KR20010061451A - A Method for Producing Spangle Free Hot Dip Galvanizing Steel Sheet - Google Patents

Abstract

PURPOSE: A process for preparing a minimum-spangle hot dip galvanized steel sheet having excellent surface external appearance by attaching finely divided particles to a steel sheet by electrostatic attraction and preventing the formation of ununiform spangles is provided, which improves surface quality of galvanized steel sheet. CONSTITUTION: In a process for inhibiting the formation of spangles by spraying water or an aqueous solution from a plurality of injection nozzles disposed toward the surface of a steel sheet before coagulation of a galvanized layer after controlling the attached amount of a plated steel sheet at a hot dip galvanized port, drops of the aqueous solution sprayed from the nozzle are subjected to passing through charged electrodes(22) consisting of a plurality of wires(21) and applied a voltage of 1kV to 150kV or 10kV to 150kV.

Description

A method for producing spangle free hot dip galvanizing steel sheet}

The present invention is a method for producing a spangle-free hot-dip galvanized steel sheet by solidifying the plating layer by spraying an aqueous solution to the unsolidified plating layer after the coating layer in the molten state is air wiped to adjust the adhesion amount It is about.

In hot-dip galvanized steel sheets, large zinc crystals (spangles) usually appear on the surface, which adversely affects the appearance after coating. In order to solve this problem, a hot dip galvanized steel sheet (hereinafter referred to as "zero spangle") is produced, which means that the size of the spangle is 1 mm or less.

At this time, as the aqueous solution used, an aqueous phosphate solution is mainly used. Droplets of aqueous solution of phosphate attached to the surface of the steel plate deprive the latent heat of the steel plate as phosphoric acid decomposes with evaporation of water, and the plated layer solidifies around the nucleus by acting as a nucleus of the P ₂ O ₅ compound remaining on the surface. . In general, one coagulation nucleus forms one spangle, so that it can be seen that one or more coagulation nuclei should be made for an area of 1 mm ² of the hot dip coating layer in order to produce zero spangles. Therefore, in the same aqueous solution injection amount, the smaller the droplets of the aqueous solution, the more the density of the coagulation nucleus is increased, which is advantageous for the preparation of vesicle spangles. In order to achieve this purpose, various spray nozzles have been developed, and nozzles with an average droplet size of 20 μm or less have been developed and are widely used in the manufacture of zero-spangle materials.

The problem with the aqueous solution spray nozzle is that the fitting mark is likely to occur. The cause of the fitting mark is due to the inclusion of large particles when spraying the aqueous solution from the nozzle. In other words, as the particle size increases, the particles increase the same kinetic energy, so that the collision marks (fitting marks) become more severe when they collide with the plating layer in the molten state. Therefore, in the aqueous solution spraying method, uniformly spraying small particles is most important for obtaining a beautiful appearance. However, in the method of spraying the aqueous solution through the nozzle, there is always a risk of fitting occurrence due to large particles because large particles and small particles are mixed.

US Pat. No. 4,500,561 is a method for preventing the occurrence of fitting marks caused by large particles. In this method, the spraying direction of the aqueous solution is sprayed in parallel with the steel sheet, and a method of electrostatically charging the droplets of the aqueous solution by the blade-shaped high voltage charging electrode positioned to face the steel sheet at the top or bottom of the nozzle. At this time, the large particles have a larger inertia force than the small particles during solution injection, so the large particles overcome the electrostatic attraction and continue to move in a direction parallel to the steel sheet so that they do not adhere to the surface of the steel sheet. Smaller and therefore adheres to the steel sheet. This method has the effect of preventing the fitting mark caused by the large particles. However, this method does not adhere to the steel plate because large droplets of the sprayed solution, if the aqueous solution is leaked to the outside of the environment is likely to be contaminated by the chemicals contained in the aqueous solution droplets to prevent this There is a problem that the capacity of the suction installation must be very large. In addition, a significant amount of the sprayed aqueous solution is not attached to the steel sheet, there is a problem that the spray efficiency is lowered.

