JPS6115945B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a plating method in which a steel strip is immersed in a molten metal plating bath after an anti-stick film is formed on the non-plating surface of the steel strip in advance. The present invention relates to a method and apparatus for applying abrasion. For the purpose of imparting corrosion resistance to a steel plate, various corrosion-resistant films are often formed on the surface of 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 plates for automobiles, which are painted after plating, applying the paint to the plated surface results in poor image clarity and a significant reduction in commercial value. 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, steel plates for automobiles, etc. are plated on only one side of the steel plate.
So-called single-sided plated steel sheets are being used, which have corrosion resistance and paintability and weldability on the other side. Molten metal plating For example, methods for manufacturing single-sided galvanized steel sheets by hot-dip galvanizing include forming an anti-galvanizing film on the side of the steel plate that does not require plating, or mechanically applying molten zinc using ultrasonic waves or rolls. There are methods such as contacting only one side of the steel plate, or polishing off the zinc on one side after both sides are plated. Among these methods, the mechanical method is technically difficult and therefore impractical, and the method of removing zinc on one side by grinding has the drawback of high cost. For these reasons, various methods for forming an anti-plating film have been proposed, and known anti-plating agents include water glass, silicone resin, oxide film, alumina, and carbon. Among these anti-glazing agents, carbon produced by incomplete combustion of hydrocarbon fuel, so-called soot, does not react with molten zinc and has very low wettability, so it has very high anti-glazing performance. . However, soot has a disadvantage in that it has poor adhesion to steel plates or other coatings, and is difficult to adhere firmly to the object to be coated, if the object is dry. In addition, although water glass has good adhesion to steel plates, etc., it has poor adhesion resistance to molten zinc, and when using water glass alone, zinc is pulled up onto the water glass when the steel plate is pulled up from the plating bath in continuous plating equipment. However, the problem was that it solidified as it was. Silicone resin has problems with thermal stability, and oxide films and alumina have the disadvantage of simultaneously pulling up molten zinc when the steel plate is pulled out of the plating bath at high speed. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a method and apparatus for producing high-speed, high-quality partially hot-dip galvanized steel strips. The present invention is a method for partially molten metal plating of a steel strip, in which an anti-plating film containing carbon powder is formed on the non-plating surface of the steel strip, and then the steel strip is immersed in a molten metal plating bath. A coating film of a solution in which a solid component is dissolved in advance is formed on the surface, and then, while the coating film is in a substantially wet state, an anti-plating film containing carbon powder is formed on the coating film. do. As a result of various studies, the present inventors have found that when coating carbon powder as an anti-plating agent, the adhesion is better when the object to be coated is substantially wet and then dried. The inventors discovered that the coating was much more tightly adhered and had a higher coating density for the same time and under the same conditions than when it was coated in a dry state, leading to the discovery of the above-mentioned invention. The above-mentioned composite (two-layer) anti-plating film in the present invention will be described in more detail below.
First, the first coating layer is formed on the non-plating surface of the steel plate by applying a solution containing dissolved solid components to the non-plating surface of the steel plate by a method such as roll coating or spraying. Here, an inorganic solution is used as the solution in which the solid component is dissolved. In particular, those with excellent heat resistance are desirable; for example, water glass and borax aqueous solutions are most useful. It is especially desirable that the water glass be one obtained by diluting a concentrated aqueous solution of an alkali silicate salt, which is usually referred to as a stock solution, with water.The concentration is such that it does not interfere with the application work and provides good adhesion.
Moreover, the concentration is appropriately selected so that a dense film can be formed after drying or vitrification by heat treatment. A general guideline is 0.1 to 30% by weight.
Preferably it is 0.5 to 20% by weight. In the case of an aqueous borax solution, as in the case of water glass, it should be selected appropriately so that coating workability and a dense film can be formed. After carbon powder is attached to the coating film of the solution in which the solid components are dissolved, it is solidified by drying or vitrified by heat treatment and converted into a solid phase. The film must be sufficiently thick or dense to prevent oxygen from entering surfaces that do not require plating. By preventing oxygen from entering,
Oxidation of the surfaces not to be plated can be prevented during alloying treatment by heat treatment after completion of plating, which is extremely convenient. In the present invention, an anti-plating film containing carbon powder is formed on a coating film (abbreviated as a first coating layer) of a solution in which a solid component is dissolved while it is in a substantially wet state. If carbon powder is attached after the first coating layer has been converted into a solid phase, sufficient adhesion cannot be obtained. The carbon powder used here can be either regular or amorphous carbon.
