JPH0551719A - Method for controlling plating amount of hot-dip metal coated steel sheet - Google Patents

Abstract

PURPOSE:To obtain a uniform plating film at a high speed by preventing a steel sheet from being cambered or vibrated by a magnetic pressure, wiping the molten metal deposited on the sheet in cooperation with a blowing gas and controlling the plating amt. of the sheet. CONSTITUTION:High-frequency current conducting paths 1a and 1b are provided to a gas wiping nozzle 2 on both sides of a steel sheet S in the longitudinal direction of the nozzle. A high-frequency current sufficient to magnetically saturate the sheet S is applied to the paths to induce an antiphase high-frequency current in the sheet S. A magnetic pressure acting on the surface of the sheet S is generated by the interaction between the induced current and the high-frequency current of the paths 1a and 1b. The sheet S is not cambered or vibrated in its width direction because of the magnetic pressure acting on the sheet S from both sides, the molten metal deposited on the sheet S is wiped in cooperation with the blowing gas, and the plating amt. of the sheet is controlled. Consequently, any trouble is not caused around the gas wiping nozzle when continuous hot-dip metal coating is carried out at a high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for wiping molten metal adhering to a steel sheet and performing coating weight of the plated steel sheet in hot metal galvanizing such as continuous hot dip galvanizing.

[0002]

2. Description of the Related Art In continuous hot dip plating, as shown in FIG. 14, a steel plate S wound and conveyed around a sink roll 4 in a hot dip bath 3 has a pinch roll 5 for pressing and plate straightening.
After being pulled up, the excess wiping amount is usually squeezed out by the gas wiping nozzle 6 on the surface of the plating bath to obtain a uniform plating thickness.

In such a plating process, if an attempt is made to increase the plate passing speed in order to increase productivity, the steel plate S
As a result, the amount of molten metal that is lifted upward is necessarily increased, and therefore the gas pressure of the gas wiping nozzle 6 needs to be increased. However, when the gas pressure of the gas wiping nozzle 6 is increased in this way, the gas jet that collides with the plate at a high speed not only scrapes off the excess molten metal downward, but also generates an associated gas flow, and this associated gas flow A part of the molten metal becomes splash, which adheres to the gas wiping nozzle to cause nozzle clogging, and as a result, the uniformity of the gas flow is impaired and the coating weight cannot be made uniform. Such a non-uniform coating weight causes not only aesthetic problems, but also non-uniform alloying after plating and load collapse during winding. There is also a problem that part of the splash redeposits on the steel plate, causing damage to the steel plate. Further, increasing the gas flow rate of the gas wiping nozzle also causes a cost increase and noise generation.

Conventionally, the following proposals have been made regarding a method of squeezing out excess molten metal in order to cope with speeding up. As disclosed in Japanese Examined Patent Publication No. 44-7444, a method of applying a high frequency magnetic field to a steel sheet, squeezing the molten metal by utilizing Lorentz force associated with an eddy current generated in the steel sheet, and using gas wiping together As disclosed in Japanese Patent Laid-Open No. 61-227158, a method in which a steady current is passed through a steel sheet, the excess molten metal is squeezed downward by a Lorentz force with a static magnetic field, and then the molten metal is delivered to a gas wiping nozzle. As shown in, by generating a static magnetic field in the out-of-plane direction of the steel sheet, Lorentz force of the induced current and static magnetic field in the molten metal generated by the movement of the steel sheet, after squeezing the excess molten metal downward, Method for reaching gas wiping nozzles JP-A-61-266560 and JP-A-62-10303
No. 33, a method of generating a moving magnetic field in the downward direction of a steel sheet and squeezing surplus molten metal downward, and then arriving at a gas wiping nozzle.

[0005]

However, the biggest drawback of these methods is that, when a magnetic field is applied to a ferromagnetic material such as a steel sheet, the steel sheet is attracted to a strong magnetic field, resulting in an unstable system. However, it is difficult to perform proper control as intended. In order to avoid such a control problem, it is necessary to widen the gap between the magnetic field generator and the steel sheet. As a result, the effect of the magnetic field is extremely limited, and the effect originally intended is not achieved. I can't get enough.

