JP2619474B2 - High-speed hot-dip galvanizing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed thinning hot-dip galvanizing method for controlling a coating weight of a steel strip running in a continuous plating method.

[Prior Art] In general, in a continuous hot-dip plating apparatus for steel strip, the control of the basis weight of plating of the steel strip is mainly performed by a gas wiping (gas injection nozzle wiping) method. In this method, air, nitrogen, gas, steam or other high-temperature, high-pressure gas is blown onto the molten plating metal adhering to the steel strip that floats by continuously passing through the hot-dip plating metal bath to generate excess plating. Is wiped off to control the plating weight per unit area. However, if thinning of the plated metal or high-speed plating of the steel strip is performed by this method, it is necessary to spray a considerably high pressure gas. There was a problem that the appearance of the product deteriorated remarkably.

Japanese Patent Application Laid-Open No. 61-2271 discloses a solution to such a problem.
No. 58, JP-A-61-266560 and the like. The invention described in these publications wipes off excess hot-dip metal by blowing gas to the hot-dip metal in a range where the electromagnetic force acts on the hot-dip metal, and the splash of hot-dip metal can be efficiently suppressed. In addition, it is possible to reduce the amount of molten metal attached and to increase the speed at which steel strip is passed.

[Problems to be Solved by the Invention] On the other hand, when the hot-dip plating is wiped off, as shown in the width cross section of the steel strip in FIG. 1, the welding adhered to the steel strip 3 near the position below the gas wiping position. The distribution of the thickness of the plated metal in the width direction of the steel sheet becomes extremely thick as shown by the line a in FIG. 1 and causes splash during gas wiping. On the other hand, in the gas injection wiping method within the electromagnetic force range, as shown by the line b in FIG. 1, the film thickness is smaller than the line a in the entire width of the plate, so that the splash is suppressed. However, in the latter case,
The film thickness is around 50-150mm inside from the steel strip end (No.1
The thickness is slightly thicker at the central portion (portion B in FIG. B line) than at the center portion (portion B in FIG. 1b), and this point determines the rate of splash generation and maximizes the effect of the electromagnetic force applied. There was a problem that not.

Means for Solving the Problems The present inventors consider the cause of the reason that the thickness of the hot-dip metal is slightly increased slightly inside the steel plate end near the lower portion of the gas wiping position of the gas injection wiping nozzle method within the electromagnetic force range. In order to clarify the results, the electromagnetic field was analyzed by the finite element method from various experiments. As a result, as shown in FIG. In the electromagnetic force distribution, as shown in FIG. 2 (a), the induced current concentrates on the plating metal at both ends of the steel strip 3, and as shown in FIG. 2 (b), the induced current and the moving magnetic field are different. The electromagnetic force acting between them will be largely directed inward, and this force causes the plated metal at the end of the steel sheet to move inward and balance the plating metal flow due to the downward electromagnetic force at the center of the steel sheet, that is, slightly less than the end of the steel sheet. Inside It was determined that the thickness of the hot-dip metal was slightly increased on the side. The present invention is based on the investigation of such causes.

That is, a magnetic substance or a conductor is installed in a range including 50 to 150 mm from the end in the width direction of the steel strip relative to the hot-dip plating metal located immediately below the gas wiping nozzle provided within a range where the electromagnetic force is provided, and is disposed below the gas wiping position. By controlling the electromagnetic force distribution applied to the hot-dip coated metal and making the film thickness distribution below the gas wiping position uniform at the center of the steel sheet, the splash compared to methods that do not perform such electromagnetic force distribution control It is intended to provide a hot-dip plating method capable of further suppressing the occurrence of thinning and further increasing the thickness and speed.

[Operation] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 3 is a view presented for explaining the method of the present invention, in which 1 is a hot-dip plating metal bath in which corrosion-resistant metals such as Al, Zn, and Sn are dissolved. Reference numeral 2 denotes an exit roll provided in the hot-dip metal bath 1. 3 is a continuously running steel strip. That is, the steel strip 3 floats through the hot-dip metal bath 1. Reference numeral 4 denotes a moving magnetic field generator, which includes a magnetic core 5 and a coil 6 through which a polyphase alternating current flows. 7 is a gas wiping nozzle and a moving magnetic field generator 4
Are provided in the moving magnetic field. In other words, the excess plating metal 8 adhering to the steel strip 2 which floats through the molten plating metal bath 1 is wiped off by the moving magnetic field generator 4 and the gas wiping nozzle 7 while controlling the plating weight per unit area. ing. 9 is a magnetic or conductive material,
As shown in FIG. 5, FIG. 5 and FIG. 6, the space between the steel strip 3 and the moving magnetic field generator 4 or the end space of the steel strip 3 or especially at the position of the hot-dip metal relative to the molten metal immediately below the gas wiping nozzle 7. In the present invention, it is preferable that the magnetic material or the conductor 9 is provided in a range including 50 to 150 mm (the portion A in FIG. 1) from the end in the width direction of the steel strip in which the film thickness tends to increase.

