JPH04276052A - Device for removing oxide in snout in hot-dip metal coating - Google Patents

Abstract

PURPOSE:To prevent the adhesion of the oxide dross of plating metal to the surface of a steel sheet to be plated and also to prevent the occurrence of plating defects by blowing an inert gas against the steel sheet to be plated in the width direction of the steel sheet in a snout in a hot-dip metal coating apparatus. CONSTITUTION:A steel strip 1, surface-cleaned by annealing in an annealing furnace 2 with nonoxidizing atmosphere, is passed through a snout 4 connected to the annealing furnace 2 and then passed through a hot-dip metal coating bath 5, such as molten Al, to undergo the formation of hot-dip aluminizing or alloyed aluminizing bath on the surface, which is pulled up from the plating bath 5. An inert gas 7 is blown through a nozzle 8 toward the width direction of the steel sheet 1 in the snout 4 to blow the oxide dross on the surface of the hot-dip aluminizing bath 5 in the snout 4 toward a dross pit 10 on the opposite side, by which the adhesion of the dross 9 to the steel strip 1 surface and the occurrence of an uncoated part in the above part can be prevented and a superior aluminizing or Al-alloy coating layer can be formed. Further, the dross 9 in the dross pit 10 is taken out toward the outside without deteriorating the inert atmosphere in the snout 4.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to oxide (dross) in a snout in a molten metal plating apparatus using molten metal such as molten aluminum, molten aluminum alloy, and molten zinc.
Relating to a removal device.

0002

2. Description of the Related Art Hereinafter, hot-dip aluminum plating will be explained as an example. Hot-dip aluminum plated products have corrosion resistance and
Stainless steel sheets have excellent heat resistance, and recently, the surface of stainless steel sheets, which generally have excellent corrosion resistance even in an unplated state, is further coated with hot-dip aluminum.

[0003] Conventionally, hot-dip aluminum-plated steel sheets have been processed by removing oils and fats adhering to the surface using a cleaning device, and then heating the steel strip in a reducing atmosphere without exposing it to the outside air, as shown in Figure 1. The plating is then introduced into the molten aluminum in the snout, which is also protected in a reducing atmosphere. In the figure, 1 is a steel strip, 2 is an annealing furnace, 3 is a turning roll, 4 is a snout, 5 is a plating bath, and 6 is a sink roll.

[0004] When applying this aluminum plating, since the aluminum in the molten state is very easily oxidized, a film of aluminum oxide is formed on the bath surface, and this film adheres to the surface of the steel strip, causing the molten aluminum and the steel strip to oxidize. As a result, so-called non-plating occurs in which no plating is performed on the adhered portion of the film. In addition, the aluminum bath temperature is set above the melting point of pure aluminum or an aluminum alloy containing a small amount of alloying components, and at this temperature dross is generated due to oxides, and in particular, dross generated in the snout adheres to the steel strip. Detracts from the quality of plated products.

[0005] In order to prevent the adverse effects of this dross, various methods have been proposed, including the following. (1) To prevent the generation of dross, the plating bath temperature was
The part of the snout connected to the aluminum plating bath, which is connected to the aluminum plating bath from the continuous annealing furnace, is heated to 50° C. or lower. (Japanese Unexamined Patent Publication No. 57-131355) (2) Use an inert gas inside the snout to prevent oxidation. (Unexamined Japanese Patent Publication No. 60-43476) (3) Aluminum oxide adhering to the steel strip is wiped off by a wiping body that comes into contact with the surface of the steel strip. (Jitsukai 53-
(4) The dew point of the protective gas at the part where the steel strip is introduced into the bath is -40.
The temperature shall be below ℃. (5) Install a dross removal rotating roll on the bath surface of the steel strip introduction part in the snout. (Unexamined Japanese Patent Publication No. 51-56738)
(6) Dross in the snout is removed by sweeping the inside of the snout with nitrogen gas containing a small amount of hydrogen and having a dew point below a specific temperature. (Japanese Unexamined Patent Publication No. 57-11390) However, each method has drawbacks, and non-plating cannot be completely prevented.

That is, in method (1), by heating the plating bath in the snout, dross is generated, even partially, and cannot completely prevent adhesion to the steel strip. In method (2), if the inside of the snout is simply filled with an inert gas, for example, dross and the like that initially adhere to the inner wall of the snout will fall onto the snout bath surface and adhere to the steel strip. Furthermore, it is not practical to remove these deposits before plating because it is industrially extremely difficult. In method (3), since aluminum oxide adhering to the steel strip is removed by wiping with a wiping body, deterioration of the wiping body is expected, so the wiping body is always kept in uniform contact with the surface of the steel strip to ensure sufficient removal. It's not realistic to do so. Further, due to the contact state, flaws occur on the surface of the steel strip, which impairs the appearance. The method shown in (4) requires a large amount of gas because this atmospheric gas protects the aluminum bath surface and performs a reductive cleaning action on the steel strip, and the dew point of this large amount of gas is kept below -40℃. To lower the temperature, it is necessary to install many dryers for gas drying, which increases equipment costs.In addition, it is difficult to maintain and manage the dew point of a large amount of atmospheric gas to below -40℃, and the dew point often rises, resulting in failure. Plating occurs. In the method (5), it is difficult to keep the removed dross away from the vicinity of the steel strip immersion bath surface at all times, and it cannot be said to be a sufficient solution for production on an industrial scale. Method (6) simply blows out with nitrogen gas, and in some cases, some of the bath may be splashed from the bath surface, adhere to the inner wall of the snout, be cooled, and fall back onto the bath surface inside the snout. As a result, it is carried into the steel strip and becomes a defect. Similarly, depending on the flow rate of nitrogen gas and the direction in which it is sprayed, the above-mentioned splash problem may occur, or if the flow rate is too small or the spray angle is too large with respect to the bath surface, sufficient effects may not be obtained.