Further, as factors that hinder the uniformity of the basis weight of the molten metal, vibration of the steel sheet and plate warpage in the width direction (so-called C
There is a warp), but none of the above-mentioned proposals has any effect on the damping of the steel plate and the correction of the plate warp. The above Japanese Patent Publication 44-
No. 7444 describes that a steel sheet passing between coils is centered between the coils by a magnetic repulsive force, which is expected to have a vibration suppressing effect on the steel sheet. When a high-frequency magnetic field is simply applied to the steel sheet, the magnetic attraction force strongly acts on the steel sheet that is a ferromagnetic body, so that the steel sheet to be passed is attracted in the coil direction, etc.
On the contrary, an unstable state is caused, and vibration suppression etc. cannot be expected at all.

As described above, the conventional method has a fundamental problem that the ferromagnetic steel sheet is attracted by the magnetic field and becomes an unstable system. Therefore, it is impossible to expect a sufficient effect as originally intended. There was a flaw.

The present invention has been made in view of such a conventional problem, and prevents the warpage and vibration of the hot-dip plated steel sheet, while maintaining a smooth finished surface originally obtained by gas wiping, at a high speed and uniformly. The present invention aims to provide a fabric weighting method that enables easy fabric weighting.

[0009]

[Means for Solving the Problems] Even if a magnetic field is simply applied to a ferromagnetic material such as a steel sheet to suppress the vibration of the steel sheet or coat the coating weight, the magnetic attraction force acts on the steel sheet, making the steel sheet more unstable. It is as described above that it is put in such a state. With respect to such a problem, the present inventors have noticed that the region showing the ferromagnetism of the steel sheet is limited to the non-saturation region as shown by the curves B to H in FIG. , If a high frequency magnetic field is applied to the steel plate to reach a sufficient saturation range,
The repulsive force generated between the current flowing through the high-frequency current path and the induced current in the steel sheet is stronger than the magnetic attraction force, and the instability associated with the magnetic attraction force is eliminated. The present invention has been completed by finding that it is possible to appropriately and effectively squeeze the molten metal in cooperation with the gas wipe by applying the voltage to a portion very close to the gas wiping location.

That is, the present invention provides a method for controlling the coating weight of a steel sheet by spraying a gas from a gas wiping nozzle onto the molten metal adhering to both sides of the steel sheet drawn from the hot dip bath above the bath surface of the hot dip bath. A high-frequency current conducting path is provided along the longitudinal direction of the nozzle portion of each gas wiping nozzle on both sides, and a high-frequency current of a sufficient magnitude to sufficiently saturate the steel plate is supplied to each high-frequency current conducting path. To induce an antiphase high-frequency current in the steel sheet, and generate a magnetic pressure acting on the steel sheet surface by the interaction between the induced current and the high-frequency current in each of the current conducting paths,
The magnetic pressure acting on both sides of the steel plate prevents warpage and vibration in the width direction of the steel plate, and wipes the molten metal adhering to the steel plate in cooperation with the above-mentioned blowing gas to provide a coating weight for the steel plate. It was designed to do.

In the present invention as described above, two or more high frequency current conducting paths can be provided at intervals in the steel sheet passing direction. That is, for example, two high-frequency current conducting paths can be incorporated in one nozzle portion at intervals in the steel plate passing direction. In addition to the inside of the nozzle portion, it is possible to provide another high-frequency current conducting path above or below the nozzle portion, or both. Further, the gas wiping nozzle incorporating the high-frequency current conducting path is generally arranged at a position substantially opposite to each other with the steel plate sandwiched therebetween, and in this case, high-frequency currents of the same phase are applied to both of the opposing high-frequency current conducting paths. Shed However, for example, when a plurality of high-frequency current conducting paths are arranged on both sides of the steel sheet as described above, the gas wiping nozzles in which the high-frequency current conducting paths are incorporated do not necessarily have to face each other with the steel sheet interposed therebetween, The positions may be shifted in the sheet passing direction. Further, in this case, there is no restriction on the phase of the current unlike the case where the gas wiping nozzle incorporating the high frequency current conducting path faces the steel plate across it.