The magnetic or conductor 9 has the following features. First, as shown in FIG. 4, in order to reduce the magnetic flux passing through both ends of the steel strip 3, the distance between the magnetic poles of the moving magnetic field generators 4, 4 is reduced. The magnetic flux is short-circuited at both ends of the steel strip, for example, a magnetic material in which electromagnetic steel sheets are laminated in a rectangular shape, or a magnetic flux passing through both ends of the steel strip due to a magnetically blocking effect of an induced current generated in a conductor. A conductor that is formed by processing Cu, Al, or the like into a rectangular shape, a diamond shape, or the like is used.

Further, the magnetic material or the conductor 9 is formed by laminating electromagnetic steel sheets in a U-shape as shown in FIG. 5 or a magnetic material in which electromagnetic steel sheets are laminated in a rectangular shape as shown in FIG. And a plurality of steel strips 3 may be arranged in the longitudinal direction of the steel strip. Furthermore, the number and size of the magnetic body and the place where the magnetic body is installed can be arbitrarily determined according to the position and magnitude of the electromagnetic force to be controlled, and the magnetic body can be made movable.

However, in the gas injection wiping nozzle method within the electromagnetic force range as shown in FIG. 3, the thickness distribution in the width direction of the molten metal under the gas wiping position is determined by the direction of the electromagnetic force induced in the molten metal by the moving magnetic field generator. And size distribution. The electromagnetic force is generated by the vector product of the induced current induced in the hot-dip metal and the magnetic flux density passing through the hot-dip metal, the direction of which is shown in FIG. 2 (b).
As shown by the arrow, near the center of the steel sheet, the direction is parallel to the moving direction of the magnetic field, but the closer to both ends, the more inward. Therefore, by controlling the induced current and magnetic flux density at arbitrary positions, the direction and magnitude of the electromagnetic force are partially controlled, the flow of the hot-dip metal on the steel strip is changed, and the film thickness distribution in the width direction is made uniform. can do.

In the present invention, the magnetic material or the conductor 9 reduces the magnetic flux passing through the hot-dip plated metal at the end of the steel strip, thereby suppressing the inward electromagnetic force of the portion A in FIG.
By reducing the inward flow of the hot-dip plating metal, it is possible to obtain a uniform and thin film thickness distribution in the width direction as shown by the line c in FIG.

On the other hand, in the case of FIG. 6, the downward electromagnetic force of the portion A in FIG. 2 (c) is strengthened, and the molten plated metal flowing inward from the end of the steel plate is accumulated in the portion and does not splash, so that the downward direction is generated. By wiping, a uniform and thin film thickness distribution can be obtained in the width direction as shown by the line c in FIG.

[Example] The apparatus shown in FIG. 5 was installed as a magnetic material in the hot-dip plating apparatus shown in FIG. 3, and wiping was performed on a continuous hot-dip zinc plating line. The moving magnetic field generator has a frequency of 1000 Hz, a magnetic flux density on the strip of 400 gauss, and a facing distance of 200 mm. The magnetic body was formed by laminating electromagnetic steel sheets so as to have a U-shape having a height of 100 mm and a thickness of 25 mm, and was installed at both ends of a steel strip below a wiping nozzle.

In the conventional electromagnetic force range in the gas jet wiping method the average basis weight was 43 g / m ² single-sided, the result according to the present invention the sheet passage rate of the strip was plated with 90m / min, an average basis weight of 3
5 g / m ² single-sided galvanized steel sheet was obtained stably. The same effect was obtained when a conductor was provided.

Further, four sets of the apparatus shown in FIG. 6 were installed a little inside from both ends of the steel sheet, and wiping was performed under the same conditions. As a result, a galvanized steel sheet having 38 g / m ^{2 on} one side was obtained.

[Effects of the Invention] As described above, according to the method of the present invention, it is possible to make the plating film thickness distribution below the gas wiping position uniform and to effectively suppress the occurrence of splash. And the industrial effect is extremely large.

[Brief description of the drawings]

FIG. 1 shows the thickness distribution of a hot-dip coated metal film below a gas wiping position by various plating methods. 2A is an eddy current distribution diagram induced by the moving magnetic field generator, and FIGS. 2B and 2C are electromagnetic force distribution diagrams. FIG. 3 is a schematic view of the hot-dip plating of the present invention. FIG. 4, FIG. 5,
FIG. 6 shows a specific example of the magnetic material or conductor 9 of FIG. DESCRIPTION OF SYMBOLS 1 ... Hot-dip plating metal bath, 2 ... Exit roll, 3 ... Steel strip, 4 ... Moving magnetic field generator, 5 ... Magnetic core,
6: coil, 7: gas wiping nozzle, 8: surplus hot-dip metal, 9: magnetic material or conductor.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-136954 (JP, A) JP-A-1-147049 (JP, A) JP-A-64-7261 (JP, A)

Claims (1)

(57) [Claims] 1. A moving magnetic field is applied to a hot-dip plated metal adhered to a steel strip that floats through a hot-dip plated metal to cause an electromagnetic force to act on the plating bath surface side. A magnetic material or a conductor is provided in a range including 50 to 150 mm from the end in the width direction of the steel strip at a position relative to the hot-dip metal immediately below the gas wiping nozzle, and the excess molten metal adhering to the steel strip is provided. A high-speed thinning hot-dip plating method characterized by wiping plated metal.