Accordingly, the present inventors have repeatedly conducted research and experiments to solve the above problems and propose the present invention based on the results, and the present invention sprays an aqueous solution to further refine the particles by the electrostatic charging effect and electrostatic attraction. By attaching the particles to the steel sheet by, by preventing the non-uniform generation of the sequins to provide a method for obtaining a mini-sparkle hot-dip galvanized steel sheet having an excellent surface appearance, an object thereof.

1 is a device configuration diagram when using a pressurized injection nozzle as an example of an apparatus for applying the method of the present invention;

2 is a block diagram of an apparatus when using an ultrasonic jet nozzle as an example of the apparatus for applying the method of the present invention.

* Description of the symbols for the main parts of the drawings *

(1) steel sheet (2) zinc zinc foot

(3) Air Knife (11) Spray Nozzle

(12) solution and air supply of pressurized nozzle

(13) Ultrasonic jet nozzles (14) Solution for supplying ultrasonic nozzles

(15) Ultrasonic nozzle power supply

(21) Wire (22) Charge Electrode

(23) High Voltage Generator (24) High Voltage Cable

The present invention for achieving the above object is to produce sequins by spraying water or an aqueous solution from a plurality of solution spray nozzles arranged to face the steel sheet surface before the plated layer is solidified after the plated amount of the plated steel plate in the hot dip plating port is adjusted In the method of suppressing, the solution droplet sprayed from the nozzle is passed through a charging electrode composed of a plurality of wires between a charging electrode to which a voltage of -1 kV to -150 kV or a voltage of 10 kV to 150 kV is applied. It relates to a steel sheet manufacturing method.

First, the theoretical background to which the present invention is proposed is described below.

Generally, solidification nuclei are generated when the zinc plating layer in the molten state is cooled, and the plating layer is solidified through the process of growing the nuclei. At this time, in order to reduce the size of the spangle, the density of coagulation nuclei per unit area must be increased in the nucleation step. In general, when the plated steel sheet in the molten state is naturally cooled, the density of the nucleus is low, and large sized spangles are produced. Accordingly, an aqueous solution spray method, which is a method of increasing the density of nuclei by spraying an aqueous solution containing a substance capable of acting as a coagulation nucleus on the surface of a steel sheet, is frequently used. In the conventional solution spraying method, the aqueous solution and the air are blown at a pressure of 1 to 4 kg / cm ² to granulate the aqueous solution. At this time, the particle size distribution of the aqueous solution is different depending on the characteristics of the nozzle, but usually has a wide size distribution of about 1 to 100 micrometers, it is not technically easy to narrow this distribution. When particles having this distribution are sprayed onto the steel sheet surface, small particles are more difficult to adhere to the steel sheet surface than large particles due to the rising airflow generated by the hot steel sheet of 420 ° C or higher. In other words, the air around the steel plate is heated by the hot steel plate, and the upward air flow exists on the surface of the steel plate.The small particles rise upward through the upward airflow because the kinetic energy is very small compared to the large particles, but the large particles overcome the upward airflow. This is because they have enough kinetic energy.

When the injection pressure is increased to give sufficient kinetic energy to the small particles, the kinetic energy of the large particles also increases. In this case, a fitting mark is generated in which the large particles collide with the molten plating layer. This is about 1mm, there is a problem that the appearance of the steel sheet is severely damaged.

In order to prevent such fitting marks, the injection pressure must be low and the particle size must be small, but this is a contradictory requirement in the nozzle technology of our company. Also, when the spray pressure is lowered, the kinetic energy of the particles is small so that the particles do not adhere to the steel sheet. The problem arises that all are scattered.

The reason for limiting the aqueous solution droplet to pass between the electrodes is to obtain the electrohydrodynamic atomizing effect (electrostatic particle). In general, when a solution particle passes through a high-voltage electric field, it is electrostatically charged, and when the charged energy is greater than the surface energy of the solution, a large particle becomes micronized (reference name "Electrostatic Atomization", author D.Michelson). That is, the sprayed aqueous solution drops electrostatically while passing through the charging electrode, thereby causing two effects in which the particles are refined. In addition, since a high voltage electric field is formed between the electrode that charges the high voltage generated by the high voltage generator and the steel plate connected to the ground, droplets of the electrostatically charged solution having the same polarity as that of the charging electrode are attracted to the steel sheet by the electrostatic attraction. Attached.