[0007]

[Problems to be Solved by the Invention] An object of the present invention is to overcome the difficulties in preventing non-plating caused by the prior art and to provide an apparatus that can perform hot-dip metal plating stably for a long period of time without any plating defects. It is something.

[0008]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention is directed to melting a steel strip from a continuous annealing furnace of an apparatus that performs hot-dip metal plating by continuously immersing a steel strip in a molten metal bath. A molten metal characterized in that the snout leading to the metal bath is provided with a nozzle directly above the molten metal bath surface for spraying an inert gas onto the molten metal bath surface from one end of the snout in the width direction of the steel strip to the other end. The present invention provides an apparatus for removing oxides in a snout in plating, and the above apparatus can have an oxide reservoir in the snout on the inner surface of the snout facing the nozzle, and the lower end of the snout prevents the snout from penetrating into the molten bath. A weir plate is provided on the nozzle side of the inner surface facing the nozzle of the moving section, the depth of penetration into the molten bath is shallower than the penetration depth of the molten bath on the outer periphery of the moving section, and the inner surface The space between the weir plate and the weir plate can be opened to the atmosphere.

[0009]

[Operation] The apparatus of the present invention will be explained with reference to the drawings. Fig. 1 is a schematic longitudinal cross-sectional view showing the positional relationship between the steel strip and the snout in the present invention, Fig. 2 is a schematic cross-sectional view showing the installation position of the spray nozzle in the present invention, and Fig. 3 is a schematic longitudinal cross-sectional view showing the positional relationship between the steel strip and the snout in the present invention. It is a perspective view showing the positional relationship with the spray nozzle, and in the figure,
1 is a steel strip, 2 is an annealing furnace, 3 is a turning roll, 4 is a snout, 5 is a plating bath, 6 is a sink roll, 7 is an inert gas, 8 is a spray nozzle, 9 is dross, and a is an inert gas This is the gap with the inner surface of the snout.

According to the method of the present invention, the dross on the surface of the plating bath 5 is blown toward the other end by the inert gas 7 which is blown from one end of the steel strip 1 in the width direction of the snout 4 toward the other end by the spray nozzle 8. This cleans the bath surface and prevents the steel strip from becoming unplated due to dross adhesion. The spraying of inert gas is effective if the gap a is made as small as possible.

[0011] In the present invention, aluminum, aluminum alloy, zinc, etc. can be used as the metal, and nitrogen gas, argon gas, etc. can be used as the inert gas, but nitrogen gas is economical. suitable for The spray angle of the inert gas to the bath surface (θ in Fig. 4)
) is preferably 1 to 10 degrees to prevent dross from blowing up and splashing.

FIG. 5 shows a cross section at the inert gas spraying position.
As shown in , when a snout with a dross reservoir 10 provided at a position where dross is blown in is used, the amount of dross that is once blown in and then circulated back to the steel strip immersion bath surface is reduced, and the uncoated rate of the coated steel sheet is reduced. . In other words, this shape of the snout prevents dross from flowing back into the part of the steel strip that enters the plating bath due to flow generated on the bath surface within the snout due to vibrations of the steel strip or changes in line speed that are unavoidable during operation. can.

Further, as shown in FIG. 6 in a longitudinal section, if the lower end of the snout is widened in the thickness direction of the steel strip, it can be distanced from the surface of the steel plate, and the effect of keeping dross away can be obtained. Figure 2
The device shown in Fig. 5 can prevent dross from adhering to the steel strip as described above, but in both cases, dross is stored in the snout, and after a long period of plating, the amount of dross stored increases. As the dross approaches the steel strip, the uncoated rate increases, making it necessary to stop the line to remove the dross.

An example of a device for removing dross generated within the snout to the outside of the snout will be explained using a schematic vertical cross-sectional view (FIG. 7) showing its operation. In the figure, reference numeral 13 denotes a moving part in which the lower end of the snout 4 is movable in the direction in which the snout enters the molten bath, and is connected to the snout body by a metal bellows 12, and is moved up and down by a piston cylinder, rack and pinion, etc. (not shown). 15 is a weir plate provided on the nozzle side of the inner surface facing the nozzle 8 of the moving part, and the penetration depth into the molten bath is shallower than the penetration depth into the molten bath on the outer periphery of the moving part; 16 is a weir plate between the inner surface and the weir plate; The space in between, 14, is a lid that opens the space to the atmosphere.

