JPS5815531B2 - Katamenyouyukinzokumetsukihohou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of plating only one side in molten metal plating.

Recently, the demand for hot-dip plated steel sheets, such as galvanized iron sheets, has been increasing due to their corrosion resistance in various applications, but when using them, it is not necessary for both the front and back sides to have the same corrosion resistance, and it is often sufficient to use only one side. .

Furthermore, resistance welding is often used in the processing and assembly of parts for automobiles, electrical appliances, etc., but this has the disadvantage that plated metal builds up on the electrodes, contaminating the electrodes and reducing weldability.

Against this background, there is a need to establish an industrial manufacturing technology for single-sided hot-dip plated steel sheets.

For this reason, methods for manufacturing single-sided hot-dip plated steel plates include, for example, stacking two plates together, welding the edges together, and cutting off the welded area after plating, or applying various chemicals such as water glass colloidal silica sol to one side for sealing. Various methods have been proposed, such as a method of applying molten metal to one side using roll coating and plating, but these methods have problems in terms of manufacturing cost, production efficiency, and quality. be.

Furthermore, there is a method for single-sided plating by forming an oxide film on one side, such as the method described in US Pat. A combustible gas is blown onto the surface to oxidize only one side, and the oxide film is maintained in a low hydrogen protective atmosphere before being introduced into a plating bath.

However, this method requires strict control of the atmospheric conditions so that no reduction of the oxide film occurs during passage through a protective atmosphere, and no oxidation occurs on the surface to be plated, that is, no oxidation-reduction occurs. The plating method is limited (Cirrus method) because it requires I-rolling and the use of a plated original plate that has been annealed in advance, so it can be said that this method is not universal in industrial production.

Therefore, the present invention relates to a low-cost, high-productivity, high-quality manufacturing method for single-sided hot-dip galvanized steel sheets. After activating the metal in the plating bath, a gas containing oxygen is blown onto the non-plated surface (the surface on which the plating is not applied) during the molten metal plating process, which is immersed in the plating bath. This is a single-sided hot-dip metal plating method in which after forming a difficult-to-clean coating, the metal is immersed in a hot-dip plating bath and plated only on the side that is not blown with oxygen gas.

In molten metal plating using the Sendzimer method, etc., the presence of trace amounts of moisture or oxygen in the reducing atmosphere will reduce the plating performance, so it is necessary to avoid the contamination of these gases in order to obtain good plated products. It is.

The present invention applies this fact to single-sided plating, in which an oxide film is formed by spraying ammonia decomposition gas (hereinafter referred to as AX gas), nitrogen gas, etc. mixed with oxygen on only one side. This prevents the alloying reaction with the molten metal and prevents the formation of the plating layer.

Oxidation spraying does not have a sealing mechanism that prevents gas from entering the reducing atmosphere, but the remaining oxygen consumed to form an oxide film reacts with hydrogen in the high-temperature atmosphere and becomes moisture, so spraying The effect on the back side (plated side) is very small.

The oxygen concentration in the gas used for spraying for surface oxidation varies depending on the line speed, the temperature of the strip at the time of spraying, the amount of gas for spraying, and the equipment used for spraying, but the inventor has conducted various research. As a result, in actual work, the oxygen concentration in the blown gas needs to be at least o, ooi%,
In addition, the upper limit for oxidation spraying is 1% if the entire amount of gas is mixed into the reducing atmosphere, from the viewpoint of workability, such as preventing non-plating due to the spraying going around to the opposite side (plated surface). It is preferable that

However, in oxidation spraying, there is no upper limit to the oxygen concentration if the gas has a sealing mechanism to prevent it from entering the reducing atmosphere after spraying.

In order to prevent the oxide film from coming into contact with the highly reducing gas again and being reduced, it is preferable to spray oxygen immediately before entering the plating bath, i.e. at the snout area, and for the same reason, the plate temperature at the time of blowing is also controlled. to 600°C or less is preferable.

The surface of the strip blown with oxygen in this way is within a range (0,0
1% or less), the color changes from pale yellow to blue as the oxygen concentration increases.

Even when the oxidized surface is immersed in a plating bath, the oxide film prevents wetting with the molten metal and alloying reaction, thereby preventing the formation of a plating layer.

After the strip comes out of the plating bath, some plated metal may mechanically adhere to the non-plated surface, but this can be removed by wiping it off with an asbestos wiper while in the molten state, or by removing it from the plastic plate after the plated metal has solidified. It can be removed by scraping it off.

The present invention will be explained in more detail with reference to the drawings.

Figure 1 shows an example of hot-dip plating using the Sendzimer method. A strip 1 is introduced into an oxidation furnace 2, where it is heated by a gas combustion flame and surface contaminants such as rolling oil that adhere to the surface are oxidized and burned. In this case, a thin oxide film is formed at the same time, and then led to the reduction furnace 3 where the oxide film is reduced to an active surface, annealed at the same time, and then cooled to a temperature suitable for plating and placed in a molten metal plating bath. Immediately before immersion, oxygen-containing gas is introduced into one side from the snout section 4 through the gas feed pipe 5 and blown to form an oxide film only on the surface. , Oxygen spraying by immersing in a plating bath performs plating only on the back side.

The reason why only the oxygen blown surface is oxidized and the back surface is not oxidized is considered to be as follows.

In other words, Figure 2 shows the equilibrium oxygen partial pressure of iron, and shows that iron is oxidized by very small amounts of oxygen, and the oxygen-containing gas blown onto the hot strip was activated. At the same time as it reacts with the strip surface to form an oxide film, the temperature rises, and excess oxygen reacts with hydrogen to become moisture.

