JPS6348944B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a method of molten metal plating in which a plating prevention coating that does not easily react with molten metal is formed on the unsatisfied areas of the material to be plated in advance, and then the entire material to be plated is immersed in a molten metal plating bath. The present invention relates to an efficient masking method using soot, particularly for the production of 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, for products that are painted after plating, such as steel sheets for automobiles, if the plating surface is painted, the sharpness 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, so-called single-sided plated steel sheets are being used for automobile steel sheets, etc., which are plated on only one side of the steel sheet to impart corrosion resistance, and the other side has paintability and weldability. Although there is a method of producing such single-sided plated steel sheets by electroplating, the thickness of the plated film obtained by the electroplating method is generally small, and it is difficult to provide sufficient corrosion resistance. In addition, in order to produce products with a large amount of plating using the electroplating method,
This is not preferable because it is necessary to reduce the sheet passing speed, resulting in poor productivity and high costs. 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 extremely difficult to continuously melt-weld only one side of a steel plate, so after performing so-called differential thickness plating, the unplated side is mechanically or electrochemically peeled off. However, it is extremely uneconomical. Methods for producing single-sided plated steel sheets using this hot-dip galvanizing method include applying phosphate treatment to one side and then plating, coating one side with water glass to prevent plating, or silicone resin. Various methods have been proposed for applying various coating agents containing as the main ingredients. However, in plating lines that have heat treatment equipment such as reduction furnaces in the line, the steel sheets are exposed to high temperatures, and the films made of phosphates, water glass, etc. change in quality, resulting in partial peeling, resulting in complete one-sided coating. I can't get a good look. Silicone resin also loses its film uniformity due to the effects of heat, making it difficult to achieve complete one-sided plating. There is also a method of using an oxide film as a plating prevention film, but if the oxide film is thin, the plating prevention power is insufficient, and if the oxide film is thick, the film may deform due to deformation of the steel plate, etc. It becomes easy to peel off, and a perfect single-sided plated steel plate cannot be obtained. Therefore, in order to eliminate the drawbacks of the conventional method, the present inventors used combustion products such as soot produced by incomplete combustion of hydrocarbon gas etc. as a plating inhibitor. I proposed a method for attaching it first. An object of the present invention is to provide a partial plating method that is even more productive by efficiently forming soot when masking a portion of a steel plate, for example, one side, with soot using the method described above. . The present invention provides a molten metal plating method in which the entire steel strip is immersed in a molten metal plating bath after an anti-plating coating is formed on a portion of the steel strip in advance. ) A hydrocarbon gas having a ratio of 0.35 to 1 is directly injected into the combustion flame of a hydrocarbon having a lower (C/H) ratio than that, causing incomplete combustion and generating soot, and the ejected A method for partially molten metal plating of a steel strip, characterized in that soot is sprayed onto a portion of the steel strip to adhere thereto. The method of the present invention is a molten metal plating method in which the entire steel strip is immersed in a molten metal plating bath after forming an anti-stick coating on a portion of the steel strip in advance.
A soot film is used as the anti-plating film, and the soot film is formed by the following method, using a gaseous raw material hydrocarbon having a C/H ratio of 0.35 to 1 and a C/H ratio smaller than that. It is characterized in that it is formed by a method in which fuel hydrocarbons are directly injected into a combustion flame to cause incomplete combustion to generate soot, which is then attached to a portion of a steel strip. The present invention will be explained in more detail below. The thermal decomposition temperature of hydrocarbons varies depending on the type, but for general hydrocarbons, the temperature is approximately
In the range of 800-1300℃. Therefore, when hydrocarbons are incompletely combusted, the amount of soot produced varies depending on the temperature distribution in the combustion flame. Figure 1 shows the results of the inventors' investigation of the relationship between the amount of soot generated and the temperature in the combustion flame while measuring the temperature of the combustion flame after incomplete combustion of a few hydrocarbons in the atmosphere. Shown below. This includes acetylene liquefied natural gas (LNG) and liquefied propane gas (LPG) as hydrocarbons.
Using this method, a 20 x 30 x 1 mm steel plate was exposed for 5 seconds to each temperature area whose temperature in the combustion flame had been measured in advance, and the average soot film thickness was determined. As is clear from FIG. 1, there is a combustion temperature range in which the most amount of soot is generated in the combustion flame. The optimal temperature varies slightly depending on the type of gas being burned, but
The temperature required to obtain 80% or more of the maximum film thickness is 850-1300°C for curve A acetylene and curve B LPG.
800-1200℃, curve C for liquefied natural gas (LNG)
The temperature will be 800-1200℃. In addition, compared to acetylene, LPG generates about 1/4 and LNG about 1/10, which is a very small amount of soot. However, acetylene is expensive compared to LPG or LNG. Furthermore, although LPG or LNG is inexpensive, it generates a small amount of soot, so in the case of single-sided continuous plating, it becomes difficult to perform sufficient masking as the sheet passing speed increases. However, it is possible to combust an inexpensive gas such as LNG as a fuel hydrocarbon, and feed acetylene gas, which generates a large amount of soot, as a feedstock hydrocarbon into the combustion flame of the fuel hydrocarbon gas, which is at an optimum temperature that generates a large amount of soot. This makes it possible to efficiently generate soot using a small amount of expensive acetylene, and enables high-quality single-sided masking without slowing down the sheet threading speed on the plating line. Examples of the present invention will be described below. Example 1 LNG was used as a fuel hydrocarbon, and acetylene was used as a raw material hydrocarbon. The flow rate of LNG was set to 5/min., and the raw material hydrocarbon gas, acetylene, was flowed at a flow rate of 1/min. burner is second
As shown in the figure, the burner nozzle is doubled, and the inside is used for fuel hydrocarbon gas.The raw material hydrocarbon gas is preheated by rotating it in a spiral shape on the circumference of the fuel hydrocarbon gas burner, and the flame temperature of the combustion flame is 1000. It was ejected into the combustion flame from a portion at ℃. For masking, use the line shown in Figure 3 and line speed 30m/
A cold-rolled steel strip with a width of 150 mm and a thickness of 0.5 mm is passed continuously at min. to form a soot layer on the unbleached surface of the steel strip, and then placed in a hot-dip galvanizing bath maintained at 460°C. It was introduced in After the plated steel sheets were cooled, the presence or absence of zinc adhesion on the unplated surfaces was examined. The results are shown in Table 1. For comparison, the table also shows the unsmearability when masking was performed by burning only acetylene gas. Non-stainability was determined by the absence of zinc adhesion at all; for example, if the number of dotted zinc adhesion was 0.1 pieces/m ² or less, it was judged as good. From the results in the table, the method of the present invention showed high soot generation efficiency and good non-staining property, whereas when only acetylene was used, at a flow rate of 10, the method of the present invention showed the same non-staining property. However, when the flow rate reached 5, the ends of the steel plate were partially plated with zinc. Furthermore, when the acetylene flow rate was 1, approximately 60% of the area of the steel plate on the non-plated side was galvanized.
From these results, the effects of the present invention are clear; efficient masking can be achieved even with a small amount of acetylene, and a complete single-sided galvanized steel sheet can be obtained.

