JPH0368746A - Method and device for decreasing sticking of dross - Google Patents

Abstract

PURPOSE:To suppress the soaring up of bottom dross by a band steel and to prevent the sticking of the dross to the plating surface of the band steel by providing a build-up part having a projecting surface in the bottom below a sink roll in a plating bath at the time of continuously forming hot dip metal coating on the surface of the band steel. CONSTITUTION:The band steel 14 is advanced from a snout 10 into a galvanizing bath 13 and is pulled up perpendicularly by a sink roll 16. While the band steel is pulled up from the plating bath 13 through guide rolls 18, the surface of the band steel 14 is galvanized. The bottom dross 20 essentially consisting of the FeZn7 by the eluted Fe of the band steel and the Zn of the plating bath deposits on the bottom of a plating cell 12 in this case and this dross sticks to the plating surface of the band steel and degrades the quality of the galvanized band steel. The projecting part of the height H higher than the deposition height (h) of the bottom dross 20 is provided in the bottom below the sink roll 16 in order to prevent such deposition. The spacing of the plating bath between this part and the bottom dross 20 is narrow and the flow velocity of the plating bath 13 is high; therefore, the deposition of the bottom dross atop the build-up part is obviated. The sticking of the dross on the surface of the galvanized band steel and the degradation in the quality are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for suppressing bottom dross from rolling up and reducing dross adhesion in continuous molten metal plating.

(Prior art) In a hot-dip galvanizing line (hereinafter, "hot-dip galvanizing" will be explained as a typical example of "hot-dip metal plating"), ordinary hot-dip galvanized steel sheets in the as-plated state,
An alloyed steel sheet (galvanized steel sheet) is manufactured which is subjected to an alloying treatment after plating, but generally these two types of steel sheets are manufactured continuously on the same line by appropriately changing the manufacturing processing conditions.

However, in the hot-dip galvanizing bath where the strip is continuously hot-dip galvanized, the Fe in the strip is eluted and dross containing FeZny as a main component is generated, and this dross is used for hot-dip galvanizing as shown in Figure 1. Deposits at the bottom of the tank.

FIG. 1 is an explanatory diagram of how bottom dross is generated and rolled up during hot-dip galvanizing, and the strip 14 sent to the plating bath 13 in the plating tank 12 via the sunuro 0 passes through the sink roll 16. It is plated while rotating, and after plating is completed, it is taken out from the plating tank via a guide roll 18.

The dross floating in the plating bath gradually accumulates at the bottom of the plating bath, forming bottom dross 20. A part of the floating dross combines with AQ in the plating bath and forms top dross 2 at the top of the bath.
Floating as 2.

The bottom dross 20 deposited in this way is sink roll 1
6 and attached to the strip 14, causing quality defects in the plated steel sheet.

If such bottom dross adheres to the strip, uneven surface areas called press bumps will occur during pressing, which will not only impair the sharpness of the image when painted, but also
This creates surface defects that form the basis of local batteries and reduce corrosion resistance, resulting in quality defects in the plated steel sheet.

Conventionally, as a general method to suppress the generation of bottom dross, the AQ content in the plating bath is enriched, and the Fe
There is a way to recover JQs as top loss.

2FeZn, +5AQ → FetAQs+14Zn However, since AQ has the effect of suppressing alloying of the hot-dip galvanized film, when the target of manufacture is alloyed steel sheet, the presence of enriched AQ as described above will cause alloying. This results in defects and quality deterioration.

(Problem to be Solved by the Invention) Currently, in North America and Canada, anti-freezing roads by spraying rock salt is widely practiced in order to prevent motor vehicle slip accidents in winter.

However, automobiles are exposed to a harsh corrosive environment, and high-corrosion-resistant surface-treated steel sheets are increasingly being used as materials. As for exterior steel sheets, alloyed steel sheets are attracting attention because they have weldability and workability comparable to those of cold-rolled steel sheets, and have excellent corrosion resistance. In particular, steel plates for exterior use are required to have good image clarity and are strongly required to be free of defects such as dross.

Against this background, there is a strong demand for the development of a technology for suppressing bottom dross adhesion onto steel sheets, even for alloyed steel sheets manufactured under conditions of low AQ concentration.

Thus, as mentioned above, the present invention suppresses the adhesion of bottom dross and improves the plating appearance without increasing the FQ concentration when manufacturing alloyed steel sheets, in response to the situation where specifications for plated steel sheets have become stricter. An object of the present invention is to provide a method and apparatus for manufacturing a plated steel sheet with excellent corrosion resistance.

