JP5600873B2 - Method for producing hot-dip steel strip - Google Patents

Description

  The present invention relates to a method for producing a hot dip galvanized steel strip such as a hot dip galvanized steel strip.

  As a method for continuously plating a steel strip, a hot dipping method is known in which a steel strip surface is plated by immersing the steel strip in a molten metal such as zinc or aluminum. This hot-dip plating method will be described by taking as an example a case where hot-dip galvanization is applied to a steel strip. A steel strip that has been cold-rolled or hot-rolled and then has its surface scale removed is made non-oxidizing or Introduced into an annealing furnace maintained in a reducing atmosphere, and after performing an annealing process that also serves to remove the surface oxide film, it was cooled to a temperature approximately the same as the temperature of the molten zinc, and the steel strip was subsequently heated to a molten zinc bath. Then, it is wound around a sink roll provided in the bath and passed through the molten zinc bath through a substantially V-shaped path, and the molten zinc adheres to the surface. And gas is sprayed from a gas wiping nozzle on both surfaces of the steel strip immediately after being drawn out from the molten zinc bath, and excess molten metal is wiped off to adjust the amount of plating adhesion.

  The hot dipping method has many advantages over the electroplating method, such as the ability to produce a plated steel strip at a low cost and the ability to easily produce a thick-plated steel strip. In particular, alloyed hot-dip galvanized steel strips manufactured by hot-dip galvanizing and then alloying the plated layer have characteristics that are excellent in corrosion resistance, weldability and workability. Although it is widely used as a belt, particularly when it is used as a steel strip for exteriors, demands for quality are becoming increasingly severe, such as high definition after painting. In addition, increased production is strongly required to meet the current needs.

  In the manufacturing process of hot dip galvanized steel strip, the wiping part is an important part that determines the quality and productivity of the product. FIG. 6 shows an example of a plating adhesion amount estimation formula. It is known that the plating adhesion amount W and the distance D between the nozzle (= gas wiping nozzle) and the steel strip are substantially proportional. This means that when the nozzle-to-steel strip distance D changes, the coating amount W becomes uneven, which leads to quality defects.

FIGS. 7A and 7B are plan views showing deformation (warpage) of the steel strip in the wiping portion and displacement from the pass line (the steel strip is shown in a horizontal section). When the steel strip is warped in a C shape in the width direction as in 7 (a) (so-called C warpage), the amount of plating adhesion is uneven between the center portion and the end portion. Here, when wiping is performed under the condition of D = 10 mm and W = 50 g / m ² , a case where C warp occurs such that the center portion approaches 1 mm from the nozzle and both ends move away from the nozzle by 1 mm. Considering that, since D = 9 mm in the central portion, the plating adhesion amount W = 45 g / m ² , and since both ends become D = 11 mm, the plating adhesion amount W = 55 g / m ² . Therefore, the unevenness of the plating adhesion amount of 10 g / m ² occurs in the plate width direction.

Moreover, when the steel strip vibrates in the out-of-plane direction as shown in FIG. 7B, uneven plating adhesion appears in a striped pattern in the line direction (longitudinal direction). The stripe pattern pitch is determined by the line speed and the plate vibration frequency. When the line speed is 150 mpm and the plate vibration frequency is 5 Hz, the stripe pattern pitch is 150/60/5 = 0.5 m. Then, when you are wiping conditions the W = 50g / ^{m 2} at D = 10 mm, if the steel strip vibrates with an amplitude ± 1 mm, will produce a coating weight unevenness of 50 ± 5g / ^{m 2} .

