 3-047956, Hei 4-099258 and 2001-164349.

As shown in FIG. 1A, Japanese Laid-Open Patent Publication No. 53-088633 provides a separate auxiliary port from a plating bath, injects molten zinc in the plating bath into the auxiliary port, cools it, and removes the dross by lowering the temperature. Methods and apparatus have been proposed. This method has a drawback in that it takes a lot of time because the dross removed from the auxiliary port is removed and the molten zinc is again supplied to the plating bath.

In Japanese Unexamined Patent Publication No. 4-099258, the molten zinc of the plating bath is transferred to an auxiliary port provided separately from the plating bath, and aluminum is added to remove the dross by changing the Fe-Al system. Since this method adds aluminum to the auxiliary port, the aluminum content is increased in the molten zinc of the auxiliary port. Therefore, in order to supply it to the plating bath, additional zinc should be added to adjust the same amount as the composition of the plating bath. There is this.

In Japanese Patent Application Laid-Open No. 3-047956, as shown in FIG. 1B, a shielding plate which suppresses the flow of the plating bath from below the sink roll is disposed between the sink roll and the bottom of the plating bath, and the bottom of the plating bath is lowered. A method and apparatus for suppressing the rise of dross have been proposed. However, since it is a technique of suppressing the rise of a bottom dross, the operation | work which removes the dross accumulated under the shielding board regularly is necessary.

As shown in FIG. 1C, Japanese Unexamined Patent Application Publication No. 2001-164349 has a shielding plate in a plating bath and a zinc ingot including aluminum therein is placed therein so that the aluminum dissolved in the ingot reacts with the bottom dross and is removed to the bath surface. A method and an apparatus thereof are proposed. This method is not capable of removing the dross of the entire bottom of the plating bath but is limited to the region near the zinc ingot. In addition, due to the concentration deviation of aluminum in a specific region of the galvanizing bath, alloying defects are caused, and the color difference partially occurs on the surface of the product.

Until now, the methods of removing the bottom dross generated from the hot dip plating bath are to remove the bottom dross by transferring the plating bath of the plating bath to the auxiliary port, or more advanced techniques to suppress the rise of the bottom dross in the plating bath or It is a technique to injure the floor dross in some areas. Due to these technical limitations, fundamental measures are required by removing the bottom dross from the entire plating bath without interruption of the plating operation or change of the plating bath components.

The present invention has been proposed to solve the above problems, and provides a drop removal method and apparatus capable of removing the entire bottom dross in the plating bath without interrupting the plating process or changing the composition of the plating bath. There is a purpose.

Dross removal method of the present invention for achieving the above object,

In the method of removing the bottom dross generated in the process of drawing the steel plate into the plating bath by plating the sink roll installed in the plating bath,

An inner bottom surface of the plating bath is inclined, and the bottom dross flows into and deposits a dross deposit provided in the inner bottom of the plating bath by the inclined surface;

Injecting a dross flotation material into the bottom dross deposited on the sedimentation part to float the bottom dross, and the floating dross is separated by the separation part provided between the dross sedimentation area and the plating area of the sink roll. Blocking outflow to the plating area of the made and comprises the step of removing the injured dross.

In the dross removing method of the present invention, the plating bath is a zinc plating bath containing aluminum, and the dross floating material is preferably aluminum powder. It is preferable that the aluminum powder is supplied with nitrogen as a transport gas.

A hot dip plating apparatus capable of removing a bottom dross according to the present invention is a hot dip plating apparatus including a plating bath and a sink roll provided in the plating bath to deposit a steel plate in the plating bath, wherein the inside of the plating bath is formed. The bottom is inclined,

A dross sedimentation portion provided on the inner bottom surface of the plating bath so that the bottom dross flows in and is deposited by this inclination;

Separation unit for separating the area of the dross precipitate and the plating area of the sink roll,

It is configured to include a supply for supplying the dross floating material to the bottom dross deposited in the dross precipitate.

In the hot dip plating apparatus of the present invention, it is preferable that the dross precipitate is formed in a region closer to the inner wall of the plating bath than the sink roll. In addition, the dross precipitation portion preferably forms a groove portion extending downward of the plating bath than the bottom inclined surface of the plating bath. The supply part may be a supply pipe that extends from the outside of the upper side of the plating bath to the deposited bottom dross.

