JPS62205259A - Hot dipping apparatus - Google Patents

Abstract

PURPOSE:To increase a slit gap and to enable high-speed thin sticking by placing heated shield plates between the surface of a molten metallic bath and wiping nozzles so that a metallic strip is surrounded by the plates. CONSTITUTION:A hot dipping apparatus is provided with a molten metallic bath 2 for hot dipping, wiping nozzles 8 for controlling the amount of a molten metal sticking to a metallic strip 6 pulled up from the molten metallic bath 2 for hot dipping, and heated shield plates 14 placed between the surface 10 of the bath 2 and the wiping nozzles 8 so that the strip 6 is surrounded by the plates 14. Splashing 12 caused by pulling up the strip 6 from the bath 2 is physically hindered by the plates 14. The molten metal sticking to the plates 14 flows down and returns to the bath 2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a molten metal plating apparatus, and particularly to a molten metal plating apparatus suitable for performing thin coating at high speed.

(Prior art) As shown in FIG.
This is done by immersing a metal strip 6 fed through a snout 4 into this molten metal bath 2 and then continuously pulling it out from there.

After lifting, the coating weight is adjusted by blowing gas from the wiping nozzle 8.

In recent years, the spread of hot-dip metal plating, such as hot-dip galvanization, has been remarkable, and in recent years, in order to further improve its economic efficiency and productivity, there has been a trend toward thinner coatings at high speeds. has been done.

In order to achieve high-speed and thin plating in hot-dip metal plating, possible measures include narrowing the so-called nozzle interval between the wiping nozzle and the metal strip, increasing the wiping gas pressure, and widening the nozzle slit gap. However, there is a limit to narrowing the nozzle interval due to vibration of the strip, etc. Further, even if the wiping gas pressure is increased, no effect can be expected if the wiping gas pressure exceeds the critical pressure.

Therefore, a method of enlarging the nozzle slit gear knob may be considered, but as a result, the gas flow rate increases, and the flow of wiping gas after hitting the metal strip hits the molten metal bath surface, causing molten metal such as zinc to This will result in an increase in the amount of money.

As schematically depicted in Fig. 2, when the gas flow rate from the wiping nozzle 8 is large, as indicated by the arrow in the figure,
The wiping gas hits the bath surface 10 at high speed, and the wiping gas hits the bath surface 1.
Splashing of molten metal 12 from 0 can be seen.

Such splashing of molten metal not only poses a danger to the surrounding area and significantly impairs work efficiency, but also causes the splashed molten metal to adhere to the lower part of the wiping nozzle, the support, etc., solidify, and become impossible to remove. . This tendency becomes more pronounced as the wiping gas pressure increases, and is one of the bottlenecks in the development of the high-speed thinning method currently required.

Problems to be Solved by the Invention The general object of the invention is to provide an apparatus which solves the problem by means of increasing the nozzle slit gap in order to achieve high speed thinning.

Furthermore, a specific object of the present invention is to provide a shielding plate between the wiping nozzle and the molten metal bath to prevent molten metal from splashing, thereby preventing the above-mentioned problems when the nozzle slit gap is increased. The object of the present invention is to provide a device that eliminates the drawbacks.

(Means for Solving the Problems) Therefore, the inventors of the present invention have conducted various studies in order to achieve this objective, and have found that the present inventors have developed a method for preventing molten metal from splashing up, and furthermore, preventing the splashed metal from adhering to the surroundings. , that it is effective to provide a shielding plate to surround the metal strip between the bath surface and the wiping nozzle;
When such a shielding plate is installed, zinc adhesion to the shielding plate becomes a problem, and I learned that heating the shielding plate is effective in preventing this. .

Therefore, after conducting various experiments using heating shielding plates, we found that
If there is a localized area where the surface temperature is lower than the melting point of zinc,
Zinc adhesion begins in that area, and once adhesion occurs, it becomes extremely difficult to remove.

