JP5803754B2 - Manufacturing method of molten metal plated steel strip - Google Patents

Description

  The present invention relates to a method for producing a molten metal plated steel strip.

  In recent years, hot-dip metal plating, particularly hot-dip galvanizing, has become widespread as an inexpensive means for ensuring corrosion resistance. Along with this, many improvements have been attempted for the purpose of improving plating quality and productivity, and they are increasingly used in more fields in the future due to the excellent characteristics of molten metal plating.

By the way, various methods of plating while controlling the atmosphere of the wiping portion have been proposed because it is possible to ensure the plating quality while improving the productivity. For example, by reducing the oxygen concentration and making the atmosphere non-oxidizing, prevent oxidization of zinc in the wiping part, and prevent top dross generation, nozzle clogging, and generation of ripple patterns on the plating surface when manufacturing zero spangle products. Has been proposed (see Patent Documents 1 to 3).
Further, in Patent Document 4, a main seal box that covers the gas wiping nozzle and a sub seal box that covers the main seal box are provided, and each seal box can be moved up and down separately, so that the top dross can be achieved without stopping the line. Is removed from the seal box. In Patent Document 5, the non-oxidizing gas ejected from the gas wiping nozzle is heated to 100 ° C. or higher, and the non-oxidizing gas contains 100 ppm or more of water vapor, so that not only top dross is generated but also Zn vapor in the seal box. Is suppressed.

Japanese Patent Publication No.57-53429 Japanese Unexamined Patent Publication No. 57-203964 JP-A-2-285060 JP-A-4-285148 JP-A-62-37361

  However, in the methods described in Patent Documents 1 to 3, although the amount of top dross generated can be reduced, when the wiping gas is blown onto the steel strip pulled up from the plating bath, the molten metal is caused by the turbulence of the jet colliding with the steel strip. The so-called splash, which scatters around, rebounds in the seal box and adheres to the plated surface after wiping, which significantly impairs the surface appearance of the plated steel strip. In addition, the method described in Patent Document 4 is not practical because the apparatus used is complicated. Furthermore, in the method described in Patent Document 5, since the dew point in the seal box must also be controlled, the apparatus becomes complicated and expensive.

The present invention has been devised to solve the above-described problems of the prior art, and it is possible to suppress the oxygen concentration in the top dross generation region with a simple device and reduce the amount of splash adhesion to the steel strip. An object of the present invention is to provide a method for producing a hot-dip plated steel strip. The summary is as follows.
[1] When an inert gas is blown from the gas wiping nozzle disposed on both surfaces of the steel strip, which is continuously pulled up from the molten metal plating bath, with the steel strip sandwiched therebetween, the width of the steel strip A pair of shielding plates narrowly having a length of at least 50 mm in the length direction of the steel strip, the steel strip so that the position of the upper end of the shielding plate is 50 mm or more and 150 mm or less below the jet port of the gas wiping nozzle A method for producing a hot-dip metal-plated steel strip, wherein the steel strip is plated while being opposed to both surfaces of the steel strip.
[2] The method for producing a molten metal plated steel strip according to [1], wherein a distance from a lower end of the shielding plate to a molten metal plating bath surface is 30 mm or more and 100 mm or less.
[3] The method for producing a molten metal-plated steel strip according to [1] or [2], wherein a difference between the width of the shielding plate and the width of the steel strip is 50 mm or more and 120 mm or less.
[4] The method for producing a molten metal-plated steel strip according to any one of [1] to [3], wherein a distance between the steel strip and the shielding plate is 30 mm or more and 80 mm or less.
[5] The melting according to any one of [1] to [4], wherein the temperature of the inert gas at a position where the inert gas collides with a steel strip is equal to or higher than a melting point of the molten metal. A method for producing a metal-plated steel strip.
In addition, the manufacturing method of the molten metal plating steel strip of this invention is applicable to the manufacturing method of various hot metal plating steel strips, such as zinc and aluminum.

  According to the present invention, by using a simple shielding plate as compared with the conventional seal box, the oxygen concentration in the top dross generation region can be suppressed, and the amount of top dross generation can be reduced. Furthermore, by reducing the amount of splash adhering to the steel strip, a hot-dip metal-plated steel strip having a beautiful surface appearance can be produced.

