WO2001055468A1

WO2001055468A1 - Method and apparatus for removing bottom dross in hot dip galvanizing bath

Info

Publication number: WO2001055468A1
Application number: PCT/JP2001/000538
Authority: WO
Inventors: Kiyoko Shinohara; Kazuo Handa; Yoshihiro Murakami; Hiromi Kobayashi
Original assignee: Kabushiki Kaisha Galva Kogyo Mihara Kojyo
Priority date: 2000-01-26
Filing date: 2001-01-26
Publication date: 2001-08-02
Also published as: AU2001228835A1; JP3569262B2

Abstract

A method for removing a bottom dross in a hot dip galvanizing bath, which comprises providing a cylindrical device having openings in its top portion and bottom portion, a means for blowing bubbles in in its bottom portion and an ingot containing metallic aluminum in its middle portion, immersing the cylindrical device in the hot dip galvanizing bath in a transferable manner, feeding bubbles by the above means and blowing the bubbles toward the bottom dross, to thereby float the ingot up in the device together with bubbles, reacting the bottom dross floated up with the ingot containing metallic aluminum, to thereby convert it into a top dross and further float it up, and removing the top dross. The method can be employed for removing a bottom dross deposited in the bottom portion of a hot dip galvanizing bath with good efficiency, while keeping the composition of the bath almost constant.

Description

Description Method and apparatus for removing bottom dross from molten zinc plating bath

Technical field

The present invention mainly removes massive bottom dross deposited on the bottom of a hot-dip galvanizing bath with a batch processing method efficiently as a top dross, and almost completely removes the composition of a hot-dip galvanizing bath solution before and after the removal of bottom dross. The present invention relates to a method and an apparatus for removing a bottomed port in a hot-dip galvanizing bath which can maintain an appropriate bath liquid composition without changing the bath liquid composition. Background art

Zinc plating is widely used for the purpose of preventing corrosion of various iron products, including galvanized iron, and the surface of the product is immersed in a molten zinc metal bath and coated with zinc metal. Things. The recent zinc plated bath, in order to stabilize the front surface gloss after plated processing, the force trace metals such as aluminum is dissolved in the plated bath ^5, throughout the course of the zinc plated, such trace metals It is necessary to maintain the concentration at a predetermined concentration. For example, in the case of ordinary zinc plating, the concentration of aluminum in the plating bath is about 20 to 80 ppm, and in the case of high-concentration aluminum zinc plating bath, it is maintained at about 3 to 7%. This is required for the quality of the finished surface condition of the plated product.

On the other hand, when the molten zinc plated work of the steel plate and steel, iron eluted in molten zinc plated tub (F e) is reacted with zinc (Z n), an alloy such as F e Z n ₇ Generate a so-called dross. Such dross is mainly composed of zinc, and also contains a small amount of iron and aluminum. The dross floats in the bath and gradually grows over time. Alloy produced as these dross, zinc, iron, different specific gravity by the content ratio of Al Miniumu, together with the low specific gravity of that of the part from zinc suspended in the bath, the top dross (F e ₂ A l ₅ ) Ascend to the bath surface. On the other hand, next to the bottom-dross is of high specific gravity than zinc (F e Z n _7), becomes partially by solid formulated bulk is deposited to a thickness of several cm~ tens cm to the bottom of the zinc bath. The floating dross mentioned above adheres to the surface of the steel plate or steel material to be subjected to the plating work, which significantly reduces the quality of zinc plating products, and reduces productivity by reducing the work speed of the plating to avoid such adhesion. And increase the production cost due to the reprocessing of defective plating. In addition, bottom dross partially floats and causes the above-mentioned adverse effects, and zinc metal is contained in a large amount of massive dross deposited at the bottom of the zinc plating bath, so that time is lost. And periodic removal of dross by costly human work had to be done. As a result, productivity was lost due to the stoppage of the bathtub operation, dangerous work to remove the dross, replenishment of zinc for adjusting the bath surface after the dross removal, and loss of zinc ingot due to the low pick-up value of the removed dross.から It causes various adverse effects from the viewpoint of cost and the like.

As a measure to reduce the adverse effects of these dross, for example, Japanese Patent Application Laid-Open No. 50-59218 discloses a method in which aluminum powder, aluminum salt or pure aluminum is added to a molten zinc plating bath to remove the dross. A method has been proposed in which the aluminum concentration is increased, and dross having a reduced specific gravity is caused to float on the surface of the plating bath, thereby removing the floated dross artificially.