The above-described dross removing method of the present invention and a hot dip plating apparatus having a dross removing function are applicable to hot dip plating in which bottom dross occurs in hot dip plating, and a representative example thereof is a galvanizing or zinc alloying process. Herein, zinc plating and alloying zinc plating will be described in detail. Those skilled in the art will understand that these specific details do not limit the invention.

Hereinafter, the present invention will be described in detail.

The present inventors completed the present invention in an effort to find a solution based on the characteristics of the hot dip plating bath to fundamentally solve the problem of the bottom dross in the hot dip plating bath. The inventors' insight into the hot dip plating process, which is the basis of the present invention, is as follows.

(1) Since the total amount of dross in the plating bath depends on the amount of Fe eluted from the steel sheet, it is difficult to suppress the occurrence of dross itself.

(2) Dross formation and growth are likely to occur in a portion where the temperature of the bath is lowered and the Al concentration of the plating bath is low, and in this case, it is deposited at the bottom of the plating bath.

(3) Fe-Al-based dross rises to the upper part of the plating bath, and the growth of Fe-Zn-based dross continues to grow over time and rapidly coarsened as it becomes a Fe-Al-Zn ternary intermetallic compound. The particle diameter is 100 µm or more. If the dross having a particle size of 100 mu m or more adheres to the plated surface of the steel sheet passing through the plating bath, irregularities of the product are generated and its appearance is significantly damaged.

(4) The bottom dross of the Fe-Al-Zn ternary compound in the plating bath is wound from the top dross or the bottom dross by stirring generated when the steel sheet passes through the plating bath. The top dross that is injured in the bath surface is often removed, but the bottom dross is difficult to remove during normal plating, so the production is stopped or replaced after the plating bath is replaced.

Therefore, there is a need for a method for effectively removing the entire bottom dross from the plating bath to an area separate from the plating area without interrupting the plating operation. On the basis of this finding, in the present invention, the bottom dross is deposited while inclining the inner bottom surface of the plating bath, and the bottom dross flows into the sedimentation section provided on the inner bottom of the plating bath to be deposited. It is characterized in that it is removed to float by dross flotation material and chemical reaction.

The present invention will be described with reference to FIG. 2, which is one example of a hot dip plating apparatus to which the present invention can be applied.

The present invention is applied to a process of drawing a steel plate into a plating bath by a sink roll provided in the plating bath.

According to the present invention, when the inner bottom surface is melt-plated in the inclined plating bath 20, the bottom dross flows into the deposition part 24 provided on the inner bottom of the plating bath by the inclined surface 22 of the inner bottom of the plating bath. And is deposited.

In the plating process, a dross flotation material is added to the deposition dross of the deposition part 24 to lift and remove the bottom dross. The dross flotation material may be appropriately selected according to the characteristics of the dross. In the case of a hot dip galvanizing bath, Fe-Zn-based dross occurs, and in this case, the Fe-Al-Zn-based dross causes injury. Therefore, aluminum (Al) is suitable for the dross flotation material in the hot dip galvanizing bath. Aluminum may be supplied in powder form, in which case it is preferable to supply nitrogen as a transport gas. That is, when aluminum is injected into the deposition dross together with nitrogen, the bottom dross is floated by the following reaction formula.

Scheme 1

2FeZn ₇ + 5Al → Fe ₂ Al ₅ + 14Zn

In the present invention, the dose of aluminum powder may be appropriately selected in consideration of the amount of deposition dross. According to one embodiment of the present invention, the aluminum powder is preferably added 0.58 ~ 5.72kg. These inputs were selected under operating conditions in which about 4 tonnes of bottom dross would occur in a plating bath with a storage capacity of 340 tonnes per week.

Arrows in Figure 2 represent the injury of the bottom dross and the injury of gas.

When nitrogen is used as a transport gas, a relatively heavy floor dross having a specific gravity of 7.1-7.2 can be secured, and it is activated to enable chemical reaction between aluminum and the bottom dross.

In the process of removing the bottom dross deposited according to the present invention, there is a possibility that the dross floating is mixed in the plating area around the sink roll. Therefore, it is preferable to prevent the floating dross of the dross sedimentation region from flowing out to the plating region of the sink roll by a separator provided between the dross sedimentation region and the plating region of the sink roll. Blocking is possible by means of separators. The separating part is possible by a blocking plate or the like.