It is sectional drawing which shows the hot dip galvanizing apparatus in the manufacturing method of the hot dip galvanized steel strip which is one Embodiment of this invention. It is sectional drawing which shows the positional relationship of the shielding board which is one Embodiment of this invention, and a gas wiping nozzle. It is a front view of the shielding board which is one Embodiment of this invention. It is a graph which shows the relationship between the distance (Lo) from a nozzle jet nozzle to the shielding board upper end, the amount of top dross, and the amount of splashes. It is a graph which shows the relationship between the distance (L) from a lower end of a shielding board to a bath surface, a top dross amount, and a splash amount. It is a graph which shows the relationship between the difference (W) of the width | variety of a steel strip, and the width | variety of a shielding board, the amount of top dross, and the amount of splashes. It is a graph which shows the relationship between the distance (D) of a steel strip and a shielding board, a top dross amount, and a splash amount. It is a graph which shows the relationship between the gas temperature (T), the top dross amount, and the splash amount in the collision position of the inert gas ejected from the gas wiping nozzle.

  In the method for producing a molten metal-plated steel strip of the present invention, the steel strip is blown with gas from a gas wiping nozzle disposed on both sides of the steel strip across the surface of the steel strip that is continuously pulled up from the molten metal plating bath. Plating. At that time, a shielding plate is used.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a hot dip galvanizing apparatus suitable for carrying out the present invention. In FIG. 1, 1 is a steel strip, 2 is a continuous furnace, 3 is a snout, 4 is a plating bath, 5 is a zinc bath, 6 is a pass roll, 7 is a support roll, 8 is a gas wiping nozzle, 9 is a top roll, Reference numeral 10 denotes a shielding plate. The shielding plate 10 is disposed below the gas wiping nozzle 8. A pair of shielding plates 10 are disposed opposite to both surfaces of the steel strip 1.

  The effect | action of the shielding board of this invention is demonstrated using FIG. 2 and FIG. FIG. 2 is a cross-sectional view showing the positions of the shielding plate and the gas wiping nozzle according to an embodiment of the present invention. Drawing 3 is a figure which looked at the shielding board which is one embodiment of the present invention from the front of the steel strip surface.

  The present invention is characterized in that the shielding plate 10 is disposed below the gas wiping nozzle 8. The distance Lo (mm) from the inert gas outlet of the gas wiping nozzle 8 to the upper end of the shielding plate 10 is not less than 50 mm and not more than 150 mm. When the distance Lo exceeds 150 mm, a top dross is generated because outside air (oxygen) flows into the space between the shielding plate 10 and the steel strip 1. On the other hand, if the distance Lo is less than 50 mm, a large amount of splash is generated directly under the gas wiping nozzle 8 having the highest wind speed, and the light is reflected by the shielding plate and adheres to the steel strip. For this reason, the amount of splash adhesion cannot be reduced.

  In the present invention, the distance L (mm) from the lower end of the shielding plate 10 to the zinc bath surface is preferably 30 mm or more and 100 mm or less. When the distance L exceeds 100 mm, the outside air (oxygen) flows in, and the amount of top dross generated increases. On the other hand, when the distance L is less than 30 mm, the generated top dross is blocked by the shielding plate 10, and is likely to be laminated between the shielding plate 10 and the steel strip 1 and adhere to the steel strip.

In the present invention, the difference W (mm) between the width of the shielding plate 10 and the width of the steel strip 1 is preferably 50 mm or more and 120 mm or less. In addition, the difference W in this invention shows the distance from the edge part of the width direction of the steel strip 1 to the edge part of the width direction of a shielding board, as shown in FIG. When the difference W exceeds 120 mm, the amount of generated top dross increases because the outside air containing oxygen flows from the outside. On the other hand, if the difference W is less than 50 mm, there is a high possibility that splash generated in a large amount at the steel strip edge portion is reflected by the shielding plate and adheres to the steel strip.
The steel strip width is 800mm to 940mm, the shield plate width is 700mm, the steel strip width is 940mm to 1080mm, the shield plate width is 840mm, the steel strip width is 1080mm to 1220mm, and the shield plate width is 980mm. A shape that can change the width of the shielding plate is desired.

  In the present invention, the distance D (mm) between the steel strip 1 and the shielding plate 10 is preferably 30 mm or more and 80 mm or less. In addition, the distance D in this invention means the space | interval of the steel strip at the time of arrange | positioning in parallel, as FIG. 2 shows. If the distance D exceeds 80 mm, the space between the steel strip 1 and the shielding plate 10 widens, so the influence of outside air (oxygen) cannot be ignored. On the other hand, when the distance D is less than 30 mm, the splash is reflected by the shielding plate 10 and easily adheres to the steel strip.

In the present invention, it is preferable that the temperature of the inert gas ejected from the gas wiping nozzle (wiping gas temperature) at a position where the inert gas collides with the steel strip is higher than the melting point of the molten metal in the plating bath.
In the present invention, when the temperature of the inert gas is higher than the melting point of the molten metal, cooling of the molten metal on the steel strip can be suppressed. As a result, since cooling of the molten zinc separated by the wiping gas can be suppressed, the top dross based on the cooled molten zinc can be reduced. On the other hand, when the temperature of the inert gas is lower than the melting point of the molten metal, the molten zinc separated by the wiping gas becomes a solid, so the cooled molten zinc becomes a part of the top dross, and as a result, the effect of reducing the top dross is reduced. Can't get.