However, when the dross is floated and separated by adding aluminum to the hot-dip galvanizing bath as described above, the dross floating in the plating bath can be removed relatively easily, but the dross in the plating bath can be locally removed. Or, a rapid change in the composition could not be achieved, and no effective means for removing bottom dross could be obtained as described below. In other words, in order to raise the aluminum content in the bottom dross and float on the bath surface by decreasing its specific gravity, it is necessary to add a large amount of aluminum to drastically change the aluminum concentration in the entire plating bath. However, it is still inadequate for the solidification that accumulates at the bottom of the plating bath and for the floating of a large amount of bottom dross, and it is extremely difficult to remove the bottom dross by such means. .

Further, in the method of adding aluminum into the plating bath, Insufficient mixing and stirring of the plating bath after the aluminum has been introduced will result in a transient increase in the number of floating ports in the bath, and such floating dross will adhere to the plating products, causing Quality will be further reduced.

As the other prior arts described above, for example, Japanese Patent Application Laid-Open Nos. Sho 56-73773, Sho 63-274750, Sho Hei 1-147047 Japanese Patent Application Laid-Open Publication No. Heisei 2-34-7661 proposes that a large-scale processing apparatus for separating dross be fixedly installed separately from a plating bath. However, these large-scale treatment tanks / devices are not effective means for removing a large amount of solidified and agglomerated bottom dross deposited at the bottom of the plating bath, regardless of the floating dross. For this reason, the removal of bottom dross in the hot-dip zinc bath is still dependent on a lot of labor and dangerous human work.

SUMMARY OF THE INVENTION The object of the present invention has been made in view of the above-mentioned problems, and has a simple structure and low cost, and removes solidified massive bottom dross deposited on the bottom of a plating bath as it is. Instead of the top dross, it is possible to remove the bottom dross efficiently and virtually without changing the composition of the bath liquid in the molten zinc plating bath. In addition, the composition of the hot-dip galvanizing bath does not change significantly, and no special treatment is required for the hot-bathing bath when resuming the hot-dip galvanizing bath. An object of the present invention is to provide a method and an apparatus for removing bottom dross. Disclosure of the invention

As described below, the present invention uses an apparatus comprising a movable cylindrical body having a specific function and a simple structure, which is immersed in a molten zinc plating bath and moved continuously or intermittently. Then, the plating bath is processed by dividing it into portions.

According to the present invention, unexpectedly, the massive bottom dross is gradually collapsed by blowing bubbles generated by the bubble blowing means provided in the cylindrical body device onto the solidified massive bottom dross. Into powder and granules. It turned out to rise with the rise. At the same time, the melting point of the metallic aluminum-containing ingot held in the tubular device of the present invention is higher than the temperature of the plating bath, and it is not expected that the ingot will be dissolved in the plating bath solution. If one bubble is present, the ingot dissolves in the plating bath and reacts with the powdery bottom dross (F e Zn ₇ ) that floats, and the top dross (F e ₂ Al ₅ ).

2 F e Z n ₇ + 5 A 1 ― F e ₂ A 1 ₅ + 1 4 Z n

By converting from the bottom dross to the top dross, the bottom dross deposited on the bottom of the bathtub can be easily removed as a top dross. In addition, the treatment according to the present invention is performed by moving the cylindrical body device so that the plating bath liquid is performed part by part, and preferably, while circulating the liquid inside and outside the cylindrical body device, Since the aluminum concentration does not change significantly, there is an advantage that no special treatment is required when the plating bath is reused.

The present invention provides a novel device comprising a movable tubular body having a specific function and a simple structure based on the above-described novel findings, and elimination of a bottom dross using the device. And has the following configuration.

(1) A method for removing bottom dross mainly composed of an alloy of zinc and iron in a molten zinc plating bath by moving a removing device continuously or intermittently in a molten zinc plating bath. It has an opening at the top and bottom, a bubble injecting means at the bottom, and a tubular body holding a metal aluminum-containing ingot at the middle part. The bottom dross is floated in the apparatus together with the bubbles by blowing bubbles into the bottom dross by the bubble blowing means, and the floated bottom dross is reacted with a metal aluminum-containing ingot to form zinc and aluminum. A molten zinc alloy characterized by being converted to a top dross mainly composed of an alloy of aluminum and floated, and removing the floated top dross. How to remove bottom dross from the bathtub.

