JP5600957B2 - Manufacturing method of molten metal plated steel strip - Google Patents

Description

  The present invention relates to a method for manufacturing a molten metal plated steel strip, and more particularly to a method for manufacturing a molten metal plated steel strip capable of reducing the occurrence of splash of molten metal during gas wiping.

  For example, a hot dip galvanized steel strip has a surface that has been cleaned and activated and is immersed in a hot dip galvanizing bath, pulled up through the sink roll in the bath, and then gas is applied from both sides of the steel strip surface. It is manufactured by scraping off the surplus plating metal adhering to the steel strip by so-called gas wiping, and adjusting it to a predetermined plating adhesion amount. Splash of molten zinc occurs during gas wiping, the splash adheres to the wiping nozzle and the production volume decreases due to nozzle cleaning, or the splash adheres to the steel strip and the quality of the plated steel strip degrades There is.

  In recent years, the demand for hot dip galvanized steel strips as rust-proof steel strips has increased. For this reason, hot dip galvanizing equipment has been required to increase the line speed and reduce the weight to improve productivity and reduce costs. Yes.

  The amount of molten zinc adhering to the steel strip pulled up from the hot dip galvanizing bath is determined by the bath temperature, that is, the viscosity of the molten zinc, the steel strip temperature and the line speed, but generally the bath temperature and the bath penetration temperature of the steel strip are constant. Therefore, the amount of molten zinc adhering to the steel strip pulled up from the hot dip galvanizing bath is uniquely determined by the line speed, and as the line speed increases, the amount of zinc adhered increases.

  When the line speed is increased, it is necessary to increase the amount of scraping of excess plating metal adhering to the steel strip by increasing the flow rate of the wiping gas. Even when thinning, it is necessary to increase the amount of scraping of the excess plating metal by increasing the flow rate of the wiping gas. However, if the flow rate of the wiping gas is increased, the amount of splash of molten zinc increases during gas wiping, and the splash adheres to the wiping nozzle and the production amount decreases due to nozzle cleaning. The problem that the quality of the plated steel strip deteriorates due to adhesion to the steel strip becomes more obvious.

  With respect to such a problem, in Patent Document 1, in the hot dip galvanizing bath, the molten metal squeezing member is fixedly installed at an appropriate interval opposite to both surfaces of the steel strip on the bath surface or the bath. There has been proposed a technology that suppresses the amount of molten zinc that is lifted from a steel strip and enables thinning and increased line speed without increasing the wiping gas ejection pressure and flow rate during gas wiping.

  However, the technique of Patent Document 1 described above is inferior in the effect of suppressing the lift amount of molten zinc unless the molten metal drawing member is brought very close to the steel strip. For this reason, there is a risk that the steel strip and the molten metal squeeze member will come into contact with each other and the quality of the steel strip will deteriorate if an attempt is made to suppress the amount of lift of the molten zinc. When the line speed is increased due to insufficient effect of reducing the amount, or when the line is thinned, it is necessary to increase the wiping gas ejection pressure and flow rate during gas wiping, resulting in the occurrence of splash. The amount increases, and the splash adheres to the wiping nozzle and decreases the productivity, or the splash adheres to the steel strip and deteriorates the steel strip quality. Therefore, when the line speed is increased or thinned, there is a problem that the occurrence of splash cannot be suppressed and good steel strip quality cannot be stably obtained.

Japanese Patent No. 3772804

  An object of the present invention is to provide a molten metal plated steel strip that can effectively reduce the occurrence of molten metal splash during gas wiping by suppressing the amount of molten zinc lifted from the steel strip pulled up from the molten metal bath. It is to provide a manufacturing method.

  In order to solve the above-mentioned problems, the present inventor has made extensive studies, and as a result, a floating body having a specific gravity smaller than that of the molten metal is floated on the surface of the molten metal, and the molten metal lifted along with the steel strip rising from the molten metal bath is scraped. As a result, it has been found that the amount of lift of the molten metal can be effectively suppressed without generating a flaw or the like in the steel strip. The present invention is based on this finding.