  In the present invention, the inert gas is not particularly limited as long as it provides a non-oxidizing atmosphere, and examples thereof include nitrogen, helium, and carbon dioxide. Although there is no restriction | limiting of the gas pressure of an inert gas, It is preferable that it is 50 kPa or more and 150 kPa or less. The temperature of the inert gas is preferably 20 ° C. or higher and 700 ° C. or lower.

  In this invention, the length of a shielding board shall be 50 mm or more from the point of operativity. Moreover, as a raw material of a shielding board, what is necessary is just a material which is hard to thermally deform, such as SS, SUS, ceramics. The thickness of the shielding plate is preferably 0.7 mm or more and 5 mm or less. In addition, it is thought that the structure which folds the horizontal width of a shielding board is suitable as a shape of a shielding board so that it can respond even if the board width changes in operation.

  In this invention, it does not restrict | limit especially as a steel strip, What is necessary is just a steel plate normally used for molten metal plating.

  In the present invention, examples of the molten metal plating bath include a zinc bath and an aluminum bath.

  Examples of the present invention will be described below.

  A shield plate was installed in a hot dip galvanized steel strip production line (hereinafter CGL), and the effect of the shield plate was verified by measuring the amount of top dross generated and the amount of splash attached. Two shielding plates were installed in parallel below the gas wiping nozzle with the steel strip as the plane of symmetry. The thickness of the shielding plate was 5 mm. Further, nitrogen was used as an inert gas ejected from the gas wiping nozzle. It was carried out in a hot dip galvanizing bath, with a line speed of 150 mpm, an inert gas temperature of 20 ° C., an inert gas pressure of 75 kPa, a steel strip width of 1000 mm, and a steel strip thickness of 0.8 mm.

The amount of top dross generated was evaluated by measuring the amount of top dross generated in one hour. Specifically, the top dross floating on the bath surface was collected after 1 hour of operation, and the weight was measured after cooling. The amount of top dross generated in one hour in normal operation without a shielding plate (line speed 150mpm, inert gas temperature 20 ° C, inert gas pressure 75kPa, steel strip width 1000mm, steel strip thickness 0.8mm) As 1, it was compared with when the shielding plate was installed.
Moreover, about the splash adhesion amount, when the circumference | surroundings including a steel strip and a gas wiping nozzle were sealed, the number of splashes adhering to the steel plate was counted. The area to be counted was a steel strip width (1000 mm in this case) × unit length (1000 mm). After passing, the steel strip was unwound and counted visually. The amount of splash adhesion during normal operation without a shielding plate was set as 1, and the verification results were compared.

First, the relationship between the distance Lo from the inert gas ejection port of the gas wiping nozzle to the upper end of the shielding plate, the amount of generated top dross, and the amount of splash adhesion was examined. The results are shown in FIG. Black in FIG. 4 indicates the amount of top dross generated and is expressed as the amount of top dross. Also, the white outline indicates the amount of splash adhesion and is expressed as the splash amount. The experiment was conducted with the distance L between the lower end of the shielding plate and the bath surface being 30 mm, the difference W between the width of the steel strip and the width of the shielding plate was 50 mm, and the distance D between the steel strip and the shielding plate was 50 mm. .
From FIG. 4, the top dross amount is the smallest when Lo = 0 mm. This is presumably because the oxygen concentration just below the gas wiping nozzle with the highest wind speed of the inert gas blown could be reduced. Moreover, the amount of top dross increased moderately in the range of 0 ≦ Lo ≦ 150, and rapidly increased when 150 ≦ Lo. This is considered to be because outside air having a high oxygen concentration flows into the space between the shielding plate and the steel strip as Lo increases. On the other hand, the splash amount is highest at Lo = 0. This is probably because a large amount of splash was generated directly under the gas wiping nozzle with the highest wind speed of the inert gas, and as a result, it was reflected by the shielding plate and adhered to the steel strip. Moreover, the amount of splash decreased as Lo increased. This is presumably because splash was scattered in a space formed between the gas wiping nozzle and the upper part of the shielding plate. In addition, since the edge splash which generate | occur | produced at the both ends of a steel strip was not able to be eliminated, the amount of splash was not completely absent. A beautiful surface appearance was obtained when the top dross amount was 0.5 or less and the splash amount was 0.4 or less. From the above results, the distance Lo can be derived as 50 mm or more and 150 mm or less. In addition, even if L, W, and D were conditions other than the above, the same result was obtained for the distance Lo.