(2) The height of the cylindrical body device is smaller than the depth of the molten zinc plating bath, and the plating bath solution containing the top dross converted from the bottom dross is opened at the top of the cylindrical body device. The method for removing a bottom dross according to the above (1), wherein the solution is discharged from a mouth into a molten zinc plating bath and circulated.

(3) The height of the cylindrical body device is larger than the depth of the molten zinc plating bath, and the plating bath liquid containing the top dross converted from the bottom dross is circulated through the cylindrical body. Bottom dross removal method.

(4) A cylindrical body having openings at the top and bottom, having a bubble blowing means at the bottom, and holding a metal-aluminum-containing ingot in the middle section, and forming the cylindrical body into a molten zinc plating bath. It is immersed so as to be able to move continuously or intermittently in it, and is blown into the bottom dross mainly composed of an alloy of zinc and iron by the bubble blowing means. The bottom dross is floated in the mold, and the raised bottom dross is reacted with an ingot containing metallic aluminum to be converted into a top dross mainly composed of an alloy of zinc and aluminum and floated to remove the raised top dross. An apparatus for removing bottom dross from a molten zinc plating bath.

(5) The cross-sectional area of the intermediate portion of the cylindrical body above the metal aluminum-containing ingot is smaller than the cross-sectional area of the lower and upper portions, and has an opening near the intermediate portion. The apparatus for removing bottom dross from a molten zinc plating bath according to the above (4), wherein the plating bath liquid is introduced from the bath.

(6) The means for generating air bubbles is composed of 10 to 90 parts by mass of an inorganic compound which thermally decomposes and foams at a temperature of the molten zinc plating bath or lower, and is thermally decomposed at a temperature of the galvanizing bath or lower. And 90 to 10 parts by mass of the nitrogen-containing organic compound to be foamed.

(4) The apparatus for removing bottom dross of a molten zinc plating bath according to (5).

(7) The method according to the present invention, wherein the bottom dross of the molten zinc plating bath according to the above (6), wherein the composition is partially exposed and coated with a coating material that does not disappear in the molten zinc plating bath. The device will be described more clearly with reference to the drawings. BRIEF DESCRIPTION OF THE FIGURES

Figure 1: Schematic diagram of an example of an apparatus used in the method for removing bottom dross from a molten zinc plating bath according to the present invention.

Fig. 2: Outline of the process of removing the bottom dross from the zinc plating tank using the apparatus of Fig. 1. Fig. 3: The bottom dross is removed using another apparatus of the present invention suitable for a relatively small zinc plating tank. The schematic diagram which shows the process of removing.

Figure 4: Graph showing the aluminum concentration distribution in the zinc plating bath in Example 1.

Figure 5: Graph showing changes in the number of dross pumpings, the number of dross debris generation, and the basic unit of zinc in the galvanizing bath of Example 1.

Explanation of reference numerals

1 2 Top opening

3 Bubble blowing means 4 Metal aluminum holding section 5 Primary mixing reaction section 6 Secondary mixing reaction section

7 Mesh bath liquid suction section 8 Tertiary mixing reaction section

9 Top opening 1 0 Plating bath

1 1 Po Tom Dross 1 2 Top Dross

2 0 Outer side wall 2 1 Internal circulation passage Best mode for carrying out the invention

FIG. 1 shows a schematic cross-sectional view of one preferred example of an apparatus used to carry out a method for removing bottom dross of a hot-dip galvanizing bath of the present invention, and FIG. 2 shows an apparatus using the apparatus of FIG. _C is an explanatory view showing the process of removing the bottom dross from the zinc plating tank.The device 1 shown in FIGS. 1 and 2 has a circular or polygonal cross section as a whole, and has a cylinder having openings at the top and bottom. Consists of a shape. The diameter and height of the cross section of the cylindrical body are determined by the size of the zinc plating tank. Inside the device 1, there is an opening at the bottom serving as a receiving port when the bottom dross 11 deposited on the bottom of the zinc plating tank floats 2, Bubble blowing means for generating bubbles 3, Metal aluminum holding part for holding metal aluminum containing ingot 4, Primary mixing reaction part 5, Secondary mixing reaction part 6, Zinc plating bath suction part 7, and Tertiary mixing It has a reaction section 8. Such a device is movably immersed in a bathtub to remove bottom dross in the area where the device is located. After the removal operation of the area where the equipment is located is completed or while the removal operation is being performed, the zinc plating bath is continuously or intermittently moved to another area.