Means of the present invention for solving the above problems are as follows.
(1) In a method for producing a molten metal-plated steel strip, the steel strip is continuously immersed in a molten metal bath, then pulled up from the molten metal bath, and the amount of coating on the steel strip is adjusted by gas wiping. A method for producing a molten metal-plated steel strip, characterized in that a large number of floating bodies are arranged on the surface of the steel bath so as to be in close contact with the steel strip pulled up from the molten metal bath.
(2) The method of manufacturing a hot-dip metal-plated steel strip according to (1), wherein the floating body has a spherical shape.

  (3) The floating body is a floating body having a specific gravity with respect to the molten metal of 0.3 to 0.7 and an average particle diameter of 5 to 10 mm, and floats on the bath surface of the steel strip lifting portion of the molten metal bath. It arrange | positions so that the height of a body layer may be 100 mm or more and 400 mm or less, The manufacturing method of the hot-dip metal-plated steel strip as described in (1) or (2) characterized by the above-mentioned.

  According to the present invention, the amount of deposit adhered by gas wiping is adjusted after reducing the amount of excess molten metal that accompanies the steel strip by the floating body provided on the molten metal bath surface. The ejection pressure and flow rate of the wiping gas during wiping can be reduced. As a result, the occurrence of splash can be reduced as compared with the prior art. According to the present invention, it is possible to increase the line speed and reduce the weight while suppressing the decrease in productivity and the deterioration in steel strip quality due to splash.

It is the schematic which shows the principal part structure of the continuous plating apparatus of the steel strip used for implementation of this invention. It is the schematic which shows the continuous plating line of the steel strip used in the Example. It is a diagram illustrating a scraping effect of the molten zinc when using Al ₂ O ₃ as a floating body placed in a molten zinc bath surface.

  Hereinafter, embodiments of the present invention will be described. In the following embodiment, a case where a molten metal is molten zinc and a floating body having a spherical shape is used as a floating body will be described.

  FIG. 1 is a schematic view showing the configuration of the main part of a continuous plating apparatus for steel strip used in the practice of the present invention. In FIG. 1, 1 is a steel strip, 2 is a hot dip galvanizing bath, 3 is a sink roll, and 4 is a wiping nozzle. 5 is a floating sphere having a specific gravity smaller than that of molten zinc, and 6 is a weir that prevents the floating sphere 5 from diffusing on the bath surface so as to be in close contact with the steel strip 1. The weir 6 is disposed so that the lower end is immersed in the bath and the upper end is on the bath, and has a substantially rectangular shape when viewed from above the bath surface, and is provided so as to surround the steel strip 1. A large number of floating spheres 5 are arranged to float on the bath surface in the weir 6 so as to be in close contact with the steel strip surface.

  In the steel strip continuous plating apparatus shown in FIG. 1, the steel strip 1 is continuously immersed in a hot dip galvanizing bath 2 held in a plating tank, and the steel that has entered the hot dip galvanizing bath 2 with a sink roll 3 in the bath. The running direction of the strip 1 is changed to the upper side of the hot dip galvanizing bath 2, and hot galvanized is attached to the surface of the strip 1, the hot galvanizing bath 2 is pulled up, and the steel strip 1 is continuously hot dip galvanized.

  In the apparatus of FIG. 1, the floating sphere 5 is disposed in close contact with the steel strip 1 at a position where the steel strip 1 rises from the bath to the bath, so that the molten zinc adhering to the steel strip 1 is lifted. As a result, it is possible to reduce the lift amount of the molten zinc onto the plating bath. Since the floating sphere 5 moves in accordance with the flow of the steel strip 1 and molten zinc, even if the floating sphere 5 contacts the surface of the steel strip 1, no quality defects such as scratches occur.

  In this way, by bringing the floating sphere 5 floating on the surface of the hot dip galvanizing bath into close contact with the steel strip 1, it becomes possible to suppress the lifting of the hot dip zinc, and the amount of excessive plating drawn by gas wiping can be reduced. it can. As a result, the occurrence of splash during gas wiping can be effectively suppressed when the line speed is increased or when the line speed is reduced. Further, during normal operation, it is possible to reduce the ejection flow rate and ejection pressure of the wiping gas, and the effect of reducing the occurrence of splash during gas wiping can be expected.