The high-frequency current conducting path to be incorporated in the nozzle needs to be provided in the width direction of the steel plate, but it is not always necessary to provide it in parallel with the plate width direction. It is possible to provide an inclination, or a part of the high-frequency current conducting path may be inclined with respect to the plate width direction. At the edge of the steel sheet, the direction of the current flowing through the steel sheet is 90 ° with respect to the current flowing through the high-frequency current conducting path, so the magnetic pressure tends to weaken near this edge. As described above, the entire length of the high-frequency current conducting path is inclined with respect to the plate width direction, or the portion facing the vicinity of the steel plate edge portion of the current conducting path is inclined with respect to the plate width direction. Is effective. When a part or all of the high-frequency current conducting path is tilted in this way, the nozzle itself may be tilted, or only the current conducting path in the nozzle portion may be tilted.

[0013]

The operation of the method of the present invention is shown in FIG. 1 (relationship diagram between magnetic flux density and magnetic field strength) showing the magnetic characteristics of a steel sheet which is a ferromagnetic material, and FIGS. 2 and 3 showing one embodiment of the present invention. It will be explained based on. 2 is a side view showing an implementation state, and FIG. 3 is a front view of the same.

In the method of the present invention, above the bath surface of the hot dip plating bath 3, a high-frequency current conducting path 1a parallel to the steel plate surface is formed on the front surface side and the rear surface side of the steel plate S drawn from the hot dip plating bath 3 and continuously threaded. The gas wiping nozzle 2 having the tip nozzle portion 1b is arranged close to the steel plate S. In this embodiment, two high-frequency current conducting paths are provided above and below the nozzle slit of each nozzle. When high-frequency currents of the same phase are passed through the high-frequency current conducting paths 1a, 1b, currents of opposite phases flow through the steel plate S. Since the current flowing through this steel plate has a direction opposite to that of the high-frequency current conducting path,
Magnetic repulsion, that is, magnetic pressure, acts on the surface of the steel sheet. However, since a ferromagnetic material such as a steel plate has a high magnetic permeability, if a current simply flows as described above,
The magnetic attraction force exceeds the repulsive force, resulting in an unstable system. Here, as the current in the high-frequency current conducting paths 1a, 1b is increased, the amplitude of the magnetic field in the steel sheet shown in FIG. 1 increases, and the time the steel sheet stays in the saturated region generally increases. As a result, the magnetic repulsive force becomes much more dominant than the magnetic attractive force above a certain magnetic field amplitude. In the present invention, a high-frequency current of a sufficient magnitude to magnetically saturate the steel sheet S in this manner is passed through the high-frequency current conducting paths 1a, 1b to obtain the necessary magnetic repulsion force. This magnetic repulsive force is due to the steel plate S
On the other hand, it is the same as the non-contact springs acting from both sides of the steel plate S, thereby suppressing the vibration of the steel plate S and correcting the C warp. Then, under such a situation that the steel plate S is damped and the plate warp is corrected, the magnetic pressure to the molten metal acting from both sides of the steel plate and the blowing gas cooperate to adhere to the steel plate. The surplus molten metal 30 is squeezed out, and an extremely uniform basis weight is possible. That is, since the magnetic pressure acts on the gas wiping position to suppress and correct the vibration and warpage of the plate and perform wiping in cooperation with the gas pressure, the molten metal can be appropriately and efficiently used even when the wiping gas pressure is low. It can be squeezed. Further, the smoothness of the plating surface is properly maintained by the gas wipe.

[0015]

2 to 8 show an embodiment of the present invention. Of these, FIGS. 2 and 3 show the high-frequency current conducting path 1a parallel to the steel plate surface in each tip nozzle portion of the pair of gas wiping nozzles 2 arranged so as to face each other across the steel plate S as described above. 1b (in this embodiment, two pairs of upper and lower high frequency current conducting paths 1a and 1b are provided inside the nozzle)
Is placed close to the steel plate, and these high-frequency current conducting paths 1a,
A high frequency current of the same phase is made to flow through 1b.

