JP2007314851A - Method for producing hot dip metal plated steel strip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a hot dip metal plated steel strip where gas wiping is performed, thus the coating weight of plating is made uniform, also, its appearance properties are improved, and further, productivity can be improved. <P>SOLUTION: A gas is injected from slit nozzles arranged on both the sides of a steel strip to the oblique lower part, the inclined angle α between the injection direction of the gas in the gas injection port of each slit nozzle and the horizontal plane is made the same, also, the distance H between the gas injection port of each slit nozzle and the bath face of molten metal is made the same, and the inclined angle α is controlled to 0.9 to 2.0°. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for continuously producing a molten metal-plated steel strip by immersing the steel strip in a molten metal housed in a plating tank, and in particular, improving the appearance properties by uniformizing the amount of plating coating. Moreover, it is related with the manufacturing method of the hot-dip metal plating steel strip which can improve productivity.

The technology of immersing a steel strip in a molten metal housed in a plating tank and then pulling it up and performing metal plating (hereinafter referred to as hot-dip metal plating) has been widely used in the manufacturing process of hot-dip galvanized steel strip and the like. Yes.
As shown in FIG. 1, an apparatus for performing molten metal plating is a method in which a steel strip 3 a (hereinafter referred to as a “base metal strip”) is continuously dipped in a molten metal 2 in a plating tank 1, and then pulled up to be molten metal plated. The steel strip 3b (hereinafter referred to as a hot-dip metal-plated steel strip) subjected to is manufactured. An arrow A in FIG. 1 indicates the traveling direction of the base steel strip 3a and the molten metal plated steel strip 3b.

  The molten metal-plated steel strip 3b is pulled up substantially vertically upward from the molten metal 2 in the plating tank 1, and is fed to an alloying apparatus as necessary. At this time, the excessively attached molten metal 2 forms droplets and flows down on the surface of the molten metal-plated steel strip 3b, resulting in uneven plating thickness and deterioration of appearance properties. Therefore, a technique for removing excess molten metal 2 adhering to the surface of the molten metal plated steel strip 3b (hereinafter referred to as wiping) has been studied.

A device for performing such wiping is disposed at a position shown as a wiping device 4 in FIG.
(a) Roll wiping: A technique in which a squeezing roll is brought into contact with both surfaces of a molten metal-plated steel strip 3b pulled up from the molten metal 2 to squeeze out excess molten metal 2.
(b) Gas wiping: The gas wiping is roughly classified into a technique of injecting gas onto both surfaces of the molten metal-plated steel strip 3b pulled up from the molten metal 2 to blow off excess molten metal 2.

Among these wiping technologies, roll wiping is liable to cause scratches on the surface of the molten metal-plated steel strip 3b, and when the conveying speed of the molten metal-plated steel strip 3b is increased, the molten metal-plated steel strip 3b breaks. There is a problem that it becomes easy.
Thus, various techniques relating to gas wiping have been studied from the viewpoint of improving the yield and productivity of the molten metal plated steel strip 3b.

  For example, Patent Document 1 discloses a technique for performing gas wiping by injecting gas obliquely upward from nozzles disposed on both sides of a molten metal plated steel strip. In this technique, excess molten metal droplets (hereinafter referred to as splash) blown off from the molten metal plated steel strip by gas are scattered upward and adhere to the molten metal plated steel sheet. As already explained, since the molten metal plated steel strip is pulled vertically upward, the splash scattered upward adheres to the wiped molten metal plated steel strip. That is, the technique disclosed in Patent Document 1 cannot provide a sufficient wiping effect.

  Patent Document 2 discloses a technique for performing gas wiping by injecting gas 5 obliquely downward from nozzles disposed on both sides of a molten metal plated steel strip. In this technique, nozzles 4a and 4b are disposed on both sides of the molten metal plated steel strip as shown in FIG. 2, and the distance between the nozzles 4a and 4b and the bath surface of the molten metal 2 is different. Therefore, the splash 7 generated at the side end of the molten metal-plated steel strip 3b is scattered downward by the gas 5 injected from the nozzle 4a located at the upper part, and adheres to the nozzle 4b located at the lower part. As a result, the nozzle 4b is clogged in the vicinity of the side end portion of the molten metal plated steel strip 3b.