  C warpage and vibration of the steel strip not only cause quality defects due to uneven plating adhesion, but also cause a decrease in productivity. The plating adhesion amount W is not only proportional to the nozzle-steel strip distance D but also proportional to the square root of the line speed LS. That is, if the line speed is increased without changing other operating conditions, the plating adhesion amount increases. In other words, in order to increase the line speed while keeping the plating adhesion amount constant, it is necessary to increase the wiping ability. There is a method of increasing the wiping gas pressure in order to increase the wiping ability. However, if the gas pressure is increased unnecessarily, defects due to splash of molten zinc called splash are likely to occur, which is not preferable. Therefore, it is effective to bring the nozzle closer to the steel strip and reduce the nozzle-steel strip distance D. However, if there is warp or vibration of the steel strip, the nozzle and the steel strip may come into contact with each other. -There is a limit in reducing the distance D between steel strips.

  Therefore, it is extremely important to improve both the quality and productivity of hot-dip galvanized steel strips in order to stabilize the plate in the wiping part, that is, to suppress warpage of the steel strip and displacement of the pass line (pass fluctuation and vibration). Become. Therefore, in the past, a plate stabilization device using an electromagnet was placed in the immediate vicinity of the wiping unit, and the attraction force of the electromagnet was appropriately controlled to suppress steel strip warpage and pass line displacement (path fluctuation and vibration). However, a technique (for example, Patent Document 1) for stabilizing the passage plate has been developed and partly put into practical use. In this method, since the electromagnet can apply a force to the steel strip in a non-contact manner, there is a merit that quality deterioration due to contact with the steel strip can be avoided.

In the method of stabilizing the passage plate at the wiping portion using the attraction force of the electromagnet, as shown in Patent Document 1, generally three or more electromagnets are arranged at a predetermined interval in the plate width direction. By arranging, warpage in the plate width direction can be corrected. This is because the steel strip normally has a C-warp. In this case, it is important that the electromagnets are located at both ends and the center of the steel strip in the width direction.
In the production line for hot dip galvanized steel strips, various sizes (plate thickness, plate width) are usually produced in one line, and in some lines the plate thickness is 0.4 to 2.3 mm. The plate width covers a range of 610 to 1850 mm. For such a wide range of plate widths, it is not easy to always place electromagnets at both ends and the center, but for example, many electromagnets are arranged in the plate width direction, and the electromagnet to be used is switched depending on the size of the steel strip. A method for realizing this is proposed (Patent Document 2). However, since the electromagnet has a certain size and the number of installations is limited, there is no guarantee that the electromagnet is reliably positioned at both ends of the steel strip.

Then, the proposal which made the electromagnet surely be located in the both ends and center part of a steel strip width direction by providing the mechanism which moves an electromagnet following a steel strip edge is also made | formed (patent document 3). In this case, good position control and vibration suppression at both end portions and the center portion in the steel strip width direction are possible, and substantially sufficient plate stabilization is achieved.
Japanese Patent Laid-Open No. 2-62355 JP-A-7-256341 JP-A-11-287564

  However, even with such a technique, satisfactory results may not be obtained when the steel strip is wide and thin. This is because when the plate width is wide, the interval between the electromagnets arranged in the width direction becomes large, and when the plate thickness is thin, the bending rigidity of the plate becomes low. This is because the steel strip hardly moves (that is, there is almost no displacement of the steel strip due to the action of the electromagnet) at a distant position, that is, in the vicinity of the center of the steel strip from the both ends of the steel strip. In other words, there is an uncontrollable place where the influence of the attraction force of the electromagnet hardly reaches.

FIG. 5 is a plan view of a wiping portion (3a, 3b indicates a gas wiping nozzle) in a state in which the steel strip S is horizontally cross-sectioned. If the band S (solid line in FIG. 5) is to be corrected, the center and both ends in the plate width direction where the electromagnet is present can be corrected to the target path position, but in the vicinity of the center slightly away from both ends (in the figure) ), The steel strip S hardly moves, and as a result, a large W-shaped warp (hereinafter referred to as “W warp”) as shown by a two-dot chain line in FIG. 5 remains. .
Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, and in the method of performing hot dipping of the steel strip while correcting the steel strip shape and the like by the plate stabilizer, for all steel strip sizes. An object of the present invention is to provide a method for manufacturing a hot-dip galvanized steel strip that realizes good shape correction and can manufacture a high-quality hot-dip galvanized steel strip with high productivity due to the stable sheet-passability at the wiping portion.

