JPS5844147B2 - Partially molten metal plating method for steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves forming a plating-preventing film that does not easily react with molten metal on the surface of the material to be plated that does not require plating, and then immersing the entire material to be plated in a molten metal plating bath. The present invention relates to a metal plating method, and particularly to a hot-dip metal plating method suitable for use in manufacturing single-sided continuous hot-dip galvanized steel sheets.

Various corrosion-resistant films are often formed on the surface of a steel plate for the purpose of imparting corrosion resistance to the steel plate.

In this case, it is common to form a corrosion-resistant film on both sides of the steel plate.

However, in the case of steel sheets for automobiles, which are coated after being plated, if the coating is applied on top of the plating film, the sharpness of the image will be poor and the commercial value will be significantly reduced.

Further, for example, the weldability of galvanized steel sheets is unfavorable because the difference between the melting point and boiling point of zinc is small, the thermal conductivity is high, and the electrodes are easily contaminated.

As mentioned above, imparting corrosion resistance to the surface of a steel sheet has properties that conflict with weldability and image clarity after painting.

For this reason, in steel sheets for automobiles, etc., only one side of the steel sheet is plated to provide corrosion resistance, and the other side is coated with paintability.
So-called single-sided plated steel sheets with weldability are being used.

Although electroplating is a method for manufacturing such single-sided plated steel sheets, the thickness of the plating film obtained by electroplating is generally thin, and it is difficult to provide sufficient corrosion resistance.

Further, in order to obtain a large amount of plating by electroplating, it is necessary to reduce the plate passing speed, which is not preferable because productivity is poor and costs are high.

On the other hand, the hot-dip plating method is widely used because a large amount of plating can be easily obtained, and it is advantageous in terms of corrosion resistance, cost, etc.

However, it is quite difficult to continuously hot-dip only one side of a steel sheet, so after applying so-called differential thickness plating, there is a method of mechanically or electrochemically peeling off the plated film on the side that does not need plating. However, it is very uneconomical.

Methods for manufacturing single-sided plated steel sheets using this hot-dip plating method include, for example, the method of performing phosphate treatment on one side and plating, as described in Japanese Patent Publication No. 42-24966, and the method of plating after applying phosphate treatment to one side, as described in Japanese Patent Publication No. 39-7112. Publication No. and Special Publication No. 3
As described in Japanese Patent Publication No. 94522, a method of coating water glass on one side to prevent plating, Japanese Patent Publication No. 51-351
As described in Japanese Patent Publication No. 74 and Japanese Patent Publication No. 518101, methods of applying various coating agents containing silicone resin or the like as a main component are known.

However, in products that require heat treatment equipment such as a reduction furnace in the plating line, the steel plate is exposed to high temperatures, and the coatings made of phosphate, water glass, etc. may partially peel off due to deterioration, resulting in complete one-sided coating. Plating cannot be obtained.

Silicone resins are also affected by heat, which impairs the uniformity of the coating and makes it very difficult to obtain perfect single-sided plating.

There is also a method of using an oxide film as a plating prevention film, but it is also difficult to obtain complete one-sided plating.

Therefore, in order to overcome the drawbacks of the conventional method, the present inventors have previously proposed a single-sided plating method using soot, that is, free carbon, produced by incomplete combustion of hydrocarbon fuel, as a plating inhibitor.

An object of the present invention is to further improve mass productivity in relation to the above invention.

The present invention relates to a hot-dip metal plating method in which the surface of a copper strip that does not require plating is coated with a plating inhibitor in advance, and then the entire steel strip is immersed in a hot-dip metal plating bath. The present invention is characterized in that the plating inhibitor is coated by thermally decomposing active free carbon to produce active free carbon, which is adhered to the surface of the steel strip that does not require plating within one-fifth of a second.

As a result of various studies, the present inventors have found that free carbon in an active state not only has superior adhesion to steel strips, but also has significantly superior plating blocking ability compared to free carbon that has lost its activity. This is what led to the discovery of the above-mentioned present invention.

