KR100311793B1 - METHOD FOR MANUFACTURING Zn-Al ALLOY PLATED STEEL SHEET - Google Patents

Abstract

PURPOSE: A method is provided which easily manufactures a Zn-Al alloy plated steel sheet in a galvanized steel sheet manufacturing line. CONSTITUTION: The method for manufacturing a Zn-Al alloy plated steel sheet comprises the steps of: fluidizing powder in a fluidized bed formation tank(240) with a gas blown from the lower part by receiving Zn-Al powder or pure aluminum powder having an average particle size of 45 microns or less and comprising 1 wt.% or more of Al and a balance of Zn from a powder supplying unit(246); forming a fluidized bed zone of powder supplied into the upper plating tank(220) by injecting the powder fluidized in the fluidized bed formation tank(240) into an upper plating tank(220); taking a charge powder in the fluidized bed zone to plus or minus so that the powder is electrically charged; fusing powder on the surface of the steel sheet by passing a hot dipped galvanized steel sheet which is heated to a temperature of 420 to 730 deg.C and grounded through the fluidized bed zone in which the powder is electrically charged; and cooling the reheated steel sheet after reheating the powder fused steel sheet to a temperature of 420 to 730 deg.C for 1 to 5 seconds.

Description

Manufacturing method of zinc-aluminum alloy plated steel sheet

The present invention relates to a method for producing a zinc-aluminum alloy plated steel sheet, and more particularly, to a method for producing a zinc-aluminum alloy plated steel sheet using aluminum powder.

Conventionally, zinc-aluminum-based alloy plated steel sheet has excellent corrosion resistance and is mainly used as an inner plate of home appliances and a steel sheet for building materials. The structure of the plating layer is generally 5-55% aluminum, 5% aluminum is called galfan, and 55% is called galvalume.

Zinc-aluminum alloy plated steel sheet cannot be manufactured by the electroplating method.

As a method of manufacturing a zinc-aluminum alloy plated steel sheet, there is Japanese Patent Laid-Open No. 51-77536. This known technique relates to a method of forming a plating layer by mixing a zinc powder and an aluminum powder and attaching it to a steel sheet surface, and then heating the steel sheet to a melting point of zinc or more and to a melting point of aluminum or less. In this method, it is difficult to uniformly attach the metal powder to the steel sheet, and it is difficult to form a uniform plating layer.

Therefore, it is currently manufactured only by the hot-dip plating method in which a steel sheet is deposited in a molten metal bath having a target plating layer composition. At this time, aluminum has a property that is easy to be oxidized, so in order to prevent the oxidation, the plating bath should be made of an inert gas, which causes a lot of manufacturing cost. In addition, in order to manufacture the galvanized steel sheet in the same line, a separate molten bath is required, in which case it takes a long time to replace the plating bath, there is a problem that the productivity is lowered. In particular, in the case of galvalume steel sheet, the temperature of the molten bath is about 600 ° C., which is higher than 450 ° C. of the galvanizing bath, making the galvalume steel sheet more difficult.

The present invention has been proposed to solve such a conventional problem, to provide a method for easily manufacturing a zinc-aluminum-based alloy plated steel sheet in the galvanized steel sheet production line, an object thereof.

1 is an exemplary configuration diagram of a zinc plating apparatus used in the present invention.

Explanation of symbols on the main parts of the drawings

220 ... upper plating tank 240 ... fluidized bed forming tank 246 ... powder feeder

The present invention for achieving the above object, a powder supply device for supplying powder, a fluidized bed forming tank for fluidizing the powder supplied from the powder supply device and a plating tank for plating the fluidized powder blown from the fluidized bed tank on the steel sheet In the plating method comprising,

The powder is supplied from the powder supply apparatus by means of a gas blown from the lower side by receiving zinc-aluminum powder or pure aluminum powder having an average particle size of 45 μm or less, aluminum being 1% or more by weight, and zinc remaining. Fluidizing; Injecting the powder fluidized in the fluidized bed forming tank into the upper plating bath to form a fluidized bed of the powder in the upper plating bath; Charging the powder of the fluidized bed with "+" or "-" to make the powder electrostatic; Fusing the powder on the surface of the steel sheet by passing the molten zinc steel sheet heated to 420-730 ° C. and passed through a fluidized bed in which the powder is electrostatically charged as described above; Re-heating the powder-fused steel sheet for 1-5 seconds at 420-730 ℃ comprises a step of cooling.

