JPH0231036B2 - HIFUKUSOSEIBUTSU - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention is applied to a graphite-based refractory, particularly a nozzle for continuous casting, to form a coating thereon, and utilized in the field of iron and steel manufacturing. (Prior technology) Conventionally, the mainstream materials for refractories such as immersion nozzles, long nozzles, and long stoppers used in continuous casting have shifted from silica graphite to alumina graphite, which has high corrosion resistance. However, since graphite is still used, embrittlement due to oxidation during the preheating process is unavoidable. Additionally, demands for improved productivity and longer life of continuous casting methods are increasing, and along with this, stable physical properties of refractories are desired. Therefore, at present, these graphite-based refractories are coated with a paint that forms an oxidation-preventing layer in advance to prevent embrittlement due to oxidation. For this purpose, due to the harsh conditions under which graphite-based refractories are used, most conventional paints have been made by using alkali silicate (potash glass, water glass, etc.) as the binder, and mixed with various frits and fillers. It was being applied. (Problems to be solved by the invention) When using conventional paints containing alkali silicate as the main binder, carbon dioxide gas in the air reacts with the paint film before the refractory is used, causing the paint film to deteriorate. There were problems with cracks and peeling. Furthermore, since the binder itself is not water resistant, there is a problem that it will dissolve and flow out if stored in a humid place for a long period of time. When these refractory products with coating defects were used, oxidation embrittlement of the refractory progressed from the defective parts of the graphite-based refractory coating, causing serious problems in operation. On the other hand, due to the usage conditions, as productivity has improved and the spalling resistance of graphite-based refractories themselves has improved, it has become possible to use refractories without preheating or to apply the paint by giving it sufficient heating time. The number of cases in which ceramics are made and then used is decreasing, and there is also a demand for forming an anti-oxidation layer without preheating. The purpose of this invention is to form a film with excellent adhesion and weather resistance at room temperature on graphite-based refractories, and to obtain a paint that exhibits heat-resistant and oxidation-resistant film properties over a wide temperature range. be. (Means for solving the problem) In the present invention, as an essential component in the coating composition,
The solution is to have silica sol, a synthetic resin emulsion that does not react with silica sol, glass frit, orthoclase, and additives. The constituent components of the present invention will be described below. Silica sol, also referred to as colloidal silica, is an aqueous silica sol, which is a colloidal solution in which ultrafine particles of high molecular weight silicic anhydride are dispersed in water. Synthetic resin emulsions that do not react with silica sol generally refer to synthetic resin emulsions that are stable even at high pH because the PH of silica sol is high and the protective colloid in the synthetic resin emulsion loses its equilibrium and is destroyed. For example, synthetic resin emulsions that do not use emulsifiers, called soap-free emulsions, are generally stable even when mixed with silica sol. Of course, it is necessary to select a synthetic resin emulsion with good water resistance. The glass frit is a ground amorphous glass with a low melting point that is generally used for producing enamel, and a commercially available product may be used. Orthoclase is a rock-forming silicate mineral, which is potassium feldspar containing KAlSi ₃ O ₈ as its main component, and may be used as long as it is used in the pottery industry. Additives include thickeners, dispersants, wetting agents, antifoaming agents, leveling agents, and PH used in ordinary water-based paints.
Conditioners, preservatives, antifungal agents, antifreeze agents, pigments, etc. are used as necessary. In order to actually prepare the coating composition of the present invention, the following blending amounts are used. However, the synthetic resin emulsion with silica sol is based on the solid component. Silica sol 1 to 5 parts by weight Synthetic resin emulsion that does not react with silica sol 1 to 10 parts by weight Glass frit 10 to 100 parts by weight Orthoclase 50 to 100 parts by weight Additives Water for dispersing 1 to 5 as appropriate As appropriate Functions of each component The silica sol acts as one of the binders, has better water resistance than conventional alkali silicate, and melts into a glass-like state together with other fillers when used. A synthetic resin emulsion that does not react with silica sol acts as another binder, and has the role of imparting water and moisture resistance to the coating before use and improving the spall resistance of the refractory. Glass frit and orthoclase are just fillers when the film dries, but during use, the glass frit and orthoclase co-melt to form a dense glass phase, and together with SiO ₂ , which is an essential component of silica sol, are used as fillers in refractories. Prevents oxidation. (Function) The coating composition of the present invention can coat refractories at room temperature,
After drying, each component has the following effects when used. From room temperature to about 400℃, the synthetic resin emulsion and silica sol act as a film that is water and moisture resistant.From about 400℃ until the glass frit melts (700℃ to 800℃), the silica sol acts as a coating film binder. have Then, from 800℃ to around 1600℃, glass frit, silica sol, and orthoclase melt in sequence and have an antioxidant effect. (Example) Examples 1 to 2 and Comparative Example 1 shown below
The effects of implementation will be explained by 6. The formulations of Examples 1-2 and Comparative Examples 1-4 are shown in Table 1 below. The ingredients in the table are silica sol and solid content.
The 30% one is a synthetic resin emulsion that does not react with silica sol and is made of styrene and acrylic resin, making it soap-free. The 40% solid content is a glass frit with a melting temperature of 750°C to 800°C, and the orthoclase emulsion is made of orthoclase. Commercially available raw materials for the ceramic industry were used. is the amount of water used for dispersion. Values are expressed in parts by weight.

[Table] Furthermore, in Comparative Examples 5 and 6, the formulation of a conventional coating paint using an alkali silicate as a binder was added to the second compound.
Shown in the table. Numerical values indicating amounts are in parts by weight.

[Table] The coating compositions of Examples and Comparative Examples having the above formulations are applied to graphite-based refractories (immersion nozzles) after the refractories are sufficiently dried. The coating composition was applied using a brush, and the application amount was 1 kg/
m ² (wet state). After application, drying was carried out in a dryer at 80°C for 24 hours. The specimens that had undergone the steps up to this point were used as test specimens for a firing test. In the firing test, the test specimen was heated in an oxidizing atmosphere from room temperature to 1000°C in about 10 minutes using a gas furnace (LP gas), and then raised to 1300°C in about 20 minutes. In the firing test, the surface condition after firing was visually confirmed. In order to confirm water resistance, the coating composition was applied to the entire surface of a thinly sliced graphite-based refractory board (5 x 10 x 1 cm).
After drying, a water resistance test and an alkali resistance test as specified in JIS K5663 Synthetic Resin Emulsion Paint Type 1 were conducted. For moisture resistance, the above test piece is hung with a thread in a glass bottle, water is poured into the bottle to the extent that it does not touch the test piece, and the bottle is left in an atmosphere at 50°C for one month. In this state (100% humidity)
Observe changes in the coating. The above test results are shown in Table 3 below.

【table】

【table】

[Table] As can be seen from the results in Table 3, according to the coating composition of the present invention, even when fired without preheating,
No abnormality occurs. In addition, since there are no problems with water resistance, alkali resistance, and moisture resistance, there is no possibility that defects will occur in the coating before use. (Effect of the invention) According to the coating composition of the invention, excellent water resistance,
Due to its alkali resistance and moisture resistance, coating defects will not occur during storage, and even if the coated refractory is used without preheating, there will be no pinholes, sagging, cissing, or spalling. Therefore, it has become possible to provide graphite-based refractories with high productivity, regardless of the length of storage period.

Claims (1)

[Claims] 1. A coating composition for a graphite-based refractory, which contains as essential components a binder of silica sol and a synthetic resin emulsion that does not react with the silica sol, and glass frit and orthoclase as fillers.