The active free carbon used in the present invention is obtained by thermally decomposing hydrocarbon fuel in oxygen starved or substantially absent conditions, but the active state is rapidly lost over time. , it is necessary to quickly attach it to the copper strip by thermal decomposition.

In the present invention, the thermal decomposition is carried out within one-fifth of a second after the thermal decomposition.

In particular, it is effective to attach it to the steel strip within 1/50th of a second.

Of course, even if the above considerations are taken, there may actually be cases where the = part activity is lost, but there is no substantial problem.

This time can be adjusted by appropriately setting the distance between the copper strip and the carbon generator and the running speed of the copper strip.

The hydrocarbon fuel used in the present invention can be either gaseous or liquid at room temperature.

Specifically, natural gas, acetylene, methane, propane,
A gas such as butane is preferable.

Furthermore, preferred liquid hydrocarbons include benzene, toluene, xylene, hexane, etc. In this case, these liquid hydrocarbon fuels should be preheated through a heat exchanger, etc., and vaporized in advance to form a gaseous state. preferable.

Furthermore, in addition to the gaseous and liquid hydrocarbon fuels described herein, any hydrocarbon fuel that can be thermally decomposed by heating can be used in the present invention.

In the present invention, the surface that does not require plating means the entire surface of one side of the copper strip, a portion thereof, or a portion of both surfaces.

In the present invention, it is preferable to use a nozzle as shown in FIGS. 1 and 2 to thermally decompose the hydrocarbon fuel and jet it out.

Reference numeral 1 indicates a nozzle body, and 2 indicates a heat transfer element for thermally decomposing hydrocarbon fuel, such as a mesh-like nichrome wire heater, which is formed by laminating several layers.

The above-mentioned FIG. 2 is a plan view cut along the line AA in FIG. 1.

It is particularly advantageous if the hydrocarbon fuel is fed into the nozzle 1 while being preheated.

The entire inside of the nozzle is heated to thermally decompose the hydrocarbon fuel supplied into the nozzle.

In order to improve heat transfer efficiency, mesh-like fins supported or integrated with the inner wall of the nozzle may be provided inside the nozzle.

As the heating means, an electric heater, high frequency heating, plasma or laser beam can be used.

When an electric heater is used, the heater may be provided inside the nozzle 1 (2 in FIGS. 1 and 2).

In addition, a catalyst such as silica or alumina is filled in the nozzle 1 (not shown) to promote the thermal decomposition reaction of hydrocarbon fuel.
By doing so, the thermal decomposition temperature can be lowered, and the yield (production efficiency) of free carbon can also be increased.

In the present invention, free carbon that did not adhere to the copper strip,
That is, excess free carbon and hydrogen gas produced by the thermal decomposition of hydrocarbon fuel are filtered through a bag filter (described in detail with reference to FIGS. 3 and 4 below) using an intake fan or the like.

) to separate carbon and hydrogen gas, and can be used for forming and maintaining a reducing atmosphere in a hydrogen gas plating device.

According to the present invention, free carbon is generated by thermal decomposition of hydrocarbon fuel and is attached to the steel strip within one-fifth of a second, so that the adhesion to the copper strip and the ability to prevent plating are maintained without losing activity. It is superior to other methods and can perform effective hot-dip metal plating, and is particularly effective for continuous plating.

Next, examples of the present invention will be shown.

Example 1 Using the continuous plating equipment shown in Fig. 3, the plating speed was 30 m.
A cold-rolled steel strip 3 with a width of 150 mm and a thickness of o and zmm was heated to remove deposits such as rolling oil on the surface of the steel strip by incineration at about 650°C in an oxidation furnace 4, and then the atmosphere was changed to 20% N2, N
The oxides on the surface of the copper strip were reduced and activated in the reduction furnace 5 maintained at 280%.

Next, in the masking chamber 7 where hydrogen was introduced, one side of the steel strip was
A free carbon layer (not shown) approximately 2 μm thick was deposited and formed.