This makes it possible to effectively remove the bottom dross and suppress the occurrence of surface defects in the steel sheet due to the flow of the bottom dross.

Removal of the floating dross may be performed by a conventional method. Usually, the dross removal is using a removal device (shovel) or a collecting device (robot).

Hereinafter, the most preferable hot dip plating apparatus that can be applied to the bottom dross removing method in the hot dip plating bath according to the present invention will be described with reference to FIG. 2.

According to the present invention, the plating bath 20 is provided with an inclined surface 22 in which the inner bottom is inclined, and is provided with a dross precipitation part 24 through which the bottom dross flows and is deposited by the inclined surface 22. The inclination angle of the inclined surface may be appropriately selected to an angle suitable for the bottom dross to flow into the sedimentation section. An angle of about 3 to 30 degrees is preferred.

The dross precipitation portion 24 is preferably composed of a groove portion extending downward of the plating bath than the inclined surface (22). The space of the groove portion can be designed according to the amount of floor dross generated in the plating bath.

In the present invention, the separation unit 26 is configured to distinguish the area of the dross precipitation unit 24 and the plating area of the sink roll 10 installed in the plating bath.

In the present invention, the region of the dross precipitation unit 24 means a region in the plating bath in which the floating dross does not affect the plating of the steel plate while the deposited bottom dross floats and is removed. This depends on the location of the dross precipitate. For example, as shown in FIG. 4, when the dross precipitation portion is formed close to one side of the plating bath 20, the dross precipitation portion may be interpreted as an upper region of the dross precipitation portion 24. When the separator 26 is moved to the sink roll 10 side, a wider area corresponds. In view of the removal side of the deposition dross, the dross sedimentation part 24 is most preferably formed near the sidewall of the plating bath on one side of the plating bath. It is desirable to be closer to the sidewall of the plating bath than is possible to the sink roll 10.

In the present invention, the plating area of the sink roll means a region in the plating bath in which the steel sheet is plated around the sink roll. In the actual plating bath, it can be interpreted as a region other than the region of the dross precipitate.

Separator 26 in the present invention is configured to block the dross to rise in the deposition section 24, the floating in the plating area of the sink roll. As an example, a blocking plate may be provided, and the blocking plate may be a stainless steel plate. The blocking plate is installed up to the upper portion of the plating bath surface to prevent the plating liquid in the region of the precipitation portion from entering the plating region.

In the present invention, the supply unit 28 for supplying the dross flotation material may be appropriately selected in consideration of reaction, injury and removal of the bottom dross deposited on the dross precipitate 24 and the floating material. For example, when the dross precipitation part 24 is formed to be close to the side of one side of the plating bath, the dross precipitation part 24 may be provided in the form of a supply pipe extending from the upper part of the plating bath to the precipitation part 24. Of course, if necessary, it may be installed on the side wall of the plating bath. For nitrogen supply, connect the supply pipe to the nitrogen gas line used in the plating factory and inject aluminum powder into it.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

The effect of the present invention was directly confirmed in the plating bath in which the bottom dross is generated about 4 tons per week in the alloy hot dip galvanizing process. The plating bath had a storage capacity of 340 tons, and the sedimentation tank was designed to accommodate 34 tons of plating solution in the sedimentation tank area. In the length of the plating bath of 4.5M, the length of the settling tank groove was 0.5M, and the depth of the groove was 0.17M. The inclination of the inner bottom was about 15 degrees. In addition, the separating portion that separates the region of the dross precipitate and the plating region of the sink roll was provided with a stainless plate. While plating in such a plating bath, aluminum powder is introduced into the deposition dross as a transport gas as shown in Tables 1 to 3, and the aluminum concentration in the lower part of the settling tank, the whole settling tank, and the surrounding plating area of the sink roll is also shown. The amount of removal of the bottom dross was measured while measuring. Tables 1 to 3 show experimental results according to the aluminum content of the plating bath. In the table, the aluminum concentration of the plating bath is a measurement of the concentration of the plating solution between the sink roll 10 and the sidewalls adjacent thereto.                     