Hereinafter, the present invention will be described in detail.

The present invention is to plate the iron on the hot-dip galvanized steel sheet using a powder plating apparatus using the electrostatic attraction proposed by the present inventors Korean Patent Application No. 97-54877, the powder plating apparatus is as shown in FIG. .

As shown in FIG. 1, the powder plating apparatus using the electrostatic force used in the present invention includes: an upper plating tank 220 in which powder is fused to a steel plate (strip) 201 heated by heating means to form a plating layer;

A fluidized bed formation tank 240 which floats the powder by the gas blown in the lower part to make the fluidized state;

A powder supply device 246 for supplying powder into the fluidized bed forming tank 240; It is configured to include.

In addition, the upper plating tank 220 should be provided with at least one electrode for charging the powder. That is, a pair of needle electrodes are provided on the sidewalls of the upper plating tank 220, or at the same time the one-shaped network electrode 229 facing each other on the basis of the steel sheet passing through the upper plating tank 220 It is provided in the upper plating tank 220 in an insulated state from the upper plating tank 220. The electrode is connected to the high voltage generator 280, and the electrode is to charge the powder to "+" or "-" to make the powder exhibits static electricity.

In addition, electrically grounding the steel sheet is performed by the tension roll 232.

The reheating furnace 230 for heating the plated steel sheet is installed at the upper portion of the upper plating tank 220 to convert the powder remaining on the plated steel sheet surface to the plated layer.

In Fig. 1, reference numeral 210 is a heating means, 211 is a sink, 212 is an air knife, 213 is a molten plating pot, 214 is a stabilizer roll 244 is a gas spray plate, 245 is a gas supply, 247 is a powder supply pipe, 250 is a cy The clone, 251 is a bag filter, 252 is a dust collector, 253 is a suction pump, 254 is a gas pipe, and 270 is a gas heating device.

According to the present invention, in order to plate zinc-aluminum or aluminum on a molten zinc steel sheet, the powder is supplied from the powder supply device 246 with aluminum in a weight ratio of 1% or more and zinc-aluminum powder or pure aluminum powder, the remainder of which is zinc. It is necessary to fluidize the powder in the fluidized bed 240 by the gas blown from. At this time, the size of the powder is preferably 45㎛ or less, because if the size of the powder is more than 45㎛ is too large compared to the thickness of the plating layer because the surface is uneven, there is a risk that the plating uniformity is damaged. In addition, when the aluminum content is less than 1%, the amount of aluminum is small, and thus the characteristics of the galvanized steel sheet are difficult to obtain. Therefore, it is preferable to use a powder containing 1% or more of aluminum. Do. The content of aluminum in the powder is determined by the aluminum content in the target plating layer.

In the present invention, the powder is fluidized in the fluidized bed forming tank 240, and the reason is as follows. Since fine metal powder has a property of agglomeration by itself, when sprayed as it is stored, a plurality of powders are aggregated and behave like one large particle, which is easy to be injected into coarse secondary particles. This is because when the coarse particles are sprayed, the effect of the electrostatic attraction becomes unsatisfactory, and variations in the adhesion amount for each steel sheet part inevitably occur, and therefore it is difficult to obtain a uniform plating layer.

Therefore, in the present invention, a fluidized bed of the powder is formed in the fluidized bed forming tank 240 provided separately from the upper plating tank 220, and the fluidized bed of the powder is transported to the upper plating tank 220.

The size of the particles suspended in the fluidized bed formation tank 240 is closely related to the pressure of the gas blown from the lower side, so that the size of the suspended particles increases as the pressure of the blown gas increases. Therefore, if the pressure of the gas to be blown is adjusted, coarse particles or secondary particles are not suspended but remain at the bottom, and only powder of a desired size can be suspended and mixed into the upper plating tank. In this way, when attached to the surface of the steel sheet in the state of fine primary particles, not only the micro uniformity of the plating layer is improved, but also the reaction rate between the aluminum and the zinc plating layer is faster, which is more advantageous in terms of uniformity. In addition to the effect that the distribution of powders in the gas is more uniform even in the macroscopic surface appearance, the effect of the spraying trajectory is further reduced as the effect of the electrostatic force applied to each particle under the voltage applied to the same electrode to obtain a more uniform plating layer. Can be.