FIG. 7(a) shows the normal state of the moving part during plating, in which the weir plate and the outer periphery of the moving part have entered the molten bath, and the inert gas 7 from the nozzle 8 As a result, the dross 9 on the bath surface is stored on the nozzle side of the weir plate 15. In order to remove the accumulated dross from the apparatus as shown in FIG. 7(a), the moving part is first pulled up to the position where the weir plate comes out of the molten bath as shown in FIG. 7(b). As a result, dross is blown into the space 16.

Next, as shown in FIG. 7C, the moving part is lowered so that the weir plate also enters the molten bath, and the lid 14 provided in the space 16 is opened to remove the dross from the apparatus. After removing the dross, the lid 14 is closed as shown in FIG. 7(a). By the above operation, the dross generated on the bath surface inside the snout can be removed without breaking the non-oxidizing atmosphere of the snout, and stable operation can be performed for a long time without increasing the unplated rate.

[0017]

[Example] Hot-dip aluminum plating of a steel strip was carried out under the following conditions. Steel strip size: 1.0 (thickness) x 900 (width) mm Line speed: 40 mpm Aluminum bath: Al-10%Si, bath temperature 650°C Inert gas: Nitrogen snout Dew point: -40°C Example 1 Figure 2 Using a device with the shape shown, the nitrogen spray angle (Fig. 4
θ) is 5 degrees, and the flow rate is 1 in the thickness direction of the snout steel strip.
50Nm3/hr (hereinafter referred to as 50Nm3/hr)
Figure 8 shows the change in unplated occurrence rate (number of unplated steel strips/total number of coated steel strips) x 100% from the start of plating, along with a comparative example in which nitrogen was not blown. When nitrogen blowing is not performed, there is not much difference from when nitrogen blowing is performed immediately after the start of plating, but as time passes, nitrogen blowing becomes stable, whereas when nitrogen blowing is not performed, no plating occurs. The incidence of is increasing.

Example 2 FIG. 9 shows the results of investigating the occurrence rate of unplated surfaces after 30 hours of operation using the apparatus having the shape shown in FIG. 2 and varying the spray angle and nitrogen flow rate. From Figure 9, the spray angle is 1
~10 degrees, nitrogen flow rate 12.5~250Nm3/hr
・m is appropriate.

Example 3 A snout having the shape shown in FIG. 5 and a snout having the shape shown in FIG. 7 were used, and the other conditions were as in Example 1. The results are shown in FIG. If vibration of the steel strip occurs,
Even in the apparatus shown in FIG. 5, the snout was filled with dross, and in order to remove it, the operation had to be interrupted and the snout opened. However, it can be seen that stable operation can be carried out with the apparatus shown in FIG. 7.

[0020]

According to the present invention, hot-dip metal plating can be carried out stably for a long time without plating defects.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view showing the positional relationship between a steel strip and a snout.

FIG. 2 is a schematic cross-sectional view showing the installation position of a blowing nozzle.

FIG. 3 is a perspective view showing the positional relationship between a steel strip, a molten bath, and a spray nozzle.

FIG. 4 is an explanatory diagram showing the spray angle of inert gas.

FIG. 5 is a schematic cross-sectional view showing one shape of the snout.

FIG. 6 is a schematic vertical cross-sectional view showing another shape of the snout.

FIG. 7 is a schematic vertical cross-sectional view showing the operation of the moving section.

FIG. 8 is a graph showing the influence of presence or absence of nitrogen blowing and plating time on the incidence of non-plating.

FIG. 9 is a graph showing the influence of nitrogen flow rate and spray nozzle angle on the non-plating occurrence rate.

FIG. 10 is a graph showing the influence of snout shape and plating time on the incidence of non-plating.

[Explanation of symbols]

1 steel strip
2 Annealing furnace 3 Turning roll
4 Snout 5 Plating bath
6 Think roll 7 Inert gas
8 Spray nozzle 9 Dross
10 Dross pool 12 Bellows
13 Moving part 14 Lid
15 Weir plate 16 Space

a Gap θ Spraying angle

Claims (3)

[Claims] Claim 1: In a snout that guides a steel strip from a continuous annealing furnace to a molten metal bath in an apparatus that performs molten metal plating by continuously immersing a steel strip in a molten metal bath, one end of the snout in the width direction of the steel strip is installed. A device for removing oxides in a snout in molten metal plating, comprising a nozzle directly above the molten metal bath surface that sprays inert gas onto the molten metal bath surface toward the other end. 2. An apparatus for removing oxides in a snout in molten metal plating, wherein the apparatus according to claim 1 has an oxide reservoir in the snout on the inner surface of the snout facing the nozzle. 3. The lower end of the snout of the apparatus according to claim 1 constitutes a moving part movable in the direction in which the snout enters the molten bath, and the movable part has a movable part on the nozzle side of the inner surface facing the nozzle. An oxide in a snout for molten metal plating, characterized in that it has a weir plate whose depth is shallower than the penetration depth of the molten bath on the outer periphery of the moving part, and the space between the inner surface and the weir plate can be opened to the atmosphere. removal device.