Aluminum concentration of plating bath before aluminum injection (%) Dose of Aluminum Powder (kg) Aluminum concentration at the bottom of the settling tank (%) Aluminum concentration throughout the settling tank (%) Aluminum concentration of plating bath after aluminum injection (%) Floor Dross Removal (kg)    0.12 0.58 0.13 0.122 0.120 144 1.15 0.14 0.124 0.120 288 1.73 0.15 0.125 0.121 432 2.30 0.16 0.127 0.121 576 3.46 0.18 0.131 0.121 864 4.61 0.2 0.134 0.122 1152 5.76 0.22 0.138 0.122 1440

Aluminum concentration of plating bath before aluminum injection (%) Dose of Aluminum Powder (kg) Aluminum concentration at the bottom of the settling tank (%) Aluminum concentration throughout the settling tank (%) Aluminum concentration of plating bath after aluminum injection (%) Floor Dross Removal (kg) 0.125 0.86 0.14 0.128 0.125 216 2.02 0.16 0.131 0.126 504 3.17 0.18 0.135 0.126 792 4.32 0.2 0.138 0.126 1080 5.47 0.22 0.142 0.127 1368

Aluminum concentration of plating bath before aluminum injection (%) Dose of Aluminum Powder (kg) Aluminum concentration at the bottom of the settling tank (%) Aluminum concentration throughout the settling tank (%) Aluminum concentration of plating bath after aluminum injection (%) Floor Dross Removal (kg) 0.13 0.58 0.14 0.132 0.130 144 1.73 0.16 0.135 0.131 432 2.88 0.18 0.139 0.131 720 4.03 0.2 0.142 0.131 1008 5.18 0.22 0.146 0.132 1296

As shown in Tables 1 to 3, it can be seen that the bottom dross can be removed without any change in the aluminum concentration in the plating area of the plating bath. The average value of the dross removal rate of Tables 1-3 is shown in Table 2 compared with the conventional case (no bottom dross removal technique applied).

division Total Deposition of Bottom Dross Al concentration in plating bath Removal rate of bottom dross Conventional example 4 tons 0.125% 88% Inventive Example 0.5 tons 0.126%

Although a number of things have been described in detail for the purpose of explanation of the invention, it is to be understood that the invention is not limited thereto. Those having substantially the same configuration as the technical idea described in the claims of the present invention and providing similar actions and effects are included in the technical scope of the present invention. For example, although the present invention has been described in detail for the galvanizing bath, it can be said that it is natural that the galvanizing bath is not possible.

As described above, according to the present invention, not only the bottom dross of the hot dip plating bath can be removed throughout the plating bath without interruption of operation, but also there is no component change of the plating bath. In addition, dross does not adhere to the surface of the steel plate due to the effective removal of the bottom dross, so that a high quality product can be mass produced.

Claims (8)

In the method of removing the bottom dross generated in the process of drawing the steel plate into the plating bath by plating the sink roll installed in the plating bath, An inner bottom surface of the plating bath is inclined, and the bottom dross flows into and deposits a dross deposit provided in the inner bottom of the plating bath by the inclined surface; Injecting a dross flotation material into the bottom dross deposited on the sedimentation part to float the bottom dross, and the floating dross is separated by the separating part provided between the dross sedimentation area and the plating area of the sink roll. The method of removing the bottom dross in the hot-dip plating bath comprising the step of blocking the outflow to the plating area of the step and removing the floating dross. The method of claim 1, wherein the plating bath is a zinc plating bath containing aluminum, and the dross flotation material is aluminum powder. The method of claim 2, wherein the aluminum powder is 0.58 to 5.72 kg of the bottom dross removal method of the hot-dip plating bath, characterized in that the input. The method of claim 1, wherein the dross flotation material is supplied with nitrogen as a transport gas. A hot dip plating apparatus comprising a plating bath and a sink roll provided in the plating bath to deposit a steel sheet in a plating solution, The inner bottom surface of the plating bath is inclined, A dross sedimentation part provided on the inner bottom surface of the plating bath so that the bottom dross flows in and is deposited by this inclination; Separation unit for separating the area of the dross precipitate and the plating area of the sink roll, Hot-dip plating apparatus comprising a supply for supplying a dross floating material to the bottom dross deposited in the dross precipitate. The hot dip plating apparatus according to claim 5, wherein the dross precipitate is formed in a region closer to the inner wall of the plating bath than the sink roll. The hot dip plating apparatus according to claim 5, wherein the dross precipitation portion forms a groove portion that extends below the plating bath rather than the bottom inclined surface of the plating bath. The hot dip plating apparatus according to claim 5, wherein the supply part is a supply pipe extending from the outside of the upper side of the plating bath to the deposited bottom dross.

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