JPH04337056A - Device and method for recovering bottom dross - Google Patents

Abstract

PURPOSE:To surely recover bottom dross in a short period of time by pulling up the bottom dross sticking to the exposed metallic surfaces of the box-shaped assembly which is provided in the bottom of a galvanizing bath cell and is partly opened together with the boxes. CONSTITUTION:The assembly of the box bodies 10, 12 which are partly opened is installed in the bottom of the galvanizing bath cell. The bottom dross is stuck and adhered to the exposed metallic surfaces and is pulled up together with the boxes upon lapse of the specified period of time, by which the bottom dross is removed. An expanded graphite sheet or woven fabric of ceramics, such as alumina, is held between the box bodies 10, 12 in order to facilitate the sepn. of the box bodies 10, 12 after pulling up from the plating bath cell, by which the box bodies 10, 12 can be taken out by each piece. The removal of the bottom dross of the galvanizing bath cell is facilitated in such a manner.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a bottom dross recovery device that can take out the bottom dross deposited in a hot-dip metal plating bath to the outside of the plating bath during hot-dip metal plating, particularly hot-dip galvanizing, and a bottom dross recovery device using the device. This invention relates to a bottom dross recovery method.

0002

2. Description of the Related Art As is already well known, in North America and Canada, roads are currently prevented from freezing by spraying rock salt to prevent motor vehicle slip accidents in winter. As a result of such spraying of rock salt, automobile bodies are exposed to a severe corrosive environment, and high corrosion-resistant surface-treated steel sheets are being used as materials. Therefore, alloyed steel sheets that have weldability and workability comparable to those of cold-rolled steel sheets and are also excellent in corrosion resistance and aesthetics are attracting attention as steel sheets for exterior use. However, in the hot-dip galvanizing tank where continuous hot-dip galvanizing of the strip is carried out, the Fe in the strip is eluted into the plating bath, producing dross whose main component is FeZn7, and this dross is deposited at the bottom of the plating tank. and forms bottom dross.

FIG. 7 is an explanatory diagram of the formation and winding up of bottom dross during such hot-dip galvanizing. In FIG. 7, a strip 3 sent to a plating tank 2 via a snout 1 is plated while going around a sink roll 4, and after plating is completed, it is taken out from the plating tank 2 via a snap roll 5. At this time, the dross floating in the plating bath gradually accumulates at the bottom of the plating tank 2 to form bottom dross 6. On the other hand, a part of the floating dross combines with Al in the plating bath and floats as top dross 7 at the top of the plating bath. The bottom dross 6 deposited in this way is rolled up into the plating bath by the accompanying flow of the strip 3 generated near the bottom of the sink roll 4, and is rolled up into the plating bath.
adheres to the surface of

As mentioned above, now that the specifications for galvanized steel sheets have become stricter, if such bottom dross 6 adheres to the surface of the strip 3, surface unevenness called press blemishes will occur during pressing, resulting in poor aesthetics. It is important to prevent the adhesion of dross because it not only worsens the corrosion resistance but also deteriorates the corrosion resistance. As the amount of dross deposited increases, dross defects occur frequently, so as a general method to prevent dross from adhering to the strip, the Al content in the plating bath is enriched and Fe2Al5 is
A method is known in which the top dross is brought to the surface and collected manually by scooping it up. 2FeZn7+5Al→ Fe2Al5 +14Zn

[
0005

[Problem to be solved by the invention] However, since Al has the effect of suppressing alloying of the plating film,
If the target of production is alloyed steel sheet, the amount is limited to the lowest possible amount, and if Al is added to promote top dross flotation, some of it will remain in the plating bath, causing poor alloying. This causes problems of quality deterioration. In particular, in view of the current demand for improved surface properties such as excellent image clarity even in alloyed steel sheets, a method for recovering dross that does not involve the addition of Al has become important.