As a result of intensive studies to solve the above problems, the present inventors have found that the position of the steel strip width direction where the influence of the attractive force of the electromagnet is most difficult (that is, when the electromagnet of the threading plate stabilization device is applied). Gas position so that the steel strip approaches the middle position of the pair of gas wiping nozzles, or the plating adhesion amount approaches the target value at the position in the width direction of the steel strip where the displacement of the steel strip due to the action of the electromagnet is the smallest. It has been found that by adjusting the position of the wiping nozzle in the thickness direction of the steel strip, it is possible to achieve good plate stabilization at the wiping portion in all steel plate sizes.
The present invention has been made based on such knowledge, and the gas wiping nozzle is appropriately positioned in the thickness direction of the steel strip so that it is not necessary to move and control the steel strip position where the attractive force of the electromagnet is difficult to reach. By adjusting, a stable plate is realized, and the gist is as follows.

[1] A pair of gas wiping nozzles for adjusting the amount of plating applied by injecting gas onto both sides of the steel strip exiting the hot dipping bath, and a steel strip facing both sides of the steel strip at a position near the gas wiping nozzle In a continuous hot dip plating apparatus equipped with a sheet plate stabilizing device having three or more electromagnets arranged at intervals in the width direction, the steel plate is deformed and / or displaced from a pass line by the sheet plate stabilizing device. Is a method for manufacturing a hot-dip galvanized steel strip, which applies continuous hot-dip plating to the steel strip,
In the steel strip width direction position where the amount of displacement of the steel strip due to the action of the electromagnet is the smallest when the electromagnet of the plate stabilizing device is applied, the steel strip approaches the middle position of the pair of gas wiping nozzles. A method for producing a hot-dip galvanized steel strip, comprising adjusting a position of a gas wiping nozzle in a steel strip thickness direction.
[2] In the manufacturing method of the above [1], when the electromagnet of the plate stabilizing device is operated, the steel strip is a pair of steel strips at the position where the displacement of the steel strip due to the action of the electromagnet is the smallest. A method for producing a hot dipped steel strip, characterized by adjusting a position of the gas wiping nozzle in a thickness direction of the steel strip so as to be positioned in the middle of the gas wiping nozzle.
[3] In the manufacturing method of [1] or [2] above, the attractive force of each electromagnet so that the warp of the steel strip is corrected in a state where the position of the gas wiping nozzle is adjusted in the thickness direction of the steel strip. A method of manufacturing a hot-dip galvanized steel strip characterized by adjusting the thickness.

[4] A pair of gas wiping nozzles that adjust the amount of plating applied by injecting gas onto both sides of the steel strip that has exited the hot dipping bath, and a steel strip facing both sides of the steel strip at a position near the gas wiping nozzle In a continuous hot dip plating apparatus equipped with a sheet plate stabilizing device having three or more electromagnets arranged at intervals in the width direction, the steel plate is deformed and / or displaced from a pass line by the sheet plate stabilizing device. Is a method for manufacturing a hot-dip galvanized steel strip, which applies continuous hot-dip plating to the steel strip,
The steel strip of the gas wiping nozzle so that the plating adhesion amount approaches the target value at the position in the steel strip width direction where the displacement amount of the steel strip due to the action of the electromagnet is the smallest when the electromagnet of the threading plate stabilization device is actuated. A method for producing a hot-dip galvanized steel strip, characterized by adjusting a position in a plate thickness direction.

  In the method of hot dip plating of steel strip while correcting the steel strip shape etc. with the plate stabilizer, it can realize good plate stabilization without causing defects such as W warp for all steel strip sizes, For this reason, a high quality hot-dip galvanized steel strip can be manufactured stably with high productivity.