That is, the general object of the present invention is to provide AQiil! An object of the present invention is to provide a technology for suppressing bottom dross adhesion to alloyed steel sheets manufactured under low-density conditions (bottom dross-rich conditions).

(Means for Solving the Problems) Therefore, in order to achieve the above-mentioned object, the present inventors have developed a method for suppressing the winding up of bottom dross and reducing dross adhesion, based on the results of hydrodynamic studies. We have discovered a device that achieves this, and have completed the present invention.

In other words, through a 1/3 water model experiment that takes into account hydrodynamically similar conditions to the plating tank found on the actual production line,
The effectiveness of various shielding plates in suppressing winding up was investigated. Based on these findings, we conducted a test using an actual plating tank and reconfirmed the effect with accuracy very close to the predicted results obtained in the model experiment, thereby completing the present invention.

Here, the gist of the present invention is to provide a raised portion in the area located below the sink roll at the bottom of the molten metal plating tank to suppress floating and rolling up of bottom dross accumulated at the bottom of the plating tank. This is a method for reducing dross adhesion to hot-dip metal plated steel sheets.

In addition, from another aspect, the present invention is characterized in that a region at the bottom of the molten metal plating tank facing the lower part of the sink roll has a raised part for suppressing the rise of bottom dross accumulated at the bottom of the plating tank. This is a device for reducing dross adhesion during special-resistant metal plating.

According to a preferred embodiment of the present invention, the shape of the raised portion is a cube, a truncated pyramid, or an upwardly convex curved surface. Although these protrusions may be formed integrally from the bottom of the container, it is generally convenient to arrange block bodies of each shape below the sink roll.

(Operation) Next, the present invention will be described in more detail with reference to the accompanying drawings, but it will be understood that these are merely illustrative of the present invention, and the present invention is not limited thereby. .

FIGS. 2(a), ω), (C)-1, and (C)-2 show examples of plating tank shapes based on the water model of the present invention. The following explanation will be given using FIG. 2. The same reference numerals as in FIG. 1 indicate the same members.

Fig. 2(a) shows an example of a rectangular parallelepiped shape, Fig. 2(a) shows an example of a trapezoid, and Fig. 2(C)-1 and (C)-2 show examples of upwardly convex curved surfaces. FIG. 2(C)-1 is an example of a spherical shape. In the figure, h is the height of the accumulated dross in contact with the ridge, and H is the height of the top of the ridge.

In the case of the illustrated example, referring to FIG. 2(a) as a representative example, the steel plate 14 to be plated entering the plating bath 13 is pulled up through the sink roll 16 and comes out, but the plating at the bottom of the sink roll is Since the bottom of the tank is raised, the flow velocity at the bottom of the sink roll 16 becomes faster, and no dross can accumulate at the bottom of the sink roll, so that the steel plate to be plated 1
4 and the rotation of the sink roll 16 do not cause the bottom dross 20 to be rolled up, and the dross does not adhere to the steel plate.

Therefore, from this, the raised part provided below the sink roll in the present invention has a specific shape as long as the flow velocity of the plating bath in that area is higher than that in the surrounding area when the plated steel plate passes through. Not restricted.

In addition, with the conventional plating tank shape, dross tends to accumulate at the bottom of the sink roll, so for example, from 70 m/win to 1
When the threading speed of the steel plate to be plated increases to 00+s/win, the dross is violently rolled up, and a large amount of dross adheres to the steel plate.

Next, the present invention will be explained in more detail with reference to Examples thereof.

Example 1 In this example, a continuous plating water model test was conducted in the following manner.

■Acrylic powder (specific gravity 1.2, particle size 250 m) was added as a simulated dross to 173 water model of an actual plating tank.

(2) The amount of acrylic powder rolled up was measured and compared using the plating tank shape of the present invention and a conventional type (without a raised part).

The shape of the raised portion at the bottom of the plating tank according to the present invention is as follows:
As already mentioned, examples include:

A, Rectangular parallelepiped shape (Figure 2 (a)), B, truncated pyramid shape (Figure 2 (b)), curved surface convex on C0 (Figure 2 (C)-1, (C)-2)
) Approximately 5 ounces of solution from the top of the strip just before the sink roll.
00 cc was sampled, and after filtration treatment, the amount of winding up was evaluated by measuring the weight of the residue.

The results of these tests are summarized in a graph in FIG. The illustrated example shows a comparison between a case where a rectangular parallelepiped type is used and a conventional device having no raised portion. As is clear from this, according to the present invention, the amount of dross hoisted is 83
% reduction.