[0006] Furthermore, in the method of enriching the Al content, a large amount of man-hours are required to recover the top dross, leading to an increase in manufacturing costs. Here, the first object of the present invention is to provide a bottom dross recovery device and method that can significantly reduce the number of recovery steps when recovering dross in a molten metal plating bath, especially bottom dross from a plating bath. It is in. The second object of the present invention is to recover bottom dross generated in the plating bath without increasing the Al concentration in the plating bath, especially when producing alloyed steel sheets under conditions where the Al concentration of the plating bath is low. An object of the present invention is to provide a bottom dross recovery device and method.

[0007]

[Means for Solving the Problems] The present inventors have conducted various studies in order to develop a means that can suppress the winding up of bottom dross and reduce the adhesion of dross to the strip. After learning that floating dross could be calmed down and the adhesion of dross to the strip could be reduced by installing a rectifying plate below the sink roll and performing hot-dip metal plating, he first applied for patent application No. 1-15083.
As No. 2, we proposed a method and device for suppressing bottom dross from rolling up. The configuration of the device according to this proposal is shown in FIG. In the figure, by installing a current plate 8 at the bottom of the plating tank 2 below the sink roll 4 and performing molten metal plating, it is possible to suppress the bottom dross from being rolled up. Note that the symbols in the figure are the same as those in FIG. 7.

[0008] By the way, the present inventors performed hot-dip metal plating using this apparatus and when the baffle plate was pulled up from the plating bath, the bottom dross adhered and solidified on the lower side of the baffle plate and It was discovered that the particles adhered to each other and were pulled up together with the current plate. When the current plate was not installed in the plating tank, the dross was in the form of sludge, and the phenomenon of dross coagulating and solidifying did not occur. Therefore, the present inventors investigated various causes of this coagulation and solidification phenomenon of bottom dross, and found that when molten metal plating is performed using the above-mentioned apparatus, the flow of the plating bath stagnates at the bottom of the current plate, causing bottom dross and the current plate to stagnate. This is thought to be due to an alloying reaction occurring between the two.

As a result of further studies, the inventors of the present invention found that by actively utilizing this adhesion and solidification phenomenon of bottom dross using appropriate means, the discharge of bottom dross out of the plating bath can be shortened. The present invention was completed based on the finding that the above-mentioned problems can be solved in a timely and reliable manner. The present invention is an apparatus for collecting bottom dross installed in a hot-dip metal plating bathtub, and the bottom dross collecting apparatus is composed of a plurality of box bodies each having at least a portion open. According to a preferred embodiment of the present invention, each box may be separable by interposing graphite or a ceramic material between each of the plurality of boxes.

In addition, from another aspect, the present invention is an apparatus for collecting bottom dross installed in a hot-dip metal plating bath, which comprises a plurality of boxes partitioned by partition walls. The bottom dross collection device is characterized in that at least a portion of each box is open to the outside. Still another aspect of the present invention is to install any of the bottom dross recovery devices described above at the bottom of a hot-dip metal plating bath to perform hot-dip metal plating, and then to take out the bottom dross recovery device from the hot-dip metal plating bath. This bottom dross recovery method is characterized in that bottom dross aggregated in the bottom dross recovery device is recovered. The present invention is applicable not only to alloyed hot-dip metal-plated steel sheets, but also to general hot-dip metal-plated steel sheets that do not require alloying treatment.

[0011]

[Operations] Hereinafter, the present invention will be explained in detail together with its functions and effects with reference to the accompanying drawings. FIGS. 1(a) to 1(e) are schematic explanatory diagrams illustrating various shapes of "a box with at least a portion open" constituting the bottom dross recovery device according to the present invention. In the figure, it is assumed that the flow of bottom dross is seen in the direction of the arrow, that is, the surface is open. The same applies to each drawing below.

FIG. 1(a) shows a rectangular parallelepiped or cubic box, for example, a box 10 with an open bottom.
) shows a box 12 similar to that shown in FIG. 1(a) with open sides; FIG. 1(c) shows a polyhedral box 14 with open sides; FIG. 1(d) shows a cylindrical box 16 with partially open sides, and FIG. 1(e)
1 and 2 respectively show a box 18 which is a cylindrical box and has an open bottom surface, but the shape of the "box with at least a part open" in the present invention is not limited to these shapes only, and other shapes may be used. It may be a polyhedron such as a regular tetrahedron, a cube, a regular hexahedron, a rectangular parallelepiped, a triangular pyramid, a cylinder, or the like.