1 and 2 show a schematic configuration of a steel strip hot dip plating equipment (for example, hot dip galvanizing equipment) used for carrying out the present invention. FIG. 1 is an overall explanatory view, and FIG. It is an arrow line view which follows the II-II line.
In FIG. 1, reference numeral 1 is a molten zinc pot, and 2 is a sink roll disposed in the molten zinc pot 1. Reference numerals 3a and 3b denote a pair of gas wiping nozzles (hereinafter simply referred to as “nozzles 3a and 3b”), which adjust the plating deposition amount by injecting gas onto both surfaces of the steel strip S exiting the hot dipping bath. The pair of gas wiping nozzles 3a and 3b can move (position adjustment is possible) in the steel strip thickness direction.

Reference numeral 4 denotes a non-contact type plate stabilizing device provided in the vicinity of the gas wiping nozzles 3a and 3b (in the present embodiment, the position immediately above). This plate stabilizing device 4 is provided on both sides of the steel strip. A plurality of (three each in the present embodiment) electromagnets 5 are arranged so as to face each other at intervals in the steel strip width direction. The electromagnet 5 is provided in at least three places so as to be opposed to the central portion and both end portions in the width direction of the steel strip. By controlling the attraction force by each of the electromagnets 5, deformation (warping, etc.) of the steel strip S Displacement relative to the pass line (pass fluctuation, vibration, etc.) is corrected. The electromagnet 5 may be provided at four or more locations.
In addition, a distance meter (not shown) is usually attached to the sheet-passage stabilizing device 4 in order to measure deformation (warp etc.) of the steel strip S and displacement (path fluctuation, vibration, etc.) from the pass line. ing.
In addition, you may arrange | position the plate | board stabilization apparatus 4 in the direct vicinity of the gas wiping nozzles 3a and 3b, or both in the direct vicinity of the gas wiping nozzles 3a and 3b.

  In the first invention of the present application, when the hot strip plating is performed on the steel strip S while the deformation of the steel strip S and / or the displacement from the pass line is corrected by the pass plate stabilizing device 4, When the electromagnet 4 is operated, the steel strip S approaches the intermediate position between the pair of gas wiping nozzles 3a and 3b at the position in the steel strip width direction where the displacement of the steel strip S due to the action of the electromagnet 5 is the smallest. In addition, the position of the gas wiping nozzles 3a and 3b in the thickness direction of the steel strip is preferably adjusted so that the steel strip S is positioned between the pair of gas wiping nozzles 3a and 3b.

FIG. 3 shows the behavior of the steel strip S and the gas wiping nozzles 3a and 3b in one embodiment of the present invention. In both FIGS. 3 (a) and 3 (b), the steel strip S is shown in a horizontal section. It is a top view of a wiping part. In the figure, c indicates an intermediate position between the pair of gas wiping nozzles 3a and 3b, and this intermediate position c is also a target pass position.
When the steel strip S having a wide plate width and a thin plate thickness is deviated from the target path position as shown in FIG. 3 (a) and is warped C, it is divided into three pieces at the center and both ends in the steel strip width direction. If the electromagnet 5 is used for correction, the steel strip S cannot be moved at a position where the attraction force of the electromagnet is difficult to reach, so that the W warp remains as shown in FIG.

  Therefore, in the present invention, the gas wiping nozzles 3a and 3b are translated in the steel strip thickness direction (the arrow direction in FIG. 3 (A)), and the position in the steel strip width direction where the attractive force of the electromagnet 5 is most difficult, that is, At the position in the width direction of the steel strip where the amount of displacement of the steel strip S due to the action of the electromagnet 5 is the smallest (the position surrounded by the circle in FIG. 3B), the steel strip S is an intermediate position between the pair of gas wiping nozzles 3a and 3b. The position of the gas wiping nozzles 3a, 3b in the steel strip thickness direction is adjusted so that the steel strip S is preferably positioned at an intermediate position c between the pair of gas wiping nozzles 3a, 3b so as to approach c. Needless to say, the steel strip S is corrected to a flat as much as possible on the premise of the relative positional relationship between the gas wiping nozzles 3a, 3b and the steel strip S, which are adjusted as described above, in the steel strip thickness direction. The attractive force of each electromagnet 5 is adjusted. As a result, as shown in FIG. 3B, the steel strip S can be corrected to a substantially flat shape without leaving a large W warp as shown in FIG.