  Moreover, in the technique disclosed in Patent Document 2, when the flow rate of the gas 5 ejected from the nozzles 4a and 4b is large, the bath surface of the molten metal 2 swells violently and the droplet rebounds from the bath surface. When splashing of the droplets occurs in this way, the droplets adhere to the molten metal-plated steel strip 3b and nozzles 4a and 4b, causing problems such as uneven plating thickness, deterioration of appearance, and nozzle clogging. Occurs.

In other words, in order to apply the technique disclosed in Patent Document 2 and avoid these problems, the flow rate of the gas 5 must be reduced, and therefore improvement in the productivity of the molten metal plated steel sheet cannot be expected.
Japanese Patent Laid-Open No. 10-306359 Japanese Patent Laid-Open No. 6-2756

  The present invention provides a method for producing a molten metal-plated steel strip that solves the above-described problems, makes the amount of coating adhesion uniform by applying gas wiping, improves appearance properties, and improves productivity. With the goal.

  In the present invention, a pair of slit nozzles are disposed on both sides of a steel strip pulled upward from the molten metal accommodated in the plating tank, and wiping is performed by blowing gas on both sides of the steel strip from the pair of slit nozzles. In a method for manufacturing a molten metal plated steel strip in which molten metal plating is performed on a steel strip, gas is injected obliquely downward from slit nozzles disposed on both sides of the steel strip, and the gas injection direction at the gas injection port of each slit nozzle And the horizontal plane, the same angle H (mm) between the gas injection port of each slit nozzle and the molten metal bath surface, and the inclination angle α of 0.9 to 2.0. It is a manufacturing method of a molten metal plating steel strip.

In the manufacturing method of the molten metal plated steel strip of the present invention, the steel strip transport speed S (m / min), the steel strip plating adhesion amount T (g / m ² ), the upper lip angle β (°) of the slit nozzle The tilt angle α is preferably set according to the lower lip angle γ (°) of the slit nozzle and the distance H (mm). Specifically, the conveyance speed S is 10 to 250 m / min, the plating adhesion T (per one side) is 10 to 100 g / m ² , the upper lip angle β is 15 to 45 °, and the lower lip angle γ is 15 to 25. It is preferable that the angle H and the distance H are 130 to 400 mm.

  The present invention is preferably applied to a hot dip galvanized steel strip.

  According to the present invention, by performing gas wiping, it is possible to make the plating adhesion amount of the molten metal plated steel strip uniform, improve the appearance properties, and improve the productivity of the molten metal plated steel strip.

  FIG. 3 is a cross-sectional view schematically showing an example of a wiping device to which the present invention is applied. In the present invention, as shown in FIG. 3, a gas 5 is blown obliquely downward from a pair of slit nozzles 4c disposed on both sides of a molten metal-plated steel strip 3b pulled up substantially vertically upward from the molten metal 2. Here, the slit nozzle 4c refers to a nozzle that injects gas from an elongated linear opening (hereinafter referred to as a gas injection port). That is, by using the slit nozzle 4c, the gas 5 can be sprayed uniformly over the entire length in the width direction of the molten metal plated steel strip 3b.

  Further, as shown in FIG. 3, if the distance between the gas injection port of the slit nozzle 4c and the bath surface of the molten metal 2 is H (mm), the distance H between the slit nozzles 4c on both sides of the molten metal plated steel strip 3b is Are the same. That is, the gas injection ports of the pair of slit nozzles 4c are arranged at the same height from the bath surface of the molten metal 2. In addition, when an angle (hereinafter referred to as an inclination angle) between a gas injection direction and a horizontal plane at the gas injection port is α (°), the inclination angles α on both sides of the molten metal plated steel strip 3b are the same. That is, the gas 5 is blown obliquely downward at the same inclination angle α from the gas injection ports of the pair of slit nozzles 4c.

  The distance between the molten metal plated steel strip 3b and the gas injection port of the slit nozzle 4c is not particularly defined. Therefore, the position where the gas 5 blown from the gas injection port collides with the molten metal plated steel strip 3b and blows off the excessive molten metal 2 (that is, the position where the splash 7 is generated) is not necessarily on both sides of the molten metal plated steel strip 3b. Not the same. The distance between the molten metal-plated steel strip 3b and the gas injection port of the slit nozzle 4c is set as appropriate in accordance with specifications such as manufacturing the molten metal-plated steel strip 3b having different plating adhesion amounts on both sides.

