JP2000042726A - Stopper head having high durability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the durable service life by forming a zirconia thermal spraying film on the surface of materials composed of a refractory material and a carbonaceous material and forming a zirconia coating film on the surface of the thermal spraying layer. SOLUTION: The thermal spraying layer having good stickiness is formed on the surface of a base material and on this surface, further thick coating layer is formed to form a stopper head having high durability. In this way, the oxidizing resistance and the wear resistance to molten metal as the weak points in the carbonaceous stopper head can be improved. Since the stickiness is weaked in the coating layer, there is a danger of peeling, but since the stickiness is strong in the thermal spraying layer, the peeling is difficult to develop. On the other hand, in the case of arranging the coating layer on the surface of the thermal spraying layer, since the stickiness is strong by using the same material or the similar material to the coating layer and the thermal spraying layer and there is no difference of the thermal expansion between both layers, a problem of the peeling as the whole body of the stopper head is eliminated. As the base material, an acidic material of silica, etc., a neutral material of alumina, etc., a basic material of magnesia, etc., and a non-oxidizing material of silicon carbide, silicon nitride, etc., are combined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nozzle stopper used for pouring molten steel from a tundish into a mold in continuous casting of steel in the steelmaking industry.

[0002]

2. Description of the Related Art In continuous casting of steel, a nozzle stopper is used together with a sliding nozzle as a method of controlling a flow rate of molten steel. Zircon-based materials have been used for the nozzle stopper head, but recently, carbonaceous materials such as alumina-carbon materials have been used for spalling resistance and seizure prevention (Japanese Patent Application Laid-Open No. 51-34
No. 216, JP-A-4-158961).

[0003]

The alumina-carbon stopper head has the advantages of high spalling resistance and less erosion and seizure, but is easily oxidized, is less susceptible to molten steel abrasion, and has the advantage of being less susceptible to molten steel. There is a problem that alumina generated by oxidation of aluminum is deposited and adhered.
If such difficulties occur vigorously, there arises an inconvenience that it is impossible to control or stop the flow of the molten steel satisfactorily.

[0004] In order to solve such inconvenience, it is conceivable to form a layer of a refractory material made of an oxide on the surface of an alumina / carbon stopper head. As a method of forming this layer, a method of forming a two-layer structure in which a refractory material made of an oxide is bonded, a method of applying a refractory material made of an oxide as a paste, and a method of spraying a refractory material made of an oxide Tried.

In a method of forming a two-layer structure using an alumina-carbon material and an oxide material, it is difficult to reduce the thickness of the oxide layer to less than several millimeters, and spalling occurs due to heat history during use, resulting in peeling. Would. On the other hand, the method of applying a refractory material composed of an oxide has a disadvantage that the adhesion strength between the alumina-carbonaceous base material and the applied layer is weak, and peeling and intrusion of the base metal easily occur. Furthermore, in the method of forming a sprayed layer on the surface of the base material, the bonding strength is considerably strong, but a very thick sprayed layer cannot be formed, and there is a drawback that the number of times of use is low, and both methods are satisfactory. Was not.

[0006]

SUMMARY OF THE INVENTION The present invention has been completed as a result of trying the above-described various methods, and aims to solve the problems of the conventional stopper head and provide a highly durable stopper head. That is, the present invention is a stopper head in which a zirconia spray coating is formed on the surface of a material made of a refractory material and a carbonaceous material, and a zirconia coating film is formed on the surface of the sprayed layer.

[0007] Comparing the adhesion between the refractory material and the base material made of a carbonaceous material for the coating layer and the thermal spray layer, the thermal spray layer is considerably stronger. This is considered to be a result of the fact that the material is strongly sprayed onto the surface of the base material in a molten state during thermal spraying, and as a result, the melted material strongly penetrates into irregularities on the surface of the base material. This effect is particularly remarkable when blasting is performed on the base material surface.

On the other hand, in the method of forming a thicker surface layer which affects the erosion resistance, the application layer is more likely to be applied. In the case of spraying, it is possible to form a layer with an arbitrary thickness, whereas in the case of spraying, if the spraying is performed at a time, the base material becomes hot, resulting in oxidation of the carbonaceous material, resulting in adhesion. Sex is extremely reduced. Repeating thermal spraying many times to form a thick thermal spray layer solves the problem of oxidation of the base material, but the thermal spray layer becomes layered, and the metal invades between layers during use, causing peeling and cracking. Therefore, a very thick sprayed layer cannot be formed.

Taking advantage of these two features, a sprayed layer having good adhesiveness is first formed on the surface of a substrate, and a thicker coating layer is formed on the surface to form a highly durable stopper head. This improves the oxidation resistance and the wear resistance of molten steel, which are disadvantages of the carbonaceous stopper head. When layers of different materials are formed on the surface of the base material, the most worrisome is separation due to a difference in thermal expansion between the two when subjected to a thermal history. As described above, there is a danger of peeling because the adhesive strength is low in the coating layer, but the thermal spraying layer has high adhesive strength and is difficult to peel. on the other hand,
When a coating layer is provided on the surface of the thermal spray layer, if both are made of the same or similar material, the adhesive force is increased and there is no difference in thermal expansion, so that the stopper head as a whole eliminates the problem of peeling. Therefore, by increasing the thickness of the coating layer, it is possible to increase the durability against erosion and abrasion due to molten steel.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The base material of the stopper head of the present invention is made of a refractory material and a carbonaceous material, and those used for ordinary refractories can be used as they are. That is, acidic materials such as silica, neutral materials such as alumina,
A basic material such as magnesia or a non-oxide material such as silicon carbide or silicon nitride is combined with a carbon material such as graphite, carbon black or pitch. Use of a fibrous material such as carbon fiber is also effective. Among them, alumina / graphite, zirconia / graphite, etc. are most suitable. The substrate can be produced in the same manner as in the case of using a conventional carbonaceous material, and may be an unfired product or a fired product.