  The above-described position adjustment of the gas wiping nozzles 3a and 3b is preferably performed so that the steel strip S is as close as possible to the intermediate position c between the gas wiping nozzles 3a and 3b, but generally the tolerance of the plating adhesion amount is about 20%. When the distance between each gas wiping nozzle 3 to the intermediate position c is L, as shown in FIG. 4, the both sides L × 0.2 from the intermediate position c in the steel strip thickness direction, as shown in FIG. The position is preferably adjusted so as to fall within the range.

The position in the width direction of the steel strip in which the amount of displacement of the steel strip S due to the action of the electromagnet 5 is the smallest is approximately near the center side from the both ends of the steel strip to about ¼ of the plate width. It can be calculated by FEM analysis in consideration of the band size, tension, and roll arrangement.
Moreover, the steel strip position in the steel strip thickness direction can be grasped by the following two methods. Therefore, the steel strip width in which the displacement amount of the steel strip S due to the action of the electromagnet 5 is minimized by these methods. The direction position can be specified.
In the first method, a plurality of distance meters are arranged side by side in the plate width direction, and the value of one distance meter closest to the position in the target width direction or the linear interpolation (weight) of the two distance meters closest to the first and second. Average value). Although there is a drawback that a lot of distance meters have to be installed, the accurate value can be grasped.

The second method is a method of estimating from the values of distance meters installed corresponding to the electromagnets at the center and both ends in the plate width direction. The simplest is a method using linear interpolation (weighted average value) of the values of the distance meter between the center part and the end part. For example, the position in the target width direction is closer to the center of the plate width by 20% from the end part. Then, the estimated value x of the steel strip position in the plate thickness direction at the target width direction position is given by the following equation.
x = x _c × 0.4 + x _e × 0.6
Where x _{c is} the measured value of the center distance meter
x _e : Measurement value of end distance meter More precisely, using a warped profile obtained by FEM analysis etc. considering steel plate size, tension, and roll arrangement, and interpolating from the distance meter values at the center and end Just do it.

In the second invention of the present application, when the continuous strip plating is applied to the steel strip S while the deformation of the steel strip S and / or the displacement from the pass line is corrected by the through plate stabilizer 4, the through plate stabilizer 4 is used. The steel strips of the gas wiping nozzles 3a and 3b are arranged so that the amount of plating adhesion approaches the target value at the position in the steel strip width direction where the amount of displacement of the steel strip S due to the action of the electromagnet 5 is the smallest. Adjust the position in the thickness direction.
In general, in the production of hot dip galvanized steel strip, an online adhesion meter is often installed to measure the adhesion distribution in the plate width direction in order to guarantee the plating adhesion according to the user's request. Therefore, based on the measured value (signal) of the adhesion meter, the position in the steel strip width direction where the attractive force of the electromagnet 5 is most difficult, that is, the steel strip width direction in which the displacement amount of the steel strip S due to the action of the electromagnet 5 is the smallest. At the position (the position surrounded by a circle in FIG. 3B), the position of the gas wiping nozzles 3a and 3b in the steel strip thickness direction is adjusted so that the plating adhesion amount approaches the target value. This eliminates the need to adjust the amount of plating applied at this position, and the steel plate position is controlled at the position in the steel strip width direction (center and both ends) where the attractive force of the electromagnet 5 reaches. You can do it.