This is because heat is taken away as the heat of fusion of zinc. Therefore, it is desirable that the overall surface temperature of the heating shield plate be above the melting point of °C, and that there should be no localized areas below the melting point. In order to prevent such a local temperature drop, it is necessary to raise the temperature considerably, which inevitably increases costs. In order to achieve a particularly high temperature at the end of the inner opening of the shield, the entire body must be at a fairly high temperature. It is inevitable that costs will further increase.

Here, the present inventors have found that this problem can be solved by inserting an induction heater coil, which is also placed around the metal strip, inside the shielding plate, which is placed so as to surround the metal strip. The present invention was completed based on the finding that this problem could be effectively solved by employing a means of induction heating.

Thus, in the broadest sense, the gist of the present invention is to provide a molten metal plating bath, a wiping nozzle for controlling the amount of plating on a metal strip pulled up from the molten metal plating bath, and a method for connecting the molten metal plating bath and the wiping nozzle. This hot-dip metal plating apparatus is equipped with a heating shielding plate disposed surrounding the metal strip at a position in between.

Here, according to preferred embodiment B of the present invention, the shielding plate is provided with an induction heater coil arranged so as to surround the metal strip, and the shielding plate is heated to a temperature higher than the melting point of the molten metal by an induction heating method. The upper surface of the shielding plate may be inclined inwardly and downwardly toward each end opposite to the metal strip. As a result, the molten metal that has once splashed onto the upper surface of the shielding plate flows down the upper surface of the shielding plate.

The above-mentioned "molten metal" includes not only molten zinc but also zinc-aluminum alloy plating and aluminum plating, and is not particularly limited as long as it does not go against the spirit of the present invention.

(effect) Next, the present invention will be further explained with reference to the drawings.

In FIG. 2, a shielding plate 14 is disposed between the molten metal bath surface 10 and the wiping nozzle 8 so as to surround the metal strip 6, as shown by the dotted line. By providing the plate, splashes on the bath surface are completely prevented. Such a shielding plate simply physically prevents molten metal from splashing, but if molten metal adheres to and accumulates on the shielding plate itself, it must be removed by some means. The shielding plate is preferably heated by an appropriate means, and the heating temperature in this case is preferably higher than the melting temperature of the molten metal.

FIG. 3 is a perspective view with the outer cover of the shielding plate 30 equipped with induction heating means used in the present invention broken down. FIG. 4 is a diagram illustrating the heating principle when an induction heater coil is used, and is a diagram cut in the middle of a metal strip in the width direction.

In the illustrated example, the shielding plate has a flat upper surface, but preferably, the shielding plate has a roof-like cross section inclined inward by, for example, 5 to 30 degrees, and is hollow inside. An induction heater coil 32 is provided inside the shielding plate 30 so as to surround the opening through which the metal strip passes. In the figure, it is indicated by diagonal lines.

The metal strip 3G leaving the molten metal bath 34 is pulled up in the direction of the white arrow in the figure.

The material of this shielding plate 30 is not particularly limited, but it is preferably a material with poor Zn wettability, such as a material whose surface is thermally sprayed with Co--W, stainless steel, etc.

Here, when the coil 32 is energized, a uniform magnetic flux distribution is generated on the outer surface of the shielding plate 30, a magnetic flux distribution is generated in the direction shown in FIG. 4, and an eddy current flows. Therefore, the eddy current flows uniformly and the whole is heated uniformly.

In this way, the eddy current flows in the closed conductor around the coil in the direction opposite to the direction of the current in the coil. Therefore, the coil shape is adjusted so that the eddy current flows uniformly throughout the shielding plate 30. By selecting the shape of the shield plate, uniform heating of the shield plate 30 can be realized.

As shown in FIG. 4, when a coil wound like a solenoid is inserted inside the shielding plate, the lines of magnetic force generated thereby generate eddy currents on the surface of the shielding plate, which causes induction heating of the shielding plate 30 itself. do.