The powder fluidized in the fluidized bed forming tank 240 is blown into the upper plating tank 220 to form a fluidized bed of the powder in the upper plating bath, and the powder in the fluidized bed is charged with static electricity to melt the earth. The powder is evenly attached to the zinc steel sheet.

The present invention uses the force of the carrier gas and electrostatic attraction to transport the powder by the force of the powder attached to the steel sheet while limiting the temperature of the steel sheet to 420-730 ℃ as a basic means for this.

The convective boundary layer is formed on the surface of the steel sheet due to the temperature difference between the powder and the steel sheet, and this hinders the access of the powder. Therefore, in the simple spraying method, the pressure of the carrier gas must be increased in order for the powder to overcome this boundary layer and the surface of the steel sheet. It can be attached to. However, at this time, there is a risk that the plating layer is non-uniform due to the difference in the injection trajectories for each steel sheet. On the other hand, since electrostatic attraction is inversely proportional to the square of the distance between two electrostatically charged objects (F ∝ 1 / r ² ), the influence of electrostatic attraction increases near the surface of the steel plate on which the convective boundary layer is formed. The transported powder can be easily attached to the steel sheet surface. By using such electrostatic attraction, even if the carrier gas pressure is lowered to the extent that it does not affect the surface of the steel sheet, the powder may adhere, so that no injection traces appear on the surface of the steel sheet. The powder that is sequentially attached to the surface is changed into a plating layer by an alloying reaction with zinc in the zinc plating layer before the surface charge is lost through the steel sheet and dropped to the surface, thereby producing an aluminum-zinc plated steel sheet.

In the present invention, it is possible to manufacture a plated steel sheet as compared with the prior art by fluidizing the powder as described above, and forming static electricity in the powder.

According to the present invention, the charging of the powder to exhibit static electricity is performed by applying a voltage to the needle electrode or the reticulated electrode 229 provided on the side wall in the upper plating bath, wherein the voltage is -1 to-. It is preferable to add -100K or 1-100kV. The reason is that if the charging voltage is less than + 1kV or -1kV, there is no electrostatic effect, and if the voltage is more than + 100kV or -100kV, there is no problem of adhesion of powder, but the electrostatic charging beyond the limit is unnecessary because the effect of voltage increase is not large. .

Next, the hot-dip galvanized steel sheet is heated in the heating means 210, and then ground on a tension roll 232, and then the hot-dip galvanized steel sheet is passed through a fluidized object in which the powder is electrostatic as described above. Is fused to form a plating layer.

The heating temperature of the hot-dip galvanized steel sheet is preferably 420-730 ℃, the reason is that when the heating temperature is less than 420 ℃ zinc does not melt and the alloying reaction does not occur, in the case of more than 730 ℃ zinc, iron alloying proceeds zinc This is because the adhesion of the plating layer is inferior.

In this case, the hot-dip galvanized steel sheet is connected to the hot-dip galvanizing process instead of the heating means 210 by a powder plating apparatus without heating by a special heating means, and then the hot-dip galvanized steel sheet is attached to the hot-dip galvanized steel sheet. Passing the next flow partner is more beneficial in terms of energy efficiency. That is, when the powder is attached immediately before the molten zinc adhered to the steel sheet surface solidifies, the plating layer is completely attached by the diffusion reaction with the molten zinc, and the upper plating layer is formed.

If the remaining powder does not react to the surface of the aluminum or zinc fused steel plate as described above, the powder is attached to the various rolls of the plating equipment, it may be necessary to prevent the dent defect. To this end, the powder is reheated after adhesion and the zinc plating layer and the zinc powder are completely alloyed. To this end, after plating, the steel sheet is reheated at a temperature of 420 ° C. to 730 ° C. for 1 second to 5 seconds. When the treatment time is at 420 ° C. or when the treatment time is less than 1 second, the remelting and alloying reaction of the galvanized layer is not sufficient, so there is no effect of reheating. When the temperature is over 730 ℃ and the processing time is over 5 seconds, the deposited aluminum forms an alloy with the zinc plated layer and simultaneously reacts with the steel plate to increase the amount of iron-aluminum intermetallic compound formed on the plated layer and the surface of the plated layer. There is a risk that the amount of aluminum is reduced and corrosion resistance is reduced, and there is also a risk that a zinc-iron alloy plating layer is formed through this intermetallic compound. In addition, there is a risk of changing the mechanical properties of the steel sheet.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

After the cold rolled steel strip was attached to the molten zinc in the hot dip galvanizing process, before the molten zinc solidified, it was plated through a mixed powder of zinc-aluminum or a fluidized aluminum powder and then reheated to prepare a plated specimen. After the plating properties were measured and the results are shown in Table 1 below.