Even if the position where the splash of the molten metal plated steel strip 3b is generated is different, the splash 7 generated at the side end portion of the molten metal plated steel strip 3b is applied to the slit nozzle 4c by making the distance H and the inclination angle α the same. It can prevent adhesion.
However, if the inclination angle α is less than 0.9 °, the splash 7 generated at the side end of the molten metal plated steel strip 3b adheres to the slit nozzle 4c on the opposite side. On the other hand, when it exceeds 2.0 °, the bath surface of the molten metal 2 undulates and the droplet rebounds. Therefore, the inclination angle α is in the range of 0.9 to 2.0 °.

The inclination angle α is determined by the conveying speed S (m / min) of the molten metal plated steel strip 3b, the coating amount T (g / m ² ) of the molten metal plated steel strip 3b, and the upper lip angle β ( °), the lower lip angle γ (°) of the slit nozzle 4c, and the distance H (mm), and the inclination angle according to these S value, T value, β value, γ value, and H value. If α is set, the effects of the present invention can be sufficiently exerted. The relationship between the S value, the T value, the β value, the γ value, the H value, and the inclination angle α may be set as appropriate according to the specifications and capabilities of the manufacturing equipment for the molten metal plated steel strip. It can be applied to automatic control by expressing it with a mathematical expression (for example, a regression equation) based on the result. Note that the upper lip angle β and the lower lip angle γ of the slit nozzle 4c indicate the angle of the upper chamfered portion and the angle of the lower chamfered portion of the gas injection port 8, respectively, as shown in FIG.

That is, the S value, the T value, the β value, the γ value, and the H value may be set in consideration of the mutual relationship so that the inclination angle α becomes a predetermined value, and need to be defined individually. There is no. However, the effect of the present invention is remarkably exhibited by individually defining these values as follows.
If the conveying speed S of the molten metal-plated steel strip 3b is less than 10 m / min, the temperature of the molten metal 2 is lowered when the gas wiping is performed by pulling it vertically upward from the molten metal 2, so that the effect of gas wiping is sufficient. I can't get it. On the other hand, when it exceeds 250 m / min, the molten metal 2 does not sufficiently adhere to the base steel strip 3a, and there is a possibility that defective plating occurs. Therefore, the conveyance speed S of the molten metal plated steel strip 3b is preferably 10 to 250 m / min. In addition, if this invention was applied to manufacture of a hot-dip galvanized steel strip, it was able to be operated without trouble at a conveying speed S of 230 m / min or more.

The coating weight T (per one side) is less than 10 g / m ² of molten metal plated steel strip 3b, there not adhere molten metal 2 in the mother steel strip 3a is sufficiently, a fear that a plating failure occurs is. On the other hand, if it exceeds 100 g / m ² , the reaction between the molten metal and the steel strip becomes insufficient, and there is a possibility that defective plating occurs. Accordingly, the plating adhesion amount T (per one side) of the molten metal plated steel strip 3b is preferably 10 to 100 g / m ² .

  If the upper lip angle β of the slit nozzle 4c is less than 15 °, the strength in the vicinity of the gas injection port 8 is insufficient, and the slit nozzle 4c may be deformed. On the other hand, when it exceeds 45 °, as shown in FIG. 5, convection 5a of gas 5 is generated above the slit nozzle 4c, and fine particles of the molten metal 2 adhere to the molten metal-plated steel strip 3b and the slit nozzle 4c. Therefore, the upper lip angle β is preferably in the range of 15 to 45 °.

If the lower lip angle γ of the slit nozzle 4c is less than 15 °, the strength in the vicinity of the gas injection port 8 is insufficient, and the slit nozzle 4c may be deformed. On the other hand, if it exceeds 25 °, the splash 7 generated at the side end of the molten metal plated steel strip 3b may adhere to the slit nozzle 4c on the opposite side. Therefore, the lower lip angle γ is preferably within a range of 15 to 25 °.
If the distance H between the gas injection port of the slit nozzle 4c and the bath surface of the molten metal 2 is less than 130 mm, the bath surface of the molten metal 2 may swell and the droplets may rebound. On the other hand, if the thickness exceeds 400 mm, the temperature of the molten metal 2 is lowered when the gas wiping is performed by pulling up vertically from the molten metal 2, so that the effect of gas wiping cannot be sufficiently obtained. Therefore, the distance H is preferably within a range of 130 to 400 mm.

