JPS6141862B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a plate brick for a sliding nozzle made of smoke-free carbon bond material with improved mechanical strength, and a method for manufacturing the same. The sliding nozzle (SN) method is widely adopted as an effective means of controlling the flow rate of molten metal, and is widely used to control the flow rate of hot metal and molten steel, especially in the steel industry where operating conditions are harsh. The SN method is roughly divided into three parts: the upper nozzle, the plate, and the lower nozzle, and each part must have its own function.
The plate brick for SN is the part that controls the flow of molten metal and requires extremely advanced functionality. In the SN method, the flow rate of molten metal is controlled by sliding two or three plate-shaped bricks with circular openings, so in order to prevent steel leakage between the plate bricks, the plate bricks are Used by crimping with pressure. Furthermore, plate bricks for SN are subjected to not only the physical effects of rapid thermal shock and abrasion caused by the molten metal flow, but also the chemical erosion effects caused by the molten metal and molten slag. Therefore, the characteristics that plate bricks for SN should possess include mechanical strength, spalling resistance, and corrosion resistance. Various efforts have been made in the past to provide plate bricks for SN with a good balance of various properties, and in general, oxide ceramic bond materials based on alumina and fired at 1300 to 1800℃ have been manufactured. Ta. These are usually impregnated with tar pitch to improve their durability, but during use, volatile components such as coal tar pitch generate smoke and bad odors, significantly deteriorating the working environment. There were flaws. Moreover, oxide ceramic bond materials have the disadvantage that normal durability cannot be ensured unless impregnated. Recently, a non-smoke alumina/carbon material has been developed that improves these shortcomings and does not reduce its durability even without impregnating it with coal tar pitch.
It is widely used and has greater durability than conventional oxide ceramic bond materials. SN plate bricks made of smoke-free carbon bond material are made by kneading a refractory mixture with a predetermined composition using tar, pitch, or synthetic resin as a binder, molding it by a conventional method, and then molding it in a reducing atmosphere. A manufacturing method in which the material is fired inside is usually adopted. Carbon bond materials have the major characteristics of being non-smoking and having excellent corrosion resistance, but since the brick structure contains carbon, the sintering phenomenon in the matrix is inhibited by carbon, so conventional It had the disadvantage of being inferior in mechanical strength compared to oxide ceramic bond materials. Therefore, although carbon bond materials have excellent corrosion resistance and spalling resistance, they tend to suffer from abrasion damage due to molten metal flow, and there is a need to improve their mechanical strength. As a countermeasure to this problem, the conventional method of adding silicon to SN plate bricks made of carbon bond material is to strengthen the strength by bonding silicon carbide through reaction sintering of silicon and carbon. However, since silicon carbide has the property of being easily dissolved in molten steel, it has problems in terms of corrosion resistance, such as promoting surface roughening of sliding surfaces during use. The present inventors have investigated various materials that have excellent mechanical strength and corrosion resistance using methods other than silicon addition for carbon bond material SN plate bricks, and have found that aluminum nitride is highly resistant to molten metal. Focusing on the fact that aluminum has excellent corrosion resistance and that the mechanical strength of bricks is greatly improved through reaction sintering between aluminum and nitrogen at relatively low temperatures, aluminum nitride is added to the raw material formulation. By adding aluminum or nitriding it, a plate brick for SN made of carbon bond material with excellent corrosion resistance and mechanical strength was obtained. When aluminum nitride is added, aluminum nitride sinters relatively well despite its high melting point, and some aluminum nitride reacts with carbon in the brick structure to produce aluminum carbide.
It develops mechanical strength and forms a dense tissue. Additionally, when nitriding with the addition of aluminum, the aluminum melts during firing and penetrates into very fine parts of the matrix, where it reacts with nitrogen in the firing atmosphere to form fine aluminum nitride. By doing so, it develops strength and forms a dense structure. The present invention, which is characterized by having an aluminum nitride bond exhibiting such excellent corrosion resistance, is completely new and unprecedented. Further, although the present invention is smokeless, it is also possible to apply a method of impregnating with tar, pitch, synthetic resin, etc. by a conventional method after firing for the purpose of further improving durability. one of. In the present invention, the total amount of refractories having chemical components of Al ₂ O ₃ , SiO ₂ and SiC is 60 to 98% by weight, and raw materials used include sintered alumina, fused alumina, calcined alumina, synthetic One or more types are selected from mullite, sillimanite group minerals, siyamoto, various clay minerals, silica stone, fused silica, amorphous silica, silicon carbide, etc., and these are adjusted to any particle size within the range of the above chemical composition. and use it.