When performing the work of removing bottom dross using the above device 1, first, the device 1 is usually settled down in a zinc plating bath. In this case, if there is an opening 2 at the bottom of the apparatus 1 and a zinc plating bath liquid suction section 7, the plating bath liquid in the plating tank enters from the suction section 7 and is filled with the plating bath liquid. It is done. Appropriately sized openings or cutouts (not shown) are provided in the bottom side wall of the device 1 so that the plating bath can be freely circulated between the device 1 and the plating bath through such openings. Is done. In this way, when the device 1 is settled down in the plating bath, the bottom of the plating bath is usually provided with metallic lead having a thickness of several cm to about 10 cm to prevent corrosion by molten zinc. Since a molten layer is provided and the bottom dross layer is deposited thereon, the bubble blowing means 3 of the apparatus 1 is provided with a force to be embedded in the bottom dross layer deposited at the bottom of the plating bath, or Preferably, it is located below the layer.

In this state, the bubble blowing means 3 of the apparatus is operated to blow air bubbles into the surface of the bottom dross 11 or the inside thereof, whereby the bottom dross solidified at the bottom of the plating bath and accumulated in a lump is unexpectedly increased. However, it disintegrates over time and becomes granular. The powdered bottom dross floats in the apparatus while being stirred with rising bubbles. The bubble blowing means 3 may have a structure in which gas for generating bubbles is sent from the outside to generate bubbles, or a gas cylinder or the like which is a source of bubbles. As a gas for generating bubbles, a gas inert to molten zinc, such as nitrogen, hydrogen, water vapor, gas carbonate, helium gas, argon gas, or ammonia is preferable. If the amount of bubbles blown from the bubble blowing means 3 is excessive, The gas stays in the device 1 for a short time, and passes through the device 1 without sufficient mixing and stirring power.On the other hand, when the mixing amount is too small, insufficient blow-up of the bottom dross and insufficient mixing and stirring occur. Since the object of the present invention will not be sufficiently achieved, it is preferable to set the range within an appropriate range.

The powdered bottom dross 11 which is blown up into the apparatus 1 by the blowing of the air bubbles and floats is mixed and stirred by the air bubbles, and reaches the metal aluminum holding section 4. In such a case, since the aluminum concentration in this portion has reached a high concentration due to the dissolution of the metal aluminum-containing ingot in the plating bath, the following reaction causes the bottom dross 11 to the top dross (F e ₂ The conversion to A l ₅ ) is performed.

2 F e Z n ₇ + 5 A 1 → F e ₂ A 1 ₅ + 1 4 Z n

The metal-aluminum-containing ingot held by the metal-aluminum holding section 4 may be a pure aluminum metal, or may be an alloy of aluminum and aluminum. Further, the shape may be rod-like or granular. Surprisingly, however, these metals, for example metallic aluminum, have a melting point of about 660 ° C, which is much higher than the galvanizing bath temperature of about 440 ° C, It is not expected to dissolve. Nevertheless, according to the present invention, it has been found that in the case where bubbles exist, the metal-containing ingot dissolves in the plating bath and the above reaction proceeds.

The amount of the metal aluminum ingot in the metal aluminum holding section 4 is preferably set at 1 theoretical equivalent, in order to supply aluminum at a concentration necessary for converting iron contained in the bottom dross into top dross by the above reaction. 0% to 130% is used. In addition, the amount of aluminum ingots can be increased to compensate for the aluminum loss associated with plating in the plating bath. When an alloy of zinc and aluminum is used as an ingot in this case, the melting temperature of the alloy can be controlled by changing the composition of the aluminum metal in the alloy. Metal zinc can be supplied to the bath at the same time.

Due to the above reaction, the bottom dross, part of which changed to top dross, The inlet port has a low specific gravity and reaches the primary mixing reaction section 5 of the apparatus by the upward flow caused by the bubbles. In the primary mixing reaction section 5, since the aluminum concentration is further increased by passing through the metal aluminum holding section 4, the bottom dross 11 floated, and further react with the aluminum to change into a top dross.