  As described above, by disposing a floating body (floating sphere) on the steel strip lifting portion of the plating bath, it is possible to scrape the molten metal (molten zinc) that adheres to the steel strip and lifts up. In order to exhibit this effect, the floating body needs to be present in contact with the steel strip where the steel strip is pulled up from the plating bath. In the steel strip lifting part, the molten metal that cannot be lifted up falls along with the steel strip that is pulled up, so in the case of a small amount of floating body, the floating body moves away from the steel strip lifting section and lifts by adhering to the steel strip. The effect of scraping the molten metal is not expressed. Therefore, the amount of the floating body needs to be an amount that exists in multiple layers at the steel strip lifting portion. By doing in this way, many floating bodies can be arrange | positioned so that it may closely contact with the steel strip pulled up from a molten metal bath.

  If the density of the floating body is close to the density of the molten metal, it will flow together with the molten metal and it will not be possible to scrape the molten metal effectively, so the density of the floating body must be smaller than the density of the molten metal. is there. However, if the density of the floating body is too small, it will be lifted together with the molten metal adhering to the steel strip, causing problems in gas wiping work or quality.

  In order to obtain the effect of scraping the molten metal, it is important to maintain the state in which the floating body is in contact with the steel strip. In order to bring the floating body into contact with the steel strip, it is preferable to increase the contact pressure of the floating body on the bath surface.

  In order to prevent the floating body from being lifted together with the molten metal and bring it into contact with the steel strip, the specific gravity of the floating body with respect to the molten metal is preferably 0.3 to 0.7, more preferably 0.4 to 0.00. 6. The ratio of the density of the floating body to the density of the molten metal (specific gravity of the floating body to the molten metal) is optimally 0.5. This is because the contact pressure of the floating body on the bath surface can be maximized with a small amount of floating body.

  The contact pressure of the floating body on the bath surface is proportional to the height of the floating body layer. When the steel strip speed increases, the floating body receives a force in the direction away from the steel strip due to the flow of molten metal, so when the steel strip speed increases, the floating body moves away from the steel strip and floats on the bath surface. Therefore, it is necessary to set the height of the floating body layer to an appropriate height in consideration of the steel strip speed so that the contact pressure does not decrease. The height of the floating body layer (floating body filling height: “h” in FIG. 1) is preferably about 100 mm when the steel strip speed is 120 mpm. In order to obtain the same effect when the line speed increases, it is necessary to increase the contact pressure of the floating body according to the fluid drag that increases in proportion to the square of the line speed. If it is about 400 mm, even if the steel strip speed is 230 mpm, the same effect as described above can be obtained. Therefore, the height of the floating body layer is preferably 100 mm or more and 400 mm or less.

  The smaller the size of the floating body, the floating body will be in contact with the steel strip uniformly without gaps, and adhesion unevenness (scraping unevenness) is less likely to occur in the width direction of the steel strip. From this point, it is preferable that the size of the floating body is small. However, if the size of the floating body is too small, the floating body is lifted together with the molten metal adhering to the steel strip, which causes gas wiping work or quality problems. In order to prevent the floating body from being lifted together with the molten metal adhering to the steel strip to prevent uneven adhesion in the steel strip width direction, the average particle size of the floating body is preferably about 5 to 10 mm.

The material of the floating body is not particularly limited as long as it has erosion resistance to the molten metal. For example, ceramics (Al ₂ O ₃ , Si ₃ N ₄ , SiC, etc.) can be used.

  As mentioned above, although embodiment of this invention was described, this invention is not restrict | limited to the said embodiment, Utilizing the thing of shapes other than a sphere as a floating body, combining various shapes and sizes. It is also possible to use it, and it is also possible to float a floating body uniformly on the bath surface without providing a weir.

  Examples of the present invention will be described. A schematic view of the continuous hot dip galvanizing line used in this example is shown in FIG. The steel strip 1 is delivered from the delivery reel 7, guided into the hot dip galvanizing bath 2 at 470 ° C., dipped and then pulled up from the hot dip galvanizing bath 2, cooled in the air cooling zone 8 and wound up. It is wound up on a reel 9.

  A weir 6 was provided at a portion where the steel strip 1 rises from the hot dip galvanizing bath 2 so as to surround the steel strip 1. The weir 6 had a steel strip width direction dimension: 300 mm, a perpendicular direction to the steel strip surface: 200 mm, a height: 300 mm, and was placed so as to be immersed 150 mm below the bath surface.

