JPS6115946B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a plating method in which a steel strip is immersed in a molten metal plating bath after an anti-plating film is formed in advance on the non-plating surface of a steel strip. The present invention relates to a method for partially molten metal plating of a steel strip, in which only a portion of the steel strip is glazed, for example, on one side. [Prior Art] In order to impart corrosion resistance to a steel plate, various corrosion-resistant coatings 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 a steel plate. However, in the case of steel plates for automobiles that are painted after plating, if the plated surface is painted, the sharpness of the image will be poor and the product value will be significantly reduced. In addition, for example, the weldability of galvanized steel sheets is determined by the fact that the difference between the melting point and boiling point of zinc is small and the thermal conductivity is large;
Further, it is not preferable because it tends to contaminate the electrode. As described above, imparting corrosion resistance to the surface of a steel plate and weldability and sharpness after painting have contradictory properties. For this reason, so-called single-sided plated steel plates are being used for automobile steel plates and the like, in which only one side of the steel plate is plated to provide corrosion resistance, and the other side has paintability and weldability. [Problems to be Solved by the Invention] Methods for producing single-sided galvanized steel sheets by molten metal plating, such as hot-dip galvanizing, include a method of forming an anti-plating film on the non-plating surface of the steel sheet, and a method of forming an anti-plating film on the surface of the steel sheet that does not require plating, Alternatively, there is a method in which molten zinc is mechanically brought into contact with only one side of the steel plate using a roll or the like, or a method in which zinc on one side is removed by grinding 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 have been proposed for forming an anti-plating film on surfaces that do not require plating, and known anti-plating agents include water glass, silicone resin, oxide film, alumina, and carbon. Among these anti-glazing agents, carbon generated by incomplete combustion of hydrocarbon fuel, so-called soot, does not react with molten zinc and has very low wettability.
Very high anti-stick performance. Also, soot is self-lubricating and the coefficient of friction of the soot surface is small, so when the steel strip is pulled out of the plating bath at high speed, the amount of molten zinc lifted up is extremely small. However, since soot is porous, even if a soot-preventing film is formed on the surface of the steel strip, oxygen from the atmosphere will enter the surface of the steel strip through this film. For this reason, after melt plating,
There is a drawback that the non-plated surface is oxidized, and in particular, when alloying is performed after plating, the oxidation progresses more rapidly since it is heated to about 500°C. On the other hand, anti-glazing materials other than soot have the drawback of simultaneously pulling up molten zinc when the steel strip is pulled out of the plating bath at high speed. [Object of the Invention] An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a plating method for producing high-quality partially hot-dip galvanized steel strip at high speed. [Means for Solving the Problems] The present invention provides a method for forming a plating prevention film containing carbon powder on the non-plating surface of a steel strip, and then immersing the steel strip in a molten metal plating bath. In the molten metal plating method, a coating film of a solution in which solid components are dissolved in advance is formed on the surface that does not require plating, and then this coating film is dried to form a layer that suppresses or substantially prevents the intrusion of oxygen. , is characterized by forming an anti-plating film containing carbon on the coating film. [Function] The composite (two-layer) anti-plating film according to the present invention will be described in further detail. 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. As the solution in which the solid component is dissolved, an inorganic solution or a synthetic resin solution is used. In particular, materials with excellent heat resistance are desirable; for example, water glass, alumina, borax aqueous solution, silicone resin varnish, or silicone rubber varnish are most useful. It is especially desirable that the water glass is made by diluting a concentrated aqueous solution of alkali silicate salts with water, which is usually called a stock solution, and its concentration is such that it does not interfere with the application work.
The concentration is appropriately selected so that good adhesion can be obtained and a dense film can be formed after drying or vitrification by heat treatment. A general guideline is 0.1 to 30% by weight, preferably 0.5 to 20% by weight.
It is. In the case of synthetic resin varnish or borax aqueous solution, the concentration is selected depending on the type of resin, but as in the case of water glass, it should be selected appropriately so that a dense film can be formed with good workability. What is important for a coating film made of a solution containing dissolved solid components is that the film be sufficiently thick or dense so as to prevent oxygen from penetrating the surfaces of the steel strip that do not require plating as much as possible. Preventing the intrusion of oxygen can prevent oxidation of surfaces not to be plated during the heat alloying treatment after completion of plating, which is extremely convenient. Coating film of solution in which solid components are dissolved (first coating layer)