If the total amount of the chemical components of Al ₂ O ₃ , SiO ₂ and SiC is less than 60% by weight, corrosion resistance will be poor, and if it exceeds 98% by weight, the effects of the present invention will be impaired. The fixed carbon content of the plate brick for SN according to the present invention is 1 to 20% by weight. If it is less than 1% by weight, the corrosion resistance will be poor and the characteristics as a carbon bond material will not be exhibited, and if it exceeds 20% by weight, the mechanical strength will be poor. Not only does the oxidation resistance deteriorate, but the oxidation resistance also deteriorates significantly. Since the amount of fixed carbon in the brick of the present invention includes fixed carbon from the organic binder and impregnating agent, the amount used as a carbonaceous raw material is slightly smaller. The carbonaceous raw materials used in the present invention include scaly graphite, earthy graphite, artificial graphite, wood graphite, pyrolytic graphite,
Examples include petroleum pitch coke, maker coke, anthracite, charcoal, carbon black, retort carbon, pyrolytic carbon from carbohydrates, pyrolytic carbon from hydrocarbons, pyrolytic carbon from synthetic resins, and grassy carbon. However, one or more types can be mentioned from among these. In consideration of dispersibility in the brick structure and corrosion resistance, the carbon powder preferably has a particle size of 200 mesh or less and a purity of 80% by weight or more. Next, the chemical component as AlN in the SN plate brick of the present invention is 1 to 20% by weight,
If it is less than 1% by weight, the corrosion resistance characteristics of the present invention will not be exhibited, and if it exceeds 20% by weight, the brick structure will become rough, easily causing trouble during firing, and not only will the manufacturing yield be reduced, but the cost will also be high. Become. Methods for adding aluminum nitride include (1) adding aluminum nitride itself to the raw material mixture and firing it in a non-oxidizing atmosphere; (2) adding aluminum to the raw material mixture and adding nitrogen-containing non-oxidizing There are three methods: (3) a method in which aluminum is nitrided by firing in a non-oxidizing atmosphere, and (3) a method in which aluminum nitride and aluminum are added together and fired in a non-oxidizing atmosphere containing nitrogen. You may also adopt this method. Although the method of directly using aluminum nitride shows excellent properties, it has the drawback of being slightly inferior in mechanical strength, whereas the method of nitriding aluminum exhibits excellent mechanical strength. The amount or ratio of aluminum nitride, aluminum, and their combined use may be arbitrarily selected within the range of the chemical composition of aluminum nitride. Aluminum nitride and aluminum should preferably have a particle size of 200 mesh or less in consideration of dispersibility and reactivity in the brick structure, and should have a purity of 70% by weight or more in order to effectively exhibit the effect of corrosion resistance. This is desirable. The particle size-adjusted raw material mixture having the composition shown above is mixed with one or more organic binders selected from tar, pitch, or synthetic resins such as phenol resins, furan resins, epoxy resins, and silicone resins. Knead at room temperature or under heating. At this time, it is desirable that the powder raw material of 200 mesh or less be uniformly dispersed during the blending. When using resin as a binder, phenolic resin is preferable from the viewpoint of fixed carbon content and cost.
When pitch is used, it is desirable to use pitch with a high softening point and a large amount of fixed carbon. Next, the mixture obtained by the above method is molded into a predetermined shape using a conventional molding machine used for molding refractory bricks, such as a friction press, an oil press, and in special cases a rubber press. Subsequently, this compact is fired in a non-oxidizing atmosphere when only aluminum nitride is used, and in a non-oxidizing atmosphere containing nitrogen when aluminum is used. Examples of the non-oxidizing atmosphere containing nitrogen include a nitrogen gas stream and a reducing atmosphere. Methods other than reducing atmosphere will increase the firing cost. In addition, in reducing atmosphere firing in which the object to be fired is embedded in carbon, which is normally used for firing carbon-containing