Figure 3 shows the influence of H2-H2O on the oxidation-reduction of iron and zinc. In any case, the strip surface is not subject to oxidation due to moisture.

Therefore, the oxygen blown onto the strip forms an oxide film, and at the same time, the remaining oxygen is heated by the sl-IJ tube and reacts with hydrogen in the high temperature atmosphere to become water. Since oxidation does not occur and the active surface is immersed in the plating bath, it is possible to plate only one side.

However, plated metals are generally susceptible to oxidation, and in the case of zinc, for example, oxidation occurs even in the presence of a small amount of water, as shown in Figure 3. It is preferable that there is little.

Therefore, in oxidizing spraying, the method of preventing gas and its products from coming into contact with the plating bath is to place the inlet for non-oxidizing gas near the bath surface, and for oxidizing spraying, place the inlet for gas in front of the bath surface. Oxidation of the plating bath can be prevented by providing a suitable sealing mechanism between the two gas inlet ports.

This sealing mechanism is illustrated in FIG. 4, for example.
A is a method in which a non-oxidizing gas inlet 8 and a gas inlet lower for oxidizing spraying are provided individually, and a slit 9 is provided in the middle to seal the oxidizing gas, and b is a method in which the gas inlet is in the case of a. Similarly, 10 is an oxidizing gas inlet, and 11 is a non-oxidizing gas inlet.

In this example, a seal roll 12 is provided as an intermediate sealing mechanism.
3, and after blowing, the gas is discharged outside the furnace from the exhaust pipe 14 by a suction device, and this blowing prevents the mixing of oxidizing gases by making the pressure in the chamber 16 more negative than the pressure inside the furnace. Various methods can be considered.

In particular, the method shown in FIG. 4C allows the spraying to increase the oxygen concentration in the gas.

It goes without saying that the present invention is not limited to the methods exemplified here.

Next, a tree will be explained about an embodiment of the present invention.

Example] In hot-dip galvanizing by the Sendzimer method, the snout part is equipped with a slit-shaped sealing mechanism, a non-oxidizing gas inlet, and a nozzle for oxidizing gas spraying, as shown in Figure 4a. A added with oxygen concentration ranging from 0 to 1%
Plating was performed by spraying X gas onto one side of the strip and covering the bath surface with nitrogen gas to prevent oxidation, and then immersing the strip in a plating bath.

At the outlet of the plating bath, the surface on which oxidizing gas was blown was wiped with an asbestos wiper, and the amount of adhesion was controlled on the back surface with a roll squeezer.

The results obtained were as follows.

From the results in Table 1, it is clear that oxygen gas spraying has a remarkable effect on the occurrence of unmetallic defects, and moreover, the oxygen concentration is 0.001.
% or more, and the plating adhesion of the plating surface shows no decrease at all due to oxygen blowing.

Example 2 In plating a 45% Pb-8n alloy using a non-oxidizing furnace method, an oxidizing gas blowing chamber as shown in Fig. 4C was provided on the snout portion, and after air was blown there, it was immersed in a plating bath. Plating was done.

When removing the plating bath, the surface to which oxidizing gas was sprayed was wiped with an asbestos wiper, and the back surface was wiped with compressed air from a slit-shaped nozzle to control the amount of adhesion.

The obtained plated steel plate showed good corrosion resistance, with no plating adhesion on the surface that was sprayed with oxidizing gas, and few pinholes on the plated surface.

Example 3 In hot-dip galvanizing pre-annealed material by the Cirrus method, a slit-shaped sealing mechanism as shown in Figure 4a, a non-oxidizing gas inlet and a nozzle for spraying oxidizing gas were arranged in the snout part, and the oxidizing gas was Spraying is 020.05% from the nozzle.
After blowing a gas having a composition of 20% H2 and the rest N2 onto only one side, plating was performed by immersing it in a plating bath.

At the outlet of the plating bath, the surface to which oxidizing gas was sprayed was wiped with an asbestos wiper, and the back surface of the plating bath was wiped with a roll squeezer to control the amount of adhesion.

As a result, there was no plating on the oxidized surface and no unplating occurred on the back surface (a single-sided hot-dip galvanized steel sheet with good plating adhesion was obtained).

[Brief explanation of the drawing]

Figure 1 shows the overall configuration of a continuous molten metal plating line using the Sendzimer method. Figure 2 is a diagram showing the equilibrium oxygen partial pressure in iron oxidation.
FIG. 3 is a diagram showing the influence of H2-H2O on the redox of iron and zinc. FIG. 4 shows an example of an apparatus for blowing oxygen-containing gas onto the surface of the plating bath and preventing the remaining gas from acting on the surface of the plating bath. 1... Strip, 2... Oxidation furnace, 3
...Reduction furnace, 4...Snout part, 5.
...Gas inlet pipe, 6... Molten metal plating bath, 7, 10, 13... Gas inlet for oxidation spraying, 8, 11.15... Non-oxidizing gas inlet, 9
...Slit, 12...Seal roll, 14...Exhaust pipe, 16...Chamber for oxidation spraying.

Claims (1)

[Claims] 1 In continuous molten metal plating, in which the surface to be plated is activated by heating in a reducing atmosphere and then immersed in a molten metal plating bath, A single-sided molten metal plating method characterized by blowing oxygen-containing gas onto only one side and then immersing it in a molten metal plating bath.