If the particle size of the carbon powder is too large, the contact area with the first coating layer will decrease and the adhesion will deteriorate, so it is preferable that the particle size is as small as possible. Practically a few microns
It is sufficient if it is less than m. The second coating layer, the anti-plating film containing carbon powder, can be formed by spraying or roll coating. The most desirable method is to incompletely combust the hydrocarbons and directly blow the combustion flame onto the first coating layer to cause the generated soot to adhere, depending on the adhesion, particle size of the powder, and hardness of the first coating layer. This is advantageous in terms of promoting phase conversion. As mentioned above, the first coating layer has high adhesion,
After conversion to a solid phase, a dense film is formed that can suppress or prevent the intrusion of oxygen. Furthermore, while the first coating layer is in a wet state, a layer of carbon powder with excellent anti-plating properties is applied on top of the first coating layer. By forming a composite anti-plating film, the adhesion of the anti-plating film to the steel plate is improved.Furthermore, the non-plating surface will not be oxidized even during alloying heat treatment, resulting in a high-quality single-sided coating. A plated steel plate is obtained. In carrying out the invention, it is advantageous to use the following plating apparatus. The apparatus for partially hot-dipping a steel strip of the present invention is an apparatus for forming a coating film of a solution containing solid components on a surface of a steel strip that does not need to be plated. A device that forms an anti-plating film containing carbon powder on top;
It is characterized in that it sequentially includes a molten metal plating bath and a device for removing the solid components and carbon powder on the non-plated surface of the steel strip. Next, the plating method and plating apparatus of the present invention will be explained in more detail with reference to the drawings. 1 to 3 are schematic cross-sectional views showing a plating apparatus according to an embodiment of the present invention. First, in FIG. 1, a solution 2 in which a solid component is dissolved, such as water glass, is coated on the non-plating surface of a steel strip 1 using a reverse coater 3 to form a first coating layer. A masking burner 4 is then applied onto this first coating layer while it is substantially wet, i.e. before it is converted into a completely solid phase, e.g. before drying or vitrification in the case of water glass. The carbon powder or here the soot is coated. Oxygen or air is supplied to the masking burner 4 along with hydrocarbons such as propane, butane, acetylene, natural gas, etc., and by mixing the hydrocarbons and oxygen or air in an appropriate ratio, soot can be efficiently removed from the combustion flame. It is starting to occur. Hydrocarbons with a high carbon element content are particularly desirable;
Acetylene gas is effective. Further, propane gas or butane gas has the advantage that carbon powder with fine particles can be obtained and a dense film can be formed.
By spraying this combustion flame onto the first coating layer, a soot film is formed and an anti-plating film is formed. Next, the steel strip 1 passes through a drying furnace 5 and enters an oxidizing furnace 6. In the drying oven, the solvent may be simply removed, or if water glass or the like is used, it may be vitrified by heat treatment. In the oxidation furnace 6, oil adhering to the plated surface of the steel strip is burned off, and then the steel strip passes through a throat 7 and enters a reduction furnace 8. In the reduction furnace 8, oxides on the plated surface of the steel strip are reduced and cleaned. Next, the steel strip 1 is immersed in a molten metal, for example, a galvanizing bath 9, drawn out into the atmosphere via a sink roll 10, and the amount of plating is adjusted by a gas injection device 11. Since a two-layer coating of the first coating layer and a soot layer is formed on the anti-plating surface of the steel strip 1, the plating metal 9 is not pulled up, and the non-plating surface is prevented from being exposed to oxygen in the atmosphere. There is no progress of oxidation, or there is very little progress. Next, the steel strip 1 enters the alloying furnace 12 and is held at a high temperature again.
The quality of the material is improved by holding it for seconds, but even at such high temperatures, because of the two-layer coating as described above,
Oxidation of surfaces not required for plating is prevented. Alloying treatment may or may not be necessary depending on the use of the plated steel strip. Next, the steel strip 1 is cooled down to room temperature by a cooling device 13, and then the two-layer coating, that is, the carbon powder and other solid components, on the non-plated surface is polished off by a brushing roll 14, and the single-sided plated steel strip is is obtained. FIG. 2 is a sectional view of a plating apparatus showing a second embodiment to which the present invention is applied. This embodiment is basically the same as that in FIG. 1, but differs in the method of forming the two-layer coating on the non-plated surface of the steel strip. A first coating layer similar to that described above is formed on the non-plating surface of the steel strip 1 using a reverse coater, and then, before the coating layer is converted into a solid phase, a fine powder injection tube 1 is coated on the steel strip 1.