The apparatus shown in FIG. 1 was installed in a hot dip galvanizing line to produce a hot dip galvanized steel strip. In addition, the slit nozzle 4c was arrange | positioned as shown in FIG. 3 as the wiping apparatus 4 in FIG. 1, and gas wiping was performed. The upper lip angle β of the slit nozzle 4c was 33 °, the lower lip angle γ was 18 °, and the distance H between the gas injection port of the slit nozzle 4c and the bath surface of the molten zinc 2 was 400 mm. Furthermore, the operation was continued for one month with the inclination angle α between the gas injection direction at the gas injection port and the horizontal plane being 1.05 °. During that period, the conveying speed S of the hot dip galvanized steel strip 3b fluctuated in the range of 30 to 150 m / min, and the plating adhesion amount T (per one side) fluctuated in the range of 25 to 60 g / m ² . This is an invention example. The average value of the conveyance speed S is as shown in Table 1.

On the other hand, as Comparative Example 1, the operation was continuously performed for one month with an inclination angle α of 0 °. During that period, the conveying speed S of the hot dip galvanized steel strip 3b fluctuated in the range of 30 to 150 m / min, and the plating adhesion amount T (per one side) fluctuated in the range of 25 to 60 g / m ² . Other conditions are the same as those of the invention example. The average value of the conveyance speed S is as shown in Table 1.
Further, as Comparative Example 2, the operation was continued continuously for one month with an inclination angle α of 0.6 °. During that period, the conveying speed S of the hot dip galvanized steel strip 3b fluctuated in the range of 30 to 150 m / min, and the plating adhesion amount T fluctuated in the range of 25 to 60 g / m ² . Other conditions are the same as those of the invention example. The average value of the conveyance speed S is as shown in Table 1.

  About the hot dip galvanized steel strip obtained by invention example and the comparative examples 1 and 2, the incidence rate of the defect resulting from adhesion of the zinc ball called a silver spot was examined visually. The results are as shown in Table 1.

  As is clear from Table 1, it can be seen that in the inventive examples, the occurrence of silver spots is suppressed, the appearance properties are improved, and the galvanizing is uniformly adhered. In addition, the conveyance speed of the hot dip galvanized steel strip 3b is increased, and productivity can be improved.

It is sectional drawing which shows typically the example of the apparatus which performs molten metal plating. It is sectional drawing which expands and shows the example of the conventional gas wiping apparatus typically. It is sectional drawing which expands and shows the example of the wiping apparatus to which this invention is applied typically. It is sectional drawing which expands and shows typically the vicinity of the gas injection port of the slit nozzle to which this invention is applied. It is a side view which expands and shows an example with a large lip angle typically.

Explanation of symbols

1 Plating tank 2 Molten metal
3a Steel strip
3b Molten metal plating steel strip 4 Wiping device
4a Upper nozzle
4b Lower nozzle
4c Slit nozzle 5 Gas 6 Sink roll 7 Splash 8 Gas injection port 9 Gas convection

Claims (4)

  A pair of slit nozzles are disposed on both sides of the steel strip pulled upward from the molten metal accommodated in the plating tank, and the steel is blown while blowing gas from the pair of slit nozzles to both sides of the steel strip. In the method of manufacturing a molten metal plated steel strip for performing molten metal plating on the strip, the gas is injected obliquely downward from the slit nozzles disposed on both sides of the steel strip, and the gas injection direction at the gas injection port of each slit nozzle And the horizontal plane, and the distance H (mm) between the gas injection port of each slit nozzle and the molten metal bath surface is the same, and the inclination angle α is 0.9 to 2.0. A method for producing a hot-dip metal-plated steel strip, characterized by: The steel strip conveyance speed S (m / min), the steel strip plating amount T (g / m ² ), the slit nozzle upper lip angle β (°), the slit nozzle lower lip angle γ ( And the inclination angle α is set according to the distance H (mm). The transport speed S is 10 to 250 m / min, the plating adhesion amount T (per one side) is 10 to 100 g / m ² , the upper lip angle β is 15 to 45 °, and the lower lip angle γ is 15 to 25 °. And the distance H is set to 130 to 400 mm.   The said molten metal is molten zinc, The manufacturing method of the molten metal plating steel strip as described in any one of Claims 1-3 characterized by the above-mentioned.

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