refractories, the object to be fired is not oxidized and nitrogen in the air is present in the firing atmosphere. A nitriding reaction of aluminum in the bricks occurs, and sufficiently good results are obtained in terms of quality including strength, and the features of the present invention are fully demonstrated. Therefore, as the firing method of the present invention, firing in a reducing atmosphere in carbon is sufficient from both the quality characteristics and economic efficiency of the fired product. The plate bricks for SN obtained by the above manufacturing method are usually impregnated with one or more of coal tar, pitch, and synthetic resin by a conventional method for the purpose of improving quality and densifying the structure. It is normal to do so. In the case of non-smoke plate bricks for SN, a heat treatment step is added to the above process to remove volatile components of the impregnating agent, but if durability is more important than the problem of smoke generation during use, impregnated Used as is. The volatile components of the impregnating agent are usually removed by heat treatment in a non-oxidizing atmosphere at 300 to 800°C, but the heat treatment temperature may be arbitrarily selected depending on the type of the impregnating agent. By repeating the impregnation treatment and heat treatment two or more times, the quality is further improved, making it suitable for use under more severe conditions. A method of adding an impregnation step using these conventional methods is also one of the embodiments of the present invention. Next, the effect of using aluminum nitride or the strength development mechanism and effect of reaction sintering of aluminum and nitrogen in the present invention will be explained. The present invention has extremely excellent corrosion resistance due to the presence of aluminum nitride in the brick structure. Aluminum nitride has a melting point of 2150-2200°C and exhibits excellent corrosion resistance against molten metal.
In addition, when aluminum is added, it reacts with nitrogen during firing and sinters to produce aluminum nitride.
It has the characteristic of expressing strength. Aluminum is 660
It has a melting point at °C, melts during firing, penetrates into the very fine parts of the matrix that are difficult to disperse during kneading and molding, and is nitrided, forming a dense structure. Due to reaction sintering, strength development is efficient and plate bricks for SN with high mechanical strength can be obtained. In addition, the starting temperature of the reaction between aluminum and nitrogen is around 600°C, so the reaction starts at a low temperature and aluminum nitride can be obtained relatively easily. The silicon carbide bond produced by the method using reaction sintering of silicon and carbon, which is a common method for reinforcing the strength of the conventional carbon bond material SN plate brick, is different from the aluminum nitride bond produced by the method of the present invention. Compared to bonding, corrosion resistance against molten metal is significantly inferior. In addition, in the present invention, not only aluminum nitride but also aluminum powder reacts with carbon in the brick structure to produce aluminum carbide, albeit in a small amount, which is advantageous in terms of corrosion resistance. Additionally, when a silica-containing raw material is used as a refractory aggregate, aluminum reduces the _SiO2 component during firing to generate silicon and alumina, and the generated silicon reacts with carbon and sinters to improve strength. Contribute to This can be said to be advantageous in terms of strength, since alumina and silicon carbide produced by reduction form a complexly intertwined structure. Furthermore, the plate brick for SN containing aluminum nitride of the present invention can be said to be advantageous in terms of corrosion resistance because even if an oxidation phenomenon occurs during use, alumina is newly generated from the aluminum nitride. For the reasons mentioned above, the product of the present invention has superior mechanical strength and significantly improved corrosion resistance compared to conventional carbon bond SN plate bricks. Examples will be described below, but the present invention is not limited to these examples. Example 1 Table 1 shows the quality of plate bricks for SN made of alumina-carbon material containing aluminum nitride, which is a feature of the present invention. Methods for obtaining aluminum nitride include a method of nitriding aluminum;
A method using aluminum nitride powder and a method using both together were used. In preparing the sample, a phenolic resin was used as a binder, and the mixture was kneaded with a predetermined aggregate, molded into a plate shape, and then embedded in coke and subjected to reduction firing. The firing atmosphere at this time is an atmosphere in which nitrogen exists in the air, and can be said to be a nitriding atmosphere in a broad sense. After firing, the pitch was impregnated and then the volatile components of the impregnated pitch were removed by heat treatment.