[0013] This box body is made of stainless steel, for example, which can react with the bottom dross in the plating bath to cause an alloying reaction and can sufficiently withstand corrosion by the plating bath.
It is composed of pure iron, mild steel, Ni alloy, etc.
As long as bottom dross aggregates and adheres, and such aggregated bottom dross does not adversely affect metal plating processing, there is no restriction to a specific material or shape. The open portions of each surface of the box are not particularly limited, as long as they can accept floating dross and aggregate bottom dross deposited inside. However, in general, FIGS. 1(a) to 1
As illustrated in (e), it is the bottom surface or the side surface. One aspect of the bottom dross recovery device according to the present invention is shown in FIG.
As shown in FIGS. 2(a) and 2(b), it is constructed by stacking a plurality of each of the boxes shown in FIG. 9
It is composed of individuals and aggregations.

FIG. 2(a) is similar to FIG. 1(a) or FIG. 1(b).
), and FIG. 2(b) shows a bottom dross recovery apparatus according to the present invention, which is constructed by assembling a plurality of box bodies 10 and 12 of FIG. 1(d) or FIG. 1(e), respectively. FIG. 2 is a schematic explanatory diagram showing a configuration example. However, in FIG. 2, the boxes are simply assembled, and if the bottom dross aggregates or adheres, they are taken out one by one and the bottom dross is collected. Note that in the same figure, arrows indicate the flow of bottom dross. By installing this box-shaped dross recovery device at the bottom of the plating bath, that is, between the sink roll in the plating bath and the bottom of the plating bath, the flow of the plating bath stagnates in the device, and the dross deposited inside the device can be removed. An alloying reaction occurs between the bottom dross and the metal material constituting the box, and the bottom dross adheres and solidifies on the device. Therefore, by pulling up the apparatus from the plating bath after a predetermined period of time, the bottom dross can also be pulled up at the same time, so the bottom dross can be recovered in a short time and without enriching the Al concentration of the plating bath.

[0015] In this apparatus, in order to facilitate the separation of each box after being lifted from the plating bath, the plating bath and the The boxes can be taken out one by one by sandwiching graphite or ceramics that have poor wettability with both dross, such as expanded graphite sheets or woven fabrics of ceramics such as alumina, magnesia, zirconia, silicon nitride, and silicon carbide. It is desirable that the dross adhered to each box body can be separated and taken out. FIG. 3 is a schematic perspective view showing another embodiment of the present invention, and is a schematic perspective view showing another embodiment of the present invention, and is
An example is shown in which partition walls 23 are appropriately provided below the shielding plate 20 disclosed in No. 50832, and a plurality of boxes 24 are respectively constructed. In the case of this example, when the bottom dross aggregates and adheres, it is necessary to take out the entire shielding plate 20 from the plating bath.

FIG. 4 is made up of a plurality of boxes 10 as in FIG. A covered lid body 30 is provided. The lid body 30 and each box body 24 may be fastened together through bolt holes 32. Note that the separation material 28 is shown filled in black in the drawing. In addition, in the bottom dross recovery device according to the present invention, in order to make the upper end surface formed thereby also function as a shielding plate as mentioned in the above publication, the entrance direction and/or exit direction of the metal plate to be plated into the plating bath is controlled. It is desirable to provide inclined surfaces that are inclined in the same direction in the lateral directions in order to suppress the bottom dross from flying up into the plating bath.

[0017]

[Example] In this example, the hot-dip galvanizing tank 2 is
Various dimensions (m
A bottom dross recovery device 50 having the following configuration was provided, and conventional alloying hot-dip galvanizing was performed. However, Fig. 5 (a
), an example using the box shown in Figure 2(b) is Type A, an example using the box shown in Figure 2(a) is Type B, and Figure 5(b) is an example using Figure 2(a). ) Type C is an example using a box body, and Type B and C are respectively shown in Figure 5.
Examples in which the boxes are assembled with a graphite sheet interposed as a separating material as shown in (c) are referred to as types D and E, respectively. The Al concentration of the hot-dip galvanizing bath is actually 0.09 to 0.1.
It was 1%.