The secondary mixing reaction section 6 of the apparatus 1 is a place where the bottom dross 11 is further transformed into a top dross by reducing the diameter of the cross section of the cylindrical body and performing high-speed and rapid mixing and stirring. In the secondary mixing reaction section 6, preferably, a plating bath solution is supplied from the plating bath solution suction section 7 to the inside of the apparatus by an ejector effect by reducing the diameter of the cross section, as shown in FIGS. 1 and 2. Incorporated in.

The zinc plating bath containing the bottom dross 11 that has passed through the secondary mixing reaction section 6 is mixed with the plating bath introduced from the plating bath suction section 7, and then the tertiary tertiary located above It moves to the mixing reaction section 8, where the reaction to the top dross can be further advanced. After the reaction has sufficiently proceeded in the tertiary mixing reaction section 8, the plating bath solution is discharged from the top opening 9 of the apparatus 1 and returned to the zinc plating bath solution 10. The plating bath discharged from the top opening 9 is mixed with the plating bath introduced from the plating bath suction unit 7, and the aluminum concentration contained therein is considerably reduced. Does not change much.

The plating bath obtained in the tertiary mixing reaction section 8 contains the top dross force generated by the reaction, but since these tops have a small specific gravity, they are formed on the surface of the plating bath at the same time. Since it floats, it can be easily removed.c.Therefore, the liquid discharged from the top opening 9 and returned to the plating bath is hardly contained in the liquid, which is within the operational problems of the plating bath. Has decreased to

As described above, placed in the zinc-plated tank, bottom dross removal Shinano force ⁵ 'et al in their areas, or after the removal or has been completed, the device 1 is to move to another part of the zinc plated tank Then remove the bottom dross in the area through the same process as above: In this way, first, the apparatus 1 is placed at one end of the zinc plating tank, and the plating tank is sequentially moved toward the other end. By doing so, the bottom dross of the entire galvanizing tank can be easily removed. FIG. 3 shows another example of a method and apparatus for removing a bottom dross according to the present invention, which is applied to a relatively small zinc plating tank. In FIG. 3, the same numerical values indicate the same as those in FIGS. 1 and 2. In FIG. 3 as well, the apparatus 1 is provided with a bottom opening 2 serving as a bottom dross receiving port, a bubble blowing means 3 for generating bubbles, and a metal aluminum holding section 4 for holding a metal aluminum containing ingot. Because of the power and the small zinc plating bath, mixing is not possible. Only the primary mixing reaction section 5 is provided. Further, the apparatus shown in FIG. 3 has a double wall having an outer wall 20 and is provided with a circulation path 21 for circulating the plating bath solution after the reaction from above to below. This is because, in the case of a small plating bath, since the liquid holding capacity of the plating bath is small, the liquid is circulated internally, so that the aluminum concentration difference between the plating bath inside and outside the device is reduced before returning to the plating bath. This is because it is preferable. Also in the apparatus shown in FIG. 3, an opening is provided in the bottom side wall, so that the inside of the apparatus and the plating solution in the plating bath can flow freely.

In the method and the apparatus for removing bottom dross according to the present invention, as the bubble blowing means, 10 to 90 parts by mass of an inorganic compound which thermally decomposes and foams at a temperature equal to or lower than the temperature of the hot-dip galvanizing bath; It has been found to be extremely advantageous when a composition containing 90 to 10 parts by mass of a nitrogen-containing organic compound which is thermally decomposed and foamed at a temperature not higher than the temperature is used.

In such a case, a device for sending gas from the outside to a hose or the like in order to generate air bubbles in the bottom dross removing device 1 is not required, so that the device can be easily stored in the device. This is because the properties of the gas to be generated, the amount generated per hour, and the generation time can be suitably controlled by the combination of the inorganic compound and the nitrogen-containing organic compound.

As used herein, the inorganic compound which thermally decomposes and foams at a temperature lower than the temperature of the zinc plating bath has a thermal decomposition temperature of preferably 120 ° C. or higher, and water and monooxidation by thermal decomposition. Those that generate gases such as carbon, carbon dioxide, ammonia, and water vapor are preferred. Preferred examples of the inorganic compound include carbonates, bicarbonates, sulfates, and phosphorus such as alkali metals such as sodium and potassium, or alkaline earth metals such as calcium. Acid salts or nitrates. Specific preferred examples include sodium carbonate, sodium bicarbonate, calcium sulfate, ammonium chloride, and the like, and a crystalline material having water of crystallization thereof. These may be synthetic or natural products, and may be used alone or as a mixture.