The distance between the nozzle and the steel strip was adjusted so that the time from the thermal decomposition of the hydrocarbon fuel until the generated active free carbon adheres to the unplated surface of the steel strip is 1/5 second or less. .

Next, the copper strip is immersed in a hot-dip galvanizing bath 9 maintained at 460°C, and the amount of zinc coating is reduced to 10 by using a plating roll 10.
After adjusting to z/ft2 and cooling, the carbon layer on the surface not requiring plating was removed using a brushing roll 11.

As a result, a complete single-sided galvanized steel sheet was obtained.

Here, free carbon uses acetylene as a hydrocarbon fuel, and the gas flow rate is 11/1ni! In addition, a gas jet nozzle 1 with a width of 160 mm and a thickness of 20 mm was used. Nichrome wires (2 shown in Fig. 1) were arranged in a mesh pattern inside the nozzle, and a current of 200 V and IOA was applied. The gas temperature at the nozzle exit was kept at 1200° C., and thermal decomposition was continuously performed and generated, so that a carbon layer was continuously attached and formed on the non-plated surface of the steel strip.

Surplus carbon and hydrogen gas are introduced into the bag filter 12, and after separating the surplus carbon, they are put into the hydrogen storage tank 14 by the pump 13, and this hydrogen gas is passed through the gas pump 1.
5 into the snout above the plating bath.

Example 2 Using the plating equipment shown in Fig. 4, the plating work was carried out as in Example 1.
One side plating was applied in the same manner as above.

However, for adhesion and formation of the carbon layer, natural gas was used as the hydrocarbon fuel, the gas flow rate was 1.5 l/min, and the same gas jet nozzle as in Example 1 was used.
The heating temperature was such that the gas temperature reached 1300℃ at the outlet of the jet nozzle, and the gap between the nozzle tip and the copper strip was 20 mm.
It was carried out continuously.

In this case, the thickness of the carbon layer was approximately 1.5 μm.

After plating, the carbon layer on the surface not to be plated was removed using a brushing roll. As a result, no zinc adhesion was observed, and a complete single-sided galvanized steel sheet was obtained.

On the other hand, for comparison, pyrolytic carbon was injected onto the copper strip,
When a test was carried out with the adhesion time set to about 1 second, the adhesion of the carbon was weak and a portion of the carbon fell off from the steel strip.

For this reason, when plating was performed by immersing it in a molten zinc bath at 460°C, approximately 10 to 1
Approximately 5% zinc was attached.

As explained above, according to the present invention, when forming free carbon, which does not easily react with molten metal, as a plating inhibitor on the non-plating surface of the steel strip, for example, a pyrolytic carbon injection nozzle is provided near the copper strip. , by forming a carbon layer on the copper strip while the pyrolytic carbon is active, the adhesion of the carbon is improved, and the effect is that completely partially plated steel sheets can be manufactured with high productivity without affecting the properties of the plated metal. has.

[Brief explanation of drawings]

FIG. 1 is a partial perspective view of the pyrolytic carbon injection nozzle used in the present invention, FIG. 2 is a plan view taken along line AA, and FIGS. 3 and 4 are implementations of the single-sided hot-dip plating method according to the present invention. It is a schematic diagram showing a continuous hot-dip metal plating apparatus used in an example. 1...Pyrolytic carbon jet nozzle, 2...
...Mesh electric heater provided in the nozzle, 3...
...Steel strip, 7...Plating bath, 12...
・Bag filter", 14...Hydrogen gas storage tank.

Claims (1)

[Claims] 1 In a hot-dip metal plating method in which the surface of the copper strip that does not require plating is coated with a plating inhibitor in advance and the entire steel strip is then immersed in a hot-dip metal plating bath, hydrocarbon fuel is pyrolyzed on the copper strip in the absence of an electric field. Partially molten metal of a steel strip, characterized in that the plating inhibitor is coated by producing active free carbon and adhering it to the unplated surface of the steel strip within one-fifth of a second. Plating method.