Next, the configuration of the present invention will be described in detail.

The present invention relates to a method of suppressing sequin formation by spraying an aqueous solution from a plurality of solution spray nozzles arranged so as to perform a steel sheet surface after the steel plate plated in the hot dip plating port is coated with an air knife before the plating layer is solidified. The solution droplets injected from the nozzles are penetrated between the high-voltage charging electrodes composed of a plurality of wires to further refine the particles by the electrostatic charging effect, and at the same time, the electrostatic charging is performed. By adhering particles to the particles, a large number of coagulation nuclei are formed, and at the same time, the steel sheet is cooled to suppress spangle formation.

The intensity of the high voltage applied to the charging electrode in the present invention has a range of -1kV to -150kV or 10kV to 150kV.

The characteristics of electricity applied to the charging electrode are as follows. That is, while generally having a similar effect to the "-" polarity or "+" polarity mode, the "-" polarity is more effective. Accordingly, in the "-" polarity, the particle refinement effect and the adhesion efficiency improvement effect are shown even at -1 kV or more, but in the case of the "+" polarity, the same effect is exhibited at 10 kV or more. The effect of the present invention is larger as the voltage increases, so it is advantageous to work at high voltage, but the voltage increase effect is no longer increased at -150kV or 150kV, and spark generation (insulation breakdown phenomenon) becomes severe, so the scope of the present invention is limited. Outside is not desirable.

As described above, the particles become fine even without increasing the injection pressure, so that the injection pressure of the solution may be a pressure that can be injected from the nozzle to penetrate the electrode in a state where the particles are granulated to some extent. In the case of the electrostatically charged particles may be mode attached to the steel sheet by the electric field. If the injection pressure is high, the movement of the particles toward the steel sheet is increased by the injection pressure rather than the electrostatic attraction, thereby increasing the risk of non-uniform adhesion, and even worse, it is desirable to lower the injection pressure as much as possible.

In view of this aspect, a pressurized injection nozzle using air may be good, but an ultrasonic injection nozzle using ultrasonic vibration is more preferable. Since the ultrasonic spray nozzles are granulated with an aqueous solution by ultrasonic energy, the kinetic energy of the particles is 1/10 to 1/100 of the pressurized spray nozzle, which is more effective in the present invention.

The spraying aqueous solution in the present invention is more effective when using a solution containing less than 2% of water-soluble phosphate in water by weight ratio in terms of weight ratio.

When using the aqueous solution containing the colloidal silica, it is possible to obtain a plating layer having a very fine crystal structure of the crystal size of the plating layer of 20μm level. The reason why finer crystals are obtained when using colloidal silica is unclear. However, if silicon contains only 0.05% or more of zinc, it may be related to the phenomenon that zinc's solidification temperature increases to 500 ° C or higher (Binary Alloy Phase). See Diagrams, vol 2, p2066, American Society for Metals). That is, a small amount of silica (SiO ₂ ) adhered to the plating layer in the molten state is reduced to silicon by molten zinc, and when the silicon is locally dissolved on the zinc plating layer, the solidification temperature of the plating layer in the vicinity is usually plated. Since the plate is higher than the steel sheet temperature of 430-470 ° C, the plating layer of the silica-attached portion acts as an effective coagulation nucleus. The effect of this colloidal silica was insufficient because the amount of silica in the solution was less than 0.1% by weight, and when the concentration of the colloidal silica became more than 2%, silica did not adhere to the surface of the plating layer and was in powder form. There is a risk of contamination of the working environment. When the colloidal silica is added to a solution containing water-soluble phosphate, the above-mentioned effect of the phosphate is simultaneously shown, which is more effective. At this time, when the concentration of the phosphate is 2% or more, the surface of the plating layer may be contaminated by excessive phosphate, which is not preferable.