After substantially drying, an anti-plating film containing carbon powder is formed thereon. There is no need to install a special drying oven for drying the coating film made from a solution containing dissolved solid components, but it can be carried out using an oxidation oven or a drying oven for drying the flux applied to the steel strip. Just do it. Carbon powder can be used in either fixed or amorphous form. 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. For practical purposes, a thickness of several μm or less is sufficient. The second film layer, the anti-plating film of carbon powder, is formed by spraying or roll coating. The most desirable method is to incompletely combust the hydrocarbons, blow the combustion flame directly onto the first coating layer, and attach the generated soot, which will improve adhesion, particle size of the powder, and conversion of the first coating layer into a solid phase. This is advantageous in terms of promoting If a dense first coating layer with high adhesion is formed after conversion to a solid phase and the intrusion of oxygen is suppressed or prevented, surfaces not to be plated will be oxidized even through alloying heat treatment, etc. High quality single-sided plated steel sheet can be obtained. In carrying out the method of the present invention, the following plating apparatus is used. That is, the apparatus for partially molten metal plating of a steel strip for carrying out the method of the present invention is an apparatus for forming a coating film of a solution containing solid components on the surface of the steel strip that does not require plating, and an apparatus for partially molten metal plating of a steel strip, which is an apparatus for forming a coating film of a solution containing solid components on the surface of the steel strip that does not need to be plated, and an apparatus for partially molten metal plating of a steel strip. After that, it is equipped with a device for forming an anti-plating film containing carbon powder on the coating film, a molten metal plating bath, and a device for removing solid components and carbon powder on the non-plated surface of the steel strip. [Example] The following plating method of the present invention will be explained in more detail with reference to the drawings. 1 to 3 are schematic diagrams showing a plating apparatus for carrying out the method 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.
form a coating layer. The steel strip 1 then enters an oxidation furnace 4 while this first coating layer is substantially wet.
In the oxidation furnace 4, oil and the like adhering to the plated surface of the steel strip are burned and the first adhered layer is dried. The steel strip 1 that has passed through the oxidation furnace 4 passes through the throat 5 and then enters the reduction furnace 6. In the reduction furnace 6, oxides on the plated surface of the steel strip are reduced and cleaned. Next, the direction of movement of the steel strip 1 is changed by a deflector roller 7, and then a plating metal 9 is precoated on the plating surface side by a precoat roller 8 placed in a reducing atmosphere. This pre-coating is a process to prevent the plated surface of the steel strip from spewing out into the atmosphere.
On the other hand, the masking burner 10 coats soot on the non-plated side, that is, on the first coating layer. Hydrocarbons such as propane, butane, acetylene, natural gas, etc., and oxygen or air are supplied to the masking burner 10, and when the ratio thereof is adjusted appropriately,
Soot is generated efficiently from the combustion flame. Hydrocarbons with a high carbon element content are particularly desirable, and acetylene gas is effective. On the other hand, propane gas or butane gas has the advantage that carbon powder with fine particles can be obtained and a dense film can be formed. This combustion flame is blown onto the first coating layer to form a soot film, which serves as an anti-plating film. Thereafter, the steel strip 1 is changed in its traveling direction by a turn roller 11, immersed in molten metal 9 in a plating bath 12, and drawn out into the atmosphere via a sink roller 13. At this time, since the non-plated surface of the steel strip 1 is coated with soot and a first coating layer that substantially prevents oxygen from entering, oxidation of the non-plated surface by oxygen in the atmosphere will proceed. There is no or only slight
Further, the molten metal 9 is prevented from being pulled up at the same time. Next, the steel strip 1 enters the alloying furnace 14 and is again held at a high temperature, for example, about 500° C. for galvanizing, for 10 to 60 seconds to improve its material quality. Even at such high temperatures, the two-layer coating prevents oxidation of surfaces that do not require plating. Alloying treatment may or may not be necessary depending on the use of the plated steel strip. After the steel strip 1 is cooled to about room temperature by a cooling device 15, the two-layer coating on the non-plated surface, that is, the carbon powder and other solid components, is ground away by a brushing roll 16, and a single-sided plated steel strip is obtained. It will be done. FIG. 2 is a diagram showing an example of another plating apparatus for carrying out the method of the present invention. This example is basically the same as the apparatus shown in FIG. , and that the turn roller 11 is omitted. After the steel strip 1 is coated with a solution 18 in which solid components are dissolved by a reverse roller 17, it is guided through an oxidation furnace 19 to a throat 20, and is heated to the non-plated side, that is, the dry side, by a masking burner 21. Soot is coated onto one coating layer. Next, the steel strip 1 is sequentially introduced into a reduction furnace 22, a plating bath 24, an alloying treatment device 26, a cooling device 27, and a brushing roller 28. In this example, one end of the reduction furnace 22 is immersed in the molten metal in the plating bath 24.
Since the plated surface of the steel strip 1 is not exposed to the atmosphere immediately before being immersed in the molten metal, it is effective in preventing oxidation. FIG. 3 is a diagram showing still another plating apparatus for carrying out the method of the present invention. The surface of the steel strip 1, whose surface has already been cleaned by degreasing and pickling, is coated with flux 29 by a flux coater 30 on the 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, a solution 31 in which solid components are dissolved is applied by a reverse coater 32 to the surface of the steel strip 1 that does not require plating, thereby forming a first coating layer. In the drying oven 33, both the flux coating layer and the first coating layer on the surface of the steel strip are dried. The dry first coating layer is exposed to an incomplete combustion flame of hydrocarbon from a masking burner 34 to coat the soot. The steel strip 1 is then led via a deflector roller 35 into a plating bath 37 by a sink roller 36. After passing through the plating bath 37, the steel strip 1 is taken up into the atmosphere and alloyed by an alloying treatment device 38. The results of galvanizing using the method shown in FIG. 1 are shown in Table 1 in comparison with the conventional method. 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 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 will only be oxidized to a very small extent. Furthermore, the soot film formed on the non-plated surface of the steel strip 1 can be formed on the steel strip 1 that has passed through the oxidation furnace. Therefore, it is possible to avoid a situation in which the soot film reaches a temperature higher than its ignition point in the oxidation furnace and burns, so there are fewer restrictions on the temperature conditions of the oxidation furnace, and higher speeds are possible.