On the other hand, the nitrogen-containing organic compound used in the present invention preferably has a thermal decomposition temperature.

It is preferable that the temperature be 120 ° C. or higher and generate a nitrogen-containing gas such as a nitrogen gas, a nitrite gas, and an ammonia gas. The nitrogen-containing gas is inert to galvanizing and covers the surface of the hot-dip zinc bath to effectively prevent the hot-dip zinc from oxidizing by contact with air. Preferred examples of such a nitrogen-containing organic compound include an azo compound, a hydrazine compound and a nitroso compound. Specific preferred examples include various compounds, among which azodicarboxylic acid bonamide, norium azodicarboxylate, N, N, dinitrosopentamethylenetetramine, hydrazodicarbonamide. , 4,4'-Monoxybis (benzenesulfonyl hydrazide, etc.) These are usually available as commercial products in the form of powder or granules.

In the present invention, the inorganic compound and the nitrogen-containing organic compound are used in the present invention as a composition containing 10 to 90 parts by mass of the former and 90 to 10 parts by mass of the latter. If the former ratio in the composition is smaller than the above range, the amount of foaming is small, and if it is larger than the above range, foaming is rapid and short, and the object of the present invention is not sufficiently achieved. Among the above ranges, a composition containing 25 to 75 parts by mass of the former and 75 to 25 parts by mass of the latter is preferable, and in particular, the former contains 40 to 60 parts by mass and the latter contains Compositions containing from 40 to 60 parts by weight are particularly preferred.

In the present invention, when the above-mentioned composition is used as the means for blowing bubbles, a force that can be used in the form of a granular mixture, and a granular mixture of such a composition, if necessary, a binder such as gypsum Can be mixed, kneaded using an appropriate medium such as water, and used as a molded article shaped into an appropriate size. In this case, the shape of the molded product may be any appropriate shape, but for convenience of transportation and handling, for example, a cylindrical shape, a rectangular tube shape, a spherical shape, and the like are selected. Further, it is preferable to use the composition, which is the bubble blowing means of the present invention, in a form in which a part thereof is exposed and coated with a coating material which does not disappear in a molten zinc bath. When the composition is immersed in the plating bath in such a coated form, the composition does not immediately decompose and foam, so that it is easy to control the degree of bubble generation and the time. In this case, by changing the exposed area by coating with the coating material, the decomposition of the composition is adjusted, the amount of generated bubbles can be controlled, and the predetermined amount of generated bubbles can be performed for a long time.

As the coating material, a material that does not disappear due to dissolution or decomposition in a molten zinc bath is preferable. In this case, the composition always covers a predetermined area with the coating material, so that a predetermined amount of bubbles can be generated for a long time. However, even if the coating material gradually dissolves, decomposes, or embrittles partially, if it is not abrupt, the amount of generated bubbles can be maintained without substantially changing.

As such a coating material, a naturally-occurring or synthetic various kinds of force ³ can be used, the paper material is preferably made of impact Karase cellulose to zinc bath, such as a gas generated by the speed and its melting or pyrolysis. As described above, the thickness of the coating material also affects the duration of the bubble generation amount, but is preferably 0.1 to 50 mm, particularly preferably 5 to 20 mm.

Example

Hereinafter, the present invention will be described in more detail with reference to examples of a method and an apparatus for removing bottom dross of a zinc plating bath of the present invention. However, it is needless to say that the present invention is not limited to these. .

Example 1

This example was carried out on an actual hot-dip galvanizing bath at Galva Kogyo Mihara Plant. The zinc plating bath had an iron box shape with a width of 2 m, a depth of 17 m and a depth of 3.4 m. The plating bath always had a plating bath volume of 75 tons. In addition, on the bottom plate of the bathtub, a molten lead layer having a thickness of about 10 cm is provided by a conventional method in order to prevent corrosion of the material iron due to zinc. About 1 0 cm was of the layers force ^s deposition of.