【table】

[Table] As mentioned above, strength is developed by nitriding aluminum or by reaction with aluminum nitride matrix. The aluminum nitride bond according to the present invention has significantly improved corrosion resistance compared to the conventional silicon carbide bond. When trial 3 of the present invention was tested in a SN device with a 150 tundish ladle, the results were as follows.
Compared to conventional products such as Test 1, the stability of the manual operation surface and corrosion resistance were excellent, and the durability was improved by about 20 to 30%. Example 2 Table 2 shows the quality of alumina-carbon materials according to the present invention using different firing methods. Note that the trial production conditions other than the firing conditions were based on the method of Example 1.

【table】

[Table] Nitriding-fired products have a larger absolute amount of aluminum nitride than reduction-fired products, so they are advantageous in terms of corrosion resistance. However, nitriding firing or firing in an inert gas stream results in very high firing costs and is not necessarily suitable. The desired effect can be sufficiently obtained even by firing in a reducing atmosphere in the presence of nitrogen, and this firing method can be said to be most suitable for the present invention in consideration of firing cost. FIG. 1 shows a scanning electron microscope image of Trial 3 in Table 2, where the solid part shows Al ₄ C ₃ +C and the slender part shows AlN. Small AlN crystals are formed throughout. FIG. 2 shows a scanning electron microscope image of Test 6 in the same table, in which the bony projections are AlN and the solid shape is Al ₄ C ₃ . FIG. 3 shows the part where the formation of layered AlN was especially noticeable in Test 7 of the same table. Example 3 Table 3 shows the quality when synthetic resin was used as the binder and when pitch was used as the binder. The test production conditions of Example 1 were followed except that when pitch was used, the mixture was kneaded under heat.

【table】

[Table] Example 4 Table 4 shows the quality of plate bricks for SN using different processing methods after firing, based on the material of Trial 2.

[Table] The quality improves as the number of impregnation treatments with pitch increases. The impregnating agent and the number of times of impregnation may be arbitrarily selected depending on the conditions of use. The reason for the increase in oxidation loss in Trials 9 and 10 is that the impregnated pitch contains volatile components or fixed carbon.

[Brief explanation of the drawing]

The attached FIGS. 1 to 3 show scanning electron microscope images of bricks of the present invention.

Claims (1)

[Claims] 1. A plate brick for a sliding nozzle made of carbon bond material, characterized in that it has an aluminum nitride bond in the matrix. 2 60 to 98% by weight of a refractory raw material consisting of one or more of alumina, silica, and silicon carbide;
1 to 20% by weight of carbon powder less than 200 mesh;
A carbon bond material sliding method characterized by kneading and molding a mixture of 1 to 20% by weight of aluminum nitride powder with an organic binder and then firing it in a non-oxidizing atmosphere.・Method for manufacturing plate bricks for nosles. 3 60 to 98% by weight of a refractory raw material consisting of one or more of alumina, silica, and silicon carbide;
A mixture of 1 to 20% by weight of carbon powder of 200 mesh or less and 1 to 20% by weight of aluminum powder of 200 mesh or less in terms of aluminum nitride was kneaded and molded using an organic binder. A method for producing plate bricks for sliding nozzles made of carbon bond material, characterized in that the plate bricks are then fired in a nitriding atmosphere. 4 60 to 98% by weight of a refractory raw material consisting of one or more of alumina, silica, and silicon carbide;
A compound consisting of 1 to 20% by weight of carbon powder of 200 mesh or less and a mixture of aluminum nitride and aluminum of 1 to 20 weight % of aluminum nitride of 200 mesh or less is kneaded and molded using an organic binder. A method for producing plate bricks for sliding nozzles made of carbon bond material, characterized in that the plate bricks are then fired in a nitriding atmosphere.