〔Effect of the invention〕

According to the present invention, a plating method for manufacturing high-quality partially hot-dip galvanized steel strip at high speed is provided.

[Brief explanation of the drawing]

1 to 3 are diagrams schematically showing a plating apparatus to which the method of the present invention is applied. 1... Steel strip, 2, 18, 31... Solution in which solid components are dissolved, 3, 17, 30, 31... Reverse coater, 4, 19... Oxidation furnace, 5, 20... Throat,
6, 22... Reduction furnace, 7, 23, 35... Deflector roller, 8... Precoat roller, 9... Molten metal, 10, 21, 34... Masking burner, 11
...Turn roller, 12, 24, 37...Plating bath,
13, 25, 36...Sync roller, 14, 26,
38... Alloying treatment device, 15, 27... Cooling device,
16, 28...Brushing roller, 29...Flux, 30...Flux coater.

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, A coating film of a solution in which solid components are dissolved in advance is formed on the surface that does not need plating, and then this coating film is dried to form a layer that suppresses or substantially prevents the intrusion of oxygen, and then carbon is applied on the coating film. 1. A method for partially molten metal plating of a steel strip, the method comprising forming an anti-plating film comprising: 2. The method for partially molten metal plating of a steel strip according to claim 1, wherein the solution in which the solid component is dissolved is at least one of water glass, alumina, and a borax aqueous solution. 3. The method for partially molten metal plating of a steel strip according to claim 1 or 2, wherein the solution in which the solid component is dissolved is a solution of a synthetic resin. 4. The method for partially molten metal plating of a steel strip according to claim 3, wherein the synthetic resin is selected from silicone resin, silicone rubber, and thermoplastic resin. 5. The steel strip according to any one of claims 1 to 4 above, characterized in that the anti-plating film containing carbon powder is formed of carbon produced by incomplete combustion of hydrocarbons. Partially molten metal plating method.