  Next, the relationship between the distance L from the lower end of the shielding plate to the bath surface, the amount of top dross, and the amount of splash was examined. The results are shown in FIG. The experiment was conducted under the conditions of W = 50 mm, Lo = 100 mm, and D = 50 mm. As L increased, the amount of top dross increased gradually, increasing rapidly from L = 100. This is thought to be because the outside air flowed in from the outside and the oxygen concentration increased as L increased. On the other hand, the amount of top dross did not increase so much in the range of L ≦ 100. This is presumably because the wind speed near the bath surface is lower than that immediately below the gas wiping nozzle. In addition, the splash did not depend on L and was a substantially constant value. A beautiful surface appearance was obtained when the top dross amount was 0.5 or less and the splash amount was 0.4 or less. From the above results, the distance L is preferably 30 mm or more and 100 mm or less. In addition, even if Lo, W, and D were conditions other than the above, the same result was obtained for the distance L.

  Next, the relationship between the difference W between the width of the steel strip and the width of the shielding plate, the amount of top dross, and the amount of splash was examined. The results are shown in FIG. The experiment was conducted under the conditions of Lo = 100 mm, L = 30 mm, and D = 50 mm. As W increases, the amount of top dross increases because outside air containing oxygen flows from the outside. On the other hand, the amount of splash decreases rapidly as W increases. This is presumably because the edge splash generated at both ends of the steel strip is scattered from between the steel strip and the shielding plate, and the splash reflected by the shielding plate is reduced. A beautiful surface appearance was obtained when the top dross amount was 0.5 or less and the splash amount was 0.4 or less. From the above results, the difference W is preferably 50 mm or more and 120 mm or less. Even if Lo, L, and D were conditions other than the above, the same result was obtained for the difference W.

  Next, the relationship between the distance D between the steel strip and the shielding plate and the amount of top dross and splash was examined. The results are shown in FIG. The experiment was conducted under the conditions of W = 50 mm, Lo = 100 mm, and L = 30 mm. As D increased, the amount of top dross increased. This is presumably because it becomes difficult to effectively reduce oxygen because the space between the steel strip and the shielding plate becomes wide. On the other hand, when the value of D was small, although the amount of top dross was small, the amount of splash increased. The splash amount increased because the splash was reflected by the shielding plate and adhered to the steel strip. A beautiful surface appearance was obtained when the top dross amount was 0.5 or less and the splash amount was 0.4 or less. From the above results, the distance D is preferably 30 mm or more and 80 or less. In addition, even if Lo, L, and W were conditions other than the above, the same result was obtained for the distance D.

  Next, the relationship between the wiping gas temperature T, the top dross amount, and the splash amount was examined. The results are shown in FIG. The experiment was conducted under the conditions of W = 50 mm, Lo = 100 mm, L = 30 mm, and D = 50 mm. When the melting point of molten zinc metal was less than 420 ° C, the amount of top dross was almost constant, but when the wiping gas was heated to 420 ° C, which is the melting point of molten zinc metal, the top dross decreased to 0.09. This is considered to be because the cooling of the molten zinc metal on the steel strip could be suppressed. The splash amount was constant regardless of the change in gas temperature.

DESCRIPTION OF SYMBOLS 1 Steel strip 2 Continuous furnace 3 Snout 4 Plating bath 5 Zinc bath 6 Pass circulation roll (sink roll)
7 Support roll 8 Gas wiping nozzle 9 Top roll 10 Shield plate

Claims (5)

  When an inert gas is blown from the gas wiping nozzle disposed opposite to both surfaces of the steel strip that is continuously pulled up from the molten metal plating bath, the steel strip is narrower than the width of the steel strip. A pair of shielding plates having a length of at least 50 mm in the length direction is sandwiched between the steel strips so that the position of the upper end of the shielding plate is 50 mm or more and 150 mm or less below the jet port of the gas wiping nozzle. A method for producing a hot-dip metal-plated steel strip, wherein the steel strip is plated so as to face both surfaces of the steel strip.   2. The method for producing a molten metal plated steel strip according to claim 1, wherein the distance from the lower end of the shielding plate to the molten metal plating bath surface is 30 mm or more and 100 mm or less.   The method for producing a hot-dip metal-plated steel strip according to claim 1 or 2, wherein the difference between the width of the shielding plate and the width of the steel strip is 50 mm or more and 120 mm or less.   The distance between the steel strip and the shielding plate is 30 mm or more and 80 mm or less, The method for producing a hot-dip metal-plated steel strip according to any one of claims 1 to 3.   The temperature of the inert gas at the position where the inert gas collides with the steel strip is equal to or higher than the melting point of the molten metal, and the molten metal-plated steel strip according to any one of claims 1 to 4 Production method.

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