Next, as can be seen from the results shown in FIG. 3, the amount of winding changes over time but becomes approximately constant after 40 minutes, so the effects of each raised portion were compared using data after 40 minutes.

For comparison, the effects of the plating tank shape of the present invention are compared and shown in relative values, assuming that the amount of roll-up in the conventional type is 100%.

Table 1 shows the test results.

Table 1 Example 2 Based on the knowledge obtained in Example 1, a test was conducted using an actual plating tank to investigate the effects of the present invention.

The test method in this example was performed as follows.

■A hot-dip galvanizing bath shown in Fig. 4 in which the raised portions were in the shape of a rectangular parallelepiped was used. For other shapes, stainless steel blocks shown in FIGS. 5(a), 5(b), and 5(c) were fixed to the bottom of a conventional plating bath, and the shapes were similar to those of the water model.

Numbers in the figure indicate dimensions (*m).

■The operation mode was limited to the production of GAI plates.

(The actual AQ concentration of the plating bath is 0.09 to 0.11%.
Met. ) ■The sample collection area was set to board width x 500III, and the number of dross adhered to the surface (contact side of the sink roll) was investigated.

Note that the number of N was 50, and data comparison was performed using a simple average.

According to these test results, as shown in Table 2, in the case of the present invention, the number of dross deposits is reduced for all raised parts, but especially when the raised part at the bottom of the plating tank is shaped like a rectangular parallelepiped. In this case, the effect was found to be significant, as was found in the water model test.

Note: See Figure 5).

Example 3 A long-term test was conducted using an actual GA plating apparatus in which the protrusion at the bottom of the plating tank shown in FIG. 4 has a cubic shape. The plate passing speed was 120 m/l1in.

As a result, an increase in dross adhesion to the plated steel plate surface was observed after 60,000 tons of steel plate was plated.When we measured the bottom dross accumulation status, we found that a large amount of dross accumulated on the snout side, and on the top surface of the ridge. An influx of dross had also begun. See Figure 6(a).

Therefore, after 70,000 tons of plating processing, the accumulated dross is pumped out of the plating tank and the height of the accumulated dross is h
After confirming that the height had been lowered from the top of the ridge, threading continued. Figure 6 (b) shows the situation of bottom dross after pumping out.
).

As a result, as shown in the graph of FIG. 7, the amount of dross deposited could be reduced to the same level as at the start of the test.

(Effects of the Invention) As explained above, according to the present invention, dross adhesion can be reduced even under bottom dross-rich conditions, which was the biggest quality issue for hot-dip galvanized alloy treated steel sheets for exterior use, without changing the AQ concentration. , can be distantly related to hydrodynamic means.

In particular, when the raised portion is cubic, it is possible to reduce bottom dross by 80%, which has great practical significance, and the industrial usefulness of the present invention is remarkable.

[Brief explanation of drawings]

Figure 1 is a schematic explanatory diagram of various dross generation situations; Figures 2 (a), (b), (C)-1, and (C)-2 each show examples of raised portions used in the present invention. Abbreviated illustration;
Figure 3 is a graph showing the results of the example of the present invention in comparison with the conventional example; Figure 4 is an explanatory diagram of the shape and dimensions of the plating bath used in the example; Figure 5 (a), middle ) and (C) are schematic perspective views of the raised portions used in the examples, respectively; Fig. 7 is a graph showing the results. 10: Snout 12: Plating bath 14: Strip 16: Sink roll 18: Guide roll 20: Bottom dross 22 Nidotsubudros

Claims (4)

[Claims] (1) To a molten metal plated steel sheet characterized by providing a raised portion in the area located below the sink roll at the bottom of the molten metal plating tank to suppress floating and lifting of bottom dross accumulated at the bottom of the plating tank. method for reducing dross adhesion. (2) When controlling the amount of bottom dross accumulated at the bottom of the plating tank, the plate is passed so that the height of the accumulated dross that comes into contact with the raised part is maintained at a level below the top of the raised part. The method for reducing dross adhesion according to claim 1. (3) In the molten metal plating tank equipment, at the bottom of the tank,
A device for reducing dross adhesion to a molten metal plated steel sheet, characterized in that the area facing the lower part of the sink roll has a raised part that suppresses the rise of bottom dross accumulated at the bottom of the plating tank. (4) The molten metal plating apparatus according to claim 2, wherein the shape of the raised portion is a cube, a truncated pyramid, or an upwardly convex curved surface.