In the present invention, a surface layer made of an oxide refractory material is formed on the surface of the above-mentioned base material, and the material is optimally a zirconia material. Zirconia-based materials also have the advantage of simultaneously preventing the deposition of precipitated alumina from molten steel. As the zirconia material, stabilized, semi-stabilized and unstabilized zirconia, alumina-zirconia material, calcia-zirconia material containing calcium zirconate, zircon, and the like can be used. In particular, zirconia and calcia-zirconia materials are preferable.

First, a zirconia thermal spray coating is formed on the surface of the base material. An existing method can be used for the thermal spraying, and plasma spraying or flame spraying is used. Is desirable. Blast treatment may be performed prior to thermal spraying. The sprayed thickness is determined depending on the conditions of use, but is preferably 0.05 to 1 mm. If the thickness is less than 0.05 mm, it is difficult to form a uniform film on the surface of the substrate, and if the thickness exceeds 1 mm, oxidation of the substrate becomes a problem.

Next, in the present invention, a coating film is further formed on the surface of the above-mentioned sprayed layer. The coating method is a method in which zirconia fine powder is suspended in an appropriate liquid or paste-like substance. It is applied to the surface of a substrate by an existing method such as brush coating, spraying or electrostatic coating to form a film. Further, a film may be formed by dissolving or suspending zirconium hydroxide, a zirconium salt or an organic zirconia compound in an appropriate solvent, followed by thermal decomposition to form a film. The thickness of the coating depends on the conditions of use, but is preferably 0.05 to 5 mm. 0.05mm
If the thickness is less than 5 mm, the applied effect is not exhibited. If the thickness exceeds 5 mm, the strain between the thermal spray layer and the thermal spray layer increases, and the film tends to peel off from the thermal spray layer.

The coating film of the present invention may be formed by simply suspending zirconia fine powder in water, alcohol, or the like. However, since there is a risk of peeling after drying, a paste-like substance is added to the coating film to form a coating film. It is good to improve the adhesiveness with the material. As a method therefor, there is a method of suspending zirconia fine powder in a paint, water glass or an aqueous solution of sodium silicate.

As the paint, various oils such as linseed oil and soybean oil, natural resins such as shellac, synthetic resins such as phenolic resin, urea resin, melamine resin, phthalic acid resin and vinyl resin, cellulose derivatives, rubber derivatives, etc. Among them, a synthetic resin paint is particularly preferable. Synthetic resin paint is difficult to separate even when zirconia fine powder is suspended,
In particular, the adhesiveness with the carbonaceous material is good.

In the method of suspending in water glass or an aqueous solution of sodium silicate, commercially available industrial water glass Nos. 1 to 3 can be used as they are, or they can be dissolved in water to have an appropriate viscosity, or a zirconia-based solution can be added to an aqueous solution of sodium silicate. A suspension prepared by adding fine powder, stirring and suspending is used.

[0017]

EXAMPLE A zirconia-based material was used to form a sprayed layer on an alumina / silicon carbide / graphitic stopper head, and then a coating layer was formed. I checked the number. Table 1 shows the results. As a comparison, a case where no surface layer was provided, and a case where only the sprayed layer and only the coating layer were provided were examined. In the zirconia materials in the table, HZ is calcia semi-stabilized zirconia, SZ is calcia-stabilized zirconia, and CZ is calcium zirconate.

[0018]

[Table 1]

The conventional alumina / silicon carbide / graphitic stopper head sprayed with a zirconia-based material and further coated with a coating layer on its surface is 1.4 to 1.4 times smaller than the conventional one without spraying. It showed 1.9 times the service life. In addition, a considerable effect was recognized as compared with the case of only the thermal spray layer or the coating layer. Further, when the sprayed layer and the coating layer in Example 2 were formed under the same conditions in reverse, peeling occurred between the coating layer and the substrate, and almost the same durability as Comparative Example 2 was obtained.

[0020]

According to the present invention, any conventional zirconia-based material sprayed onto a stopper head made of a material and a coating layer is further formed on the surface of the stopper head does not perform the conventional spraying, or a sprayed layer or a coating layer. It shows higher service life compared to the case of only one, and clearly shows the effect of the combined use of thermal spraying and coating.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Saburo Matsuo 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Inside Nippon Steel Corporation Yawata Works (72) Inventor Mineo Uchida 3-chome Minamikata, Okayama City, Okayama Prefecture No. 2-19 (72) Inventor Osamu Matsuura 10F term at 500 Minamikoto, Okayama City, Okayama Prefecture (reference) 4E014 GA01

Claims (1)

[Claims] 1. A highly durable stopper head characterized in that a zirconia spray coating is formed on the surface of a material comprising a refractory material and a carbonaceous material, and a zirconia coating film is formed on the surface of the sprayed layer. .