[Table] Example 2 Using the same continuous plating line as in Example 1,
City gas (LNG) was used as the fuel hydrocarbon, and benzene vaporized gas was used as the raw material hydrocarbon. The city gas flow rate is set to 6/min., and the benzene vaporized gas is set to 0.5/min.
It was flowed at a flow rate of /min. The burner shown in Figure 2 is used for masking, and the temperature in the city gas combustion flame is
Benzene vapor gas was ejected from the 1100°C part. The benzene solution was heated to 120°C by the combustion exhaust gas during masking, and the benzene was vaporized into a gaseous state, which was then introduced into the raw material hydrocarbon preheating tube. The plating conditions were the same as in Example 1, one side was galvanized, and the non-stainability was examined. Table 2 shows the results. As is clear from the table, the method of the present invention had a high soot generation efficiency and exhibited good stain resistance. As described above, according to the present invention, although the amount of soot generated is large, the consumption of expensive fuel can be reduced, and a complete single-sided plated steel plate can be manufactured with high productivity.

[Table] A part of the steel strip as used in the present invention means one side, a part thereof, or a part of both sides.

[Brief explanation of drawings]

Fig. 1 is a graph showing the relationship between combustion temperature and soot generation amount due to incomplete combustion of hydrocarbon gas, Fig. 2 is a sectional view showing the structure of a soot masking burner used in an embodiment of the present invention, and Fig. 3 The figure is a schematic diagram showing a single-sided melt-plating device used in one embodiment of the present invention. 1... Raw material hydrocarbon flow rate adjustment valve, 2... Oxygen flow rate adjustment valve, 3... Fuel hydrocarbon flow rate adjustment valve,
4... Preheating tube for raw material hydrocarbon, 5... Nozzle for raw material hydrocarbon, 6... Burner nozzle for fuel hydrocarbon, 7... Continuous furnace, 8... Steel strip, 9... Deflector roll, 10... ...Snout, 11...Masking chamber, 12...Burner, 13...Hot dip galvanizing bath, 14...Plating roll.

Claims (1)

[Claims] 1. In a molten metal plating method in which an anti-stick coating is formed on a portion of the steel strip in advance and then the entire steel strip is immersed in a molten metal plating bath, the anti-stick coating is made of a soot coating, and the soot The coating is 0.35 to 1
A gaseous raw material hydrocarbon having a C/H ratio of
A steel characterized by being formed by directly injecting a fuel hydrocarbon with a lower C/H ratio into a combustion flame to cause incomplete combustion to generate soot, which is then attached to a portion of the steel strip. Method of partially molten metal plating of strips.