Ceramic spheres made of Al ₂ O ₃ having a specific gravity of 0.59 with respect to zinc and an average particle diameter of 6.5 mm are floated on the molten zinc in the weir 6 as the floating body 5, the plate width: 100 mm, the plate thickness: 0.00. A 2 mm steel strip was passed at a line speed of 60 mpm to 120 mpm, and the film thickness after plating was measured. The results are shown in FIG.

  FIG. 3 shows the results when there is no floating body in the weir and when the filling height of the floating body in the weir is 60 mm, 80 mm, and 100 mm.

  When the filling height of the floating body is 60 mm, when the line speed is 60 mpm, the film thickness after plating is less than when there is no floating body, and the effect of suppressing the amount of lift of molten zinc by the floating body is obtained, When the line speed is more than 60 mpm, the film thickness after plating is almost the same as that when there is no floating body, and the effect of suppressing the amount of lift of molten zinc by the floating body is not obtained. However, by increasing the filling height of the floating body, it is possible to obtain the effect of suppressing the lift amount of the molten zinc even when the line speed is increased. The film thickness after plating when the line speed was increased to 120 mpm was 1110 μm when there was no floating body, but when the filling height of the floating body was 100 mm, the film thickness after plating was 782 μm, and the molten zinc Has been reduced by 29.5%.

  If the filling height of the floating body is low, if the line speed increases, the flow velocity in the vicinity of the steel strip increases and the floating body cannot contact the steel strip. On the other hand, when the filling height of the floating body is high, the floating body can come into contact with the steel strip even if the line speed is increased, so that it is considered that the effect of suppressing the amount of lift of molten zinc can be exhibited. From this result, in order to obtain an effect of suppressing a sufficient lift amount of molten zinc when the line speed is 120 mpm, it is preferable to set the filling height of the floating body to 100 mm or more.

Next, Table 1 shows the results of investigating the effect of suppressing the lift amount of molten zinc when the material of the floating body is changed. Table 1 shows the film thickness after plating and the effect of suppressing the lifting amount of molten zinc when a spherical floating body having a diameter of 6.5 mm is used, the line speed is 120 mpm, and the filling height is 100 mm. There are three types of materials: Al ₂ O ₃ , Si ₃ N ₄ , and SiC. The effect of suppressing the lifting of molten zinc was evaluated by the reduction ratio (%) of the lifting amount with respect to the film thickness after plating when there was no floating body.

  Although any material has the effect of suppressing the lift amount of molten zinc, the effect of suppressing the lift is greater when the specific gravity with respect to zinc is close to 0.5. This is considered to be because when the specific gravity of the floating body with respect to the molten metal is 0.5, the contact pressure of the floating body on the bath surface with the steel strip is maximized. Therefore, in order to obtain a sufficient lifting amount suppressing effect, it is desirable that the specific gravity of the floating zone with respect to the molten metal is close to 0.5. In either case, there was no quality defect such as a thread due to floating bodies, and there was no problem with product quality.

  INDUSTRIAL APPLICABILITY The present invention can be used as a method for producing a molten metal plated steel strip that can reduce the occurrence of molten metal splash during gas wiping. The method of the present invention is also suitable as a method for producing a hot-dip metal-plated steel strip excellent in productivity and a method for producing a hot-dip hot-dip metal-plated steel strip.

1 Steel strip 2 Hot dip galvanizing bath (molten metal bath)
3 Sink roll 4 Wiping nozzle 5 Floating sphere (floating body)
6 Weir 7 Dispensing reel 8 Air cooling zone 9 Take-up reel

Claims (3)

In the method of manufacturing a molten metal-plated steel strip in which a steel strip is continuously immersed in a molten metal bath and then pulled up from the molten metal bath and the amount of plating on the steel strip is adjusted by gas wiping, the bath surface of the molten metal bath A large number of floating bodies are arranged so as to be in close contact with the steel strip pulled up from the molten metal bath , and the floating body has a specific gravity with respect to the molten metal of 0.3 to 0.7 and an average particle diameter of 5 to 10 mm. method for manufacturing a molten metal plated steel strip, characterized in float der Rukoto within range. The method of manufacturing a hot-dip metal-plated steel strip according to claim 1, wherein the floating body has a spherical shape. The floating body, melting the height of the floating layer on the bath surface of the steel strip pulling portion of the metal bath according to claim 1 or 2, characterized in that arranged so as to be 100mm above 400mm below the melting metal plating Steel strip manufacturing method.

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