As a device for removing bottom dross, an apparatus having the form shown in FIG. 1 was used. The device was a square tube with a square cross section of 1.1 m wide and 1.1 m depth and a height of 3.05 m. Openings (height 30 cm x width 100 cm) through which the plating bath liquid can flow were provided on opposite side walls at the bottom of the cylindrical body. In addition, as a bubble blowing means, 10 bubble blowing ports are provided at a position 10 cm from the bottom toward the lower side of an inert gas (mixed gas of helium and argon) introduced from outside through a hose. At a position 40 cm from the bottom, a zinc / aluminum alloy ingot (composition: 30% zinc, 70% aluminum) was stored and held in a mesh so as not to float. In the middle part of the cylindrical body at a height of about 100 cm from the bottom, the cross section is narrowed to 40 cm in width and 40 cm in depth, and this part has a diameter of 20 cm. There were four openings around the periphery.

The amount of aluminum stored in the removal device is 0.002% to 0.005%, which is the aluminum concentration required to convert the bottom dross in the plating bath to the top dross and the aluminum concentration in the zinc plating bath. It is the sum of the amount of ^ ffi salary to maintain and was calculated according to the following formula.

That is, zinc.aluminum alloy amount (kg) 2 [input zinc amount (ton) X 0.8 + bottom dross removal amount (kg) X 0-03] no 0.7

In the above equation, 0.8 is a coefficient for calculating the amount of aluminum required to maintain the aluminum concentration in the plating bath solution. Were determined. In 0.03, the average composition of bottom dross is 97% for zinc and 396 for iron, so the amount of aluminum required to convert from bottom dross to top dross is approximately * equivalent to iron in the bottom dross. It is based on the theory of.

Thus, the amount of zinc-aluminum alloy attached to the removal device is calculated as (10 x 0.8 + 10), with the input zinc amount being 10 tons / day and the bottom dross removal amount being 1,000 kg g times. 0 0 X 0. 03) /0.7 = 54 kg. The amount of the zinc-aluminum alloy is an amount that gradually dissolves in the zinc plating bath in 30 minutes. The bottom dross removing device was settled down at one end of a zinc plating bath. In this case, the bubble outlet provided in the removing device was positioned below the bottom dross layer deposited on the bottom of the plating bath. Thus, the above inert gas was blown out from the bubble blow-out opening in the shredder, so that bubbles were blown into the bottom dross.

In this way, the bubbles were continuously moved toward the other end of the zinc plating tank while blowing bubbles into the bottom dross. The moving speed was 0.553 mZ, and the zinc tank was moved from one end to the other end in 30 minutes. The time required for such movement is 30 minutes, which is the same as the time required for the zinc-aluminum alloy mounted in the shredder to dissolve in the plating bath. Due to the blowing of the air bubbles, massive bottom dross deposited on the bottom of the bathtub became powdery and granulated and floated, and a considerable amount of plating generated by reaction with aluminum was observed on the valley surface. The top loss that floated on the plating bath surface was easily removed manually.

This removal operation was periodically tested three times a week for six months, and the condition of the zinc plating tank was examined before and during the test. The results are shown in FIGS. Fig. 4 is a graph showing the aluminum concentration distribution in the zinc plating bath solution of the example, and Fig. 5 shows the changes in the number of dross pumping of the zinc plating bath, the number of occurrences of dross flaws in the plated product, and the zinc basic unit in the example. It is a graph shown.

As can be seen from FIGS. 4 and 5, as a result of the work of removing the bottom dross, in the embodiment, the aluminum concentration in the zinc plating bath and the composition of the zinc plating bath were extremely uniform and stable. Could be maintained. In addition, the number of dross pumping in the zinc plating tank will be drastically reduced, and the zinc consumption per unit weight of the steel material to be plated will be improved compared to the conventional method, reducing the average by 8 kg / ton. did it.

Example 2

Use 16.2 kg of pure aluminum metal ingot instead of zinc alloy alloy ingot. The foaming agent composition was stored in the tube, and two cellulose paper cylindrical tubes (diameter 90 mm, length 200 mm) each having an open rain end were used. In addition, the removal equipment was not moved continuously in the plating bath, but was moved intermittently in the plating bath, which stopped at one location for 3 minutes. Except for this, the procedure was the same as in Example 1.

