JPH04276051A - Hot-dip metal coating method - Google Patents

Abstract

PURPOSE:To stably apply hot-dip metal coating to a steel strip for a long time while preventing the occurrence of uncoating due to dross adhesion in a snout. CONSTITUTION:In a snout introducing a steel strip into a molten metal bath, an inert gas is blown against the molten metal bath surface from one end, in the width direction of the steel strip, of the snout toward the other end. Hot-dip aluminizing or hot-dip aluminum alloy coating can be performed while regulating the blowing of nitrogen gas to 12.5-250Nm<3>/hr per meter in the width direction of the steel strip in the snout and also regulating blowing angle to 1-10 deg..

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of molten metal plating using molten metals such as molten aluminum, molten aluminum alloys, and molten zinc.

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. (Japanese Unexamined Patent Publication No. 60-43476) (3) The 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 inside the snout is removed by blowing out the inside of the snout with nitrogen gas containing a small amount of hydrogen and having a dew point below a specific temperature. (Japanese 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 plate surface to ensure sufficient removal. is not realistic. 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.
In order to lower the dew point below -40°C, it is necessary to install many dryers for gas drying, which increases equipment costs, and it is difficult to maintain and manage the dew point of a large amount of atmospheric gas below -40°C.
The dew point often rises and unplated surfaces occur. 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 a method for stably performing hot-dip metal plating 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 problems, the present invention provides a molten metal plating method in which a steel strip is continuously immersed in a molten metal bath. This method provides a molten metal plating method characterized in that an inert gas is sprayed onto the molten metal bath surface from one end of the snout in the width direction of the steel strip to the other end in the leading snout, and nitrogen is used as the inert gas. Using gas, the amount of nitrogen gas sprayed per 1 m in the thickness direction of the steel strip of the snout is 12.5 to 2.
Plating of molten aluminum or molten aluminum alloy can be performed at a rate of 50 Nm3/hr and by setting the spraying angle to the molten metal bath surface at 1 to 10 degrees with respect to the bath surface.

[0009]

[Operation] The method of the present invention will be explained using the drawings. FIG. 1 is a schematic vertical cross-sectional view showing the positional relationship between the steel strip and the snout in the device used in the present invention, FIG. 2 is a schematic cross-sectional view showing the installation position of the spray nozzle in the device used in the present invention, and FIG. 1 is a perspective view showing the positional relationship between the steel strip, the molten bath, and the spray nozzle in the apparatus used in the invention;
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, a is an inert gas and a snout This is the gap between the inner surface and the inner surface.

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 in the width direction of the steel strip 1 of the snout 4 toward the other end by the spray nozzle 8, This cleans the bath surface,
It is possible to prevent non-plating due to dross adhesion on the steel strip. 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 Hot-dip metal plating of aluminum or aluminum alloy is performed by applying nitrogen gas at a rate of 1.25 to 250 Nm3/hr (hereinafter referred to as 1.25 to 250 Nm3/hr・m) per meter of the steel strip thickness direction of the snout, as shown in FIG. ), Figure 4
By setting the spray angle θ shown in 1 to 10 degrees, the unplated rate can be made 0.5% or less.

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, when the lower end of the snout is expanded in the thickness direction of the steel strip, the dross floating on the bath surface moves away from the steel strip, resulting in the shape shown in FIG. You can get the same effect as using a snout.

[0014]

[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 spray angle (θ in Figure 4) was 5 degrees, the flow rate was 50 Nm3/hr・m, and Figure 7 shows the incidence of non-plating from the start of plating, along with a comparative example in which no nitrogen was blown. It shows the transition of (number of unplated steel strips/total number of coated steel strips) x 100%. Immediately after the start of plating, when nitrogen blowing is not performed, there is not much difference from when nitrogen blowing is performed, 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 Using the apparatus having the shape shown in FIG. 2, the occurrence rate of non-plating was investigated after 30 hours of operation while varying the spray angle and nitrogen flow rate. The results are shown in FIG. From Figure 8, 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. 2 and a snout having a dross reservoir having the shape shown in FIG. 5 were used, and the other conditions were as in Example 1.
It was carried out as follows. The results are shown in FIG. When vibrations occur in the steel strip, the effectiveness of the shape shown in FIG. 5 is shown, and it can be seen that stable operation can be carried out.

[0017]

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

FIG. 8 is a graph showing the influence of nitrogen flow rate and spray nozzle angle on the incidence of non-plating.

FIG. 9 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 a gap
θ Spraying angle

Claims (2)

[Claims] Claim 1: In a molten metal plating method in which a steel strip is continuously immersed in a molten metal bath, in a snout that leads the steel strip from a continuous annealing furnace to the molten metal bath, one end of the snout in the width direction of the steel strip is separated from the other end of the snout in the width direction of the steel strip. A molten metal plating method characterized by spraying an inert gas onto the surface of a molten metal bath. [Claim 2] Nitrogen gas is used as the inert gas, and the amount of spray per meter in the thickness direction of the steel strip of the snout is 12.5 to 12.5.
2. The molten metal plating method according to claim 1, wherein molten aluminum or molten aluminum alloy is plated at a rate of 250 Nm<3>/hr and at an angle of 1 to 10 degrees relative to the bath surface.