Also in the second invention of this application, the steel strip width direction position with the least amount of displacement of the steel strip S due to the action of the electromagnet 5 can be specified by the method described above.
In general, since the adhesion meter is installed several tens of meters or more downstream from the wiping unit, there is a drawback of having a time delay, but path deviation and C warpage do not change greatly within the same coil. It won't be a big problem. On the other hand, since the adhesion amount data is normally continuously measured in the plate width direction, there is an advantage that the value at the target width direction position can be accurately grasped as an actual measurement value instead of an estimated value.
In addition, this invention is applicable to manufacture of arbitrary hot dip galvanized metal strips, such as hot dip galvanized steel strips, hot dip galvanized aluminum alloy plated steel strips, and aluminum plated steel strips.

Whole explanatory drawing which shows schematic structure of the hot-dipping equipment of the steel strip used for implementation of this invention It is an arrow line view which follows the II-II line | wire in FIG. Explanatory drawing which shows the behavior of the steel strip and gas wiping nozzle in one Embodiment of this invention In this invention, explanatory drawing which shows the preferable range of the steel strip position with respect to the intermediate position c of a pair of gas wiping nozzles Explanatory drawing which shows the behavior of the steel strip in the wiping part of the conventional hot dipping equipment Explanatory diagram showing the relationship between the amount of plating adhesion, the distance between the nozzle and steel strip, and the line speed Explanatory drawing which shows the change of the distance between nozzle-steel strip by C curvature and vibration of steel strip

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molten zinc pot 2 Sink roll 3a, 3b Gas wiping nozzle 4 Passing plate stabilization apparatus 5 Electromagnet S Steel strip

Claims (4)

A pair of gas wiping nozzles that adjust the amount of plating applied by injecting gas onto both sides of the steel strip that has exited the hot dipping bath, and in the width direction of the steel strip facing both sides of the steel strip in the vicinity of the gas wiping nozzle In a continuous hot dip plating apparatus equipped with a sheet plate stabilization device having three or more electromagnets arranged at intervals, the sheet plate stabilization device corrects deformation of the steel strip and / or displacement from the pass line. Meanwhile, a method for manufacturing a hot-dip galvanized steel strip, which applies continuous hot dip plating to the steel strip,
In the steel strip width direction position where the amount of displacement of the steel strip due to the action of the electromagnet is the smallest when the electromagnet of the plate stabilizing device is applied, the steel strip approaches the middle position of the pair of gas wiping nozzles. A method for producing a hot-dip galvanized steel strip, comprising adjusting a position of a gas wiping nozzle in a steel strip thickness direction.   Gas is applied so that the steel strip is positioned in the middle of the pair of gas wiping nozzles at the position in the width direction of the steel strip where the displacement of the steel strip due to the action of the electromagnet is the smallest when the electromagnet of the plate stabilizer is applied. 2. The method of manufacturing a hot-dip galvanized steel strip according to claim 1, wherein the position of the wiping nozzle in the thickness direction of the steel strip is adjusted. The attraction force of each electromagnet is adjusted so that the warp of the steel strip is corrected in a state in which the position of the gas wiping nozzle in the steel strip thickness direction is adjusted. Manufacturing method of hot dipped steel strip. A pair of gas wiping nozzles that adjust the amount of plating applied by injecting gas onto both sides of the steel strip that has exited the hot dipping bath, and in the width direction of the steel strip facing both sides of the steel strip in the vicinity of the gas wiping nozzle In a continuous hot dip plating apparatus equipped with a sheet plate stabilization device having three or more electromagnets arranged at intervals, the sheet plate stabilization device corrects deformation of the steel strip and / or displacement from the pass line. Meanwhile, a method for manufacturing a hot-dip galvanized steel strip, which applies continuous hot dip plating to the steel strip,
The steel strip of the gas wiping nozzle so that the plating adhesion amount approaches the target value at the position in the steel strip width direction where the displacement amount of the steel strip due to the action of the electromagnet is the smallest when the electromagnet of the threading plate stabilization device is actuated. A method for producing a hot-dip galvanized steel strip, characterized by adjusting a position in a plate thickness direction.

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