4 and 5, the high-frequency current conducting paths 1a and 1b are incorporated in the respective tip nozzle portions of the gas wiping nozzle 2 facing each other, and another high-frequency current conducting path 1a 'is provided below each nozzle. In this example, 1b 'is arranged close to the steel plate S. In this example, the phases of the currents in the upper and lower high frequency current conducting paths are opposite to each other, but they may have the same phase.

FIG. 6 shows a high-frequency current conducting path 1 on both sides of the steel plate.
The wiping nozzles 2 in which a and 1b are incorporated are vertically arranged without sandwiching the steel plates to face each other, and separate high-frequency current conducting paths 1a ′ and 1b are provided above and below each of them.
This is an example of the case where the high frequency current conducting paths are arranged in a zigzag pattern as a whole. In this case, a current having a phase opposite to that of the high-frequency current flowing in each individual high-frequency current conducting path flows in the steel sheet, and the magnetic pressure from the opposite direction is alternately applied to the steel sheet S in the steel sheet passing direction. Will work. In this example, the phases of the currents flowing through the high-frequency current conducting path are opposite between the front surface side and the rear surface side of the steel sheet, but the phases may be the same. That is, the phase of the current flowing through the high frequency current conducting path is arbitrary.

At the edge of the steel sheet, the direction of the current flowing through the steel sheet is 9 with respect to the current flowing through the high frequency current conducting path.
Since the relationship is 0 °, the magnetic pressure tends to weaken in the vicinity of this edge portion. To solve such a problem, the high frequency current conducting path is inclined with respect to the plate width direction, or the steel sheet of the current conducting path is inclined. It is effective to provide a portion facing the vicinity of the edge with an inclination in the plate width direction. FIG. 7 shows the former example, in which the entire lengths of the high-frequency current conducting paths 1a and 1b incorporated in the wiping nozzles 2 on both sides of the steel plate have an appropriate inclination with respect to the plate width direction. Further, FIG. 8 shows a portion 11 of the high-frequency current conducting paths 1a and 1b facing the vicinity of the edge of the steel plate, which is inclined with respect to the plate width direction. The configuration as described above is applicable to each of the above embodiments.

The present inventors conducted the following simulation analysis in order to verify the effect of the present invention. This analysis is based on the following analysis conditions for the arrangement example of the high-frequency current conducting path shown in FIG. 4, based on the following analysis conditions: Coil cross-sectional dimension: 30 × 50 mm Coil current: 3 × 10 ⁴ A Frequency: 3000 Hz Steel plate thickness: 2. 3 mm Steel plate relative permeability: 1 When the steel plates are located at the center positions 15 mm apart from both high-frequency current conducting paths, the steel plates are 5 mm and 10 mm from the center position on one side of the high-frequency current conducting paths, respectively.
It carried out about three levels when it shifted each time. This analytical model is shown in FIG. As a result of this analysis, the one-sided amplitude of the magnetic field strength under these conditions is 160000 A / m, and in the steel sheet having typical B to H curves as shown in FIG. 1 and Table 1,
It was found that the steel sheet was completely in the saturated region. FIG. 10 shows an analysis example of one cycle of the maximum magnetic pressure in this case. According to this, the time when the magnetic attraction force exceeds the magnetic pressure is 6% or less, and the maximum value of the magnetic pressure is 5 times the magnetic attraction force. It is found that the magnetic pressure can be applied to the steel sheet extremely stably even though the steel sheet is a ferromagnetic material.

Next, an example of analyzing the distribution of time-averaged magnetic pressure average values on the steel plate surface will be shown. FIG. 11 shows the distribution of magnetic pressure when the steel sheet is at the center position of both current conducting paths, and FIGS. 12 and 13 show the distribution of each magnetic pressure when the steel sheet is deviated by 5 mm and 10 mm to the current conducting path side on one side from the center position. Shows. According to this, when the steel plate deviates from the center position, a force to push the steel plate toward the center as a whole works. This magnetic pressure increases as the steel sheet approaches the high-frequency current conducting path, so that it effectively acts on the centering action of the steel sheet and is effective in preventing vibration. It is also effective as a correction force for C warpage, and the total C
It can be seen that the warp amount can be suppressed within 0.5 mm.