The magnetic lines of force generated by the solenoid-shaped coil pass through the shield plate, generating eddy currents on the surface.
Heat is generated due to the resistance of the shield plate itself.

Moreover, the eddy current flowing through the shielding plate itself is uniform, its surface temperature is not low at the cutting part, and the side surfaces are also heated, so the temperature distribution is good. In the case of galvanizing, a heating temperature of about 400°C has some effect, but it is preferably higher than the melting point of the molten metal, and in the case of zinc, 420°C or higher.

In addition, the shape of the shielding plate is arbitrary as long as the magnetic lines of force act effectively and the eddy current forms a closed loop. It can be made into a shape that allows it to be washed away by the action of gravity.

In contrast to the indirect heating method using a resistance heater through an intermediate insulating layer, the induction heating method has extremely high heating efficiency, reaching a maximum of 70%.

Furthermore, when a thin plate is heated by induction using a solenoid coil, there is a portion inside the thin plate where eddy current is canceled, so it is necessary to make the frequency of the current flowing through the induction coil extremely high. This is the so-called skin effect. However, if the object to be heated is placed outside the solenoid coil, the frequency does not necessarily have to be high because eddy current cancellation does not occur.It is possible to use commercial frequency 50112 or GOIIz, but in terms of efficiency, High frequency 3
KIIz level is desirable.

Next, the present invention will be explained in more detail in connection with examples.

EXAMPLE When a high frequency current (not shown in FIG. 4) was applied to the shielding plate under the following conditions, the electric power required to uniformize the surface temperature of the shielding plate to 500 DEG C. was 36 -.

Construction surface high frequency current: 3KI+2. ．． 100OV, 250
AKVA: 250KVA Power factor cos φ; 0.2 Pin: 50KW Efficiency near 2% Pnet: 36KW When this shield plate was assembled as shown by the dotted line in Figure 2 and hot-dip metal plating was performed, the temperature distribution around the shield plate was was as shown in Figure 5. Note that the size of the passage opening of the metal strip was 2200×100I.

As is clear from this, the temperature reached 700°C on the metal strip side at any position on the shielding plate. Furthermore, although the temperature at the center of the shielding plate is 400°C, which is slightly lower than the melting point of zinc, a sufficient effect is not observed.

Therefore, for example, even if high-speed plating is performed at a depth of 180 m/a+in, almost no splashes of molten metal, in this case molten zinc, will be seen, and even if splashes of molten zinc are seen, the shielding plate will maintain the temperature sufficiently high over the entire width. Therefore, such deposited zinc flows down the top surface of the shielding plate and returns to the plating bath, and does not cause any trouble to the plating work.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram of a conventional molten metal plating apparatus, and Fig. 2 is a conceptual explanation of the installation position of the shield plate used in the apparatus according to the present invention and the manner in which molten metal splash occurs. Figure 3 is a perspective view with the top surface of the shielding plate used in the present invention removed, and Figure 4 shows a solenoid-type induction heater coil inside the shielding plate used in the 'AW according to the present invention. An explanatory diagram of the heating principle when arranged, and FIG. 5 is a graph showing the temperature distribution of the shielding plate used in the device according to the present invention.

Claims (3)

[Claims] (1) a molten metal plating bath, a wiping nozzle for controlling the amount of plating on the metal strip pulled up from the molten metal plating bath, and a wiping nozzle surrounding the metal strip at a position between the molten metal plating bath and the wiping nozzle; A molten metal plating device equipped with a heating shield plate arranged in combination. (2) The shielding plate is provided with an induction heater coil disposed inside to surround the metal strip, and is heated to a temperature higher than the melting point of the molten metal by an induction heating method. Device. (3) The apparatus according to claim 2, wherein the upper surface of the shielding plate is inclined inwardly and downwardly toward each end opposite to the metal strip.