In addition, the steel sheet temperature range when spraying the aqueous solution by the method limited in the present invention requires a steel sheet temperature from the start of spraying at a temperature higher than the solidification temperature of the steel sheet, that is, at least until solidification starts. Do. After solidification is started by the method of the present invention, a conventional plating solution can be obtained by adopting a conventional aqueous solution spraying method.

That is, the steel sheet is solidified during the process of moving to the upper side after exiting the hot-dip plating bath to form a complete plating layer. In order to achieve the object of the present invention, spraying should be started when the plating layer is in a molten state, and at least solidification is performed. It should be done until it starts. If the spraying is terminated before the solidification of the plated layer starts, the solidification nuclei generated before the redissolved, causing spangles to appear. Therefore, in the apparatus to which the present invention is applied, the length in the steel plate advance direction must satisfy more than that.

Next, an example of an apparatus for performing the mini-spangle manufacturing method of the present invention will be described.

Figure 1 is an example of a molten plated steel sheet manufacturing apparatus when using a pressure spray nozzle, Figure 2 is an example of a molten plated steel sheet manufacturing apparatus when using an ultrasonic spray nozzle. That is, a plurality of spray nozzles 11 are disposed to face the steel sheet in order to spray the aqueous solution toward the steel sheet 1, and are installed in parallel with the steel sheet in the width direction of the steel sheet between the nozzle steel sheets, the length being greater than the width of the steel sheet. A charging electrode 22 composed of a long dozen wires 21, and a high voltage generator 23 capable of applying a voltage of -1 kV to -150 kV or a high voltage of 10 kV or more or 150 kV or less to the charging electrode. At this time, the charging electrode has a form in which a plurality of wires with a diameter of 0.1-0.3mm are installed at intervals of at least 1mm and at most 300mm, and are chemically stable to chemicals such as tungsten wire and stainless steel, and charge high voltage electricity. Anything you can do is fine.

The plating method using the plating apparatus as described above is as follows.

That is, after the steel sheet 1 passes through the hot dip plating foot 2, the steel sheet proceeds upwards. Molten zinc excessively adhered to the steel sheet surface is removed by the air knife 3. A solution spray nozzle is installed on the upper part of the air knife so that the aqueous solution is sprayed toward the surface of the steel sheet through the plurality of spray nozzles 11 before the plating layer is solidified. At this time, the spraying direction of the aqueous solution is to perform the surface of the steel sheet through the charging electrode 22 made of a plurality of wires (21). There is a need for a solution and air supply 12 capable of supplying a constant pressure of solution and air when using a pressurized spray nozzle. The spraying conditions at this time are satisfied if the air or aqueous solution is 0.5 to 4 kg / cm ² . Alternatively, ultrasonic spray nozzles may alternatively be used in place of the pressurized spray nozzles, in which case a solution supply device 14 suitable for this and a power supply device 15 for the ultrasonicator are required. The ultrasonic frequency at this time is satisfied in the range of 18 kHz to 120 kHz. The charging electrode is connected to the high voltage generator 23 by the high voltage cable 24. The high voltage generator may apply a high voltage of -1kV to -150kV or 1kV to 150kV to the charging electrode. The number and arrangement of nozzles required in the apparatus of the present invention, the size and installation position of the charging electrode are determined by the width of the steel sheet, the traveling speed of the steel sheet and the thickness of the steel sheet, the temperature of the plated steel sheet, and the injection amount of the aqueous solution per nozzle. However, the solution is preferably sprayed to be wider than the width of the steel sheet, and the width of the charging electrode is also preferably larger than the width of the steel sheet. In addition, the apparatus should be installed at a position lower than the height at which the subconductor begins to solidify from the ground, and should be able to spray at least until the plated layer begins to solidify.

Further, in the charging electrode, the spacing between the wires is determined by the voltage applied to the charging electrode, but when the voltage of -50kV to -150kV is applied, the proper spacing is preferably within at least 1mm and at most 300mm. If the electrode distance is less than 1mm, the spacing between the electrodes is too narrow, there is a possibility that the water droplets impinge on the electrode and then a large drop of water generated between the electrodes to reduce the spraying efficiency, when the distance between the wire is 300mm or more In the middle, the strength of the electric field is weakened, and the particles passing therein are weakly electrostatically charged and do not have sufficient effect.