5, fine carbon powder 1 is deposited on the first coating layer.
6 is sprayed and sticks. This fine carbon powder injection tube 15 is used to inject soot or other carbon powder using compressed gas, and a pressure control valve 17 is used to control the injection pressure to an appropriate level so that the first coating layer on the surface not to be plated is scattered. is adjusted to Next, the steel strip 1 passes through a drying furnace 5 and enters an oxidizing furnace 6 where oil and the like on the mating surface are burned and removed. From here on, a single-sided plated steel strip is obtained by the same process as shown in FIG. FIG. 3 is a sectional view of a plating apparatus showing a third embodiment to which the present invention is applied. The steel strip 1, which has already been degreased, pickled, and whose surface has been cleaned, is coated with flux 18 by a flux coater 19 on its plating surface. Flux is used to remove impurities on the surface of the steel strip and a very slight oxide film generated after pickling. For example, a mixed aqueous solution of zinc chloride and ammonium chloride is used. On the other hand, after a first coating layer similar to that described above is formed by the reverse coater 3 on the non-plating surface of the steel strip 1, before the coating layer is converted into a solid phase, a first coating layer is applied to the non-plating surface. A masking burner 4 provided thereon applies an incomplete combustion flame of hydrocarbon onto the first coating layer to coat the first coating layer with soot. Next, the steel strip 1 is passed through a deflector roll 20
It is then guided into a molten metal plating bath 9 by a sink roll 10. Steel strip 1 after passing through plating bath 9
is lifted into the atmosphere, the amount of plating is adjusted by a gas injection device 11, and then alloyed by an alloying treatment furnace 12 as required. Next, after being cooled to around room temperature in a cooling device 13, carbon powder and other solid components on the non-plated surface are removed by a brushing roll 14, thereby obtaining a single-sided plated steel strip. According to experiments conducted by the present inventors, the results of galvanizing using the method shown in FIG. 1 are shown in the table below along with comparative examples of the conventional method.

[Table] When the present invention is applied, it is possible to prevent the molten metal from being pulled up when the steel plate is pulled up from the plating bath, so the plating speed limit is 200 m/min or more, which is significantly improved compared to the conventional method. In addition, since the first coating layer with high adhesion forms a film of carbon powder in a substantially wet state, the entire anti-plating film adheres extremely tightly to the non-plating surface of the steel plate. In particular, even if the steel plate comes into contact with various rolls during continuous plating treatment, the plating prevention film does not peel off, and a high-quality partially plated steel plate can be obtained. Furthermore, since it is a two-layer anti-plating film, even if alloying treatment is performed, the surfaces that do not require plating will not be oxidized at all or can be suppressed to a very small amount of oxidation. In the present invention, when passing through the oxidation furnace 6, the drying furnace or the heat treatment furnace 5 is not necessarily necessary and can be omitted. This is because the oxidation furnace has a drying or heat treatment function. The present invention is not limited to the above embodiments, and can be applied to hot-dip plating of aluminum, lead, tin, etc. in addition to zinc. Furthermore, the term "partial hot-dip plating" as used in the present invention means plating on one side of a steel strip, a part thereof, or a part of both sides. As described above, according to the present invention, a high quality single-sided plated steel plate can be obtained at high speed.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views showing the structure of a plating apparatus according to an embodiment of the present invention. 1... Steel strip, 2... Solution in which solid components are dissolved, 3...
Reverse coater, 4... Masking burner, 5... Drying furnace or heat treatment furnace, 6... Oxidation furnace, 8... Reduction furnace, 9... Plating bath.

Claims (1)

[Scope of Claims] 1. A method for partially molten metal plating of a steel strip, in which a plating prevention film containing carbon powder is formed on the non-plating surface of the steel strip, and then the steel strip is immersed in a molten metal plating bath, Forming a coating film of water glass or borax aqueous solution in advance on a surface that does not require plating, and then forming an anti-plating film containing carbon powder on the coating film while the coating film is substantially wet. A method for partially molten metal plating of a steel strip, characterized by: 2. The plating method according to claim 1, wherein the anti-plating film containing carbon powder is formed from carbon produced by incomplete combustion of hydrocarbons.