The foaming agent composition is a kneaded mixture of 3 kg of sodium bicarbonate (average particle size of 2 μπι) and 7 kg of benzenesulfonyl hydrazide (average particle size of 2 μτη) in water. The molded article was molded so as to be housed in the above-mentioned cylindrical tube. Further, the cylindrical tube containing the molded product is held horizontally at the bottom of the removing device so that when the removing device is immersed in the plating bath, both ends of the cylindrical tube are positioned below the bottom dross layer. Placed in

As a result, almost the same results as in Example 1 were obtained for the aluminum concentration distribution in the galvanizing bath solution and the number of times the dross was pumped in the galvanizing bath, but the basic zinc unit was zinc per weight of the steel material to be plated. The consumption could be reduced by an average of 10 kg Z tonnes, which could be further improved compared to Example 1. In addition, in the case of Example 2, in addition to using an inexpensive pure aluminum metal ingot instead of the expensive zinc-aluminum alloy, the weight of the ingot could be reduced to about 30%. Industrial applicability of the invention

Advantageous Effects of Invention According to the present invention, a novel bottom dross in a molten zinc plating bath capable of efficiently removing dross at low cost with a simple structure without substantially changing the bath liquid composition in the molten zinc plating bath. Removal method and equipment provided.

According to the present invention, the bottom dross in the zinc plating bath is converted to a top dross and efficiently removed, and the aluminum concentration and the composition of the zinc plating bath are maintained in a uniform and stable state. As a result, the finished condition of the plated product is improved and its quality is greatly improved. In addition, the number of times dross is pumped up in the zinc bath is drastically reduced, which reduces the work of pumping dangerous dross. Also contributes to safe operation. Furthermore, the unit consumption of zinc per unit weight of the steel material to be melted is reduced, and costs can be reduced.

Claims

The scope of the claims

1. In a method of removing a bottom dross mainly composed of an alloy of zinc and iron in a hot-dip galvanizing bath by moving a removing device continuously or intermittently in a hot-dip galvanizing bath, And a tubular body having an opening at the bottom, a bubble blowing means at the bottom, and a metal aluminum-containing ingot at the middle part, and the removing device is provided in a molten zinc plating bath. The bottom dross are blown into the apparatus together with the bubbles by blowing the bubbles to the bottom dross by the bubble blowing means, and the floated bottom dross is reacted with the metal aluminum-containing ingot. Molten zinc zinc, which is converted to a top dross mainly composed of an alloy of zinc and aluminum and floated, and the floated top dross is removed. How to remove the bottom dross of the bathtub.

2. The height of the tubular body is smaller than the depth of the hot-dip galvanizing bath, and the plating bath solution containing the top dross converted from the bottom dross is transferred from the top opening of the tubular body device into the hot-dip galvanizing bath solution. 2. The method for removing bottom dross according to claim 1, wherein the bottom dross is discharged and circulated.

3. The bottom dross according to claim 1, wherein the height of the cylindrical body is larger than the depth of the hot-dip galvanizing bath, and the plating bath liquid containing the top dross converted from the bottom dross is circulated through the cylindrical body. Removal method.

4. A cylindrical body having openings at the top and bottom, having a bubble blowing means at the bottom, and holding a metal aluminum-containing ingot in the middle section, and forming the cylindrical body into a molten zinc plating bath. It is immersed in a liquid so as to be movable continuously or intermittently, and is disposed. By the bubble blowing means, bubbles are blown into a bottom dross mainly composed of an alloy of zinc and iron, and the bottom dross is blown together with the bubbles into a cylinder. The bottom dross thus reacted is reacted with a metallic aluminum-containing ingot to produce zinc and aluminum. Bottom dross in a hot dip galvanizing bath, characterized in that the top dross is converted to a top dross mainly made of alloy with

5. The cross-sectional area of the middle portion of the cylindrical body above where the metallic aluminum-containing ingot is located is smaller than the cross-sectional areas of the lower portion and the upper portion, and has an opening near the middle portion. 5. The apparatus for removing a bottom dross of a molten zinc plating bath according to claim 4, wherein the plating bath liquid is introduced into the cylindrical body.

6. The bubble blowing means contains 10 to 90 parts by mass of an inorganic compound which thermally decomposes and foams below the temperature of the hot-dip galvanizing bath, and a foam which decomposes and foams below the temperature of the hot-dip galvanizing bath. 6. The apparatus for removing bottom dross from a hot dip galvanizing bath according to claim 4, which is a composition containing 90 to 10 parts by mass of a nitrogen organic compound.

7. The apparatus for removing bottom dross in a molten zinc plating bath according to claim 6, wherein the composition is partially exposed and coated with a coating material that does not disappear in the molten zinc plating bath.