As for the integrated types A, B, and C, the amount of dross deposited was measured every month, and immersion was repeated again to continue operation. Separate type types D and E have an expanded graphite sheet and a woven ceramic fabric sandwiched between them, and each box is separated and removed each time it is lifted.
Only the box body was replaced with a new one. The relationship between the number of months that has passed and the amount of dross adhesion is shown graphically in Figure 6(a). Figure 6(b)
) shows the correlation between the monthly collection amount and the cumulative total in a graph. On the other hand, FIG. 6(c) is a graph showing the correlation between the number of days elapsed and the Fe concentration in the bath with and without a type C bottom dross recovery device.

From these, the following can be seen. (1) When repeatedly immersed, the amount of dross adhering increases in proportion to the number of days that have passed, indicating that adhesion is progressing. (2) In the case of the separation type, when the box was pulled up six times every month, separation was performed with dross adhered to the inner surface of the box, and the separation was completed without any problems. (3) As a result of measuring the Fe concentration in the plating bath for one month after the start of plating using atomic absorption spectrometry, it was found that according to the present invention, dross is prevented from floating by adhering to the metal box; There was no increase in concentration. In comparison, in the conventional method that does not use a dross recovery device, the Fe concentration sharply increased after 10 days passed and the amount of plating exceeded 9000 tons. (4) In the case of using a separate type with a ceramic woven fabric sandwiched in between, the operation was carried out in exactly the same manner, and similar results were obtained. As described above, it has been found that according to the present invention, a cleaner plating solution can be ensured compared to conventional methods, and this state can be maintained for a long period of time.

[0020]

[Effects of the Invention] According to the present invention, bottom dross can be easily recovered in a cohesive state without enriching the Al content in the plating bath. Furthermore, since dross adheres to the metal box during plating and promotes adhesion, the amount of floating dross in the bath due to winding is reduced, making it possible to clean the plating bath, and other practical benefits of the present invention. is large and has great significance in industry.

[Brief explanation of drawings]

FIG. 1A to FIG. 1E are schematic explanatory views showing examples of boxes constituting a bottom dross recovery device according to the present invention.

FIGS. 2(a) and 2(b) are schematic explanatory diagrams showing how boxes are assembled.

FIG. 3 is a schematic illustration of another modification of the invention.

FIG. 4 is a schematic illustration of yet another modification of the present invention.

FIGS. 5(a) to 5(c) are explanatory diagrams of an example of the arrangement of the bottom dross recovery device seen in the embodiment of the present invention.

FIG. 6(a) to FIG. 6(c) are graphs summarizing the results of Examples.

FIG. 7 is a schematic diagram illustrating how bottom dross is deposited in a conventional metal hot-dip plating bath.

FIG. 8 is a schematic explanatory diagram of a molten metal plating tank provided with a current plate.

[Explanation of symbols]

10, 12, 16, 18, 24: Box 20:
Shielding plate 22: Partition wall 28: Separation material 30: Cover body 32: Bolt hole

Claims (4)

[Claims] 1. A bottom dross recovery device installed in a hot-dip metal plating bathtub to recover bottom dross, the bottom dross recovery device comprising a plurality of box bodies each having at least a portion open. 2. The bottom dross recovery device according to claim 1, wherein each of the plurality of box bodies is configured to be separable by interposing graphite or ceramic material between each of the plurality of box bodies. 3. A device installed in a hot-dip metal plating bathtub to collect bottom dross, comprising a plurality of boxes divided by partition walls, at least a part of each of which is located outside the bath. A bottom dross recovery device characterized by being open to 4. After installing the bottom dross recovery device according to any one of claims 1 to 3 at the bottom of a molten metal plating bath and performing molten metal plating, the bottom dross recovery device is removed from the bottom of the molten metal plating bath. A method for recovering bottom dross, which comprises taking out and collecting aggregated bottom dross in the bottom dross recovery device.