In the present invention, the plating characteristics measured the adhesion, plating uniformity and coating property of the plating layer, and the results were shown, but the measuring method is as follows.

First, 1) the adhesion of the plated layer was evaluated to the extent that the plated steel sheet was peeled off during the 45 degree bending test, "◎" the level at which the plated layer was not peeled at all, "○" the level at which the peeled trace appeared, and the peeled trace was Relatively clear levels are indicated by "Δ", and the level of peeled almost all of the plating layers is indicated by "X".

2) Plating uniformity is visually observed and uniform in appearance. Scanning microscope magnifies upper plated tissue 2000 times and has uniform structure without pin hole. "◎", uniform appearance but uniform structure If not, " ○ ", the appearance is uneven, and if the structure is not uniform, " △ " and the state in which the plating layer is not formed is indicated by " X ".

3) The paintability is marked by X when phosphate crystal is uniform and coating appearance is uniform due to phosphate treatment of plated steel sheet, and when phosphate crystal or appearance is not uniform.

No. Powder size (㎛) Voltage (kV) Reheating Temperature (℃) Reheat time (sec) Al% in powder Plating adhesion Plating Uniformity Adhesion One 50 -50 500 3 55 ○ X ○ 2 5 0 650 7 5.5 X X X 3 5 -50 415 7 5.5 X ○ X 4 5 +50 500 0.5 55 X ○ ○ 5 5 +50 500 3 0.8 ○ ○ X 6 10 +50 600 One 1.0 ○ ○ ○ 7 10 -50 730 3 55 ○ ○ ○ 8 5 -One 420 3 100 ○ ○ ○ 9 5 +100 500 3 80 ○ ○ ○ 10 5 +100 500 5 5.5 ○ ○ ○ 11 45 +1 500 2 30 ○ ○ ○

As shown in Table 1, at least one of the properties of the plating adhesion, the plating layer uniformity and the corrosion resistance of Comparative Example (No. 1-4) appeared poor, which is one or more of the plating factors of the present invention This is because it is outside the limit of. On the other hand, the plated layer (No. 6-10) prepared in the condition range according to the present invention was satisfied with all the plating adhesion, plating layer uniformity and coating.

As described above, the present invention provides a zinc-aluminum-based alloy plated steel sheet which uses less inert gas than the conventional alloy plating method by the conventional hot dip plating method and solves the problem of lowering productivity due to replacement of the plating bath. It can work.

Claims (3)

In the plating method comprising a powder supply device for supplying powder, a fluidized bed forming tank for fluidizing the powder supplied from the powder supply device, and an upper layer plating tank for plating the fluidized powder blown from the fluidized bed tank on the steel sheet, The powder is supplied from the powder supply apparatus by means of a gas blown from the lower side by receiving zinc-aluminum powder or pure aluminum powder having an average particle size of 45 μm or less, aluminum being 1% or more by weight, and zinc remaining. Fluidizing; Injecting the fluidized powder in the fluidized bed forming tank into the upper plating bath to form a fluidized bed of the powder supplied in the upper plating bath; Charging the powder of the fluidized bed with "+" or "-" to make the powder electrostatic; Fusing the powder on the surface of the steel sheet by passing the molten zinc steel sheet heated to 420-730 ° C. and passed through a fluidized bed in which the powder is electrostatically charged as described above; And reheating the powder-fused steel sheet at 420-730 ° C. for 1-5 seconds and cooling the zinc-aluminum-based alloy plated steel sheet. The method of claim 1, wherein the hot-dip zinc steel sheet is passed through a fluidized bed after the hot-dip zinc is solidified after attaching the hot-dip zinc in the hot dip plating process instead of heating. The method of claim 1, wherein the charging of the powder is performed at a voltage of -1 to -100 kV or 1 to 100 kV.

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