Based on these results, in the conventional plating equipment as shown in FIG. 14, the conventional gas wiping nozzle 6 is replaced with an apparatus corresponding to FIGS. 4 and 5 at a position 400 mm above the plating bath surface. The unit weight of the hot-dip galvanized steel sheet was implemented. In this experiment, the plate width of the steel plate and the current conditions were the same as in the above simulation analysis, and the line speed was 150 m / min and the gas flow rate was 190 m / s.

As a result, the C-warp of the steel sheet at the wiping point according to the method of the present invention was completely corrected and the vibration was 1 mm.
It was possible to suppress the amplitude within the range, and there was no generation of splash or noise as in the case of performing high pressure gas wiping as in the past, and it was possible to perform extremely uniform plating basis weight with a low gas spraying pressure. .. It was also confirmed that galvanization with a basis weight of 35 g / m ² , which was difficult with a conventional gas wiping method at a line speed of 150 m / min, could be easily performed.

[0023]

[Table 1]

[0024]

According to the present invention described above, the problem around the gas wiping nozzle, which has been a bottleneck in the speedup of continuous hot-dip plating in the past, is solved, and high-speed plating with a uniform film thickness is made possible. is there.

[Brief description of drawings]

[Fig. 1] Relationship diagram between magnetic flux density of steel sheet and magnetic field strength

FIG. 2 is a side view showing an embodiment of the present invention.

FIG. 3 is a front view of the embodiment shown in FIG.

FIG. 4 is a side view showing another embodiment of the present invention.

5 is a front view of the embodiment shown in FIG.

FIG. 6 is a side view showing another embodiment of the present invention.

FIG. 7 is a front view showing another embodiment of the present invention.

FIG. 8 is a front view showing another embodiment of the present invention.

FIG. 9 is an explanatory diagram showing an analytical model in a simulation for calculating a magnetic pressure exerted on a steel sheet by a high frequency current conducting path.

10 is a graph showing an example of analysis of one cycle of maximum magnetic pressure in the analysis of FIG.

11 is a graph showing the distribution of magnetic pressure when the steel sheet is in the center position in the analysis of FIG.

FIG. 12 is a graph showing the distribution of magnetic pressure when the steel sheet is displaced from the center position by 5 mm in the analysis of FIG. 9.

FIG. 13 is a graph showing the distribution of magnetic pressure when the steel sheet is displaced 10 mm from the center position in the analysis of FIG. 9.

FIG. 14 is an explanatory view showing a conventional hot dip plating and basis weight method.

[Explanation of symbols]

1, 1a, 1b ... High-frequency current conducting path, 2 ... Gas wiping nozzle, 3 ... Hot dip plating bath, 11 ... Part, 30 ... Molten metal, S ... Steel plate

Claims (2)

[Claims] 1. A method for controlling the coating weight of a steel sheet by spraying gas from a gas wiping nozzle onto molten metal adhering to both sides of a steel sheet drawn from the hot dip bath above the bath surface of the hot dip bath. A high-frequency current conducting path along the longitudinal direction of the nozzle portion of the gas wiping nozzle is provided, and a high-frequency current of a sufficient magnitude to sufficiently magnetically saturate the steel sheet is passed through each high-frequency current conducting path to the steel sheet. Induction of high-frequency current of opposite phase, magnetic force acting on the steel sheet surface is generated by the interaction of this induction current and the high-frequency current of each current conducting path, the steel sheet by the magnetic pressure acting from both sides of the steel sheet, The plate width and the vibration in the width direction, and the molten metal adhering to the steel plate is wiped in cooperation with the blowing gas to plate the steel plate. A coating method for hot dip plated steel sheet, which is characterized in that 2. A high-frequency current conducting path is provided in the nozzle portions of the gas wiping nozzles on both sides of the steel sheet so as to face each other with the steel sheet interposed therebetween, and the high-frequency current conducting paths are sufficient to sufficiently saturate the steel sheet. 2. A hot-dip galvanized steel sheet basis weight method according to claim 1, wherein high-frequency currents of different magnitude and having the same phase are applied.