It is advantageous if the injection pressure of the solution is as low as possible in the proper solution injection between the electrodes, in this respect also ultrasonic spray nozzles can be used.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

Air-wiping a steel plate in which 0.8 mm thick steel plate was deposited in a plating bath having a composition of Pb 0.012% and Al 0.18% by weight was applied at 150 g / m ² per plate, and then the voltage under the conditions shown in Table 1 below. The molten plated steel sheet was prepared by applying and spraying by applying the solution and the spray conditions of the composition as shown in Table 1. The surface appearance of the manufactured hot-dip galvanized steel sheet was observed and the size of the spangles was measured. The results are shown in Table 1 below.

Applied voltage Use solution Injection conditions Surface Appearance / (Spangle Size, mm) Phosphoric Acid Silica air Aqueous solution Comparative Example 1 0kV 2% One% 1kg / cm ² One Create Spangles (5) Comparative Example 2 -0.5kV " " 4 One Fitting mark (2) Comparative Example 3 +8 kV " " 4 One Fitting mark (2) Inventive Example 1 -50kV 3% 3% 4 One Small amount of staining (0.1) Inventive Example 2 +70 kV 3% 0.05% 4 One Small amount of staining (0.1) Inventive Example 3 -1kV One% 2% 4 One Uniformity (1) Inventive Example 4 -10kV 0.5% 0.1% 2 0.8 Uniform (0.5) Inventive Example 5 -30kV One% 0.5% 1.0 0.5 Uniform (0.5) Inventive Example 6 -50kV 2% 0.5% 1.0 0.5 Uniform (0.1) Inventive Example 7 -70 kV 2% 0.5% 1.2 0.8 Uniform (0.05) Inventive Example 8 -100kV 2% 0.5% 1.2 0.8 Uniform (0.02) Inventive Example 9 -150kV 2% 0.5% 1.2 0.8 Uniform (0.02) Inventive Example 10 + 10kV 2% 0.5% 4 One Uniformity (1) Inventive Example 11 + 30kV 2% 0.5% 2 One Uniform (0.5) Inventive Example 12 + 150kV 2% 0.5% 1.2 0.8 Uniform (0.02) Inventive Example 13 -50kV 2% 0.5% Ultrasonic nozzle 18kHZ Uniform (0.5) Inventive Example 14 + 100kV 2% 0.5% Ultrasonic Nozzle 120kHZ Uniform (0.5)

As can be seen in Table 1, Inventive Example (1-14) satisfying the conditions of the present invention was found to have a uniform surface appearance.

According to the present invention as described above, by applying a voltage of the appropriate range to the re-electrode electrode during the manufacture of the zero sequin hot-dip galvanized steel sheet, it is not only easy to manufacture a hot-dip galvanized steel sheet without sequins, but also improves the surface quality of the manufactured steel sheet It is effective.

Claims (4)

A method of suppressing sequin formation by spraying water or an aqueous solution from a plurality of solution spray nozzles arranged so that the steel plate plated in the hot dip plating port faces the steel plate surface after the plating deposition is adjusted and before the plating layer is solidified. A method for producing a hot-dip galvanized steel sheet, comprising a plurality of wires penetrating the solution droplets injected from the nozzles and passing through a charging electrode to which a voltage of -1 kV to -150 kV or 10 kV to 150 kV is applied. The method of claim 1, The aqueous solution is a method for producing a hot-dip galvanized steel sheet, characterized in that the water-soluble phosphate is 2% or less by weight, and 0.1-2% silica. The method of claim 1, The plurality of wires is a method of manufacturing a hot-dip galvanized steel sheet, characterized in that the 0.1-0.3mm wire is installed with a minimum interval of 1mm, 300mm maximum The method of claim 1, The nozzle is a double-fluid pressurized nozzle or a method of manufacturing a hot-dip galvanized steel sheet without sequins, characterized in that the ultrasonic injection nozzle of frequency 18-120kHz